title: Film speed

text: Another example occurs where a camera's shutter is miscalibrated and consistently overexposes or underexposes the film; similarly, a light meter may be inaccurate. One may adjust the EI setting accordingly in order to compensate for these defects and consistently produce correctly exposed negatives.


title: Film speed

text: Upon exposure, the amount of light energy that reaches the film determines the effect upon the emulsion. If the brightness of the light is multiplied by a factor and the exposure of the film decreased by the same factor by varying the camera's shutter speed and aperture, so that the energy received is the same, the film will be developed to the same density. This rule is called reciprocity. The systems for determining the sensitivity for an emulsion are possible because reciprocity holds over a wide range of customary conditions. In practice, reciprocity works reasonably well for normal photographic films for the range of exposures between 1/1000 second to 1/2 second. However, this relationship breaks down outside these limits, a phenomenon known as reciprocity failure.


title: Film speed

text: The size of silver halide grains in the emulsion affects film sensitivity, which is related to granularity because larger grains give film greater sensitivity to light. Fine-grain film, such as film designed for portraiture or copying original camera negatives, is relatively insensitive, or "slow", because it requires brighter light or a longer exposure than a "fast" film. Fast films, used for photographing in low light or capturing high-speed motion, produce comparatively grainy images.


title: Film speed

text: Kodak has defined a "Print Grain Index" (PGI) to characterize film grain (color negative films only), based on perceptual just-noticeable difference of graininess in prints. They also define "granularity", a measurement of grain using an RMS measurement of density fluctuations in uniformly exposed film, measured with a microdensitometer with 48 micrometre aperture. Granularity varies with exposure — underexposed film looks grainier than overexposed film.


title: Film speed

text: Some high-speed black-and-white films, such as Ilford Delta 3200, P3200 T-Max, and T-MAX P3200 are marketed with film speeds in excess of their true ISO speed as determined using the ISO testing method. According to the respective data sheets, the Ilford product is actually an ISO 1000 film, while the Kodak film's speed is nominally 800 to 1000 ISO. The manufacturers do not indicate that the 3200 number is an ISO rating on their packaging. Kodak and Fuji also marketed E6 films designed for pushing (hence the "P" prefix), such as Ektachrome P800/1600 and Fujichrome P1600, both with a base speed of ISO 400. The DX codes on the film cartridges indicate the marketed film speed (i.e. 3200), not the ISO speed, in order to automate shooting and development.


title: Film speed

text: In digital camera systems, an arbitrary relationship between exposure and sensor data values can be achieved by setting the signal gain of the sensor. The relationship between the sensor data values and the lightness of the finished image is also arbitrary, depending on the parameters chosen for the interpretation of the sensor data into an image color space such as sRGB.


title: Film speed

text: For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called "ISO" setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm ("expanded ISO"). A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo.


title: Film speed

text: Digital cameras have far surpassed film in terms of sensitivity to light, with ISO equivalent speeds of up to 4,560,000, a number that is unfathomable in the realm of conventional film photography. Faster processors, as well as advances in software noise reduction techniques allow this type of processing to be executed the moment the photo is captured, allowing photographers to store images that have a higher level of refinement and would have been prohibitively time-consuming to process with earlier generations of digital camera hardware.


title: Film speed

text: The ISO standard ISO 12232:2006 gave digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model. Three of the techniques in ISO 12232:2006 were carried over from the 1998 version of the standard, while two new techniques allowing for measurement of JPEG output files were introduced from CIPA DC-004. Depending on the technique selected, the exposure index rating could depend on the sensor sensitivity, the sensor noise, and the appearance of the resulting image. The standard specified the measurement of light sensitivity of the entire digital camera system and not of individual components such as digital sensors, although Kodak has reported using a variation to characterize the sensitivity of two of their sensors in 2001.


title: Film speed

text: The "Recommended Exposure Index" (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model's EI choices arbitrarily. The choices are based solely on the manufacturer's opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called "pattern" metering) is used.


title: Film speed

text: The "Standard Output Sensitivity" (SOS) technique, also new in the 2006 version of the standard, effectively specifies that the average level in the sRGB image must be 18% gray plus or minus 1/3 stop when the exposure is controlled by an automatic exposure control system calibrated per ISO 2721 and set to the EI with no exposure compensation. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB JPEG—and not to output files in raw image format. It is not applicable when multi-zone metering is used.


title: Film speed

text: The CIPA DC-004 standard requires that Japanese manufacturers of digital still cameras use either the REI or SOS techniques, and DC-008 updates the Exif specification to differentiate between these values. Consequently, the three EI techniques carried over from ISO 12232:1998 are not widely used in recent camera models (approximately 2007 and later). As those earlier techniques did not allow for measurement from images produced with lossy compression, they cannot be used at all on cameras that produce images only in JPEG format.


title: Film speed

text: The "saturation-based" (SAT or S) technique is closely related to the SOS technique, with the sRGB output level being measured at 100% white rather than 18% gray. The SOS value is effectively 0.704 times the saturation-based value. Because the output level is measured in the sRGB output from the camera, it is only applicable to sRGB images—typically TIFF—and not to output files in raw image format. It is not applicable when multi-zone metering is used.


title: Film speed

text: The two "noise-based" techniques have rarely been used for consumer digital still cameras. These techniques specify the highest EI that can be used while still providing either an "excellent" picture or a "usable" picture depending on the technique chosen.


title: Film speed

text: An update to this standard has been published as ISO 12232:2019, defining a wider range of ISO speeds.


title: Film speed

text: ISO speed ratings of a digital camera are based on the properties of the sensor and the image processing done in the camera, and are expressed in terms of the luminous exposure "H" (in lux seconds) arriving at the sensor. For a typical camera lens with an effective focal length "f" that is much smaller than the distance between the camera and the photographed scene, "H" is given by


title: Film speed

text: where "L" is the luminance of the scene (in candela per m²), "t" is the exposure time (in seconds), "N" is the aperture f-number, and


title: Film speed

text: is a factor depending on the transmittance "T" of the lens, the vignetting factor "v"("θ"), and the angle "θ" relative to the axis of the lens. A typical value is "q" = 0.65, based on "θ" = 10°, "T" = 0.9, and "v" = 0.98.


title: Film speed

text: where formula_9 is the maximum possible exposure that does not lead to a clipped or bloomed camera output. Typically, the lower limit of the saturation speed is determined by the sensor itself, but with the gain of the amplifier between the sensor and the analog-to-digital converter, the saturation speed can be increased. The factor 78 is chosen such that exposure settings based on a standard light meter and an 18-percent reflective surface will result in an image with a grey level of 18%/ = 12.7% of saturation. The factor indicates that there is half a stop of headroom to deal with specular reflections that would appear brighter than a 100% reflecting diffuse white surface.


title: Film speed

text: The "noise-based speed" is defined as the exposure that will lead to a given signal-to-noise ratio on individual pixels. Two ratios are used, the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio. These ratios have been subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance. The noise is defined as the standard deviation of a weighted average of the luminance and color of individual pixels. The noise-based speed is mostly determined by the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter.


title: Film speed

text: In addition to the above speed ratings, the standard also defines the "standard output sensitivity" (SOS), how the exposure is related to the digital pixel values in the output image. It is defined as


title: Film speed

text: where formula_11 is the exposure that will lead to values of 118 in 8-bit pixels, which is 18 percent of the saturation value in images encoded as sRGB or with gamma = 2.2.


title: Film speed

text: The standard specifies how speed ratings should be reported by the camera. If the noise-based speed (40:1) is "higher" than the saturation-based speed, the noise-based speed should be reported, rounded "downwards" to a standard value (e.g. 200, 250, 320, or 400). The rationale is that exposure according to the lower saturation-based speed would not result in a visibly better image. In addition, an exposure latitude can be specified, ranging from the saturation-based speed to the 10:1 noise-based speed. If the noise-based speed (40:1) is "lower" than the saturation-based speed, or undefined because of high noise, the saturation-based speed is specified, rounded upwards to a standard value, because using the noise-based speed would lead to overexposed images. The camera may also report the SOS-based speed (explicitly as being an SOS speed), rounded to the nearest standard speed rating.


title: Film speed

text: For example, a camera sensor may have the following properties: formula_12, formula_13, and formula_14. According to the standard, the camera should report its sensitivity as


title: Film speed

text: The SOS rating could be user controlled. For a different camera with a noisier sensor, the properties might be formula_15, formula_16, and formula_17. In this case, the camera should report


title: Film speed

text: as well as a user-adjustable SOS value. In all cases, the camera should indicate for the white balance setting for which the speed rating applies, such as daylight or tungsten (incandescent light).


title: Film speed

text: Despite these detailed standard definitions, cameras typically do not clearly indicate whether the user "ISO" setting refers to the noise-based speed, saturation-based speed, or the specified output sensitivity, or even some made-up number for marketing purposes. Because the 1998 version of ISO 12232 did not permit measurement of camera output that had lossy compression, it was not possible to correctly apply any of those measurements to cameras that did not produce sRGB files in an uncompressed format such as TIFF. Following the publication of CIPA DC-004 in 2006, Japanese manufacturers of digital still cameras are required to specify whether a sensitivity rating is REI or SOS.


title: Film speed

text: A greater SOS setting for a given sensor comes with some loss of image quality, just like with analog film. However, this loss is visible as image noise rather than grain. APS- and 35 mm-sized digital image sensors, both CMOS and CCD based, do not produce significant noise until about "ISO 1600".


title: Jason Dolley

text: Jason Scott Dolley (born July 5, 1991) is an American actor and musician, known for his roles in Disney Channel shows and movies. These include Newton "Newt" Livingston III on "Cory in the House", Virgil Fox in "Minutemen", Connor Kennedy in "Read It and Weep", Pete Ivey in "Hatching Pete", and PJ Duncan on "Good Luck Charlie".


title: Jason Dolley

text: Jason Scott Dolley was born in Los Angeles, California on July 5, 1991. He has an older brother named Jeffrey (Born 1989). In 2010, he took college courses in philosophy at Moorpark College and at California Lutheran University.


title: Jason Dolley

text: Dolley gained his first stage experience at 11 when he and one of his brothers performed the Abbott and Costello "Who's on First?" routine in a school talent show.


title: Jason Dolley

text: His first acting jobs came that same year. He won the lead role in the award-winning short film titled "Chasing Daylight". He was then cast by director Mel Gibson to be T.J. Savage on the ABC series "Complete Savages". After "Complete Savages" was canceled, he starred in the film "Saving Shiloh" as Marty Preston, in the Disney Channel Original Movie "Read It and Weep" as Connor Kennedy and in the film "The Air I Breathe."


