S. . Aburub, N. F. Ab Manaf, A. M. Rohisham, N. N. M. Zain, N. Nordin, and N. Y. Rahim, “Silica modified with choline chloride/urea DES for ligand-free Cu(II) adsorption: Scientific paper”, J. Serb. Chem. Soc., vol. 91, no. 7-8, pp. 809–822, Aug. 2026.