Mass Transfer Limitations Research Articles

Room Temperature Electrochemical-Shock Synthesis of Solid-Solution Medium-Entropy Alloy Nanoparticles for Hydrogen Evolution.

For millennia, humankind has discovered great benefits in alloying materials. Over the past 100 years, a renaissance in nanoscience has cemented the importance of nanoparticles in a variety of fields ranging from energy storage and conversion to cell biology. While many synthetic strategies exist for nanoparticle and alloy nanoparticle formation, new methods are necessary to create nanoparticles under unprecedented conditions. Here, we demonstrate a simple technique to electrodeposit solid-solution alloy nanoparticles at room temperature. When metal salts of platinum, gold, and palladium are confined to nanodroplets suspended in oil, and then a nanodroplet collides with a sufficiently negative-biased electrode to reduce the metal salts at the mass-transfer limitation, solid-solution alloy nanoparticles form. High-angle annular dark-field scanning transmission electron microscopy and single atom energy dispersive X-ray spectroscopy confirm the solid-solution microstructure of the nanoparticles. The results also confirm the nanodroplet's ability to tune alloy microstructures from amorphous to solid-solution. We further extend our technique by adding salts of silver, which lead to the synthesis of polycrystalline medium-entropy alloys. Finally, we go on to show the application of our midentropy alloys toward renewable and clean energy devices by highlighting their electrocatalytic activity toward hydrogen evolution reaction. Our method is unrivaled in its simplicity and will find applications across various fields of study.

Fibrillated Films for Suspension Catalyst Immobilization—A Kinetic Study of the Nitrobenzene Hydrogenation

The immobilization of suspension catalysts in flexible, fibrillated films offers a promising solution to the mass transfer limitations often encountered in three-phase hydrogenation reactions. This study investigates the catalytic performance and mass transfer properties of fibrillated films in the hydrogenation of nitrobenzene to aniline, comparing them to free-flowing powdered catalysts. Fibrillated films were prepared from Pd/C catalysts with varying thicknesses (100–400 µm), and their performance was evaluated through kinetic studies in both batch reactors and microreactors. The specific activity of the films was significantly influenced by film thickness with thinner films demonstrating lower mass transfer limitations. However, mass transfer limitations were observed in thicker films, prompting the development of alternative film designs, including enhanced macro-porous films and sandwich structures. These modifications successfully minimized diffusion limitations, achieving similar specific activity to the powder catalysts while maintaining the mechanical stability of the films. This work demonstrates the feasibility of using fibrillated films for continuous catalytic processes and highlights their potential for efficient catalyst reuse, avoiding filtration steps and enhancing process sustainability. Furthermore, while PTFE remains indispensable for producing such films due to its mechanical and thermal stability, ongoing research focuses on identifying more environmentally friendly alternatives without compromising performance.

Model-based optimization strategies for direct hydrogenation of carbon dioxide to dimethyl ether

This study discusses model-based optimization strategies for CO2 hydrogenation to dimethyl ether (DME) over a CuZnZr (CZZ) and ferrite (FER) mixed catalyst system in a packed-bed reactor configuration. A two-dimensional axisymmetric, nonisothermal packed-bed reactor model was developed using COMSOL Multiphysics 6.2 software. The model solves two-dimensional (radial and axial) heat and mass transport equations in the packed-bed and integrates intraparticle diffusion and heat transfer in a 1D approach. This powerful feature differs from a traditional porous media approach and takes into account any heat and mass transfer limitations that may exist. Analysis shows that the heat transfer limitations are negligible, but strong internal mass transfer limitations were observed at 10 ≤ WHSV ≤ 90 h−1 on the FER catalyst and at 240 °C. The optimum catalyst composition (i.e., mixing ratio) varies depending on the operating regime. The FER catalyst weight in the mixture can be as low as 5 wt.%, but the ideal composition depends on the internal mass transfer limitation and its relationship with the operating regime (i.e., weight hourly space velocity, temperature). A catalyst composition of 80 wt.% CZZ and 20 wt.% FER was suggested; this composition can provide high CO2 conversion and DME production rates at a wide range of temperatures and flow rates.

