Adsorptive Removal of Methylene Blue using Activated Carbon Derived from Waste Coffee Grounds

In this work, activated carbon derived from waste coffee grounds (CG -AC) was synthesized using zinc chloride (ZnCl2) as the activating agent.The CG-AC was then employed as an adsorbent for the removal of methylene blue (MB) from aqueous solutions.Adsorption isotherm data were evaluated using the Langmuir, Freundlich, and Temkin models.The Langmuir model, with a correlation coefficient of 0.9998, showed the best fit for the adsorption of MB on CG-AC, with the maximum monolayer adsorption capacity calculated at 176 mg/g.Kinetic studies were conducted using pseudo -first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD) models.The R values indicated that the PSO model provided a more accurate description of the adsorption kinetics.The plot of qt versus t 1/2 in the IPD model demonstrated multi-linear behavior, suggesting that the adsorption occurred in multiple stages.Thermodynamic analysis was performed at temperatures ranging from 25 to 34 C, where negative G values and positive H values confirmed the spontaneity and endothermic nature of the adsorption process.Additionally, the positive S value indicated a strong affinity of MB molecules for the CG-AC.These results suggest that CG-AC could be a promising adsorbent for treating wastewater containing high levels of dyes.