Internal pore decoration with polydopamine nanoparticle on polymeric ultrafiltration membrane for enhanced heavy metal removal

Novel ultrafiltration-adsorption membranes (UFAMs) were designed via decorating the walls of membrane internal pores with polydopamine (PDA) nanoparticles for heavy metals removal. Specially, self-polymerized dopamine solution was penetrated through the polyethersulfone (PES) UF membrane from reverse direction (i.e., from bottom to top) by circulatory filtration, leading to the formation of a PDA nanoparticle coating around the walls of finger-like pores (labeled as PES/PDA-R). The conventional PDA-decorated membrane (labeled as PES/PDA-F) prepared with forward filtration was used for comparison. The results indicated that the introduction of PDA nanoparticles on the walls of internal pores endowed the PES/PDA-R membrane with enhanced UF performance and remarkable adsorption capacity for heavy metals. PES/PDA-R membrane exhibited ascendant bovine serum albumin (BSA) rejection (92.9%) and maintainable pure water flux (166   L/m 2   h). The static adsorption capacities for Pb 2+ , Cd 2+ and Cu 2+ on PES/PDA-R membranes were 20.23   mg   Pb/g, 17.01   mg   Cd/g and 10.42   mg   Cu/g, respectively, which are 1.69, 2.25 and 1.91   times higher than that of the PES/PDA-F membranes. Importantly, dynamic filtration experiments revealed 4.13   times adsorption capacity for Pb 2+ was achieved on PES/PDA-R membrane over PES/PDA-F membrane. The significant enhancement of dynamic adsorption capacity on PES/PDA-R membrane is derived from the three dimensional distribution of PDA nanoparticles on the cross section of PES membrane which provide the more active sites and increase the contact time between PDA and metal ions. This novel approach paves a way to design specific composite membranes for a cost-effective water treatment.