Metabolic Versatility of acetogens in syngas Fermentation: Responding to varying CO availability.

Syngas fermentation using acetogenic bacteria offers a promising route for sustainable chemical production. However, gas-liquid mass transfer limitations and efficient co-utilization of CO and H2 pose significant challenges. This study investigated the kinetics of syngas conversion to acetate by Acetobacterium wieringae and Clostridium species in batch conditions under varying initial CO partial pressures (19 - 110 kPa) in batch cultures. A. wieringae strains, exhibited superior growth in all gas compositions, with a maximum growth rate of 0.104 h-1. The distinct CO, H2, and CO2 consumption patterns revealed metabolic flexibility and adaptation to varying syngas compositions. Notably, A. wieringae strains and C. autoethanogenum achieved complete CO and H2 conversion, with C. autoethanogenum also exhibiting net CO2 uptake. These findings provide valuable insights into the distinct metabolic capabilities of these acetogens and contribute to the development of efficient and sustainable syngas fermentation processes.

Biofilm mass transfer and thermodynamic constraints shape biofilm in trickle bed reactor syngas biomethanation

Syngas (H2, CO2, CO) produced thermochemically from lignocellulosic biomass is an underexploited source for resource recovery and valorisation through its biological conversion for the production of a wide range of chemicals and fuels. Syngas biomethanation is one such promising bioconversion pathway, displaying interesting features such as high conversion efficiency and product selectivity, as methane is the sole product of the process. The biological conversion of syngas to high purity biomethane is still typically associated with a number of challenges related to the syngas composition, CO toxicity, and gas–liquid mass transfer limitations. In this work, the syngas biomethanation process carried out in trickle bed reactors was investigated at its boundary conditions to explore the limits of the process, focusing on syngas composition and mass-transfer conditions potentially limiting process performance. The process was found to be robust when exposed to CO excess, but highly sensitive to H2 excess, which caused severe inhibition even under small amounts of excess H2. This implies that biomethane purity comparable to natural gas can be achieved by addition of renewable H2, but this requires precise control to avoid process failure. Modulating the liquid recirculation rate and gas residence time allowed for a maximum methane productivity of 9.8 ± 0.5 mmol CH4 h−1 Lreactor−1 with full conversion of H2 and CO at a gas residence time of 1 h. Nevertheless, increasing the gas–liquid mass transfer with increasing liquid recirculation rate did not lead to increased methane productivity, which suggested additional rate-limiting bottlenecks in the process. Careful investigation of other factors potentially limiting the process led to the conclusion that diffusive transport of syngas components in the biofilm was the main bottleneck of the process. This diffusive limitation leads to a scenario of severe substrate scarcity in the biofilm phase that conditions the thermodynamic feasibility of the different biochemical reactions involved in syngas biomethanation. In turn, these thermodynamic constraints were found to drive the stratification of microbial groups and sequential consumption of syngas components along the height of the reactor

Unlocking Molecular Interactions of Biredox Eutectic Electrolyte for Non‐Aqueous Symmetrical Organic Redox Flow Batteries

