Synthesis and characterization of Cu-Cu2O/reduced graphene oxide for enhanced iodide adsorption through multiple pathways

Fabricating efficient copper-based adsorbents for radioactive iodine removal is crucial for environmental protection and waste volume reduction, particularly in the treatment of radioactive waste from hospitals. In this study, a composite of reduced graphene oxide (RGO) supported by Cu-Cu2O nanocrystals (Cu-Cu2O/RGO-3) was synthesized via a one-step method and evaluated for its effectiveness in iodide removal from water. The composite was comprehensively characterized using XRD, SEM, FT-IR, and XPS analyses. The effects of copper content, pH, contact time, iodide concentration, temperature, and coexisting anions on iodide uptake were systematically investigated. In the Cu-Cu2O/RGO-3 composite, copper primarily existed as metallic Cu, along with a small amount of Cu2O. Cu-Cu2O/RGO-3 exhibited a significantly higher I- adsorption capacity compared to Cu powder, effectively reducing I- concentrations from 8.6 to 0.029 mg/L within just 3 min, demonstrating a rapid uptake rate for trace I-. Furthermore, the maximum adsorption capacity reached 152.1 mg/g at pH 7.0, surpassing that of many reported copper-based adsorbents. The composite showed selectivity in the presence of competing ions like Cl-, NO3-, and SO42-, but HCO3- at higher concentrations inhibited I- adsorption. Post- adsorption analysis revealed that iodine was present solely as CuI. XPS analysis indicated that residual carboxyl groups in RGO facilitated the oxidation of Cu and promoted redox reactions between Cu(OH)2 and Cu, providing multiple pathways for generating additional Cu+ ions, thereby enhancing I- adsorption. This study offers a practical approach for modifying carbon-based materials with copper compounds, emphasizing the potential of copper-based materials for effective iodide purification in wastewater treatment.