Increased adsorption of aqueous zinc species by Ar/O2 plasma-treated carbon nanotubes immobilized in hollow-fiber ultrafiltration membrane

•Pristine CNT were functionalized using Ar/O2 plasma treatment technique.•Plasma treatment increased the surface oxygen content, and modified surface functionality of CNT.•CNT membranes were tested for the adsorptive filtration of Zn2+ from synthetic and real wastewater.•Functionalized CNT membranes exhibited superior heavy metal sorption capacity.•CNT membranes were efficiently regenerated under acidic condition, showing a reusable potential.