Understanding adsorption mechanisms and metal ion selectivity of superparamagnetic beads with mesoporous CMK-3 carbon and commercial activated carbon

This study investigates, the adsorption capacities of synthesized magnetic hybrid beads containing ordered mesoporous carbon (CMK-3) and commercial activated carbon (commercial AC) for Cd (II), Ni (II), and Hg (II) ions adsorption in single and ternary systems. The order of maximum adsorption capacity was Cd (II) > Ni (II) > Hg (II) in both beads and systems. L13 beads containing CMK-3 exhibit superior adsorption efficiency compared to L3 beads with commercial AC, attributed to the large surface area, enhanced accessibility to adsorption sites, and the presence of O=C bonds, as well as other elements such as F-. Adsorption of all metal ions was described by Freundlich isotherm in L3 beads in both systems, meanwhile in L13 beads, Langmuir and Freundlich models described adsorption differently in both systems and among metal ions, indicating a more complex process. According to the reported maximum adsorption capacity values, L3 beads exhibit a greater affinity for Hg (II) ions, while L13 beads show a higher affinity for Cd (II) and Ni (II) ions. Adsorption in both beads occurred through several mechanisms involving surface complexation, ion-exchange, precipitation, physical and chemical processes. These findings highlight the importance of material design in optimizing adsorption performance for environmental applications, with potential for further enhancement of adsorption capacities and selectivities through future research.