Copper nanoparticles sensitized TiO2 nanotube arrays electrode with enhanced photoelectrocatalytic activity for diclofenac degradation

Copper nanoparticles (NPs) deposited on the surface of self-organized highly ordered TiO2 nanotube arrays (Cu/TiO2 NTs) were synthesized by electrochemical anodization and the successive ionic layer adsorption and reaction technique. The morphology, elemental composition, crystallinity, light absorption ability and photoelectrochemical property of the as-prepared Cu/TiO2 NTs electrode were distinguished based on various characterizations. X-ray photoelectron spectroscopy showed that the Cu NPs existed as Cu(II)O and Cu(I)2O on the TiO2 surface. The current-voltage curve of Cu/TiO2 NTs electrode indicated a rectifying behavior. The surface sensitization of TiO2 NTs by CuO and Cu2O NPs enhanced the absorption of visible light. Meanwhile, the enhanced charge separation was demonstrated by electrochemical impedance spectroscopy, transient photocurrent response and photovoltage measurements. Besides, Cu/TiO2 NTs electrode showed more effective photoconversion efficiency and enhanced photoelectrocatalytic activity towards the degradation of diclofenac than pure TiO2 NTs electrode under simulated solar light irradiation, which was attributed to the synergistic effects between nanotubular structures of TiO2 and uniformly dispersed copper nanoparticles, as well as the small bias potential. Furthermore, the photoelectrocatalytic mechanism was proposed and the possible radical species involved in the photoelectrocatalytic degradation of diclofenac were analyzed by active species trapping. The Cu/TiO2 NTs electrode exhibited high reusability.