Facile Surface Engineering of Ag–In–Zn–S Quantum Dot Photocatalysts by Mixed-Ligand Passivation with Improved Charge Carrier Lifetime

Abstract

I–III–VI quantum dots (QDs) play an important role in visible-light-driven photocatalysis due to their unique optical properties and widely tunable bandgap. However, these materials suffer from rich defect states and high charge carrier recombination. In this work, a facile mixed-ligand method was developed for the manipulation of the optical and photocatalytic properties of multinary Ag–In–Zn–S QDs by introducing 3-mecaptopropionic acid (MPA) into the l-cysteine (Cys) capped QDs system during synthesis. The effect and mechanism of MPA addition was systematically investigated. With the increase of MPA/Cys, the photoluminescence (PL) quantum yield (QY) of the QDs shows an obvious increase at the first stage (MPA/Cys < 5:5), whereas the particle size and UV–Vis absorption remain almost unchanged. Photocatalytic properties of QDs shows similar trend as PL QY with the increase of MPA/Cys, where the hydrogen production rate was doubled with MPA/Cys = 5:5. With ascorbic acid (AA) as the sacrificial reagent, the MPA/Cys capped QDs gave a hydrogen production rate as high as 6.64 mmol g−1 h−1, which is comparable to the state-of-the-art results but without any cocatalyst, indicating the fascination of the simple mixed-ligand method. Further mechanism study indicates that the introduced MPA resulted in dramatic increase of the PL lifetime and the reduction of nonradiative decay, which can be ascribed to the strong passivation effect of MPA. The MPA/Cys capped QDs also show compressed charge recombination as indicated in electrochemical impedance spectra, slightly more negative ζ-potential and reduced hydrated particle radius, which may also contribute to the improved charge transfer for photocatalysis. Our method provides a super simple strategy for the defect manipulation of the Ag–In–Zn–S QDs without the sacrifice of charge transfer, which could be a useful guideline for efficient QDs-based visible-active photocatalysts. Mixed-ligand-modified Ag–In–Zn–S quantum dots with improved hydrogen production were prepared.