News Article | April 17, 2017
Adsorptive heat transformation systems such as adsorption thermal batteries and chillers can provide space heating and cooling in a more environmental friendly way. However, their use is still hindered by their relatively poor performances and large sizes due to the limited properties of solid adsorbents. Here, the spray-drying continuous-flow synthesis of a new type of solid adsorbents that results from combining metal-organic frameworks (MOFs), such as UiO-66, and hygroscopic salts, such as CaCl has been reported. These adsorbents, commonly named as composite salt in porous matrix (CSPM) materials, allow improving the water uptake capabilities of MOFs while preventing their dissolution in the water adsorbed; a common characteristic of these salts due to the deliquescence effect. It is anticipated that MOF-based CSPMs, in which the percentage of salt can be tuned, are promising candidates for thermal batteries and chillers. In these applications, it is showed that a CSPM made of UiO-66 and CaCl (38% w/w) exhibits a heat storage capacity of 367 kJ kg−1 , whereas a second CSPM made of UiO-66 and CaCl (53% w/w) shows a specific cooling power of 631 W kg−1 and a coefficient of performance of 0.83, comparable to the best solid adsorbents reported so far.
News Article | April 27, 2017
The prediction of a periodic shift in the orbit (which is technically called precession in celestial mechanics) of Mercury and the subsequent confirmation of this additional shift in orbit from real observations, was one of the greatest triumphs of general relativity developed by Einstein about 102 years ago. This is one of the important effects which occur in solar system bodies passing close to the sun because orbital velocities increase considerably when bodies come near the sun and when the velocities increase substantially, relativistic effects can become important (Figure 1). The other effect is from the periodic gravitational influences of Jupiter (technically called the Kozai mechanism in celestial mechanics) from the Newtonian theory which make the orbit narrower and narrower (or in other words, more and more elliptical) and make the orbiting body come closer and closer to the sun after every subsequent revolution. These gradual gravitational effects from Jupiter have led to the production of some exceptionally spectacular sungrazing comets (i.e. comets which come very close to the sun and hence very bright in appearance from our planet) in Earth's history. Previous works in solar system science have looked into these effects separately for some bodies, but in our present study, we look at the interesting scenarios when we have the combination of both these effects in solar system bodies. Our calculations show that these periodic gravitational influences from Jupiter can lead to rapid enhancements in orbital shifts due to general relativity by virtue of the bodies coming closer to the sun after every passage around the sun. Sometimes the bodies can have extreme close approaches to the sun which eventually lead to collision with the sun, induced by these periodic effects from Jupiter. A good example which shows this property in our studies is comet 96P/Machholz 1 which undergoes rapid sun approaching phases and eventually falls into the sun in about 9,000 years from present time. During its final journey just before the collision with sun, we find that the orbital shifts due to general relativity can peak to about 60 times that of the orbital shift of Mercury, which is a record high value in the context of solar system bodies observed so far. Furthermore this comet undergoes a reversal in its reference orbital direction (technically called an inclination flip in celestial mechanics) due to Jupiter's systematic gravitational effects. Our study shows for the first time an example of a solar system body which shows all these previously mentioned effects and traits overlapping in a neat way. This makes this study new and unique from previous orbit studies of similar solar system objects. Moreover we find that the combination of both above-said effects have important consequences in the realm of impact studies on Earth from small solar system bodies. Our calculations show that even a small orbital shift due to general relativity can vary greatly the closest orbit distance between the solar system body and Earth. Jupiter's periodic effects can enhance the general relativistic effects in some solar system orbits. This leads to close approach scenarios between solar system bodies changing significantly. This in turn plays an important role in studying and assessing long term impact threat estimates on Earth, which can create interesting and remarkable features like craters and meteor storms on our Earth. Our planet has been bombarded with different solar system bodies