查看更多>>摘要：Microporous, mesoporous and hydrophobic silica materials with high specific surface area are obtained by an easy and cheap sol-gel synthesis. The effect of pore size and of water content on gas adsorption and separation are investigated. We also identified the relative amounts of different types of water in the porous silica, around 25% and 75% for bound and free water. The kinetics of rehydration is extremely slow, 60% recovery after 4 days implying that the material can be used as is over several hours. Adsorption isotherms of pure gaseous CO2 and CH4, and of their mixtures at different pressures, show that among the materials synthesised, the microporous hydrophilic silica exhibits the best performance in terms of CO2 adsorption capacity (2.8 mmol.g(-1)) and a separation factor over 10 at low CO2 content and low pressure. Both properties are highly sensitive to the presence of residual water and to terminal chemical groups. This work highlights the possibility to develop competitive and cheap silica materials that could be scaled up to industrial uses.
查看更多>>摘要：As a new type of electrode material, transition metal silicates anode has drawn increasing attention owing to high theoretical capacity, sufficient reserves and nontoxicity. Herein, a unique flower-shaped cobalt silicate was fabricated via an alkali-assisted hydrothermal synthesis method, which feathered large specific surface area and abundant meso-pores. Serving as an anode material for lithium ion batteries, the hierarchical CoSiO2 material exhibited excellent cycling stability (1111 mAh g(-1) at 0.1 A g(-1) after 200 cycles) and superior rate capability (411 mAh g(-1) at 10 A g(-1)). The novel structure of F-CoSiO2 anode not only provided abundant active sites for electrochemical reactions and effectively facilitated the migration of Li ions during charge-discharge process, but also contributed to the primary pseudocapacitive charge storage behaviors. This work may open up opportunities in structure design and represent the enormous potential of hierarchical transition metal silicate as practical advanced electrode for lithium storage.
查看更多>>摘要：To improve composite zeolite film loading quality, ZSM-5 zeolite film was modified by loading with SAPO-34 via TPABr. A series of composite zeolite films was prepared under different modification conditions. The crystal morphology and surface topography of the samples were characterized using XRD, SEM, FTIR and EDS. The results showed that the loading effect was best at a concentration of 15,000 mg L-1 and a modification duration of 60 min. By zeta potential analysis, this method leads two kinds of crystal get different charge in the secondary hydrothermal crystallization synthetic gel system and they electrostatically adsorb each other. Furthermore, the composite film had good reaction performance in MTA reaction. TG analysis indicated that it tends to produce soft coke. This modification method may provide some insights for the synthesis of other composite zeolites.
查看更多>>摘要：Significant concerns have been raised over the adsorption of tetracyclines from aquatic environments. In this paper, hierarchically porous MIL-53(Cr) was synthesized by in situ synthesis for the first time and the influence of mesopores on tetracycline adsorption was investigated. Benefiting from the high mesoporous volume, more TC molecular could enter the channel to interact with adsorption sites, and the adsorption capacity of 20-AA-MIL-53 (Cr) for TC increased twelvefold, up to 148.5 mg/g. In addition, various kinetic models have also been used to investigate the adsorption process of tetracycline. Particularly, considering the molecular size of TC about 12.9 angstrom x 7.4 angstrom, Elovich and intraparticle diffusion kinetic models were used to testify that the external mass transfer of TC on 20-AA-MIL-53(Cr) was much higher than that on MIL-53(Cr) when the pore size was expanded to 2-3 nm. What's more, the results of water stability test revealed the excellent water stability of 20-AA-MIL-53(Cr) for over 5 days. This study described a simple method for the preparation of hierarchical porous MIL-53(Cr) and explored the effect of mesopores on the adsorption of TC, so as to propose that hierarchical porous MIL-53(Cr) can be used as a potential adsorbent in water adsorption treatment.
查看更多>>摘要：As a typical reaction process catalyzed by acid sites, the alkylation of benzene with methanol significantly depends on the distribution of acid sites in zeolite. Herein, an MCM-22 zeolite with regulated acid sites and framework aluminum (AlF) siting was successfully synthesized by the insertion of boron. Proper boron incorporation can bring to a concentration of the Bronsted acid sites (BSites) in the 10-membered ring (10MR) sinusoidal channels, which provide a good shape-selective space for alkylation of benzene with methanol. Meanwhile, the decrease in BSites in the supercages and external pockets leads to an alleviation of the coking process and formation of ethylbenzene, enhancing the catalytic life and capacity of containing deposits.
