Enhanced ammonium removal from aquatic systems by a novel copolymer

A novel copolymer was used as an adsorbent for enhanced ammonium removal in an aqueous system; different ratios of styrene–acrylic acid copolymers were synthesized by random free radical polymerization and followed by a sulfonation of styrene (acrylic acid 25%–sulfonated styrene 75%) copolymer [P(AA25/SS75)] attained the highest ammonium adsorption capacity (55.8 mg/g) due to the electrostatic attraction between positively charged NH4+ and negatively charged –COO− and –SO3- groups. FTIR spectra for sulfonated polymers illustrated the appearance of characteristic peaks at 100–1,200 cm−1 indicating that the copolymers were successfully sulfonated. The influence of different experimental factors (i.e., contact time, pH, NH4+ concentration, adsorbent dose) on ammonium ion adsorption was investigated; three adsorption isotherm models including Langmuir, Freundlich, and Temkin were used to study the adsorption mechanism. The results indicated that the equilibrium of adsorption can be reached within 30 min; the highest adsorption capacity can be achieved around pH 7. Furthermore, Freundlich isotherm was the most suitable for fitting the experimental data which might expose the heterogeneity of the adsorbent surface. The regeneration and reusability studies were also implemented, and results showed that P(AA25/PSS75) was stable and regenerable using (1 M) sulfuric acid as a desorbing agent over five cycles.