Influence of synthesis parameters on sol–gel transition and physical properties of Nb2O5 mesoporous ambigels

In this study, Nb 2 O 5 alcogels and mesoporous ambigels were formed via a new acid-catalyzed polymeric synthesis pathway using NbCl 5 as a precursor. The effect of hydrolysis, catalyst, and propylene oxide molar ratios on sol–gel transition, rheological properties, and physical properties of Nb 2 O 5 ambigels were investigated. A common behavior for the sol–gel transition of Nb 2 O 5 on the viscosity vs. time curves was identified. The molar ratios of H 2 O:Nb +5 and HNO 3 :H 2 O 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 Nb 2 O 5 nanoparticles. An increase in the molar ratios of HNO 3 :H 2 O (lower pH) increased the surface area and pore volume of Nb 2 O 5 , and yielded a finer nanostructure of Nb 2 O 5 mesoporous ambigels. Graphical Abstract