Crystallization Pathway of Size-Controlled SnO2 Nanoparticles Synthesized via a Nonaqueous Sol-Gel Route

This paper deals with the crystallization pathway of tin dioxide nanoparticles of a few nanometers synthesized via a nonaqueous sol-gel route based on the etherolysis of a tin tetrachloride (SnCl4) precursor. Two different ethers were used as oxygen donors: diisopropyl ether ((Pr2O)-Pr-i) and dibenzyl ether (Bn2O). The solvothermal treatments of SnCl4 in (Pr2O)-Pr-i at different temperatures and reaction times revealed in the early stages of the reaction the formation of an organic polymeric phase in which crystalline nanoparticles are embedded. In the case of the SnCl4-Bn2O system, the formation of a brownish polymer containing crystalline oxidic nanoparticles and the production of water were evidenced. With both ethers, an unexpected intermediate disordered nanocrystalline phase is formed, which progressively transforms into rutile-type SnO2 nanoparticles. The formation of the polymeric phase, which is suspected to act as a trap for the nanoparticles, freezes the intermediate phase, limits the particle growth, and delays the restructuration into the rutile-type structure. The degradation of the polymer phase in the case of (Pr2O)-Pr-i and/ or the water action in the case of Bn2O are finally able to destabilize the nanoparticle-polymer assembly and to induce the restructuration of the nanoparticles.