In situ synthesis of WS₂ QDs for sensing of H₂O₂: Quenching and recovery of absorption and photoluminescence

In most studies, liquid-exfoliated tungsten disulfide quantum dots (WS₂ QDs) were synthesized at pH∼4 (acidic) and generally unstable. Therefore, a figment synthesis technique for creating stable WS₂ QDs is essential. Here, functionalized blue fluorescent WS₂ QDs were fabricated with a single-step hydrothermal growth method at pH∼11 without any subsequent modifications. Functional groups in the WS₂ QDs give great stability, water dispersibility, and significant photoluminescence (PL) which depends on excitation wavelength. PL shows a multiexponential decay, probably as a result of the overlap of emissions from different emitting states. The absorption and PL of WS₂ QDs were extremely sensitive to hydrogen peroxide (H₂O₂) in water. The absorption and PL of WS₂ QDs quenched strongly and linearly with increasing H₂O₂ concentration from 0.33 nM to 594 µM. The quenching of both absorption and PL by H₂O₂ recovered nearly 100 % by adding 0.1 N HCl. The PL quenching/recovery showed cyclic stability for more than nine cycles, and the limit of detection (LoD) of H₂O₂ was estimated to be 1.7 × 10^-6 M. The oxidation from W(IV) to W(VI) and subsequent reduction are considered to induce quenching of absorption/PL and recovery. PL decay profiles of WS₂ QDs were also measured, and excited-state dynamics of the emitting state of WS₂ QDs in the presence of H₂O₂ have been discussed. Thus, the fluorescent WS₂ QDs having significant emission quantum yield can detect H₂O₂ with excellent cyclic stability and sensitivity in an aqueous environment, which will be further used for biological applications.