Efficient multi-pollutant removal: The role of Keggin polyoxometalates in polysulfone-chitosan blend membranes

Membrane filtration is a vital area in separation science, providing an effective method for water purification due to the unique properties of membranes. This study presents the development of blend membranes composed of polysulfone (PS), chitosan (CS), and polyvinyl alcohol (PVA), incorporating two types of Keggin polyoxometalates: K₈[α-SiW₁₁O₃₉] ({SiW₁₁}) and K₄[α-SiW₁₂O₄₀] ({SiW₁₂}) at a concentration of 0.05 to 1.0 wt% each. Our findings reveal that the incorporation of 0.1 wt% {SiW₁₁} results in an optimum membrane exhibiting high porosity, a finger-like pore structure, and enhanced hydrophilicity. This membrane achieves a water flux of 34.8 L/m²h and significantly enhances the simultaneous removal of multiple pollutants. Specifically, this membrane achieved rejection rates of >88 % for heavy metal ions (Ni²⁺, Cu²⁺, and Pb²⁺) and > 98 % for organic dyes (Congo Red and Methylene Blue). The improved rejection rates and water fluxes observed with the optimal amounts of polyoxometalates (POMs) can be attributed to the combined effects of surface charge (Donnan effect), size exclusion, and adsorption at the binding sites of the POMs. Notably, the nanofiltration membrane containing {SiW₁₁} outperformed the one with {SiW₁₂} in filtering multi-contaminant solutions, underscoring its superior effectiveness.