Christopher KesslerRobin SchuldtSebastian Emmerling
10页
查看更多>>摘要：Sorption of gases in micro- and mesoporous materials is typically interpreted on the basis of idealized structural models where real structure effects such as defects and disorder are absent. For covalent organic frameworks (COFs) significant discrepancies between measured and simulated adsorption isotherms are often reported but rarely traced back to their origins. This is because little is known about the real structure of COFs and its effect on the sorption properties of these materials. In the present work molecular simulations are used to obtain adsorption isotherms of argon, nitrogen, and carbon dioxide in the C0F-LZU1 at various temperatures. The (perfect) model COF has a BET surface that is higher than the experimental BET surface by a factor of approximately 1.33, suggesting defects or inclusions are present in the real structure. We find that the saturation adsorption loading of small gaseous species in COF-LZU1, as determined from grand canonical Monte Carlo simulations, is also higher by approximately the same factor compared to the experimental saturation loading. The influence of interlayer slipping on the shape of the adsorption isotherm and the adsorption capacity is studied. Comparison between simulation and experiment at lower loadings suggests the layers to be shifted instead of perfectly eclipsed. The sensitivity of the adsorption isotherms in this regime towards the underlying framework topology shows that real structure effects have significant influence on the gas uptake. Accounting for layer slipping is important to applications such as catalysis, gas storage and separation.
查看更多>>摘要：The thermal stability of MOFs refers to resist degradation of their structure, upon exposure to heat. It may depend on the type of linkers, metal SBUs, metal-ligand interaction, and type of packing of MOF. Many applications of MOF compounds require high thermal stability so that their frameworks do not collapse upon thermal treatment. A straightforward method based on a Quantitative Structure-Property Relationship (QSPR) was established to achieve a precise model to estimate the thermal stability of MOF compounds having zinc SBUs due to their importance in recent researches. The proposed model was developed based on descriptors including the number of nitrogen and zinc atoms, the interactions between heteroatoms of linkers and metal centers, and various molecular fragments. A logarithm of experimental thermal stability (log TS) of 151 MOFs is applied to develop a precise model. The coefficients of determination (R~2) for the training and test sets were obtained 0.999 and 1.000, respectively. The Root Mean Square Error for Prediction (RMSEP) of log TS of training and test sets are 0.003 and 0.001, respectively. According to resulted statistical parameters, the novel model is robust and efficient satisfactory.
查看更多>>摘要：In the past decades, due to the worst effect of hexavalent chromium on human and environmental health, people have been committed to removing hexavalent chromium from industrial wastewater. In recent years, metal organic frameworks (MOFs) adsorbents have attracted more and more attention in the removal of pollutants from water. Here, an efficient and selective adsorbent(UiO-66-PRAA) was prepared by modified UiO-66-NH2 with phenothiazine-N-rhodanine to remove Cr(VI) ion from wastewater. The maximum absorption capacity of UiO-66-PRAA at 303 K and pH = 2 was 333.67 mg/g for Cr(VI). Which is higher than that of bare UiO-66-NH2. Elovich kinetic and Sips isotherm models are more suitable for describing the adsorption process of Cr(VI) on UiO-66-PRAA, which indicates that the process is a chemically controlled multilayer adsorption. In addition, the removal mechanisms include chelation, ion exchange and reduction. The adsorbent still shows good adsorption performance under the coexistence of different ions. The excellent cycle performance of UiO-66-PRAA confirms its high potential in removing Cr(VI) from polluted water. In general, UiO-66-PRAA has been shown well adsorption properties and reusability, and our finding might provide a new idea for developing efficient and reusable adsorbent to remove Cr(VI) from wastewater.
