【作者】 黄立英；

【导师】 程晓农；

【作者基本信息】 江苏大学 ， 材料学， 2013， 博士

【摘要】 随着现代社会的快速发展,能源短缺和环境污染问题严重影响和威胁着人类的生活。光催化技术作为一种绿色高级氧化技术,在环境污染治理和能源开发领域有着广泛的研究和应用。开发高效、高稳定性光催化剂已经成为光催化研究的热点。本论文旨在充实新型可见光催化材料石墨相氮化碳(g-C3N4)在光催化领域的应用,合成了高可见光催化活性的g-C3N4/MoO3、 WO3/g-C3N4、CeO2/g-C3N4和皂土/g-C3N4新型复合光催化材料,并考察了复合材料在降解环境有机污染物领域的应用。采用XRD、XPS、SEM、TEM、 BET、DRS、PL等测试手段对所合成的光催化剂的结构、形貌、光催化性能及其构效关系进行深入研究。具体研究内容如下：1.通过超声分散-热处理法合成了g-C3N4/MoO3复合光催化材料。采用XRD、SEM、HRTEM、IR、XPS、DRS等方法对光催化材料进行表征分析。XRD分析表明,g-C3N4的掺杂未改变Mo03的晶体结构。SEM和HRTEM分析结果显示g-C3N4与Mo03形成了异质结界面。DRS分析发现复合材料与MoO3相比在可见光区的吸收增强。可见光催化降解亚甲基蓝(MB)实验表明,g-C3N4/MoO3光催化降解MB符合一级反应动力学特征,其中g-C3N4/MoO3(7%)复合材料具有最高的光催化活性,光照3h后MB降解率达93%,其降解速率常数分别为单体Mo03和g-C3N4的4.2倍和1.9倍。构效关系研究表明,复合材料的高活性来源于Mo03和g-C3N4之间形成异质结结构,促进了光生电子和空穴的分离。2.采用二步煅烧法合成了WO3/g-C3N4复合光催化材料。运用TG、XRD、 SEM-EDS、TEM、HRTEM、XPS、IR、DRS等方法对光催化材料进行表征分析。XRD、IR、XPS、SEM-EDS结果表明复合材料由W03和g-C3N4组成。SEM、TEM和HRTEM分析结果显示W03与g-C3N4形成紧密的异质结界面。DRS分析发现W03的引入拓宽了g-C3N4在可见光区的吸收。比表面与吸附实验表明WO3/g-C3N4具有比g-C3N4更大的比表面积和暗反应吸附容量。可见光催化降解MB实验表明,WO3/g-C3N4光催化降解MB符合一级反应动力学特征,其中WO3/g-C3N4(9.7%)复合材料具有最高的光催化活性,光照2h后MB降解率达97%,其降解速率常数分别为单体W03和g-C3N4的4.2倍和2.9倍。光催化降解4-氯酚(4-CP)实验排除了染料敏化作用。PL和EIS结果显示WO3/g-C3N4具有比g-C3N4更强的光生电子和空穴分离能力。光催化机理分析表明W03和g-C3N4之间的能带位置有利于光生电子和空穴的迁移和分离,从而提高材料的光催化活性。3.通过二步煅烧法合成了CeO2/g-C3N4复合光催化材料。采用TG、XRD、 IR、TEM、HRTEM、XPS、DRS等方法对光催化材料进行表征分析。XRD、 IR和XPS结果表明复合材料由Ce02与g-C3N4组成。TEM和HRTEM结果显示Ce02紧紧粘附在g-C3N4的表面。比表面和吸附实验表明,CeO2/g-C3N4具有比g-C3N4更高的比表面积和暗反应吸附容量。可见光催化降解MB实验表明,CeO2/g-C3N4光催化降解MB符合一级反应动力学特征,其中CeO2/g-C3N4(13.0%)复合材料具有最高的光催化活性,光照2h后MB降解率达95%,其降解速率常数分别为单体Ce02和g-C3N4的12.2倍和3.1倍。光催化降解4-CP和总有机碳(TOC)测试结果验证了CeO2/g-C3N4是一种高效催化剂。PL和光电流测试表明CeO2/g-C3N4具有比g-C3N4更强的光生电子和空穴分离能力。光催化机理分析表明Ce02和g-C3N4之间的能带位置有利于光生电子和空穴的迁移和分离,从而提高材料的光催化活性。4.通过一步煅烧法合成了皂土改性g-C3N4复合光催化材料。采用XRD、 TG、TEM、IR、XPS、DRS等方法对光催化材料进行表征分析。XRD、IR、 XPS结果表明复合材料由皂土与g-C3N4组成。TEM结果表明,皂土/g-C3N4复合材料具有蓬松的片状结构,皂土和g-C3N4形成紧密接触的界面。DRS分析发现复合材料在可见光区的吸收明显增强。比表面与吸附实验表明皂土/g-C3N4具有比g-C3N4更高的比表面积和暗反应吸附容量。可见光催化降解MB实验表明,皂土/g-C3N4光催化降解MB符合一级反应动力学特征,其中皂土/g-C3N4(0.10)复合材料具有最高的光催化活性,降解速率常数为单体g-C3N4的2.5倍。PL和光电流测试表明皂土/g-C3N4具有比g-C3N4更强的光生电子和空穴分离能力。光催化机理分析表明皂土层间所带负电荷与g-C3N4光生电子和空穴存在静电吸引作用,从而有利于g-C3N4光生电子和空穴的迁移和分离,促进本体g-C3N4的光催化活性的提高。更多还原

