杂多酸H₃PW₁₂O₄₀对有机染料光降解的催化作用

【作者】 张涛；

【导师】 李克斌；

【作者基本信息】 西北大学 ， 物理化学， 2010， 硕士

【摘要】 水体中有机染料的去除和降解一直是化学和环境工作者关注的研究领域。在这一领域中,光催化法由于能够破坏甚至矿化有机污染物而成为研究热点。本文研究了紫外光辐照下磷钨酸(H3PW12040)对有机染料光解脱色的催化作用。该方法和常规半导体光催化法相比,对某些偶氮染料有很好的氧化还原脱色性能,在应用中具有操作方便,处理效率高,负载方便等优点,因而成为除半导体光催化外最具发展前景的水体中有机污染物降解方法。本文采用间歇式光反应器进行实验,开展了以下工作：(1)分别以偶氮染料酸性大红3R和直接大红4BE为探针物,考察了H3PW12040对其光催化氧化降解性能,探讨了H3PW12040浓度,染料初始浓度对其光催化氧化反应速率的影响；并对反应机理进行了探讨。(2)研究以异丙醇为电子给体,磷钨酸对酸性大红3R和直接大红4BE的UV催化还原脱色性能。探讨了H3PW12040用量、异丙醇用量和染料初始浓度对其光催化还原脱色的影响。研究了H3PW12O40对含有不同偶氮键数目染料的光催化还原脱色性能,在对各染料结构参数进行量子化学计算机模拟的基础上,由多元线性回归得到H3PW12O40光催化还原偶氮染料时反应速率常数与染料结构参数间的定量关系。(3)研究了异丙醇作为电子给体,表面活性剂对偶氮染料直接耐晒黑G的H3PW12O40光催化还原脱色影响。考察了表面活性剂种类、十六烷基三甲基溴化铵用量、不同十六烷基三甲基溴化铵用量下H3PW12O40用量对直接耐晒黑G光催化还原脱色的影响。(4)通过浸渍法将H3PW12O40负载于壳聚糖/层析硅胶(CTS/SiO2)上,得到了复合材料PW12/CTS/Si02,由SEM、EDX、FTIR、UV-Vis DRS和XRD方法对PW12/CTS/Si02进行了表征。研究了PW12/CTS/Si02对偶氮染料直接耐晒黑G的光催化还原脱色性能及吸附性能。通过以上实验得到如下结果：(1)H3PW12O40能够催化酸性大红3R和直接大红4BE的光降解,染料的催化光解过程符合表观一级动力学。H3PW12O40浓度对性大红3R和直接大红4BE的光解有很大影响,在酸性大红3R和直接大红4BE的用量分别为40 mg/L和600 mg/L时,染料有最佳的脱色速率常数,分别为0.0714 min-1和0.1164 min-1；在试验染料浓度范围内,染料光催化反应速率随其初始浓度增加而减小；UV-vis光谱表明,反应体系中染料和H3PW12040之间形成了复合物。H3PW12040对其他偶氮染料的光催化氧化实验表明,随着染料分子中偶氮键数目增多,其发生氧化降解的速率逐渐降低。在染料结构因素中前线轨道能量差AE,染料的脂溶性常数ClogP,最高占据轨道能量EhOMO、染料的分子量Mw对氧化反应速率常数κ有影响,它们之间存在关系：logk=-0.216-0.522ΔE+0.159 EHOMO-0.274ClogP+0.002MW。(2)以异丙醇为电子给体时,H3PW12O40能够使酸性大红3R和直接大红4BE发生光催化还原脱色。试验染料浓度范围内,酸性大红3R的光催化还原过程符合Langmuir-Hinshelwood方程,直接大红4BE的光催化脱色速率随着染料浓度升高逐渐降低。异丙醇浓度和H3PW12O40浓度在对染料的光催化还原过程中存在交互影响。盐浓度增大会降低H3PW12040光催化还原酸性大红3R和直接大红4BE的反应速率常数。H3PW12040光催化还原偶氮染料的研究中,表观一级反应速率常数kobs和染料结构参数之间符合logkobs=-1.707-4.385Ev+0.922ΔE-0.063ELUMO关系式。(3)表面活性剂对H3PW12O40 UV催化还原直接耐晒黑G脱色有明显影响,影响结果与表面活性剂的种类和用量有关。阴离子表面活性剂十二烷基苯磺酸钠对直接耐晒黑G的光催化还原有抑制作用,阳离子表面活性剂十六烷基三甲基溴化铵,非离子表面活性剂聚乙二醇600、OP-10对直接耐晒黑G的UV催化还原脱色有加速作用。在十六烷基三甲基溴化铵的浓度为0.05-0.31 mol/L时,增加十六烷基三甲基溴化铵的浓度能够相应提高直接耐晒黑G的UV还原脱色速率。(4)在制备复合材料PW12/CTS/Si02时,硅胶和壳聚糖的质量比1/1,浸渍浓度为8 g/L磷钨酸溶液,载体CTS/SiO2和PW12溶液的固液比为1/20(g/mL),浸渍1次时,所得复合材料对直接耐晒黑G的光催化还原脱色性能最好。SEM、EDX、FT-IR、UV-Vis DRS和XRD对复合材料PW12/CTS/Si02的表征结果表明,PW12已经完整的负载到载体CTS/SiO2上。对50 mg/L直接耐晒黑G,在溶液pH=4.0,异丙醇浓度为0.13 mol/L,催化剂PW12/CTS/Si02用量为2g/L时,PW12/CTS/Si02对直接耐晒黑G的光催化还原脱色速率最高,速率常数为0.0639 min-1。PW12/CTS/Si02对直接耐晒黑G的吸附性能研究结果显示,随溶液pH升高吸附量增加,随吸附剂用量增加吸附量减小；PW12/CTS/Si02对直接耐晒黑G的吸附过程符合准二级化学吸附动力学规律。更多还原

【Abstract】 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.更多还原