查看更多>>摘要：In the present study, the adsorptive potential of hypercrosslinked polymers (HCPs) was investigated for the removal of phenol from aqueous solutions. Herein, two HCPs were one-step synthesized by the Friedel-Crafts reaction using 4,4'-biphenyldiol (BPD) or hydroquinone (HQ) as the building unit and 1,4-bis(chloromefhyl)benzene (DCX) as the external crosslinker. The results showed that the HCPs, derived from BPD and DCX (called as BPD-D), exhibited more excellent pore structures with the higher surface area of 697 m~2 g~(-1) and the micropore volume of 0.23 cm~3 g~(-1) and allowed for the extremely fast equilibrium adsorption of phenol, attributed to the hierarchical pore structure and the great hydrophilicity; meanwhile, the maximum adsorption capacity of BPD-D towards phenol was calculated to be 156.74 mg g~(-1). Moreover, the adsorption equilibrium and kinetic processes of BPD-D towards phenol were well described by the Freundlich model (R~2 > 0.99) and the pseudo-second-order kinetic model (R~2 > 0.9999) at 303 K. Moreover, negative changes in Gibbs free energy and enthalpy reflect that the adsorption of BPD-D for phenol is a spontaneous and exothermic process. In addition, adsorption performances were investigated under different conditions, e.g., the initial concentrations of phenol, the dosage of the BPD-D, the initial pH of phenol aqueous solution and recyclability. Our finding demonstrates that HCPs show potential application prospects in the removal of organic pollutants from wastewater.
查看更多>>摘要：The abundant of cellulose biomass resources and the projected global market escalations for allied chemicals and fuels inferred that large-scale valorization would benefit the global energy and chemical industries. In line with this strategy, the paper carefully reviewed and examined resourceful literature on the potentials of solid acids for cellulose-to-glucose reaction and the transformation into fuels/chemicals. It initially evaluated the cellulose to glucose path by considering ionic liquids as the media for hydrolysis. The influence of employing sulfonated mesoporous carbon systems was adequately explored. In addition to critical analysis of the cellulose to sugar alcohols, the paper also analyzed the role of Fe-modified zeolites for glucose upgrading. It simultaneously discussed the parameters necessary for process upgrade and addressing catalyst-stability challenges. We have also provided new directions for further investigations in line with the findings established.
查看更多>>摘要：The rational design and facile preparation of highly efficient bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) still remain challenge. Herein, we report the facile preparation of a bifunctional electrocatalyst consisting of FeCo alloy nanoparticles embedded in ultralong N-doped carbon nanotube (denoted FeCo/LNCNT) by capitalizing on the coordination interaction between triphenylimidazole-containing crosslinked polymer and metal salts followed by the two-step pyrolysis under the presence of melamine. The FeCo alloy nanoparticles play the crucial role in the formation of ultralong carbon nanotube with increasing pyrolysis time under the assistance of melamine. The resulting FeCo/LNCNT manifests remarkable ORR and OER activity together with outstanding durability. The small potential gap (0.756 V) of FeCo/LNCNT demonstrates a promising application as ORR/OER bifunctional elctrocatalyst. The assembled zinc-air battery using FeCo/LNCNT as the air anode exhibits higher open-circuit voltage (1.52 V), specific capacity (779 mAh g~(-1)_(Zn)) and power density (144 mW cm~(-2)) than the Pt/Ir counterpart. Notably, the zinc-air battery assembled with FeCo/LNCNT can remain stable for more than 600 cycles without significant voltage drop and efficiency loss, representing an excellent cycling stability.
查看更多>>摘要：Materials developed for radionuclide adsorption need to resist harsh conditions, i.e. be robust against ionizing radiation. In this work, we evaluated the degradation of mesoporous silicas (SBA-15) grafted with hydroxypir-idinone, acetamide phosphonate and propionamide phosphonate ligands under electron irradiation. The ligands contained amide and/or phosphinic acid functional groups, which made them able to bind to actinides. Degradation of the grafted ligand was assessed by identifying and quantifying the gas produced under irradiation using gas chromatography, as well as characterizing the grafted ligands before and after irradiation by means of FT-IR, XPS and TGA techniques. Irradiation led to the degradation of amide functional groups and to the production of amine and carboxylic acid groups. Corresponding reaction mechanisms were proposed. The sorption behavior of the grafted SBA-15 materials for thorium was also studied. SBA-15 materials grafted with acetamide phosphonate and propionamide phosphonate ligands were shown to be able to adsorb thorium. The propionamide phosphate ligand was the most efficient, with an equilibrium sorption capacity of 95 mg g~(-1). This capacity remained stable up to a 1 MGy irradiation dose and underwent a 20% decrease after 4 MGy of irradiation. Therefore, this material is potentially interesting for the treatment of liquid outflows contaminated by actinides produced in nuclear facilities.
