基于氮化碳光催化材料的设计及其可见光降解环境有机污染物的研究
发布时间：2018-08-20 13:16
【摘要】：当今社会经济迅猛发展,随之而来的能源短缺以及生态环境问题,已然成为人类关心的热点,而对环境污染控制和净化的研究也已成为亟待全球科学家攻克的重要难题。光催化技术是一种绿色的高级氧化技术,在光的照射下,半导体材料能够活化氧气分子或水分子,使之产生具有活性的自由基,降解和消除掉各种环境污染物。光催化技术不仅能够有效的利用太阳能,将其转化为氢能等容易为人类所用的能源,从而解决资源短缺等问题;还能够把有毒、有害的有机、无机环境污染物降解或者矿化为低毒性甚至无毒性的物质,降低对环境造成的污染。然而,以二氧化钛(Ti02)为代表的传统半导体氧化物光催化剂,因其本身能带结构局限,存在对光的响应范围较窄等问题,导致对太阳能的利用率较低,同时其本身还有稳定性较差等缺点,这些因素都限制了其在光催化领域的发展和应用。因此,如何实现光能的有效转换,寻找和制备具有宽光谱响应范围、高量子效率且易回收利用等优势的光催化材料是亟待研究者解决的关键科学性问题。目前,以石墨相氮化碳(g-C3N4)为代表的非金属层状材料,其特殊的电子结构,使之展现出独特的性能,同时它还具备良好的热稳定性、化学稳定性,成为科研工作者研究和关注的热点。另外该材料成本低廉,具有合适的能带结构,其禁带宽度(Eg)约为2.7 eV,是类似于石墨的片层结构材料,可以从多种富含氮元素的天然材料中制得。g-C3N4在可见光照射下即可光解水、光催化降解多种污染物,是一种理想的可见光响应型光催化剂。但光谱吸收范围窄、比表面积小、光生电子-空穴对复合率高等缺陷影响了其光催化性能的提升。本论文以g-C3N4为研究中心,通过多种修饰改性方法,改善其光催化性能,在对该材料进行微观结构表征以及光催化性能评价基础上,对其性能提升的原因及作用机制进行了详细的分析,主要研究内容如下:首先,以多层g-C3N4为基底材料,通过半导体复合的方法来提高其可见光催化性能。采用离子交换法分别制备了银/氯化银(Ag/AgCl)和碘化银(AgI)纳米颗粒改性的g-C3N4纳米复合材料(Ag/AgCl/g-C3N4和AgI/g-C3N4),一方面扩展了g-C3N4可以利用的可见光范围;另一方面利用二者之间的协同效应促进光生电子-空穴对的分离,提升其光催化降解性能。利用多种表征方法分别对Ag/AgCl/g-C3N4和AgI/g-C3N4纳米复合材料的微观结构和形貌进行分析,并深入考察了 Ag/AgCl/g-C3N4和AgI/g-C3N4纳米复合光催化剂在可见光照射下降解环境有机污染物的性能。结果表明,随着Ag/AgCl和AgI含量的升高,复合光催化剂在可见光区的吸收逐渐增强。在可见光的照射下,AgCl/g-C3N4中会有部分Ag单质出现,形成Ag/AgCl/g-C3N4复合纳米材料,Ag单质的等离子共振效应以及材料之间构建的协同作用共同提升了光催化性能,然而该体系仍存在稳定性较差的问题;相比之下,AgI具有更强的光催化活性,与g-C3N4的复合可增强AgI的稳定性,二者之间的协同作用有助于光生电子-空穴对的迁移和分离,最终使复合材料的光电流强度和光催化活性等均得到显著提高。其次,与石墨材料相比,二维以及三维结构的石墨烯材料具有更优越的光电性质和表面特性。而层状g-C3N4材料与石墨结构相似,层间以范德华力相连,比表面积较小,影响了其光催化性能。借鉴石墨烯的研究思路,以多层g-C3N4材料为基底,通过剥离、自组装等方式将其制备成二维或者三维结构,打破g-C3N4材料层间的范德华力,增大其表面积并提升其光催化性能。采用溶剂剥离法,控制合成了二维类石墨烯型氮化碳(GL-C3N4),该材料具有较高的比表面积、有效的电子-空穴对分离率和优越的光电性能,在可见光照射下,GL-C3N4的光电流强度和光催化活性都得到了显著的提高。另外,在二维GL-C3N4研究的基础上,进一步在离子液体的辅助下,将体相g-C3N4转变为具有三维网络结构的g-C3N4水凝胶。运用多种表征手段结合理论计算研究了三维网络结构g-C3N4水凝胶形成的机理,据此提出了一个将层状材料剥离转化成稳定的三维水凝胶的普适性方法。研究表明,三维网络结构g-C3N4水凝胶具有特殊的电子结构和光学特性,可拓展g-C3N4在光学等领域的应用,这为后期湿法化学的研究以及纳米材料光电特性的调控提供了新的方法和思路。综合二维GL-C3N4与三维g-C3N4水凝胶光催化特性的研究可以发现:二维GL-C3N4因具有较大的表面积和优异的光生载流子转移和分离效率,而具备更优的光催化性能。最后,为进一步提升二维GL-C3N4的光催化性能,而向其中引入具有宽光吸收范围、高量子效率、强光生载流子迁移能力的新型纳米材料,利用复合材料的协同效应提升其电子-空穴对的分离效率及其对可见光的吸收能力。基于此,设计制备了 ZnS/GL-C3N4以及GL-MoS2/C3N4复合材料,并将其应用于光催化降解有机污染物。研究结果显示,在可见光照射下,不同维度的纳米复合材料光催化降解有机污染物的活性优于纯GL-C3N4材料。随着复合材料单体间接触面积的增加,建立了载流子的快速传输通道,加速了界面电荷的转移能力,能够显著改善GL-C3N4的光电化学性质。同时,复合纳米材料提高了对可见光的利用率,实现了有机污染物的高效、深度降解。该研究工作展示的独特策略可以扩展到其他纳米复合体系中,也为合理设计和优化其他重要的化学和催化反应提供了新的研究思路和实验手段。
[Abstract]:Nowadays, with the rapid development of society and economy, energy shortage and ecological environment problems have become the focus of human concern, and the study of environmental pollution control and purification has become an important problem to be solved by scientists all over the world. Materials can activate oxygen molecules or water molecules to produce active free radicals, degrade and eliminate various environmental pollutants. Photocatalytic technology can not only effectively utilize solar energy, convert it into hydrogen energy and other easily used energy for mankind, thereby solving the shortage of resources and other problems; but also can poisonous, harmful organic, inorganic. Degradation or mineralization of environmental pollutants into low toxic or even non-toxic substances can reduce environmental pollution. However, traditional semiconductor oxide photocatalysts, represented by titanium dioxide (Ti02), have a narrow range of response to light due to their limited energy band structure, resulting in low utilization of solar energy, and at the same time, their photocatalytic activities are limited. These factors limit its development and application in the field of photocatalysis. Therefore, how to realize the effective conversion of light energy, find and prepare photocatalytic materials with broad spectral response range, high quantum efficiency and easy recycling are the key scientific problems to be solved by researchers. Previously, graphite-phase carbon nitride (g-C3N4) as a representative of non-metallic layered materials, its special electronic structure, so that it shows a unique performance, while