【作者】 陈浪；

【导师】 尹双凤；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2013， 博士

【摘要】 光催化在直接利用太阳能解决环境污染和能源短缺两大问题上表现出潜在的应用前景。在过去几十年里，这一领域正逐步地深入发展。光催化剂作为光催化的核心部分，研究和开发具有高活性的可见光催化剂成为光催化领域的难点和热点。目前光催化剂主要分为以氧化钛(TiO2)为代表的含TiO2光催化剂和不含TiO2的光催化剂两大类。这些光催化剂主要存在以下不足中的一点或者几点：(1)仅能吸收太阳光中的紫外光部分(仅占太阳光能量的4%)，在可见光区几乎没有响应；(2)催化剂对光的吸收效率不高；(3)光生电子和空穴的分离效率低；(4)光催化剂的稳定性差，容易发生光腐蚀；(5)光催化剂的制备过程复杂，需要引入有毒有害溶剂或者结构导向剂；(6)光催化剂难以实现规模化生产；(7)在太阳光下活性不高等。因此，开发绿色、简单、容易规模化生产的光催化剂合成方法，制备高效、稳定的可见光催化剂，揭示光催化剂与光催化活性之间的构效关系，是当前光催化领域的主要发展方向。本文结合含铋光催化剂大多具有可见光响应的优点以及通过构建异质结能够有效提高光催化剂活性的特点，采用简单的方法制备了一系列具有异质结的铋基复合光催化剂。采用多种表征手段对催化剂的结构、组成、形貌等物理化学性质进行表征分析，以在可见光下降解难降解的有机染料作为模型反应考察所制备催化剂的活性，并关联催化剂的结构与活性之间的构效关系。主要的研究内容与结果如下：1)以L-赖氨酸作为表面活性剂，采用乙二醇-水混合溶剂热法首次制得花生状单斜BiVO4(m-BiVO4)和空心多孔花生状Bi2O3-BiVO4复合光催化剂。在350W氙灯下照射40min，Bi2O3-BiVO4复合光催化剂能够完全降解亚甲基蓝(MB，2×10-5mol/L)，而BiVO4和Bi2O3对MB的光催化降解率仅为70%和20%，这可能是由于复合光催化剂多孔结构和粗糙表面有利于催化剂对光的吸收，有利于光生电子和空穴的产生；同时在Bi2O3和BiVO4间形成p-n结，能够有效地促进光生电子和空穴的分离，从而提高了BiVO4的可见光催化活性。2)在L-赖氨酸辅助溶剂热法制备花生状BiVO4的基础上，通过调变原料中的AgNO3量控制合成不同形貌和不同组成的复合物光催化剂，以期进一步改善BiVO4的光催化活性。当Ag的负载量为6.5wt%时，所得复合物为空心、多孔花生状，而且Ag颗粒均匀分布于BiVO4表面。Ag/BiVO4在可见光下催化降解亚甲基蓝和罗丹明-B (浓度均为2×10-5mol/L)的活性明显高于BiVO4以及Bi2O3-BiVO4复合光催化剂。这可能是由于Ag的引入不仅能够通过等离子体共振来扩展催化剂对可见光的吸收范围；而且由于Ag与BiVO4之间形成肖特基结(Schottky junction)能够有效地转移BiVO4上的光生电子，从而促进光生电子和空穴的有效分离。该一步法制备的Ag/BiVO4比采用传统光还原法制备的Ag/BiVO4具有更高的光催化活性，为制备贵金属负载纳米材料提供了新的方法。3)首先在无表面活性剂的情况下采用水热法制备空心管状Bi2O3，然后采用刻蚀-再生长法制备空心树状Bi2O3-Bi2S3复合光催化剂。该合成方法简单，无需引入有毒有害的有机溶剂或者结构导向剂等。所制备的复合催化剂在可见光下催化降解罗丹明-B的活性高于单独Bi2O3和Bi2S3。这可能是由于该复合光催化剂与Bi2O3基体相比其对可见光的吸收能力明显增强，而且存在Bi2O3-Bi2S3异质结有利于光生电子空穴的有效分离。4)采用乙二醇作溶剂，L-赖氨酸作结构导向剂，硫氰化钾和硫脲为硫源，采用一步溶剂热法制备出多孔海绵状和刺猬状的三维有序CuS-Bi2S3复合光催化剂。复合光催化剂能够有效提高Bi2S3在可见光下催化降解罗丹明-B等染料的光催化活性。这可能是由于复合物由超薄纳米片(20nm左右)或者长径比较大的纳米棒组成，有利于光生电子和空穴的迁移；另一方面形成的CuS-Bi2S3异质结能够有效抑制由于硫化铋价带和导带太近导致的光生电子和空穴的复合。此外，该复合光催化剂对含有罗丹明-B和结晶紫的混合染料溶液也具有较好的光催化活性。5)首次在室温下以水作溶剂、L-赖氨酸做结构导向剂快速合成了三维有序花状BiOX (X=Cl、Br、I)，这为制备BiOX光催化剂提供了一种绿色、快速、节能且具有普适性的新方法；还在室温下以十六烷基三甲基溴化铵(CTAB)作表面活性剂，水作溶剂快速合成了花状Bi2O2CO3和BiOI-Bi2O2CO3复合光催化剂。复合光催化剂不仅在可见光下表现出比单独BiOI和Bi2O2CO3更高的活性；而且该复合光催化剂对多种染料均具有普遍适用性和良好的稳定性，催化剂重复使用十次其活性基本不变。这可能是由于在BiOI和Bi2O2CO3间形成异质结(p-n结)，能够促进BiOI-Bi2O2CO3复合物中光生电子和空穴的有效分离。该合成方法简单，容易实现大规模生产，具有潜在的工业应用价值；该方法有望用于其他含铋非金属氧化物光催化剂的合成。更多还原

