Using ESR to Analyze Some Oxidants Enhancing TiO2 to Produce Hydroxyl Radicals under Visual Lights

Several oxidants, KMnO₄, K₂Cr₂O₇ and CuCl₂ could enhance photo-degradation organic pollutants through titanium dioxide (TiO₂) in solution. By orthogonal experimental design and variance analysis study, the optimal de-coloring Acid Orange 7 (AO7) could be determined among different types and concentrations of oxidants as well as different wavelength of visual lights. The optimal removal of color could reach 99% and 92% for total organic carbon (TOC). Using 5,5-dimethyl-l-pyrroline-noxide (DMPO) to scavenge the hydroxyl radicals (*OH) produced during photocatalysis reaction and to analyze by the Electron Spin Resonance Spectrum (ESR), the effects of oxidants were to promote the production of OH as TiO₂ shining even by visual lights which the wavelengths were less than the excitation energy of band-gap.