Numerical modelling and characterization of nanofiltration membranes for the separation of carbohydrate mixtures

The results of an experimental and computational investigation of the selective separation of carbohydrates on nano‐membranes in cross‐flow filtration are reported. Two commercial membranes (NF270‐400 and TFC‐SR3) were characterised in terms of permeability and rejection of carbohydrate solutions. It is shown that the membranes can be used to recover glucose and galactose from their mixtures with lactose. The permeate flux is shown to depend on sugar concentration, with permeate flux decreasing as the concentration increases. Quantitative evaluation using numerical analysis of the above flow and separation process showed that the performance of nano‐membranes can be captured and reproduced with sufficient accuracy, thereby reducing the number of experiments require to evaluate the suitability of membranes in different applications. A Fickian approach is adopted to model the separation, and is shown to be effective.     

Photocatalytic desulfurization of dibenzothiophene by NiCo2O4 nanospinel obtained by an oxidative precipitation process modeling and optimization

This paper reports for the first time, synthesis of NiCo₂O₄ nano spinel by green oxidative precipitation and its performance in photocatalytic desulfurization of dibenzothiophene (DBT) from gas oil model at different process conditions under visible light. The as-produced nanostructure was characterized by X-ray diffraction, Fourier transform infrared, UV–VIS diffuse reflective spectroscopy, energy-dispersive X-ray spectrometry and scanning electron microscopy. The experiments for the study of different photocatalytic conditions were designed by response surface methodology and a second-order regression model was developed with a determination coefficient (R²) of 0.9769. Pareto analysis predicted that the relative importance of process factors for DBT removal is as follows: irradiation time?>?reaction temperature?>?photocatalyst dosage?>?DBT concentration. The promising results for DBT removal were concluded by photo desulfurization over the nano spinel. The study confirmed that nano spinels could be an alternative and cheap photocatalyst for desulfurization from the oil products.     

Colored amorphous silica-based powder with TiN nanocrystals precipitated by ammonolysis of Ti–Si–O ternary glass

Coloration of amorphous silica powder containing titania was investigated by nitridation in an ammonia flow. The oxide precursors were obtained by the hydrolysis of a mixture of tetraethyl orthosilicate (TEOS) and tetrabutoxy titanium (TBT). The color changed with the amount of TBT in the mixture, the hydrolysis pH and the ammonolysis temperature. The original white color of the 8 mol% TBT powder hydrolyzed under basic pH conditions changed to pale goldenrod at 700°C, then to dark olive green at 800°C, and further darkened with increasing ammonolysis temperature. A steel-blue color appeared at 900°C for the powder obtained with 3 mol% TBT, and increased in darkness at 1000°C. A similar bluish color was observed for powders obtained by acidic hydrolysis after ammonolysis above 900°C, and this was independent of the amount of titania, although the chroma decreased with increasing firing temperature for the powder with 3 mol% TBT. The ammonolysis powder products were characterized using X-ray diffraction (XRD), electron probe micro analysis (EPMA), transmission electron microscopy-electron energy-loss spectroscopy (TEM-EELS), scanning transmission electron microscopy-high-angle annular dark-field imaging (STEM-HAADF) and Ti–K edge X-ray absorption fine structure (XAFS). The color change was related to both precipitated TiN nanocrystals and residual titanium in the amorphous silica matrix. The TiN exhibited a goldish reflection and also plasmonic absorption from light blue to gray depending on the TiN crystallite size. The plasmonic absorption and resonance of nanocrystalline TiN will be useful similarly to that of gold in nanotechnology for various kinds of energy application.     

Effects of a Protic Ionic Liquid on the Reaction Pathway during Non-Aqueous Sol–Gel Synthesis of Silica: A Raman Spectroscopic Investigation

The reaction pathway during the formation of silica via a two-component “non-aqueou” sol-gel synthesis is studied by in situ time-resolved Raman spectroscopy. This synthetic route is followed with and without the addition of the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide (C₂HImTFSI) in order to investigate its effect on the reaction pathway. We demonstrate that Raman spectroscopy is suitable to discriminate between different silica intermediates, which are produced and consumed at different rates with respect to the point of gelation. We find that half-way to gelation monomers and shorter chains are the most abundant silica species, while the formation of silica rings strongly correlates to the sol-to-gel transition. Thus, curling up of linear chains is here proposed as a plausible mechanism for the formation of small rings. These in turn act as nucleation sites for the condensation of larger rings and thus the formation of the open and polymeric silica network. We find that the protic ionic liquid does not change the reaction pathway per se, but accelerates the cyclization process, intermediated by the faster inclusion of monomeric species.     

