Kinetic and Thermodynamic Study on Removal of PAH from Water using the Performance of Modified Natural Adsorbent

The adsorption process is an economical, low-energy, and environmentally friendly approach to purify water contaminated with polycyclic aromatic hydrocarbons (PAHs). Clay (CL), as a natural adsorbent, represents a class of materials particularly well-suited for this adsorption purpose. This study aims to assess the viability of utilizing chemically modified clay, organoclay (OCL), for the removal of PAH contaminants compared to unmodified clay. The synthesis of modified clay involved the use of CTAB surfactant with cationic exchange capacity. To create water-based PAH solutions, the required amount of PAH was first dissolved in methanol and then diluted to the final concentration with deionized water. To estimate the adsorption mode, Freundlich, Langmuir, and Temkin models were fitted with the experimental isotherm data. Additionally, to investigate the basic process of the PAH adsorption mechanism, pseudo-first-order, pseudo-second-order, and Roginsky-Zeldovich models were applied, with the results best fitting the pseudo-second-order model. The kinetic results indicated that the pseudo-second-order kinetic model, with high correlation coefficients, was more suitable than the other kinetic models. The maximum change in entropy (ΔS) obtained was equal to -53.25 J (mol K) −1. Furthermore, the negative values of the change in enthalpy (ΔH) indicate that both physical and chemical adsorption play a role in the adsorption process. Overall, the prepared modified clay is highly effective in removing PAHs and demonstrated an improved ability to adsorb this organic contaminant compared to other conventional methods.