Review on bimetallic-deposited TiO2: preparation methods, charge carrier transfer pathways and photocatalytic applications

Plasmonic metal structure that can host size-tunable optical properties and tailored catalytic surface active sites elicits peculiar functionalities upon integrating with semiconductors. In the case of metal-semiconductor composites, formation of Schottky barrier height and surface plasmon resonance (SPR) effect stimulated by the metallic dispersion cooperatively separates the charge carriers and alters the optical response to longer wavelength region, respectively, which are of paramount importance in the light-induced redox reactions. From the view point of attaining maximum synergy, bimetallic deposition over the titania support has impelled interest due to the supportive interactions arising from metal-metal and metal-TiO2 heterojunctions. In this review article, bimetallic systems constituting mainly Cu, Ni, Au, Ag, Pd and Pt over the titania surface are discussed under the light of preparative methods, their distribution, electronic interactions between the metals and with the titania support, charge carrier transfer pathways, structural stability and optimized content towards achieving maximum efficiency in various applications such as pollutant degradation, CO2 reduction, H-2 evolution reaction (HER) and in the functional group conversion of few organic compounds. The role of each metal in the bimetallic system and the effects arising from structure-morphology features of titania are considered to furnish insightful discussion into this exquisite heterojunction. The bimetallic deposition over the other emerged semiconductors are briefly surmised to attest the versatility of this strategy and its reliability from several prospects are brought to the fore to provide the room for developing efficient bimetallic-semiconductor heterostructures.