Chromium Terephthalate Research Articles

Nanocavity in hollow sandwiched catalysts as substrate regulator for boosting hydrodeoxygenation of biomass-derived carbonyl compounds.

Hydrodeoxygenation of oxygen-rich molecules toward hydrocarbons is attractive yet challenging in the sustainable biomass upgrading. The typical supported metal catalysts often display unstable catalytic performances owing to the migration and aggregation of metal nanoparticles (NPs) into large sizes under harsh conditions. Here, we develop a crystal growth and post-synthetic etching method to construct hollow chromium terephthalate MIL-101 (named as HoMIL-101) with one layer of sandwiched Ru NPs as robust catalysts. Impressively, HoMIL-101@Ru@MIL-101 exhibits the excellent activity and stability for hydrodeoxygenation of biomass-derived levulinic acid to gamma-valerolactone under 50°C and 1-megapascal H2, and its activity is about six times of solid sandwich counterparts, outperforming the state-of-the-art heterogeneous catalysts. Control experiments and theoretical simulation clearly indicate that the enrichment of levulinic acid and H2 by nanocavity as substrate regulator enables self-regulating the backwash of both substrates toward Ru NPs sandwiched in MIL-101 shells for promoting reaction with respect to solid counterparts, thus leading to the substantially enhanced performance.

Immobilization of Silver(I) Ions on Amino-Functionalized Chromium(III) Terephthalate with Organophosphine and its C-H Carboxylation of a Heteroaromatic Compound.

A newly designed heterogenized catalyst that incorporates silver(I) ions with 2-(dicyclohexylphosphaneyl)acetaldehyde (PCy2 aldehyde) into amino-functionalized chromium(III) terephthalate is developed. Silver(I) ions were robustly immobilized on the amino-functionalized chromium(III) terephthalate, which contains an imine bond formed by the reaction with PCy2 aldehyde. The Ag(I) ion is coordinated with the phosphine in the imine group to create MIL-101-AP(Ag). Characterizations were carefully carried out according to the synthetic steps. The catalytic performance of MIL-101-AP(Ag) was evaluated through the C-H carboxylation of thiophene-2-carbonitrile, achieving a 10 % yield with a turnover number of 1.0. The recyclability of the MIL-101-AP(Ag) catalyst was successfully demonstrated with five cycle, with no loss in activity and selectivity observed. This approach, which involves the formation of an imine bond to facilitate silver loading with phosphine on amino-functionalized MIL-101(Cr), exhibits significant potential for both CO2 fixation and C-H carboxylation, thereby highlighting the modified material's promise as a sustainable catalyst.

Low-temperature synthesis and characterization of porous chromium terephthalate MIL-101(Cr) and its photocatalytic degradation of phenanthrene

Low-temperature synthesis and characterization of porous chromium terephthalate MIL-101(Cr) and its photocatalytic degradation of phenanthrene

A bioluminescent earthworm luciferase mimetic MIL-101(Cr)-MOF for enhanced luciferin chemiluminescence and H2O2 sensing

A sensitive and rapid method was introduced in this research for the detection of H2O2 based on luciferase mimetic. Luciferase mimetic of bioluminescent earthworm was synthesized using a metal–organic framework (MOF). The luminol was loaded into the chromium terephthalate MOF MIL-101(Cr) pores and applied in the luciferin chemiluminescence (CL) system with an outstanding performance. The samples exhibited prominent catalytic performance of luciferase mimetic in the luciferin chemiluminescence system for H2O2 sensing with high sensitivity in the linear range of 1 × 10−2– × 10−10 mol/L and detection limit of 1.251 × 10−11 mol/L (R2 = 0.9944). The effects of the key factors were explored by response surface methodology (RSM) based on a Box–Behnken design (BBD). Thanks to its features such as low cost, rapid response, and portability, this enzyme mimetic could be a promising platform for CL sensing, offering great potential for the construction of a CL H2O2 sensor for biotechnology and clinical diagnostic purposes.

