Bjork, Emma M.Oden, MagnusWu, ZhixingVagin, Mikhail...
11页
查看更多>>摘要：Oxygen evolution reaction (OER) is critical for producing high purity hydrogen and oxygen via electrocatalytic water splitting. In this work, single crystalline, nanoporous nickel oxide (NiO) was prepared using a hydro thermal, soft-templated synthesis route followed by calcination at different temperatures. It is shown that the NiO crystals have a cubic lattice, and the pore size can be tuned from similar to 1 to similar to 70 nm by varying the calcination temperature, i.e. variation from micro to macroporosity. The NiO's catalytic performance as electrocatalysts was evaluated in OER, both thermodynamically and kinetically. Mesoporous NiO with calcination temperature of 400 degrees C had the lowest overpotential (335 mV) required @ 10 mA/cm(2) accompanied with the highest turnover frequency value and mass activity among of the obtained NiO electrocatalysts. The study shows that the electrocatalytic activity of nanoporous NiO outperforms that of commercial catalyst Ir/C (similar to 360 mV @ 10 mA/cm(2)). Microporous NiO possess the highest specific surface area and electrical double layer capacitance, while the nonporous NiO particles have the highest specific activity and BET activity of the catalysts. It is concluded that the minimization of voltage losses by the nanoscale enlargement of the electrocatalyst surface area shows the coherence between gas adsorption and electrocapacitive measurements. Conversely, the OER kinetics showed deterioration with surface area maximization due to the impediment of ionic transport inside the micropores. This work demonstrates the importance of morphology optimization to obtain an efficient OER electrocatalyst with low required overpotential and kinetic loss.
Ahmed, MostafaKotp, Mohammed G.Mansoure, Tharwat HassanLee, Rong-Ho...
9页
查看更多>>摘要：Conjugated microporous polymers (CMPs) have considered as organic porous polymers featuring combination of p-conjugated skeletons with permanent micro-porosity. In the present study, we report the synthesis of carbazoletethered conjugated microporous polymers, BC-Py-CMP and BC-BF-CMP, respectively, through the SuzukiMiyaura coupling polymerization of the novel 3,3',6,6'-tetraboronic-pinacolate-9,9'-bicarbazole (BC-4Bpin) with 1,3,6,8-tetrabromopyrene (Py-4Br) and 3,3',6,6'-tetrabromo-9,9'-bifluorenylidene (BF-4Br). These CMPs exhibited extraordinary thermal stabilities (up to ca. 694 and 569 degrees C) and high surface areas (up to ca. 1030 m(2) g(-1)). Moreover, the as-prepared BC-BF-CMP exhibited a high specific capacitance of 260 F g(-1) at 0.5 A g(-1) and showed outstanding cycling stability, having 89.60% capacitance retention of its authentic capacitance over 6000 cycles. The excellent electrochemical capacitances of the BC-BF-CMP were presumably due to the 9,9 '-BF could easily accept one electron, causing the reduced form acquiring greater aromaticity by meeting Huckel's requirements, as a result improving the electron transporting properties. Such CMPs tend to have tremendous potential to be used as a high-performance supercapacitors in energy storage systems.
查看更多>>摘要：Nitrogen-doped ordered mesoporous carbon (NMC) was prepared via an organic-inorganic co-assembly method to support ZnO for the efficient removal of H2S at room temperature. NMCs with large BET specific surface areas, copious ordered mesopores, and controllable nitrogen doping worked cooperatively with uniformly dispersed ZnO, to improve desulfurization capability at room temperature. Among these, NMC-2 possessed a BET surface area as high as 1172 m(2)/g, a large pore volume of 1.09 cm(3)/g, and a conducive nitrogen content. The appropriate residual ordered mesopores after ZnO loading provided a fast-H2S-diffusion channel in NMC-2-20%, an accessible interfacial area (925 m(2)/g), and a sufficient space for product storage (0.9 cm(3)/g). The introduction of nitrogen as Lewis basic sites not only promoted the dissociation of H2S but also accelerated the lattice diffusion rate during the desulfurization process. The synergy of the above advantages resulted in an excellent desulfurization performance of 151.2 mg/g. This study presents the effective application of NMC as a support for ZnO for a fine desulfurization at room temperature.
