Abstract
Graphitic carbon nitride (g-C3N4) is a promising semiconductor material which has been widely studied in nanoscience. However, the effect of modifying the performance of g-C3N4 is still under debate. In this communication, we show the size and functional group effects on the g-C3N4 using density functional theory (DFT) calculations. It was found that a molecule with six repeated g-C3N4 units (g-C3N4-6) could be the smallest unit that converges to the limit of its HOMO–LUMO gap. Calculations of g-C3N4-6 with varying numbers of substituted C≡N, C=O, and O−H functional groups show that C≡N and C=O could narrow down the HOMO–LUMO gap, while O−H could slightly raise the gap. This study shows that the change of substituents could tune the band gap of g-C3N4, suggesting that rationally modifying the substituent at the edge of g-C3N4-based materials could help to significantly increase the photocatalytic properties of a metal-free g-C3N4.
Highlights
Graphitic carbon nitride (g-C3N4) is a promising metal-free polymeric n-type semiconductor which has attracted huge interest during the past decade [1,2,3,4]
Since the primary works done by Wang et al [5], which showed that g-C3N4 is a promising photocatalyst for hydrogen evolution under visible light, g-C3N4 has been widely studied as a cost-effective photocatalyst for many reactions, such as carbon dioxide reduction [6,7,8] and photodegradation [1,9,10,11]
We examine how the HOMO−LUMO gap changes with the g-C3N4 size and correlates with the substituted functional group using density functional theory (DFT) calculations
Summary
Graphitic carbon nitride (g-C3N4) is a promising metal-free polymeric n-type semiconductor which has attracted huge interest during the past decade [1,2,3,4]. To narrow down the band gap of g-C3N4-based materials, doping with transition metal ions has been proven as an efficient strategy (e.g., cave [12,13,14] and interlayer [15] dopings). A better understanding of the mechanisms of band gap tuning would be beneficial to the future design and understanding of high-performance modified g-C3N4 materials.
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