Constructing defect-related subband in silver indium sulfide QDs via pH-dependent oriented aggregation for boosting photocatalytic hydrogen evolution.

Surface engineering of quantum dots (QDs) plays critical roles in tailoring carriers' dynamics of I-III-VI QDs via the interplay of QDs in aggregates or assembly, thus influencing their photocatalytic activities. In this work, an aqueous synthesis and the followed pH tuned oriented assembly method are developed to prepare network-like aggregates, dispersion, or sheet-like assembly of GSH-capped Silver Indium Sulfide (AIS). FTIR, DLS, and HRTEM investigation revealed that surface protonation or deprotonation of QDs occurred at pH < 6 or pH > 12 favors the formation of network-like aggregates with various defects or sheet-like assembly with perfect crystal lattice, respectively, via the surface charge induced interaction among AIS QDs. Further UV-vis, steady and transient PL investigation confirm the narrowed band gaps and the prolonged PL lifetime of the acidic network-like aggregates. As a result, the optimized network-like aggregates (3.0-AIS) exhibits superior photocatalytic H evolution (PHE) rates (5.2 mmol·g·h), about 113 times that of alkaline sheet-like assembly (13.0-AIS) or 2.7 times higher than that of dispersed AIS QDs (AIS-8.0). The formation of defects and their roles in PHE mechanisms are discussed. This work is expected to give some new insight for designing efficient non-cadmium/non-novel metal I-III-VI photocatalysts for boosting PHE.