of different sizes throughout its orbital history (Figure 2) and these signatures in the form of craters act as a crucial tool to understand the evolution and dynamics of our Earth (which is the focus theme of CEED based at UiO). The modern telescopic surveys are scanning the sky continuously to find solar system objects which could potentially come very close to the Earth and become a threat for our Earth in future. Today's precise observations aided by large telescopes in different parts of the world and detailed theoretical calculations augmented by supercomputing facilities (like USIT NOTUR computing clusters) aim to come up with better models in the context of short term and long term impact hazard studies to make Earth a safer place in the larger picture of our existence. More information: A. Sekhar et al. Change in general relativistic precession rates due to Lidov–Kozai oscillations in Solar system, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stx548
News Article | April 18, 2017
By taking advantage of facile preparation and sensitive recognition capacity, the first example of a fluorescence system based on Eu(III) functionalized UiO(bpdc) (UMOFs) has been constructed for effective combination of ions recognition and logic computing. All the ions, including Hg2+, Ag+, and S2− in the system are water harmful, which can be recognized through affecting energy transfer or framework structure. By the self-assembling, competing and connecting with each other, Eu(III)@UMOFs and the ions have achieved the implementation of Boolean logic network system connecting the elementary logic operations (NOR, INH, and IMP) and integrative logic operation (OR + INH), also obtaining computing keypad-lock security system by sequential logic operation. To deal with uncertain information in the analog region of nonlinear response (fluorescence and concentration), soft computation through the formulation of fuzzy logic operation has been constructed. On the basis of Boolean logic and fuzzy logic, one intelligent molecular searcher can be realized by taking chemical events (Hg2+, Ag+, and S2−) as programmable words and chemical interactions as syntax. Considering the particularity of all the input ions, the approach is helpful in developing the advanced logic program based on Eu(III)@UMOFs for application in environmental monitoring.
News Article | April 14, 2016
During their life, plants constantly renew themselves. They sprout new leaves in the spring and shed them in the fall. No longer needed, damaged or dead organs such as blossoms and leaves are also cast off by a process known as abscission. By doing so, plants conserve energy and prepare for the next step in their life cycle. But how does a plant know when it is the right time to get rid of unnecessary organs? Researchers from the University of Geneva (UNIGE) and the University of Oslo (UiO) now shed light on this process. It is regulated by receptor proteins located at the surface of specific cells that form a layer around the future break point. When it is time to shed an organ, a small hormone binds to this membrane receptor and, together with a helper protein, the abscission process is initiated. Their findings are now published in the journal eLife.
News Article | April 6, 2016
Optical fiber chemical sensors based on optical absorption feature high specificity, fast response, and a much longer lifetime compared to other chemical sensors, qualities that offer significant potential for application in pollution monitoring, environmental protection, and hazardous-material detection. Now by integrating metal organic framework (MOF) materials—a new class of highly porous crystalline material—with optical fibers, researchers from Victoria University and Monash University, Australia, have co-developed a novel, highly sensitive chemical sensor based on an optical fiber coated with a thin film of a specific MOF (namely, UiO-66), which could be potentially used for real-time detection of heavy organic contaminants such as herbicides or pesticides in water. In a paper published this week in the journal Optics Letters, from The Optical Society (OSA), the researchers described their work. "Metal organic frameworks (MOFs) are networks of metal atoms linked and separated by carbon-based (organic) compounds. The UiO-66 MOF we used in the experiment is made from Zirconium and is well known for the stability in water," said Stephen Collins, professor of engineering, Victoria University, Australia. "We have demonstrated for the first time that the advanced porous material MOFs can be coated onto the end-face of optical fibers to create a novel, faster and more sensitive chemical sensor potentially used for measuring heavy organic contaminants on site and in real-time." Collins said various porous adsorbents such as pyrene-labeled