In this study, the researchers wanted to find out if potato peels (PP) and modified potato peels (MPP) could be used to remove Cu (II) ions from water solutions. The effect of adsorption parameters such as pH, contact time, adsorbent dose, and initial concentration were systematically optimized, and the adsorption kinetics and isotherms were investigated for potential use in real sample operations. The physicochemical properties and morphological structure of the adsorbent were investigated using scanning electron microscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy to understand the Cu (II) ion adsorption mechanism. The studies carried out at different temperatures provided a deeper understanding of the adsorption capacities of the adsorbents. The Cu (II) ion removal capacities of PP were determined as 30.95, 32.67, and 35.33 mg/g at 25, 35, and 45 °C, respectively. Under the same conditions, the removal capacities of MPP were found to be 76.33, 80.64, and 86.20 mg/g, respectively. Further investigation of the adsorption kinetics showed that the experimental data fit the pseudo-second-order model for both PP and MPP adsorbents. Thermodynamic analyses revealed that the adsorption of Cu(II) ions onto the adsorbents was an endothermic process and spontaneous. PP and MPP could be reused for several cycles without losing their adsorption performance after successful regeneration with 0.10 M HCl. The mechanism of Cu (II) ion removal was explained by intermediary ion exchange, surface precipitation, and interaction between surface functionalities of PP and MPP. Therefore, highly functional PP and MPP could be promising adsorbents for efficient Cu (II) ion removal from aqueous solutions.