新型生物炭/石墨相氮化碳复合材料的可控制备及其光催化性能研究

Biochar-based composites show promising adsorption properties and hold great potential for environmental applications. However, they still suffer from the drawback of low degradation efficiency of organic contaminants. Therefore, the design and development of biochar-based composites with both adsorptive and photocatalytic capabilities are of great significance for their application in environmental pollution remediation. With a relatively narrow band gap, suitable conduction and valence bands, metal-free g-C3N4 is appropriate for harvesting UV–vis light for the degradation of organic pollutants. However, the rapid recombination of charge carriers, poor visible-NIR light utilization, as well as low specific surface area seriously restricts its photo-catalytic activity. In this proposed project, we expect to achieve a breakthrough to solve the above challenges through the structure and mechanism innovations. A novel biochar composite with catalytic function (g-C3N4/biochar) combining the advantages of biochar and metal-free graphite-phase carbon nitride (g-C3N4) are synthesized and tested for antibiotic removal efficiency and mechanisms. The surface electron transfer is accelerated by optimizing the redox properties and the molecular adsorption/activation properties of the composites. Characterizations are performed to investigate the mechanisms of the interface structure, electron transfer process, and the synergistic effect between the components on the antibiotic degradation performance at molecular and atomic level. The strong adsorption capacity of biochar rapidly enriches the contaminates on the surface of the composites, and the electron transfer between the interfaces is supposed to be accelerated; g-C3N4 provides free radicals and electron holes, produces electron transfer process, and enables in-situ regeneration of biochar. The implementation of this project is suspected to provide some scientific basis for the fabrication, design, and application of metal-free, low-cost, “green”, and effective biochar-based catalyst with excellent organic contaminants degradation efficiency.

生物炭复合材料可以极大拓展生物炭的应用范围，但到目前为止还存在对有机污染物降解能力弱的瓶颈问题。研究环境相容性好、兼具吸附-光催化协同效应的生物炭光催化复合材料是解决这一问题的关键。不含金属的石墨相氮化碳（g-C3N4）因其可利用可见光且环境友好在光催化领域备受青睐，但其缺点在于吸附能力弱、光生电子和空穴复合速率快。本项目拟通过可控制备方法，将g-C3N4吸收可见光、低带隙能、高催化能力等优点和生物炭比表面积大、吸附能力强的优势相结合，获得不含金属、催化活性高、环境友好的g-C3N4/生物炭新型材料。通过表征手段，从分子、原子层面探讨复合材料表面结构、电子转移过程和组分间协同作用机理。以典型抗生素恩诺沙星为代表，研究复合材料在可见光下对水中抗生素的光催化降解特性，并阐明吸附-光催化协同反应机制。本项目对开发新型不含金属的生物炭催化剂、促进生物炭在环境领域的应用具有重要理论意义。

生物炭复合材料可以极大拓展生物炭的应用范围，但到目前为止还存在对有机污染物降解能力弱的瓶颈问题。研究环境相容性好、兼具吸附-光催化协同效应的生物炭光催化复合材料是解决这一问题的关键。不含金属的石墨相氮化碳（g-C3N4）因其可利用可见光且环境友好在光催化领域备受青睐，但其缺点在于吸附能力弱、光生电子和空穴复合速率快。本项目通过可控制备方法，将g-C3N4吸收可见光、低带隙能、高催化能力等优点和生物炭比表面积大、吸附能力强的优势相结合，获得不含金属、催化活性高、环境友好的g-C3N4/生物炭新型材料，并阐明其通过吸附-催化协同降解水中抗生素恩诺沙星（EFA）的效能与机制。. 研究结果表明：（1）与原始生物炭相比，球磨生物炭对EFA的吸附能力有了显著提升，在可见光照射下可以产生更多的•O2-，这有利于EFA的光催化降解。300 ℃下热解的生物炭经球磨后表现出最高的EFA降解率（80.2％，BC300为13.9％）和矿化率（66.4％，BC300为0％）。（2）在此基础上，通过球磨法制备的g-C3N4/生物炭复合材料经表征后证明g-C3N4和生物炭实现了有效的连接。与单纯的g-C3N4相比，所有g-C3N4/生物炭复合材料对EFA的吸附和光催化性能均有所增强。生物炭的加入丰富了材料中的含氧官能团，增强了对光的吸收能力和电子-空穴对分离效率，从而增强了材料的光催化能力。50％ g-C3N4/生物炭对EFA的光降解效率最高，为81.1％，吸附效率为63.2％，而单纯g-C3N4分别为27.3％和19.0％。自由基捕获实验表明，•O2-和h+是光催化去除过程中的主要活性物质。基于表征和实验结果，我们得出复合材料对EFA的吸附主要受静电作用、H键结合以及与含氧官能团和比表面积有关的表面吸附控制，在复合材料对EFA的光降解过程中，光激发产生的电子跃迁到导带后，生物炭可以作为电子受体及时地将电子从导带转移到生物炭表面，促进电荷分离以提升复合材料的光催化作用。项目对开发新型不含金属的生物炭催化剂、促进生物炭在环境领域的应用具有重要理论意义。