title: Jason Dolley

text: In 2006, Dolley appeared in Duracell's commercial "Trusted Everywhere" Campaign "Amazon". Dolley was part of the Yellow team in the second edition of the "Disney Channel Games", broadcast in mid-2007. From 2007 to 2008, Dolley starred in the Disney Channel show "Cory in the House". In 2008, he appeared in the film "Minutemen" as Virgil Fox and was in the third edition of the Disney Channel Games on the Green Team. Dolley also guest-starred as the prince in "Imagination Movers". In 2009, Jason starred in the Disney film "Hatching Pete" as Pete Ivey. In 2010, Dolley began appearing in his second Disney Channel Original Series, "Good Luck Charlie" as P.J. Duncan.


title: Jason Dolley

text: When asked about his role in the Disney Channel Original Series family sitcom, "Good Luck Charlie", he replied, "I like the realness of it. I like the more authentic tone. I like the family sitcom. That's something different for Disney, which also appealed to me." He also said in a different interview, "When I read the script, I was like, 'Oh, this is kind of cool. This is a little different. It has a "Full House" kind of feel. It's very family-friendly. Families can sit down and watch this and get a real laugh. I think that's what's been cool about it from the start and what's still cool about it today."


title: Jason Dolley

text: Dolley and cast appeared in a feature-length Christmas Disney Channel Original Movie based on the series titled "Good Luck Charlie, It's Christmas!", which aired on December 2, 2011. He also voiced the character Rumble in Disney Channel's animated film "Pixie Hollow Games", which also stars Brenda Song, Tiffany Thornton, and Zendaya.


title: YTV (Canadian TV channel)

text: YTV is a Canadian English language specialty channel owned by YTV Canada, Inc., a subsidiary of Corus Entertainment. The channel and its programming is targeted at children and young teenagers; its name was originally thought to be an abbreviation for "Youth Television", though the channel's website has denied this.


title: YTV (Canadian TV channel)

text: The channel was launched on September 1, 1988 by owners Rogers Media and CUC Broadcasting upon launch. In 1995, Shaw Communications acquired CUC's 34% stake and in 1998, it acquired Rogers' remaining interest of the channel, before Shaw's media division was spun off to form Corus Entertainment in 1999. Under Corus ownership, YTV sources most of its programming from U.S.-based Nickelodeon and launched its own dedicated TV channel several years later.


title: YTV (Canadian TV channel)

text: YTV operates two time shifted feeds, running on both Eastern and Pacific Time Zone schedules, and is available in over 11.0 million households in Canada as of 2013.


title: YTV (Canadian TV channel)

text: The channel was licensed by the Canadian Radio-television and Telecommunications Commission (CRTC) in 1987 by Rogers Cable and CUC Broadcasting.


title: YTV (Canadian TV channel)

text: The channel launched on September 1, 1988 at 7:00 p.m., with the first program being a special party celebrating the launch of YTV, hosted by John Candy. At launch, Rogers held 75% of the channel while CUC owned 25%.


title: YTV (Canadian TV channel)

text: In 1995, Calgary-based Shaw Communications acquired CUC's stake of 34% ownership of YTV. Shaw acquired Rogers' remaining share in 1998 to take full control of it. In 1999, the media assets of Shaw were spun off to form Corus Entertainment.


title: YTV (Canadian TV channel)

text: Two Corus specialty channel applications for YTV extensions, YTV POW!, an internationally sourced kids' action, adventure and superhero genre, and YTV OneWorld, targeting children from age 9 to 17 with travel, humour, games, and STEM were approved on September 18, 2008. The YTV Oneworld license was used to launch Nickelodeon Canada.


title: YTV (Canadian TV channel)

text: Current YTV original programming include hosted programming blocks, such as "The Zone". In addition to original programming, YTV has historically acquired and co-produced programming with the U.S cable network Nickelodeon.


title: YTV (Canadian TV channel)

text: Starting in September 1990, YTV called their program jockeys "PJs" in the same vein as disc jockey (DJ) or video jockey (VJ). Current hosts of these segments have since dropped the moniker as of the mid-1990s.


title: YTV (Canadian TV channel)

text: Treehouse is a Category A cable and satellite specialty channel which airs programming targeted to preschoolers, from 2 to 5. It launched on November 1, 1997. The channel's name is taken from YTV's now-defunct children's programming block, "The Treehouse". Treehouse is carried nationwide throughout Canada and it broadcasts its programming without commercial interruption.


title: YTV (Canadian TV channel)

text: Nickelodeon is a Category B cable and satellite specialty channel that was launched on November 2, 2009, and is based on the U.S. cable channel Nickelodeon. Like its counterparts in the U.S. and elsewhere, Nickelodeon airs programs aimed at children to younger teenagers, targeted at 7—11. including both live action series and animation.


title: YTV (Canadian TV channel)

text: In July 2005, Corus Entertainment partnered up with Comcast Corporation to launch a cable video-on-demand service called "Vortex on Demand" in the United States. The deal consisted of 393 30 minute animation TV series from the Nelvana library; it aired programs such as "Cadillacs & Dinosaurs" and "Medabots". The service was discontinued in mid-2007.


title: YTV (Canadian TV channel)

text: In 2008, Corus Entertainment began offering a video-on-demand service called "Bionix On Demand" to Canadian cable providers. Rogers Cable and Shaw Cable were the only providers to offer the service. The service offered older and newer anime programs that did not air on YTV itself. The video-on-demand service was previously titled "YTV Anime On Demand". Bionix On Demand was discontinued on December 17, 2009, and was replaced by YTV On Demand.


title: YTV (Canadian TV channel)

text: YTV GO was a TV Everywhere mobile app available on the App Store and Google Play Store. It was available at no extra charge to all subscribed customers of Access Communications, Bell Satellite TV, Cogeco, Shaw Cable, Shaw Direct, Telus, and VMedia. It offered episodes of various programming from YTV. The app operated between September 2015 and May 1, 2019.


title: Cait O'Riordan

text: Caitlín O'Riordan (born 4 January 1965) is a British musician of Irish and Scottish descent. She played bass guitar for the Irish punk/folk band the Pogues from 1983 to 1986. She later played with Elvis Costello (her husband from 1986 to 2002) as well as several other projects. She uses the name Rocky O'Riordan on social media and for her Sirius-XM radio show, "The Rocky O'Riordan Show".


title: Cait O'Riordan

text: Caitlín O'Riordan was born in Nigeria to Irish and Scottish parents, who moved to London when the Nigerian Civil War broke out in 1967. She heard the Nips' song "Gabrielle" on the radio in 1979, and subsequently met future Pogues' frontman Shane MacGowan, who was working at Rocks Off Records, where she went to purchase the record.


title: Cait O'Riordan

text: In 1982, she was invited by MacGowan to join his newly forming band Pogue Mahone. She appeared on the group's first two albums, "Red Roses for Me" and "Rum Sodomy & the Lash, the EP Poguetry in Motion", and several early singles, before leaving in 1986. Besides playing bass, she provided vocals for "I'm a Man You Don't Meet Every Day" on "Rum Sodomy & the Lash", and for "Haunted" on the soundtrack to Alex Cox's film "Sid and Nancy". The Pogues' most commercially successful song, "Fairytale of New York" from "If I Should Fall from Grace with God", was written as a duet for O'Riordan and MacGowan, but the band eventually recorded it with Kirsty MacColl singing the female part. O'Riordan and Costello are mentioned in the lyrics to "Fiesta" from "If I Should Fall from Grace with God".


title: Cait O'Riordan

text: In 1983, she became the singer in Darryl Hunt's jazz band Pride of the Cross. Hunt had originally planned to ask Wendy May of the Boothill Foot Tappers to be the singer. When he told O'Riordan, she laughed at him and said she ought to do it. At the audition the band told her that she couldn't sing. During her time with Pride of the Cross, she sang lead on their only single, "Tommy's Blue Valentine".


title: Cait O'Riordan

text: She acted in the 1987 Alex Cox film, "Straight to Hell", as the singing dancehall girl Slim McMahon, and also in the 1988 Frank Deasy film "The Courier".


title: Cait O'Riordan

text: O'Riordan became involved with Elvis Costello in 1985, while he was producing the Pogues' album "Rum Sodomy & the Lash"; they married on 17 May 1986. Her former Pride of the Cross bandmate Darryl Hunt filled in for her on several shows during the Pogues' 1986 U.S. tour, and he replaced her permanently when she left later that year to join Costello on his "King of America" tour.


title: Cait O'Riordan

text: She co-wrote the track "Lovable" from that album, and wrote, co-wrote, and appeared on songs on Costello's subsequent albums "Blood & Chocolate", "Spike" and "Mighty Like a Rose". O'Riordan and Costello divorced in 2002. In a 2008 interview with the "Irish Independent", she denied ever having formally married Costello: "We weren't married...It was a kind of Muslim 'I divorce you' kind of thing."


title: Cait O'Riordan

text: In 2004, she joined Pogues' guitarist Phil Chevron's re-united band the Radiators; that year she toured with the Pogues for the first time in 18 years. She left the Radiators and was replaced in February 2006 by Jesse Booth, and went on to form a band of divorcées named PreNup with Hothouse Flowers guitarist Fiachna Ó Braonáin.


title: Cait O'Riordan

text: In 2018 O'Riordan joined Pogues tin whistle player Spider Stacy to perform Pogues songs accompanied by Cajun music band Lost Bayou Ramblers under the name Poguetry. In February and March 2020 Poguetry played an eight date tour of the US.


title: Cait O'Riordan

text: Since 2020 O'Riordan has hosted a weekly radio show, "The Rocky O'Riordan Show" on U2-X Radio, an artist-branded channel which is part of SiriusXM.


title: Metal–organic framework

text: Metal–organic frameworks (MOFs) are a class of compounds consisting of metal ions or clusters coordinated to organic ligands to form one-, two-, or three-dimensional structures. The organic ligands included are sometimes referred to as "struts" or "linkers", one example being 1,4-benzenedicarboxylic acid (BDC).


title: Metal–organic framework

text: More formally, a metal–organic framework is a crystalline material with organic ligands containing potential voids. In most cases for MOFs, the pores are stable during the elimination of the guest molecules (often solvents) and could be refilled with other compounds. Because of this property, MOFs are of interest for the storage of gases such as hydrogen and carbon dioxide. Other possible applications of MOFs are in gas purification, in gas separation, in water remediation, in catalysis, as conducting solids and as supercapacitors.