it also has good thermal stability, chemical stability, has become a research focus of researchers. In addition, the material is low-cost, with appropriate band structure, its band gap width (Eg) (2.7 eV) is a kind of lamellar structure material similar to graphite, which can be prepared from a variety of natural materials rich in nitrogen. g-C3N4 can photolyse water under visible light and photocatalytic degradation of a variety of pollutants. It is an ideal visible light-responsive photocatalyst. However, it has a narrow spectral absorption range, small specific surface area and photogenerated electron-hole pairing. In this paper, g-C3N4 was modified by various modification methods to improve its photocatalytic performance. Based on the microstructure characterization and photocatalytic performance evaluation of the material, the reasons and mechanism of its performance improvement were analyzed in detail. The main contents are as follows: Firstly, the visible photocatalytic properties of the multilayer g-C3N4 were improved by the semiconductor composite method. The Ag/AgCl and AgI nanoparticles modified g-C3N4 nanocomposites (Ag/AgCl/g-C3N4 and AgI/g-C3N4) were prepared by ion exchange method, respectively. On the other hand, the synergistic effect between them was used to promote the separation of photogenerated electron-hole pairs and enhance their photocatalytic degradation performance. The microstructure and morphology of Ag/AgCl/g-C3N4 and AgI/g-C3N4 nanocomposites were analyzed by various characterization methods, and Ag/AgCl/g-C3N4 and AgI/g-C3N4 and AgI/g-C3N were investigated in depth. The results show that the absorption of Ag/AgCl and AgI increases with the increase of Ag/AgCl and AgI content. Under the visible light irradiation, some Ag elements appear in AgCl/g-C3N4 and form Ag/AgCl/g-C3N4 composite nanomaterials, Ag elements. Plasma resonance effect and the synergistic effect between the materials enhance the photocatalytic performance, but the stability of the system is still poor; in contrast, AgI has stronger photocatalytic activity, and the combination of AgI and g-C3N4 can enhance the stability of AgI. The synergistic effect between AgI and g-C3N4 can facilitate the photogenerated electron-hole pair migration. Secondly, compared with graphite materials, two-dimensional and three-dimensional graphene materials have superior photoelectric properties and surface properties, while the layered g-C3N4 materials have similar structure to graphite, and the layers are connected by van der Waals force, and the specific surface area is larger. Using graphene as a reference, multi-layer g-C3N4 materials were prepared into two-dimensional or three-dimensional structures by peeling and self-assembly, breaking the van der Waals force between the layers of g-C3N4 materials, increasing its surface area and improving its photocatalytic performance. The two-dimensional class was synthesized by solvent peeling method. Graphene-type carbon nitride (GL-C3N4) has high specific surface area, effective electron-hole separation rate and excellent photoelectric properties. Under visible light irradiation, the photocurrent intensity and photocatalytic activity of GL-C3N4 have been significantly improved. In addition, on the basis of two-dimensional GL-C3N4 research, further assisted by ionic liquids, The bulk g-C3N4 was transformed into g-C3N4 hydrogel with three-dimensional network structure. The formation mechanism of the three-dimensional network structure g-C3N4 hydrogel was studied by using a variety of characterization methods and theoretical calculations. A general method was proposed to transform layered materials into stable three-dimensional network structure g-C3N4 hydrogel. Hydrogels have special electronic structure and optical properties, which can expand the application of g-C3N4 in optics and other fields. This provides new methods and ideas for the later study of wet chemistry and the regulation of