【作者】 沈敏；

【导师】 陈浩；

【作者基本信息】 华中农业大学 ， 食品科学， 2011， 博士

【摘要】 随着工业化发展带来的环境污染日益严重,越来越多的有毒有害物质通过大气、水体和土壤进入食品从而危及人类的健康。环境污染因素已成为威胁食品安全的重要因素之一,而半导体光催化剂在解决环境污染方面有着巨大的应用前景。由于光催化剂的晶相、比表面积、微观形貌和表面结构等性质与性能直接相关,因此,通过改变制备方法和条件来实现晶相、尺寸、微观形貌和表面结构等局部可控的微／纳米材料的制备,探讨其形成机理及其对光催化性能的影响具有重要的理论价值和实际意义。为此,本论文开展了具有特殊微观形貌和暴露晶面的NiMoO4、PbMoO4和Bi2Mo06的合成研究,深入探讨了反应条件等对产物的晶相、微观形貌、暴露晶面、光吸收和光催化性能的影响,初步揭示了其形成机理,并推测光催化材料具有较高的催化活性的内在因素。最后,选择高活性具有可见光响应的光催化材料用于对食品安全构成较大隐患的抗生素的光催化降解研究。主要内容如下：(1)采用简单的水热法制备了具有一维结构的NiMoO4·0.91H2O纳米棒,探讨了反应条件对产物晶相、微观形貌的影响。在500-900℃下煅烧5小时得到单斜晶相的a-NiMoO4,其微观形貌仍为纳米棒结构。将a-NiMoO4负载Ag后考察其光催化降解罗丹明B的活性,相比于a-NiMoO4,负载Ag后光催化降解活性有明显的增强。(2)采用十六烷基三甲基溴化铵(CTAB)为晶面导向剂,通过简单的水热法成功制备了(001)面优势暴露的PbMoO4微晶体。讨论了CTAB的加入量和水热温度对PbMoO4微晶体微观形貌与暴露晶面的影响。实验结果表明,控制CTAB加入量与水热温度能够控制(112)与(001)晶面的衍射峰强度比(I112/I004)。当CTAB浓度为0.05mol/L时,180℃水热反应24h得到的产品表现出明显的(001)优先暴露,I12/I004=0.08。另外,所得(001)晶面优先暴露的PbMoO4微晶体的光催化降解罗丹明B(RhB)活性优于常规水热法制备的(112)晶面优势暴露的PbMoO4微晶体以及商用二氧化钛光催化剂(P25)。(3)在HN03辅助的条件下,通过调节水热反应条件可控地制备了具有分等级结构的PbMoO4微米球,并初步探讨了水热温度、水热时间和HNO3浓度对产物的微观形貌、晶相及其光吸收性能的影响及其形成机理。实验结果表明,在0.5-1.0mol/L的HN03溶液中160℃水热反应24 h制备得到由-230 nm的板状微米片自组装形成的直径为5-10μm的微米球；不存在HNO3时,只得到了不规则的PbMoO4纳米粒子和由纳米粒子组成的团聚体。这一简单的制备方法可以为合成其他分等级结构的微/纳米材料提供了一条可供借鉴的途径。光催化降解实验结果表明,分等级的PbMoO4微米球表现出卓越的光催化性能。(4)采用简单的水热反应,通过调节pH值成功制备了(010)面优势暴露的Bi2Mo06纳米片。并初步探讨了水热pH、水热时间、水热温度和CTAB浓度对产物的晶相、微观形貌及其光吸收性能的影响及其形成机理。结果表明,控制水热pH能够控制(131)与(010)晶面的衍射峰强度比(I131/I010)。当pH=10时,140℃水热反应72 h得到的产品表现出明显的(010)优先暴露,I131/I010=0.54。光催化降解实验结果表明,该(010)晶面暴露的Bi2Mo06纳米片表现出更优越的光催化降解性能。(5)利用具有可见光响应的(010)晶面暴露的Bi2M006纳米片作为光催化剂,应用于对食品安全构成较大隐患的抗生素-土霉素(OTC)和四环素(TC)的光催化降解研究。探讨了溶液pH,催化剂的用量,初始浓度等对光催化降解OTC和TC的影响。结果表明,对于初始浓度为20 mg/L的OTC和TC溶液,加入140 mg光催化剂,在pH=11的条件下,可见光照射1h即可降解42.1%的OTC和58.8%的TC。对OTC和TC的光催化降解动力学曲线符合Langmuir-Hinshelwood模型,其动力学常数分别为0.00664和0.00845 mmin-1。利用自由基清除剂来考察在光催化过程中由哪些活性物质起主要作用。结果表明,空穴对光催化降解OTC和TC起主要作用。更多还原