Separation of 1‐Naphthol from Wastewater Using HF‐Free Microwave‐Assisted Synthesized MIL‐101(Cr): Kinetics, Thermodynamics and Reusability Studies**

AbstractMicrowave‐assisted synthesis of Chromium (III) Terephthalate Metal Organic Framework, MIL‐101(Cr), was achieved in an aqueous media in the absence of hydrofluoric acid (HF). The synthesized material was characterized using Fourier transform infrared spectroscopy, powder X‐ray diffraction, nitrogen adsorption/desorption isotherms and field emission scanning electron microscope. Results indicate that the synthesized MIL‐101(Cr) using microwave irradiation poses higher surface area than those obtained using autoclave in a conventional oven method. Adsorptive removal of 1‐naphthol from aqueous solution using synthesized MIL‐101(Cr) was evaluated at various temperatures and concentrations. The Langmuir and Freundlich isotherms are used to describe the adsorption equilibrium behavior. The pseudo–second order and intraparticle kinetic models were applied to understand the rate limiting step and the mechanism of 1‐naphthol adsorption. The thermodynamic analysis of solid‐liquid system was investigated. The synthesized MIL‐101(Cr) showed higher 1‐naphthol adsorption capacity, compared to other adsorbents like biochar and multiwall carbon nanotube.

Optimization of the Adsorption/Desorption Contribution from Metal-Organic-Heat-Carrier Nanoparticles in Waste Heat Recovery Applications: R245fa/MIL101 in Organic Rankine Cycles

The efficient recovery of low temperature waste heat, representing from 25% up to 55% of the energy losses in industrial processes, still remains a challenge and even Organic Rankine Cycles (ORCs) experience a strong efficiency decay in such a low temperature operating range (T < 150 °C). In similar heat transfer processes, several nanofluids have been proposed as a solution for increasing heat transfer efficiency, but they produced only moderate enhancements of the heat transfer efficiency in comparison with pure fluids. This paper aims at numerically assessing the potential gain in efficiency deriving from the application of an unconventional type of nanoparticles, the metal-organic heat carriers (MOHCs), in the ORC field. In comparison with standard nanoparticles, these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption, with a theoretically high potential for boosting the heat transfer capacity of ORC systems. In this paper a numerical model was developed and customized for considering the adsorption/desorption processes of the pure fluid R245fa (pentafluoropropane) combined with a crystal structure for porous chromium terephthalate (MIL101). The R245fa/MIL101 nanofluid behavior was experimentally characterized, defining proper semi-emipirical correlations. Then, an optimization procedure was developed, combining the numerical model with a PSO algorithm, to optimize the thermodynamic conditions in the ORC so as to maximize the contribution of desorption/absorption processes. The results confirm the increase in net power output (+2.9% for 100 °C) and in expander efficiency (+2.4% for 100 °C) at very low heat source temperature. The relevance of tuning the operating cycle and the nanofluid properties is also demonstrated.

Immobilization of a trimeric ruthenium cluster in mesoporous chromium terephthalate and its catalytic application.

Molecular trimeric ruthenium carboxylate clusters (Ru3 clusters) have been introduced into the pore channels of mesoporous metal-organic framework chromium terephthalate [MIL-101(Cr)] by employing a facile two-step post-synthetic strategy in which diamine hooks anchored on the framework metal nodes of the MOF are used to covalently immobilize the Ru3 clusters. The catalytic activity of the isolated Ru3 clusters in the pore channels of the MOF was significantly improved compared to the bulk counterpart.

Tandem Synthesis of ϵ‐Caprolactam from Cyclohexanone by an Acidified Metal‐organic Framework

AbstractTandem synthesis of ϵ‐caprolactam, one of the largest scaled commercial chemicals, is highly desired from the viewpoint of cost, energy, and environment. However, relevant studies have remained largely underexplored. By using a one‐pot strategy, we encapsulated phosphotungstic acid (PTA) into a chromium terephthalate metal‐organic framework (MOF), MIL‐101, for the efficient tandem conversion of cyclohexanone to ϵ‐caprolactam. The highly dispersed PTA in the MOF matrix showed a high yield of ϵ‐caprolactam through a tandem oximation‐Beckmann rearrangement reaction at 100 °C for 12 h. Moreover, MIL‐101‐PTA was recycled three times, with only a slight loss in their catalytic performance. To the best of our knowledge, this represents the first report using acidified MOF for a tandem oximation‐Beckmann rearrangement reaction.

