Presence Of Metal-organic Framework Research Articles

Phosphoric Acid Electrolyte Uptake and Retention Analysis on UiO‐66‐NH2 Polybenzimidazole Nanocomposite Membranes

ABSTRACTHigh‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) have a major advantage over low‐temperature fuel cells due to their better tolerance to higher carbon monoxide content in the hydrogen feed, simpler fuel processing, and better heat management. However, a key challenge in the development of HT‐PEMFCs is the potential for acid leaching from phosphoric acid‐doped polybenzimidazole membranes, which can reduce overall fuel cell performance. This study investigates the effect of post‐synthetic modification of the UiO‐66‐NH2 metal–organic framework (MOF) on the acid electrolyte uptake and retention of MOF/poly(4,4ʹ‐diphenylether‐5,5ʹ‐bibenzimidazole) (OPBI) nanocomposite membranes. Thermogravimetric analysis (TGA) was used to correlate the membrane properties with acid uptake. This work revealed that the presence of MOF with functional groups that can form hydrogen bonds with phosphoric acid molecules was able to alleviate the acid retention in the OPBI membrane with lower acid uptake. TGA demonstrated that the lower bound moisture content in the nanocomposite membranes was correlated to the lower acid uptake. In addition, the thermal stability of the nanocomposite membranes was found to improve.

A Porous Multi‐Stimuli‐Responsive Liquid Crystal Elastomer Actuator Enabled by Mof Loading

AbstractA porous actuator is prepared using a liquid crystal elastomer (LCE) loaded with metal‐organic framework (MOF) nanoparticles (MIL‐88A). While the swellable MOF additive endows the LCE actuator with nanoscale pores, after its removal by chemical etching, macroporous LCE actuator is obtained. This LCE‐MOF actuator displays several interesting features. 1) Selective etching allows the actuator in water to curl in one direction and then reverse the curling direction owing to differential water absorption of the nano‐ and macroporous layers. 2) The stretching‐induced alignment of mesogens in the actuator is little affected by the presence of MOF and substantially retained after water uptake, so that an actuation deformation can be generated either by water absorption or thermally induced order‐disorder phase transition. 3) Assisted by the UV irradiation used for polymer cross‐linking, magnetic iron oxide FeO appears to be formed after chemical etching, which allows the actuator to gain the ability to move on water surface guided by a magnet. 4) The in situ formation of magnetic iron oxide in the macroporous actuator also provides an enhanced photothermal effect, making light‐driven locomotion of the actuator more effective. The use of active porogen like MOF opens a new way to explore porous LCE actuators.

Performance investigations of carbon based consolidated composite adsorbents effective for adsorption cooling systems

• Composite adsorbent with activated carbon has been developed and characterized. • Presence of metal organic framework improves surface properties of composites. • Expanded graphite powder in the composites improves thermal conductivity. • Volumetric uptake of newly composite is 24.38% more than activated carbon. This paper proposes a new composite adsorbent synthesized by employing activated carbon as the parent element with expanded natural graphite and metal organic framework as secondary elements. The binder used in the composite is polyvinylpyrrolidone. The parameters such as surface area, pore volume, thermal conductivity, and adsorption/desorption of adsorbate are studied in depth for the proposed combinations. The characteristic study suggests Composite B, having a material composition of activated carbon 70 % in weight, expanded graphite powder 10 % and metal organic framework 10 % and binder 10 % as the favourable choice for adsorption cooling system. The surface area and pore volume of the composite B is determined to be 1597 ± 26 m 2 /g and 0.93 cm 3 g −1 , respectively. The thermal conductivity of the composite B is determined to be 0.29 Wm -1 K −1 , which is 55.17 % greater than the parent material activated carbon at atmospheric temperature. The Dubinin-Radushkevich equation has been used to fit adsorption uptake measurement, and it is found that the maximum adsorption of the composite B as 0.983. A performance study of a single bed adsorption cooling system with a cooling capacity of 600 W has been conducted with activated carbon/composite B as adsorbent and ethanol as the refrigerant. The performance parameters such as the coefficient of performance and specific cooling power of the adsorption cooling system using consolidated adsorbent is obtained as 0.61 and 198 Wkg −1 , respectively. The coefficient of performance obtained by using the consolidated adsorbent/ethanol is 21.31 % higher than the system using activated carbon/ethanol as the working pair. The results shows that the suggested composite material's enhanced surface area, pore volume, and thermal conductivity can improve the performance of the adsorption cooling system and can be employed as a viable alternative for conventional adsorbents.

