Mechanochemical synthesis of ternary heterojunctions TiO(A)/TiO(R)/ZnO and TiO(A)/TiO(R)/SnO for effective charge separation in semiconductor photocatalysis: A comparative study.

TiO, ZnO, and SnO metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO with either ZnO or SnO in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO from anatase to rutile and yields ternary heterojunction of the type TiO(A)/TiO(R)/ZnO and TiO(A)/TiO(R)/SnO (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO(A)/TiO(R)/ZnO heterojunction is attributed to the formation of Ti-V defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti and Zn. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.