Sucrose-derived carbon spheres for rapid solid-phase extraction and trace cadmium removal from aqueous media

Cadmium (Cd²⁺) contamination in water remains a major environmental concern, creating a strong demand for sorbents that are both efficient and economically accessible. In this study, uniform carbon spheres (CSs) were prepared from sucrose through a simple hot-oil thermochemical process conducted under ambient pressure, avoiding the need for pressurized equipment. The resulting CSs exhibited a specific surface area of approximately 375 m² g^-1 and were enriched with oxygen-containing functional groups, which are favorable for metal-ion interaction. The adsorption behavior toward Cd²⁺ was evaluated through equilibrium, kinetic, and solution-condition experiments. The material showed a maximum adsorption capacity of 5.04 mg g^-1, and the equilibrium data were best represented by the Langmuir isotherm model, indicating monolayer adsorption on a relatively homogeneous surface. Analysis using the Dubinin-Radushkevich model suggested that Cd²⁺ uptake occurred predominantly through physical interactions. Kinetic results showed very fast adsorption, with equilibrium reached within 120 s, and the uptake process was better described by the Elovich model. Adsorption performance was most favorable near neutral pH, whereas increased ionic strength and competing ions caused a moderate reduction in Cd²⁺ uptake, most likely because of site competition and reduced access to active binding sites. In addition, the synthesized CSs demonstrated effective solid-phase extraction (SPE) behavior, enabling rapid separation from the aqueous phase and Cd²⁺ recovery above 99% after elution with dilute nitric acid. These results suggest that sucrose-derived CSs are a promising low-cost and rapidly acting sorbent for cadmium removal and sample preconcentration in water treatment applications.