Contrast on COD photo-degradation in coking wastewater catalyzed by TiO2 and TiO2–TiO2 nanorod arrays

This paper deals with photo-degradation of chemical oxygen demand (COD) in coking wastewater catalyzed by TiO2 nanorod arrays (TNAs) and special secondary structural TiO2–TiO2 nanorod arrays (TTNAs). The photo-catalysts, TNAs and TTNAs, were prepared by hydrothermal process and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). Well-aligned TNAs and TTNAs were prepared on the pretreated quartz substrates. It is proved that Rutile TiO2 crystal seeds induce the nucleation and growth of TNAs preferably and the controllable synthesis of TTNAs with different secondary morphologies via hydrothermal approach could be achieved. Chemical oxygen demand analyses, photochemical kinetic analysis and Fourier Transform infrared spectroscopy (FTIR) analysis have been carried out to obtain the details of the photo-catalytic degradation and mineralization of contaminants. The results show that these nanoscale catalysts exhibit high photo-catalytic activities in degradation of COD in coking wastewater and TTNAs have significant advantages in COD removal. The optimum degradation efficiencies of COD reach 77.3% and 89.8% respectively using TNAs and TTNAs with catalyst addition of 0.04 g L−1 in 60 min reaction period. The effects of operating parameters on photo-degradation efficiency and the kinetics of COD photocatalytic degradation were investigated and discussed.