基于动力学控制的氮化碳基多元光解水体系的构筑与性能研究

The slow kinetics of water oxidation by carbon nitrides is the “bottleneck” for hydrogen production via overall water splitting. A new species of carbon nitride, poly(triazine imide) (PTI) is more favorable than conventional graphitic carbon nitride for oxygen production due to its more positive valence band. In this proposal, we will focus on the design and construction of photocatalytic systems derived from PTI/ZnO heterojunction, which has been successfully synthesized by our group recently. The multicomponent systems could be fabricated via surface modification or in situ synthesis. Different cocatalysts deposited with PTI/ZnO will be synthesized. This surface modification not only inhibits recombination of photo-generated electron-hole pairs but also reduces the excessive energy barrier for O-O formation. An alternative pathway for the fabrication of multicomponent systems is direct addition of catalysts possessing high catalytic activity for H2O2 decomposition. This in situ synthesis could constitute composite photocatalysts for water splitting via a stepwise two-electron/two-electron process which is kinetically favored with respect to the fourelectron process. Thus a higher reaction rate may be achieved. The photocatalytic water-splitting performance of the obtained composite catalysts will be evaluated. The photocatalytic reaction mechanism will also be investigated. This multicomponent photocatalytic system could promote the understanding of fundamental photocatalysis mechanism and contribute to the overall water splitting in a practical way.

氮化碳光催化分解水时产氧困难是其真正实现全解水制氢的瓶颈。新型氮化碳聚三嗪亚胺（PTI）由于具有更低的价带位置而比传统石墨相氮化碳在产氧上更具优势。本项目以申请人新近开发的PTI/ZnO异质结为基体，分别采用“原位合成”和“表面修饰”两种方法，构筑基于动力学控制的多元复合光催化体系，改善光解水产氧性能：（1）通过直接添加一系列能够分解H2O2的催化剂，原位合成多元复合材料，以动力学上更有利的两步、两电子光解水反应代替反应速率低的四电子反应，提高产氧反应速率；（2）通过在PTI/ZnO表面修饰不同的助催化剂，并调节助催化剂的尺寸形貌和负载量，达到抑制光生电子和空穴的复合、降低产氧反应活化能的目的。评价体系的光催化分解水性能，研究光催化反应机理，确定影响光催化性能的关键因素，为真正实现太阳光全解水制氢提供理论依据。

氮化碳光催化分解水时产氧困难是其真正实现全解水制氢的瓶颈。本研究拟分别通过两种方法来提升氮化碳的产氧性能，以实现全解水：(1)新型氮化碳聚三嗪亚胺（PTI）由于具有更低的价带位置而比传统石墨相氮化碳（g-C3N4）在产氧上更具优势，以PTI代替g-C3N4为基底，有望突破产氧瓶颈；(2)通过助催化剂表面修饰，提供产氧活性位点，提高光解水产氧反应速率。但在研究的过程中发现，PTI的产氢活性较低，因此改善其光解水产氢性能也是最终实现全解水的重要一环。基于此，本研究着眼于前期开发的PTI/ZnO体系，主要进行了两方面的工作：一方面通过向PTI的前驱体中加入碳源，构筑C-PTI/ZnO多元异质结，提高PTI的导带位置，在热力学上增加其产氢驱动力；另一方面通过在PTI与ZnO间引入电子传递介质氮掺杂的石墨烯量子点，加快两相间的电子传递，实现了体系光催化产氢性能的提升。另外，分别在氮化碳表面修饰了单原子钴和超细MnO2作为产氧助催化剂，极大改善了体系的产氧性能，从而实现了基于氮化碳的光催化全解水。