摘要
能源与环境是二十一世纪人类面临和亟待解决的两大世界性的问题。自从1972年日本科学家Fujishima和Honda在二氧化钛电极上发现光催化分解水以来,太阳光诱导光催化反应被普遍认为是一种将太阳能转化为氢能源的有效途径,可以有效解决能源短缺问题；随后,人们又发现光催化反应还拥有速度快、条件温和、无二次污染、降解有机物完全等优越性能而成为一种理想的环境污染治理技术。因此采用半导体化合物进行光催化分解水产氢(能源光催化)以及光催化降解污染物(环境光催化)受到了人们的普遍关注。本论文就能源光催化与环境光催化两个方面分别对硫化镉与二氧化钛的光催化活性的提高进行了研究。
在能源光催化方面,我们通过简便的溶剂热法制备出一种硫化镉-石墨烯纳米复合材料,然后对其做了以下的表征和测试：X射线衍射分析、透射电子显微分析、比表面积和孔径分析、紫外-可见漫反射光谱分析、X射线光电子能谱分析、红外光谱分析和可见光催化分解水产氢活性分析。结果发现,复合物中的石墨烯促进了硫化镉半导体的结晶,增大了其比表面积,且适量的石墨烯可大大增加复合物的催化活性。原料中,氧化石墨烯与二水醋酸镉的最佳质量比为1.0wt%,此时复合物以乳酸为牺牲剂,在0.5wt%贵金属Pt的的共催化作用下的可见光催化分解水产氢速率可高达1.12mmol·h-1,420nm处相应的表观量子效率为22.5%。结果说明石墨烯不仅可以作为半导体纳米颗粒的良好载体,还能作为电子的捕获者和传输者,大大延长光生载流子的寿命。这一研究不仅说明了石墨烯作为半导体材料的载体在光催化分解水制氢方面的作用,还揭示了石墨烯基材料在能源转化领域中的潜在应用。
在环境光催化方面,我们利用阴离子掺杂的方法对二氧化钛进行改性,先将钛酸丁酯和一种BMIM+BF4-离子液体的水溶液进行水热处理,再对所制得的粉体进行短时间的不完全煅烧,得到新型的氟化硼碳共掺杂二氧化钛纳米颗粒。我们对所制得的催化剂做了以下的表征和测试：X射线衍射分析、透射电子显微分析、比表面积和孔径分析、X射线光电子能谱分析、紫外-可见漫反射光谱分析和可见光催化降解罗丹明B染料活性分析。结果发现,离子液体在制备过程中可同时作为二氧化钛的形貌控制剂和掺杂剂。表面氟化可以增强二氧化钛对阳离子染料罗丹明B的表面吸附；硼掺杂可以在二氧化钛中生成Ti3+能级和氧空位,延长光生载流子的寿命；而碳掺杂有利于催化剂的可见光响应。因此,优化的形貌和氟、硼、碳共掺杂的协同作用共同导致所制备的催化剂拥有理想的可见光催化活性,其中最佳样品的降解表观速率常数为2.78×10-2min-1,比商用P25的速率常数(1.16×10-2min-1)高了140%。这种新型的氟化硼碳共掺杂锐钛矿二氧化钛纳米颗粒的制备方法及其优异的光催化活性和高稳定性为形貌可控的多元素掺杂半导体材料的合成提供了新的思路,更进一步的促进了光催化在环境方面的应用。
In the21st century, energy and environment are the two major global problems to be solved. Since Japanese scientists Fujishima and Honda found the photocatalytic splitting of water on titanium dioxide electrode in1972, sunlight induced photocatalytic reaction has been generally considered to be a way to convert solar energy into hydrogen energy, which can effectively solve the energy shortage; then, it has been found that the photocatalytic reaction also has many advantages like mild conditions, no secondary pollution, complete degradation of organic matters, and so on, which can become an ideal environment pollution control technology. Therefore, the semiconductor photocatalytic hydrogen production (energy photocatalysis) and photocatalytic pollutant degradation (environmental photocatalysis) are in a widespread concern. In this paper, the improvement of the photocatalytic activity of cadmium sulfide and titanium dioxide for energy and environmental photocatalysis, respectively, were studied.
For energy photocatalysis, a graphene-CdS nanocomposite material was prepared by a solvothermal method, followed with the characterizations and tests such as X-ray diffraction analysis, transmission electron microscopy, N2adsorption-desorption, UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy and visible-light photocatalytic hydrogen production analysis. It was found that graphene nanosheets in the composite enhance the crystallinity and the specific surface areas of CdS clusters, and a low amount of graphene can dramatically improve the photocatalytic activity. The optimal weight percentage of graphene was found to be1.0wt%, which resulted in a high visible-light photocatalytic H2-production rate of1.12mmol-h-1and corresponding apparent quantum efficiency of22.5%at420nm with0.5wt%Pt as a cocatalyst. The results demonstrate that the unique features of graphene make it an excellent supporting material for semiconductor nanoparticles as well as an electron collector and transporter to separate photogene rated electron-hole pairs. This work not only demonstrates the potential of graphene as a support for CdS nanoparticles in photocatalytic hydrogen production, but also highlights more generally the potential application of graphene-based materials in the field of energy conversion.
For energy photocatalysis, fluorinated B/C co-doped anatase TiO2nanoparticles were prepared by a hydrothermal method followed with a controlled calcination process. The characterizations and tests such as X-ray diffraction analysis, transmission electron microscopy, N2adsorption-desorption, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, and visible-light photocatalytic RhB degradation analysis were carried out. It was found that the ionic liquid (IL) BMIM+BF4-played dual roles in the formation of the photocatalyst. One is to control the structure, making TiO2crystals grow uniformly with large specific surface area due to the "capping effect" of IL; the other is to behave as the F, B, and C dopant sources. In the doped TiO2, the surface fluorination favors the absoroption of RhB molecules in the TiO2/dye system, B doping induces the formation of Ti3+level and oxygen vacancies and improves the quantum efficiency, and C doping is responsible for the strong visible-light response of the photocatalyst. Thus, the modified mophology and synergic contributions of F, B and C dopants result in the excellent visible-light photocatalytic degradation rate of RhB, which is140%higher than that of commercial P25. The novel fluorinated B/C co-doped anatase TiO2nanoparticles with outstanding photocatalytic performance and the proposed contributions of specific active species involved in the dye degradation could provide new insights on the design of morphology-controlled multi-doped semiconductor materials, and be very promising for wide environmental applications.
引文
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