Unique photoluminescence response of MoS2 quantum dots over a wide range of As (III) in aqueous media.

We report the solvothermal synthesis of MoS2 based quantum dots (QDs) and the performance evaluation of bare QDs for the detection of aqueous As (III) oxidative state at room temperature and neutral pH over a vast range (0.1 ppb to 1000 ppb). Concentration-dependent photoluminescence (PL) of the QDs enhances up to 50 ppb and then suppresses till 1000 ppb. It shows two distinctive slopes for enhancement and suppression. The enhancement is possibly due to the passivation of trap states or defects. The formation of tiny glassy As2S3 particles on the QD surface may be the possible reason for suppression. The pattern of optical absorption of QDs follows the similar patterns of PL. Still, it shows an enhanced absorbance in the near UV range below 300 nm, which increases with As (III) concentration up to 50 ppb and then decreases following the PL pattern. The MoS2 QDs were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis, and PL spectroscopy. The enhancement and suppression results were excellently fitted with the modified Stern-Volmer equation. The detection of arsenic is possible using these linear fit equations as calibration curves.