Nanoparticle Route for the Preparation in Aqueous Medium of Mesoporous TiO2 with Controlled Porosity and Crystalline Framework

Abstract

Mesoporous TiO2 with tunable pore size and mono-, bi-, and tricrystalline frameworks was prepared from titania nanoparticles synthesized by a sol−gel method. The synthesis was performed by using an amphiphilic triblock copolymer, Pluronic F127, as a structure-directing agent and titanium isopropoxide as a precursor. The structure-directing agent was added in a presynthesized colloidal suspension composed of bicrystalline titania nanoparticles dispersed in an aqueous medium. By varying the ratio between the number of ethoxy units and the number of titanium atoms (EO/Ti), mesoporous TiO2 materials with controlled pore size were synthesized. Materials were characterized by TG/DTA, XRD, SEM, TEM, and N2 adsorption−desorption analysis. In the absence of copolymer, the porosity was low, indicating efficiently packed TiO2 nanoparticles. As the EO/Ti ratio was increased, the average pore size and the specific surface area became larger, whereas the crystallite size of anatase and brookite became smaller. The addition of copolymer induced the enrichment of the brookite polymorph, prevented particle growth, and delayed the formation of rutile. Bimodal (mesoporous−macroporous) N-doped titania with a pure anatase framework was obtained by using diethanolamine (DEA) as the source of nitrogen.