Synthesis of catalytic polypropylene membranes enabling visible-light-driven photocatalytic degradation of dyes in water

• A catalytic membrane was synthesized by PIL grafting and POM loading.
• The membrane shows photocatalytic properties under visible light.
• The membrane can degrade 0.02 g/L dye solution in 10 min by cycled filtration.
• High pH and salts deteriorate catalytic performance.
• The membrane has good reusability and long term stability.

A novel catalytic membrane was synthesized by grafting a poly(ionic liquid) (PIL) onto polypropylene (PP) membrane followed by complexing with polyoxometalate (POM). The membrane was successfully used for degradation of dyes in water under visible light. PP nonwoven fabric membrane (PP NWF) was firstly modified by photoinduced grafting of poly(1-(4-vinylbenzyl)-3-methylimidazolium chloride) (PVBMC) and then anchored with POM H3PMo12O40. The modified membranes PP-g-PVBMC and PP-g-PVBMC-POM were characterized by FT-IR, FESEM and XPS. The results indicate that the PIL–POM composites were successfully immobilized on the membrane surface. By optimizing the synthetic conditions, a PVBMC grafting degree of 370 μg/cm2 and a POM loading of 312 μg/cm2 can be achieved. Acid orange 7 (AO7) was used as a model dye molecule to evaluate the photocatalytic performance of the membrane. By static soaking the membrane in solution, the catalytic membrane was demonstrated to be able to degrade 95% of AO7 in 0.02 g/L of solution in 120 min with the irradiation of two 55 W fluorescent lamps. By cycled filtration of the solution, a membrane disc of 47 mm diameter can degrade 70% of the AO7 in 250 mL of 0.02 g/L solution in only 10 min. High pH and the presence of inorganic salts can deteriorate the photocatalytic activity of the membrane. The cycled use and the long-term stability test indicate that the membrane has good reusability and stability as a catalytic membrane.