We present a simple approach for producing photoluminescent MoS2quantum dots (QDs) using commercial MoS2powder as a precursor along with NaOH and isopropanol. The synthesis method is particularly easy and environmentally friendly. The successful intercalation of Na+ions into MoS2layers and subsequent oxidative cutting reaction leads to the formation of luminescent MoS2QDs. The present work, for the first time, shows the formation of MoS2QDs without any additional energy source. The as-synthesized MoS2QDs were characterized using microscopy and spectroscopy. The QDs have a few layer thicknesses and a narrow size distribution with an average diameter of ∼3.8 nm. Nitrobenzene (NB), an industrial chemical, is both toxic to human health and dangerously explosive. The present MoS2QDs can be used as an effective photoluminescent probe, and a new turn-off sensor for NB detection. The selective quenching was operatedviamultiple mechanisms; electron transfer between the nitro group and MoS2QDs through dynamic quenching and the primary inner filter effect (IFE). The quenching has a linear relationship with NB concentrations from 0.5 μM to 11 μM, with a calculated detection limit of 50 nM.