Karaagaclioglu, I. EthemKaratas, DenizOzyildirim, OmerCelik, Mehmet S....
10页
查看更多>>摘要：In this work, the arsenic (As2O3) amount in colemanite ore was reduced from 4551 to 425 ppm using decrepitation. The crystal and amorphous states of products were determined by XRD measurements and the thermo-dynamic properties of samples were examined by DSC-TGA analysis. Elemental arsenic was analyzed using an ICP-ES/MS analyzer. As a result of the characterizations, a majority of the arsenic mass was found in the waste material for all temperatures. It was concluded that arsenic is carried on the surface of gangue minerals in the calcination process. Moreover, the decrepitated arsenic compounds tend to accumulate back on solid surfaces thus the amount of arsenic was found to be higher than the amount found in literature which is lower than 100 ppm. Therefore the affinity of arsenic compounds to montmorillonite and colemanite surfaces were further studied comparatively using molecular dynamics (MD) and Monte Carlo (MC) simulations. The resulting energy and density profiles show that the arsenic compounds have a higher affinity towards the montmorillonite surface. The simulation results reflect the decrease of accumulation amount on the surfaces with increasing temperature in parallel with the experimental measurements.
查看更多>>摘要：Strong absorption, thin thickness, wide-bandwidth as well as lightweight of microwave absorption materials (MAMs) are highly desirable. In this study, the mesoporous silica skeleton embedded by FeRu/(Fe, Ru)(3)O-4 magnetic nanoparticles (FR/FRO-mSiO(2)) were designed and fabricated by vacuum impregnation and reduction sintering methods. The minimum reflection loss (RLmin) of the FR/FRO-mSiO(2) composite with a metal mass ratio of 46% was-61.1 dB at a thickness of 2.0 mm, and the covered absorption bandwidth (RL < -10 dB) reached 6.8 GHz. In combination of Density functional theory (DFT) calculation, microstructure characterizations and electromagnetic characteristics, we found that the interface polarization and magnetic enhancement at the interfaces of FeRu-(Fe, Ru)(3)O-4, the local dipole moment, and the abundant propagation channels for the incident microwaves, endowed by the unique component and construction of FR/FRO-mSiO(2), contributed together to the excellent microwave absorption capability of FR/FRO-mSiO(2). This work provides a promising porous structure to broaden efficient bandwidth and strengthen microwave absorption intensity with lightweight.
查看更多>>摘要：A series of clathrasils, including AST, DOH, MTN, and DDR topologies, was synthesized in an acidic medium. The general composition of the initial system was 1 SiO2: 0.3-0.5 SDA: 0.1-0.5 HF/NH4F: 0-0.3 HBr: 10-50H(2)O in the pH range of 2-6, where SDA stands for organic amines or ammonium ions as the structure-directing agents. And the hydrothermal syntheses were performed in the 150-200 degrees C temperature range. Besides elaborating the synthesis recipes and product characterizations, the study also attempted to elucidate the origins of slow crystallization kinetics. It was found that the thermodynamic stabilities of the SDA@Framewrok-SiO2 compounds play an overwhelming role in the crystalline phase selection. The finding of this study can be used as a guidance of silica-based porous materials synthesis under acidic conditions.
查看更多>>摘要：Constructing plate-like zeolites with the controllable acidity represents an efficient strategy to promote their catalytic performance in methanol-to-olefins conversion. Herein, the plate-like H[Al/Ga]MFI zeolites with the similar crystal morphology but controllable acidity have been prepared via a fluoride-assisted low-temperature crystallization approach. The acidic properties of the plate-like zeolites are determined by NH3-TPD and probeassisted 1H and 31P MAS NMR spectroscopy. The impact of acidity including the strength and density of the platelike H[Al/Ga]MFI on the dual-cycle mechanism and the corresponding catalytic performance in the methanol-topropylene conversion is subsequently confirmed. Reducing the acid strength and density can efficiently suppress the aromatic-based cycle, and thus hinder the accumulation of the polycyclic aromatics. The plate-like H[Ga]MFI zeolites with weak acid strength and most suitable acid density can well balance the dual-cycle mechanism, thereby achieving high propylene selectivity and long catalyst lifetime simultaneously.
