The adsorption behavior of Pb(II) and Cd(II) on carboxymethylcellulose-chitosan modified magnetic alkaline Ca-bentonite (MACB/C-C) was investigated in detail to elucidate the underlying mechanisms governing heavy metal removal. The composite’s high performance stems from synergistic interactions between its structural framework and functional surface groups. X-ray diffraction (XRD) analysis of MACB/C-C before and after metal adsorption revealed the formation of new crystalline phases, including hydrocerussite (Pb₃(CO₃)₂(OH)₂) and cerussite (PbCO₃), which are indicative of surface precipitation. These precipitates likely originated from carbonate ions released by the ACB matrix and the decomposition of carboxylate groups from CMC under alkaline conditions. The presence of excess hydroxyl groups on the surface further promoted the transformation of PbCO₃ into more stable hydrocerussite, confirming the role of pH-dependent speciation in the removal process.
FT-IR spectroscopy showed distinct shifts in the –COOH (1630 cm⁻¹) and –NH₂ (3430 cm⁻¹) stretching vibrations after adsorption, suggesting that both carboxylate and amino groups participated in complexation with Pb(II) and Cd(II). The deprotonation of these functional groups at higher pH values enhanced their coordination ability, leading to strong chelation and ion exchange. Additionally, the surface charge density of MACB/C-C increased with rising pH, promoting electrostatic attraction between negatively charged functional groups and positively charged metal cations. This is supported by zeta potential measurements showing a shift toward more negative values above pH 5, consistent with greater anionic character.
Kinetic studies using intra-particle diffusion models revealed multi-stage adsorption: an initial rapid uptake due to external surface adsorption, followed by gradual diffusion into the porous structure. The presence of the C-C film slightly slowed the diffusion rate, as evidenced by lower diffusion constants (ki,1) for MACB/C-C compared to MACB, indicating that the coating acts as a diffusion barrier but enhances stability. Nevertheless, equilibrium was achieved within 3 hours, demonstrating efficient mass transfer despite the film layer.
Thermodynamic analysis indicated spontaneous and endothermic adsorption processes, with positive ΔS values suggesting increased randomness at the solid-liquid interface. The calculated ΔG values were negative across all temperatures, confirming favorable adsorption. Moreover, the Langmuir model provided the best fit (R² > 0.99), implying monolayer coverage on homogeneous active sites. The high qmax values (483 mg·g⁻¹ for Pb(II), 123 mg·g⁻¹ for Cd(II)) reflect the abundance of accessible binding sites created by the C-C film and the inherent affinity of ACB for divalent metals.IL-22 ProteinBiological Activity
A schematic representation of the proposed mechanism illustrates that Pb(II) and Cd(II) removal occurs through three concurrent pathways: (1) surface precipitation via carbonate and hydroxide formation, (2) complexation with –COO⁻ and –NH₂ groups, and (3) ion exchange with exchangeable cations in the clay lattice.PEG10 Antibody supplier The combination of these mechanisms ensures high selectivity and capacity even in complex aqueous matrices.PMID:35066027 Furthermore, the robustness of the C-C coating prevents Fe₃O₄ leaching and maintains structural integrity during repeated use. This multifunctional mechanism not only explains the superior performance of MACB/C-C but also provides a design blueprint for future development of smart, multifunctional adsorbents for heavy metal remediation.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com