Hybrid membranes from sulphonated poly (2, 6-dimethyl-1, 4-phenylene oxide) and sulphonated nano silica for alkali recovery

• SPPO/sulphonated nano silica (SNS) hybrid membranes were prepared.
• The membranes showed high separation performance in the alkali recovery.
• Sulphonic groups at the interfacial region played an assistant transport.

Hybrid membranes for diffusion dialysis were prepared by incorporating sulphonated nano silica particles into sulphonated poly (2, 6-dimethyl-1, 4-phenylene oxide) (SPPO) matrix. The membranes with ion exchange capacities (IECs) of 1.87–2.00 mmol/g possessed favorable thermal stability and alkali resistance. They were tested in NaOH/Na2WO4 feed solution via diffusion dialysis (DD) process. Results showed that as-prepared hybrid membranes exhibited better separation performance under the temperature higher than 35 °C. The highest hydroxide flux (UOH) reached 0.015 m/h at 55 °C with a separation factor around 34. The pure SPPO (as control) exhibited much lower UOH values at the investigated temperature range though its separation factor was higher. The structure and physico-chemical properties of the hybrid membranes were investigated to better understand the DD results. Sulfonic groups at the surface of nano silica particles were believed to enhance the transport of Na+ and i.e., promoted the diffusion of OH−.