Adsorption and quantitative fluorescence-based measurement of ammonium ions using a chitosan-based hydrogel combined with p-hydroxybenzoic acid

Ammonium removal in high-density fish cultures is highly reliant on time-consuming and costly biological treatment methods. Therefore, the development of cheap and rapid chemical methods has recently garnered increasing attention. Our study developed a dissolved ammonium removal method using a chitosan-based hydrogel (Cht-HG) modified with 0.3 mM of p-hydroxybenzoic acid (Cht-0.3PHBA-HG). Our proposed method enabled the adsorption and measurement of dissolved ammonium via fluorescence detection. In the ammonium adsorption test, the maximum adsorption capacities (q(m)) of Cht-HG and Cht-0.3PHBA-HG were 11.6 mg g(-1) and 19.9 mg g(-1), respectively. Cht-0.3PHBA-HG exhibited a relatively elevated adsorption capacity (i.e., 1.71-fold higher adsorption efficiency) due to the morphological and chemical modifications attributed to p-hydroxybenzoic acid (PHBA). These findings were confirmed by our chemical characterization and adsorption test results. Particularly, the adsorbed ammonium atomic percentages (at.%) of Cht-HG-NH4 and Cht-0.3PHBA-HG-NH4 were 6.33 % and 15.2 %, respectively. Compared to Cht-HG, the adsorption properties of Cht-0.3PHBA-HG were more stable in a pH range of 2-8. Moreover, we quantitatively analyzed the oxidation of the combined PHBA at different dissolved ammonium concentrations (0.1-5.0 mM) using fluorescence detection. The fluorescence sensitivity of ammonium was maintained, even in high concentrations of common electrolytes (Ca2+, K+, Mg2+, Na+, and PO43-). The ammonium adsorption mechanisms of Cht-0.3PHBA-HG were strongly consistent with the pseudo-first order (PFO), pseudo-second order (PSO), and Langmuir models. In addition to its role as an adsorbent, Cht-0.3PHBA-HG could also be used to detect ammonium in real time. (c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Removal of ammonium in high-density fish cultures is traditionally achieved through time-consuming and costly biological treatments. In this study, a chitosan-based hydrogel modified with p-hydroxybenzoic acid was developed as a cheap and rapid chemical method for ammonium removal. The modified hydrogel showed enhanced adsorption capacity and stability compared to the unmodified hydrogel. Additionally, the hydrogel could be used for real-time detection of ammonium.