Mechanochemical synthesis of molybdenum disulfide quantum dots with enhanced dye adsorption and photocatalytic performance

Wet-mechanochemical exfoliation of molybdenum disulfide (MoS2) flakes into MoS2 quantum dots (QDs) using various exfoliation agents is studied, and the photoluminescence, adsorption and photocatalytic activities of QDs toward the degradation of rhodamine B (RhB) are evaluated. The application of ethanol as the low-boiling point (≈78 °C) exfoliation agent leads to the formation of E-MoS2 QDs (4.6 nm) with 1T-crystalline modification, dominately functionalized with hydroxyl groups. Initial MoS2 provides a weak adsorption capacity (27 mg/g), while no photocatalytic activity is observed under LED-light irradiation. E-MoS2 QDs exhibit a poor photocatalytic performance, but an excellent RhB adsorption with an equilibrium capacity of 180 mg/g under dark condition. In contrast, the application of N-Methyl-2-pyrrolidone (NMP) as the high-boiling point (≈202 °C) exfoliation agent leads to the fabrication of N-MoS2 QDs (4.8 nm) with stable 2H-crystalline modification. N-MoS2 QDs exhibits a limited adsorption capacity (32 mg/g), but an excellent stability and photocatalytic performance. At the photocatalyst dosage of 0.1 g/L, the degradation rate of dye (20 mg/L) is recorded at 100 % after 140 min of LED-light (450 nm) illumination. Reusability of N-MoS2 QDs in photocatalysis process is confirmed. Appropriate energy band gap, together with the surface amino/carboxyl functional groups are discussed to be responsible for enhanced light-induced intramolecular electron transfer, thus photocatalytic performance of the material.