【作者】 王铮；

【导师】 李风亭；

【作者基本信息】 同济大学 ， 环境科学， 2007， 博士

【摘要】 纳米半导体光催化技术作为一种有效的环境污染物治理方法被广泛研究。纳米氧化锌（纳米ZnO）作为一种重要的光催化剂，是极少数几个可以实现量子尺寸效应的氧化物半导体材料，更被证实在某些实验条件下具有比TiO₂更高的催化性能，近年来引起人们广泛关注，在污染物光催化降解方面显示出良好的应用前景。针对普通单一光催化半导体催化效率低的特点，对光催化剂的开发研究具有重要意义。目前对纳米ZnO的改性研究不如TiO₂广泛，所以如何对纳米ZnO光催化剂进行性能改进还需要一定的研究。并且对光催化降解机理等还有待于进一步的研究和完善。本文着眼于纳米ZnO的性能改进研究，利用一种既简单又廉价的合成路线制备高效的复合ZrO₂／ZnO光催化剂。这种新型催化剂不仅进一步拓宽了ZnO的复合氧化物型光催化剂的研究领域，并且通过其对偶氮染料的吸附和降解动力学以及降解途径的分析也进一步完善了光催化技术的机理研究，对其应用到实际废水中有机污染物的光催化治理过程中，具有一定的现实意义。采用共沉淀-热分解法制备了复合ZrO₂／ZnO光催化剂，利用XRD、SEM、TEM、TG-DTA和FT-IR等对其进行了表征，通过酸性红B的等温吸附实验和紫外光催化降解实验，系统地研究了不同锌源、煅烧温度、煅烧时间、Zr复合比例等对ZrO₂／ZnO光催化剂结构和催化活性的影响。通过实验结果证实了ZrO₂的复合降低了ZnO的粒径，提高了它的光催化活性，2.5％ZrO₂／ZnO的光催化效率相对纯ZnO提高了11％，略好于P25 TiO₂。考察了染料初始浓度、催化剂投加量、溶液pH值、溶液温度、过氧化氢浓度、光强、乙醇等因素对紫外光催化降解酸性红B的影响。光催化反应对反应体系的温度不敏感，溶液温度降低对反应速率和平衡吸附量影响不大。其它因素都能显著影响光催化反应的进行。催化剂投加量和过氧化氢都存在一个最佳浓度，超过最佳浓度反而会降低反应效果。溶液pH值是通过改变催化剂表面电性而引起吸附物种的改变来影响反应效果，在等电点附近酸性红B处理效果最差。除Ag⁺外，Fe³⁺、Fe²⁺和Mn²⁺都能提高酸性红B在催化剂表面的平衡吸附量，但只有Fe³⁺和Ag⁺能够通过抑制电子-空穴的复合而起促进作用，Fe²⁺和Mn²⁺浓度越高阻碍作用越明显。NO₃^-离子作用不明显，SO₄^2-和Cl^-通过竞争吸附和捕获·OH抑制吸附和降解过程。IO₄^-在紫外光作用下能够生成·OH从而对反应起到促进作用。在太阳光条件下，2.5％ZrO₂／ZnO同样具有较高的光催化效率。通过等温吸附实验考察了催化剂用量、酸性红B初始浓度和溶液pH值对平衡吸附量的影响，并运用Langmuir和Freundlich等温吸附模型对酸性红B在ZnO和2.5％ZrO₂／ZnO表面的吸附规律进行模拟，然后分别计算并对比各参数值以及吸附自由能Δ_adG°来研究它们吸附性能的差异，说明2.5％ZrO₂／ZnO不仅具有较高的吸附能力，而且相对纯ZnO有所提高。酸性红B的光催化降解反应符合L-H准一级动力学模型。通过考虑中间产物等竞争吸附的影响对该模型进行修正。分别计算ZnO和2.5％ZrO₂／ZnO的修正前后的L-H反应动力学模型中各参数值以及半衰期表观值和计算值。说明2.5％ZrO₂／ZnO相对ZnO的较高的光催化活性，中间产物等对反应起到延迟作用。根据降解过程中TOC、pH、SO₄^2-、NO₃^-和NH₄⁺无机离子生成量以及UV-Vis光谱变化来分析酸性红B的脱色降解过程。随着反应的进行，脱色率不断提高，但是TOC的去除相对缓慢一些。根据溶液中总S和总N的理论值与实际检测值推断酸性红B的降解过程中-SO₃^-磺酸基和N的转化过程。脱-SO₃^-磺酸基和脱色反应均为初始反应，大部分N是以N₂形式释放出。总而言之，通过酸性红B的等温吸附实验和光催化降解实验结果，证明了本文合成的新型2.5％ZrO₂／ZnO复合光催化剂具有较高的吸附性能和催化活性，通过ZrO₂的复合提高了纳米ZnO的光催化性能，达到了既定目标，并且通过对偶氮染料酸性红B的影响因素和降解机理的研究不仅进一步充实了光催化机理内容也为该技术应用于实际污水处理提供了必要的参考。更多还原

