Influence of synthesis parameters on sol–gel transition and physical properties of Nb 2 O 5 mesoporous ambigels

In this study, Nb2O5 alcogels and mesoporous ambigels were formed via a new acid-catalyzed polymeric synthesis pathway using NbCl5 as a precursor. The effect of hydrolysis, catalyst, and propylene oxide molar ratios on sol–gel transition, rheological properties, and physical properties of Nb2O5 ambigels were investigated. A common behavior for the sol–gel transition of Nb2O5 on the viscosity vs. time curves was identified. The molar ratios of H2O:Nb+5 and HNO3:H2O significantly influenced the gelation time, the rheological properties of alcogels, as well as the physical properties of the respective ambigels. The gels presented yield stress and shear-thinning behavior with different degrees of thixotropy. Microstructure analysis of the ambigels revealed a mesopore network formed by interconnected Nb2O5 nanoparticles. An increase in the molar ratios of HNO3:H2O (lower pH) increased the surface area and pore volume of Nb2O5, and yielded a finer nanostructure of Nb2O5 mesoporous ambigels.