用化学需氧量指数法研究亚甲基蓝的可见光光电催化脱色反应机理

Study on Photoelectrocatalytic Decolorization Mechanism of Methylene Blue Under the Visible-light Irradiation by Measuring Chemical Oxygen Demand Index

以玻璃碳(GC)为基底材料,采用电化学沉积法结合连续化学浴沉积法制备了CuInSe2/Ag3PO4@AgIO4/GC复合光电极,并利用此电极研究了亚甲基蓝(MB)的可见光光电催化脱色反应过程.通过监测反应体系紫外-可见吸收光谱、水相红外吸收光谱和化学需氧量指数(COD)等变化对其脱色反应机理进行了研究.结果表明,在固定可见光辐照时间、强度和光电极受光面积的条件下,当光电极外加偏压设为0.61 V(vs. SCE), H2O2促进剂的初始浓度为0.42 mmol/L, 0.15 mol/L Na2SO4支持电解质的pH为2.7时,对0.050 mmol/L的亚甲基蓝溶液光电催化降解45 min时其脱色率与矿化率的比值为8.5;并观察到伴随MB分子的脱色反应过程逐渐有少量有机沉淀产物生成,表明MB经光电催化脱色反应后其分子的吩噻嗪母核结构仅发生了部分降解,但并未彻底矿化为无机物;结合紫外和红外光谱实验结果提出了光电催化MB脱色反应的机理.

A new type of composite photoelectrode, CuInSe2/Ag3PO4@AgIO4/GC, was prepared by combining the electrochemical deposition and the sequential chemical bath deposition method and the photocatalytic decolorization reaction of methylene blue(MB) under visible-light irradiation condition was deeply studied using the modified electrode. By means of the in-situ measurements of ultraviolet-visible absorption spectra, water-phase infrared spectra and chemical oxygen demand values(COD) for the sampled electrolyte solution, the decolorization mechanism of methylene blue was investigated in a visible-light photoelectrocatalytic reaction process. Under the fixed experimental conditions such as the visible-light irradiation time and intensity and light-receiving area of photoelectrode, other experimental conditions were also optimized as follows: the applied bias of 0.61 V(vs. SCE), the 0.42 mmol/L initial concentration of H2O2 as a reaction promoter, the pH=2.7 of 0.15 mol/L Na2SO4 supporting electrolyte and 0.050 mmol/L MB as the initial reaction solution. Therefore, it was found that the ratio of decolorization rate to mineralization rate could reached 8.5 at the irradiation reaction time of 45 min, and a small amount of organic precipitation was formed along with the decolo-rization reaction of methylene blue. These results indicated that the phenothiazine mother nucleus of methylene blue molecular structure was only partially degraded in decolorization reaction process, and was not completely mineralized into the inorganic substances. Furthermore, on referring to the experimental evidences of ultraviolet-visible(UV-Vis) spectroscopy and Fourier transform infrared(FTIR) spectroscopy, a possible mechanism was proposed, which could more perfectly explain the essence of the visible-light photoelectrocatalytic decolorization reaction of methylene blue dye.