| Degradation of organic dyes in water has paid much attention by many researchers. Photocatalytic degradation is the mostly used method for the degradation of organic contamiants such as dyes in water. In this paper, photocatalytic technology was used in the degradation of several organic dyes such as acid red 3R (abb. AR3R), direct scarlet 4BE (abb. DS4BE) by using H3PW12O40 (abb. PW12) as photocatalyst. The photocatalytic decomposition of organic dyes were conducted in a batch photoreactor. The following works were carried out:(1) The azo dyes AR3R and DS4BE were selected as probes to investigate their degradation by PW12 photocatalytic oxidation. The influence of the concentration of PW12 and initial concentration of dyes on photocatalytic decolorization of the selected dyes were investigated. In addition, the photocatalytic oxidation mechanism were explored. (2) Photocatalytic decolorization of AR3R and DS4BE by PW12 under isopropanol (abb. IS) as electron donor was investigated. The effects of dose of PW12, IS and initial concentration of dyes on its photocatalytic reduction were thoroughly examined. The explore of realationship between rate constant kobs of dyes and its character parameters was also done. (3) The influence of surfactants on the photocatalytic reduction of direct black G (abb. DBG) were also conducted. In this study, effects of speise of surfactant, dose of cetyltrimethylammonium bromide (abb. CTAB), and concentration of PW12 on the photocatalytic reduction of dye were studied. (4)The heterogeneous photocatalyst PW12/CTS/Si02 was prepared by impregnation method using CTS/SiO2 as loader. The characteristics of prepared combined catalyst was analyzed by using SEM, EDX, FTIR, UV-visDRS and XRD, the photocatalytic property and adsorption property of PW12/CTS/Si02 was tested by using DBG as selected contaminants.The following results were obtained:(1) The process of photodegradation of AR3R and DS4BE can been catalysis by PW12, the disappear of organic dyes can been describes by the first order kinetics. The photo catalytic degradation of dyes reaches the maximum reaction rate constant when the concentration of PW12 reaches 40 mg/L and 600 mg/L, respectively. The UV-vis spectrum reveals the complex formed between dyes and PW12. The relationship between reaction rate constant k and the character parameters of the organic dyes could described by the equation logk=-0.216-0.522ΔE+0.159EHOMO-0.274ClogP+0.002MW. (2) By using IS as an electron donor, AR3R and DS4BE could been reduced by PW12 in the presence of UV irradiation. Langmuir-Hinshelwood equation can be used to illustrate the process of photocatalytic reduction of AR3R. Initial concentration of dyes and ionic strength has negative effects on the photocatalytic reduction of AR3R and DS4BE. The concentration of IS and PW12 has positive effects to the process. The relationship between the reaction rate constant kobs of photocatalytic reduction of azo dyes and the character parameters of the dyes used in the experiments can been used to express as logkobs=-1.707-4.385Ev+0.922ΔE-0.063 ELUMO.(3) Cationic and nonionic surfactants accelerates the bleaching of the azo dye DBG in the prensence of IS by using PW12 as the catalyst, while anoionic surfactant LAS hined the reductive decolorization of DBG. The reaction rate constant increased by increasing the concentration of CTAB. (4) The prepared photocatalyst consisting of PW12, chitosan, and SiO2 was optimized. When the mass ratio of chitosan to SiO2 is 1:1, and 2.0 g of combined loader of chitosan-SiO2 was impregnated one time in 20 mL of 8 g/L of PW12, The obtained photocatalyst shows the highest photocatalytic efficiency for the decoloriaztioon of DBG under UV in the presence of IS. SEM, EDX, FT-IR, UV-vis DRS were employed to characterize the combined catalytst. The results revealed that the polyoxometalates can been loaded on CTS/SiO2 with its perfect Keggin type. The optimum dose of PW12/CTS/Si02 to the photocatalytic reduction of DBG is 2.0 g/L. The adsorption of DBG to PW12/CTS/Si02 submit to the second order adsorption kinetics. |
PDF Full Text Request