Defect-Rich Molybdenum Sulfide Quantum Dots for Amplified Photoluminescence and Photonics-Driven Reactive Oxygen Species Generation

Transition metal dichalcogenide (TMD) quantum dots (QDs) with defects have attracted interesting chemistry due to the contribution of vacancies to their unique optical, physical, catalytic, and electrical properties. Engineering defined defects into molybdenum sulfide (MoS2) QDs is challenging. Herein, by applying a mild biomineralization-assisted bottom-up strategy, blue photoluminescent MoS2 QDs (B-QDs) with a high density of defects are fabricated. The two-stage synthesis begins with a bottom-up synthesis of original MoS2 QDs (O-QDs) through chemical reactions of Mo and sulfide ions, followed by alkaline etching that creates high sulfur-vacancy defects to eventually form B-QDs. Alkaline etching significantly increases the photoluminescence (PL) and photo-oxidation. An increase in defect density is shown to bring about increased active sites and decreased bandgap energy; which is further validated with density functional theory calculations. There is strengthened binding affinity between QDs and O-2 due to lower gap energy ( increment E-ST) between S-1 and T-1, accompanied with improved intersystem crossing (ISC) efficiency. Lowered gap energy contributes to assist e(-)-h(+) pair formation and the strengthened binding affinity between QDs and O-3(2). Defect engineering unravels another dimension of material properties control and can bring fresh new applications to otherwise well characterized TMD nanomaterials.