N空位、O掺杂多孔空心棱柱状石墨相氮化碳的可控合成及其光催化固氮性能

Recently, bulk graphitic carbon nitride has emerged as suitable photo, electro and heterogeneous catalyst for various reactions due to their tunable electronic properties, high stability, and low price. Concerning over some drawbacks of ordinary bulk graphitic carbon nitride such as small surface area, low separation efficiency and poor mobility of photogenerated carriers, and focusing on key scientific issues including the effect of monomers and solvents, the formation mechanism of carbon-nitrogen materials, this proposal is to develop new methods to synthesize nitrogen-deficient and oxygen-doped graphitic carbon nitride with porous hollow prismatic structure toward its utilization as active catalysts for nitrogen photofixation under visible light, and to elucidate the photocatalytic activity as a function of its structural, chemical, and physical properties. This work will alter the elements ratio and spatial organization by using monomers with different element ratio and compositions in order to control the properties of the final materials. Advanced characterization techniques will be used to study the structure, morphology, atomic composition, chemical binding energies alongside the interactions between the individual components, the materials band gap, energy band position, lifetime of the photogenerated excitons and recombination processes. The implementation of the project would be valuable not only in theory for graphitic carbon nitride materials, but also with potential value in engineering practice of nitrogen photofixation.

针对普通石墨相氮化碳存在比表面积小、光生载流子的分离效率和迁移率低等缺点，围绕聚合物单体和溶剂对超分子自组装过程的影响、碳氮基纳米材料的形成机制及微观结构与催化性能间的关系等关键科学问题，本项目拟开展N空位、O掺杂多孔空心棱柱状石墨相氮化碳的可控合成及其可见光催化固氮性能研究。将采用单一氮源，在合成棱柱状自组装超分子前驱体的基础上，经高温热缩合获得目标产物。多孔空心棱柱状的结构将有助于提高比表面积，防止石墨相氮化碳出现团块层层堆叠的现象，从而提升光生载流子的迁移速率。项目将探索此类材料形成过程中的形貌、结构、原子组成、化学键能等信息，将通过相关表征手段分析，推断催化材料形成机理和演化规律，阐明N空位、O掺杂对石墨相氮化碳微结构和光催化固氮性能的影响，研究光催化固氮反应机理以及反应过程中有效活性自由基物种的性质和作用。该项目的开展将对碳氮基材料的结构设计及其光催化固氮等应用研究提供依据。

半导体光催化是一种利用半导体将太阳能转换为高能化学能的绿色技术，在可再生清洁能源生产和污染物修复领域有着巨大的应用前景。本项目针对普通石墨相氮化碳存在比表面积小、光生载流子的分离效率和迁移率低等缺点，围绕聚合物单体和溶剂对超分子自组装过程的影响、碳氮基纳米材料的形成机制及微观结构与催化性能间的关系等关键科学问题，本项目开展了N空位、O掺杂多孔空心棱柱状石墨相氮化碳的可控合成及其可见光催化固氮性能研究。选取二氰二胺为唯一氮源，通过浓硝酸的初步改性，再采用简单的低温水热和后续煅烧两步工艺，成功制备具有氮空位和氧掺杂的空心多孔棱柱状石墨相氮化碳。结果显示，所制得的空心棱柱状石墨相碳氮化碳呈现出疏松的海绵状外壁和明显的多孔隙结构，比表面积高达220.16 m2 g-1。此石墨相氮化碳催化剂在可见光照射下具有较高的固氮率和良好的循环稳定性，其光催化固氮的机理可提出如下：在可见光照射下，含氮空位和氧掺杂的石墨相氮化碳发生电荷分离，产生光生电子-空穴对，随后导带上的光生电子迅速转移到氮空位诱导的中间带，从而俘获的电子与氮空位上的活性氮分子反应生成氨。催化剂优异的光催化固氮性能可归因于其独特的疏松多孔的空心棱柱结构，氮空位的活性位点的充分暴露，更负的导带位置，合适的可见光响应以及光生电子-空穴对的有效分离。项目的实施不仅具有理论意义，而且将有助于推进实现半导体光催化技术的实用化进程。