title: Metal–organic framework

text: The synthesis and properties of MOFs constitute the primary focus of the discipline called (from Latin , "small net"). In contrast to MOFs, covalent organic framework (COFs) are made entirely from light elements (H, B, C, N, and O) with extended structures.


title: Metal–organic framework

text: MOFs are composed of two main components: an inorganic metal cluster (often referred to as a secondary-building unit or SBU) and an organic molecule called a linker. For this reason, the materials are often referred to as hybrid organic-inorganic materials. The organic units are typically mono-, di-, tri-, or tetravalent ligands. The choice of metal and linker dictates the structure and hence properties of the MOF. For example, the metal's coordination preference influences the size and shape of pores by dictating how many ligands can bind to the metal and in which orientation.


title: Metal–organic framework

text: To describe and organize the structures of MOFs, a system of nomenclature has been developed. Subunits of a MOF, called secondary building units (SBU), can be described by topologies common to several structures. Each topology, also called a net, is assigned a symbol, consisting of three lower-case letters in bold. MOF-5, for example, has a pcu net.


title: Metal–organic framework

text: Attached to the SBUs are bridging ligands. For MOF's, typical bridging ligands are di- and tricarboxylic acids. These ligands typically have rigid backbones. Examples are benzene-1,4-dicarboxylic acid (BDC or terephthalic acid, biphenyl-4,4-dicarboxylic acid (BPDC), and the tricarboxylic acid trimesic acid.


title: Metal–organic framework

text: The study of MOFs has roots in coordination chemistry and solid-state inorganic chemistry, but it developed to form a new field. In addition, MOFs are constructed from bridging organic ligands that remain intact throughout the synthesis. Zeolite synthesis often makes use of a "template". Templates are ions that influence the structure of the growing inorganic framework. Typical templating ions are quaternary ammonium cations, which are removed later. In MOFs, the framework is templated by the SBU (secondary building unit) and the organic ligands. A templating approach that is useful for MOFs intended for gas storage is the use of metal-binding solvents such as N,N-diethylformamide and water. In these cases, metal sites are exposed when the solvent is evacuated, allowing hydrogen to bind at these sites.


title: Metal–organic framework

text: Four developments were particularly important in advancing the chemistry of MOFs. (1) The geometric principle of construction where metal-containing units were kept in rigid shapes. Early MOFs contained single atoms linked to ditopic coordinating linkers. The approach not only led to the identification of a small number of preferred topologies that could be targeted in designed synthesis, but was the central point to achieve a permanent porosity. (2) The use of the isoreticular principle where the size and the nature of a structure changes without changing its topology led to MOFs with ultrahigh porosity and unusually large pore openings. (3) Post- synthetic modification of MOFs increased their functionality by reacting organic units and metal-organic complexes with linkers. (4) Multifunctional MOFs incorporated multiple functionalities in a single framework.


title: Metal–organic framework

text: Since ligands in MOFs typically bind reversibly, the slow growth of crystals often allows defects to be redissolved, resulting in a material with millimeter-scale crystals and a near-equilibrium defect density. Solvothermal synthesis is useful for growing crystals suitable to structure determination, because crystals grow over the course of hours to days. However, the use of MOFs as storage materials for consumer products demands an immense scale-up of their synthesis. Scale-up of MOFs has not been widely studied, though several groups have demonstrated that microwaves can be used to nucleate MOF crystals rapidly from solution. This technique, termed "microwave-assisted solvothermal synthesis", is widely used in the zeolite literature, and produces micron-scale crystals in a matter of seconds to minutes, in yields similar to the slow growth methods.


title: Metal–organic framework

text: Some MOFs, such as the mesoporous MIL-100(Fe), can be obtained under mild conditions at room temperature and in green solvents (water, ethanol) through scalable synthesis methods.


title: Metal–organic framework

text: A solvent-free synthesis of a range of crystalline MOFs has been described. Usually the metal acetate and the organic proligand are mixed and ground up with a ball mill. Cu(BTC) can be quickly synthesised in this way in quantitative yield. In the case of Cu(BTC) the morphology of the solvent free synthesised product was the same as the industrially made Basolite C300. It is thought that localised melting of the components due to the high collision energy in the ball mill may assist the reaction. The formation of acetic acid as a by-product in the reactions in the ball mill may also help in the reaction having a solvent effect in the ball mill. It has been shown that the addition of small quantities of ethanol for the mechanochemical synthesis of Cu(BTC) significantly reduces the amounts of structural defects in the obtained material.


title: Metal–organic framework

text: A recent advancement in the solvent-free preparation of MOF films and composites is their synthesis by chemical vapor deposition. This process, MOF-CVD,


title: Metal–organic framework

text: was first demonstrated for ZIF-8 and consist of two steps. In a first step, metal oxide precursor layers are deposited. In the second step, these precursor layers are exposed to sublimed ligand molecules, that induce a phase transformation to the MOF crystal lattice. Formation of water during this reaction plays a crucial role in directing the transformation. This process was successfully scaled up to an integrated cleanroom process, conforming to industrial microfabrication standards.


title: Metal–organic framework

text: Numerous methods have been reported for the growth of MOFs as oriented thin films. However, these methods are suitable only for the synthesis of a small number of MOF topologies. One such example being the vapor-assisted conversion (VAC) which can be used for the thin film synthesis of several UiO-type MOFs.


title: Metal–organic framework

text: High-Throughput (HT) methods are a part of combinatorial chemistry and a tool for increasing efficiency. Basically, there are two synthetic strategies within the HT-methods: On the one hand the combinatorial approach, here all reactions take place in one vessel, which leads to product mixtures and on the other hand the parallel synthesis, here the reactions take place in different vessels. Furthermore, a distinction is made between thin films and solvent-based methods.


title: Metal–organic framework

text: Solvothermal synthesis can be carried out conventionally in a teflon reactor in a convection oven or in glass reactors in a microwave oven (high-throughput microwave synthesis). The use of a microwave oven changes, in part dramatically, the reaction parameters.


title: Metal–organic framework

text: In addition to solvothermal synthesis, there have been advances in using supercritical fluid as a solvent in a continuous flow reactor. Supercritical water was first used in 2012 to synthesize copper and nickel-based MOFs in just seconds. In 2020, supercritical carbon dioxide was used in a continuous flow reactor along the same time scale as the supercritical water-based method, but the lower critical point of carbon dioxide allowed for the synthesis of the zirconium-based MOF UiO-66.


title: Metal–organic framework

text: In high-throughput solvothermal synthesis, a solvothermal reactor with (eg) 24 cavities for teflon reactors is used. Such a reactor is sometimes referred to as a multiclav. The reactor block or reactor insert is made of stainless steel and contains 24 reaction chambers, which are arranged in four rows. With the miniaturized teflon reactors, volumes of up to 2 mL can be used. The reactor block is sealed in a stainless steel autoclave; for this purpose, the filled reactors are inserted into the bottom of the reactor, the teflon reactors are sealed with two teflon films and the reactor top side is put on. The autoclave is then closed in a hydraulic press. The sealed solvothermal reactor can then be subjected to a temperature-time program. The reusable teflon film serves to withstand the mechanical stress, while the disposable teflon film seals the reaction vessels. After the reaction, the products can be isolated and washed in parallel in a vacuum filter device. On the filter paper, the products are then present separately in a so-called sample library and can subsequently be characterized by automated X-ray powder diffraction. The informations obtained are then used to plan further syntheses.


title: Metal–organic framework

text: Pseudomorphic mineral replacement events occur whenever a mineral phase comes into contact with a fluid with which it is out of equilibrium. Re-equilibration will tend to take place to reduce the free energy and transform the initial phase into a more thermodynamically stable phase, involving dissolution and reprecipitation subprocesses.


title: Metal–organic framework

text: Inspired by such geological processes, MOF thin films can be grown through the combination of atomic layer deposition (ALD) of aluminum oxide onto a suitable substrate (e.g. FTO) and subsequent solvothermal microwave synthesis. The aluminum oxide layer serves both as an architecture-directing agent and as a metal source for the backbone of the MOF structure. The construction of the porous 3D metal-organic framework takes place during the microwave synthesis, when the atomic layer deposited substrate is exposed to a solution of the requisite linker in a DMF/HO 3:1 mixture (v/v) at elevated temperature. Analogous, Kornienko and coworkers described in 2015 the synthesis of a cobalt-porphyrin MOF (Al(OH)TCPP-Co; TCPP-H = 4,4,4,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate), the first MOF catalyst constructed for the electrocatalytic conversion of aqueous CO to CO.


title: Metal–organic framework

text: Although the three-dimensional structure and internal environment of the pores can be in theory controlled through proper selection of nodes and organic linking groups, the direct synthesis of such materials with the desired functionalities can be difficult due to the high sensitivity of MOF systems. Thermal and chemical sensitivity, as well as high reactivity of reaction materials, can make forming desired products challenging to achieve. The exchange of guest molecules and counter-ions and the removal of solvents allow for some additional functionality but are still limited to the integral parts of the framework. The post-synthetic exchange of organic linkers and metal ions is an expanding area of the field and opens up possibilities for more complex structures, increased functionality, and greater system control.


title: Metal–organic framework

text: Post-synthetic modification techniques can be used to exchange an existing organic linking group in a prefabricated MOF with a new linker by ligand exchange or partial ligand exchange. This exchange allows for the pores and, in some cases the overall framework of MOFs, to be tailored for specific purposes. Some of these uses include fine-tuning the material for selective adsorption, gas storage, and catalysis. To perform ligand exchange prefabricated MOF crystals are washed with solvent and then soaked in a solution of the new linker. The exchange often requires heat and occurs on the time scale of a few days. Post-synthetic ligand exchange also enables the incorporation of functional groups into MOFs that otherwise would not survive MOF synthesis, due to temperature, pH, or other reaction conditions, or hinder the synthesis itself by competition with donor groups on the loaning ligand.


title: Metal–organic framework

text: Post-synthetic modification techniques can also be used to exchange an existing metal ion in a prefabricated MOF with a new metal ion by metal ion exchange. The complete metal metathesis from an integral part of the framework has been achieved without altering the framework or pore structure of the MOF. Similarly to post-synthetic ligand exchange post-synthetic metal exchange is performed by washing prefabricated MOF crystals with solvent and then soaking the crystal in a solution of the new metal. Post-synthetic metal exchange allows for a simple route to the formation of MOFs with the same framework yet different metal ions.