AbstractBiredox deep‐eutectic solvents (DESs)‐based electrolytes have shown unique features in non‐aqueous asymmetrical redox flow batteries (RFBs) that can potentially mitigate the crossover issue. However, strong intermolecular interactions among the electrolyte constituents in DESs bring in practical challenges such as limited mass transfer rates, slow redox kinetics, and degraded cyclability. Here, by using a novel biredox‐type DES based on 4‐methoxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (4‐MeO‐TEMPO) and 3,3′‐dimethylazobenzene (3,3′‐Azo) as a model electrolyte system, the intermolecular interaction involving in the biredox DESs is unlocked by first‐principles calculations, and their influence on the electrochemical performance of biredox DESs couples is systematically investigated in comprehensive consideration of the solvents and the supporting salts. It demonstrates that employing tetrabutylammonium bis‐trifluoromethane sulfonimidate‐acetonitrile as the supporting electrolyte synergistically weakens the intermolecular interactions within the DESs, thereby significantly promoting the redox kinetics and electrochemical reversibility in non‐aqueous symmetrical RBFs. With such an optimized electrolyte, a prototype symmetrical cell under static mode is capable of delivering a high output voltage of ∼2.15 V, a decent cyclability, and the exceptional rate capability with a current density of 25 mA cm−2. This study provides a simple yet effective way to develop advanced RFBs with dependable electrolyte regulation.

In Situ Constructed Magnetic Core‐Shell Hydrogen‐Bonded Organic Framework‐on‐Metal–Organic Framework Structure: an Efficient Catalyst for Peroxymonosulfate Activation

AbstractZeolite imidazole‐based framework (ZIF‐67), a notable class of metal–organic frameworks (MOFs), shows promise in activating peroxymonosulfate (PMS) for pollutant degradation due to its uniformly distributed cobalt ions. However, its nanoparticle form and the elution of cobalt ions during use cause challenges in recycling and the risk of secondary pollution. In this study, a magnetic core‐shell hydrogen‐bonded organic framework (HOF) on the MOF (HOF‐on‐Fe3O4/ZIF‐67) is successfully prepared. The porous HOF shell not only protects the active sites and mitigates cobalt ion leaching but also reduces mass transfer limitations, ensuring sustained catalytic performance. The magnetic Fe3O4 core enhances electron transfer between cobalt ions, boosts catalytic efficiency, and facilitates easy separation and recycling. This core‐shell structure effectively activates PMS, achieving 100% removal of Rhodamine B, a model wastewater dye, within 10 min (Rh B = 50 mg L−1, HFZ = 150 mg L−1, PMS = 1.5 mm, pH = 7, room temperature). Furthermore, under the protection of the HOF shell, cobalt ion leaching is minimized to a negligible value (0.14 mg L−1) after 5 cycles of use. The research provides fresh perspectives into the development of core‐shell composite materials with improved performance and recyclability in wastewater treatment.

Synergistic enhancement in hydrodynamic cavitation combined with peroxymonosulfate fenton-like process for bpa degradation: New insights into the role of cavitation bubbles in regulation reaction pathway

The combination of hydrodynamic cavitation (HC) and Fenton-like oxidation technology can dramatically enhance the pollutant removal capacity, however, the synergistic effect of cavitation and catalysts on reactive oxygen species (ROS) generation remained enigmatic. In this study, we established a combined system based on HC and Ce-MnFe2O4 activated peroxymonosulfate (PMS) for BPA removal, and attentions were paid on the role of cavitation bubbles. The results show that the combination of HC in Ce-MnFe2O4 activated PMS could mediate the degradation of BPA from the non-radical pathway dominated by 1O2 to •O2− dominated radical pathway. Both controlled experiments and theoretical calculations revealed that the cavitation bubbles with different sizes play the dominant role in ROS generation. The microjets produced by the collapse of cavitation bubbles could create a large number of oxygen vacancy defects on Ce-MnFe2O4 surface, which modify the activation barrier of PMS and facilitate the generation of •O2− thermodynamically. The stable existing cavitation bubbles with the size of 100∼400 nm could create considerable gas-liquid interface. The molecular dynamics simulations show that the nano bubbles can concentrate the BPA and increase the probability of contacts between BPA and Ce-MnFe2O4, hence effectively solve the issues of short lifetime of •O2− radicals and limited mass transfer distance to strengthen the reaction. In addition, the PMS/Ce-MnFe2O4/HC system not only achieves the satisfied COD (95 %) and TOC (65 %) removal efficiency but also enabled the BPA-contaminated water with a low energy cost of 0.065 kWh·m−3 and oxidant cost, highlighting the application potential of the HC technology for contaminated water.

