Coupling TiO2 nanotubes photoelectrode with Pd nano-particles and reduced graphene oxide for enhanced photocatalytic decomposition of diclofenac and mechanism insights

In order to improve the separation efficiency of photogenerated charge carriers and photocatalytic (PC) performance of TiO2 nanotubes (TiO2 NTs) photoelectrode, Pd nanoparticles and reduced graphene oxide co-modified TiO2 NTs (Pd-RGO/TiO2 NTs) photoelectrode was fabricated through two-step electrodeposition in this study. Subsequently, physicochemical properties of the resulting samples were investigated through SEM, XRD, XPS and Raman techniques. Additionally, the generation of (OH)-O-center dot was detected by fluorescence spectra using terephthalic acid as the probing molecule. Furthermore, the photoelectrochemical properties of Pd-RGO/TiO2 NTs photoelectrode were studied through UV-vis DRS, photocurrent density and electrochemical impedance spectroscopy. As a result, Pd-RGO/TiO2 NTs photoelectrode exhibited a significantly enhanced photocurrent density of 0.111 mA cm(-2) and charge carrier concentration of 1.43 x 10(19) cm(-3), as well as efficient PC performance of 58.4% for the degradation of diclofenac aqueous solution. Moreover, the enhanced-PC mechanism was proposed. The efficient visible PC performance of Pd-RGO/TiO2 NTs photoelectrode could mainly be attributed to the co-modification of Pd and RGO species, which could not only improve the light harvesting property, but also the effective separation of photogenerated charge carriers. Furthermore, the enhanced PC mechanism for degradation of diclofenac was proposed and confirmed. This study provides an effective strategy to fabricate TiO2 NTs-based photoelectrode which could be applied in the fields of organic pollutants elimination and wastewater treatment. (C) 2015 Elsevier B.V. All rights reserved.