title: Metal–organic framework

text: In addition to modifying the functionality of the ligands and metals themselves, post-synthetic modification can be used to expand upon the structure of the MOF. Using post-synthetic modification MOFs can be converted from a highly ordered crystalline material toward a heterogeneous porous material. Using post-synthetic techniques, it is possible for the controlled installation of domains within a MOF crystal which exhibit unique structural and functional characteristics. Core-shell MOFs and other layered MOFs have been prepared where layers of have unique functionalization but in most cases are crystallographically compatible from layer to layer.


title: Metal–organic framework

text: In some cases MOF metal node has an unsaturated environment, and it is possible to modify this environment using different techniques. If the size of the ligand matches the size of the pore aperture, it is possible to install additional ligands to existing MOF structure. Sometimes metal nodes have a good binding affinity for inorganic species. For instance, it was shown that metal node can perform an extension, and create a bond with the uranyl cation.


title: Metal–organic framework

text: Another approach to increasing adsorption in MOFs is to alter the system in such a way that chemisorption becomes possible. This functionality has been introduced by making a composite material, which contains a MOF and a complex of platinum with activated carbon. In an effect known as hydrogen spillover, H can bind to the platinum surface through a dissociative mechanism which cleaves the hydrogen molecule into two hydrogen atoms and enables them to travel down the activated carbon onto the surface of the MOF. This innovation produced a threefold increase in the room-temperature storage capacity of a MOF; however, desorption can take upwards of 12 hours, and reversible desorption is sometimes observed for only two cycles. The relationship between hydrogen spillover and hydrogen storage properties in MOFs is not well understood but may prove relevant to hydrogen storage.


title: Metal–organic framework

text: MOFs have potential as heterogeneous catalysts, although applications have not been commercialized. Their high surface area, tunable porosity, diversity in metal and functional groups make them especially attractive for use as catalysts. Zeolites are extraordinarily useful in catalysis. Zeolites are limited by the fixed tetrahedral coordination of the Si/Al connecting points and the two-coordinated oxide linkers. Fewer than 200 zeolites are known. In contrast with this limited scope, MOFs exhibit more diverse coordination geometries, polytopic linkers, and ancillary ligands (F, OH, HO among others). It is also difficult to obtain zeolites with pore sizes larger than 1 nm, which limits the catalytic applications of zeolites to relatively small organic molecules (typically no larger than xylenes). Furthermore, mild synthetic conditions typically employed for MOF synthesis allow direct incorporation of delicate functionalities into the framework structures. Such a process would not be possible with zeolites or other microporous crystalline oxide-based materials because of the harsh conditions typically used for their synthesis (e.g., calcination at high temperatures to remove organic templates). Metal-Organic Framework MIL-101 is one of the most used MOFs for catalysis incorporating different transition metals such as Cr. However, the stability of some MOF photocatalysts in aqueous medium and under strongly oxidizing conditions is very low.


title: Metal–organic framework

text: Zeolites still cannot be obtained in enantiopure form, which precludes their applications in catalytic asymmetric synthesis, e.g., for the pharmaceutical, agrochemical, and fragrance industries. Enantiopure chiral ligands or their metal complexes have been incorporated into MOFs to lead to efficient asymmetric catalysts. Even some MOF materials may bridge the gap between zeolites and enzymes when they combine isolated polynuclear sites, dynamic host–guest responses, and a hydrophobic cavity environment. MOFs might be useful for making semi-conductors. Theoretical calculations show that MOFs are semiconductors or insulators with band gaps between 1.0 and 5.5 eV which can be altered by changing the degree of conjugation in the ligands indicating its possibility for being photocatalysts.


title: Metal–organic framework

text: Like other heterogeneous catalysts, MOFs may allow for easier post-reaction separation and recyclability than homogeneous catalysts. In some cases, they also give a highly enhanced catalyst stability. Additionally, they typically offer substrate-size selectivity. Nevertheless, while clearly important for reactions in living systems, selectivity on the basis of substrate size is of limited value in abiotic catalysis, as reasonably pure feedstocks are generally available.


title: Metal–organic framework

text: Among the earliest reports of MOF-based catalysis was the cyanosilylation of aldehydes by a 2D MOF (layered square grids) of formula Cd(4,4-bpy)(NO). This investigation centered mainly on size- and shape-selective clathration. A second set of examples was based on a two-dimensional, square-grid MOF containing single Pd(II) ions as nodes and 2-hydroxypyrimidinolates as struts. Despite initial coordinative saturation, the palladium centers in this MOF catalyze alcohol oxidation, olefin hydrogenation, and Suzuki C–C coupling. At a minimum, these reactions necessarily entail redox oscillations of the metal nodes between Pd(II) and Pd(0) intermediates accompanying by drastic changes in coordination number, which would certainly lead to destabilization and potential destruction of the original framework if all the Pd centers are catalytically active. The observation of substrate shape- and size-selectivity implies that the catalytic reactions are heterogeneous and are indeed occurring within the MOF. Nevertheless, at least for hydrogenation, it is difficult to rule out the possibility that catalysis is occurring at the surface of MOF-encapsulated palladium clusters/nanoparticles (i.e., partial decomposition sites) or defect sites, rather than at transiently labile, but otherwise intact, single-atom MOF nodes. "Opportunistic" MOF-based catalysis has been described for the cubic compound, MOF-5. This material comprises coordinatively saturated ZnO nodes and a fully complexed BDC struts (see above for abbreviation); yet it apparently catalyzes the Friedel–Crafts tert-butylation of both toluene and biphenyl. Furthermore, para alkylation is strongly favored over ortho alkylation, a behavior thought to reflect the encapsulation of reactants by the MOF.


title: Metal–organic framework

text: The porous-framework material [Cu(btc)(HO)<nowiki>]</nowiki>, also known as HKUST-1, contains large cavities having windows of diameter ~6 Å. The coordinated water molecules are easily removed, leaving open Cu(II) sites. Kaskel and co-workers showed that these Lewis acid sites could catalyze the cyanosilylation of benzaldehyde or acetone. The anhydrous version of HKUST-1 is an acid catalyst. Compared to Brønsted vs. Lewis acid-catalyzed pathways, the product selectivity are distinctive for three reactions: isomerization of a-pinene oxide, cyclization of citronellal, and rearrangement of a-bromoacetals, indicating that indeed [Cu(btc)] functions primarily as a Lewis acid catalyst. The product selectivity and yield of catalytic reactions (e.g. cyclopropanation) have also been shown to be impacted by defective sites, such as Cu(I) or incompletely deprotonated carboxylic acid moities of the linkers.


title: Metal–organic framework

text: MIL-101, a large-cavity MOF having the formula [CrF(HO)O(BDC)], is a cyanosilylation catalyst. The coordinated water molecules in MIL-101 are easily removed to expose Cr(III) sites. As one might expect, given the greater Lewis acidity of Cr(III) vs. Cu(II), MIL-101 is much more active than HKUST-1 as a catalyst for the cyanosilylation of aldehydes. Additionally, the Kaskel group observed that the catalytic sites of MIL-101, in contrast to those of HKUST-1, are immune to unwanted reduction by benzaldehyde. The Lewis-acid-catalyzed cyanosilylation of aromatic aldehydes has also been carried out by Long and co-workers using a MOF of the formula Mn[(MnCl)BTT(CHOH)]. This material contains a three-dimensional pore structure, with the pore diameter equaling 10 Å. In principle, either of the two types of Mn(II) sites could function as a catalyst. Noteworthy features of this catalyst are high conversion yields (for small substrates) and good substrate-size-selectivity, consistent with channellocalized catalysis.


title: Metal–organic framework

text: The MOF encapsulation approach invites comparison to earlier studies of oxidative catalysis by zeolite-encapsulated Fe(porphyrin) as well as Mn(porphyrin) systems. The zeolite studies generally employed iodosylbenzene (PhIO), rather than TPHP as oxidant. The difference is likely mechanistically significant, thus complicating comparisons. Briefly, PhIO is a single oxygen atom donor, while TBHP is capable of more complex behavior. In addition, for the MOF-based system, it is conceivable that oxidation proceeds via both oxygen transfer from a manganese oxo intermediate as well as a manganese-initiated radical chain reaction pathway. Regardless of mechanism, the approach is a promising one for isolating and thereby stabilizing the porphyrins against both oxo-bridged dimer formation and oxidative degradation.


title: Metal–organic framework

text: Most examples of MOF-based catalysis make use of metal ions or atoms as active sites. Among the few exceptions are two nickel- and two copper-containing MOFs synthesized by Rosseinsky and co-workers. These compounds employ amino acids(L- or D-aspartate) together with dipyridyls as struts. The coordination chemistry is such that the amine group of the aspartate cannot be protonated by added HCl, but one of the aspartate carboxylates can. Thus, the framework-incorporated amino acid can exist in a form that is not accessible for the free amino acid. While the nickel-based compounds are marginally porous, on account of tiny channel dimensions, the copper versions are clearly porous.


title: Metal–organic framework

text: The Rosseinsky group showed that the carboxylic acids behave as Brønsted acidic catalysts, facilitating (in the copper cases) the ring-opening methanolysis of a small, cavityaccessible epoxide at up to 65% yield. Superior homogeneous catalysts exist however.


title: Metal–organic framework

text: Kitagawa and co-workers have reported the synthesis of a catalytic MOF having the formula [Cd(4-BTAPA)(NO)]. The MOF is three-dimensional, consisting of an identical catenated pair of networks, yet still featuring pores of molecular dimensions. The nodes consist of single cadmium ions, octahedrally ligated by pyridyl nitrogens. From a catalysis standpoint, however, the most interesting feature of this material is the presence of guest-accessible amide functionalities. The amides are capable of base-catalyzing the Knoevenagel condensation of benzaldehyde with malononitrile. Reactions with larger nitriles, however, are only marginally accelerated, implying that catalysis takes place chiefly within the material's channels rather than on its exterior. A noteworthy finding is the lack of catalysis by the free strut in homogeneous solution, evidently due to intermolecular H-bonding between bptda molecules. Thus, the MOF architecture elicits catalytic activity not otherwise encountered.


title: Metal–organic framework

text: In an interesting alternative approach, Férey and coworkers were able to modify the interior of MIL-101 via Cr(III) coordination of one of the two available nitrogen atoms of each of several ethylenediamine molecules. The free non-coordinated ends of the ethylenediamines were then used as Brønsted basic catalysts, again for Knoevenagel condensation of benzaldehyde with nitriles.


