Selective Cu(II) Adsorption Using a Smart Amine-Functionalized and Activated Carbon-Supported CeO ₂ @SiO ₂ Composite

A novel composite adsorbent, AC-CeO2@SiO2-DETA, was developed for the selective removal of Cu(II) and Pb(II) from binary aqueous solutions, with enhanced affinity and selectivity toward Cu (II) ions. This engineered material was synthesized through the coprecipitation of cerium oxide and silica onto activated carbon, followed by surface functionalization with diethylenetriamine (DETA). Batch experiments revealed the highest efficiency at pH 6, where Cu(II) exhibited stronger coordination with DETA due to its higher affinity for nitrogen-containing functional groups. Under optimized conditions (200 mg/L of each metal ion, 0.01 g/10 mL adsorbent, pH 6), Cu(II) was completely removed with 100% selectivity over Pb(II) from the aqueous solution. A maximum adsorption capacity of 200 mg/g was achieved, outperforming previously reported adsorbents. The mechanism was attributed to a competitive coordination process in which Cu(II), owing to its higher affinity for amine groups, effectively displaced preadsorbed Pb(II) from the DETA sites, consistent with HSAB theory and the Irving–Williams series. Desorption experiments using 0.1 M HCl achieved complete recovery of Cu(II), and the adsorbent maintained 87% of its initial efficiency after ten adsorption–desorption cycles, indicating remarkable reusability. In fixed-bed column studies, a competitive displacement mechanism was observed, where Cu(II) fully replaced Pb(II) between 60 and 165 min, achieving a capacity of 55 mg/g. Cu(II) desorption in the column exceeded 90% efficiency within 30 min and remained above 76% after five cycles. These results demonstrate the superior efficiency, selectivity, and stability of AC-CeO2@SiO2-DETA to be used as an adsorbent for the removal and recovery of Cu(II) ions in complex aqueous systems, such as wastewaters.