Energy Band Engineering and Defect Passivation in AgInGaS ₂ Quantum Dots for Photocatalytic CO ₂ Reduction

Heavy-metal-free photocatalysts for solar-driven CO 2 reduction represent a sustainable pathway toward carbon-neutral fuel production. Ternary chalcogenide AgInS 2 (AIS) quantum dots (QDs), nanoscale semiconductors (typically 2–5 nm) whose optoelectronic properties are intrinsically governed by quantum confinement and high surface-to-volume ratios, offer an environmentally benign alternative but suffer from insufficient reduction potential and rapid charge recombination. In this work, we demonstrate that Ga 3+ doping into AIS (AIGS) QDs simultaneously engineers band edges and suppresses defect-mediated charge recombination. Systematic compositional tuning of AIGS QDs yields optimized photocatalytic CO 2 reduction performance, achieving CH 4 and CO production rates of 16.7 μmol g –1 h –1 ─a 6.2-fold improvement over pristine AIS QDs. Combined spectroscopic, electrochemical, and density functional theory investigations establish that Ga 3+ doping upshifts the conduction band minimum to enhance thermodynamic driving force while reducing defect states that serve as recombination centers. Transient spectroscopy confirms prolonged charge-carrier lifetimes in AIGS QDs, directly correlating with improved photocatalytic performance. This integrated band engineering and defect passivation strategy provides an efficient way for designing high-performance, heavy-metal-free QD photocatalysts for artificial photosynthesis.