Preparation And Photocatalytic Activity Of G-C₃N₄-based Composite Photocatalysts

In recent years, with the rapid development of modern industry, the economic life level of human beings is improved. Meanwhile, the overexploitation of energy and the serious of environmental pollution has become a serious threat to the survival and development of human beings. The environment and energy problem are also a threat to the sustainable development need to be solved. Semiconductor Semiconductor photocatalytic technology, which utilizes the energy of natural sunlight, has emerged as one of the most promising technologies in solving the environment pollution and energy crisis. Recently, Polymeric graphite phase carbon nitride (g-C3N4) as a stable, cheap and nometel visible-light photocatalyst has attracted a great deal of interest in organic pollutant degradation, and water splitting due to its special electronic band structure, high thermal and chemical stability. In order to improve the quantum efficiency of g-CsN4, based on the deep understand of research background and development history, this thesis constructed g-C3N4 based heterostructure photocatalysts to reduce the recombination of photoinduced electron-hole pairs and expand the light response and studied the photocatalytic activities systematically. In this thesis, on one hand, we investagate the effect of different mass ratio on photocatalytic activities; on the other hand, we study the influence of the band offset in heterojunction photoelectrochemical properties and provides a new viewpoint to improve the photocatalytic activity by constructing multilevel structure. This thesis provides new guidance for the design of new efficient visible-light photocatalysts. The main research contents are listed as follow:In the first chapter, we briefly introduce the research background, the development history and the fundamental of semiconductor photocatalytic technology. Also, we systemtically study the research backgrand of g-C3N4-based heterostructure photocatalysts. In addition, the research ideas and content of this thesis are briefly introduced.In chapter 2, we presented a systematic investigation of the microscopic mechanism of interface interaction, charge transfer and separation, as well as their influence on the photocatalytic activity of heterojunctions by a combination of theoretical calculations and experimental techniques for the g-C3N4/Bi2MoO6 composite. XRD, FT-IR, XPS, SEM and UV-vis analyses are carried out to describe the properties of the as-prepared samples. The heterojunctions exhibite enhanced photocatalytic activities for RhB degradation compared with g-C3N4 and Bi2MoO6. This resulted from a reduced photogenerated electron-hole recombination, caused by the transfer of electrons from g-C3N4to Bi2MoO6. This heterostructure photocatalyst has potential in environmental remediation applications.In chapter 3, we present a systematic investigation of the preparation of g-C3N4/Bi2MoO6 photocatalysts and the hetero structure photocatalysts possess excellent photocatalytic activities under the visible-light irradiation. Band offset is a dominant factor in governing the photocatalytic performance of heterostructure photocatalysts. The g-C3N4 samples prepared from diverse precursors show different band structures between 2.3-2.7 eV. On this basis, we constructed a series of g-C3N4/m-LaVO4 heterojunctions with diverse g-C3N4. UV-vis spectra and X-ray photoelectron spectroscopy measurements were carried out to determine the band gap value and the valence band position of the heterojunctions and concluded that:first, the valence band offset (VBO) of the different heterojunctions are similar, meanwhile the conduction band offset (CBO) show significant differences and the normalized reaction rate is enhanced with the increase of the CBO value; second, the g-C3N4/g-C3N4/m-LaVO4 three-phase heterojunctions composed of m-LaVO4 and mixed g-C3N4 show the highest photocatalytic activities, which is mainly due to the construction of multilevel structure. This work investigates the influence of the band offset in heterojunction photoelectrochemical properties and provides a new viewpoint to improve the photocatalytic activity by constructing multilevel structure.In chapter 4, we summarize the conclusions and innovative points of this dissertation, and preview the further studies.