Mixed matrix membranes based on NH2-MIL-53 (Al) and 6FDA-ODA polyimide for CO2 separation: Effect of the processing route on improving MOF-polymer interfacial interaction

This work compares the effect of two different fabrication routes on the gas separation performance of mixed matrix membranes (MMM). Flat-sheet symmetric membranes based on 6FDA-ODA as the matrix and 10–20 wt% metal–organic frameworks (MOF) MIL-53 (Al) and NH2-MIL-53 (Al) as fillers were fabricated via two approaches. In approach A, the MOF was incorporated at the early stage of the polyimide synthesis and the 6FDA-ODA polymerization reaction took place in the presence of MOF, while approach B followed the traditional solution mixing technique of MMM preparation. From the samples produced, XRD, N2 adsorption at 77 K, ATR-FTIR, FEG-SEM, TGA-DTG, DMA and density measurements were used to characterize the MOF structure and the membrane properties. Then, single and mixed gas separation performances were evaluated for CO2, CH4 and N2 at 2 and 5.5 bar and 35 °C. As a result of better interfacial interactions between NH2-MIL-53 (Al) and polyimide via hydrogen bonding, the MMM-A series showed excellent dispersion in the polymer matrix compared to MMM-B. At 10 wt% NH2-MIL-53, the membrane prepared by approach A showed 100% improvement in CO2/CH4 mixed gas separation factor (50:50 vol% CO2:CH4 at 35 °C and 5.5 bar) compared to that of neat 6FDA-ODA, which is 27% better than the membrane prepared by approach B. Better interfacial compatibility also improved the thermal and mechanical properties of the MMM, which confirms the efficiency of this approach for the NH2-MIL-53 (Al)/6FDA-ODA system. On the other hand, unfunctionalized MIL-53 (Al) MMM showed no difference between approach A and B in improving the gas separation performance.

Thin-film nanocomposite membranes incorporated with water stable metal-organic framework CuBTTri for mitigating biofouling

Thin-film composite (TFC) polyamide membranes are the most commonly used membrane materials for reverse osmosis (RO) processes; however, the high biofouling propensity is one of major limitations to the widespread application of TFC membranes. In this study, we developed an antibiofouling thin-film nanocomposite (TFN) membrane by incorporating a copper-based water-stable metal-organic framework (MOF), CuBTTri, in the active layer. Results showed that the presence of MOFs in the TFN active layer significantly increased membrane water permeability without compromising selectivity. Furthermore, the incorporation of CuBTTri imparted the TFN membrane with efficient antibacterial properties. After 24 h contact, the colony forming units (CFU) of Pseudomonas aeruginosa on the TFN membrane (with a dosage of 0.1% MOF) was 3.4% of that on the pristine membrane, demonstrating a strong antibiofouling behavior. The cross-flow filtration tests further confirmed the antibiofouling performance of the TFN membrane, with a significantly lower flux decline (∼36%) compared to the control (∼70% flux decline). The TFN membranes also had a thinner biofouling layer and less quantity of biofoulants on their surface compared to the TFC membrane. The antibiofouling properties of the TFN membrane were associated with bacterial membrane potential depolarization and cell damage due to the contact with MOF. These results highlight the potential of water-stable MOFs to be used as functional materials to fabricate antibiofouling TFN membranes for advanced water and wastewater treatment.

Zn-free MOFs like MIL-53(Al) and MIL-125(Ti) for the preparation of defect-rich, ultrafine ZnO nanosheets with high photocatalytic performance

Metal organic frameworks (MOFs) are exploited in many applications of materials science and very recently were investigated as precursors or reagents for material synthesis. In a new way different from previous approaches, here we introduce for the first time the synthesis of metal oxide MxOy in the presence of M-free MOF acting partially as a sacrificial template and as a provider of doping metal atom. We demonstrate this approach in the case of ZnO prepared by a simple hydrothermal method in the presence of a Zn-free MOF like MIL-53(Al) or MIL-125(Ti). The resulting ZnO show low content of Al or Ti < 2% and properties are significantly different depending on whether MIL-53(Al) or MIL-125(Ti) are used or if no MOF is present. The nature and presence of MOF has different major effects on the morphology, the specific surface area of as prepared ZnO and also on the oxygen defects in its crystal structure. Corroborating the XPS, UV–vis DRS, PL, EPR and DFT studies evidence the role of such O-defects on band gap narrowing for samples calcined at 400 °C. These exhibit high efficiency in photodegradation of methyl orange (MO) compared to ZnO prepared in MOF-free conditions or previous literatures. The kinetics of MO degradation is different depending on the morphology, the specific surface and oxygen defects. The present data open the door to a new approach of the synthesis of metal oxides and a control of their properties.