Weatherability of hybrid organic–inorganic silica protective coatings on glass

Currently, there is a growing interest in the application of silicon-based technologies for the development of advanced hybrid organic–inorganic coatings with strong weatherability. In this study, the sol–gel process is used to prepare such coatings on glass and their resistance to weathering effects is assessed afterwards. Various sols were prepared by mixing a silica-based inorganic matrix (tetraethyl orthosilicate) with different quantities of silica alkoxides functionalised with various organic groups. Subsequently, the sols were dip-coated onto glass samples at low temperatures without any heat treatment. The coatings prepared were analysed before and after three model ageing tests simulating various weathering parameters. After ageing, the best performing coatings showed good overall homogeneity and transparency (optical microscopy, SEM), improved water repellency and adhesion to the glass substrate (static contact angle measurements, cross-cut tape tests) and no colour or chemical composition changes (UV–VIS, FTIR). Compared with commercial hybrid silica products, the alkyl- and methacryloxy-functionalised silica coatings particularly displayed improved homogeneity, elasticity and barrier properties. Thus, these low temperature coatings, easily applicable to thin films, appear to fulfil the main requirements for the protection of the glass exposed to weathering phenomena.     

二氧化硅气凝胶复合隔热材料研究进展

二氧化硅气凝胶具有高孔隙率、低热导率等特点,使其成为新型超级隔热材料。然而,二氧化硅气凝胶的柔韧性、整体性差,并且常温干燥制备的气凝胶在高温时热导率迅速上升,这些都大大限制了二氧化硅气凝胶的应用。近些年,通过原位溶胶-凝胶法和模压成型法制备得到的二氧化硅气凝胶复合隔热材料,在一定程度上提高了其韧性、整体性和高温隔热性能,使得二氧化硅气凝胶作为单独块体隔热材料成为可能。本文阐述了二氧化硅气凝胶隔热材料的隔热机理,综述了近年来抗辐射型、纤维增强型和聚合物增强型二氧化硅气凝胶复合隔热材料的研究现状,最后讨论了该领域今后研究趋势。     

纳米多孔SiO_2气凝胶的表面修饰和吸附特性(英文)

采用溶胶-凝胶法,通过表面修饰等工艺,在常压条件下制备出高气孔率的疏水性 SiO2气凝胶。表面修饰能够调节气凝胶内部纳米多孔结构和增大比表面积。表面修饰采用三甲基氯硅烷,其 Si-CH3基团能取代原有气凝胶表面的 O-H 基团,使其具有疏水特性。用扫描电镜,红外光谱以及孔径分布仪对其结构和表面基团进行了表征,对其吸附特性进行了测试。结果表明,SiO2 气凝胶具有纳米多孔结构,且有较好的疏水特性,其吸附性能较活性炭纤维和活性炭颗粒高 3～4 倍,再吸附容量基本不变,是一种极好的高吸附材料,具有广阔应用前景。     

ESR study of silica‐filled SBR with different rubber/filler interactions

Silica‐filled styrene–butadiene rubber (SBR) unvulcanizates and their vulcanizates with different rubber/filler interactions were prepared by using several kinds of coupling agents. Tensile tests and electron spin resonance (ESR) measurements were carried out for both unvulcanized and vulcanized samples to get information on the effects of filler/rubber interactions on the breakdown of carbon–carbon (C? C) linkages in SBR and carbon–sulfur (C? S? C, C? S? S? C) linkages at the crosslinked points between rubber and sulfur by a tensile force. The combination of ESR results and stress–strain data suggested that with increasing the mechanical energy applied to the samples by the stretching, the carbon–sulfur linkages around silica particles were broken first, followed by the breakdown of carbon–sulfur and C? C linkages in the rubber matrix. The assignment of ESR spectrum was also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Porous mullite ceramics through diphasic gels of large boehmite and small silica particles

Mullite formation process has been studied in stoichiometric mullite (3Al₂O₃·2SiO₂) diphasic gel containing large boehmite (1 m) and small silica (10 nm) particles. It has been found that initial mullitization did not take place inside the silica phase (cristobalite), but took place in the defect -alumina phase. -alumina was stabilized by silica when the temperature was below 1350°C. At temperatures above 1350°C, mullite crystallized directly. It was suggested that silica diffused into the pores (<1.8 nm) of -alumina and prevented the collapse of -alumina pore structure. On the other hand, when silica was not present, the pore structure of -alumina collapsed and -alumina crystallized at 1100°C. Porous mullite ceramics were obtained by using special diphasic gels containing large boehmite and small silica particles.