A novel sodium Iron silicate composite with chitosan for efficient removal of Cd(II) ions from water.

Cadmium ions constitute a major threat to human health and the environment owing to their toxicity, bioaccumulation, and persistence in water bodies, causing renal dysfunction, cancer, and cardiovascular diseases. Hence, this study reports the facile fabrication of a novel sodium iron oxide silicate@amorphous sodium iron silicate product (S1) and its chitosan composite (S1@chitosan) for the high-performance separation of Cd(II) ions from aquatic environments. The Brunauer-Emmett-Teller surface area, total pore volume, and mean pore diameter of S1 were 94.97 m/g, 0.5853 cm/g, and 25.65 nm, respectively, while those for S1@chitosan were 30.94 m/g, 0.09518 cm/g, and 12.31 nm, respectively. The reduction in pore diameter, pore volume, and surface area confirms the successful functionalization of S1 with chitosan, as the chitosan coating partially blocks and fills the pores, reducing the available surface area and porosity. Also, scanning electron microscope (SEM) images revealed an uneven surface morphology for S1 and a more textured and rougher surface for S1@chitosan, supporting the incorporation of chitosan. Besides, energy-dispersive X-ray spectroscopy (EDX) and CHN analyses affirmed the existence of chitosan in the composite through the detection of carbon and nitrogen elements, characteristic of chitosan. The optimum conditions for the removal of Cd(II) ions were determined to be a contact time of 70 min for S1 and 50 min for S1@chitosan, a pH of 7.50, and a temperature of 298 K. The maximum sorption capacities were 284.09 mg/g for S1 and 389.11 mg/g for S1@chitosa. The removal mechanism for S1 primarily involves ion exchange, while S1@chitosan utilizes both ion exchange and complexation through the amino and hydroxyl groups of chitosan. Regeneration using HCl confirmed the effective reusability of both adsorbents over five successive cycles. The adsorption process was found to be chemical, exothermic, and best described by the pseudo-second-order kinetic model and Langmuir isotherm.