A practical and theoretical study of the mechanical kinetics of ascorbic acid adsorption on a new clay surface

Abstract

Ascorbic acid is considered one of the weak phenolic acids, as practical experiments have shown that it can adhere to the adsorbent clay particles by forming electrostatic forces, hydrogen bonds, and the loss of positive protons if the adsorbent material contains electron density on the surface because it contains more than one hydroxyl alcohol and phenolic group. Phenolic hydroxyl groups act as weak acids that can lose a proton and convert to the phenoxide ion since ascorbic acid contains two contiguous phenolic hydroxyl groups. We note that the loss of hydrogen protonation gives a more stable product, which is 1,2 di-ketones. Therefore, the dissociation of ascorbic acid increases as the base medium increases. In this research we have studied the effect of adding sand (a natural substance) on the presence (activity) of ascorbic acid in the aqueous medium, adsorption technology was used in this study through which the most important factors affecting the adsorption process of ascorbic acid molecules were identified. The kinetic models were applied such as pseudo-first and second-order on the adsorption process, which is considered as a complex process that passes through several steps. In this study, the adsorption of ascorbic acid is in agreement with the pseudo-first and second-order models by obtaining a linear relationship with a high correlation coefficient as well as the experimental and theoretical capacity values of the adsorption process are equal. The Langmuir and Freundlich isotherms were used to describe the relationship between the adsorbent and adsorbate substance through the capacity of adsorption, the energy bonding, and favorite of adsorption, the results of adsorption are in agreement with Langmuir isotherm. The thermodynamic parameters (∆G, ∆H, ∆S) for the adsorption process were calculated. To obtain more information about the adsorption process, this study confirms some conclusions, the modified Arrhenius equation was applied to the results of the adsorption process, by studying the potential sticking of ions on the surface of the clay. This study comprehensively highlights the nature of the adsorption of ascorbic acid ions on the surface of the clay .The theoretical side of the ascorbic acid adsorption process for the oxides present on the adsorbent surfaces was studied using the (DFT) theory, and it was found that the theoretical results corresponded with the practical results. Ascorbic acid is transformed by negative charges and double bonds to a more stable di-ketone compound. The adsorption mechanism has been proposed, which corresponds to the practical results reached, Finally, to prove the adsorption mechanism, the resulting compound was diagnosed using an infrared spectrum.