Sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide)/nano silica hybrid membranes for alkali recovery via diffusion dialysis

Hybrid membranes for alkali recovery were prepared by incorporating nano silica particles into sulfonated poly(2,6-dimethyl-1,4-phenyleneoxide) (SPPO). The membranes possess ion exchange capacities (IECs) of 1.48-1.69 mmol/g, water uptake (WR) of 71-74%, swelling degree of 73-78% as well as favorable thermal stability and alkali resistance. They were investigated in NaOH/Na2WO4 feed solution for alkali recovery via diffusion dialysis (DD) at various temperatures. Results show that the as prepared hybrid membranes exhibit better separation capacity with the highest hydroxide flux (UOH) of 0.014 m/h at 55 °C and an acceptable separation factor of 34.5. The pure SPPO (as control) exhibits much lower UOH values at the investigated temperature range. The structure and physico-chemical properties of the hybrid membranes were investigated to better understand the DD results. Hydroxyl groups at the surface of nano silica particles are believed to play an important role in OH− diffusion.