Adsorption properties of ammonium nitrogen from aqueous solutions using sodium humate/poly(sodium acrylate) hydrogel

Background: Water is the most critical and essential component on Earth for meeting the daily needs of human beings. Ammonium nitrogen (NH4-N) is a water pollutant that can significantly affect aquatic flora and fauna. In this study, a series of poly(sodium acrylate) (PANa)-based hydrogels containing various amount of eco-friendly sodium humate (SH) were designed for ammonium nitrogen adsorption. Method: The interpenetrating polymer hydrogels (PASH-0.05, PASH-0.1, and PASH-0.15) were synthesized through thermal radical polymerization of neutral sodium acrylate (ANa) and SH in the presence of ammonium persulfate as an initiator. Additionally, poly(sodium acrylate) (PANa) without SH was prepared for comparison. The chemical structure, microstructure, thermal stability and water adsorption properties of the obtained hydrogels were comprehensively characterized. Finally, adsorption results and behavior under ammonium chloride solution were evaluated. Significant findings: The PASH-0.1 hydrogel, with a composition of 0.1 wt% SH, exhibited the highest ammonia nitrogen adsorption capacity (11.2 mg g-1), which was 5.2% higher than that of the PANa hydrogel (10.7 mg g-1) under similar testing conditions. Additionally, adsorption isotherm and kinetic analyses were investigated. Furthermore, the hydrogels demonstrated good stability and reusability, retaining more than 80% of the initial adsorption capacity after nine adsorption-desorption cycles.