monomer, silica sol-gel and zeolites have been studied recently by scientists for detecting hazardous compounds. However, the low porosity and small pores of the above adsorbents limit their use in the sensing area to small molecules. That is, they cannot detect larger or heavy organic molecules (e.g. herbicides or pesticides) in water. Metal organic frameworks are about 10 times more porous than any material previously known, so they can absorb larger molecules. MOFs form as crystals and careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. To fabricate the MOF-fiber sensor, the researchers removed the polymer coating of a conventional single mode fiber several centimeters from the end and activated the fiber surface using plasma. Then, the fiber was placed in MOF liquid solution and heated at 120 degrees Celsius for 24 hours, which allowed the activated fiber surface to attract the MOF to grow on the end-face of the fiber, resulting in a MOF thin film of 17- to 22-micrometer thickness. Collins explained that the MOF-fiber sensor can be used as an in-fiber Fabry-Perot interferometer, which is a well-established method for detecting the "optical thickness" of a thin film by studying the interference signals generated by the film interfaces. As the MOF-fiber sensor absorbs more and more contaminants, the optical thickness of the MOF thin film increases accordingly, leading to a change in the interference spectra. By using the established optical model and mathematical procedure, the researchers can calculate the optical thickness of the MOF thin film from the experimentally measured interference spectra, and hence infer the concentration of contaminants in water. In the experiment, Collin's team used the MOF-fiber sensor to detect a specific contaminant in water called Rhodamine-B (RhB) dye, a bright pink dye known as Opera Rose, which is used in the textile industry and is known to be potentially carcinogenic if ingested. "Our experimental results showed a positive detection response of the MOF-fiber sensor to RhB in water down to 48 parts per million or 0.1 millimolar, which is a very promising result, demonstrating the sensor's ability to detect pollutants at a low concentration before the pollution goes worse," said Collins. He explained the high sensitivity and fast response of the MOF-fiber sensor are attributed to the MOF's ability to pre-concentrate molecules, which can be imaged as a sponge "soaking" up molecules into its pores. Additionally, the MOF sponge selectively absorbs molecules to fit into its pores and rejects unfit ones, which enhance the sensor's sensitivity and reliability. The researchers also found the sensor's absorption process of RhB dye is non-reversible, which is ideal for long-term monitoring where RhB concentrations are minimal and a marked increase in the dye's concentration would be recognized easily, said Collins. "While the non-reversible mode suits many applications, we have also developed methods of releasing absorbed molecules by shining light down the fiber, which would make the sensor re-usable," Collin said. The researchers' next step is to further explore the MOF-fiber sensor's responses to other heavy organic contaminants such as pesticides and herbicides in water. More information: M. Nazari, M. Forouzandeh, C. Divarathne, F. Sidiroglou, M. Martinez, K. Konstas, B. Muir, A. Hill, M. Duke, M. Hill and S. Collins. "UiO-66 MOF End-Face-Coated Optical Fiber in Aqueous Contaminant Detection" Optics Letters 41, 1696 – 1699. DOI: 10.1364/OL.41.001696
News Article | March 8, 2016
Physical delivery of anticancer drugs in controlled anatomic locations can complement the advances being made in chemo-selective therapies. To this end, an optical fiber catheter is coated in a thin layer of metal organic framework UiO-66 and the anticancer drug 5-Fluorouracil (5-FU) is deposited within the pores. Delivery of light of appropriate wavelength through the fiber catheter is found to trigger the release of 5-FU on demand, offering a new route to localized drug administration. The system exhibits great potential with as much as 110 × 10−6 m of 5-FU delivered within 1 min from one fiber.
News Article | April 7, 2016
Researchers at UiO and NCMM have discovered that the system used by bacteria to transport magnesium is so sensitive that it can detect a pinch of magnesium salt in a swimming pool.
News Article | August 30, 2016
A UiO-66 core with various sizes acts as heterogeneous nucleation center and enables aniline polymerization under ambient conditions. The as-synthesized UiO-66@PAN possesses uniform size and excellent dispersibility in aqueous solution. UiO-66@PAN can be internalized by cancer cells via endocytosis, and indicates significant photothermal therapeutic effect in vitro, and can effectively inhibit the growth of colon cancers in vivo.
