<p>The selective removal of copper ions from acidic aqueous solutions was investigated using a crystal violet (CV) modified cation exchanger. The C100 resin, a sulfonated polystyrene-divinylbenzene copolymer, was functionalized with CV dye via a hydrothermal process to introduce nitrogen-based complexation sites. Successful modification and subsequent copper uptake were confirmed through characterization by SEM, TEM, EDX, and FTIR, with the distinct color change from green to blue indicating specific Cu-N complex formation. Batch adsorption studies demonstrated that the C100/CV composite exhibits high selectivity and capacity for Cu(II). The maximum adsorption capacity was determined to be 637&#xa0;mg g⁻¹ at pH 5.0 and 30&#xa0;°C, with the process following the Langmuir isotherm and pseudo-second-order kinetics. Thermodynamic analysis revealed the adsorption process to be endothermic and non-spontaneous under the experimental conditions, a finding attributed to the energy-intensive diffusion of copper ions into the gel phase of the polymeric matrix. A critical finding from column studies was the material’s superior selectivity for Cu(II) over common competing ions such as Ca²⁺, significantly outperforming the unmodified parent resin. The exhausted adsorbent was efficiently regenerated using 20 bed volumes of 36% HCl and maintained over 77% of its initial capacity after five cycles, demonstrating excellent reusability. The results establish C100/CV as a robust and selective material for the recovery of copper from contaminated water and acidic waste streams.</p> Graphical abstract <p>Adsorption of Cu⁺² on HC-100-CV.</p> <p></p>