Rapid ammonium adsorption using TEMPO-oxidized microcrystalline cellulose

Abstract

As low as 1 ppm concentration of ammonia poses a significant threat to fish in fish farms, necessitating effective ammonia removal method to mitigate its concentration. Herein, this study explored the application of cellulose, a cost-effective and versatile green polymer, modified through TEMPO-mediated oxidation, for the first time for ammonia removal from water. The TEMPO-oxidized cellulose, with carboxylate group content of 0.78 mmol/g, exhibited adsorption capacity of 8.21 mg/g (empirically, 9.465 mg/g based on the Langmuir isotherm model) at pH of approximately 7.0. This capacity is comparable to existing carbon-based sorbents for ammonia reduction, and it indicates nearly 100% utilization of carboxylate adsorption sites. Notably, equilibrium adsorption was achieved within 5 minutes. The ammonium adsorption data aligns well with the Langmuir model, suggesting a monolayer chemical adsorption process. The adsorption performance of the material remained relatively stable within a pH range of 5 to 9, but it was significantly influenced by the presence of competing ions. The primary mechanisms governing material performance in ammonia removal involve electrostatic interactions and hydrogen bonding between the introduced carboxylate groups and ammonium ions. This study also delves into a comprehensive discussion on performance comparisons, alternative modification methods, cost competitiveness, and potential applications of the post-adsorption material.