Regulation of Electron Cloud Density by Electronic Effects of Substituents to Optimize Photocatalytic H2 Evolution of Carbon Dots

Carbon dots (CDs) have a wide light absorption range, which are promising candidates for photocatalytic water splitting H₂ evolution, but they show low activity for hydrogen evolution reaction (HER) due to the slow transfer efficiencies of photogenerated carriers. The electron cloud density of photocatalyst is essential for the separation and migration of photogenerated carriers. In this study, the effect mechanism of electron cloud density regulated by the substituents with different electronic effects on the photocatalytic HER of glucose-based CDs is clarified. CDs-SO₃H and CDs-OH are first obtained by introducing electron-drawing group (─SO₃H) and electron-donating group (─OH) using a tailoring post-processing strategy. Experimental results show that the H₂ yield catalyzed by CDs-SO₃H is 89.95 µmol•g^-1 in 4 h, which is about four times that of CDs, and 7.4 times that of CDs-OH. The ─SO₃H induces a much negative energy band and high electron cloud density on CDs edges, promoting the separation and transfer of photogenerated carriers; while the CDs-OH exhibits a high positive charge density and an upward energy band, hindering the surface complexation of electron-hole pairs and HER. This study will provide an insight into the design of CDs catalysts with efficient photocatalytic HER at a molecular level.