Quercetin–Copper Complexation-Based Porous Polymer for Chromium, Mercury, and Cadmium Metal Ion Adsorption: Experimental and Computational Study

Heavy metal ions in water bodies pose a serious threat to human health and the environment. To overcome this issue, we developed a polymeric quercetin–copper complex (QC) as a novel adsorbent for heavy metal removal. This material was characterized using different techniques. Its structure was also investigated using density functional theory (DFT) calculations, which revealed the formation of a highly stable 2:1 complex between quercetin and Cu²⁺ ion. The QC polymer exhibited >95% adsorption efficiency for removing heavy metals under acidic and neutral pH conditions. The adsorption capacities were 2.50, 0.77, and 0.54 mmol/g for Cr³⁺, Hg²⁺, and Cd²⁺ ions, respectively, under neutral pH conditions. DFT calculations also indicated high adsorption energies of −34.32, −15.10, and −12.37 eV for Cr³⁺, Hg²⁺, and Cd²⁺, respectively. The QC polymer was easily recovered and reused for removal studies of these metal ions without showing a significant loss in its adsorption capacity.