News Article | December 8, 2016
Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well-intergrown UiO-66 metal-organic framework membranes fabricated on prestructured yttria-stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m−2 h−1 and excellent separation factor (>45 000) for separating water from i-butanol (next-generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.
News Article | November 2, 2016
The coordinatively unsaturated metal sites (CUSs) inside MOFs can be readily tuned to adjust interactions between MOFs and reactants, to activate targeted chemical bonds in reactants and thereby to lower the reaction-energy barrier of the desired chemical transformation22. We explore this concept with MOF sandwich nanostructures that are then used as hydrogenation catalysts (Supplementary Fig. 1). The nanostructures contain a layer of platinum (Pt) nanoparticles encapsulated between a core and a shell made of MIL-101, which contains either Fe3+ or Cr3+ trimers, connected with 1,4-benzenedicarboxylate (BDC) linkers (Fig. 1a and Supplementary Note 1)19, 20, 21. All synthesized products are of uniform octahedral shape, with 2.8-nm Pt nanoparticles immobilized between the MIL-101 core and shell (Fig. 1b–l and Supplementary Figs 2–13). Catalytic performance is evaluated using five typical sandwich nanostructures: two MIL-101(Fe)@Pt@MIL-101(Fe) systems with shell thicknesses of about 9.2 nm and 22.0 nm (denoted as MIL-101(Fe)@Pt@MIL-101(Fe)9.2 and MIL-101(Fe)@Pt@MIL-101(Fe)22.0; Fig. 1b–e and Supplementary Figs 8, 9); one MIL-101(Cr)@Pt@MIL-101(Cr) with a shell thickness of around 5.1 nm (denoted as MIL-101(Cr)@Pt@MIL-101(Cr)5.1; Fig. 1f, g and Supplementary Fig. 10); and two MIL-101(Cr)@Pt@MIL-101(Fe) systems with shell thicknesses of around 2.9 nm and 8.8 nm (denoted as MIL-101(Cr)@Pt@MIL-101(Fe)2.9 and MIL-101(Cr)@Pt@MIL-101(Fe)8.8; Fig. 1h–l, Supplementary Figs 11–13 and Supplementary Note 2). All of the materials contain single crystalline MIL-101 with a face-centred-cubic (fcc) structure, and a lattice fringe of 2.6 nm that corresponds to the (222) planes of MIL-101 (ref. 19; Fig. 1c–k and Supplementary Figs 14–16). The embedded Pt nanoparticles exhibit high crystallinity, with an interplanar spacing of 0.23 nm that corresponds to the (111) planes of fcc platinum (Fig. 1e, k, insets). Table 1 summarizes the results obtained when using the sandwich MIL-101@Pt@MIL-101 nanostructures as catalysts for the selective hydrogenation of cinnamaldehyde (A) to cinnamyl alcohol (B), along with results for Pt nanoparticles, MIL-101 and MIL-101@Pt as controls (see also Fig. 1, Supplementary Figs 2–7, and Supplementary Tables 1, 2). Because the C=O and C=C groups in A are both possible hydrogenation targets, we expect a product mixture containing the targeted cinnamyl alcohol (B), as well as hydrocinnamaldehyde (C) and phenyl propanol (D). For a more meaningful evaluation of selectivity for the desired product B, we first compared the catalysts’ performances at the same conversion level (about 45%) of A. We found no noticeable hydrogenation of A by MIL-101 (Table 1, entry 9), whereas Pt nanoparticles catalyse this reaction with a turnover frequency (TOF) of 372.4 h−1 and a selectivity for B of only around 18.3% (Table 1, entry 8), consistent with density functional theory (DFT) predictions (Supplementary Fig. 17). The third controls—the MIL-101@Pt nanostructures—exhibit dramatically increased selectivity for B (Table 1, entries 6 and 7), with 86.4% for MIL-101(Fe)@Pt and 44.0% for MIL-101(Cr)@Pt. This remarkable promotion of selective hydrogenation of the C=O bond by MIL-101 is probably due to the CUSs in MIL-101 acting as Lewis acid