石墨相氮化碳材料的可控制备及光催化降解环境有机污染物研究

发布时间：2018-06-02 15:23

本文选题：光催化 + 可见光　；参考：《江苏大学》2017年博士论文

【摘要】：半导体光催化技术对解决能源和环境危机具有重要的意义。光催化技术通过半导体光催化剂吸收清洁、可再生的太阳能,在温和的条件下实现光催化氧化还原反应。制备高活性、高选择性、高稳定性、廉价的光催化剂是光催化技术实现大规模应用的关键。以二氧化钛(Ti02)为代表的传统光催化剂的带隙宽,只能被紫外光激发,这极大地阻碍了 Ti02作为光催化剂的发展。因此,廉价、高效、高稳定的可见光催化剂的开发备受关注。本文将材料的可控合成、先进的表征和机理研究“三位一体”相结合,用于廉价、高效、高稳定性的具有可见光响应能力的石墨相氮化碳(g-C3N4)材料的设计和制备,以提高单体g-C3N4在可见光照射下催化降解环境有机污染物的性能。同时,根据所制备的g-C3N4材料的性能、结构、组成等之间的构效关系深入研究光催化性能增强机制。在本论文中,我们通过调控g-C3N4的组成来提高其对可见光的吸收和光生电子-空穴对的分离效率;通过调节g-C3N4的维度来提高光生电荷的分离和传输能力,以改善其光催化降解污染物的活性;并通过调控g-C3N4的光生电荷的迁移来实现光生载流子的生成,以提高其光催化降解污染物的性能。本文的主要研究成果如下:1.以纳米立方体的Ce02负载g-C3N4为体系,通过调控复合物的组成来研究Ce02/g-C3N4光催化降解环境有机污染物的性能。研究结果表明,Ce02的引入抑制了 g-C3N4的光生载流子的复合。负载在单体g-C3N4表面的Ce02具有规则的立方体形貌,且尺寸在3-10 nm,小尺寸的CeO2具有量子限制效应。光生载流子的有效分离和量子限制效应共同作用于光催化反应,提升了 Ce02/g-C3N4复合物的光催化活性。2.采用机溶剂液相剥落法合成了二维类石墨烯氮化碳,通过优化不同的有机溶剂,调控类石墨烯氮化碳的层厚,并研究了类石墨烯氮化碳的光催化降解环境有机污染物的性能。研究发现,由于类石墨烯氮化碳在Z-轴方向上只有几个原子层厚度,极大地缩短了光生载流子从其体相迁移到表面的距离。因此,类石墨烯氮化碳的光生载流子得到有效的分离。同时,由于类石墨烯氮化碳具有较大的比表面积,其能提供更多的吸附位点和活性位点,从而有效地提升其光催化降解环境有机污染物性能。3.采用热氧化法控制合成了单原子层氧掺杂g-C3N4 (O-g-C3N4)纳米片光催化材料,通过调控锻烧时间和次数,宏量制备了具有原子层结构的氧掺杂g-C3N4纳米片,并将其应用于光催化降解环境有机污染物。研究发现,在空气气氛下,多层氮化碳被逐步裁剪成二维结构,并最终形成单原子层结构。少量的O有效地掺杂于g-C3N4纳米片结构中。单原子层的O-g-C3N4纳米片在Z-轴方向只有一层,其光生载流子迁移到催化剂表面的距离大大缩短,有利于提升光生载流子的迁移速率;且二维单原子结构和O的引入还抑制了单原子层的O-g-C3N4的光生载流子复合率,提升了其光催化降解环境有机污染物的性能。此外,单原子层的O-g-C3N4纳米片能光催化降解多种有机污染物。与P25相比,单原子层的O-g-C3N4紫外光催化降解4-CP的性能也得到了明显的提升。4.采用非模板法制备二维超薄多孔氧掺杂g-C3N4纳米片(PUOCNs),并研究了二维多孔结构和O掺杂对g-C3N4光催化降解环境污染物性能的影响。通过锻烧使g-C3N4膨胀;随后在常温下,通过混合酸氧化法制备了 PUOCNs。研究发现,二维超薄多孔结构和O的引入提升了 g-C3N4光催化降解环境有机污染物的性能。其中,PUOCNs的二维超薄多孔结构不仅大大缩短了光生载流子的迁移距离,而且提供了更多的吸附位点和活性位点。此外,O的引入使材料的电荷分布发生了改变,光生载流子的寿命得到了延长,提高了其参与光催化反应的概率,从而提升了 PUOCNs的光催化性能。PUOCNs的光催化降解有机污染物MO的活性比单体g-C3N4提升了 71倍。5.构建了具有电子定向迁移能力的Ag/2D-C3N4/CNTs光催化复合材料,协同地利用Ag的等离子效应和CNTs的导电性来提升2D-C3N4光催化材料的光生载流子的生成、迁移和分离,从而提升了其光催化降解环境有机污染物的性能。在可见光照射下,Ag/2D-C3N4/CNTs复合物中Ag纳米立方体的表面等离子共振效应被激发产生热电子并注入2D-C3N4的导带中与2D-C3N4的光生电子汇集。随后,在2D-C3N4导带上的高密度的电子通过具有优良导电性的CNTs迁移到催化剂的表面参与光催化反应。Ag纳米立方体和CNTs两者协同作用于2D-C3N4,从而提高了 Ag/2D-C3N4/CNTs复合物可见光催化降解环境有机污染物的性能。6.以二维层状结构的α-Fe203/2D g-C3N4为体系,通过水热法先合成了α-Fe203,随后通过与三聚氰胺分步多次煅烧形成二维结构的Z-型机制复合光催化剂:α-Fe2O3/2D g-C3N4。在可见光照射下,α-Fe2O3导带上的光生电子与2D g-C3N4价带上的光生空穴通过α-Fe2O3和2D g-C3N4形成的致密界面进行复合,而留在α-Fe203价带上的光生空穴和留在2D g-C3N4导带上的光生电子能有效地参与光催化氧化还原反应。这不仅提高了单一组分光催化剂的氧化还原能力,还抑制了其光生电子-空穴对的复合。通过同步辐射表征发现α-Fe203是与2D g-C3N4中的碳原子发生相互作用,从而提高了 Z-型机制光催化剂α-Fe203/2D g-C3N4光催化降解环境有机污染物的性能。
[Abstract]:Semiconductor photocatalytic technology is of great significance for solving the crisis of energy and environment. Photocatalytic technology absorbs clean, renewable solar energy through semiconductor photocatalyst, and realizes photocatalytic redox reaction under mild conditions. The preparation of high activity, high selectivity, high stability and cheap photocatalyst is realized by photocatalysis technology. The key of scale application. The band gap of the traditional photocatalyst represented by titanium dioxide (Ti02) is wide and can only be excited by ultraviolet light, which greatly hinders the development of Ti02 as a photocatalyst. Therefore, the development of cheap, high efficient and highly stable visible light catalyst has attracted much attention. This paper has studied the controllable synthesis of materials, advanced characterization and mechanism research. The combination of "Trinity" is used for the design and preparation of graphite phase carbon nitride (g-C3N4) materials with visible light response capacity for low cost, high efficiency and high stability, in order to improve the performance of the organic pollutants in the photocatalytic