title: Metal–organic framework

text: A third approach has been described by Kim Kimoon and coworkers. Using a pyridine-functionalized derivative of tartaric acid and a Zn(II) source they were able to synthesize a 2D MOF termed POST-1. POST-1 possesses 1D channels whose cross sections are defined by six trinuclear zinc clusters and six struts. While three of the six pyridines are coordinated by zinc ions, the remaining three are protonated and directed toward the channel interior. When neutralized, the noncoordinated pyridyl groups are found to catalyze transesterification reactions, presumably by facilitating deprotonation of the reactant alcohol. The absence of significant catalysis when large alcohols are employed strongly suggests that the catalysis occurs within the channels of the MOF.


title: Metal–organic framework

text: The metals in the MOF structure often act as Lewis acids. The metals in MOFs often coordinate to labile solvent molecules or counter ions which can be removed after activation of the framework. The Lewis acidic nature of such unsaturated metal centers can activate the coordinated organic substrates for subsequent organic transformations. The use of unsaturated metal centers was demonstrated in the cyanosilylation of aldehydes and imines by Fujita and coworkers in 2004. They reported MOF of composition {[Cd(4,4-bpy)(HO)] • (NO) • 4HO} which was obtained by treating linear bridging ligand 4,4-bipyridine (bpy) with . The Cd(II) centers in this MOF possesses a distorted octahedral geometry having four pyridines in the equatorial positions, and two water molecules in the axial positions to form a two-dimensional infinite network. On activation, two water molecules were removed leaving the metal centers unsaturated and Lewis acidic. The Lewis acidic character of metal center was tested on cyanosilylation reactions of imine where the imine gets attached to the Lewis-acidic metal centre resulting in higher electrophilicity of imines. For the cyanosilylation of imines, most of the reactions were complete within 1 h affording aminonitriles in quantitative yield. Kaskel and coworkers carried out similar cyanosilylation reactions with coordinatively unsaturated metals in three-dimensional (3D) MOFs as heterogeneous catalysts. The 3D framework [Cu(btc)(HO)] (btc: Benzene-1,3,5- tricarboxylate) (HKUST-1) used in this study was first reported by Williams "et al." The open framework of [Cu(btc)(HO)] is built from dimeric cupric tetracarboxylate units (paddle-wheels) with aqua molecules coordinating to the axial positions and btc bridging ligands. The resulting framework after removal of two water molecules from axial positions possesses porous channel. This activated MOF catalyzes the trimethylcyanosilylation of benzaldehydes with a very low conversion (<5% in 24 h) at 293 K. As the reaction temperature was raised to 313 K, a good conversion of 57% with a selectivity of 89% was obtained after 72 h. In comparison, less than 10% conversion was observed for the background reaction (without MOF) under the same conditions. But this strategy suffers from some problems like 1) the decomposition of the framework with increase of the reaction temperature due to the reduction of Cu(II) to Cu(I) by aldehydes; 2) strong solvent inhibition effect; electron donating solvents such as THF competed with aldehydes for coordination to the Cu(II) sites, and no cyanosilylation product was observed in these solvents; 3) the framework instability in some organic solvents. Several other groups have also reported the use of metal centres in MOFs as catalysts Again, electron-deficient nature of some metals and metal clusters makes the resulting MOFs efficient oxidation catalysts. Mori and coworkers reported MOFs with Cu paddle wheel units as heterogeneous catalysts for the oxidation of alcohols. The catalytic activity of the resulting MOF was examined by carrying out alcohol oxidation with HO as the oxidant. It also catalyzed the oxidation of primary alcohol, secondary alcohol and benzyl alcohols with high selectivity. Hill "et al." have demonstrated the sulfoxidation of thioethers using an MOF based on vanadium-oxo cluster VO building units.


title: Metal–organic framework

text: Functional linkers can be also utilized as catalytic sites. A 3D MOF {[Cd(4- BTAPA)(NO)] • 6HO • 2DMF} (4-BTAPA=1,3,5-benzene tricarboxylic acid tris [N-(4-pyridyl)amide], DMF=N,N-dimethylformamide) constructed by tridentate amide linkers and cadmium salt catalyzes the Knoevenagel condensation reaction. The pyridine groups on the ligand 4-BTAPA act as ligands binding to the octahedral cadmium centers, while the amide groups can provide the functionality for interaction with the incoming substrates. Specifically, the – NH moiety of the amide group can act as electron acceptor whereas the C=O group can act as electron donor to activate organic substrates for subsequent reactions. Ferey "et al." reported a robust and highly porous MOF [Cr(μ-O)F(HO)(BDC)] (BDC: Benzene-1,4- dicarboxylate) where instead of directly using the unsaturated Cr(III) centers as catalytic sites, the authors grafted ethylenediamine (ED) onto the Cr(III) sites. The uncoordinated ends of ED can act as base catalytic sites, ED-grafted MOF was investigated for Knoevenagel condensation reactions. A significant increase in conversion was observed for ED-grafted MOF compared to untreated framework (98% vs 36%). Another example of linker modification to generate catalytic site is iodo-functionalized well-known Al-based MOFs (MIL-53 and DUT-5) and Zr-based MOFs (UiO-66 and UiO-67) for the catalytic oxidation of diols.


title: Metal–organic framework

text: The entrapment of catalytically active noble metals can be accomplished by grafting on functional groups to the unsaturated metal site on MOFs. Ethylenediamine (ED) has been shown to be grafted on the Cr metal sites and can be further modified to encapsulate noble metals such as Pd. The entrapped Pd has similar catalytic activity as Pd/C in the Heck reaction. Ruthenium nanoparticles have catalytic activity in a number of reactions when entrapped in the MOF-5 framework. This Ru-encapsulated MOF catalyzes oxidation of benzyl alcohol to benzyaldehyde, although degradation of the MOF occurs. The same catalyst was used in the hydrogenation of benzene to cyclohexane. In another example, Pd nanoparticles embedded within defective HKUST-1 framework enable the generation of tunable Lewis basic sites. Therefore, this multifunctional Pd/MOF composite is able to perform stepwise benzyl alcohol oxidation and Knoevenagel condensation.


title: Metal–organic framework

text: MOFs might prove useful for both photochemical and polymerization reactions due to the tuneability of the size and shape of their pores. A 3D MOF {[Co(bpdc)(bpy)] • 4DMF • HO} (bpdc: biphenyldicarboxylate, bpy: 4,4-bipyridine) was synthesized by Li and coworkers. Using this MOF photochemistry of "o"-methyl dibenzyl ketone ("o"-MeDBK) was extensively studied. This molecule was found to have a variety of photochemical reaction properties including the production of cyclopentanol. MOFs have been used to study polymerization in the confined space of MOF channels. Polymerization reactions in confined space might have different properties than polymerization in open space. Styrene, divinylbenzene, substituted acetylenes, methyl methacrylate, and vinyl acetate have all been studied by Kitagawa and coworkers as possible activated monomers for radical polymerization. Due to the different linker size the MOF channel size could be tunable on the order of roughly 25 and 100 Å. The channels were shown to stabilize propagating radicals and suppress termination reactions when used as radical polymerization sites.


title: Metal–organic framework

text: Several strategies exist for constructing homochiral MOFs. Crystallization of homochiral MOFs via self-resolution from achiral linker ligands is one of the way to accomplish such a goal. However, the resulting bulk samples contain both enantiomorphs and are racemic. Aoyama and coworkers successfully obtained homochiral MOFs in the bulk from achiral ligands by carefully controlling nucleation in the crystal growth process. Zheng and coworkers reported the synthesis of homochiral MOFs from achiral ligands by chemically manipulating the statistical fluctuation of the formation of enantiomeric pairs of crystals. Growing MOF crystals under chiral influences is another approach to obtain homochiral MOFs using achiral linker ligands. Rosseinsky and coworkers have introduced a chiral coligand to direct the formation of homochiral MOFs by controlling the handedness of the helices during the crystal growth. Morris and coworkers utilized ionic liquid with chiral cations as reaction media for synthesizing MOFs, and obtained homochiral MOFs. The most straightforward and rational strategy for synthesizing homochiral MOFs is, however, to use the readily available chiral linker ligands for their construction.


title: Metal–organic framework

text: Homochiral MOFs have been made by Lin and coworkers using 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BINAP), 1,1-bi-2,2-naphthol (BINOL) as a chiral ligands. These ligands can coordinate with catalytically active metal sites to enhance the enantioselectivity. A variety of linking groups such as pyridine, phosphonic acid, and carboxylic acid can be selectively introduced to the 3,3, 4,4, and the 6,6 positions of the 1,1'-binaphthyl moiety. Moreover, by changing the length of the linker ligands the porosity and framework structure of the MOF can be selectively tuned.


title: Metal–organic framework

text: Lin and coworkers have shown that the postmodification of MOFs can be achieved to produce enantioselective homochiral MOFs for use as catalysts. The resulting 3D homochiral MOF {[Cd(L)Cl]• 4DMF • 6MeOH • 3HO} (L=(R)-6,6'-dichloro-2,2'-dihydroxyl-1,1'-binaphthyl-bipyridine) synthesized by Lin was shown to have a similar catalytic efficiency for the diethylzinc addition reaction as compared to the homogeneous analogue when was pretreated by Ti(OPr) to generate the grafted Ti- BINOLate species. The catalytic activity of MOFs can vary depending on the framework structure. Lin and others found that MOFs synthesized from the same materials could have drastically different catalytic activities depending on the framework structure present.


title: Metal–organic framework

text: Another approach to construct catalytically active homochiral MOFs is to incorporate chiral metal complexes which are either active catalysts or precatalysts directly into the framework structures. For example, Hupp and coworkers have combined a chiral ligand and bpdc (bpdc: biphenyldicarboxylate) with and obtained twofold interpenetrating 3D networks. The orientation of chiral ligand in the frameworks makes all Mn(III) sites accessible through the channels. The resulting open frameworks showed catalytic activity towards asymmetric olefin epoxidation reactions. No significant decrease of catalyst activity was observed during the reaction and the catalyst could be recycled and reused several times. Lin and coworkers have reported zirconium phosphonate-derived Ru-BINAP systems. Zirconium phosphonate-based chiral porous hybrid materials containing the Ru(BINAP)(diamine)Cl precatalysts showed excellent enantioselectivity (up to 99.2% ee) in the asymmetric hydrogenation of aromatic ketones.


