Claisen–Schmidt Condensation Catalyzed by Metal‐Organic Frameworks

Metal‐organic framework [Fe(BTC) (BTC=1,3,5‐benzenetricarboxylic acid)] is a convenient heterogeneous catalyst for the carbon‐carbon bond forming reaction in toluene between acetophenone and benzaldehyde to give selectively chalcone in high yield. Fe(BTC) appears as a general catalyst able to synthesize selectively different chalcone derivatives bearing various functionalities. Fe(BTC) could be recycled with no significant loss of catalytic efficiency and crystallinity in subsequent runs.     

Efficient Removal of Anionic Organic Dyes from Aqueous Solution with Cu‐Organic Frameworks

Cu‐metal‐organic frameworks (Cu‐MOFs) were synthesized in one step using copper acetate, glutamic acid, and small‐molecular organic amines at room temperature. Organic amines served as modulators to modify the structure of Cu‐MOFs. Characterization results proved that the addition of modulators changes the surface morphology. Batch adsorption data indicated high adsorption capacities for anionic organic dyes with glutamic‐Cu‐triethylamine (Glu‐Cu‐TA), higher than that of most MOFs reported. An acid pH was the optimum adsorption parameter. The easy regeneration of recycled Cu‐MOFs suggested there were weak intermolecular interactions between Cu‐MOFs and dyes. The main adsorption forces included electrostatic interaction, ion exchange, π‐π complexation, and hydrogen bonds.     

Removal of Dibenzothiophene from Diesels by Extraction and Catalytic Oxidation with Acetamide‐Based Deep Eutectic Solvents

A series of acetamide‐based deep eutectic solvents (DESs) with different proportions were prepared. Extraction and catalytic oxidation desulfurization (ECODS) of the acetamide‐based DESs were investigated and the process was optimized. Such DESs with a molar ratio of acetamide and p‐TsOH of 1/3 (C₂H₅NO/3p‐TsOH) exhibits such a remarkable catalytic activity that the dibenzothiophene (DBT) removal could reach 100 % under optimized conditions. C₂H₅NO/3p‐TsOH was used for the oxidative desulfurization of actual commercial diesel. The sulfur removal of diesel achieved up to 98 %. C₂H₅NO/3p‐TsOH could be recycled six times and the desulfurization activity was slightly decreased. Evaluation of the mechanism indicated that oxidative desulfurization (ODS) was realized via dual activation of acetamide‐based DESs. A novel and effective way for deep desulfurization of diesel is provided.     

Modeling of the Adsorptive Desulfurization of Diesel Fuel in a Fixed‐Bed Column

Adsorptive desulfurization enables the attainment of ultra‐low sulfur content in hydrocarbon fuels by removing the refractory sulfur compounds, which are difficult to remove in hydrodesulferization (HDS) processing when sulfur concentrations below 10 mg kg^–1 must be attained. In this work, diesel fuel was desulfurized by adsorption using activated carbon as an adsorbent and the adsorption was carried out in a fixed‐bed column. The output sulfur content of less then 0.7 mg kg^–1 was achieved for the lowest flow rate of 1.0 cm³min^–1 and the highest bed depth of 28.4 cm at 50 °C. In all the experiments, at least one output sample contained less then 10.0 mg kg^–1 of sulfur with a longest achieved breakthrough time of 11.8 h. A mathematical model of the fixed‐bed adsorber was applied to describe the kinetics and to estimate the breakthrough curves. The model equations included a differential material balance for a liquid phase and a mass transfer rate expression. The ability of the model to fit the experimental data was shown to be satisfactory.     

MOF‐Based Mixed‐Matrix Membranes in Gas Separation – Mystery and Reality

Microporous additives like nanosized metal‐organic framework (MOF) particles can improve the gas separation performance of polymer membranes. These membranes which consist of added filler particles in a continuous polymer phase are called mixed‐matrix membranes (MMM). While inorganic zeolites and organic polymers do not match well, the preparation of defect‐free MOF‐based MMMs is much easier. However, some problems can also occur during the preparation. Solutions how to avoid them and prepare perfect MMMs are given. In practical gas separation, the selectivity of the MMMs was found to be even higher than predicted by the Maxwell model.     

Metal‐Organic Polyhedra: Catalysis and Reactive Intermediates

The catalytic nature of self‐assembled metal‐organic polyhedra gives an entirely new dimension to the reactivity and properties of molecules within a well‐defined confined space. Encapsulation of a range of guests brings about not only host‐guest interactions but also gives rise to unusual reactivities with selectivity and stabilization of various reactive intermediates. This review briefly covers the synthesis of self‐assembled metal‐organic polyhedra and elaborates their influence in different chemical reactions as well as in the stabilization of unstable chemical species.