Numerical analysis on the fate and transport of TiO2 nanoparticles in fractured porous media: Addressing intrinsic heterogeneities in sorptive mass transfer

The aggregation and slow migration of nanoparticles in aqueous media have caused serious concerns about their fate and impacts in the subsurface environment. Anthropogenic release and distribution of TiO2 nanoparticles (TNP) have immense potential for surface adsorption, occlusion, impregnation, bioaccumulation, and phase partition into various environmental compartments, and the actual risks in their interactions are still unknown. In an attempt to realize the extent of source zone migration of TNP in a fracture-skin-matrix (F-S-M) medium, a numerical model is developed and analyzed for sensitivity of certain features of the flow field. In addition, the sorptive mass transfer is simulated under four characteristic scenarios with varying assumptions pertaining to the intrinsic heterogeneities. The simulation results highlight the non-selective regulatory role of the skin in providing temporary interfacial space for reversible adsorption between the fracture and the matrix as well as in retarding the desorption rate. A preferential detachment of TNP is observed to be favored by the enhanced properties of skin due to the similarity in diffusion and dispersion coefficients. Out of the four scenarios, the two-site model and two-step model simulated the dynamic pore-filling features of adsorption pertaining to the heterogeneities in TNP and F-S-M characteristics. The results demonstrate that the proposed numerical could fairly detect the transition between local equilibrium and dynamic adsorption-desorption cycles that would eventually determine the mass transfer limitations and the extent of elution of TNP along the flow.

Effective multi-biocatalyst system with reusable NADH for transformation of glycerol to value-added dihydroxyacetone

Glycerol-based biorefinery can be a highly profitable process by producing highly value-added products such as dihydroxyacetone via combined catalytic strategies. Here, two-enzyme system is adopted for the transformation of glycerol into highly valuable dihydroxyacetone as well as cofactor regeneration at the same time. Glycerol dehydrogenase (GDH) and alcohol dehydrogenase (ADH) are co-immobilized within magnetically separable and spherical mesocellular silica foam (Mag-S-MCF), to prepare NER-(GDH/ADH). In details, GDH and ADH are adsorbed into the mesopores of Mag-S-MCF, and further crosslinked within the mesopores of Mag-S-MCF. The resulting nanoscale enzyme reactors (NER) of crosslinked GDH and ADH molecules within the bottle-neck structured mesopores can effectively prevent larger sized crosslinked enzyme aggregates from being leached out of smaller mesopores, due to the bottle-neck mesopore structure of Mag-S-MCF, as well as stabilize the activity of GDH and ADH upon chemical crosslinking, effectively preventing the denaturation of enzyme molecules. More importantly, the proximity of GDH and ADH molecules within mesopores of NER improves the efficiency of cofactor-mediated dual-enzymatic reactions by relieving mass-transfer limitations and improving cofactor recycling in an effective way, expediting both glycerol oxidation and dihydroxyacetone generation at the same time. As a result, the DHA concentration of NER-(GDH/ADH) and the simple mixture of NER-GDH and NER-ADH were 410 μM and 336 μM, respectively. To the best of our knowledge, this report is the first demonstration of stabilized nanoscale multi-enzyme reactor system, equipped with efficient cofactor regeneration within confined mesopores, for efficient glycerol transformation to high-valued dihydroxyacetone.Graphical

Monomer Transport via Collision in Emulsion Polymerization

AbstractOne of the questions still remaining regarding emulsion polymerization is the issue of mass transfer versus reaction limitation since, by its nature, emulsion polymerization requires monomer transport across an aqueous phase. This question is brought into focus lately by the growing use of miniemulsion polymerization in which the monomer transport step is much less important. This paper will explore the possible rate of monomer transport via collision and ratio this to the maximum rate of polymerization using the Damkohler analysis formality. Results indicate that systems relying on monomer transport by collision will be almost universally monomer‐transport‐limited, thus exhibiting lower‐than‐expected rates of polymerizations.

