Lignin-ultrasound method: Enhancement of antimicrobial capacity of MoS₂-containing films

To improve the antimicrobial ability of MoS₂-containing films, we used lignin and triple-frequency ultrasound for liquid-phase exfoliation (LPE) to obtain MoS₂ nanosheets. Photoresponsive antimicrobial films with MoS₂ nanosheets, lignin, polyvinyl alcohol and deep eutectic solvents were subsequently prepared. Lignin functionalized the MoS₂ nanosheets by chemically linking with S in MoS₂ and significantly improved the exfoliation efficiency. Tri-frequency ultrasound produces beneficial effects on the LPE process by creating a more homogeneous sound field and a stronger degree of cavitation. The concentration of MoS₂ nanosheets in the exfoliating solution could reach 1.713 mg/mL under the effect of lignin-ultrasound. The antimicrobial ability of the films was analyzed, and the colony-forming units of E. coli and S. aureus could be reduced from 7 × 10⁶ to 1 × 10⁶ cfu/mL under the irradiation of infrared. The lignin in the film undergoes depolymerization and demethoxylation under the irradiation of infrared to have a more phenolic hydroxyl structure, which confers the growth inhibition ability of the films for bacteria that cannot be in close contact with the film. The method we used has some significance for the preparation of MoS₂ nanosheets, and composite films prepared from MoS_2, and lignin can be used in food packaging, wound antimicrobials, and other fields.