Ecofriendly method for removal of cadmium ions and synthesis of cadmium oxide nanoparticles using a new generation of amine-functionalized cellulose

Abstract

We present a new-generation, amine-decorated cellulose adsorbent (CDAM) engineered to overcome the inherent limitations of unmodified cellulose in the sequestration of heavy metals. By covalently grafting branched amine functionalities onto a crosslinked cellulose network, CDAM introduces a dense array of nitrogen-donor sites and enhanced porosity, as confirmed by FTIR (appearance of –NH– peaks), XPS (shifts in N 1s indicating quaternary and imine nitrogen), TGA (improved thermal stability), ¹H/¹³C-NMR (chemical shifts consistent with successful grafting), and GC-MS (molecular fragmentation patterns). This tailored surface chemistry enables CDAM to achieve a record-high Cd²⁺ adsorption capacity of 483.7 mg g⁻¹ under optimized conditions (pH 5.5, 30 min contact, 298 K), substantially outperforming benchmark bio-sorbents. Kinetic studies reveal a pseudo-second-order mechanism, indicative of chemisorption, while equilibrium data conform closely to the Langmuir isotherm, demonstrating monolayer coverage on a homogeneous set of active sites. Thermodynamic analysis (ΔH° = +10.4 kJ mol⁻¹, ΔS° = +53 J mol⁻¹ K⁻¹, ΔG° < 0) confirms that Cd²⁺ uptake is endothermic, entropically driven, and spontaneous, with increased randomness at the solid–liquid interface due to desolvation effects. High-resolution XPS of Cd-loaded CDAM shows the emergence of Cd 3d peaks at 405.1 eV and 411.9 eV alongside shifted N 1s binding energies, directly validating metal coordination to imine and amine nitrogen. CDAM exhibits excellent reusability, retaining over 90% of its initial capacity after seven adsorption–desorption cycles with 0.25 M HCl elution, highlighting its practical viability. In a real-world demonstration, CDAM was deployed to treat acid leachates from cadmium-rich Wadi Um-Gheig rock samples. Quantitative Cd²⁺ recovery was achieved, and the purified metal ions were subsequently transformed into high-purity CdO nanoparticles. The resulting CdO exhibits a crystalline monoclinic structure (XRD), uniform nanorod morphology (TEM), and a surface area of 58.4 m² g⁻¹ (BET), illustrating the dual role of CDAM in environmental remediation and resource valorization. These findings position CDAM as a sustainable, high-performance platform for cadmium removal and value-added nanoparticle synthesis, with broad implications for water treatment and circular-economy strategies.