| Due to the over-exploitation and irrational utilization of coal, oil and other fossil fuels, it has been a great challenge for mankind to overcome the problems of environment pollution and energy shortage. As a new method, photocatalysis technology is green, clean, and sustainable, because it can split water to generate H2 and degrade pollutions by using solar energy directly. The most reported photocatalysts like TiO2 suffer from the disadvantages of low ultilization of solar energy, fast recombination of photo-induced carriers, and poor quantum yeild, which limited their practical application. Thus, exploring new photocatalyst with visible light response, high quantum yeild and stability is a research hotspot of this area in current. In recent years, a new nonmetal photocatalyst, graphitic carbon nitride (g-C3N4) has received increased attention because of its advantages of cheap price and stable, physico-chemical properties stable and environmental friendly character. But the photocatalysis activity of g-C3N4 is relatively low, because of its low surface areas and fast recombination of photo-induced carriers. Several modification methods have been proposed to improve the photocatalitic activity of g-C3N4, such as:texture modification, element doping, co-polymerization, and coupled with other materials. Compared with the bulk g-C3N4, nanoporous g-C3N4 possesses controllable morphology, higher surface area, and a lot of active sites on the surface, which can increase the photocatalitic activity of g-C3N4. In this dissertation, we focus on exploring new methods to synthesize nanoporous g-C3N4 (npg-C3N4), and further to modifiy porous g-C3N4 by coupling CdS QDs or sulfur doping, by which the photocatalitic activity of g-C3N4 was expected to further increased because of the synergistic effect of two modification methods. The research details and results are as follows:1. Mesoporous carbon nitride (mpg-C3N4) was prepared by using a hard-templating method. Dicyandiamide (DCDA) was chose as the precursor, and SBA-15 was used as the template. DCDA and SBA-15 were mixed by ultrasonic method. After calcination and removing the template, mpg-C3N4 was obtained. The results showed that mpg-C3N4 possessed a high surface area with 222.1 m2/g and an average pore diameter with 3.8 nm. As a result, the physical adsorption to Rhodamine B dye (RhB) of mpg-C3N4 was improved twice times than that of g-C3N4, and the photocatalytic activity of mpg-C3N4 was also improved by double.2. Exploring a template-induced method for the synthesis of npg-C3N4 by using Triton X-100 as the template and melamine as the precursor. The melamine sulfate with regular structure was prepared by using concentrated sulfuric acid. Then npg-C3N4 with high surface areas can be obtained after calcination. The results showed that the as prepared samples possessed a high surface area (up to 130 m2/g), increased absorption intensity and extened absorption range of visible light. The BET surface areas of the samples could be modified by changing the Triton X-100 adding amounts and the heating temperature, and the best condition is mTX/mMA=0.5 and 580?. As a result, the photodegradation rate of npg-C3N4 for Rhodamine B dye was greatly improved, and the reaction rate constant of npg-C3N4 was increased to almost 20 times of that of bulk g-C3N4.3. CdS QDs was further loaded on npg-C3N4 to construct a heterojunction between them. The results indicated that CdS QDs can disperse on the surface of npg-C3N4 homogeneously and form the heterojunction structure. The porous structure of npg-C3N4 could inhibit the aggregation effects of CdS QDs in the composite process. The BET surface area of npg-C3N4 showed little decrease after adding CdS QDs, but its visible light adsorption was greatly extended. As a result, the photocatalitic activity of CdS/npg-CN was obviously increased than that of each single component, and the CdS/npg-CN showed good stability. Meanwhile, the photo corrosion effect of CdS was inhibited to some extent.4. The synthesis of sulfur doped npg-C3N4 rods (Spg-C3N4) in one pot. Melamine and trithiocyanuric acid was used to form a hydrogen bond supermolecular complex in aqueous solution by a self-assembly method. The Spg-C3N4 was obtained by directly heating the supermolecular complex. The effect of heating temperature on the structures and properties was investigated. The results indicated that Spg-C3N4 possessed large BET surface area (up to 52 m2/g), and the BET surface area increased with increasing the heating temperature. Compared with g-C3N4, the absorption intensity and absorption range of visible light of Spg-C3N4 all increased. As a result, the photodegradation rate of Rhodamine B dye on the Spg-CN samples was greatly improved, and its reaction rate constant was almost 11 times of that of bulk g-C3N4. |
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