sites that interact with the C=O bond and activate it23. A Fourier transform infrared (FTIR) survey shows an obvious redshift of the ν bond of A after mixing with MIL-101, while the ν bond remains unaltered, confirming a selective interaction between the C=O bond of A and MIL-101 (Supplementary Fig. 18). DFT calculations with consideration of spin-polarization effect—aimed at understanding the origin of the interaction between MIL-101 and A—show that the five-coordinated metal nodes in the Fe OCl(COO) H O or Cr OCl(COO) H O trimers of supertetrahedral MIL-101 cells serve as active sites that interact with the C=O group of A (Supplementary Fig. 19)19. The calculated adsorption energy of A over the Fe OCl(COO) H O and Cr OCl(COO) H O trimers is −1.26 eV and −1.01 eV, respectively (Fig. 2); that is, binding between the trimers and A through Fe–O or Cr–O interactions is thermodynamically favoured, with the interaction between A and Fe OCl(COO) H O being the stronger one (Supplementary Figs 20–22 and Supplementary Note 3). The calculated reaction energies for hydrogenation of A to B or C over MIL-101(Fe)@Pt are −2.15 eV and −1.89 eV (Fig. 2a), indicating that the formation of B (selectivity approximately 86.4%) is energetically favoured over that of C (selectivity roughly 9.6%). In the case of MIL-101(Cr)@Pt, the corresponding reaction energies for B and C formation are −0.69 eV and −0.92 eV, respectively (Fig. 2b), indicating a smaller difference in the selectivity of B (roughly 44.0%) over C (about 40.0%). These results confirm the experimental observation that the CUSs in MIL-101 preferentially interact with the C=O group (rather than the C=C group) of A and activate it, giving rise to the improved selectivity for the formation of product B. We also note that at a conversion level of 45%, TOF values are 122.1 h−1 for MIL-101(Fe)@Pt and 372.4 h−1 for MIL-101(Cr)@Pt (Table 1, entries 6 and 7), indicating that MIL-101(Cr) does not affect the catalytic activity of Pt nanoparticles whereas MIL-101(Fe) causes a considerable decrease. X-ray photoelectron spectroscopy (XPS) measurements reveal a partial transfer of electrons from the Pt nanoparticles to MIL-101(Fe)24 (Fig. 3a, b, d and Supplementary Note 4), whereas there is no obvious electron transfer between from the Pt nanoparticles to MIL-101(Cr) (Fig. 3a, c, d). This suggests the reduced electron density of Pt nanoparticles in MIL-101(Fe)@Pt as a possible cause of the decreased hydrogenation activity. This is further supported by DFT calculations showing that the negative binding energy of hydrogen atoms (ΔE ) on a platinum(111) (2 × 2) surface increases with positive charging of the platinum surface (Supplementary Fig. 23), with the resulting stronger surface binding of the hydrogen atoms reducing the catalytic activity of MIL-101(Fe)@Pt25. Guided by these observations, and given that MIL-101 possesses two characteristic pore windows (of about 1.3 nm and 1.5 nm) that are large enough to accommodate A (1.05 nm × 0.65 nm; Supplementary Table 2 and Figs 24, 25), we next explored the sandwich MIL-101@Pt@MIL-101 structure as an ideal catalyst for selective hydrogenation of A to B. Entries 1–5 in Table 1 confirm that coating with MIL-101 shells of different thicknesses considerably enhances the selectivity for B: the selectivity with MIL-101(Cr)@Pt@MIL-101(Cr)5.1 is 79.2%, while using MIL-101(Cr) or MIL-101(Fe) cores that are coated with MIL-101(Fe) shells gives selectivities that are always higher than 94%. The improved selectivities are accompanied by a decrease in TOF values, which is expected because the MIL-101 shells slow down reactant and product diffusion. Coating with MIL-101(Fe) leads