【Abstract】 With the development of our society, the problems of energy shortage and environment pollution affect our living standard. Photocatalytic technology is one of green technologies, which has been widely used in environmental pollutant treatment and energy development. Visible-light-driven photocatalysts with high activity and stability had attracted a great deal of attention. In order to take better advantage of the new visible-light photocatalytic graphene carbon nitride (g-C3N4) in photocatalytic application, a series of composites (g-C3N4/MoO3, WO3/g-CaN4CeO2/g-C3N4and bentonite/g-C3N4) with high photocatalytic activity have been synthesized. These resulting materials were characterized by XRD, XPS, SEM, TEM, BET, DRS, PL and photocatalytic activity test, the relationship between the structure of the photocatalyst and the photocatalytic activities were also discussed in details. The main content and conclusions are summarized as follows:1. g-C3N4/MoO3composite photocatalysts were prepared with an ultrasonic dispersion-heat treatment method. The photocatalysts were characterized by XRD, SEM, HRTEM, IR, XPS and DRS etc. XRD showed the crystal phase structure of g-C3N4and MoO3were not changed after hybridization. SEM and HRTEM showed the hybrid interfaces were formed between the g-C3N4and MoO3. DRS showed the absorption edges of g-C3N4/MoO3composites shifted significantly to longer wavelengths compared with MoO3. The photocatalytic degradation of methylene blue (MB) over g-C3N4/MoO3composites followed the pseudo-first-order reaction model. The g-C3N4/MoO3(7%) composite exhibited the highest photocatalytic activity:the degradation efficiency of MB was93%under visible light irradiation for3h; the photoreaction kinetics constant value was almost4.2and1.9times as high as that of the pure MoO3and g-C3N4, respectively. The enhancement of visible light photocatalytic activity in g-C3N4/MoO3should be assigned to the effective separation and transfer of photogenerated charges originating from the heterojunction interface between MoO3and g-C3N4.2. WO3/g-C3N4composite photocatalysts were prepared by a calcination process with varying the content of WO3. The photocatalysts were characterized by TG, XRD, SEM-EDS, TEM, HRTEM, XPS, IR and DRS etc. XRD, IR, SEM-EDS and XPS showed that the composite photocatalysts were constituted by WO3and g-C3N4. SEM, TEM and HRTEM confirmed the tight hybrid interface was formed between WO3and g-C3N4. DRS showed the absorption edges of WO3/g-C3N4composites shift to longer wavelengths compared with the pure g-C3N4. BET showed the enlarged surface area of WO3/g-C3N4composites compared with g-C3N4and the increased surface area offers more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over WO3/g-C3N4composites followed the pseudo-first-order reaction model. The WO3/g-C3N4(9.7%) composite exhibited the highest photocatalytic activity: the photocatalytic degradation efficiency of MB was97%under visible light irradiation for2h; the photoreaction kinetics constant value was4.2times and 2.9times as high as that of the pure WO3and pure g-C3N4, respectively. The degradation of4-chlorophenol (4-CP) results showed the mechanism was not the dye sensitization effect. PL and EIS analysis confirmed the more efficient separation of electron-hole pairs compared with pure g-C3N4. The remarkably increased performance of WO3/g-C3N4was ascribed mainly to the suitably band positions for WO3/g-C3N4composites to improve the separation efficiency of photogenerated electron-hole pairs.3. CeO2/g-C3N4composite photocatalysts were successfully prepared by a simple mixing-calcination technique. The CeO2/g-C3N4nanocomposites were characterized by TG, XRD, IR, TEM, HRTEM, XPS and DRS etc. TEM and HRTEM showed the CeO2were combined tightly on the surface of g-C3N4. BET showed the enlarged surface area of CeO2/g-C3N4composites compared with g-C3N4and the increased surface area offered more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over CeO2/g-C3N4composites followed the pseudo-first-order reaction model in the degradation of MB. The CeO2/g-C3N4(13.0%) composite exhibited the highest photocatalytic activity:the photocatalytic degradation efficiency of MB was95%under visible light irradiation for2h; the photoreaction kinetics constant value was about12.2times and3.1times as high as that of CeO2and g-C3N4, respectively. The results of the degradation of4-CP and the TOC confirmed CeO2/g-C3N4composites were photocatalyts with high activity. The PL and PT analyses confirmed the efficient separation of electron and pairs under visible light. The remarkably increased performance of CeO2/g-C3N4was ascribed mainly to the well-matched overlapping band-structures for CeO2/g-C3N4composites to improve the separation efficiency of photogenerated electron-hole pairs.4. Layered bentonite/g-C3N4composite photocatalysts were synthesized through a conventional calcination method and systematically characterized by XRD, TG, TEM, IR, XPS and DRS etc. XRD, IR and XPS showed that the composite photocatalyst were constituted by bentonite and g-C3N4. TEM showed the bentonite/g-C3N4composites were constituted by abundant fluffy sheets. DRS showed the absorption edges of bentonite/g-C3N4composites shifted significantly to longer wavelengths compared with the pure g-C3N4. BET showed the enlarged surface area of bentonite/g-C3N4composites compared with g-C3N4and the increased surface area offered more surface active sites for adsorption and photocatalytic reaction. The photocatalytic degradation of MB over bentonite/g-C3N4composites followed the pseudo-first-order reaction model. The bentonite/g-C3N4(0.1) composite showed the highest efficiency for the degradation of MB. The photoreaction kinetics constant value of bentonite/g-C3N4(0.1) was about2.5times as high as that of g-C3N4. Results showed the enhanced photoactivity was mainly attributed to the efficient migration of the photogenerated electrons and holes of g-C3N4, which were induced by the electrostatic interaction between g-C3N4and negatively charged bentonite.更多还原