Preparation of polyethersulfone/plant-waste-particles mixed matrix membranes for adsorptive removal of cationic dyes from water

This paper focuses on the preparation of porous mixed matrix membranes (MMMs) by filling plant waste particles in polyethersulfone (PES), specifically for adsorptive removal of cationic dyes from water. Three kinds of plant wastes, including banana peel, tea waste, and shaddock peel, were adopted as fillers to fabricate the MMMs via water-vapor-induced phase inversion. The prepared particles and MMMs were characterized by BET, FTIR, SEM, TGA, zeta potential, porosity, and ion-exchange capacity (IEC). In batch process, the saturated dye adsorption capacities of plant waste particles were found to be 1055-1173 mg/g particles for methylene blue and 1085-1244 mg/g particles for methyl violet 2B, which are larger than the corresponding results of biosorbents reported in the literature. The adsorptivities of the MMMs were essentially contributed from the filled plant waste particles. Desorption greater than 95% could be achieved with the use of 1 M KSCN in 80% methanol, indicating that the cationic dyes were bound with the MMMs through a combination of electrostatic interaction, hydrophobic interaction, and hydrogen bonding. In the dead-end (flow-through) operation with one piece of 25 mm MMM disc at 1 mL/min, the original dye removal and recovery efficiencies could be successfully retained after three adsorption/desorption cycles no matter the feed was dilute solution (5 mg/L, pH 4) or synthetic dye wastewater (200 mg/L methylene blue, 100 g/L Na2SO4, pH 10). The dynamic adsorption capacity for a 10 cm×10 cm membrane module was also investigated in both the cross-flow and dead-end modes. The MMM performance could be effectively repeated at a larger membrane area scale in the dead-end operation.