Abstract <p>The treatment of water contaminated with heavy metal ions requires the development of efficient and environmentally sustainable biosorbents. Chemical modification of cellulose by incorporating functional groups such as imidazole rings is expected to enhance its adsorption capacity. Cellulose functionalized with imidazole groups was prepared through selective oxidation of neat cellulose with periodate for preparing dialdehyde cellulose, which underwent Schiff base condensation with 1-(3-aminopropyl)imidazole. The incorporation of imidazole grafts can tailor the physicochemical properties and structural features of the material to enhance its suitability for heavy metal adsorption. To confirm the structural and thermal modifications, the chemically functionalized cellulose was investigated by FT-IR spectroscopy, TGA, and SEM. The single metal adsorption showed that the maximum adsorption of Cd(II) and Cu(II) were 312 and 278&#xa0;mg/g. The adsorption results were best described by the Langmuir isotherm and the pseudo-second-order kinetic model, indicating the most accurate fit among the models tested. Thermodynamic parameters indicated that the adsorption is spontaneous and endothermic, with increased entropy favoring adsorption at higher temperatures for the investigated metal ions. The cellulose derivative retained 74% and 72% of its adsorption efficiency for Cd(II) and Cu(II), respectively, after five regeneration cycles, demonstrating good reusability.</p> Graphical abstract <p></p>