High-efficiency PVP-PVDF/MXene membranes for dyeing wastewater nanofiltration: A dual strategy of tuning nanochannels and enhancing electrostatic adsorption

Membranes were widely applied in the zero discharge of industrial wastewater. The improvement of nanofiltration efficiency was a persistent objective in industrial wastewater treatment. Efficient PVP-PVDF/MXene membranes were fabricated via adjusting the molecular weight of polyvinylpyrrolidone (PVP) and the dosage of MXene nanosheets. PVP-PVDF/MXene membrane predominantly owned a mesoporous structure with a key pore size distribution ranging from 2 to 5 nm. PVP influenced the abundant vertical and horizontal nanochannels of PVP-PVDF/MXene membranes. The lamellar structure of MXene nanosheets created tortuous pathways in the membrane and increased transport path length. They mutually determined water flux and rejection of dyes in various wastewater treatment. Methylene blue (MB) was mainly rejected through the size exclusion effect in nanochannels. MXene nanosheets supplied specific surface area, hydrophilicity and negatively charged functional groups. First-principles calculations revealed an adsorption energy of −7.89 eV, which was attributed to the strong interaction between MXene nanosheets and MB. MXene nanosheets promoted MB rejection. The optimal PVP-PVDF/MXene membrane prepared by 10,000 Da PVP and 0.008 g MXene achieved the highest water flux of 372.09 L·m −2 ·h −1 and MB rejection of 99.07% under ultra-low pressure condition of 0.02 bar. Flux recovery rate of PVP-PVDF/MXene membranes was 86.97% in MB treatment. They possessed excellent antifouling and recovery capacities. PVP-PVDF/MXene membrane was a potential candidate for application in wastewater treatment.