Ag-exchanged mesoporous chromium terephthalate with sulfonate for removing radioactive methyl iodide at extremely low concentrations in humid environments

The development of efficient adsorbents to remove radioactive methyl iodide (CH3I) in humid environments is crucial for air purification after pollution by nuclear power plant waste. In this work, we successfully prepared a post-synthetic covalent modified MIL-101 with a sulfonate group followed by the ion-exchange of Ag (I), which is well characterized by diffuse reflectance FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and the hydrophobic index (HI). After modification of the MOFs, we applied functionalized MIL-101 obtained by either one-pot synthesis (MIL-101-SO3Ag) or a post-synthetic modification process (MIL-101-RSO3Ag, R = NH(CH2)3) to remove the CH3I at an extremely low concentration (0.31 ppm) in an environment with very high relative humidity (RH 95%). Enhanced hydrophobicity of the surface-modified MIL-101 was evaluated by examining the HI with the competitive adsorption of water and cyclohexane vapor, with a high surface area maintained, as confirmed by Ar physisorption. Interestingly, the post-synthetically modified MIL-101-RSO3Ag showed exceptional adsorption performance as determined by its decontamination factor (DF = 195,350) at 303 K and RH 95%. This performance was in comparison to Ag (I)-exchanged 13X zeolite and MIL-101-SO3Ag, which include much higher amounts of Ag. Furthermore, MIL-101-RSO3Ag retained ~94–100% of its fresh adsorbent performance during five cycle repetitions.

Metal-organic framework/zeolite nanocrystal/polyvinylidene fluoride composite ultrafiltration membranes with flux/antifouling advantages

In this study, hydrophilic zirconium 1,4-dicarboxybenzene (UiO-66) and chromium (III) terephthalate (MIL-101) metal-organic frameworks (MOFs) and faujasite (FAU) zeolite nanocrystals were synthesized successfully and incorporated into polyvinylidene fluoride (PVDF) matrix as nanofillers to fabricate mixed matrix membranes (MMMs) via non-solvent induced phase separation (NIPS) process. The effects of casting solution temperature and casting speed as two important factors in membrane fabrication via phase inversion method on performance and structure of the neat PVDF membrane were investigated. Then, various contents of the synthesized nanofillers were loaded into the PVDF matrix and the effects of the synthesized nanofillers on hydrophilicity, pure water flux (PWF), morphology and antifouling properties of the fabricated MMMs were explored. Antifouling studies were also performed using Bovine serum albumin (BSA). The obtained results demonstrated that incorporation of the synthesized nanofillers into the PVDF membrane has positive effect on performance and structure of the fabricated MMMs and the MMM containing 0.1 wt% MIL-101 showed the best performance with water flux of 360 LMH, BSA rejection of 100%, irreversible fouling of 22.2% and flux recovery ratio of 77.7%. This work highlighted the potential application of the MOFs as effective nanofillers for MMM fabrication.

An Effective Hybrid Heterogeneous Catalyst to Desulfurize Diesel: Peroxotungstate@Metal-Organic Framework.

A peroxotungstate composite comprising the chromium terephthalate metal–organic framework MIL-101(Cr) and the Venturello peroxotungstate [PO4{WO(O2)2}4]3− (PW4) has been prepared by the impregnation method. The PW4@MIL-101(Cr) composite presents high catalytic efficiency for oxidative desulfurization of a multicomponent model diesel containing the most refractory sulfur compounds present in real fuels (2000 ppm of total S). The catalytic performance of this heterogeneous catalyst is similar to the corresponding homogeneous PW4 active center. Desulfurization efficiency of 99.7% was achieved after only 40 min at 70 °C using H2O2 as an oxidant and an ionic liquid as an extraction solvent ([BMIM]PF6, 2:1 model diesel/[BMIM]PF6). High recycling and reusing capacity was also found for PW4@MIL-101(Cr), maintaining its activity for consecutive oxidative desulfurization cycles. A comparison of the catalytic performance of this peroxotungstate composite with others previously reported tungstate@MIL-101(Cr) catalysts indicates that the presence of active oxygen atoms from the peroxo groups promotes a higher oxidative catalytic efficiency in a shorter reaction time.