查看更多>>摘要：Chemical condensation of layers of silicates has been often proposed as an alternative to thermal condensation, finding limited success. The formation of the industrially relevant MCM-22 zeolite (MWW IZA code) from a mild hydrothermal precursor is the most important example of 2D-3D aluminosilicate condensation. Silanols of opposed layers have been condensed by acid-driven dehydration in concentrated nitric acid, as confirmed by powder XRD and Si-29 NMR spectroscopy, implying interlayer template extraction and corresponding dealumination. Milder acid treatments favour template extraction and shrinkage of interlayer distance, but do not provide significant silanol condensation. Template extraction is further favoured by degradation of the organics in the presence of a Cu2+ homogeneous catalyst.
查看更多>>摘要：Fe2O3 are attractive anode materials for lithium-ion batteries because of their large theoretical capacity and low cost. However, due to their low conductivity, large volume variation and unstable solid electrolyte interface (SEI), their cycling stability is poor. Herein, we developed a simple and general strategy to address these issues. The well-designed yolk-shell Fe2O3@C nanospheres with the inner Fe2O3 nanoparticles are protected by highly graphitized and interconnected carbon shells prepared by oxidizing commercial acetylene black. The obtained yolk-shell Fe2O3@C nanospheres provide sufficient interior void to buffer the volumetric variation of the inner Fe2O3 nanoparticles during cycling. Furthermore, the highly-graphitized and perforated mesoporous carbon shells facilitate fast electron transfer and ions transportation during the charge/discharge process. Benefiting from these structural advantages, the yolk-shell Fe2O3@C nanospheres provide good cyclic stability which still retain 929 mAh g(-1) after 200 cycles at the current density of 0.1 A g(-1) and elevate Li+ diffusion coefficient from 3.867 x 10(-13) to 6.321 x 10(-11) m(2) s(-1). This work provides a new perspective to design the yolk-shell metal oxides@C framework for exploring the high-performance Li-ion batteries.
查看更多>>摘要：Silica aerogel is fabricated through replacement of solvent by the air, so that this stage is of high relevance to achieve appropriate physical properties. Although, evaporation under ambient pressure is considered as simplest drying technique, but leads to irreversible shrinkage and collapse of gel network. Here, we improve the efficiency of ambient pressure drying via increasing the strength of gel network through physically reinforcement of the gel network using recycled polyethylene terephthalate (rPET) fibers. The polymeric phase of rPET was then removed from structure using thermal treatment. Also, the effect of using four different sonication time, from 5 to 35 min, on enhancement of aerogel properties was also investigated. the prepared silica aerogels exhibit a high surface area and porosity and using more sonication time was led to better properties. According to results, surface area and porosity were increased from 593 m(2)/g and 93% up to 691 m(2)/g and 96% by enhancing sonication time from 5 min to 35 min, respectively. The reason is thought to be related to create further dispersion among silanol groups and fibers surface. As well, the fabricated silica aerogels showed mesopores structure along with a narrow and uniform pore size. These results indicate the high efficiency of proposed method for synthesize of silica aerogel.
Kweon, SungjoonKim, Young WooJo, DonghuiShin, Chae-Ho...
10页
查看更多>>摘要：The surface properties of a catalyst support not only influence the chemical states of the impregnated metals, but also the catalytic performance. Here, we systematically investigated the role of support morphology and defect concentration on the catalytic activity for dry reforming of methane (DRM) by comparing three-dimensional (3D) and two-dimensional (2D) aluminosilicate, borosilicate, and deboronated MCM tWenty-tWo (MWW)-type cat-alysts. Changes in the surface properties by delamination and/or deboronation as well as their influence on the formation of nickel silicates were experimentally demonstrated. Density functional theory (DFT) calculations were also performed to estimate the stabilization of metallic Ni clusters by the introduction of silanol defect sites on the MWW-type support. The delaminated-deboronated 2D MWW-type catalyst with the highest concentration of nickel silicates, and accordingly, the highest amount of silanol defect sites exhibited remarkable CH4 and CO2 conversions as well as stability for DRM. Unlike conventional Ni/gamma-Al2O3, the Ni species in nickel silicate 2D MWW-type catalysts were readily reduced to metallic Ni even without pre-reduction by H-2, which is advantageous for practical applications.
NSTL
Elsevier