Effect of Surface Trap States on Photocatalytic Activity of Semiconductor Quantum Dots

摘要

Semiconductor quantum dots (QDs) are promising photocatalysts for water splitting due to the large specific area, but the influence of surface trap states on the photocatalytic activity of QDs is still not fully understood yet. To answer this question, CdSe QDs with the same morphology, diameter, crystal structure, and energy level are prepared following a hydrazine hydrate (N2H4) promoted synthesis strategy and conventional hydrothermal synthesis method. Through various characterizations and analysis, it is found that the conventional hydrothermal synthesized CdSe QDs (H-CdSe QDs) have a high concentration of Cd-involved shallow electron trap states, which seriously hinder the charge separation and transfer between CdSe and cocatalysts. In contrast, the N2H4 promoted synthesis strategy provides an energy-saving, low-cost, and facile pathway to eliminate the surface shallow electron traps, ensuring an efficient charge separation and H-2 production in CdSe QDs. As a result, the N2H4-promoted synthesized CdSe QDs (N-CdSe QDs) produce 44.5 mL (1998 mu mol) H-2 in 7 h, roughly 1.6 times higher than that of H-CdSe QDs (27.5 mL, 1236 mu mol). Because the surface trap states are widespread in semiconductor QDs, it is believed that our study provides valuable guidance on the design and preparation of QDs for photocatalysis.