photoelectric properties of nanomaterials. Finally, in order to further enhance the photocatalytic performance of two-dimensional GL-C3N4, new nano-materials with wide optical absorption range, high quantum efficiency and strong photo-induced carrier migration ability were introduced into the GL-C3N4 photocatalyst. Based on this, ZnS/GL-C3N4 and GL-MoS2/C3N4 composites were designed and fabricated and applied to photocatalytic degradation of organic pollutants. With the increase of the contact area between the composite monomers, a fast carrier transport channel was established, which accelerated the transfer of interfacial charges and significantly improved the photoelectrochemical properties of GL-C3N4. At the same time, the utilization of visible light was enhanced and the organic pollutants were increased. The unique strategies demonstrated in this work can be extended to other nanocomposite systems and provide new research ideas and experimental means for the rational design and optimization of other important chemical and catalytic reactions.
【学位授予单位】：江苏大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;X50
[Abstract]:Nowadays, with the rapid development of society and economy, energy shortage and ecological environment problems have become the focus of human concern, and the study of environmental pollution control and purification has become an important problem to be solved by scientists all over the world. Materials can activate oxygen molecules or water molecules to produce active free radicals, degrade and eliminate various environmental pollutants. Photocatalytic technology can not only effectively utilize solar energy, convert it into hydrogen energy and other easily used energy for mankind, thereby solving the shortage of resources and other problems; but also can poisonous, harmful organic, inorganic. Degradation or mineralization of environmental pollutants into low toxic or even non-toxic substances can reduce environmental pollution. However, traditional semiconductor oxide photocatalysts, represented by titanium dioxide (Ti02), have a narrow range of response to light due to their limited energy band structure, resulting in low utilization of solar energy, and at the same time, their photocatalytic activities are limited. These factors limit its development and application in the field of photocatalysis. Therefore, how to realize the effective conversion of light energy, find and prepare photocatalytic materials with broad spectral response range, high quantum efficiency and easy recycling are the key scientific problems to be solved by researchers. Previously, graphite-phase carbon nitride (g-C3N4) as a representative of non-metallic layered materials, its special electronic structure, so that it shows a unique performance, while it also has good thermal stability, chemical stability, has become a research focus of researchers. In addition, the material is low-cost, with appropriate band structure, its band gap width (Eg) (2.7 eV) is a kind of lamellar structure material similar to graphite, which can be prepared from a variety of natural materials rich in nitrogen. g-C3N4 can photolyse water under visible light and photocatalytic degradation of a variety of pollutants. It is an ideal visible light-responsive photocatalyst. However, it has a narrow spectral absorption range, small specific surface area and photogenerated electron-hole pairing. In this paper, g-C3N4 was modified by various modification methods to improve its photocatalytic performance. Based on the microstructure characterization and photocatalytic performance evaluation of the material, the reasons and mechanism of its performance improvement were analyzed in detail. The main contents are as follows: Firstly, the visible photocatalytic properties of the multilayer g-C3N4 were improved by the semiconductor composite method. The Ag/AgCl and AgI nanoparticles modified g-C3N4 nanocomposites (Ag/AgCl/g-C3N4 and AgI/g-C3N4) were