The influence of the textural characteristics of the hierarchical porous carbons on the removal of lead and cadmium ions from aqueous solution

Developing efficient adsorbent materials for water treatment is deemed as one of the key solutions towards mitigating the contaminated water problem. Herein, several Hierarchical Porous Carbons (HPCs) with large mesopore volumes (up to 3 cm³/g) and a wide range of BET surface areas (747–1037 m²/g) were synthesized, and their heavy metal removal behaviors were investigated. Specifically, simulated lead and cadmium aqueous solutions were used to investigate the HPCs adsorption performance towards lead and cadmium removal. All the HPCs demonstrated high affinities towards lead removal compared with cadmium. Additionally, a systematic investigation was carried out to understand the structure—performance relationships for the HPCs. Interestingly, varying the adsorbent pore structure leads to different adsorbent behavior for lead compared with cadmium. The textural characteristics of the HPCs have a limited effect on the removal of cadmium ions. Accordingly, to expedite cadmium removal from aqueous samples, factors other than textural characteristics (i.e., surface chemistry) might enhance the removal process. Conversely, the removal of lead ions can be significantly controlled by the HPCs pore structure. HPC1221 (with 17 nm mesopore size, 2.8 cm³/g pore volume, 907 m²/g) showed the maximum adsorption capacity value of 12.32 mg/g for Cd²⁺ and 89 mg/g for Pb²⁺ compared to other HPCs. The significant adsorption parameters were evaluated using the response surface methodology (RSM) design. We believe that the reported insights for the structure–performance relationships will be useful for better designing highly efficient adsorbent materials.