查看更多>>摘要：Covalent organic frameworks (COFs) with excellent porosity and pre-designable structure have emerged as ideal and promising organic scaffolds for broad applications such as in gas storage, heterogeneous catalysis and fluorescence sensing. Herein, a hydrazone-based COF was synthesized by the condensation of 2,5-bis(2-methoxyethoxy) terephthalohydrazide (BMTH) with 1,3,5-triformylbenzene (TFB) under solvothermal conditions. The resulting COF material (TFB-BMTH) exhibits high crystallinity, excellent porosity with a BET surface area of 632 m(2) g(-1) and good thermal and chemical stability. The photoactive TFB-BMTH shows significant catalytic activity and recyclability in photocatalytic oxidative hydroxylation of arylboronic acid. The high photocatalytic performance of TFB-BMTH could be attributed to the effective light-harvesting platform with the efficient generation, migration and separation properties of photogenerated charge pairs in such a system. In addition, TFBBMTH showed significant fluorescence quenching for the sensing of Cu2+ . X-ray photoelectron spectroscopy and Fourier transform infrared techniques verified the interaction between Cu2+ and functional units in TFB-BMTH. This work demonstrates the development of multifunctional COFs and makes important contributions to functional exploration in heterogeneous organic transformation and sensing applications.
查看更多>>摘要：The synthesis of zeolites without using an organic structure-directing agent (OSDA) offers great environmental and economic advantages; however, the zeolites being formed are not stabilized by the organic molecules and kinetic control of the synthesis ensuring high yield and purity of the phases is challenging for many zeolites. For OSDA-free synthesis of an Al-rich *BEA zeolite, this study shows that the zeolite is formed as a metastable phase that can undergo transformation immediately after completion of its crystallization to form a thermodynamically more stable MOR zeolite according to Ostwald's rule of stages. The OSDA-free zeolite synthesis is a dynamic process in which crystallization and dissolution occur simultaneously. As soon as a thermodynamically more stable MOR zeolite begins to form in the synthesis mixture, its formation causes depletion of the Al and Si from the synthesis mixture, and, because of the desaturation of the synthesis gel, the original *BEA zeolite begins to dissolve rapidly under hydrothermal conditions. The formation of targeted and parasitic zeolite structures is fundamentally affected by the Al and Si sources. Sources of Al and Si with suitable solubility and the presence of stable zeolite *BEA seeds allow kinetic control to direct the exclusive formation of *BEA zeolite up to a relatively high yields. Then, however, the MOR zeolite phase appears in the product and its formation becomes predominant. This study demonstrates the crucial importance of kinetic control for the selective formation of metastable zeolites in the OSDA-free synthesis.
Ma, Yik-KenChia, StephenDaou, T. JeanKhoerunnisa, Fitri...
9页
查看更多>>摘要：Silicoaluminophosphate Number 34 (SAPO-34) crystallized using novel N-heterocyclic organic template-1-propylpyridinium hydroxide ([PPy]OH)-as an excellent catalyst for the production of ethyl levulinate biofuel is reported. First, the time-dependent crystallization study of SAPO-34 using various spectroscopy, microscopy and analytical techniques is performed and it reveals that the precursor undergoes several important crystallization steps, namely dissolution of reactants (induction), nucleation and crystal growth of SAPO-34, before it transforms into a more metastable SAPO-36 crystalline phase. The resulting SAPO-34 solid (Si0.198Al0.475P0.327O2) exhibits high porosity (S-BET = 673 m(2)/g, V-Tot = 0.27 cm(3)/g) and high Si content (Si/(Si + Al + P) = 0.198) which contribute to high surface acidity (2.52 mmol/g) as confirmed by the NH3-TPD analysis. The SAPO-34 catalyst shows 93.4% conversion to ethyl levulinate via esterification of levulinic acid with ethanol just within 20 min at 190 degrees C under non-microwave instant heating, which is considered very fast as compared to other systems. In addition, high catalyst recyclability is observed even after fifth cycle of reaction, thus offering another promising pathway for crystallizing zeolites using this new class of template that are beneficial for catalytic biofuel upgrading process.
NSTL
Elsevier