【Abstract】 Photocatalysis, one important potential method for environmental remediation andclean energy production by using solar energy, has been developing quickly in the pastdecades. Photocatalyst is the core part of photocatalysis. Development of highly efficientand visible light driven photocatalysts is still a big challenge and has being a hot topic inthe field of photocatalysis. Many photocatalysts have been developed in the past decadesand can be divided into two categories: TiO2or TiO2-containing photocatalysts,non-TiO2-containing photocatalysts. However, the reported photocatalysts have one ormore disadvantages below:(1) only be excited by ultraviolet light which takes only4%of the solar energy;(2) low light absorption efficiency;(3) low efficiency in chargecarriers separation;(4) unstable and serious photocorrosion;(5) complicated preparationmethods, requirement of toxic solvent and/or structure-directing agent;(6) difficulty inlarge-scale synthesis;(7) low photocatalytic activity under the irradiation of solar light.So developing of green and facile methods for scale-up synthesis of high-efficiency,stable and visible-light-driven photocatalysts is a great issue in photocatalysis technique.What’s more, the study on the relationship between photocatalytic performances andstructures of catalysts is another great issue.Considering that most of the bismuth-containing photocatalysts can be excited undervisible light and construction of heterojunctions can enhance photocatalytic activities. Aseries of bismuth-containing composite photocatalysts with heterojunctions weresynthesized by facile methods in this thesis. The physical and chemical properties of theas-prepared samples were characterized by various techniques. The photocatalyticactivities were evaluated by degradation of organic dyes under visible light irradiationand the relationship between strucutures and catalytic performances was invesitigated.Listed below are the results:1) By a simple solvothermal method using ethylene glycol and water as solutionand L-lysine as surfactant, peanut-like BiVO4and hollow, porous Bi2O3-BiVO4composite were successfully synthesized. The Bi2O3-BiVO4composite showed highactivity towards methylene blue (MB，2×10-5mol/L) degradation under a Xe lamp (350W), much higher than BiVO4and Bi2O3. This could be ascribed to the porous andunsmooth surface of the Bi2O3-BiVO4composite, which is favorable for light absorptionand thus enhance the amount of photogenerated charges. Then the charge carriers could be efficiently separated on the p-n junctions between Bi2O3and BiVO4.2) Ag-doped BiVO4composites with hollow and porous structures were preparedby keeping the Ag amount at6.5wt%. The hollow and porous Ag/BiVO4showed highervisible-light-driven catalytic activity than BiVO4towards degradation of dyes(rhodamine B and methylene blue,2×10-5mol/L, respectively). The results could beowing to the enhancement of visible light absorption ability by multiple scattering oflight and plasma resonance of Ag on the surface. What’s more, the schottky junctionbetween Ag metal and BiVO4can promote charges separation. It also showed muchhigher activity than Ag/BiVO4composite prepared by traditional method (namely aphotoreduction method for Ag doping).3) The hollow and branched Bi2O3-Bi2S3composite was synthesized from Bi2O3microtubes by a so-called corrosion-regrowth method. The preparation process is simpleand environmental-friendly, without using any organic solvent or toxic surfactants. Thecomposite showed higher activity than Bi2O3and Bi2S3towards Rh-B degradation undervisible light irradiation. It was deduced that the good photocatalytic activity is closelyrelated to high visible light absorption ability of the composite and the presence ofheterojunctions between Bi2O3and Bi2S3.4) Porous spongy-like and urchin-like CuS-Bi2S3composites were successfullysynthesized using Bi(NO3)3·5H2O as Bi source, potassium thiocyanate (PT) and thiourea(TU) as sulfur sources, respectively. The porous spongy-like composites were composedfrom ultrathin nanoplates (about20nm) which intercrossed with each other, and theurchin-like ones composed from nanoneedles radially grown from a center. Thevisible-light-driven photocatalytic activity of Bi2S3towards dyes decomposition (Rh-B,crystal violet and a mixture of them) was greatly improved by coupling with CuS.Because the ultrathin nanoplates as well as the nanoneedles are favorable for chargestransfer; the recombination of photogenerated electrons and holes on Bi2S3can be greatlyprevented due to the presence of heterojunctions between CuS and Bi2S3.5) For the first time, flower-like BiOX (X=Cl, Br, I), Bi2O2CO3andBiOI-Bi2O2CO3composites were fast synthesized at room temperature using water assolvent, L-lysine and cetyltrimethyl ammonium bromide (CTAB) as surfactant,respectively. It provides a green, fast, energy-saving and universal way for thepreparation of BiOX photocatalyst or other bismuth-containing oxides. TheBiOI-Bi2O2CO3composite showed much higher activity for dyes degradation undervisible light than BiOI and Bi2O2CO3, since the p-n junctions were formed, and thevisible light absorption and charges separation abilities of the compoiste were enhanced. It also showed good reusability and stability, there is no apparent loss of activity after10cycles. The composite photocatalyst will find wide applications in wastewater treatmentdue to its high activity, stability and simple for scale-up preparation prodedure.更多还原