Enhanced adsorption of Pb²⁺ by the oxygen-containing functional groups enriched activated carbon

Lead is one of the primary pollutants found in water and poses significant toxicity risks to humans; thus, it is necessary to investigate techniques for removing it economically and efficiently. In order to enhance the removal capacity of Pb²⁺, coconut shell-based activated carbon (AC) was modified with introducing oxygen-containing functional groups (OFGs) via nitric acid (HNO₃) or hydrogen peroxide (H₂O₂) modification in this study. The characterization results show that after oxidation treatment, the content of OFGs increased, and the textural properties of the samples do not change significantly. This indicates that the modification conditions used in this study effectively introduced OFGs while avoiding the adverse effects on physical adsorption ability of AC caused by oxidation treatment. The Pb²⁺ adsorption capacities of the AC modified with 10 M HNO₃ and 30 wt.% H₂O₂ were 4.26 and 3.64 times that of the pristine AC, respectively. The experimental data can be well fitted using the Langmuir isotherm model and the Elovich kinetic model, suggesting that the adsorption of Pb²⁺ on AC belongs to single-layer adsorption, and chemical adsorption dominates the adsorption process. In summary, the hydrothermal-assisted HNO₃/H₂O₂-modified coconut shell-based AC shows great potential in efficiently removing Pb²⁺ from solutions, offering a solution for utilizing coconut shell waste.