Fabrication of nitrogen-doped graphene quantum dots hybrid membranes and its sorption for Cu(II), Co(II) and Pb(II) in mixed polymetallic solution

•N-GQDs hybrid membranes were prepared via hydrothermal and sol–gel routes.•Competitive sorption of Cu2+, Co2+ and Pb2+ in multi–metals solution was studied.•Mechanism showed that Cu2+ sorption on N-GQDs membranes followed Elovich model.•Desorption testing evidenced that EDTA-2Na was a best desorbent for Cu2+ reuse.•Regeneration cycle proved that N-GQDs hybrid membranes can be reused.