title: Metal–organic framework

text: Some MOF materials may resemble enzymes when they combine isolated polynuclear sites, dynamic host–guest responses, and hydrophobic cavity environment which are characteristics of an enzyme. Some well-known examples of cooperative catalysis involving two metal ions in biological systems include: the diiron sites in methane monooxygenase, dicopper in cytochrome c oxidase, and tricopper oxidases which have analogy with polynuclear clusters found in the 0D coordination polymers, such as binuclear Cu paddlewheel units found in MOP-1 and [Cu(btc)] (btc=benzene-1,3,5-tricarboxylate) in HKUST-1 or trinuclear units such as { } in MIL-88, and IRMOP-51. Thus, 0D MOFs have accessible biomimetic catalytic centers. In enzymatic systems, protein units show "molecular recognition", high affinity for specific substrates. It seems that molecular recognition effects are limited in zeolites by the rigid zeolite structure. In contrast, dynamic features and guest-shape response make MOFs more similar to enzymes. Indeed, many hybrid frameworks contain organic parts that can rotate as a result of stimuli, such as light and heat. The porous channels in MOF structures can be used as photocatalysis sites. In photocatalysis, the use of mononuclear complexes is usually limited either because they only undergo single- electron process or from the need for high-energy irradiation. In this case, binuclear systems have a number of attractive features for the development of photocatalysts. For 0D MOF structures, polycationic nodes can act as semiconductor quantum dots which can be activated upon photostimuli with the linkers serving as photon antennae. Theoretical calculations show that MOFs are semiconductors or insulators with band gaps between 1.0 and 5.5 eV which can be altered by changing the degree of conjugation in the ligands. Experimental results show that the band gap of IRMOF-type samples can be tuned by varying the functionality of the linker. An integrated MOF nanozyme was developed for anti-inflammation therapy.


title: Metal–organic framework

text: Implementing MOFs in industry necessitates a thorough understanding of the mechanical properties since most processing techniques (e.g. extrusion and pelletization) expose the MOFs to substantial mechanical compressive stresses. The mechanical response of porous structures is of interest as these structures can exhibit unusual response to high pressures. While zeolites (microporous, aluminosilicate minerals) can give some insights into the mechanical response of MOFs, the presence of organic linkers as opposed to zeolites, makes for novel mechanical responses. MOFs are very structurally diverse meaning that it is challenging to classify all of their mechanical properties. Additionally, variability in MOFs from batch to batch and extreme experimental conditions (Diamond anvil cells) mean that experimental determination of mechanical response to loading is limited, however many computational models have been made to determine structure-property relationships. Main MOF systems that have been explored are zeolitic imidazolate frameworks (ZIFs), Carboxylate MOFs, Zirconium-based MOFs, among others. Generally, the MOFs undergo three processes under compressive loading (which is relevant in a processing context): amorphization, hyperfilling, and/or pressure induced phase transitions. During amorphization linkers buckle and the internal porosity within the MOF collapses. During hyperfilling the MOF which is being hydrostatically compressed in a liquid (typically solvent) will expand rather than contract due to a filling of pores with the loading media. Finally, pressure induced phase transitions where the structure of the crystal is altered during the loading are possible. The response of the MOF is predominantly dependent on the linker species and the inorganic nodes.


title: Metal–organic framework

text: Several different mechanical phenomena have been observed in zeolitic imidazolate frameworks (ZIFs), the most widely studied MOF for mechanical properties due to their many similarities to zeolites. General trends for the ZIF family are the tendency of the Young's modulus and hardness of the ZIFs to decrease as the accessible pore volume increases. Another study has shown that under hydrostatic loading in solvent the ZIF-8 material expands as opposed to contracting. This is a result of hyperfilling of the internal pores with solvent. A computational study demonstrated that ZIF-4 and ZIF-8 materials undergo a shear softening mechanism with amorphizing (at ~ 0.34 GPa) of the material under hydrostatic loading, while still possessing a bulk modulus on the order of 6.5 GPa. Additionally, the ZIF-4 and ZIF-8 MOFs are subject to many pressure dependent phase transitions.,


title: Metal–organic framework

text: Carboxylate MOFs come in many forms and have been widely studied. Herein, HKUST-1, MOF-5, and the MIL series are discussed as representative examples of the carboxylate MOF class.


title: Metal–organic framework

text: HKUST-1 consists of a dimeric Cu-paddlewheel that possess two pore types. Under pelletization MOFs such as HKUST-1 exhibit a pore collapse. Although most carboxylate MOFs have a negative thermal expansion (they densify during heating), it was found that the hardness and Young's moduli unexpectedly decrease with increasing temperature from disordering of linkers. It was also found computationally that more a more mesoporous structure has a lower bulk modulus. However, an increased bulk modulus was observed in systems with a few large mesopores versus many small mesopores even though both pore size distributions had the same total pore volume. The HKUST-1 shows a similar, "hyperfilling" phenomenon to the ZIF structures under hydrostatic loading.


title: Metal–organic framework

text: MOF-5 has tetranuclear nodes in an octahedral configuration with an overall cubic structure. MOF-5 has a compressibility and Young's modulus (~14.9 GPa) comparable to wood, which was confirmed with density functional theory (DFT) and nanoindentation. While it was shown that the MOF-5 can demonstrate the hyperfilling phenomenon within a loading media of solvent, these MOFs are very sensitive to pressure and undergo amorphization/pressure induced pore collapse at pressures from 0 - 10.3 MPa when there is no fluid in the pores.


title: Metal–organic framework

text: MIL-53 MOFs possesses a "wine rack" structure. These MOFs have been explored for anisotropy in Young's modulus due to the flexibility of loading, and the potential for negative linear compressibility when compressing in one direction, due to the ability of the wine rack opening during loading.


title: Metal–organic framework

text: Zirconium-based MOFs such as UIO-66 are a very robust class of MOFs (attributed to strong hexanuclear <chem>Zr_6</chem> metallic nodes) with increased resistance to heat, solvents, and other harsh conditions, which makes them of interest in terms of mechanical properties. Determinations of shear modulus and pelletization have shown that the UIO-66 MOFs are very mechanically robust and have high tolerance for pore collapse when compared to ZIFS and carboxylate MOFs. Although the UIO-66 MOF shows increased stability under pelletization, the UIO-66 MOFs amorphized fairly rapidly under ball milling conditions due to destruction of linker coordinating inorganic nodes.


title: Metal–organic framework

text: However unless the hydrogen gas is compressed, its volumetric energy density is very low, so the transportation and storage of hydrogen require energy-intensive compression and liquefaction processes. Therefore, development of new hydrogen storage methods which decrease the concomitant pressure required for practical volumetric energy density is an active area of research. MOFs attract attention as materials for adsorptive hydrogen storage because of their high specific surface areas and surface to volume ratios, as well as their chemically tunable structures.


title: Metal–organic framework

text: Compared to an empty gas cylinder, a MOF-filled gas cylinder can store more hydrogen at a given pressure because hydrogen molecules adsorb to the surface of MOFs. Furthermore, MOFs are free of dead-volume, so there is almost no loss of storage capacity as a result of space-blocking by non-accessible volume. Also, because the hydrogen uptake is based primarily on physisorption, many MOFs have a fully reversible uptake-and-release behavior. No large activation barriers are required when liberating the adsorbed hydrogen. The storage capacity of a MOF is limited by the liquid-phase density of hydrogen because the benefits provided by MOFs can be realized only if the hydrogen is in its gaseous state.


title: Metal–organic framework

text: The extent to which a gas can adsorb to a MOF's surface depends on the temperature and pressure of the gas. In general, adsorption increases with decreasing temperature and increasing pressure (until a maximum is reached, typically 20-30 bar, after which the adsorption capacity decreases). However, MOFs to be used for hydrogen storage in automotive fuel cells need to operate efficiently at ambient temperature and pressures between 1 and 100 bar, as these are the values that are deemed safe for automotive applications.


title: Metal–organic framework

text: The U.S. Department of Energy (DOE) has published a list of yearly technical system targets for on-board hydrogen storage for light-duty fuel cell vehicles which guide researchers in the field (5.5 wt %/40 g L by 2017; 7.5 wt %/70 g L ultimate). Materials with high porosity and high surface area such as MOFs have been designed and synthesized in an effort to meet these targets. These adsorptive materials generally work via physical adsorption rather than chemisorption due to the large HOMO-LUMO gap and low HOMO energy level of molecular hydrogen. A benchmark material to this end is MOF-177 which was found to store hydrogen at 7.5 wt % with a volumetric capacity of 32 g L at 77 K and 70 bar. MOF-177 consists of [ZnO] clusters interconnected by 1,3,5-benzebetribenzoate organic linkers and has a measured BET surface area of 4630 m g. Another exemplary material is PCN-61 which exhibits a hydrogen uptake of 6.24 wt % and 42.5 g L at 35 bar and 77 K and 2.25 wt % at atmospheric pressure. PCN-61 consists of [Cu] paddle-wheel units connected through 5,5,5-benzene-1,3,5-triyltris(1-ethynyl-2-isophthalate) organic linkers and has a measured BET surface area of 3000 m g. Despite these promising MOF examples, the classes of synthetic porous materials with the highest performance for practical hydrogen storage are activated carbon and covalent organic frameworks (COFs).


title: Metal–organic framework

text: Practical applications of MOFs for hydrogen storage are met with several challenges. For hydrogen adsorption near room temperature, the hydrogen binding energy would need to be increased considerably. Several classes of MOFs have been explored, including carboxylate-based MOFs, heterocyclic azolate-based MOFs, metal-cyanide MOFs, and covalent organic frameworks. Carboxylate-based MOFs have by far received the most attention because


title: Metal–organic framework

text: The most common transition metals employed in carboxylate-based frameworks are Cu and Zn. Lighter main group metal ions have also been explored. Be(OH)(BTB), the first successfully synthesized and structurally characterized MOF consisting of a light main group metal ion, shows high hydrogen storage capacity, but it is too toxic to be employed practically. There is considerable effort being put forth in developing MOFs composed of other light main group metal ions, such as magnesium in Mg(BDC).


title: Metal–organic framework

text: The following is a list of several MOFs that are considered to have the best properties for hydrogen storage as of May 2012 (in order of decreasing hydrogen storage capacity). While each MOF described has its advantages, none of these MOFs reach all of the standards set by the U.S. DOE. Therefore, it is not yet known whether materials with high surface areas, small pores, or di- or trivalent metal clusters produce the most favorable MOFs for hydrogen storage.


title: Metal–organic framework

text: High hydrogen uptake is attributed to overlapping attractive potentials from multiple copper paddle-wheel units: each Cu(II) center can potentially lose a terminal solvent ligand bound in the axial position, providing an open coordination site for hydrogen binding.


