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随着工农业的迅速发展,多组分复合污染系统广泛分布于自然环境中,例如电镀废水、污水处理厂污泥、城市生活垃圾等.自1972年光催化劈裂水产氢被发现以来,光催化技术已被广泛应用于解决环境污染问题.一方面,光生电子在酸性条件下能将重铬酸根(Cr_2O_7~(2–))中高毒性的Cr(Ⅵ)还原成低毒性的Cr(Ⅲ).另一方面,水中有机污染物通过光催化氧化过程可被降解为二氧化碳和水.然而在目前的光催化领域,大部分研究者专注于新型光催化剂的开发,并在单组份光催化系统中测试所开发材料的光催化活性,而忽视了蕴藏在光催化反应本身中的科学问题.事实上,将光催化技术应用于复合污染系统具有非常大的现实意义.少数研究者试图通过光催化过程处理多组分废水.然而,在复合污染系统中的协同光催化效应和机理尚未明确.近几年,基于可见光响应、环境友好、成本低等优点,作为一种不含金属的半导体光催化剂,石墨相氮化碳(g-C_3N_4)已被广泛应用于环境光催化领域.然而在实际应用中,g-C_3N_4的光催化活性却较差,因为聚集态层状结构不但限制了光生载流子的表面迁移,而且还增加了光催化反应的传质阻力.因此,人们尝试形貌控制策略来提高g-C_3N_4的光催化活性,例如氮化碳纳米片、空心球、量子点的构建.在前期工作中,我们通过一种简单的前驱体预处理策略使用盐酸和乙二醇共处理的三聚氰胺作原料成功制备出了多孔石墨相氮化碳(pg-C_3N_4),因其具有丰富的多孔微观结构而表现出了卓越的光催化活性.本文初步研究了在酸性条件下使用所制备g-C_3N_4或pg-C_3N_4光催化还原水中Cr(Ⅵ)成Cr(Ⅲ)的反应.然后在不同p H条件下进一步研究了在Cr(Ⅵ)和4-氯酚(4-CP)复合污染系统中的协同光催化效应.结果发现,与单组分光催化系统相比,在Cr(Ⅵ)和4-CP复合污染系统中Cr(Ⅵ)的还原效率和4-CP的降解效率同时提高,即在Cr(Ⅵ)和4-CP复合污染系统中存在协同光催化效应.最后讨论了在Cr(Ⅵ)和4-CP复合污染系统中的协同光催化效应可归因于pg-C_3N_4的电子转移作用加速了Cr_2O_7~(2–)和4-CP之间的氧化还原反应.在用稀H_2SO_4调节p H至3的Cr(Ⅵ)和4-CP复合污染系统中,由于Cr_2O_7~(2–)中氧原子的电子云密度较低,因此Cr_2O_7~(2–)和4-CP之间的氧化还原反应通过pg-C_3N_4的电子转移作用易于进行,因而表现出明显的协同光催化效应.
With the rapid development of industry and agriculture, multi-component composite pollution systems are widely distributed in the natural environment, such as electroplating wastewater, sewage treatment plant sludge, municipal solid waste, etc. Since 1972, photocatalytic cleavage of aquatic hydrogen was discovered, photocatalytic The technology has been widely used to solve the problem of environmental pollution.On the one hand, photoelectron can reduce the high toxic Cr (Ⅵ) in dichromate (Cr_2O_7 ~ (2-)) into low toxicity Cr (Ⅲ) under acidic condition. On the other hand, organic pollutants in water can be degraded into carbon dioxide and water through photocatalytic oxidation process.However, in the current field of photocatalysis, most researchers focus on the development of new photocatalysts and in single-component photocatalytic system Test the photocatalytic activity of the developed materials, while ignoring the scientific problems contained in the photocatalytic reaction itself.In fact, the application of photocatalytic technology to complex pollution system has a very great practical significance.Many researchers tried to pass the photocatalytic process However, the synergistic photocatalytic effect and mechanism in complex pollution systems are not yet clear.In recent years, based on the visible light response, environment-friendly, low cost Point, as a metal-free semiconductor photocatalyst, graphite carbon nitride (g-C_3N_4) has been widely used in the field of environmental photocatalysis.However, in practical applications, g-C_3N_4 photocatalytic activity is poor, Because the aggregated layered structure not only limits the surface migration of photo-generated carriers, but also increases the mass transfer resistance of photocatalytic reaction.Therefore, people try to control the morphology of g-C_3N_4 to improve the photocatalytic activity, such as nitriding Carbon nanosheets, hollow spheres and quantum dots.In the previous work, we successfully prepared porous graphite phase carbonitride by using a simple precursor pretreatment strategy using melamine co-treated with hydrochloric acid and ethylene glycol as raw materials (pg-C_3N_4), because of its rich porous microstructure showed excellent photocatalytic activity.In this paper, the preliminary study of the use of the prepared g-C_3N_4 or pg-C_3N_4 photocatalytic reduction of Cr (Ⅵ) in acidic conditions, (Cr (Ⅵ)) and Cr (Ⅵ), and then the synergistic photocatalytic activity in Cr (Ⅵ) and 4-chlorophenol (4-CP) Compared with catalytic systems, Cr (Ⅵ) and 4 -CP composite pollution system, the reduction efficiency of Cr (Ⅵ) and the degradation efficiency of 4-CP are improved at the same time, that is, there is synergistic photocatalytic effect in Cr (Ⅵ) and 4-CP complex polluted systems.Finally, ) And 4-CP complex pollution system can be attributed to the electron transfer of pg-C_3N_4 accelerates the redox reaction between Cr_2O_7 ~ (2) and 4-CP.Using dilute H_2SO_4 to adjust p In Cr (Ⅵ) and 4-CP complex systems from H to 3, due to the lower electron cloud density of oxygen atoms in Cr 2 O 7 ~ (2-), the redox between Cr 2 O 7 ~ (2-) and 4-CP The reaction is facilitated by the electron transfer of pg-C_3N_4 and thus shows a significant synergistic effect of photocatalytic activity.