Control of the polymerization process of multicomponent (Si, Ti, Zr) sols using chelating agents

Abstract A new experimental strategy was developed to obtain SiTi Zr oxide transparent sols via the sol–gel process. A pre-hydrolyzed tetraethyl orthosilicate (TEOS) sol was used as the Si precursor. Five chelating agents were used to stabilize monomeric Ti and Zr precursors, avoiding precipitation. The sols were characterized by UV–Vis spectroscopy in order to characterize the Ti and Zr species obtained. The sols were also studied by 29 Si NMR, small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric (TGA) and differential thermal analyses (DTA). Based on the study of series of SiTi, SiZr and SiTiZr UV–Vis spectra obtained with every chelating agent, we assigned the bands. In some cases it was possible to assign the bands to the chelation of Ti and Zr specifically. The stability of the SiOTi and SiOZr bonds from sols to oxides was demonstrated by FTIR spectroscopy. A strong influence of the molecular structure of the chelating agents in the sols was observed by 29 Si NMR, and in the oxides by the TGA and DTA studies. The chelating agent that allowed to obtain a homogeneous pore size structure after thermal treatment at 873 K was isoeugenol.