Chemical Transformations of Vanadium-Containing Silica Gel in Contact with Water Vapor According to AFM and ESDR Data

Abstract— The adsorption of water by highly porous silica gels under dynamic conditions was studied by atomic force microscopy (AFM) and electronic spectroscopy of diffuse reflection (ESDR). It was found that a liquid sorbate meniscus is formed in the throats of the pores, which prevents the access of H₂O molecules to the intrapore space of silica gel. It was shown that on the surface of IVS-1 silica gel, H₂O molecules are coordinated on vanadium oxide centers, increasing the coordination number of vanadium atoms to 5 and 6 in a ratio of 1 : 1. The range of the vanadium oxide monolayer resistance to hydrolytic degradation was revealed, and it was proposed to regenerate IVS-1 when the silica gel reaches a dark red color, which corresponds to the adsorption of ~2.5 mmol H₂O/g.