Electrochemical method for synthesis of a ZnFe ₂O ₄/TiO ₂ composite nanotube array modified electrode with enhanced photoelectrochemical activity

An electrode with intimate and well-aligned ZnFe ₂O ₄/TiO ₂ composite nanotube arrays is prepared via electrochemical anodization of pure titanium foil in fluorine-containing ethylene glycol, followed by a novel cathodic electrodeposition method. The deposition of ZnFe ₂O ₄ is promoted in the selfaligned, vertically oriented TiO ₂ nanotube arrays but minimized at the tube entrances. Thus, pore clogging is prevented. Environmental scanning electron microscopy, energy-dispersive X-ray spectra, high-resolution transmission electron microscopy, X-ray diffraction patterns, and X-ray photoelectron spectroscopy indicate that the as-prepared samples are highly ordered and vertically aligned TiO ₂ nanotube arrays with ZnFe ₂O ₄ nanoparticles loading. The TiO ₂ nanotubes are anatase with the preferential orientation of <101> plane. Enhanced absorption in both UVand visible light regions is observed for the composite nanotube arrays. The current-voltage curve of ZnFe ₂O ₄-loaded TiO ₂ nanotube arrays reveals a rectifying behavior. The enhanced separation of photoinduced electrons and holes is demonstrated by surface photovoltage and photocurrent measurements. Meanwhile, the photoelectrochemical investigations verify that the ZnFe ₂O ₄/TiO ₂ composite nanotube array modified electrode has a more effective photoconversion capability than the aligned TiO ₂ nanotube arrays alone. In addition, the photoelectrocatalytic ability of the novel electrode is found enhanced in the degradation of 4-chlorophenol. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.