Three-dimensional porous SiC/BDD electrode with long-term robustness and enhanced electrochemical degradation performance for refractory organic pollutants

Boron-doped diamond (BDD) electrodes with a three-dimensional (3D) porous network structure can overcome the mass transfer limitations and increase substantially the utilization rate of active oxygen species. Nonetheless, the 3D porous network structure was invariably built using metallic substrates, which inherently have inferior stability because of their non-corrosion resistance and the severe thermal mismatch between BDD films and substrates. Herein, we reported, for the first time, the use of a commercially porous silicon carbide (SiC) as the substrate to construct a 3D SiC/BDD electrode to simultaneously alleviate the problematics of substrate corrosion and thermal mismatch. This novel electrode exhibited a long-term service lifetime of 800 h in 3 M H2SO4 under the current density of 50 mA cm−2, over 500 times longer than the conventional metallic substrate-based BDD electrodes. The optimum p-SiC/BDD electrode exhibited a high oxygen evolution potential of 2.04 V vs. SHE, a low charge transfer resistance of 18.4 Ω, a high mass transfer coefficient of 2.78 × 10−5 m s−1, and a thin diffusion layer thickness of 25.2 μm. The proposed electrode had a threefold larger pseudo-first-order reaction rate constant than a flat BDD electrode, although it consumed just a fourth of the latter’s electric energy. The superior performance was attributable to an increased mass transfer rate confirmed by computational fluid dynamics (CFD) simulations as well as a high yield of reactive oxygen species verified by electron spin resonance (ESR). Furthermore, the proposed SiC/BDD electrode could work effectively under different water matrices in the presence of diverse salt electrolytes, thus paving a new avenue for the structure design of robust non-active anode materials.

Square-wave pulsed potential driven electrocatalytic degradation of 4-chlorophenol using Fe-Ni/rGO/PPy@NF three dimensional electrode

To develop an energy-efficient system for the removal of chlorinated organic pollutants, Fe-Ni/reduced graphite oxide/polymerized polypyrrole@nickel foam was constructed as a catalytic cathode for pulsed electrocatalytic degradation, where cathode-catalyzed production of hydrogen radicals (H*) and hydroxyl radical (·OH) generated at the anode led to dechlorination of 4-chlorophenol (4-CP), and dechlorination products were mineralized and degraded under the action of·OH. When energy was continuously supplied to the reaction system in the constant potential mode, the 4-CP concentration near the electrode was insufficient, limiting the reaction rate. Conversely, in the square-wave pulsed potential mode, mass transfer limitations were mitigated, significantly enhancing reaction efficiency and reducing energy consumption. At −1.2 V (vs. Ag/AgCl), the 4-CP removal efficiency reached 93.79 % in the pulsed potential mode, surpassing the constant potential mode's performance of 81.40 %. The synergistic periodic oscillation of the potential, direct electron transfer, and catalytic generation of active free radicals in the pulsed potential mode reduced intermediate concentrations and increased 4-CP mineralization, while the degradation pathway remained unchanged. This research presents a method for the efficient treatment of chlorinated organic pollutants in water using pulsed electrocatalytic degradation.

