Removal of CdS-QDs pollutant from wastewater by interconnected Ca/Al layered double hydroxides with hierarchical mesoporous calcite and chitosan hydrogel

Cadmium sulfide quantum dots (CdS-QDs) have found extensive use in optoelectronic and biomedical technologies but their high solubility and instability in aqueous environments were identified to enforce significant environmental and health concerns due to leaching of Cd²⁺ ions. The aim of this investigated is devoted to achieve effective CdS-QDs removal from aquatic systems via assembly of a novel nanobiocomposite of hierarchical mesoporous calcite embedded in a chitosan hydrogel reinforced into CaAl layered double hydroxides for the formation of HMC@CH@CaAl-LDH. Structural and compositional analyses (FT-IR, XRD, SEM/TEM, EDX, BET, and TGA) confirmed the successful integration of mesoporous calcite and CaAl-LDH within the chitosan matrix, yielding a thermally stable, mesoporous hybrid with abundant functional groups and high surface reactivity. Adsorption experiments revealed a maximum CdS-QDs removal efficiency of 97.4% (pH 7) with a rapid equilibration at 35 min. Kinetic modeling showed excellent agreement to pseudo-second-order model, referring to chemisorption mechanism which is supported by Elovich and intraparticle diffusion assessments. Isotherm analysis demonstrated a good conformity to the Langmuir model (R² = 0.995), providing monolayer adsorption of CdS-QDs on homogeneous sites of HMC@CH@CaAl-LDH, while Freundlich, D-R, Temkin, and Flory–Huggins models highlighted surface heterogeneity and spontaneous thermodynamic feasibility (ΔG° = − 7.50 kJ/mol). Thermodynamic parameters verified the spontaneous occurrence of the process with an endothermic character. The HMC@CH@CaAl-LDH nanobiocomposite also showed durable reusability via sustaining greater than 70% of its initial efficiency after four cycles. HMC@CH@CaAl-LDH achieved > 90% removal of CdS-QDs from wastewater matrices. These results demonstrate that the evaluated HMC@CH@CaAl-LDH is a robust, sustainable, and superior performance in CdS-QDs remediation from contaminated water.