Microporous Zirconia–Titania Composite Membranes Derived from Diethanolamine‐Modified Precursors

Abstract

Inorganic microporous materials show great potential for applications in industrial catalysis, separation technology, membranes, sensors, and optical devices. The most common amorphous, microporous inorganic material is silica. Due to its small pores and straightforward synthesis, amorphous silica has been considered as a promising material for membrane applications. However, its moderate hydrothermal stability limits its extended application in harsh environments.[1] Of particular interest as alternative materials for stable, high-performance membranes are sol-gel-derived amorphous oxides of transition metals, such as titania and zirconia. These materials show superior stability compared to silica; [2] however, their synthesis is complicated by the high reactivity of the required precursors.[3] To date, a few groups have been able to prepare amorphous titania and zirconia membranes for aqueous nanofiltration.[4]Herein, we describe the preparation and characterization of microporous zirconia-titania composite membranes. Preparation has been carried out via two different synthesis routes. The first route is based upon using the diethanolamine-stabilized heterometallic precursor Zr{l-g 3 -NH(C 2 H 4 O) 2 } 3 [Ti-(O i Pr) 3 ] 2 (1).[5] The second route involves synthesis using 2, a mixture of zirconium n-propoxide, titanium n-propoxide, and diethanolamine in a molar ratio equivalent to that in 1. Figure 1a shows thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) data for uncalcined powders derived from either 1 or 2. The data are similar for both powders. A sharp initial weight loss is observed with an onset at 50°C, corresponding to the removal of adsorbed solvent molecules. A gradual decrease in weight is subsequently observed up to 300°C. This is attributed to the removal of ligands from the outer surface of the material. Mass spectrometry confirmed the presence of nitrogen in the sweep gas, originating from the amine groups of the ligands. In the range ∼ 300-350°C, a sharp decrease in weight is observed, which is accompanied by a large change in the heat flow centered at 350°C. This can be attributed to the removal of ligands located inside the material. Mass spectrometry again confirmed a high concentration of nitrogen in the sweep gas. A further increase of temperature to 450-600°C causes removal of the remaining alkoxide ligands.The DSC data suggest that crystallization occurs at ∼ 750°C, as evidenced by the sharp exothermic peak at this COMMUNICATIONS

Sol–gel derived mesoporous and microporous alumina membranes

“…This temperature is considerably higher than that of the crystallization of gamma phase from colloidal boehmite particles [38]. Spijksma et al [44] also reported crystallization at around 750°C in the microporous titania-zirconia composite membranes derived from diethanolamine modified precursors which was considerably higher than *400°C for pure titania and zirconia.…”

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

“…Inorganic membranes that can separate hydrogen from CO 2 -containing gas streams with subsequent CO 2 sequestration, offer great potential for integration in pre-combustion CO 2 capture technologies and, hence, being a rather hot topic in the present membrane research field. Several inorganic materials have been proposed to be used as gas separation membranes for such purpose, including zeolites [6][7][8][9], carbon [10][11][12][13], silica and metal oxides [35,36]. Among these, silica-based microporous membranes with the pore size tailored to the gas molecular range is one of the most promising materials since Uhlhorn et al [37] firstly found their molecular sieving performances in 1989.…”

Hybrid Organic–Inorganic Microporous Membranes with High Hydrothermal Stability for the Separation of Carbon Dioxide

“…Different research groups have undertaken numerous attempts to improve the hydrothermal stability of sol-gel derived microporous silica membranes, including (1) modification of the amorphous silica matrix by doping with metal or transition-metal ions (e.g., Ni, Co, Mg, Al, Zr, Ti, Fe, Nb, and others); [4] (2) dispersion of methyl (ÀCH 3 ) functional groups into the silica matrix, so as to make its structure more hydrophobic; [9,10] and (3) use of alternatives to tetraethyl orthosilicate (TEOS) as the source for the alkoxide, such as transition-metal alkoxides or bridged bis-silyl precursors. [11][12][13][14] None of these attempts have succeeded in developing a high-enough membrane performance combined with a sufficient long-term hydrothermal stability to the degree required for application to industrially relevant gas streams and temperatures.Herein, we report on sol-gel derived microporous hybrid inorganic-organic membranes for enhanced CO 2 separation. These are prepared by co-hydrolysis and condensation of the ethylene-bridged bis-silyl precursor 1,2-bis(triethoxysilyl)-ethane (BTESE) and niobium penta(n)butoxide, and subsequent coating of the polymeric sol on an alumina-based multilayer support.…”