Kinetics of photoelectrocatalytic degradation of nitrophenols on nanostructured TiO2 electrodes

In the present work, titanium oxide (TiO2) nanotubes were directly grown by the electrochemical oxidation of titanium substrates at 20 V in a nonaqueous electrolyte (DMSO/HF). The morphology and microstructure of the synthesized TiO2 photocatalysts were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The kinetically photoelectrochemical degradation of 2-nitrophenol (2-NPh) and 4-nitrophenol (4-NPh) at the TiO2 nanotubes was examined, individually and when they were mixed together. It was found that the photoelectrochemical degradation of 2-NPh is faster than that of 4-NPh. In order to determine the kinetic behavior of 2-NPh and 4-NPh in the course of the photoelectrocatalytic oxidation of their mixtures, an experimental design with 36 samples and a test set with 6 samples were used to build up a partial least-squares (PLS) model. The degradation of both 4-NPh and 2-NPh became slower in the binary mixture compared with the individual degradation rates of the 4-NPh and 2-NPh. The present work has demonstrated that UV-vis spectroscopy coupled with PLS calibration can be used to in situ monitor the concentration changes, providing a novel approach to determine the competitive effects of different organic pollutants during water purification and wastewater treatment.