Cu(II) adsorption on 2-thiouracil-modified Luffa cylindrica biochar fibres from artificial and real samples, and competition reactions with U(VI).

•2-thiouracil modified biochar fibres present extraordinary affinity and adsorption capacity, 486.9 mg/g, for Cu(II) ions.•Stable inner-sphere complexes formed after Cu(II) adsorption on modified fibres, via -N and -S atoms in the ligand.•Competition reactions of Cu(II)-U(VI) reveal selective removal of Cu(II) using the 2-thiouracil modified biochar fibres.•Selectivity of the modified fibres was also verified via real sample adsorption experiments, using AMD samples.