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

Wet-mechanochemical exfoliation of molybdenum disulfide (MoS 2 ) flakes into MoS 2 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-MoS 2 QDs (4.6 nm) with 1T-crystalline modification, dominately functionalized with hydroxyl groups. Initial MoS 2 provides a weak adsorption capacity (27 mg/g), while no photocatalytic activity is observed under LED-light irradiation. E-MoS 2 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-MoS 2 QDs (4.8 nm) with stable 2H-crystalline modification. N-MoS 2 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-MoS 2 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.