degradation of the environmental pollutants by the visible light irradiation of the monomer g-C3N4. At the same time, the properties, structure, composition and so on of the g-C3N4 materials are prepared. In this paper, we improve the absorption of visible light and the separation efficiency of the photoelectron hole pair by regulating the composition of g-C3N4 in this paper. By adjusting the dimension of g-C3N4, we can improve the separation and transmission of light generated charge, so as to improve the photocatalytic activity of photocatalytic degradation of pollutants. In order to improve the performance of photocatalytic degradation of pollutants by regulating the migration of photogenerated charge of g-C3N4, the main research results of this paper are as follows: 1. the Ce02/g-C3N4 photocatalytic degradation of environmental organic pollutants by Ce02/g-C3N4 photocatalyst was studied by using g-C3N4 as the system of nano cubes. The results show that the introduction of Ce02 inhibits the recombination of the photogenerated carriers of g-C3N4. The Ce02 loaded on the surface of the monomer g-C3N4 has a regular cube shape, and the size is 3-10 nm, and the small size CeO2 has the quantum confinement effect. The effective separation of the light carrier and the quantum confinement effect co act on the photocatalytic reaction and the enhancement. The photocatalytic activity of the Ce02/g-C3N4 complex was used to synthesize the two dimensional graphene like carbon nitride by means of liquid phase stripping in the machine solvent. By optimizing the different organic solvents, the thickness of the carbon nitride of graphene like carbon was regulated. The performance of the photocatalytic degradation of the environmental organic contaminants was studied. There are only a few atomic layers in the direction of the Z- axis, which greatly shortens the distance of the photogenerated carrier from its body to the surface. Therefore, the photogenerated carrier of carbon like carbon nitride can be effectively separated. At the same time, it can provide more adsorption sites and active sites because of the larger specific surface product of carbon like carbon nitride. In order to effectively improve the photocatalytic degradation of environmental organic pollutant performance.3., a single atomic layer oxygen doped g-C3N4 (O-g-C3N4) nanoscale photocatalyst was synthesized by thermal oxidation, and the oxygen doped g-C3N4 nanoscale with atomic layer structure was prepared by controlling the time and times of the calcination, and applied to the photocatalytic degradation. The study found that in the air atmosphere, the multilayer nitriding carbon was gradually cut into two dimensional structure and finally formed a single atomic layer structure. A small amount of O was effectively doped in the structure of g-C3N4 nanoscale. The O-g-C3N4 nanoscale of the single atomic layer was only one layer in the direction of the Z- axis, and the distance of the photogenerated carrier to the surface of the catalyst. It can greatly shorten the migration rate of the photogenerated carrier, and the introduction of two dimensional monatomic structure and O also inhibits the photogenerated carrier recombination rate of O-g-C3N4 in the single atomic layer, and improves the photocatalytic degradation of the environmental organic pollutants. In addition, the O-g-C3N4 nanoscale of the single atomic layer can photocatalytic degradation of various organic pollutants. Compared with P25, the performance of O-g-C3N4 UV photocatalytic degradation of 4-CP in