Authors: Yu Chao Tang, Xian Huai Huang, Han Qing Yu, Wei Hua Li, Chang Nian Wu
Abstract: The photochemical degradation mechanisms of an azo dye Direct Red 4BS and Methyl Orange on hematite in the presence of H2O2 were investigated. The decolorization of azo dyes was attributed to the forming surface complex between specific bond of the dyes and hematite, which facilitate the electron transfer from hematite to azo bond. No mineralization of azo dyes occurred in the presence of visible irradiation, only chromogenic group destroyed in the photo-chemical reaction process. Surface complex between azo dyes and hematite will be destroyed under alkaline solution which suggested the active site or the formed surface complex had been destroyed by OH–. Chemical adsorption of the azo dyes on hematite was critical factor which affect the decolorization efficiency of the photoreaction.
1612
Authors: Wen Jie Zhang, Qian Li, Hong Bo He
Abstract: The functions of applied potential to the photoelectrocatalytic degradation process of methyl orange were investigated. When using 0.05 M NaCl and under different applied potentials, the degradation rate increased obviously with increasing applied potential. When the applied potential was between 0.6 V-1.0 V, the degradation rate was enhanced drastically. The detected current values got larger as the applied potential increased from 0 up to 1.2 V. There was no direct electro-degradation to the dye in the solution. The applied potential and the irradiated light had synergetic effect when they were applied to the solution at the same time. While after irradiation for 0 to 60 min, with the increasing reaction time, methyl orange absorption peak intensity shrank obviously. The azo and benzene groups in methyl orange degraded totally under photocatalytic process.
521
Authors: Shu Fang Mei, Ya Nan Liu
Abstract: Degradation of Reactive Black 5 in aqueous solution was studied by double-dielectric barrier discharge, degradation efficiency and degradation mechanism has been investigated. Results shows that during in ten minutes degradation, decolorization efficiency can reach 98.76%,COD and TOC could not be reduce observably, while the biodegradability has been greatly improved, the BOD5/COD ratio increase from 0.079 to 0.495.Decolorization efficiency is higher than that of mineralization, decolorization follows the first order kinetics with a constant rate of 0.4008 min-1. pH of the solution decrease gradually, but the conductivity increase during the degradation process. The ions of sulfate, nitrate, acetic acid, and oxalic acid have been found in the final treated sample and their concentrations increase with the reaction time. Chromophore group is damaged firstly and the solution has been decolorized efficiently, the degradation of benzene ring and naphthalene ring is more difficult than that of the azo bond, and the reduction or disappearance of absorption peaks indicates that the aromatic ring of KN-B was degraded partly.
1616
Authors: Huan Yan Xu, Xue Li, Yan Li, Ping Li, Wei Chao Liu
Abstract: An active dye, Methyl Orange (MO) was employed as the target pollutant to evaluate the photocatalytic activity of TiO2/schorl composite and the kinetics and thermodynamics of this process was emphasized in this work. Langmuir–Hinshelwood kinetic model was employed for the kinetic studies and the results revealed that the process of MO photocatalytic discoloration by TiO2/schorl composite followed one order reaction kinetic equation under different conditions. The reaction rate constant (k) increased with initial MO concentration decreasing. When the catalyst dosage or solution pH increased, k values increased and then decreased. The possible reasons for these phenomena were discussed. Finally, the thermodynamic parameters ΔG, ΔH, ΔS were obtained by the classical Van't Hoff equation.
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