Electrochemically Assisted Photocatalytic Degradation of 4-Chlorophenol by ZnFe₂O₄−Modified TiO₂ Nanotube Array Electrode under Visible Light Irradiation

Abstract

A well-aligned ZnFe₂O₄/TiO₂ composite 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 ZnFe₂O₄ nanoparticles were highly dispersed inside the TiO₂−NTs but minimized at the tube entrances. The structure and optical properties of the TiO₂ nanotubes 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 ZnFe₂O₄ and 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).