Effect of Nb content on hydrothermal stability of a novel ethylene-bridged silsesquioxane molecular sieving membrane for H2/CO2 separation

Ultrathin Reduced Graphene Oxide/Organosilica Hybrid Membrane for Gas Separation

Here, reduced graphene oxide (r-GO) nanosheets were embedded in an organosilica network to assemble an ultrathin hybrid membrane on the tubular ceramic substrate. With the organosilica nanocompartments inside the r-GO stacks and the intensified polymerization, r-GO sheets endow the as-prepared hybrid membranes with high H₂ and CO₂ separation performance. The resulting selectivities of H₂/CH₄ and CO₂/CH₄ are found to be 223 and 55, respectively, together with gas permeance of approximately 2.5 × 10^-7 mol·m^-2·s^-1·Pa^-1 for H₂ and 6.1 × 10^-8 mol·m^-2·s^-1·Pa^-1 for CO₂ at room temperature and 0.2 MPa. To separate larger molecules from H₂, the H₂/C₃H₈ and H₂/i-C₄H₁₀ selectivities are as high as 1775 and 2548, respectively. Moreover, at 150 °C and 0.2 MPa, the hybrid membrane retains high separation performances with ideal selectivities higher than 200 and 30 for H₂/CH₄ and CO₂/CH₄, respectively, which are attractive for gas separation and purification of practical applications.

Organosilica-Based Membranes in Gas and Liquid-Phase Separation

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with steam or a liquid-phase under high temperature. These attributes make them outperform pure silica membranes. In this review, types of precursors, preparation method, and synthesis factors for the construction of organosilica membranes are covered. The effects that these factors exert on characteristics and performance of these membranes are also discussed. The incorporation of metals, alkoxysilanes, or other functional materials into organosilica membranes is an effective and simple way to improve their hydrothermal stability and achieve preferable chemical properties. These hybrid organosilica membranes have demonstrated effective performance in gas and liquid-phase separation.

Hydrothermal stability investigation of micro- and mesoporous silica containing long-range ordered cobalt oxide clusters by XAS

This work investigates the hydrothermal stability of cobalt doped silica materials with different Co/Si molar ratios (0, 0.05, 0.10, and 0.25). The resultant materials were characterized by N2 sorption and chemical structures by Raman and X-ray absorption spectroscopy before and after a harsh hydrothermal exposure (550 °C, 75 mol% vapour and 40 h). The cobalt silica materials showed a lower surface area loss from 48% to 12% with increasing Co/Si molar ratio from 0.05 to 0.25 and relatively maintaining their pore size distribution, while pure silica exhibited significant surface area reduction (80%) and pore size broadening. For low cobalt loading sample (Co/Si = 0.05), the cobalt was highly dispersed in the silica network in a tetrahedral coordination with oxygen and a small proportion of Co-Co interaction in the second shell. Long range order Co3O4 was observed when Co/Si molar ratio increased to 0.10 and 0.25. The hydrothermal exposure did not affect the local cobalt environments and no cobalt-silicon interaction was observed by X-ray absorption spectroscopy. The hydrothermal stability of the silica matrix was attributed to the physical barrier of cobalt oxide in opposing densification and silica mobility under harsh hydrothermal conditions.

Redox structural control of Pd and PdO silica matrices

Pd crystallite sizes within silica were controlled by calcination in either oxidation or reduction conditions. Control was imparted by the temperature of decomposition of the PdCl₂ precursor, and thus the degree of condensation of the silica matrix.

Mass-fractal growth in niobia/silsesquioxane mixtures: a small-angle X-ray scattering study

The nucleation and growth of niobium pentaethoxide (NPE)-derived clusters in ethanol, through acid-catalyzed hydrolysis/condensation in the presence and absence of the silsesquioxane 1,2-bis(triethoxysilyl)ethane (BTESE), was monitored at 298-333 K by small-angle X-ray scattering. The data were analyzed with a newly derived model for polydisperse mass-fractal-like structures. At 298-313 K in the absence of BTESE the data indicated the development of relatively monodisperse NPE-derived structures with self-preserving polydispersity during growth. The growth exponent was consistent with irreversible diffusion-limited cluster agglomeration. At 333 K the growth exponent was characteristic for fast-gelling reaction-limited cluster agglomeration. The reaction yielded substantially higher degrees of polydispersity. In the presence of BTESE the growth exponents were substantially smaller. The smaller growth exponent in this case is not consistent with irreversible Smoluchowski-type agglomeration. Instead, reversible Lifshitz-Slyozov-type agglomeration seems to be more consistent with the experimental data.