single atomic layer also improved the performance of 4-CP, and.4. was prepared by non template method to prepare two-dimensional ultrathin porous oxygen doped g-C3N4 nanoscale (PUOCNs) by non template method. The effect of two-dimensional porous structure and O doping on the performance of g-C3N4 photocatalytic degradation of environmental contaminants was studied. At the normal temperature, PUOCNs. studies have been prepared by the mixed acid oxidation method. It is found that the two-dimensional ultrathin porous structure and the introduction of O enhance the performance of g-C3N4 photocatalytic degradation of environmental organic pollutants. Among them, the two-dimensional ultrathin porous structure of PUOCNs not only greatly shortens the migration distance of the photogenerated carrier, but also provides more adsorption sites. In addition, the introduction of O makes the charge distribution of the material changes, the lifetime of the photogenerated carrier is prolonged, the probability of its participation in the photocatalytic reaction is increased, and the photocatalytic activity of the PUOCNs is enhanced by the photocatalytic degradation of the organic pollutant MO, which is 71 times higher than that of the monomer g-C3N4, and the electricity is constructed with electricity. Ag/2D-C3N4/CNTs photocatalytic composites with the ability of subdirectional migration are used to enhance the photocatalytic degradation of environmental organic pollutants by using the plasma effect of Ag and the conductivity of CNTs to enhance the performance of photocatalytic degradation of organic pollutants in the 2D-C3N4 photocatalyst. Ag/2D-C3N4/CNTs composite under visible light irradiation. The surface plasmon resonance effect of the Ag nanometers in the substance is excited to produce hot electrons and into the photoelectron collection of 2D-C3N4 in the guide band of 2D-C3N4. Then, the high density electrons in the 2D-C3N4 conduction band migrate to the surface of the catalyst through the CNTs with excellent conductivity, and participate in the photocatalytic reaction between the.Ag nanometers and the CNTs. The synergistic effect on 2D-C3N4, thus improving the performance of the Ag/2D-C3N4/CNTs complex in the visible photocatalytic degradation of environmental organic pollutants,.6. with two-dimensional layered structure of alpha -Fe203/2D g-C3N4, first synthesized alpha -Fe203 by hydrothermal method, and then by calcining with melamine multiple steps to form a two-dimensional structure of Z- type mechanism composite photocatalysis. Agent: alpha -Fe2O3/2D g-C3N4. is irradiated by visible light, the photogenerated holes on the valence band of the alpha -Fe2O3 conduction band and the 2D g-C3N4 valence band are compounded by the dense interface formed by the alpha -Fe2O3 and 2D g-C3N4, while the photogenerated holes on the alpha -Fe203 valence band and the photoelectrons left on the 2D g-C3N4 Guide band are effectively involved in the photocatalytic redox reaction. It not only improves the redox ability of the single component light catalyst, but also inhibits the recombination of the photogenerated electron hole pair. Through the synchrotron radiation characterization, it is found that the alpha -Fe203 is interacting with the carbon atoms in the 2D g-C3N4, thus improving the Z- type photocatalyst alpha -Fe203/2D g-C3N4 for the photocatalytic degradation of the environmental organic pollutants. Performance.
【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;O644.1;X505

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