Novel phase transfer catalysis coupled with bifunctional oxidation for enhanced remediation of groundwater polluted with multiple NAPL: Performance and mechanisms

Structural differences among non-aqueous phase liquids (NAPLs) result in varying oxidation rates, limiting mass transfer between NAPLs and oxidants and seriously impairing the effectiveness of remediation via traditional in-situ chemical oxidation. To tackle this challenge, a novel approach is proposed for remediating multi-NAPL-polluted groundwater that leverages phase transfer catalysis (PTC) to enhance heterogeneous mass transfer by transferring oxidants from groundwater to NAPLs. Meanwhile, “oxidation-in-situ activation” is achieved through bifunctional oxidation using permanganate and peroxymonosulfate (PP). The proposed approach is referred to PTC-PP in this study. Herein, trichloroethene (TCE) and benzene serve as a representative multi-NAPL system. Experimental results indicated that PP significantly improved degradation efficiency of benzene in multi-NAPL system by at least 60.8% compared to single-oxidant systems, and further enhancement (17.6%) was achieved when PP was combined with PTC compared to PP alone. Dissolved Mn(II) and MnO2 generated by MnO4− reduction effectively activated peroxymonosulfate in PTC-PP system, with colloidal MnO2 being the most effective activator. Consequently, SO4•−, O2•− and 1O2 were formed in both NAPL and aqueous phases, while •OH was formed in aqueous phase, playing a crucial role in benzene oxidation. In phase transfer process of PTC-PP, the proportion of MnO4− transferred to benzene exceeded that to TCE. This finding illustrated that nondirectional phase transfer of oxidants posed a challenge for simultaneous promotion of TCE and benzene degradation. However, TCE and benzene removal efficiencies were both >75.7% by applying peroxymonosulfate after KMnO4 addition. These findings lay the theoretical groundwork for PTC-PP application in groundwater remediation.

Modeling Polystyrene Nanoplastics Degradation in Water via Photo-Fenton Treatment: A Shrinking-Particle Approach

In this study, kinetic models for the photo-Fenton oxidation of polystyrene nanoplastics (NPs) in water were developed, considering particles with decreasing diameters. Various reaction parameters affecting the oxidation rate, such as particle size (140−909nm), agitation speed (250−1000rpm), and operating temperature (25 and 60 °C) were investigated. Oxidation progress was evaluated through turbidity measurements, TEM, and FTIR analysis, while leached intermediates were identified via Pyr-GC-MS and IC. Due to changes in NPs surface reactivity, the overall reaction rate was divided into two stages, following a free-radical mechanism. Using equations derived from the classic Shrinking Core Model, the oxidation of NPs was determined to proceed under chemical reaction control, with negligible mass transfer limitations. Additionally, the Prout-Tompkins model was found to accurately represent the degradation process. The proposed mechanisms and models provide valuable insights for describing and predicting the advanced oxidation of NPs under different operating conditions and treatment methods.

Photoaging enhances the leaching of di(2-ethylhexyl) phthalate and transformation products from polyvinyl chloride microplastics into aquatic environments

Increasing chemical pollution is a threat to sustainable water resources worldwide. Plastics and harmful additives released from plastics add to this burden and might pose a risk to aquatic organisms, and human health. Phthalates, which are common plasticizers and endocrine-disrupting chemicals, are released from polyvinyl chloride (PVC) microplastics and are a cause of concern. Therefore, the leaching kinetics of additives, including the influence of environmental weathering, are key to assessing exposure concentrations but remain largely unknown. We show that photoaging strongly enhances the leaching rates of di(2-ethylhexyl) phthalate (DEHP) by a factor of 1.5, and newly-formed harmful transformation products, such as mono(2-ethylhexyl) phthalate (MEHP), phthalic acid, and phthalic anhydride from PVC microplastics into the aquatic environment. Leaching half-lives of DEHP reduced from 449 years for pristine PVC to 121 years for photoaged PVC. Aqueous boundary layer diffusion (ABLD) is the limiting mass transfer process for the release of DEHP from pristine and photoaged PVC microplastics. The leaching of transformation products is limited by intraparticle diffusion (IPD). The calculated mass transfer rates can be used to predict exposure concentrations of harmful additives in the aquatic environment.

