Thermal tuning of nanocomposites for superior cadmium ion adsorption

Cadmium (Cd(II)) ions are hazardous, non-biodegradable pollutants known for their bioaccumulative nature and severe risks to human health and aquatic ecosystems. This study presents the synthesis and application of a Co_0.89Mg_0.79Mn_1.46O_3.98@C nanocomposite, fabricated employing the Pechini sol-gel approach and subsequently calcinated at 600 ^oC (C600) and 800 ^oC (C800), for enhanced elimination of Cd(II) ions from aqueous environments. The C600 and C800 samples exhibited maximum uptake capacities of 280.11 mg/g and 206.19 mg/g, respectively. X-ray diffraction (XRD) analysis confirmed a cubic structure for both samples, with crystallite sizes of 51.66 nm (C600) and 87.09 nm (C800). Field emission scanning electron microscopy (FE-SEM) analysis clarified that C600 consisted of smaller, irregular grains, while C800 displayed larger, smoother particles. Elemental composition was verified by energy-dispersive X-ray spectroscopy (EDX), revealing elevated manganese and cobalt content in C800, attributed to enhanced incorporation at elevated temperatures. The superior adsorption performance of C600 was ascribed to its reduced crystallite size in addition to greatest surface area. Regeneration studies demonstrated excellent desorption efficiencies using 3 M HCl: 99.69% for C600 and 99.35% for C800, with both maintaining high removal efficiency over five adsorption-desorption cycles. Thermodynamic assessments indicated the process is exothermic, spontaneous, and dominated by physisorption. Kinetic modeling followed the pseudo-second-order model, while isotherm analysis fit the Langmuir-type isotherm, suggesting single-layer adsorption occurring uniformly across the adsorbent surface.