【作者】 张江；

【导师】 康飞宇；

【作者基本信息】 清华大学 ， 材料科学与工程， 2012， 博士

【摘要】 Bi₂Wo₆作为一种窄带隙半导体，其禁带宽度为2.7eV，表现出优异的可见光催化性能。然而，由于Bi₂Wo₆分子量较大，通常获得的Bi₂Wo₆晶粒尺寸较大而导致光生电荷载流子的复合几率较高，因而实际中Bi₂Wo₆的光催化活性并不高。为了获得高活性的Bi₂Wo₆光催化剂，本论文采用水热法对Bi₂Wo₆进行不同非金属元素I、S、N和C的掺杂改性，通过XRD、SEM、TEM、红外光谱、Raman、XPS及DRS等分析表征手段对改性Bi₂Wo₆的晶相结构、显微结构、光学性质及掺杂元素的化学态进行研究，并探讨了不同改性方式对光催化性能的影响。由于I原子半径较大，很难置换晶格氧而发生置换掺杂。本论文通过对样品中I元素化学态的研究，提出了I2和I-对Bi₂Wo₆晶体的表面共掺杂机理。光吸收性质和RhB的光催化降解结果表明：表面掺杂物I2和I-不仅增加了可见光响应能力，而且还可以有效提高光生电子和空穴的分离效率，最终导致可见光催化活性提高。与I元素相比，S原子半径相对小一些，但仍比氧原子半径大很多，因而只有一小部分S掺杂进入Bi₂Wo₆晶格，另一部分则形成了Bi2S3晶相。Bi2S3是一种窄带隙半导体，可以对Bi₂Wo₆起到光敏化作用而导致带隙的窄化。S掺杂和Bi2S3/Bi₂Wo₆异质结的协同作用导致可见光响应和光催化活性提高。不同于I掺杂和S掺杂，由于N原子半径与O原子半径接近，容易置换晶格氧而形成置换掺杂。研究采用尿素为氮源对Bi₂Wo₆进行N掺杂，显著提高了Bi₂Wo₆的可见光催化活性。将TiO₂包覆在N掺杂Bi₂Wo₆的颗粒表面形成TiO₂/N-BWO异质结，样品的紫外光和可见光催化活性均显著提高。N掺杂可以窄化带隙，而TiO₂/N-BWO异质结可有效抑制光生电荷载流子的复合。C原子半径与O原子半径接近，但稍大于N原子半径，也可有效实现晶格氧的置换掺杂。研究中采用石墨烯作为碳源对Bi₂Wo₆进行掺杂改性，不仅形成了石墨烯/Bi₂Wo₆异质结，而且实现了Bi₂Wo₆的C掺杂。该方法克服了N掺杂过程中N源易挥发的缺点，实现了C元素的有效置换掺杂。C掺杂可以有效窄化带隙，提高可见光响应能力；石墨烯/Bi₂Wo₆异质结可以有效提高光生电子的迁移速度。更多还原

【Abstract】 Bi₂Wo₆was regarded as a narrow band gap semiconductor with a band energy of2.7eV， exhibiting the excellent visible-light-induced photocatalytic performance.However, in general, a larger crystalline size of Bi₂Wo₆was obtained owing to its largemolecular weight, which resulted in a higher recombination rate of photo-inducedcharge carriers. Thus, the photocatalytic activity of Bi₂Wo₆was lower than thetheoretical value in practice use. To obtain the highly active Bi₂Wo₆photocatalyst, inthis work, the modification of Bi₂Wo₆was carried out by the doping of differentnonmetallic elements of I, S, N and C via a hydrothermal method. The crystalline phasecomposition, microstructure and optical properties of modified Bi₂Wo₆and thechemical states of doping elements were investigated by XRD、SEM、TEM、FT-IR、Raman、XPS and UV-Vis diffuse reflectance spectra. Moreover, the effects of differentmodification methods on the photocatalytic performances were also discussed.The substitution of lattice oxygen was very difficult to be carried out owing to thelarge atomic radius of iodine species. In this study, the mechanism of the surfaceco-doping of I2and I-was proposed by the analysis of the chemical states of iodinespecies. The photo-absorption property and the photo-degradation of RhB indicated thatI2and I-as the surface dopant not only improved the visible-light photo-responsivity,but also enhanced the separation of photo-induced electrons and holes efficiently,resulting in the enhanced visible-light-induced photocatalytic activity.The atomic radius of sulfur is smaller than that of iodine, but is larger than that ofoxygen. Therefore, only one small amount of sulfur was doped into the lattice ofBi₂Wo₆, the other of sufur was used to form the crystalline phase of Bi2S3. Bi2S3as asemiconductor with a narrow band gap, would result in the narrowing of band gap bythe photosensitization for Bi₂Wo₆. The improved visible-light photoresponsivity andphotocatalytic activity were caused by the synergetic effect of sulfur-doping andBi2S3/Bi₂Wo₆heterojunction.Different from the cases of iodine-doping and sulfur-doping, the substitutionaldoping was prone to be carried out by the substitution of the lattice oxygen atom withnitrogen atom owing to the similar atomic radius of nitrogen and sulfur elements. The nitrogen-doping of Bi₂Wo₆was carried out by using urea as a nitrogen source,improving the visible-light-induced photocatalytic activity. The TiO₂/N-BWOheterojunction was formed by the coating of TiO₂on the surface of nitrogen-dopedBi₂Wo₆particles, resulting in the enhanced ultraviolet-light and visible-light-inducedphotocatalytic activities. Nitrogen doping resulted in the narrowing of band gap, whilethe TiO₂/N-BWO heterojunction inhibited the recombination of photo-induced chargecarriers efficiently.Although the atomic radius of carbon species is slightly larger than that of nitrogenspecies, the lattice oxygen atom was also substituted efficiently by carbon atom owingto the similar atomic radius of carbon and oxygen elements. The doping modification ofBi₂Wo₆was carried out using graphene as a carbon source. The carbon doping andgraphene/Bi₂Wo₆heterojunction was formed together. The substitutional doping ofcarbon species was obtained efficiently by avoiding the disadvantage of nitrogen sourcein the procedure of nitrogen doping. The narrowing of band gap was caused by thecarbon doping, improving the visible-light photo-responsivity. The efficient transfer rateof photo-induced electrons was caused by the heterojunction of graphene/Bi₂Wo₆.更多还原