查看更多>>摘要：A zeolite-templated carbon (ZTC) material was synthesized using a vapor phase impregnation method. This ZTC exhibited an outstandingly high specific surface area of 3100 m~2 g~(-1) along with a considerable total pore volume of 1.74 cm~3 g~(-1). The properties of this ZTC were optimized by controlling the deposition process of the furfuryl alcohol, used as the carbon precursor, on the sodium-bearing zeolite Y template (FAU-type framework structure). The ZTC was then used as a negative electrode in a sodium battery setup. A high first discharge capacity of 1714 mAh·g~(-1) for the ZTC was obtained, of which 16% was reversible. In addition, atomistic simulations confirmed that a theoretical capacity of 552 mAh·g~(-1) for the ZTC containing six sodium ions per supercage was reasonably achieved. The new vapor phase impregnation method presented here and applied for the synthesis of ZTC using sodium-bearing zeolites is highly reproducible and scalable, paving the way for the development of future applications.
查看更多>>摘要：Zeolite nanosheets (ZNs) offer improved micropore accessibilities and transport properties for enhanced molecular catalysis and separations. However, practical application of the ZN materials is hampered by the lack of efficient synthesis methods. Here, a ZN self-seeded method is demonstrated for single-step reproduction of flower-like assemblies of very large MFI ZN plates. The ZN plates are ～60 nm-thick stacks of 4-nm-thick single-crystal sheets. The ZN flower growth involves terrace nucleation on the seed surfaces and subsequent ZN epitaxial growth in [010] orientation directed by a diquaternary agent. The open architecture of the assemblies prevented collapse and agglomeration of ZNs during thermal activation that effectively preserved the interconnected intra-sheet and inter-sheet micropore system. Thus, the ZN assemblies exhibited markedly enhanced molecular adsorption capacity and transport diffusivity for the probing xylene molecules as compared to the conventional crystals. The ZN assembly and its harvestable very large-sized ZNs have the potential for developing high-performance ZN adsorbents, catalysts, and molecular-sieve membranes.
查看更多>>摘要：A set of novel materials, denoted M/ZrO2@C(MIL) (M = Ru, Rh, Pd & In), were prepared by thermal transformation of MIL-140C containing 10% bipyridine linkers (MIL-140C-10), to provide sites for metal coordination within the framework. These materials were transformed into active catalysts for CO2 hydrogenation when heated in a gas mixture of H2 and CO2 (3:1), at 500 °C. The thermal treatment provided high surface area catalysts with high stability and high Ru or Rh metal dispersion which were very effective for the hydrogenation of CO2 to CH4, giving a CH4 production of 3.0-3.7 mol/g Ru/h or 4.2-4.3 mol/g Rh/h (at 400 °C, 33 bar and WHSV 23 L/h/g cat.). PXRD, XPS and TEM indicated that the effective catalysts consisted of nanoparticles of Ru~0 (2-5 nm) or Rh~0 (6 nm) associated with larger ZrO2 nanoparticles (10-20 nm), which were dispersed upon carbonaceous ribbons. Interestingly, at 250-350 °C, Pd/ZrO2@C(MIL) yielded mainly CO rather than CH4, with some CH3OH. The CH4 and CO production were not stable at 400 °C. TEM results for this catalyst indicated Pd~0 and ZrO2 nanoparticles (initially 20 nm and 10-20 nm diameter, respectively). The lower, unstable activity compared to Ru and Rh could have been due to the initially larger Pd particles and their tendency to grow in size with reaction time. In/ZrO2 has mainly been used to catalyse CH3OH production, but In/ZrO2@C(MIL) gave less CH3OH than In/monoclinic ZrO2 and was less selective. At 400 °C In/ZrO2@C(MIL) was a stable, reverse-water-gas-shift catalyst (producing 0.9 mol CO/g In/h at WHSV 20 L/g cat/h). The In was well dispersed in the ZrO2-C and of small particle size. The poor selectivity for methanol may have been due to the tetragonal phase of the ZrO2 and the low surface In concentration.
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