     

Metal‐organic frameworks for highly efficient adsorption of dibenzothiophene from liquid fuels

By taking desulfurization of liquid fuels as a demonstrative example, a bottom‐up selection was performed to find the metal‐organic frameworks (MOF)‐type adsorbents with highly efficient adsorption performance of large molecules. Through carefully analyzing the adsorption mechanism for typical S‐heterocyclic compounds like dibenzothiophene (DBT), PCN‐10 was selected in consideration of the simultaneous inclusion of several kinds of interactions in the framework. Experimental results demonstrate that this MOF exhibits extraordinary high DBT adsorption capacity (75.24 mg S g^?1), showing record uptake among all the reported porous materials for the removal of thiophenicsulfur from fuels (below 1000 ppm_wS), to the best of our knowledge. Moreover, the removal rate for the low sulfur concentration (50 ppm_wS) can reach beyond 99%. This strategy can be conveniently extended to the screening and design of MOFs for the efficient removal of other important large guest molecules. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4491–4496, 2016     

ZIF‐8 SURMOF Membranes Synthesized by Au‐Assisted Liquid Phase Epitaxy for Application in Gas Separation

Metal‐organic frameworks (MOFs) exhibit a huge potential for gas separation. ZIF‐8 is an interesting candidate due to its high thermal stability and its pore properties. By liquid phase epitaxy, the growth of the highly oriented surface‐anchored MOF ZIF‐8 on non‐porous and porous surfaces has been proven. The preparation of monolithic ZIF‐8 thin films supported by porous α‐Al₂O₃ substrates modified by a thin layer of Au is investigated. The layer‐by‐layer deposition process accomplished via a dipping procedure results in the formation of defect‐ or crack‐free membranes, preliminary characterized by the determination of ethane and ethene permeance.     

Metal‐organic gels of simple chemicals and their high efficacy in removing arsenic(V) in water

Metal‐organic gels (MOGs) have emerged as a class of functional materials that show great potential applications in the field of catalysis, energy storage, template synthesis, and environmental technology. The construction of functional MOGs and the control of functionality are still challenging due to complicated chemicals or routes involved in previous works. Here we report a series of tunable multifunctional MOGs by directly gelating between Fe³⁺ and simple chemicals, propanedioic acid (H₂PA), succinic acid (H₂SA), glutaric acid (H₂GA), and fumaric acid (H₂FA) in ethanol. The obtained MOGs exhibit self‐healing property and good conductivity, and were used for high efficacy removal of arsenic (As) in water. The ease, low cost, and scalability of the assembly process combined with multifunctionality make these MOGs be potentially applied in the fields of energy storage and sewage disposal. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3719–3727, 2018     

Removal of arsenic from simulated groundwater by GAC‐Fe: A modeling approach

A study on kinetics and equilibrium is presented on the adsorption of arsenic species from simulated groundwater containing arsenic (As(III):As(V)::1:1), Fe and Mn in concentrations of 0.188 mg/L, 2.8 mg/L and 0.6 mg/L, respectively, by iron impregnated granular activated charcoal (GAC‐Fe). Also presented is the interaction effect of As, Fe and Mn on the removal of arsenic species from water, which simulates contaminated groundwater. Among conventional models, pseudo second‐order kinetic model and Freundlich isotherm were adequate to explain the kinetics and equilibrium of adsorption process, respectively. However, in comparison to conventional isotherm empirical polynomial isotherm provided a more accurate prediction on equilibrium specific uptakes of arsenic species. Effects of initial concentrations of As, Fe and Mn on the removal of total arsenic (As(T)), As(V) & As(III) have been correlated within the error limit of ?0.2 to +5.64%. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

A Crystalline Catalyst Based on a Porous Metal‐Organic Framework and 12‐Tungstosilicic Acid: Particle Size Control by Hydrothermal Synthesis for the Formation of Dimethyl Ether

The strategy for obtaining a crystalline catalyst based on a porous copper‐based metal‐organic framework and 12‐tungstosilicic acid with different particle sizes is reported. Through the control of hydrothermal synthesis and some simple treatments, catalyst samples with average particle diameters of 23, 105, and 450 μm, respectively, were prepared. This crystal catalyst has both the Brønsted acidity of 12‐tungstosilicic acid and the Lewis acidity of the copper‐based metal‐organic framework, and has high density of accessible acid sites. Its catalytic activity was fully assessed in the dehydration of methanol to dimethyl ether. The effect of particle size on the catalytic activity of catalyst was studied, in order to select the particle size appropriate for avoiding the diffusion limitation in heterogeneous gas‐phase catalysis. In the selective dehydration of methanol to dimethyl ether, this catalyst exhibited higher catalytic activity than the copper‐based metal‐organic framework, γ‐alumina, and γ‐alumina‐supported 12‐tungstosilicic acid catalysts. It showed high catalytic performances, even at higher space velocity or in the presence of excess water. In addition, the catalyst was also preliminarily assessed in the formation of ethyl acetate from acetic acid and ethylene. It also exhibited a high activity which was comparable with that of silica‐supported 12‐tungstosilicic acid catalyst.     

