The Mechanism Of Degradation Of Phenolic Compounds By Ozone-basic Technology

Phenolic organic compond is a recalcitrant compound, it is carcinogenic and toxic to plants, animals, and human even at law concentration. Phenolic organic compond is on the US Environmental Protection Agency list of priority pollution. Recently, the technique of ozone-basic has revealed widely prospect in application for the treatment of phenolic wastewater and has become focuses of advanced oxidation process.In the present work, the degradation efficiency and mechanism of mineralization of 4-chloro-3,5-dimethylphenol (PCMX) in aqueous solution were investigated in laboratory-scale experiments in which pH, initial concentration, Ozone (O₃) dose, temperature and the reaction temperature were varied using ultraviolet ozonation (UV/O₃ oxidation). To explore the capability of the advanced oxidation processes for the rapid removal of biocides, we examined the total organic carbon (TOC) reduction of dissolved 4-chloro-3,5-dimethylphenol (PCMX) in water with the combination of ultraviolet irradiation and ozonation (UV/O₃). The effect of operating variables was investigated as a function of pH value, ozone dosage, bulk temperature and the initial concentration of PCMX. The rate of PCMX mineralization increases with an increase in ozone dose up to 3.1 g h^-1, and a decrease in the initial concentration from 100 mg L^-1 to 250 mg L^-1. The optimal pH value in this reaction was found to be 4.0, whereas temperature has both positive and negative influences on the UV/O₃ process. Intermediates formed during PCMX degredation were detected by gas chromatography coupled with mass spectrometry (GC/MS) and ion chromatography (IC). On the basis of these results, we propose a tentative degradation pathway.Furthermore, TiO₂ nanostructures with various morphology and crystallite phases were synthesized by a hydrothermal method, followed by calcination using Degussa P25 as precursor. The nanotube, nanorod and nanowire forms were obtained by varying the hydrothermal temperature, and the anatase: rutile ratios were adjusted by controlling the annealing temperature. The catalytic activity of the samples was evaluated by degradation of phenol in aqueous solution in the presence of ozone. We found that the initial degradation rates (IDR) of phenol were dominated primarily by the surface HO groups. Thus, with the help of transmission electron microscopy (TEM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses, the number of surface HO groups per unit area of TiO₂ was correlated with the morphology and crystallite phases. Finally, we conclude that the vast surface area and higher rutile phase ratios are favourable for the catalytic ozonation of phenol, and the morphology of TiO₂ had negligible effect in our experiments.