Fabrication of n-TiO2/p-CuO thin-film heterojunction for efficient photocatalytic degradation of toxic organic dyes and reduction of metal ions in solution

Abstract

The article describes the fabrication of a thin-film TiO2/CuO heterostructure on fluorine-doped tin oxide (FTO)-coated glass substrate. The phase and surface microstructures of the heterostructure were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM) analyses. Spectroscopic analysis was carried out with a UV–Vis spectrophotometer. A p–n heterojunction was found to develop between the top layer CuO and the bottom layer TiO2; obtained through I–V measurement carried out using a KEITHLEY Semiconductor Characterization System (4200 SCS). An enhanced photodecomposition of dyes was observed for the TiO2/CuO heterostructure compared to pristine TiO2 or CuO thin films. For RhB, the photodegradations in the presence of TiO2, CuO and TiO2/CuO films, respectively, with 1 mL H2O2 while for MB, the photodegradations with TiO2, CuO and TiO2/CuO films, respectively, with 1 mL H2O2. The photoreductions were about 23%, 78% and 95% in the presence of TiO2, CuO and TiO2/CuO films, respectively. Enhanced photodecomposition has been attributed to the facile transportation of electrons and holes in the opposite directions at the junction of CuO/TiO2 with reduced recombination of charge of carriers, which allowed rapid generation of active species (•OH radicals, OH− and •O2− ions). A faster reduction of toxic metal ions by the heterostructure was also observed compared to the single thin films.