to an additional decrease in catalytic activity, owing to the interfacial electron-transfer effect (Fig. 3 and Supplementary Fig. 23). Our MIL-101@Pt@MIL-101 catalysts combine exceptionally high selectivity and conversion efficiency (Table 1, entries 10–14, and Supplementary Table 3), and outperform state-of-the-art catalysts (Supplementary Table 4). MIL-101(Cr)@Pt@MIL-101(Fe)2.9, for example, exhibits excellent selectivity (95.6%) and almost full conversion (99.8%) (Supplementary Fig. 26). Moreover, reusability tests indicate that for MIL-101(Cr)@Pt@MIL-101(Fe)2.9, both the conversion efficiency of A and the selectivity for B remain almost unchanged over five successive catalytic cycles (Supplementary Figs 26–30, 31a), with the stability of the system being further verified by XRD and transmission electron microscope (TEM) measurements (Supplementary Figs 31b, 32) that show no evidence for structural or morphological differences between fresh and used catalysts. Excellent catalytic stability is also obtained with MIL-101(Fe)@Pt@MIL-101(Fe)9.2 (Supplementary Fig. 33). To further confirm that the integration of Pt nanoparticles and CUSs into a single sandwich nanostructure results in useful selective hydrogenation capabilities, we used MIL-101@Pt@MIL-101 to hydrogenate smaller-sized α,β-unsaturated aldehydes. Acrolein (0.69 nm × 0.51 nm), with no substituents on C=C bond, branched 3-methyl-2-butenal (0.79 nm × 0.60 nm), and furfural (0.81 nm × 0.64 nm), with a furan ring (see Supplementary Fig. 34 for structures), are all converted through preferential hydrogenation of the C=O group over the C=C group (Table 1, Supplementary Tables 5–7 and Supplementary Figs 35–37). Conversion efficiencies are 52.7%, 59.9% and 98.5%, respectively, with selectivities for hydrogenation of the C=O group being 97.3%, 92.5% and 99.8%. When compared with other catalysts26, 27, MIL-101(Fe)@Pt@MIL-101(Fe)22.0 also exhibits excellent selectivity towards allyl alcohol (Table 1, entries 24 and 25; Supplementary Note 5 and Supplementary Table 8). To explore the generality of the catalyst preparation method, we also synthesized28, 29, 30 the sandwich structures MOF-525(Zr)@Pt@MOF-525(Zr)26.5, MOF-74(Co)@Pt@MOF-74(Co)8.4, UiO-66(Zr)@Pt@UiO-66(Zr)11.2, and UiO-67(Zr)@Pt@UiO-67(Zr)24.1 (Supplementary Table 2 and Supplementary Figs 38–45), which catalysed the hydrogenation of A with conversion efficiencies of 35.2%, 35.0%, 90.0% and 69.4%, respectively, and selectivities towards B of 85.0%, 70.1%, 65.0% and 73.0%, respectively (Supplementary Figs 46–49 and Supplementary Table 9). Finally, as an example of a system containing different metal nanoparticles, we also prepared MIL-101(Fe)@Ru@MIL-101(Fe)8.3, which hydrogenated A with a conversion efficiency of 48.7% and a selectivity towards B of 58.5% (Supplementary Figs 50–52 and Supplementary Table 10). These results illustrate the generality of the concept of using CUSs in MOFs as a means of tuning the selectivity of the hydrogenation of α,β-unsaturated aldehydes. Moreover, using commercial Pt/C (carbon) and Pt/Fe O for the hydrogenation of A (Supplementary Figs 53, 54) resulted in conversion efficiencies of 98.1% and 54.5% and selectivities towards B of 39.9% and 84.5%, respectively (Supplementary Table 11), with the different selectivities suggesting that Fe-based supports favour the hydrogenation of C=O groups over C=C groups (although not to the extent seen with the sandwich forms of catalysts). Taken together, our observations confirm the considerable potential of MOFs as a new generation of heterogeneous catalytic supports that may prove effective when targeting important but highly challenging reactions.