title: Metal–organic framework

text: To date, hydrogen storage in MOFs at room temperature is a battle between maximizing storage capacity and maintaining reasonable desorption rates, while conserving the integrity of the adsorbent framework (e.g. completely evacuating pores, preserving the MOF structure, etc.) over many cycles. There are two major strategies governing the design of MOFs for hydrogen storage:


title: Metal–organic framework

text: The general trend in MOFs used for hydrogen storage is that the greater the surface area, the more hydrogen the MOF can store. High surface area materials tend to exhibit increased micropore volume and inherently low bulk density, allowing for more hydrogen adsorption to occur.


title: Metal–organic framework

text: High hydrogen adsorption enthalpy is also important. Theoretical studies have shown that 22-25 kJ/mol interactions are ideal for hydrogen storage at room temperature, as they are strong enough to adsorb H, but weak enough to allow for quick desorption. The interaction between hydrogen and uncharged organic linkers is not this strong, and so a considerable amount of work has gone in synthesis of MOFs with exposed metal sites, to which hydrogen adsorbs with an enthalpy of 5-10 kJ/mol. Synthetically, this may be achieved by using ligands whose geometries prevent the metal from being fully coordinated, by removing volatile metal-bound solvent molecules over the course of synthesis, and by post-synthetic impregnation with additional metal cations. and are great examples of increased binding energy due to open metal coordination sites; however, their high metal-hydrogen bond dissociation energies result in a tremendous release of heat upon loading with hydrogen, which is not favorable for fuel cells. MOFs, therefore, should avoid orbital interactions that lead to such strong metal-hydrogen bonds and employ simple charge-induced dipole interactions, as demonstrated in Mn[(MnCl)(BTT)].


title: Metal–organic framework

text: An association energy of 22-25 kJ/mol is typical of charge-induced dipole interactions, and so there is interest in the use of charged linkers and metals. The metal–hydrogen bond strength is diminished in MOFs, probably due to charge diffusion, so 2+ and 3+ metal ions are being studied to strengthen this interaction even further. A problem with this approach is that MOFs with exposed metal surfaces have lower concentrations of linkers; this makes them difficult to synthesize, as they are prone to framework collapse. This may diminish their useful lifetimes as well.


title: Metal–organic framework

text: MOFs are frequently sensitive to moisture in the air. In particular, IRMOF-1 degrades in the presence of small amounts of water at room temperature. Studies on metal analogues have unraveled the ability of metals other than Zn to stand higher water concentrations at high temperatures.


title: Metal–organic framework

text: To compensate for this, specially constructed storage containers are required, which can be costly. Strong metal-ligand bonds, such as in metal-imidazolate, -triazolate, and -pyrazolate frameworks, are known to decrease a MOF's sensitivity to air, reducing the expense of storage.


title: Metal–organic framework

text: In a microporous material where physisorption and weak van der Waals forces dominate adsorption, the storage density is greatly dependent on the size of the pores. Calculations of idealized homogeneous materials, such as graphitic carbons and carbon nanotubes, predict that a microporous material with 7 Å-wide pores will exhibit maximum hydrogen uptake at room temperature. At this width, exactly two layers of hydrogen molecules adsorb on opposing surfaces with no space left in between.


title: Metal–organic framework

text: 10 Å-wide pores are also of ideal size because at this width, exactly three layers of hydrogen can exist with no space in between. (A hydrogen molecule has a bond length of 0.74 Å with a van der Waals radius of 1.17 Å for each atom; therefore, its effective van der Waals length is 3.08 Å.)


title: Metal–organic framework

text: Structural defects also play an important role in the performance of MOFs. Room-temperature hydrogen uptake via bridged spillover is mainly governed by structural defects, which can have two effects:


title: Metal–organic framework

text: Structural defects can also leave metal-containing nodes incompletely coordinated. This enhances the performance of MOFs used for hydrogen storage by increasing the number of accessible metal centers. Finally, structural defects can affect the transport of phonons, which affects the thermal conductivity of the MOF.


title: Metal–organic framework

text: Adsorption is the process of trapping atoms or molecules that are incident on a surface; therefore the adsorption capacity of a material increases with its surface area. In three dimensions, the maximum surface area will be obtained by a structure which is highly porous, such that atoms and molecules can access internal surfaces. This simple qualitative argument suggests that the highly porous metal-organic frameworks (MOFs) should be excellent candidates for hydrogen storage devices.


title: Metal–organic framework

text: Adsorption can be broadly classified as being one of two types: physisorption or chemisorption. Physisorption is characterized by weak van der Waals interactions, and bond enthalpies typically less than 20 kJ/mol. Chemisorption, alternatively, is defined by stronger covalent and ionic bonds, with bond enthalpies between 250 and 500 kJ/mol. In both cases, the adsorbate atoms or molecules (i.e. the particles which adhere to the surface) are attracted to the adsorbent (solid) surface because of the surface energy that results from unoccupied bonding locations at the surface. The degree of orbital overlap then determines if the interactions will be physisorptive or chemisorptive.


title: Metal–organic framework

text: Adsorption of molecular hydrogen in MOFs is physisorptive. Since molecular hydrogen only has two electrons, dispersion forces are weak, typically 4-7 kJ/mol, and are only sufficient for adsorption at temperatures below 298 K.


title: Metal–organic framework

text: A complete explanation of the H sorption mechanism in MOFs was achieved by statistical averaging in the grand canonical ensemble, exploring a wide range of pressures and temperatures.


title: Metal–organic framework

text: Two hydrogen-uptake measurement methods are used for the characterization of MOFs as hydrogen storage materials: gravimetric and volumetric. To obtain the total amount of hydrogen in the MOF, both the amount of hydrogen absorbed on its surface and the amount of hydrogen residing in its pores should be considered. To calculate the absolute absorbed amount ("N"), the surface excess amount ("N") is added to the product of the bulk density of hydrogen (ρ) and the pore volume of the MOF ("V"), as shown in the following equation:


title: Metal–organic framework

text: The increased mass of the MOF due to the stored hydrogen is directly calculated by a highly sensitive microbalance. Due to buoyancy, the detected mass of adsorbed hydrogen decreases again when a sufficiently high pressure is applied to the system because the density of the surrounding gaseous hydrogen becomes more and more important at higher pressures. Thus, this "weight loss" has to be corrected using the volume of the MOF's frame and the density of hydrogen.


title: Metal–organic framework

text: The changing of amount of hydrogen stored in the MOF is measured by detecting the varied pressure of hydrogen at constant volume. The volume of adsorbed hydrogen in the MOF is then calculated by subtracting the volume of hydrogen in free space from the total volume of dosed hydrogen.


title: Metal–organic framework

text: There are six possible methods that can be used for the reversible storage of hydrogen with a high volumetric and gravimetric density, which are summarized in the following table, (where is the gravimetric density, is the volumetric density, "T" is the working temperature, and "P" is the working pressure):


title: Metal–organic framework

text: Of these, high-pressure gas cylinders and liquid hydrogen in cryogenic tanks are the least practical ways to store hydrogen for the purpose of fuel due to the extremely "high" pressure required for storing hydrogen gas or the extremely "low" temperature required for storing hydrogen liquid. The other methods are all being studied and developed extensively.


title: Metal–organic framework

text: The high surface area and atomic metal sites feature of MOFs make them a suitable candidate for electrocatalysts, especially energy-related ones.


title: Metal–organic framework

text: Until now, MOFs have been used extensively as electrocatalyst for water splitting (hydrogen evolution reaction and oxygen evolution reaction), carbon dioxide reduction, and oxygen reduction reaction. Currently there are two routes: 1. Using MOFs as precursors to prepare electrocatalysts with carbon support. 2. Using MOFs directly as electrocatalysts. However, some results have shown that some MOFs are not stable under electrochemical environment. The electrochemical conversion of MOFs during electrocatalysis may produce the real catalyst materials, and the MOFs are precatalysts under such conditions. Therefore, claiming MOFs as the electrocatalysts requires "in situ" techniques coupled with electrocatalysis.


title: Metal–organic framework

text: A potential application for MOFs is biological imaging and sensing via photoluminescence. A large subset of luminescent MOFs use lanthanides in the metal clusters. Lanthanide photoluminescence has many unique properties that make them ideal for imaging applications, such as characteristically sharp and generally non-overlapping emission bands in the visible and near-infrared (NIR) regions of the spectrum, resistance to photobleaching or "blinking", and long luminescence lifetimes. However, lanthanide emissions are difficult to sensitize directly because they must undergo LaPorte forbidden f-f transitions. Indirect sensitization of lanthanide emission can be accomplished by employing the "antenna effect", where the organic linkers act as antennae and absorb the excitation energy, transfer the energy to the excited state of the lanthanide, and yield lanthanide luminescence upon relaxation. A prime example of the antenna effect is demonstrated by MOF-76, which combines trivalent lanthanide ions and 1,3,5-benzenetricarboxylate (BTC) linkers to form infinite rod SBUs coordinated into a three dimensional lattice. As demonstrated by multiple research groups, the BTC linker can effectively sensitize the lanthanide emission, resulting in a MOF with variable emission wavelengths depending on the lanthanide identity. Additionally, the Yan group has shown that Eu- and Tb- MOF-76 can be used for selective detection of acetophenone from other volatile monoaromatic hydrocarbons. Upon acetophenone uptake, the MOF shows a very sharp decrease, or quenching, of the luminescence intensity.


title: Metal–organic framework

text: Regarding the first point, nanoscale MOF (NMOF) synthesis has been mentioned in an earlier section. The latter obstacle addresses the limitation of the antenna effect. Smaller linkers tend to improve MOF stability, but have higher energy absorptions, predominantly in the ultraviolet (UV) and high-energy visible regions. A design strategy for MOFs with redshifted absorption properties has been accomplished by using large, chromophoric linkers. These linkers are often composed of polyaromatic species, leading to large pore sizes and thus decreased stability. To circumvent the use of large linkers, other methods are required to redshift the absorbance of the MOF so lower energy excitation sources can be used. Post-synthetic modification (PSM) is one promising strategy. Luo et al. introduced a new family of lanthanide MOFs with functionalized organic linkers. The MOFs, deemed MOF-1114, MOF-1115, MOF-1130, and MOF-1131, are composed of octahedral SBUs bridged by amino functionalized dicarboxylate linkers. The amino groups on the linkers served as sites for covalent PSM reactions with either salicylaldehyde or 3-hydroxynaphthalene-2-carboxyaldehyde. Both of these reactions extend the π-conjugation of the linker, causing a redshift in the absorbance wavelength from 450 nm to 650 nm. The authors also propose that this technique could be adapted to similar MOF systems and, by increasing pore volumes with increasing linker lengths, larger pi-conjugated reactants can be used to further redshift the absorption wavelengths. Biological imaging using MOFs has been realized by several groups, namely Foucault-Collet and co-workers. In 2013, they synthesized a NIR-emitting Yb-NMOF using phenylenevinylene dicarboxylate (PVDC) linkers. They were observed cellular uptake in both HeLa cells and NIH-3T3 cells using confocal, visible, and NIR spectroscopy. Although low quantum yields persist in water and Hepes buffer solution, the luminescence intensity is still strong enough to image cellular uptake in both the visible and NIR regimes.