Mesoporous Metal-Organic Framework MIL-101 at High Pressure.

The chromium terephthalate MIL-101 is a mesoporous metal-organic framework (MOF) with unprecedented adsorption capacities due to the presence of giant pores. The application of an external pressure can effectively modify the open structure of MOFs and its interaction with guest molecules. In this work, we study MIL-101 under pressure by synchrotron X-ray diffraction and infrared (IR) spectroscopy with several pressure transmitting media (PTM). Our experimental results clearly show that when a solid medium as NaCl is employed, an irreversible amorphization of the empty structure occurs at about 0.4 GPa. Using a fluid PTM, as Nujol or high-viscosity silicone oil, results in a slight lattice expansion and a strong modification of the peak frequency and shape of the MOF hydroxyl vibration below 0.1 GPa. Moreover, the framework stability is enhanced under pressure with the amorphization onset shifted to about 7 GPa. This coherent set of results points out the insertion of the fluid inside the MIL-101 pores. Above 7 GPa, concomitantly to the nucleation of the amorphous phase, we observe a peculiar medium-dependent lattice expansion. The behavior of the OH stretching vibrations under pressure is profoundly affected by the presence of the guest fluid, showing that OH bonds are sensitive vibrational probes of the host-guest interactions. The present study demonstrates that even a polydimethylsiloxane silicone oil, although highly viscous, can be effectively inserted into the MIL-101 pores at a pressure below 0.2 GPa. High pressure can thus promote the incorporation of large polymers in mesoporous MOFs.

Multicomponent transport model-based scaling up of long-term adsorptive filtration of MOF incorporated mixed matrix hollow fiber membrane: Treatment of textile effluent

The present work describes the preparation and detailed characterization of porous chromium terephthalate metal–organic framework (MOF) impregnated polyacrylonitrile based hollow fiber membrane. The hollow fibers were characterized by their surface morphology, zeta potential, permeability, average pore diameter, molecular weight cut off (MWCO) and contact angle. Variation of MOF concentration upto 10 wt% resulted in 43% reduction in membrane permeability. The corresponding change in MWCO was from 140 kDa to 70 kDa. The addition of MOF made the membrane more hydrophilic and at 10 wt% MOF, the contact angle was reduced to 52° from 86°. The Fourier Transform Infrared Spectra (FTIR) of mixed matrix membrane (MMM) showed that there existed strong chemical interaction between MOF particles and polymer backbone, precluding the leaching of MOF from the membrane matrix over long term use. The MOF incorporated MMM exhibited tremendous adsorption capacity (197–260 mg/g for 10 wt% MOF doped fiber) towards reactive dyes commonly used in the textile industry. As the dye removal by MMM hollow fiber was based on the adsorption mechanism, the breakthrough behavior of the membrane was important to estimate the membrane life and onset of membrane regeneration. In the present work, a detailed two-dimensional transient transport model was developed for a multi-component real-life textile effluent from the first principles using the equation of continuity, momentum balance, species balance based on convective-diffusive-adsorptive solute transport in the hollow fiber. The model results were validated with the experimental data of a textile effluent having four reactive dyes. The multicomponent model was used for scaling up the actual hollow fiber based filtration system and the performance curve was generated relating the breakthrough volume, number and length of fibers.

