Electrochemically assisted photocatalytic degradation of 4-chlorophenol by ZnFe₂O₄-modified TiO₂nanotube array electrode under visible light irradiation

A well-aligned ZnFe2O4/TiO2composite nanotube array (ZnFe2O4/TiO2-NTs) electrode with visible-light activity was successfully prepared using a two-step electrochemical process of anodization and a novel cathodic electrodeposition method followed by annealing. The ZnFe2O4nanoparticles were highly dispersed inside the TiO2-NTs but minimized at the tube entrances. The structure and optical properties of the TiO2nanotubes and the derived composites have been well characterized. The composites displayed a strong photo response in the visible region and low recombination rate of the electron-hole pairs. In addition, the synthesized ZnFe2O4/TiO2-NTs electrode showed much higher photocurrent density in the visible region than pure TiO2-NTs electrode. The dramatically enhanced electrochemically assisted photocatalytic activity of the composite electrode was evaluated in the decomposition of 4-chlorophenol and dichloroacetate under visible light irradiation (420 nm < λ < 600 nm). The improved photoelectrocatalytic (PEC) activity is derived from the synergetic effect between ZnFe2O4and TiO2, which promoted the migration efficiency of photogenerated carriers at the interface of the composite and enhanced the efficiency of photon harvesting in the visible region. The degradation of 4-chlorophenol was monitored by measuring Cl-concentrations and analyzing reaction intermediates by high-performance liquid chromatography-mass spectroscopy (HPLC-MS).