A New Generation of Porous Polymer Materials from Polystyrene Waste: Synthesis and Adsorption of Nitrate Anions in Aqueous Media

A simple approach was developed to efficiently graft diethylene triamine onto polystyrene waste using succinic anhydride as a tracer to remove nitrate anions from aqueous solutions. Infrared spectroscopic data showed characteristic signs at 3395 cm−1 and 1695 cm−1 corresponding to N-H and C=O (ester and amide), confirming the grafting of DETA onto PS. The zeta potential study showed that the PS-Succ-DETA adsorbent had a pHiep of 8.2, and its charge was positive when the pH was lower than the pHiep. Parameters affecting nitrate adsorption, such as dosage, initial concentration, pH, and contact time, were studied. The adsorption data corresponded well to the Langmuir isotherm with an R2 correlation coefficient of 0.998, and the adsorption capacity was found to be 195.65 mg/g. The adsorption kinetics of NO3− ions by PS-Succ-DETA corresponded perfectly to the PS-II model, with an R2 coefficient of 0.999. The negative value of ΔG (−10.02 kJ/mol), ΔH (−18.76 kJ/mol), and ΔS (−28.83 J/K/mol) indicates that NO3- adsorption is spontaneous exothermic and suggests a decrease in randomness at the solid-liquid interface during the adsorption. The mechanism of adsorption of nitrate ions onto PS-Succ-DETA occurs via electrostatic interactions and hydrogen bonds between the NO3− ions and the -NH2 and NH functions of PS-Succ-DETA.