Surface charge-switchable polyacrylonitrile/cellulose acetate/soluble eggshell membrane protein (PAN/CA/SEP) mixed matrix membrane for methylene blue removal

• Structured PDA-PAN/CA/SEP pH-responsive membranes were prepared for MB removal. • Optimum conditions for the batch adsorption of PDA-PAN/CA/SEP were obtained. • Structured PDA-PAN/CA/SEP shows better dynamic filtration performance than control. • PDA-PAN/CA/SEP exhibits nearly 100% affinity towards MB over MO. • PDA-PAN/CA/SEP shows 66% retention after 10 regeneration cycles. The textile industry consumes over 700,000 tonnes of synthetic dyes annually, generating dye-polluted wastewater harmful to the environment. Thus, this study investigated the potential of electrospun microfibrous membranes (EMMs) for dye remediation. Two types of membranes were synthesised in this study: a flat sheet membrane (control) and a microfibrous membrane with a pH-sensitive charge-switchable surface for enhanced adsorption of methylene blue (MB) and methyl orange (MO). The microfibrous membrane is fabricated via direct-write electrospinning (DWES) using a modified 3D printer equipped with a 30 kV direct current (DC) power supply, resulting in a unique triangular pore network. The electrospinning solution comprises polyacrylonitrile (PAN), cellulose acetate (CA), and soluble eggshell membrane protein (SEP), with dopamine (PDA) grafted onto the surface to introduce pH sensitivity. Generally, the EMMs exhibited high surface area, porosity, mechanical robustness, and controllable wettability, making these membranes ideal for dye removal. Characterisation confirmed a well-defined pore network, surface charge migration, high thermal stability, and excellent permeability. Batch adsorption studies revealed an adsorption capacity of 21.80 mg/g under optimal conditions influenced by MB concentration, shaking speed, temperature, and reaction time. Dynamic adsorption studies demonstrated the high selectivity of EMMs (MB selectivity was 6.28 times greater than MO), recyclability (effective for 10 cycles), and strong cationic dye affinity (100 %), outperforming the flat sheet membrane (24.1 % higher adsorption capacity). The adsorption followed a Freundlich-like multilayer model and pseudo-second-order kinetics. Thermodynamic analysis revealed spontaneous adsorption at low temperatures, enhancing energy efficiency. In summary, this study offered a sustainable approach for mitigating dye pollution in textile wastewater, aligning with global water conservation efforts.