Novel composite activated carbon/chitosan nanoparticles (ACh) were synthesized by dipping and incorporated into poly(ether)sulfone (PES) based nanofiltration membranes, to investigate their effect on the membrane properties and performance. The hydrophobic activated carbon nanoparticles were functionalized with hydrophilic chitosan to increase their dispersibility and hydrophilicity. The FTIR and SEM analysis confirm the formation of composite nanoparticles decisively. UV–vis spectra of activated carbon before and after modification with chitosan confirmed a better dispersion of composite nanoparticles. An improvement of hydrophilicity and porosity were obtained by increasing the concentration of composite nanoparticles up to 0.5 wt%. The water flux was also increased from 21 to 30 (L/m2 h) by utilizing composite nanoparticles up to 0.5 wt%. The mean pore size was decreased for all concentrations of composite nanoparticles, due to their great dispersion. The membrane roughness was declined from 19.2 nm (average roughness) for PES to 5.9 nm for a membrane including 0.5 wt% nanoparticles. The surface SEM image of a membrane containing 0.5 wt% nanoparticles confirmed the reduction of pore size after addition of nanoparticles to the casting solution. The results showed a sharp increase of salt rejection in all concentrations of ACh; the highest value was 97% for 1 wt%. The membrane with 0.5 wt% nanoparticles was found having optimal properties; its performance was tested by analyzing the antifouling performance. The flux recovery was found twice higher than that of a corresponding PES membrane.