Synthesis, Characterizations, and Adsorption Isotherms of CO2 on Chromium Terephthalate (MIL-101) Metal-organic Frameworks (Mofs)

Synthesis, Characterizations, and Adsorption Isotherms of CO2 on Chromium Terephthalate (MIL-101) Metal-organic Frameworks (Mofs)

Nitro functionalized chromium terephthalate metal-organic framework as multifunctional solid acid for the synthesis of benzimidazoles

In the present work, nitro functionalized chromium terephthalate [MIL-101(Cr)-NO2] metal- organic framework is prepared and characterized by powder X-ray diffraction (XRD), elemental analysis, infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area. The inherent Lewis acidity of MIL-101(Cr)-NO2 is confirmed by FT-IR spectroscopy using CD3CN as a probe molecule. The performance of MIL-101(Cr)-NO2 as bifunctional catalyst (acid and redox) promoting the synthesis of wide range of benzimidazoles has been examined by catalyzed condensation on acid sites and subsequent oxidative dehydrogenation. The catalytic activity of MIL-101(Cr)-NO2 is found to be superior than analogues catalysts like MIL-101(Cr)-SO3H, MIL-101(Cr)-NH2, UiO-66(Zr), UiO-66(Zr)-NO2, MIL-100(Fe) and Cu3(BTC)2 (BTC: 1,3,5-benzenetricarboxylate) under identical reaction conditions. The structural stability of MIL-101(Cr)-NO2 is supported by leaching analysis and reusability tests. MIL-101(Cr)-NO2 solid is used five times without decay in its activity. Comparison of the fresh and five times used MIL-101(Cr)-NO2 solids by powder XRD, SEM and elemental analysis indicate identical crystallinity, morphology and the absence of chromium leaching, respectively.

Molecular Encapsulation of Trimeric Chromium Carboxylate Clusters in Metal-Organic Frameworks and Propylene Sorption.

Oxo-bridged trimeric chromium acetate clusters [Cr3 O(OOCCH3 )6 (H2 O)3 ]NO3 have been encapsulated for the first time in the mesoporous cages of the chromium terephthalate MIL-101(Cr). The isolated clusters in MIL-101(Cr) have increased affinity towards propylene compared to propane, due to generation of a new kind of pocket-based propylene-binding site, as supported by DFT calculations.

Application of Chromium and Cobalt Terephthalate Metal Organic Frameworks as Catalysts for the Production of Biodiesel from Calophyllum inophyllum Oil in High Yield Under Mild Conditions

This paper describes the application of chromium(III) terephthalate (Cr-Tp) and cobalt(II) terephthalate (Co-Tp) metal organic frameworks, as heterogeneous acid catalysts to avoid the yield reduction caused by saponification during the process of biodiesel production using Calophyllum inophyllum oil. The catalysts were mainly characterized using spectroscopic (FTIR), microscopic (SEM, energy-dispersive X-ray spectroscopy) and X-ray diffractive techniques. The surface acidity and the thermal stability of the catalysts were determined using Hammett indicator and thermo-gravimetric methods, respectively. The catalysts were employed for the pre-esterification of free fatty acid content of the oil before subjecting the oil for the transesterification of its triglyceraldehyde content. The pre-esterification was performed through a couple of successive catalytic cycles under milder conditions [25°, 1 atm, and 2/1 MeOH/oil (w/w) ratio] than the conditions reported so far. The study revealed that the successful pre-esterification required these catalysts in very small amount (< 2.5% by oil weight) and occurred within very short time (2 h for the 1st cycle and 2–4 h for the 2nd cycle), reducing the acid value of C. inophyllum oil significantly (88%) from 56.91 to ~ 6.5 mg KOH g−1. The catalytic activity of these catalysts remained unchanged even after the 10th cycle of catalyst reuse. More importantly, the yield of biodiesel obtained from C. inophyllum oil in this way was significantly high (~ 93%) and free from saponification.