Recovery and Separation of Metal Ions from Aqueous Solutions by Solvent‐Impregnated Resins

The recovery and separation of metals from aqueous solutions is one of the research hotspots in hydrometallurgy, environment protection, analytical chemistry, etc. Much attention has been paid to solvent‐impregnated resins (SIRs) since these were firstly proposed for the extraction of metals. SIRs are characterized by high efficiency and selectivity, convenient preparation, and easy operation because they combine the unique advantages of solvent extraction and ion exchange. The preparation and features of SIRs are summarized and their applications in the extraction of various metals from solutions are reviewed. In addition, the equilibrium, thermodynamics, and sorption kinetics of the metals onto SIRs are elucidated in detail.     

Highly Efficient and Metal‐Free Aerobic Hydrocarbons Oxidation Process by an o‐Phenanthroline‐Mediated Organocatalytic System

A highly efficient o‐phenanthroline‐mediated, metal‐free catalytic system has been developed for oxidation of hydrocarbons with dioxygen in the presence of N‐hydroxyphthalimide; various hydrocarbons were efficiently and high selectively oxidized, e.g., ethylbenzene to acetophenone in 97% selectivity and 76% conversion, under mild conditions.     

Preparation and Characterization of the Newly Synthesized Metal‐Complexing‐Ligand N‐Methacryloylhistidine Having PHEMA Beads for Heavy Metal Removal from Aqueous Solutions

The aim of this study was to investigate in detail the performance for removal of heavy metal ions of beads composed of poly(2‐hydroxyethyl methacrylate) (pHEMA) to which N‐methacryloylhistidine (MAH) was copolymerized. The metal‐complexing ligand MAH was synthesized by using methacryloyl chloride and histidine. Spherical beads with an average size of 150–200 μm were obtained by the radical suspension polymerization of MAH and HEMA conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, p(HEMA‐MAH) beads had a specific surface area of 17.6 m²/g. The synthesized MAH monomer was characterized by NMR; p(HEMA‐MAH) beads were characterized by swelling studies, FTIR and elemental analysis. The p(HEMA‐MAH) beads with a swelling ratio of 65%, and containing 1.6 mmol MAH/g, were used in the adsorption/desorption experiments. Adsorption capacity of the beads for the selected metal ions, i. e., Cu(II), Cd(II), Cr(III), Hg(II) and Pb(II), were investigated in aqueous media containing different amounts of these ions (10–750 mg/L) and at different pH values (3.0–7.0). Adsorption equilibria were established in about 20 min. The maximum adsorption capacities of the p(HEMA‐MAH) beads were 122.7 mg/g for Cu(II), 468.8 mg/g for Cr(III), 639.4 mg/g for Cd(II), 714.1 mg/g for Pb(II) and 1 234.4 mg/g for Hg(II). pH significantly affected the adsorption capacity of MAH incorporated beads. The chelating beads can be easily regenerated by 0.1 M HNO₃ with high effectiveness. These features make p(HEMA‐MAH) beads a potential candidate for heavy metal removal at high capacity.     

Removal of sulfamethoxazole from waters and wastewaters by conductive‐diamond electrochemical oxidation

BACKGROUND: Sulfamethoxazole (SMX, used as a model bacteriostatic antibiotic) is persistent to conventional biological treatments of wastewaters. In this work, conductive‐diamond electrochemical oxidation (CDEO) was found to be an effective technology for its removal from the effluents of conventional wastewater treatment plants. RESULTS: The use of CDEO has been evaluated for the removal of the antibiotic SMX from water and wastewaters. The results show that CDEO can reduce the concentration of this organic pollutant to values below 0.1 µg dm^?3. The variation of the SMX concentration during electrolysis shows a complex shape with a plateau zone that increases in size with the initial concentration of SMX. This complex trend is not observed in the changes of TOC, which seems to indicate that the CDEO of SMX solutions does not lead directly to the generation of carbon dioxide as a final product. A tentative reaction pathway has been proposed based on a thorough analysis of the reaction mixture, in which the main intermediate products were identified. The use of liquid chromatography time‐of‐flight mass spectrometry (LC‐TOFMS) allowed the identification of nine organic intermediates (with M_w 98, 108, 172, 173, 197, 203, 227, 269 and 287) during the electrolysis and the concentration of these compounds depends on the initial SMX concentration and on the current density applied. CONCLUSIONS: CDEO is able to reduce the concentration of the organic pollutant below 0.1 mg dm^?3. SMX removal is faster than that of TOC. This fact indicates the formation of reaction intermediates. Analytical techniques show that nine reaction intermediates are generated in the system, and that their concentration depends on the initial SMX concentration and on the current density used. Copyright © 2012 Society of Chemical Industry