Evaluating the Efficiency of Two-Parameter Adsorption Isotherm Models in the Adsorption of Methylene Blue

This study investigated the adsorption process of methylene blue cationic dye by silver nanoparticles synthesized using extract Tragopogon buphthalmoides. The effectiveness of various parameters, including adsorbent dosage, pH, contact time, and temperature, was evaluated in terms of their effects on the efficiency of dye removal. The study determined that the optimal conditions for dye removal were a pH of 10, an adsorbent dosage of 0.2 g, a contact time of 60 min, and a temperature of 25°C. Then, Ten different isotherm models including Langmuir, Dubinin-Radushkevich (DR), Harkins-Jura, Freundlich, Jovanovic, Temkin, Fowler-Guggenheim, Halsey, Flory-Huggins, and Hill-de Boer were performed based on the optimal conditions. The calculations were fully presented to obtain the constants of each isotherm, and for greater accuracy in selecting the dominant isotherm, some other error functions, such as SSE (sum of squared errors), MSE (mean squared error), and RMSE (root mean square error) were also used. The Freundlich and Halsey isotherms were identified as the dominant models with the highest degree of correlation coefficient (R2= 0.9913) and least error values (SSE= 0.0229, MSE= 0.00229, RMSE= 0.0047). According to the values of the isotherm constants of Freundlich, n= 1.5087 and Kf = 27.0287, it is quite clear that the adsorption process has occurred physically and there is weak interaction between the adsorbate and adsorbent due to the heterogeneous adsorption of multiple layers on the surface of the adsorbent. The Langmuir isotherm determined the qmax (maximum adsorption capacity) to be 181.8182 mg/g, and the RL (separation factor) was found to be 0.5677, indicating favorable adsorption. The results of this study showed that the order of dye adsorption conformity in the studied isotherms was Temkin Jovanovic Dubinin-Radushkevich Harkins-Jura Langmuir Flory-Huggins Fowler-Guggenheim Hill-de Boer Halsey, and Freundlich. It is clearly shown from the plots that there was adsorption of methylene blue in more than a monolayer, and this exhibits heterogeneity of the surface.