科研之友
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摘要
Graphitic carbon nitride (g-C3N4) has been considered to be a promising photocatalyst due to its photoresponse under visible light. It is known that different types of oxygen groups would be normally remained on g-C3N4 during synthesis, and g-C3N4 with oxygen groups was reported to have promising photocatalytic performance experimentally. To understand the mechanism of the enhanced photocatalytic performance of g-C3N4 with oxygen groups, density functional theory (DFT) calculations were carried out in this work to investigate the band structures of g-C3N4 with different types of oxygen groups (-COOH, -OH or =O) systematically, thus predicting its capability of activation of electron-hole pair. In addition, in order to consider the position of oxygen groups on g-C3N4 and its corresponding effect on the band structure, graphitic carbon nitride nanoribbons (CNNR) is built. It is found that only -OH and =O groups can be stably attached at the center of CNNR, while all the three types of groups are stable at the edges. Additionally, -COOH or -OH group binding with N atoms (N-COOH or N-OH) can reduce the bandgap of CNNR significantly, and the bandgap further reduces sharply at high concentration of N-COOH or N-OH, while attaching =O does not change its bandgap much regardless the position of the groups expect replacing H atom at the right edge. Therefore, attaching N-OH at the middle, replacing H atoms by =O at the right edge and attaching N-COOH or N-OH at both sides are promising ways to reduce the band gap of CNNR and thus may improve the generation of electron-hole pair. Furthermore, the higher the concentration of the oxygen groups, the better the performance it has.
