Adsorption of ammonium nitrogen in water by modified bentonite compounded with carboxymethyl-β-cyclodextrin

Abstract

The present study investigates the potential for adsorption of ammonia nitrogen by carboxymethyl-β-cyclodextrin (CMCD) composite acidified calcined bentonite (bent)/SiO₂. The prepared materials were characterized using structural and morphological analysis, surface electrical analysis, elemental composition analysis, and specific surface area analysis. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses after the adsorption of ammonia nitrogen were used to investigate the adsorption mechanism. The experimental adsorption data were matched using the Langmuir and Freundlich isotherm models. The experimental results showed that the maximum adsorption capacity of acidified calcined bent/SiO₂/CMCD for ammonia nitrogen was 18.8 mg g⁻¹ (C₀ = 50 mg L⁻¹; pH = 10). The pseudo-secondary kinetic model (correlation coefficient of 0.9925) and the Freundlich model (correlation coefficient of 0.998) fitted the experimental results very well. From the adsorption thermodynamics results, it can be inferred that the adsorption process of ammonia nitrogen is a spontaneous exothermic process. The mechanism of adsorption of ammonia nitrogen may be related to electrostatic interactions, ion exchange and hydrogen bonding.