Maximum SiO2 layer thickness by utilizing polyethylene glycol as the surfactant in synthesis of core/shell structured TiO2–SiO2 nano-composites

Abstract

TiO2-SiO2 nano-composites with the core/shell structure have been prepared by means of a technique based on an extension of well-known Stober process. In this way, the silica coating of TiO2 nano-particles in the presence of various commercially available surfactants of cationic, anionic and nonionic has been conducted with the aim to increase barrier properties against UV (UV block- ing) radiation, in order to optimize photo-killing ability of the TiO2 nano-particles and decline of the high photo- catalytic property of titania. The influences of varying coating parameters such as time and temperature on the silica content of nano-composites have been studied and optimum conditions for attaining a thick layer of SiO2 have been determined. Electro-phoretic mobility measurements indicated that the silica coating shifted the iso-electric point of titania toward that of a typical pure colloidal silica. Surface elemental composition of core/shell structured TiO2-SiO2 nano-composites was verified by using energy dispersive X-ray analysis. It was found that maximum silica shell thickness can be obtained in the presence of polyethylene glycol as a nonionic surfactant at 80 � C for 360 min. The photo-catalytic activities were evaluated by the degradation of an aqueous solution of methylene blue under UV light irradiation. In addition, the resultant opti- mum nano-composites have been characterized by FE- SEM, TEM, BET, FTIR and UV-Vis spectroscopy.