Enhanced adsorption of nicotinic acid by different types of Mg/Al layered double hydroxides: synthesis, equilibrium, kinetics, and thermodynamics

Abstract

The aim of this study was to investigate the effect of different ions in the interlayer spaces of layered double hydroxides (LDHs) with different Mg/Al ratios on the adsorption of aqueous nicotinic acid (NAc). For this purpose, three types of LDHs were synthesized for NAc removal using the co-precipitation method with different Mg/Al ratios to include chloride or nitrate anions between the layers (Cl-LDH2:1, NO3-LDH3:1, and NO3-LDH2:1). The LDHs were characterized with Fourier transform infrared spectroscopy, X-ray diffraction, and inductively coupled plasma mass spectrometry, and the effects of initial acid concentration, time, temperature and adsorbent amount on NAc adsorption were investigated. The results showed that the Langmuir equilibrium isotherm model was the best for all three LDHs, and among the kinetic models, the pseudo-second-order agreed the most with experimental data. ΔG, ΔH, and ΔS were calculated for all LDHs, and according to the data, the adsorption of NAc was endothermic and spontaneous. When all the results were evaluated comparatively, it was found that NO3-LDH2:1, with a 2:1Mg/Al ratio and nitrate ions between the layers, has the best NAc adsorption capacity.