Design of double-component metal–organic framework air filters with PM2.5 capture, gas adsorption and antibacterial capacities

A biodegradable cellulose-based air filter (Ag-MOFs@CNF@ZIF-8) with multi-layer structure was fabricated by in situ generation of double-component metal-organic frameworks (MOFs) and reinforcement of cellulose nanofiber (CNF). It exhibits good filtration performance, gas adsorption, antibacterial activity and mechanical property. The presence of MOFs could enhance the interaction between the filter and particulate matter (PM) and significantly improve the specific surface area of the composite filter. Thus, the filtration efficiency of the composite filter could reach 94.3% for PM2.5 and the nitrogen adsorption capacity increased to 109 cm3 g−1. Furthermore, the Ag-MOFs@CNF@ZIF-8 filter exhibited excellent antibacterial activity against Escherichia coli with an inhibition zone diameter of 18.1 mm. The compressive strength of the composite filter could be up to 501 kPa, approximately 3.8 times higher than that of pure cellulose filter. Herein, this composite filter has a great application potential in PM2.5 removal, toxic gas adsorption and healthcare fields.

Preparation of a monolithic magnetic stir bar for the determination of sulfonylurea herbicides coupled with HPLC

A hybrid material of metal organic frameworks (MOFs) and monoliths was developed and used for stir bar sorption extraction (SBSE) of five sulfonylurea herbicides. It was prepared in a glass tube (4 mm I.D.) by thermal polymerization using modified neodymium supermagnetic (Nd2Fe14B) powders as the component substrates, the organic polymerization solutions and ethyl cellulose as the adhesion agent. The prepared stir bar was characterized by scanning electron micrography (SEM) and X-ray diffraction (XRD). It was successfully applied for the determination of sulfonylurea herbicides in soil and lake water samples coupled with high-performance liquid chromatography (HPLC). The extraction and desorption factors affecting the performance of sulfonylurea herbicides were evaluated in detail. Under the optimum conditions, the extraction efficiency of the hybrid stir bar was obviously higher than the blank stir bar without UIO-66(Zr)-NH2. Linear ranges were 10–700 μg/L for thifensulfuron-methyl (TIM), amidosulfuron (AS) and metsulfuron-methyl (MSM) and 10–800 μg/L for sulfosulfuron (SSF) and tribenuron-methyl (TBM), respectively. The obtained detection limits were in the ranges of 0.04–0.84 μg/L with the recoveries of 68.8–98.1% for the real samples. The novel stir bar possessed excellent advantages of both supermagnetic performance and large specific surface areas in the presence of MOFs and monoliths, which was potentially an optimal adsorbent for environmental analysis.

Mixed matrix membranes based on amine and non-amine MIL-53(Al) in Pebax® MH-1657 for CO 2 separation

Abstract Mixed matrix membranes (MMM) based on poly(ether-b-amide) or Pebax® as the matrix and MIL-53(Al)/NH2-MIL-53(Al) metal–organic frameworks (MOF) as fillers were prepared by solution casting. The objective of the work was to determine the effect of MOF functionalization and concentration on the permeability and selectivity of different gases (CH4, N2, H2 and CO2). Scanning electron microscopy (SEM) confirmed that good particle dispersion up to the optimum content was obtained, while Fourier transform infrared spectroscopy (FTIR) confirmed the successful MOF inclusion in MMM. The MMM thermal and mechanical stability were verified by thermogravimetric (TGA) and dynamic mechanical (DMA) analyses, respectively. Finally, the gas separation performances were investigated via single gas and mixed gas permeation tests at 35 °C and 10 bar. The results show that CO2 single gas permeability, as well as CO2/CH4 and CO2/N2 ideal selectivity, were enhanced by introducing either MIL-53(Al) or NH2-MIL-53 (Al), while the highest CO2 permeability (149 Barrer) was obtained at 10 wt% NH2-MIL-53 with a 174% improvement over the neat Pebax® value. The highest ideal selectivity for CO2/CH4 and CO2/N2 was 23.3 (51% increase) and 59.4 (49% increase) also at 10 wt% MIL-53, respectively. Higher CO2 permeability and selectivity was attributed to high porosity introduced by the presence of MOF, as well as the selective adsorption of CO2 on MOF. For mixed gas results, it was found that 20 wt% NH2-MIL-53 had significant CO2/CH4 separation performance, particularly at low CO2 volume fraction (20 vol%) with a separation factor as high as 69.4. Overall, the results showed that MOF surface modification can be necessary under specific conditions.

Metal-Organic Frameworks Invert Molecular Reactivity: Lewis Acidic Phosphonium Zwitterions Catalyze the Aldol-Tishchenko Reaction.

