Carbon-dots-mediated highly efficient hole transfer in I-III-VI quantum dots for photocatalytic hydrogen production

Abstract

The extraction of photogenerated holes is of great significance for the improvement of both the efficiency and stability of photocatalysts. In this work, carbon dots (CDs) were used to modify the hole transporting ligand ferrocenecarboxylic acid (FcA) by simple hydrothermal treatment to obtain CDs-FcA hybrids, which were further combined with Ag-In-Zn-S (AIZS) quantum dots (QDs) to form AIZS-CDs-FcA composites by in-situ synthesis. CDs act as an effective hole transfer intermediate between FcA and AIZS QDs. The optimal hydrogen production rate reached 2.3 mmol g−1 h-1 with 4 % CDs and 0.64 % FcA, which is 5.8 and 2.9 times to that of AIZS QDs and AIZS-FcA, respectively. Moreover, with ascorbic acid as the hole sacrificial agent, time-resolved photoluminescence study indicates a dramatically boosted hole transfer rate in AIZS-CDs-FcA (1.97 × 1010 s-1 mM-1), compared to AIZS QDs (1.11 × 108 s-1 mM-1) and AIZS-FcA (7.28 × 108 s-1 mM-1). When 2.5 % Ni2+ was further added for electron extraction, the hydrogen production rate reached 13.1 mmol g-1 h-1 under the synergistic electron/hole extraction, achieving a 31.9-fold enhancement compared to pure AIZS QDs. This work points out for the first time the critical role of CDs as hole transfer mediator and shines light on the design of novel hole extraction reagents for photocatalysis employing the charge accumulation characteristic of carbon-based materials.