Modeling catalyst effectiveness factor with space-fractional derivative using Haar wavelet collocation method

Abstract Mass transfer limitations may considerably affect the rate of a heterogeneous catalytic process. The catalyst effectiveness factor is a quantitative measure of the impact of the diffusion process inside a catalyst particle. The effectiveness factor is derived from the solution of the steady-state reaction-diffusion problem. Herein, we simulate the steady-state reaction-diffusion equation with space-fractional derivative and linear reaction kinetics. The solution to the problem is obtained numerically using the Haar wavelet collocation method. The effect of the anomalous diffusion exponent on the catalyst effectiveness factor and process parameters, e.g. reactor volume and catalyst mass, is demonstrated. We anticipate that the process efficiency will be notably improved by changing the diffusion regime from standard to superdiffusive.

Roles of silica coating on nanosized zero-valent iron in sequential reduction–oxidation process in a system containing persulfate

A sequential reduction–oxidation process using silica-coated nanosized zero-valent iron (nZVI) particles (nZVI@SiO2) and persulfate for mineralizing recalcitrant compounds was developed, and the effects of the process on nitrobenzene were evaluated. This sequential process significantly enhanced contaminant mineralization, which could not be effectively achieved by reduction or oxidation alone. The nZVI@SiO2 rapidly reduced nitrobenzene to aniline, then the aniline concentration gradually decreased after persulfate had been added and initiated sequential oxidative degradation. The SiO2 coating on the nZVI@SiO2 limited outward mass transfer of reaction products and increased the efficiency with which nitrobenzene was converted into aniline. Slow release of Fe(II) caused by the coating caused persulfate activation and subsequent aniline oxidation to be more sustained and efficient than without the coating. The final nitrobenzene–aniline mineralization efficiency was higher for the nZVI@SiO2/persulfate system than the nZVI/persulfate system. The SiO2 coating of the nZVI@SiO2 particles was an excellent protective layer, protecting the particles from undesirable consumption through reactions with groundwater components. nZVI@SiO2 particle transformations during the sequential process were investigated, and the operating conditions were optimized to maximize the recalcitrant compound removal efficiency. The results indicated that nZVI@SiO2 and persulfate could be used to mineralize organic contaminants in groundwater through sequential reduction–oxidation.

The Central Role of Oxo Clusters in Zirconium‐Based Esterification Catalysis

Oxo clusters are a unique link between oxide nanocrystals and Metal‐Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO‐66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface‐to‐volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO‐66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent‐free reactions with sterically hindered alcohols (hexanol, 2‐ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X‐ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.

Highly Mesoporous Zr‐Based MOF‐Fabric Composites: A Benign Approach for Expeditious Degradation of Chemical Warfare Agents and Simulants

AbstractRecent research has demonstrated the degradation of organophosphonates through hydrolysis using microporous UiO–66–NH2‐fabric composites. Yet, challenges remain due to the limitations of organophosphonates accessing active sites in large, engineered granules. To address this, an innovative approach to integrate mesoporous UiO–66–NH2 onto various fabrics is provided, thereby overcoming previous mass transfer limitations. Mesoporosity in the UiO–66–NH2‐fabric is attributed to the amphoteric cocamidopropylbetaine (CAPB) surfactant which templates the mesochannel construction. Unexpectedly, because the synthesis is aqueous, benign, low temperature (60°C), and avoids strong acids and toxic solvents, it is compatible with fragile supports such as untreated cotton. The UiO–66–NH2‐fabric composite formed using treated polypropylene (PP) attains a BET specific surface area of 360 m2 g−1comp. Remarkably, the mesoporous UiO–66–NH2‐composites exhibit a pore volume as large as 0.2 cm3 g−1comp, 33% in the mesoporous range, which is higher than other previous reports. Practically, the mesoporous UiO–66–NH2‐treated PP composite enhances the rate of methyl paraoxon (DMNP) degradation, showing a t1/2 value that is 15 times faster than microporous UiO–66–NH2 composites measured under the same conditions. Similar trends are observed in the degradation of actual nerve agents. These composites hold significant potential across diverse applications, including filtration, protection, and catalysis.