Ammonium (\: NH₄^+) is a widely used fertilizer; however, its presence in water sources poses significant risks to both human health and the environment. To address this issue, it is necessary to implement cost-effective strategies that control fertilizer release, mitigate environmental impact, and remove \: NH₄^+ from water sources for reducing negative processes such as eutrophication. In this study, oxidized cassava starch was synthesized using sodium hypochlorite (NaClO) as an oxidizing agent to introduce carboxylic groups, which can interact favorably with \: NH₄^+ ions. The oxidation of starch was evaluated at different NaClO concentrations and pH values, and the resulting materials were characterized by ATR-FTIR, TGA, SEM, carboxyl content determination, and swelling assays. Oxidation was confirmed by ATR-FTIR and TGA results. The optimal conditions were determined to be pH 7 and 2% NaClO, which produced the highest carboxyl content (0. 19 ± 0. 017) and a high gel fraction (82. 6 ± 1. 8%). Additionally, the materials exhibited a porous surface and high-water retention capacity, indicating hydrogel formation resulting from hydrogen bonding between starch polymer chains. The adsorption potential of the material for \: NH₄^+ was evaluated, achieving a high retention capacity of 2790. 3 ± 37. 8 mg/g. This suggests a possible precipitation of the ion on the hydrogel surface; however, this was not observed experimentally. The adsorption process followed a Freundlich isotherm and a pseudo-second-order kinetic model, indicating that adsorption occurs primarily through electrostatic interactions and in multilayers, likely involving the precipitation of \: NH₄^+ on the material’s surface. In addition, the material exhibited a slow-release behavior, with less than 20% of \: \: NH₄^+\: released over 26 days. These results demonstrate that the material possesses a high potential for \: NH₄^+\: adsorption and controlled release, making it suitable for applications in both controlled nutrient delivery and the removal of cationic pollutants from contaminated water sources.
Chamorro et al. (2026) studied this question.