Isotherm, kinetic and thermodynamic studies for the adsorption of methylene blue on almond leaf powder

Abstract

In this study almond leaf powder (ALP) was used as an adsorbent for the methylene blue (MB) removal. The initial MB concentration, interaction time and temperature effects were investigated in a batch experimental system. The equilibrium data was modelled using Langmuir, Freundlich and Temkin adsorption isotherms, while kinetic parameters were determined using the pseudo first order (PFO), pseudo second order (PSO) and intra-particle diffusion (IPD) models. It was noted that the Freundlich model was the most convenient option compared to the Langmuir and Temkin models. The Freundlich model coefficients increased as the temperature increased, proving that adsorption process is favorable at higher temperatures. The results also indicated that the experimental and calculated qe values were close to each other, which shows that this process fits the PSO kinetic model with higher R2 values than other two models. Kinetic constants became closer to both temperatures and the initial concentrations and qe values increased with the increase in the concentration of MB. The initial MB concentration increased from 10 to 60 mg/L, while the adsorption capacity on ALP increased from 1.46 to 9.24 mg/g, 1.61 to 9.71 mg/g and 1.89 to 10.71 mg/g for 298, 308 and 323 K, respectively. Gibbs free energy, enthalpy and entropy of this separation process were determined as -1737.1 J/mol, 14.776 kJ/mol and 55.413 J/mol, respectively. Results of this study showed that ALP can be an alternative material for dye removal.