【Abstract】 With the industrialization of the increasingly serious environmental pollution caused by more and more toxic and harmful substances through the atmosphere, water and soil into the food and thus endanger human health. Environmental factors have become important factors threatening food security, one of the semiconductor photocatalyst in solving environmental pollution has a great prospect. As photocatalyst crystalline phase, specific surface area, morphology and surface structure are directly related to the nature and properties. Thus, by changing the preparation methods and conditions to achieve the crystalline phase, size, morphology and surface structure of local control of micro/nano materials, to explore the formation mechanism of its photocatalytic properties, which has important theoretical and practical significance. Hence, in the present paper, NiMoO4 nanorods, PbMoO4 microcrystals with preferentially exposed (001) facets, hierarchical PbMoO4 microspheres and Bi2MoO6 microcrystals with preferentially exposed (010) facets were prepared. Moreover, the effects of reaction conditions on crystalline phase, morphology, exposed crystal facets, light absorption and photocatalytic performance of the obtained samples were also primarily discussed, which is initially revealed their formation mechanism, and speculated the underlying factors on the photocatalytic material with high photocatalytic activity. The photocatalysis degradation of two antibiotics widely used in both human and veterinary medicine:oxytetracycline (OTC) and oetracycline (TC) in aqueous were investigated by Bi2MoO6 nanoplates with preferentially exposed (010) facets under visible light irradiation. The detail researches and the conclusions are summarized as follows:1. One dimensional NiMoO4·0.91H2O nanorods has been synthesized by a facile hydrothermal method. The effect of different synthetic conditions on the morphologies of the final products was investigated. NiMoO4·0.91H2O nanorods can be further converted to monoclinic a-NiMoO4 nanorods by calcinating at 500-900℃for 5 h without significant alteration of the nanorod structure. The photocatalytic property of the obtained a-NiMoO4 nanorods and Ag-loaded a-NiMoO4 nanorods has been tested by degradation of Rhodamine B (RhB) under UV light irradiation.2. Lead molybdate (PbMoO4) microcrystals with preferentially exposed (001) facets have been synthesized by a facile surfactant-assisted hydrothermal process in the presence of cetyltrimethylammonium bromide (CTAB). The effects of the CTAB addition amount, hydrothermal temperature on the morphologies and the crystal facets of PbMoO4 were investigated in detail. Experimental results indicate that the diffraction peak intensity ratio of (112) to (001) crystal facets for the product can be delicately controlled by simply adjusting the addition amount of CTAB and hydrothermal temperature. And the products derived from hydrothermal treatment at 180℃for 24 h in the presence of 0.05 mol/L CTAB exhibit an obvious exposed (001) facets with minimum peak intensity ratio (I112/004=0.08) of the (112) and (004) crystal facets. Moreover, the obtained PbMoO4 with preferentially exposed (001) facets exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under UV light irradiation in comparison with the PbMoO4 obtained in absence of CTAB and the commercial phototcatalyst (P25).3. Hierarchical PbMoO4 microcrystals were synthesized via a simple nitric acid-assisted hydrothermal process without addition of template or organic directing reagent. The scheelite-type tetragonal PbMoO4 with various hierarchical microstructures can be controllably fabricated by adjusting the experimental conditions such as hydrothermal temperature, time and nitric acid concentration. Experimental results indicate that hierarchical PbMoO4 microspheres with a size of 5-10μm, which are assembled by slablike microcrystals with an average thickness of～230 nm, can be obtained from a hydrothermal treatment at 160℃for 24 h in the presence of HNO3 solution, whereas only irregular particles and aggregations are obtained without HNO3 solution. The hierarchical PbMoO4 microspheres show more excellent photocatalytic activity than the irregular PbMoO4 particles for the degradation of rhodamine B (RhB) under UV light irradiation. Furthermore, a possible nitric acid-assisted formation mechanism for the hierarchical PbMoO4 microspheres is proposed, which might represent a new fabrication strategy for other nano/microstructures with desired morphology.4. Bismuth molybdate (Bi2MoO6) nanoplates with preferentially exposed (010) facets have been synthesized by a facile hydrothermal process. The effects of pH, hydrothermal temperature and the CTAB addition amount on the morphologies and the crystal facets of Bi2MoO6 were investigated in detail. Experimental results indicate that the diffraction peak intensity ratio of (131) to (010) crystal facets for the product can be delicately controlled by simply adjusting the pH value of the reactant. And the products derived from pH=10 at 140℃for 72 h in the presence of 0.03 mol/L CTAB exhibit an obvious exposed (131) facets with minimum peak intensity ratio (I131/I010=0.54) of the (131) and (010) crystal facets. Moreover, the obtained Bi2MoO6 nanoplates with, preferentially exposed (010) facets exhibits greatly enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light irradiation.5. The aim of this study is the evaluation of photocatalysis to degrade two antibiotics widely used in both human and veterinary medicine:oxytetracycline (OTC) and oetracycline (TC), in Bi2MoO6 aqueous suspension under visible light irradiation. The effects of catalyst amount, initial pH value, and initial concentration of each substrate on the photocatalytic degradation rates were investigated in detail. Experimental results indicate that pH has a significant effect on OTC and TC degradation. The optimal values of the operation parameters under the related constraint conditions were found at pH= 11.0, BilMoO6 concentration of 1.4 g/L and initial concentration of 20 mg/L. Under this condition,42.1% of OTC and 58.8% of TC were degraded under visible light irradiation for 60 min, respectively. The disappearance of these two compounds follows a pseudo-first-order kinetics according to the Langmuir-Hinshelwood (L-H) model and the rate constants were 0.00664 and 0.00845 min-1 for OTC and TC, respectively. It was observed that the surface reaction on BiiMoO6 played a important role in the degradation of OTC and TC, and the further study of reactive oxygen species (ROSs) indicated that the photohole (h+) was responsible for the major degradation of OTC and TC.更多还原