Influence of alkaline 2D carbon nitride nanosheets as fillers for anchoring HPW and improving conductivity of SPEEK nanocomposite membranes

In the present study, novel composite membranes were prepared based on sulfonated poly (ether ether ketone)/phosphotungstic acid/carbon nitride nanosheets (SPEEK/HPW/g-C3N4). The alkaline ultrathin g-C3N4 nanosheets in the membranes behaved like “double-sided adhesive”, forming hydrogen bonds with the HPW molecules to anchor hydrophilic HPW without leaking. Moreover, the amine groups of nanosheets formed acid–base pairs with –SO3H of the SPEEK polymer matrix, facilitating the Grotthuss-type transport of proton to improve conductivity. The g-C3N4 inorganic particles provided tortuous pathways for methanol transport to suppress the methanol permeability coefficient. The selectivity of the SPEEK/HPW/g-C3N4-1.0 was 2.3 times higher than that of SPEEK/HPW and 1.5 times higher than that of pristine SPEEK. SPEEK/HPW/g-C3N4 hybrid membranes exhibited stable and durable operation for 240 h under 100% RH at 60 °C. Moreover, membranes exhibited superior mechanical property, with maximum elongation at break of 223.3%.