Synthesis of a chromium terephthalate metal organic framework and use as nanoporous adsorbent for removal of diazinon organophosphorus insecticide from aqueous media

MIL-101(Cr), as a chromium terephthalate metal organic framework (MOF), is synthesized hydrothermally and used for removal of diazinon from aqueous media. Different methods such as FT-IR, FE-SEM, TGA, XRD and BET analysis were applied for characterization of prepared MIL-101(Cr). The results revealed that MIL-101(Cr) has octahedral structure, 96% crystallinity, thermal stability up to 550 °C and about 2600 m2/g BET surface area with microporous structure. Adsorption experiments were designed by Design expert software and the effect of parameters such as pH (2–10), temperature (25–61 ), contact time (5–85 minutes) and adsorbent dosage (0.1–0.9 g/L) was investigated. Adsorption process was optimized by response surface methodology (RSM) and the optimum conditions of adsorption process was achieved in pH 6.5, temperature 25 °C, contact time 64 minutes and adsorbent dosage 0.74g/L which is lead to 96% removal of diazinon. In order to investigate the reusability and life time of MIL-101(Cr), the adsorbent is used in five successive cycles for adsorption of diazinon in fresh samples and good results are obtained. Langmuir and Freundlich isotherm models were deliberated by adsorption equilibrium data and Langmuir model show better conformity (R2 = 0.985) with the experimental results. Kinetic study was carried out using pseudo first order, pseudo second order and intraparticle diffusion kinetic models. Experimental data were better fitted to the pseudo second order with a correlation coefficient of 0.997 which signified that the experimental outcome of the adsorption of diazinon was a chemical adsorption.

Diaminomaleonitrile functionalized double-shelled hollow MIL-101 (Cr) for selective removal of uranium from simulated seawater

Hollow metal-organic frameworks (MOFs) have attracted wide interest because of their unique core-shell structure. As a novel uranium adsorbent, diaminomaleonitrile (DAMN) functionalized double-shelled hollow (DSHM) metal-organic framework of chromium(III) terephthalate was prepared by a post-synthetic method of grafting amino group onto coordinatively unsaturated sites (CUS). TEM, XRD, nitrogen sorption and FT-IR spectrometry were used to characterize the obtained DAMN functionalized hollow MOF. The maximum capacity of uranium adsorption is 601 mg g−1, which exceeds all known functionalized MIL-101 uranium adsorption materials. The optimal adsorption pH is 8 which is close to the pH of seawater. Furthermore, the high selectivity of uranium and high adsorption rate in simulated seawater provide a promising prospect to introduce DSHM-DAMN for the extraction of uranium from seawater. In this work, we first applied hollow MOF for uranium adsorption, which greatly improves the uranium adsorption performance of MOF materials; we also explored the practical application of hollow MOF materials.

Effect of solvent nature on propylene glycol oxidation with tert-butyl hydroperoxide over metal-organic framework Cr-MIL-101.

The effect of solvent nature on conversion, product yields and reaction kinetics of selective propylene glycol oxidation with tert-butyl hydroperoxide over porous chromium terephthalate Cr-MIL-101 used as a heterogeneous catalyst is considered. Differences in hydrogen bonding of propylene glycol molecules in different solvents and adsorption of components of the reaction mixture on the active sites of the catalyst are studied by Fourier-transformed infrared spectroscopy. The characteristics of the solvent are shown to play a key role in the process under consideration. In the case of aprotic solvents, the oxidant utilization efficiency, the propylene glycol conversion and the product yields are significantly higher in comparison with those in protic solvents. The protic solvents can adsorb on the active sites of the catalyst which leads to a decrease of their accessibility for the reagents. The initial rate of propylene glycol oxidation decreases linearly with the increasing of the diameter of molecules of the protic solvents. DFT calculations support the competitive adsorption of the molecules of protic solvents on Cr active sites of MIL-101. In the aprotic solvents, the reactivity and distribution of propylene glycol molecules in the solution are determined by the involvement of hydroxyl groups of the substrate into the intermolecular interactions. The ability of the aprotic solvents to break the hydrogen bond network in the associates of propylene glycol is responsible for the concentration of the substrate molecules in the pores of Cr-MIL-101. The highest selectivities towards hydroxyacetone for Cr-MIL-101 catalyst are obtained in solvents, where the initial rates of propylene glycol oxidation are the lowest ones.