Microwave assisted photocatalytic degradation of pentachlorophenol in aqueous TiO2 nanotubes suspension

TiO2/SiO2 (Ti:Si = 10:1) nanoparticles were first prepared by ultrasound-assisted hydrolysis and then treated by 10 M NaOH at 110 °C for 20 h to form titania nanotubes. The formed samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2-adsorption, UV–vis absorption spectra and ESR spectrometer. Result indicates that the samples prepared are nanotubular structure with opened ends. The diameter of nanotubes is about 10 nm and their length is about 100 nm. The surface area of TiO2 nanotubes is 286 m2/g. The ESR signals show that there are more OH on the surface of TiO2 nanotubes than that on the surface of TiO2/SiO2 nanoparticles. The photocatalytic degradation of PCP on TiO2 nanotubes assisted by microwave in aqueous solution was investigated. The result indicates that the degradation rate in the microwave assisted photocatalysis process (MPC) is faster than that in other processes including microwave assisted photolytic (MDP), microwave alone process (MP) and dark process (DP). The photocatalytic activity of TiO2 nanotubes is higher than that of P25 and TiO2/SiO2 nanoparticles. It may be contributed to the capacity of absorption to the UV–vis irradiation and specific surface area among the photocatalysts. PCP is effectively degraded in the MPC on TiO2 nanotubes. The removal of 40 mg/L PCP is 93.5% and the CODcr decrease is 51.8% in 20 min. Along with the degradation of PCP, pH of solution decreases from 10.32 to 7.5 and the dechlorination is completed in 12 min. The major intermediates of PCP in MPC on TiO2 nanotubes were identified by GC/MS, including tetrachlorophenols, trichlorophenols, tetrachlorocatechol, tetrachlorohydroquinone. Based on the results, the possible photocatalytic degradation pathways of PCP on TiO2 in MPC were proposed.