Facile One-Pot Synthesis of Cu_xO/TiO₂ Photocatalysts by Regulating Cu Oxidation State for Efficient Solar H₂ Production

Development of highly efficient Cu x O/TiO 2 photocatalysts by regulating the oxidation state of Cu exclusively in either single or mixed oxidation state(s) is desirable but difficult to achieve without employing any external reagents. The present work describes a one-pot synthesis strategy to obtain Cu x O/TiO 2 photocatalysts with Cu in +1 and/or +2 by using a suitable combination of ethylene diamine tetra acetic acid (EDTA) and ethylene diamine, carefully varying the Cu content, and heat treatment process. Cu x O/TiO 2 nanocomposite catalysts were characterized thoroughly by physicochemical methods. Textural analysis indicates a high dispersion of Cu x O on porous TiO 2 with p–n heterojunctions between them in Cu x O/TiO 2 catalysts. UV–visible spectral analysis suggests the presence of Cu x O on TiO 2 with significantly extended absorption from the UV to the visible region. X-ray photoelectron spectroscopy (XPS) analysis indicates a strong synergetic interaction between TiO 2 and Cu x O due to the comparable CB potential and p–n heterojunction at the interface among them. Photoelectrochemical studies demonstrate excellent charge-carrier separation efficiency, low charge-transfer resistance, and high double-layer capacitance with Cu 2 O/TiO 2 photocatalysts. Photocatalytic efficacy of a Cu x O/TiO 2 nanocomposite in thin-film form has been demonstrated for solar hydrogen generation in sunlight. The incorporation of Cu + in TiO 2 largely improves the H 2 production, and all of the Cu x O/TiO 2 nanocomposites in thin-film form exhibited higher efficiency compared to their particulate/suspension counterpart. Among the composite catalysts, TiCu-1 in thin-film form, with Cu exclusively in +1 oxidation state, exhibited a high hydrogen production rate of 7.06 mmol/h·g, which is 6 times higher than its suspension counterpart; also catalysts containing mixed Cu-oxidation states exhibited about 60–70% activity as that of TiCu-1. The superior performance of Cu 2 O/TiO 2 nanocomposites in thin-film form was due to their enhanced light harvesting ability, high mass transfer rate, and easy accessibility of the reactant species to the active sites.