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Effective bandgap narrowing of Cu-In-Zn-S quantum dots for photocatalytic H2 production via cocatalyst-alleviated charge recombination


Development of single-component photocatalysts with narrow bandgaps (2.0-3.0 eV) has been one of the most important goals for photocatalytic H2 production, for which I-III-VI multinary sulfides play an important role due to their widely tunable composition-dependent bandgap. However, simultaneous bandgap narrowing and photocatalytic activity enhancement in the I-III-VI sulfides are often hard to achieve due to increased defect states. Here, a series of Cu-In-Zn-S quantum dots (QDs) were synthesized by a facile hydrothermal method focusing on a more profound understanding of bandbap tuning and the subsequent effect on the photocatalytic process by controlling Cu content. Bandgap of the QDs can be effectively tuned from 2.90 eV to 1.98 eV with increasing Cu:In ratio from 0.05:10 to 2.5:10 and a color change from light yellow to dark red. The QDs show photocatalytic H2 production activity even without any cocatalyst, but it quickly started to decrease with Cu/In ratio over 0.1:10 (bandgap of 2.59 eV), which highly limits the potential for visible light photocatalysis. Interestingly, Pt-loading effectively enhanced not only the tolerance of Cu incorporation, but also enabled high H2 production activity even with further bandgap narrowing down to ~2 eV. The best photocatalytic performance of 456.4 μmol h-1 g-1 was achieved for Cu:In:Zn ratio of 1:10:5 with a bandgap of 2.27 eV. This increased tolerance of Cu content may result from the combined effect of charge separation by Pt as the cocatlayst that alleviated the Cu-induced charge recombination. The enhanced charge separation was proved by the photoluminescence quenching of the QDs with cocatalyst. Electrochemical impedance spectroscopy was further used to study the charge separation property of this photocatalytic system. This is the first observation of the cocatalyst-enhanced tolerance of Cu resulted from the competition of cocatalyst-induced charge separation and defect-induced charge recombination in multinary sulfides, which provides an interesting view and design guideline for narrow bandgap photocatalysts.

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Publication details

The article was received on 30 Sep 2017, accepted on 08 Nov 2017 and first published on 09 Nov 2017

Article type: Research Article
DOI: 10.1039/C7QI00607A
Citation: Inorg. Chem. Front., 2017, Accepted Manuscript
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    Effective bandgap narrowing of Cu-In-Zn-S quantum dots for photocatalytic H2 production via cocatalyst-alleviated charge recombination

    L. Tan, Y. Liu, B. Mao, B. Luo, G. Gong, Y. Hong, B. Chen and W. Shi, Inorg. Chem. Front., 2017, Accepted Manuscript , DOI: 10.1039/C7QI00607A

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