The Photocatalytic Degradation Of Organic Dyes With Graphene And Carbon Nitride Based Composites

With the rapid development of national economy, more and more industrial pollutants and solid waste are discharged without treatment, which makes serious destruction of the ecological environment for human survival. Because the industrial waste water and domestic wastewater often contain a variety of refractory organic pollutants, water pollution treatment draw more and more global attention and become an important subject of environmental protection. Traditionally, the methods of treatment of organic wastewater include physical, chemical and biological methods. However, these traditional methods have low removal efficiency, high cost, and accompanied by secondary pollution. Therefore, development an efficient and environmentally friendly method to handle water pollution is an urgent issue. Recent years, photocatalytic technologies capture great interest as a kind of “green” technology for degrading toxic pollutants.Photocatalysis includes the following three procedures :Semiconductor materials produced electron-hole pairs by absorbing a certain amount of energy;Produced electrons and holes move to the surface of the semiconductor; Photo-generated electrons and holes participates the organic reactions on the surface of the catalyst, and generates carbon dioxide and water. However, the limited utilization of sunlight and high recombination rate of the photo-generated electron-hole pairs of the pure photocatalysts have restricted the applications of photocatalysis. So far, various approaches have been introduced to extend the absorption of sunlight and induce the separation of photo-generated electron-hole pairs to improve the photocatalytic activity for photocatalysts.Graphene and graphite-like carbon nitride as new carrier materials have many excellent characteristics, such as large surface area, strong adsorption capacity and excellent electrical conductivity. In recent years, researchers have confirmed the construction of graphene and graphene-like based photocatalysis can not only retain their excellent performance, but also produce synergies. Graphene and graphene-like photocatalysis can improve the conductivity of materials and adsorption properties. Moreover, they can also suppress the combination of photo-generated electron-hole pairs. Based on the above analysis, we synthesize graphene and graphite-like based composites by a facile solvothermal route and hydrothermal method. We study their morphology, structure, properties, and the photocatalytic activity. The main research content and the results are as follows:In Chapter 2, three-dimensional BiOCl_0.75Br_0.25/graphene（BG） microspheres have been synthesized via a facile solvothermal route. As the carrier of BiOCl_0.75Br_0.25 semiconductors, graphene improve the performance of photocatalytic BiOCl_0.75Br_0.25 effectively. First of all, graphene reinforce the adsorption ability of the composites. Second, with the introduction of graphene, BG hybrids exhibited a strong absorption in both UV and visible range. Third, the efficient transfer of photo-induced electrons between BiOCl_0.75Br_0.25 and graphene facilitated the electron–hole separation, and thus improves the photocatalytic activity. The BG5.0 demonstrates the highest photocatalytic activity with 97.8% Rh B degradation in 25 min. The photocatalytic mechanism reports that the decomposition of Rh B is mainly a deethylated process. The Ë™O2- and h+ as dominant active species undergo the main responsibility to degrade the dye.In Chapter 3, a series of g-C₃N₄-Sb₂S₃/Sb4O5Cl2（SCL-CX） composite photocatalysts were successfully prepared via a hydrothermal method. With the introduction of g-C₃N₄, the absorption of the composite in visible light range increased and a red shift phenomenon appeared. The enhanced light absorption of the composite samples may lead to produce more electron-hole pairs under the same visible light irradiation and thus res ult in a higher photocatalytic activity. After g-C₃N₄ was coated, the SBET of SCL-C2（the weight of g-C₃N₄ 170mg） increased to 4.6 m2 g-1.With the introduction of g-C₃N₄, the emission intensity of the SCL-C2 photocatalysts significantly decreased. The results illustrated that the efficient transfer of photo-induced electrons between g-C₃N₄ and SCL facilitated the electron-hole separation, and thus improved the photocatalytic activity. Moreover, the SCL-C2 demonstrates the highest photocatalytic activity with 95% MO degradation in 1h.To further understand the organic matter concentration in the degraded solution, TOC and COD were also tested. The result showed that the decay of TOC and COD was 5.0% and 20.0% for SCL-C2, respectively. The low mineralization may be caused by some byproducts being stable and difficult to decompose.