Photodegradation performance and mechanism of 4-nonylphenol by WO3/TiO2 and TiO2 nanotube array photoelectrodes

TiO2 Nanotube arrays (TNA) and WO3-coated TNA photoelectrodes were fabricated using an in situ anodization and pulse electrochemical deposition technology. The performance of the TNA photoelectrodes in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of 4-nonylphenol (4-NP) was investigated. The effects of the initial pH and the anions on the degradation rates and reaction mechanism of 4-NP were studied by the photoluminescence (PL) spectra and electrochemical impedance spectra (EIS). The degradation of 4-NP was fitted to a first-order reaction, and the apparent kinetic constants were 1.9 x 10(-2) min(-1) for TNA photoelectrodes and 2.4 x 10(-2) min(-1) for WO3/TNA photoelectrodes. When a bias potential of 1.0 V was applied, the values for TNA and WO3/TNA photoelectrodes increased to 2.5 x 10(-2) and 3.0 x 10(-2) min(-1), respectively. The degradation of 4-NP was controlled by a charge-transfer process one. WO3-decorated TNA photoelectrodes could increase the adsorption of 4-NP and promote its degradation. For the TNA and WO3/TNAs photoelectrodes, acid and alkaline solutions could facilitate the formation of hydroxyl radicals, whereas the removal of 4-NP was inhibited. The presence of SO42-, Cl-, HCO3- and NO3- has a negative effect on the formation of center dot OH, so did the removal of 4-NP. For the TNA photoelectrodes, the inhibition effect of HCO3- on the formation of hydroxyl radicals and the removal of 4-NP was the most serious compared with that of SO42-, Cl- and NO3-, while for the WO3/TNA photoelectrodes the inhibition effect of NO3- on the removal of 4-NP was maximum.