An investigation of the adsorption of Congo red dye on two naturally occurring adsorbents Hydroxyapatite and Bentonite: An Experimental Analysis, DFT calculations, and Monte Carlo simulation

Abstract

Congo Red (CR) dye is classified as a toxic and carcinogenic substance, posing significant health and environmental risks. To address this issue, the adsorption efficiency of CR on natural bentonite and hydroxyapatite (HA) was systematically studied. The adsorbents were successfully characterized by XRD, FTIR, and SEM analysis. Optimization through the Box-Behnken method identified the optimal conditions (pH = 6.5, initial dye concentration = 150 mg/L, and adsorbent mass = 1.5 g/L), resulting in maximum removal of CR of 95 % for HA and 84 % for bentonite. 2.6.2. Monte Carlo (MC) simulations provided insights into the spontaneous and favorable adsorption behavior, particularly under acidic conditions, driven by van der Waals interactions. Kinetic studies revealed that the adsorption followed a pseudo-second-order model (R2 = 0.99). Furthermore, regeneration tests demonstrated that HA and bentonite retained 75 % and 60 % of their adsorption capacities, respectively, after five cycles, indicating their potential for sustainable reuse in dye removal. The exceptional adsorption efficiency and reusability of these natural adsorbents make them promising candidates for environmental remediation, contributing to a deeper understanding of the underlying adsorption mechanisms.

Keywords

• Congo red dye
• Hydroxyapatite
• Bentonite
• Molecular dynamics
• DFT