In situ synthesis of graphene/WO3 co-decorated TiO2 nanotube array photoelectrodes with enhanced photocatalytic activity and degradation mechanism for dimethyl phthalate

Graphene and WO3 co-decorated TiO2 nanotube array (GR-WO3/TNA) photoelectrodes were fabricated using in-situ anodization and electrodeposition method. The effects of deposition time, initial pH, anions, cations and electron acceptor on photocatalytic performance of GR-WO3/TNA photoelectrodes were studied. The photocatalytic degradation process and mechanism of dimethyl phthalate (DMP) were explored by analyzing the kinds of active radicals and intermediates. Results showed that the degradation rate of DMP by GR-WO3/TNA photoelectrodes could reach 75.1% after 120 min illumination. The degradation efficiency of DMP gradually decreased with the increase of initial pH. Some anions (SO42-, Cl-, HCO3- and NO3-) showed significant inhibitory effect, whereas Ca2+ and Mg2+ exhibited little effect on the DMP degradation. GR-WO3/TNA photoelectrodes have excellent durability and stability, and the degradation rate of DMP decreased less than 2% after 10 recycles. The photocatalytic degradation of DMP was mainly due to the participation of hydroxyl radical (center dot OH) and O-2(center dot-). DMP molecules were transformed to carboxylic acid substances, CO2 and H2O by hydroxylation, dealkylation, broken bonds and open-loop. This work indicated that the GR-WO3/TNA photoelectrode, with high photocatalytic activity and stability, were a promising candidate for the efficient and non-toxic treatment of environmental pollutants and further application in water purification.