| With the development of the society, energy shortage and environment pollution problem has already become the hot topics that catch much attention. The study of environmental pollution control and purification has become the world's important topic for all the scientists. Photocatalytic technology is a kind of green, advanced oxidation technology, which has a broad application prospect in the field of pollution control and energy transformation. The principle of photocatalytic technology is based on semiconductor materials that can activate molecular oxygen and water molecules under the light excitation to produce free radicals with strong oxidation properties,which can not only convert low density of solar energy into hydrogen with high density solving the problem of energy shortage, but also can mineralize the toxic and harmful organic or inorganic environment pollutant into low toxicity, non-toxic material to reduce the environment pollution. Therefore photocatalytic technology is regarded as a low cost, environment friendly advanced oxidation technology and a green way for efficiently eliminating various kinds of trace organic pollutants.However, traditional photocatalysts, such as TiO2, are facing with narrow light response range,low quantum conversion efficiency,low utilization rate of solar energy and poor stability, becoming the bottleneck that restricts the development and application of the photocatalytic technology. Thus, finding photocatalytic materials with high quantum efficiency, easy to recycle and wide spectral response range is the prerequisite to realize energy efficient conversion.At present,graphitic carbon nitride (g-C3N4),one of the representatives of non-metallic materials, possess excellent optical and electrical properties and chemical stability,becoming the research hotspot. As we know,g-C3N4 with the bandgap 2.7 eV, similar to graphite layer structure, can be easily obtained by the calcination of varieties of raw material with rich nitrogen element, such as cyanide diamine, melamine and urea. g-C3N4 is an ideal visible light response materials that can split water into hydrogen and degrade kinds of organic pollutants under visible light irradiation. Unfortunately, g-C3N4 with narrow scope of spectral absorption,small specific surface area and the high electron-hole recombination rate hinders its photocatalytic performance. Herein, g-C3N4, as a type of widely used photocatalysts,was taken as object in this study, and kinds of modification such as nanocomposites have been synthesized to significantly improve the photocatalytic performance for degrading the organic pollutants and medical antibiotics in water. Based on characterization of microstructure materials and their photocatalytic performance, the reaction mechanisms of photocatalytic degradation of organic pollutants were systematically investigated. The main work was shown in the following parts:Firstly, semiconductor nanocomposite as an effective strategy was employed for optimizing and improving the photocatalytic performance based on multilayer g-C3N4.Ion exchange method was used to synthesize the Ag/AgCl and AgI modified g-C3N4 nanocomposites of Ag/AgCl/g-C3N4 and AgI/g-C3N4, respectively, which not only expand the light response range, but also promote the photon-generated carrier separation and improve the photocatalytic degradation performance, owing to the synergistic effect of both compositions. Varieties characterizations were employed to analysize the microstructure and morphology of the Ag/AgCl/g-C3N4 and AgI/g-C3N4 nanocomposites, respectively, and the photocatalytic degradation of organic pollutants under visible light based on the Ag/AgCl/g-C3N4 and AgI/g-C3N4 nanocomposites were also intensively investigated, respectively. The results showed that the intensity for visible light adsorption was improved with the increasing Ag/AgCl or AgI content.For AgCl/g-C3N4, part of metallic Ag can be produced on the surface under visible light irradiation, forming the Ag/AgCl/g-C3N4 nanocomposties. The plasmon resonance effect of Ag and the synergistic effect between Ag/AgCl and g-C3N4 contributed to the enhanced photocatalytic performance, but with poor stability under several cycles testing. AgI possesses good photocatalytic activity and their stability can also be improved when anchored with g-C3N4. Meanwhile the synergetic effect between AgI and g-C3N4 was beneficial for the photo-generated electrons and holes separation and transportation, which eventually promoted the enhancement of the photocurrent intensity and photocatalytic activity of the nanocomposites.Compared with graphite material,two-dimension (2D) or three-dimension (3D)graphene possesses better photoelectric properties and surface characteristics. And the bulk g-C3N4 is similar to graphite material, in which the layers are connected by the force of van der Waals with small surface area, resulting in low photocatalytic performance. Inspired by this, we try to transform the bulk g-C3N4 into 2D or 3D nanostructure by exfoliation or self assembly with the assistance of solvents or ionic liquids, breaking the van der Waals force between the g-C3N4 interlayer and enlarging the surface area that promotes the photocatalytic performance. Firstly, liquid-phase exfoliation methods were employed to exfoliate bulk carbon nitride into few layers structure similar to graphene (GL-C3N4). The as-obtained GL-C3N4 showed large surface area and enhanced photocatalytic activity. Meanwhile, on the basis research of the 2D GL-C3N4, we further demonstrated that a simple ionic liquids (ILs) assisted hydrothermal process, can convert bulk g-C3N4 into a stable 3D foam-like network hydrogel. Our study employs spectroscopic and computational tools to unravel the gelation mechanism, and provides a rational approach towards the stabilization of 2D materials in hydrogels. Additionally, we believe it draws a general route to create multifunctional gels. In addition, the 3D foam-like network hydrogel exhibited special electronic and optical properties, which possessed a significant application value in the optical filed. This work also paves the way and provides a new idea for further controllable regulation of the photoelectric properties nanometer based on wet chemistry methods. The comparation study of photocatalytic performance based on 2D GL-C3N4 and 3D foam-like network hydrogel, confirms that the 2D GL-C3N4 possesses superior photocatalytic performance than that of 3D foam-like network hydrogel due to its enhanced surface area and excellecnt photo-generated carrier transfer and separation efficiency.Finding that coupling 2D GL-C3N4 with other visible-light-response materials with synergistic effect can produce multi-functional photocatalytic nanomaterials with the properties of inexpensive, highly active, visible light response. We designed and synthesized the GL-C3N4 nanocomposite materials, such as ZnS/GL-C3N4 and GL-MoS2/C3N4 by a variety of methods. These materials could be applied to photocatalytic degradation of different environmental pollutants. Experimental results showed that the surface modification of g-C3N4 could significantly improve the electrochemical properties of the g-C3N4 nanocomposites photocatalysts,exhibiting efficient photocatalytic performance for the organic pollutants degradation, which was superior to that of the pure GL-g-C3N4. The increasing contact areas between the monomer of nanocomposites could build a channel for efficient charge transfer, which would achieve an efficient and deep degradation of organic pollutants. The research exhibited unique strategy that can be extended for other hybrid nanomaterials fabrication, providing a new idea and experimental method for the design and optimization of other important chemical and catalytic reaction. |
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