prepared by ion exchange method, respectively. On the other hand, the synergistic effect between them was used to promote the separation of photogenerated electron-hole pairs and enhance their photocatalytic degradation performance. The microstructure and morphology of Ag/AgCl/g-C3N4 and AgI/g-C3N4 nanocomposites were analyzed by various characterization methods, and Ag/AgCl/g-C3N4 and AgI/g-C3N4 and AgI/g-C3N were investigated in depth. The results show that the absorption of Ag/AgCl and AgI increases with the increase of Ag/AgCl and AgI content. Under the visible light irradiation, some Ag elements appear in AgCl/g-C3N4 and form Ag/AgCl/g-C3N4 composite nanomaterials, Ag elements. Plasma resonance effect and the synergistic effect between the materials enhance the photocatalytic performance, but the stability of the system is still poor; in contrast, AgI has stronger photocatalytic activity, and the combination of AgI and g-C3N4 can enhance the stability of AgI. The synergistic effect between AgI and g-C3N4 can facilitate the photogenerated electron-hole pair migration. Secondly, compared with graphite materials, two-dimensional and three-dimensional graphene materials have superior photoelectric properties and surface properties, while the layered g-C3N4 materials have similar structure to graphite, and the layers are connected by van der Waals force, and the specific surface area is larger. Using graphene as a reference, multi-layer g-C3N4 materials were prepared into two-dimensional or three-dimensional structures by peeling and self-assembly, breaking the van der Waals force between the layers of g-C3N4 materials, increasing its surface area and improving its photocatalytic performance. The two-dimensional class was synthesized by solvent peeling method. Graphene-type carbon nitride (GL-C3N4) has high specific surface area, effective electron-hole separation rate and excellent photoelectric properties. Under visible light irradiation, the photocurrent intensity and photocatalytic activity of GL-C3N4 have been significantly improved. In addition, on the basis of two-dimensional GL-C3N4 research, further assisted by ionic liquids, The bulk g-C3N4 was transformed into g-C3N4 hydrogel with three-dimensional network structure. The formation mechanism of the three-dimensional network structure g-C3N4 hydrogel was studied by using a variety of characterization methods and theoretical calculations. A general method was proposed to transform layered materials into stable three-dimensional network structure g-C3N4 hydrogel. Hydrogels have special electronic structure and optical properties, which can expand the application of g-C3N4 in optics and other fields. This provides new methods and ideas for the later study of wet chemistry and the regulation of photoelectric properties of nanomaterials. Finally, in order to further enhance the photocatalytic performance of two-dimensional GL-C3N4, new nano-materials with wide optical absorption range, high quantum efficiency and strong photo-induced carrier migration ability were introduced into the GL-C3N4 photocatalyst. Based on this, ZnS/GL-C3N4 and GL-MoS2/C3N4 composites were designed and fabricated and applied to photocatalytic degradation of organic pollutants. With the increase of the contact area between the composite monomers, a fast carrier transport channel was established, which accelerated the transfer of interfacial charges and significantly improved the photoelectrochemical properties of GL-C3N4. At the same time, the utilization of visible light was enhanced and the organic pollutants were increased. The unique strategies demonstrated in this work can be extended to other nanocomposite systems and provide new research ideas and experimental means for the rational design and optimization of other important chemical and catalytic reactions.
【学位授予单位】：江苏大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;X50
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