The influence of metal–organic frameworks (MOFs) as additives is herein described for the reaction of n-alkyl aldehydes in the presence of methylvinylketone and triphenylphosphine. In the absence of a MOF, the expected Morita–Baylis–Hillman product, a β-hydroxy enone, is observed. In the presence of MOFs with UMCM-1 and MOF-5 topologies, the reaction is selective to Aldol-Tishchenko products, the 1 and 3 n-alkylesters of 2-alkyl-1,3-diols, which is unprecedented in organocatalysis. The (3-oxo-2-butenyl)triphenylphosphonium zwitterion, a commonly known nucleophile, is identified as the catalytic active species. This zwitterion favors nucleophilic character in solution, whereas once confined within the framework, it becomes an electrophile yielding Aldol-Tishchenko selectivity. Computational investigations reveal a structural change in the phosphonium moiety induced by the steric confinement of the framework that makes it accessible and an electrophile.

Nano-sized metal organic framework to improve the structural properties and desalination performance of thin film composite forward osmosis membrane

In the present study, nano-sized metal-organic framework (MOF) particles consisting of silver (I) and 1,3,5-benzene tricarboxylic acid were synthesized and applied to improve the structural properties as well as desalination performance of thin-film composite (TFC) forward osmosis (FO) membranes. The MOF nanocrystals were incorporated into the polyamide layer of membranes through interfacial polymerization. Characterizations by Field emission scanning electron microscopy and X-ray photoelectron spectroscopy enabled the detection of MOF nanocrystals within the selective layer of the resultant membranes. The MOF incorporation led to changes of the membrane active layer in terms of hydrophilicity and transport properties, without detrimental effects on the layer selectivity. These features enhanced pure water permeability of the membranes to 129%, which was provided through 0.04% MOF loading of the organic phase during interfacial polymerization. As a result, the modified membrane exhibited an enhanced FO seawater desalination performance in comparison with the control membrane. The performance stability of TFC membrane was also improved by presence of MOF in active layer (as seen by a water flux decline of about 7% for modified membrane against about 18% for unmodified membrane when tested with real seawater). This study demonstrates the potential of MOF particles to enhance desalination performance of TFC membranes in FO systems.

Configurations, band structures and photocurrent responses of 4-(4-oxopyridin-1(4H)-yl)phthalic acid and its metal-organic frameworks

4-(4-oxopyridin-1(4H)-yl)phthalic acid (H2L) and three H2L-based metal-organic frameworks (MOFs) formulated as ZnL(DPE)(H2O)·H2O (DPE=(E)-1, 2-di(pyridine −4-yl)ethene) (1), CdL(H2O)2 (2) and CdL (3) were synthesized and structurally characterized by single-crystal X-ray diffraction. The free H2L ligand shows an enol-form and the L2− ligand in the three MOFs exists as the keto-form. Density functional theory (DFT) calculations indicate H2L and the three MOFs possess different band structures. Due to the existence of the N-donor, DPE in MOF 1, the conduction band (CB) minimum and band gap of MOF 1 are much lower than those of H2L. And MOF 1 yielded much larger photocurrent density than H2L upon visible light illumination. Electrochemical impedance spectroscopy (EIS) shows the interfacial charge transfer impedance in the presence of MOF 1 is lower than that in the presence of H2L. The hydrous MOF 2 and the anhydrous MOF 3 are both constructed by Cd(II) and L2−, and they can be reversibly transformed to each other. However, MOFs 2 and 3 possess different CB minimums and VB maximums, and their band gaps are much larger than that of MOF 1.

The Influence of Cu3(BTC)2 metal organic framework on the permeability and perm‐selectivity of PLLA‐MOF mixed matrix membranes

ABSTRACTPoly(l‐lactic acid) (PLLA) ‐ 20% (w/w) and Cu3(BTC)2 metal organic framework (MOF) based mixed matrix membranes (MMMs) were fabricated by a vertical corotating twin screw microcompounder followed by an injection molding process. Water vapor, CO2, O2, and selected aroma mass transfer properties of PLLA and PLLA MMMs were evaluated. The CO2/O2 perm‐selectivity of PLLA (αCO2/O2) MMMs increased from 7.6 to 10.3 with the incorporation of 20% Cu3(BTC)2 MOF. Gravimetric permeability studies of trans‐2‐hexenal performed at 23°C and 50% RH indicated that permeability coefficient of PLLA MMMs increased by around 60% as compared to regular PLLA film. However, no changes in mass transfer rates were observed for acetaldehyde. Furthermore, the thermal processing parameters as well as the presence of MOF did not show any significant effect on the molecular weight of the PLLA matrix nor on the crystalline structure of the Cu3(BTC)2 MOF, which was confirmed by both gel permeation chromatography and X‐ray diffraction studies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42764.