蜂窝状Bi2WO6/TiO2中空微球的微孔淀粉模板法合成及其可见光催化降解乙烯基础研究

Ethylene which is produced by respiration of postharvest fruit and vegetable is one of the main causes leading to the decay of fruit and vegetable. Nano-TiO2 has a capacity of photocatalytic degradation of ethylene. However, the main drawbacks of TiO2 are its relatively large band-gap and low photocatalytic efficiency, which limit its practical application. In the program, microporous starch, as a template, combines Bi2WO6 semiconductor with nano-TiO2 semiconductor to compose a honeycomb hollow microsphere which has high specific surface area. On a macro level, the amplitude bound of ethylene degradation rate under visible light is studied to find how much an impact hollow microspheres have on the degradation rate; on a micro level, the relationship with the structure and performance of the microspheres and its photocatalytic activity is also researched; in theory, the mechanism of action relating to the composite of Bi2WO6 and TiO2 along with the structure of honeycomb hollow microspheres will be explored in the first time to discover how the composite improves ehtylene' degradation under visible light. All the studies are expected to find a new approach to improve TiO2 photocatalytic activity and a new photocatalytic synergistic effect. Meanwhile, optimal preparation conditions of hollow microspheres which could degrade ethylene rapidly will be found, as well as photocatalytic reaction optimization conditions and establishing dynamic model. Through this research, we could both offer theoretical guidance and practical basis for the preparation of the new visible light catalytic material which have special morphologies, and open a new avenue for the removal of ethylene in fruit and vegetable storage environment, and then lay the foundation for the development of the new technology for fruit and vegetable preservation.

采后果蔬因呼吸作用产生的乙烯是造成其腐烂变质的主要原因之一。纳米TiO2 具有光催化分解乙烯能力，但带隙能较宽，光催化效率低，使其实际应用受到限制。本项目以微孔淀粉为模板，将钨酸铋（Bi2WO6）和纳米TiO2两种半导体复合构筑出高比表面积的蜂窝状中空微球。从宏观上研究制备的中空微球对提高可见光催化降解乙烯的可能幅度；从微观上研究微球的结构、性能与其可见光催化活性的关系；从理论上探明Bi2WO6与TiO2复合以及蜂窝状中空微球结构所产生的提高可见光催化降解乙烯的机制，有望发现能增强TiO2可见光催化活性的新途径及新的光催化协同效应。找出在可见光下能较快降解乙烯的中空微球的最佳制备条件和进行光催化反应的优化条件并建立动力学模型。通过研究既能为特殊形貌的新型可见光催化材料的制备提供理论指导和实践依据，又能为果蔬贮藏环境中乙烯的脱除技术开辟新途径，进而为果蔬保鲜新技术的开发奠定基础。

乙烯（又称植物催熟激素）是造成果蔬腐烂变质的主要原因，清除果蔬贮藏环境中乙烯对果蔬保鲜具有重要意义。本项目通过溶剂热法制备出较高可见光催化活性的TiO2-Bi2WO6纳米复合材料，在溶剂热法的基础上，采用碳微球模板和无模板法设计合成出TiO2-Bi2WO6中空微球，采用XRD、SEM、TEM、Raman光谱、UV-Vis、XPS等分析技术对复合材料和中空微球的结构进行表征，并研究了纳米复合材料和中空微球可见光催化降解乙烯的性能。研究表明，TiO2-Bi2WO6复合材料呈片状，粒径约30nm左右，通过溶剂热法掺杂改性，使纳米TiO2进入到Bi2WO6晶格中，形成交错式二元异质结，并细化了复合材料的平均晶格粒径，从而拓宽了复合材料的可见光响应范围，使光生电荷载流子得以有效分离，复合材料对乙烯的降解率明显提高，分别是纳米TiO2和Bi2WO6粉体的3.19倍和1.35倍。TiO2-Bi2WO6中空微球呈球状中空结构，直径约1μm，与纯TiO2和Bi2WO6中空微球相比，复合中空微球晶体表面氧空缺和晶格缺陷增多，Ti、Bi、W共享部分氧原子，形成Ti-O-Bi键和Ti-O-W键，其吸收波长阈值拓展到430nm，禁带宽为2.884eV，在可见光下对乙烯的降解率高达19.9%，是Bi2WO6中空微球的2.06倍和TiO2粉体的3.54倍。通过TiO2与Bi2WO6复合，设计合成出中空微球结构，可使材料的比表面大大增加，禁带宽度更窄，具有更高的量子效率和更强的捕光能力，宏观上表现出更优越的可见光催化活性。