title: Metal–organic framework

text: The development of new pathways for efficient nuclear waste administration is essential in wake of increased public concern about radioactive contamination, due to nuclear plant operation and nuclear weapon decommission. Synthesis of novel materials capable of selective actinide sequestration and separation is one of the current challenges acknowledged in the nuclear waste sector. Metal–organic frameworks (MOFs) are a promising class of materials to address this challenge due to their porosity, modularity, crystallinity, and tunability. We can use every building blocks of MOF structure for actinide incorporation. First, we can synthesise the MOF starting from actinide salts. In this case actinides go to the metal node. In addition, in terms of metal nodes we can do either metal nodes extension, or we can do cation exchange. Also we can use organic linkers and functionalize it with a groups capable of actinide uptake. And the last but not least, we can use porosity of MOFs to incorporate an contained guest molecules and trap them in a structure by installation of additional or capping linkers.


title: Metal–organic framework

text: The synthesis, characterization, and drug-related studies of low toxicity, biocompatible MOFs has shown that they have potential for medical applications. Many groups have synthesized various low toxicity MOFs and have studied their uses in loading and releasing various therapeutic drugs for potential medical applications. A variety of methods exist for inducing drug release, such as pH-response, magnetic-response, ion-response, temperature-response, and pressure response.


title: Metal–organic framework

text: In 2010 Smaldone et al., an international research group, synthesized a biocompatible MOF termed CD-MOF-1 from cheap edible natural products. CD-MOF-1 consists of repeating base units of 6 γ-cyclodextrin rings bound together by potassium ions. γ-cyclodextrin (γ-CD) is a symmetrical cyclic oligosaccharide that is mass-produced enzymatically from starch and consists of eight asymmetric α-1,4-linked D-glucopyranosyl residues. The molecular structure of these glucose derivatives, which approximates a truncated cone, bucket, or torus, generates a hydrophilic exterior surface and a nonpolar interior cavity. Cyclodextrins can interact with appropriately sized drug molecules to yield an inclusion complex. Smaldone's group proposed a cheap and simple synthesis of the CD-MOF-1 from natural products. They dissolved sugar (γ-cyclodextrin) and an alkali salt (KOH, KCl, potassium benzoate) in distilled bottled water and allowed 190 proof grain alcohol (Everclear) to vapor diffuse into the solution for a week. The synthesis resulted in a cubic (γ-CD) repeating motif with a pore size of approximately 1 nm. Subsequently, in 2017 Hartlieb et al. at Northwestern did further research with CD-MOF-1 involving the encapsulation of ibuprofen. The group studied different methods of loading the MOF with ibuprofen as well as performing related bioavailability studies on the ibuprofen-loaded MOF. They investigated two different methods of loading CD-MOF-1 with ibuprofen; crystallization using the potassium salt of ibuprofen as the alkali cation source for production of the MOF, and absorption and deprotonation of the free-acid of ibuprofen into the MOF. From there the group performed in vitro and in vivo studies to determine the applicability of CD-MOF-1 as a viable delivery method for ibuprofen and other NSAIDs. In vitro studies showed no toxicity or effect on cell viability up to 100 μM. In vivo studies in mice showed the same rapid uptake of ibuprofen as the ibuprofen potassium salt control sample with a peak plasma concentration observed within 20 minutes, and the cocrystal has the added benefit of double the half-life in blood plasma samples. The increase in half-life is due to CD-MOF-1 increasing the solubility of ibuprofen compared to the pure salt form.


title: Metal–organic framework

text: Since these developments many groups have done further research into drug delivery with water-soluble, biocompatible MOFs involving common over-the-counter drugs. In March 2018 Sara Rojas and her team published their research on drug incorporation and delivery with various biocompatible MOFs other than CD-MOF-1 through simulated cutaneous administration. The group studied the loading and release of ibuprofen (hydrophobic) and aspirin (hydrophilic) in three biocompatible MOFs (MIL-100(Fe), UiO-66(Zr), and MIL-127(Fe)). Under simulated cutaneous conditions (aqueous media at 37 °C) the six different combinations of drug-loaded MOFs fulfilled "the requirements to be used as topical drug delivery systems, such as released payload between 1 and 7 days" and delivering a therapeutic concentration of the drug of choice without causing unwanted side effects. The group discovered that the drug uptake is "governed by the hydrophilic/hydrophobic balance between cargo and matrix" and "the accessibility of the drug through the framework". The "controlled release under cutaneous conditions follows different kinetics profiles depending on: (i) the structure of the framework, with either a fast delivery from the very open structure MIL-100 or a slower drug release from the narrow 1D pore system of MIL-127 or (ii) the hydrophobic/hydrophilic nature of the cargo, with a fast (Aspirin) and slow (Ibuprofen) release from the UiO-66 matrix."


title: Metal–organic framework

text: Recent research involving MOFs as a drug delivery method includes more than just the encapsulation of everyday drugs like ibuprofen and aspirin. In early 2018 Chen et al., published detailing their work on the use of MOF, ZIF-8 (zeolitic imidazolate framework-8) in antitumor research "to control the release of an autophagy inhibitor, 3-methyladenine (3-MA), and prevent it from dissipating in a large quantity before reaching the target." The group performed in vitro studies and determined that "the autophagy-related proteins and autophagy flux in HeLa cells treated with 3-MA@ZIF-8 NPs show that the autophagosome formation is significantly blocked, which reveals that the pH-sensitive dissociation increases the efficiency of autophagy inhibition at the equivalent concentration of 3-MA." This shows promise for future research and applicability with MOFs as drug delivery methods in the fight against cancer.


title: Metal–organic framework

text: In 2014 researchers proved that they can create electrically conductive thin films of MOFs (Cu(BTC) (also known as HKUST-1; BTC, benzene-1,3,5-tricarboxylic acid) infiltrated with the molecule 7,7,8,8-tetracyanoquinododimethane) that could be used in applications including photovoltaics, sensors and electronic materials and a path towards creating semiconductors. The team demonstrated tunable, air-stable electrical conductivity with values as high as 7 siemens per meter, comparable to bronze.


title: Metal–organic framework

text: (2,3,6,7,10,11-hexaiminotriphenylene) was shown to be a metal-organic graphene analogue that has a natural band gap, making it a semiconductor, and is able to self-assemble. It is an example of conductive metal organic framework. It represents a family of similar compounds. Because of the symmetry and geometry in 2,3,6,7,10,11-hexaiminotriphenylene (HITP), the overall organometallic complex has an almost fractal nature that allows it to perfectly self-organize. By contrast, graphene must be doped to give it the properties of a semiconductor. Ni(HITP) pellets had a conductivity of 2 S/cm, a record for a metal-organic compound.


title: Metal–organic framework

text: In 2018 researchers synthesized a two-dimensional semiconducting MOF (Fe(THT)(NH), also known as THT, 2,3,6,7,10,11-triphenylenehexathiol) and showed high electric mobility at room temperature. In 2020 the same material was integrated in a photo-detecting device, detecting a broad wavelength range from UV to NIR (400–1575 nm). This was the first time a two-dimensional semiconducting MOF was demonstrated to be used in opto-electronic devices.


title: Metal–organic framework

text: <chem>Cu3(HHTP)2</chem>as a 2D MOF structure, and there are limited examples of materials which are intrinsically conductive, porous, and crystalline. Layered 2D MOFs have porous crystalline structure showing electrical conductivity. These materials are constructed from trigonal linker molecules (phenylene or triphenylen) and six functional groups of –OH, -<chem>NH2</chem>, or –SH. The trigonal linker molecules and square-planarly coordinated metal ions such as <chem>Cu^{2+}</chem>,<chem>Ni^{2+}</chem>, <chem>Co^{2+}</chem>, and <chem>Pt^{2+}</chem> form layers with hexagonal structures which looks like Graphene in larger scale. Stacking of these layers in the c direction shown in Figure 6 can build one-dimensional pore system. Graphene-like 2D MOFs have shown decent conductivities. This makes them a good choice to be tested as electrode material for evolution of hydrogen from water, oxygen reduction reactions, supercapacitors, and sensing of volatile organic compounds (VOCs). Among these MOFs, <chem>Cu3(HHTP)2</chem> has exhibited the lowest conductivity, but also the strongest reaction in sensing of VOCs.


title: Metal–organic framework

text: Biomolecules can be incorporated during the MOF crystallization process. Biomolecules including proteins, DNA and antibodies could be encapsulated within ZIF-8. Enzymes encapsulated in this way were stable and active even after being exposed to harsh conditions (e.g. aggressive solvents and high temperature). ZIF-8, MIL-88A, HKUST-1, and several luminescent MOFs containing lanthanide metals were used for the biomimetic mineralization process.


title: Metal–organic framework

text: MOF's small, tunable pore sizes and high void fractions are promising as an adsorbent to capture CO. MOFs could provide a more efficient alternative to traditional amine solvent-based methods in CO capture from coal-fired power plants.


title: Metal–organic framework

text: MOFs could be employed in each of the main three carbon capture configurations for coal-fired power plants: pre-combustion, post-combustion, and oxy-combustion. The post-combustion configuration is the only one that can be retrofitted to existing plants, drawing the most interest and research. The flue gas would be fed through a MOF in a packed-bed reactor setup. Flue gas is generally 40 to 60 °C with a partial pressure of CO at 0.13 - 0.16 bar. CO can bind to the MOF surface through either physisorption (via Van der Waals interactions) or chemisorption (via covalent bond formation).


title: Metal–organic framework

text: Once the MOF is saturated, the CO is extracted from the MOF through either a temperature swing or a pressure swing. This process is known as regeneration. In a temperature swing regeneration, the MOF would be heated until CO desorbs. To achieve working capacities comparable to the amine process, the MOF must be heated to around 200 °C. In a pressure swing, the pressure would be decreased until CO desorbs.