【Abstract】 Nano-semiconductor photocatalytic technique has received considerable attentionfor treatment of environment pollutants. As an important photocatalyst, nano zincoxide （ZnO） was one of several semiconductors which could realize quantum sizeeffect and sometimes has better photocatalytic activities than TiO₂. In recent years, ithave attracted comprehensive attentions and showed a good prospect of applicationfor photocatalytic degradation of pollutants. But the photocatalytic efficiency ofsingle photocatalyst is relatively low, so it is of great importance to exploit novelphotocatalysts. At present, there are fewer studies on modification of nano ZnO thanTiO₂ so that how to improve its activities still need to be researched. And thephotocatalytic degradation mechanism still needs further study and perfection.The aim of this paper is to improve the photocatalytic activities of ZnO and prepareZnO-based composite catalysts coupled with ZrO₂ with excellent property by asimple and cheap synthesis route. The novel photocatalyst not only enlarge the typeof coupled oxide conductors with ZnO, but also perfect the photocatalyticmechanisms by kinetics of adsorption and degradation, and analysis of the reactionpathway. Moreover, it is of practical significance to realize its large-scale applicationin treatment of organic pollutants.The composite photocatalyst ZrO₂/ZnO was prepared by co-precipitation andthermal decomposition method, was characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM）, transmission electron microscopy （TEM）,differential thermal analysis-thermogravimetry （TG-DTA） and Fourier TransformInfrared （FT-IR）, and the effect of zinc source, calcinations temperature, calcinationstime and coupling ratio of Zr on the phase and catalytic property of ZrO₂/ZnO wasinvestigated. The results showed that owing to coupling with ZrO₂, the averagecrystallite size of 2.5％ZrO₂/ZnO was decreased, and its photocatalytic efficiency onacid red B was increased 11％, compared to pure ZnO, and slightly better thanDegussa P25 TiO₂, which showed photocatalytic activities of ZnO was improved.The influence of operational variables, such as initial dye concentration, catalyst dosage, pH, solution temperature, hydrogen peroxide concentration, light intensityand ethanol on UV photodegradation of acid red B was investigated. As thephotocatalytic reaction is not sensitive to solution temperature, and the decrease ofsolution temperature has limited impact on the reaction. Other factors have asignificant impact on the reaction. There is an optimal concentration of catalyst andhydrogen peroxide, and over it the reaction efficiency will be reduced. The effect ofpH on the reaction efficiency was affected by the change of electric adsorptionspecies on the catalyst surface and the worst effect was observed at isoelectric pointof 2.5％ZrO₂/ZnO. Except Ag⁺, Fe³⁺, Fe²⁺ and Mn²⁺ can improve the adsorption ofAcid Red B on the catalyst surface. Ag⁺ and Fe³⁺ favored the photocatalyticdegradation of acid red B, which was caused by the reduction of electron/holerecombination, the negative effect of Fe²⁺ and Mn²⁺ is enhanced with the increase oftheir concentration. NO₃^- has little effect on the reaction rate and adsorption of acidred B on catalyst surface. The inhibiting effect of SO₄^2-和Cl^- was caused by theircompetitive adsorption and capturing hydroxyl radical. IO₄^- can produce·OH topromote the reaction under UV. Under sunlight, 2.5％ZrO₂/ZnO still possesses higherphotocatalytic property.The effect of catalyst dosage, initial dye concentration and solution pH on theequilibrium adsorption amount of acid red B on catalyst in the adsorption isothermexperiment was investigated. The Langmuir and Freundlich isotherm adsorptionmodel was used to simulate the adsorption kinetics of acid red B on pure ZnO and2.5％ZrO₂/ZnO. Then their model parameters and free adsorption energy△_adG°were calculated and compared to study the differences of their adsorption properties.The results showed that 2.5％ZrO₂/ZnO not only have excellent adsorption property,but also was increased compared to pure ZnO.The photocatalytic degradation of acid red B follows L-H kinetic model. Themodel was modified for considering the competitive adsorption of intermediates. Thekinetic parameters before and after modification, the apparent and simulated half-lifevalues were calculated. It was showed 2.5％ZrO₂/ZnO has better photocatalyticproperty than pure ZnO and the intermediates have the inhibiting action.The decolorization and degradation of acid red B was analyzed according to the TOC decrease, pH variation, inorganic ion production of the dye solutions, such asSO₄^2-, NO₃^- and NH₄⁺, and change of UV-Vis spectra. With the reaction proceeded,decolorization rate was increased, but TOC removal was slower. The transformationof -SO₃^- and -N=N- in the degradation of acid red B was inferred from differencesbetween the theoretical value and the detected value of total S and total N. The -SO₃^-release and decolorization was the initial step, with the nitrogen of azo grouptransformed predominantly to N₂.To sum up, according to the experimental results of isothermal adsorption andphotocatalytic degradation of acid red B, if was proven that 2.5％ZrO₂/ZnOcomposite photocatalyst have higher adsorption and catalytic property and nano ZnOwas improved through coupling with ZrO₂, which achieve the research objective.Studies on the influence factors and degradation mechanism further enriched thephotocatalytic theory and provide the necessary information for the actual wastewatertreatment.更多还原