Adsorption of Malachite Green from Deionized Water and Seawater Using Coconut Shell Granular Activated Carbon: Kinetics, Isotherms, and Thermodynamics Analysis

In the field of aquaculture industry uses malachite green, for treating fungal and parasitic infections in freshwater and seawater; however, it carries risks to the environment and human health alike This research investigates how coconut shell granular activated carbon (CSGAC) derived from agricultural waste as a sustainable bioresource has the ability to adsorb malachite green (MG) with a focus on its effectiveness, in removing MG from water sources. FTIR analysis highlights the significance of the hydrogen bond and π-π interactions in adsorption. Comprehensive statistical analysis suggests that the pseudo-2nd order model is the best kinetic model for governing the adsorption of MG adsorption in deionized water and seawater. The next best models were Pseudo-nth order and the Fractal-like Pseudo-2nd Order model for deionized water and hyperbolic tangent and mixed -1,2 order for deionized water and seawater, respectively, in descending order. The diffusion models of Boyd’s film diffusion and the intraparticle diffusion model of Wang and Guo-modified Weber-Morris model were utilised to study the process of MG adsorption into CSGAC. The findings point to pore diffusion as the process with the lowest rate of change. The first segment of the Wang and Guo-modified Weber-Morris model passes through the origin, indicating a confirmation of Boyd’s intraparticle diffusion model above. The best isothermal models were Langmuir, Jovanovic, Brouers–Sotolongo, Unilan, and Moreau, and in seawater, the top models were Jovanovic, Langmuir, Brouers–Sotolongo, Redlich-Petersen and Fritz-Schlunder III. The obtained maximum adsorption values for the top model clearly show that adsorption in seawater causes a drop of Qm (mg/g) value from 72.029 (deionized water) to 51.409 (seawater). Thermodynamics study using a nonlinear van’t Hoff plot gave ΔG° values (ΔG° < 40) indicative of physisorption. The study indicates the suitability of CSGAC as a good sorbent for MG, both in deionized water and in seawater.