Acid-functionalized porous polymer as an adsorbent for the highly efficient removal of ammonia nitrogen from aqueous solutions

Background

Wastewater from agriculture, animal husbandry, and industrial activities contains ammonium nitrogen (NH₄-N), a pollutant that contributes to environmental degradation. Porous polymers are currently considered an emerging candidate for wastewater treatment due to their high porosity, abundant adsorption sites and low-cost preparation.

Method

In this study, a new type of porous polymer (C-Daba), containing a carboxyl group in its structure, was prepared through a traditional Schiff-base condensation reaction. For comparision, a carboxyl-free analogous polymer, C-Bda, was also synthesized. These two porous polymers are amorphous, but they exhibit good thermal stablility and chemical resistance. The synthesized polymers were tested as adsorbents for ammonium chloride (NH₄Cl) solution.

Significant findings

C-Daba (5.25±0.62 mg g^-1) exhibited a slightly higher ammonia nitrogen adsorption capacity compared to C-Bda (2.98±0.96 mg g^-1). To enhance adsorption capacity, C-Daba was treated with NaOH to form the a -COONa containing polymer, named C-Daba-Na. As a result, the C-Daba-Na compound exhibited a dramatic enhancement in adsorption capacity, reaching 19.26±1.79 mg g^-1 at a similar testing ammonium chloride concentration of 25 mg l^-1. Additionally, adsorption isotherm, kinetic and thermodynamic analyses of the C-Daba-Na compound were conducted. The C-Daba-Na also demonstrated good reusability, retaining >75 % of its initial adsorption capacity after five adsorption-desorption cycles.