基于蒙脱石层间域的石墨相氮化碳纳米片的限域合成及机理

Graphitic carbon nitride g-C3N4 is the latest metal-free visible-light photocatalyst. Nano-sizing the macro morphology and modifying the electronic structure are the two major approaches to improve the photocatalytic performance of g-C3N4 under visible light. The current processes of synthesizing the g-C3N4 nanosheets need to synthesize the bulk g-C3N4 firstly and then process it into nanosheets by thermal etching or solvent ultrasonic delamination, which not only surfer from the shortages of low productivity and poor thickness controllability but also restrict the modification of the electronic structure of g-C3N4 nanosheets. Therefore, in this research, (1) a novel process is proposed to directly synthesize and synchronously modify g-C3N4 nanosheets within the confined interlayer nano-space of natural montmorillonite; three kinds of visible-light photocatalyst, g-C3N4 nanosheets, g-C3N4 nanosheet intercalated montmorillonite nanocomposites, and non-metal element doped g-C3N4 nanosheets, will be synthesized with high productivities; (2) the mechanisms of the intercalation of precursors into the interlayer nano-space of montmorillonite and the subsequent nano-space confined polycondensation, the effect of the nano-space confined synthesis environment on the structure, composition and photocatalytic performance of as-synthesized carbon nitride, the synergetic photocatalysis mechanism between carbon nitride nanosheet and montmorillonite, and, the modification mechanism of carbon nitride nanosheet by non-metal elements, will be investigated to preliminarily establish a theory of the nano-space confined synthesis of graphitic carbon nitride.

石墨相氮化碳（g-C3N4）是最新发现的新型非金属可见光光催化剂。氮化碳的纳米化和电子结构优化是提高其可见光催化性能的两个重要途径。当前，氮化碳纳米片需通过先合成氮化碳体相材料再进行热力刻蚀或溶剂超声剥片的方法间接性制备，不仅产率低、厚度可控性差，而且阻碍了氮化碳纳米片的电子结构的优化。为此，本项目①提出利用天然蒙脱石层间域进行氮化碳纳米片的直接限域合成与同步掺杂改性，高产率地制备氮化碳纳米片、纳米片/蒙脱石复合材料、非金属元素掺杂纳米片等可见光光催化剂；②研究各种前驱体对蒙脱石的插层机理、蒙脱石层间限域热缩聚机理、纳米限域合成环境对氮化碳组成、结构及可见光催化性能影响机理、氮化碳纳米片与蒙脱石的协同光催化机制、非金属元素对氮化碳纳米片的掺杂改性机理，以期形成氮化碳纳米限域合成及改性理论体系，为利用层状矿物直接限域合成氮化碳纳米片及其电子结构同步优化提供理论和技术参考。

本项目以天然矿物为模板，利用矿物晶体层间域及表界面，实现g-C3N4在纳米尺度的可控生长，获得了一系列g-C3N4纳米材料，并探索了材料合成机理及光催化活性提升机制。主要研究结论如下：（1）单氰胺可通过气相插层进入天然粘土矿物蒙脱石层间，经热处理可在层间限域缩聚成为g-C3N4，将蒙脱石刻蚀去除之后，可获得g-C3N4纳米片；（2）利用三聚氰胺的升华特性，可通过气相沉积法，在高岭石、埃洛石等矿物的表面生长纳米级g-C3N4，将矿物模板刻蚀去除后，可获得g-C3N4的多孔纳米片、多孔纳米管、纳米空心球基介孔材料；（3）将双氰胺包裹在石盐晶体中，通过热缩聚可限域生长Na掺杂的多孔g-C3N4纳米片；（4）利用水镁石热分解产生的水汽为绿色环保的气模板，可干扰并调控g-C3N4的晶体生长程度，获得纯的或元素掺杂的多孔g-C3N4纳米片；（5）g-C3N4的结构纳米化会引起层间距的减小和单元层的平坦化，并提供更多的活性位点，有利于光生电荷向界面传输并参与光催化反应，使其以贵金属Pt纳米颗粒为助催化剂、三乙醇胺为牺牲剂的可见光光催化产氢性能显著优于体相g-C3N4。本项目的研究结果，可为进一步基于天然矿物进行低成本、高性能的g-C3N4基纳米复合材料的设计合成及其非贵金属辅助的光催化应用研究提供理论依据和技术支撑。