Study of the influence of some DCCAs on the structure of sol–gel silica membranes

We obtained silica gel membranes by sol–gel processing. In order to study the effect of some drying control chemical additives, we used an alkoxide/additive molar ratio of 1/1. The performance of the drying additives in obtaining crack-free gels was evaluated through monolithicity measurements. The structural evolution occurring in the interconnected network of the membranes during thermal treatment was monitored by Fourier transform infrared spectroscopy, structural density measurements and nitrogen gas sorption. The degree of cross-linking of the silica network was inferred from the frequency of the Si–O(Si) vibration in the range. We noted that in the presence of formamide and N,N-dimethylformamide, the Si–O–Si bonds are stronger and belong to a more cross-linked structure. Changes in the chemical properties of the membranes, evaluated by quantities of molecular water and silanol groups on their surface, were monitored by absorption bands in the range of 3800–3000 cm⁻¹. Membranes obtained with additives have surfaces covered by a large content of isolated silanol groups even when annealed at 800 °C. The membrane obtained in the presence of amide has larger pore volume and its pore structure is in the range of mesoporosity. The membranes without additive and with propylene carbonate are microporous. Formamide and N,N-dimethylformamide allowed the preparation of crack-free membranes stabilized at high temperatures.