Comparative performance of functional adsorbent materials for sustainable metal ion recovery

Heavy metal contamination in water systems poses serious environmental and health risks, necessitating the development of efficient and sustainable treatment technologies. This study explores the adsorption performance of six adsorbent materials for heavy metal removal from aqueous solutions, focusing on two Ti 3 C 2 T x MXenes synthesized through LiF/HCl and NH 4 HF 2 /citric acid etching, commercial activated carbon, α-MnO 2 , and two biomass-derived activated carbons. The materials were characterized using XRD, FTIR, SEM, EDX, and BET analyses, revealing key differences in morphology, surface chemistry, and elemental composition. Adsorption experiments targeting Cr 6+ , Pb 2+ , Zn 2+ , and five other heavy metal ions demonstrated that Ti 3 C 2 T x - NH 4 HF 2 exhibited the highest adsorption capacities due to its delaminated structure and oxygen-rich surface. While other materials like α-MnO 2 and biosourced activated carbons with much higher specific surface area showed moderate to limited performance, the findings reiterate the critical role of surface functionality over plain surface area. The results also highlight how equilibrium-driven experiments at realistic conditions offer a more conservative and reliable assessment compared to previously reported methods. This work supports the potential of functionalized MXenes as promising materials for efficient adsorption of various heavy metal cations in wastewater treatment.