Adsorption of Acid Blue 25 on peach seed powder: Isotherm, kinetic and thermodynamic studies

Abstract

In the present study peach seed powder (PSP) was used as an adsorbent to remove Acid Blue 25 (AB25) a commonbasic dye, from aqueous solution. The adsorption experiments were carried out in a batch system and the effects ofinitial concentration, interaction time and temperature were investigated. The Langmuir, Freundlich and Temkinadsorption isotherms were used to model the equilibrium data. The kinetic parameters were determined by the pseudofirst order (PFO), pseudo second order (PSO) and intra-particle diffusion (IPD) models. According to the results, theFreundlich isotherm model is a more convenient option compared with the Langmuir and Temkin models. TheFreundlich model coefficients increased as the temperature increased, which shows that the adsorption processbecomes more favorable with higher temperature. The experimental and calculated $q_e$ values close to one anotherindicated that this process fits the PSO kinetic model with higher $R^2$ values than the other two models. Kinetic constantsbecome closer to both the temperatures and initial concentrations and $q_e$ values increases with the increasingconcentration of AB25. The initial dye concentration increased from 25 to 150 mg $L^{-1}$, while the dye adsorption capacityonto PSP increased from 4.80 to 39.01 mg $g^{-1}$, from 5.57 to 44.27 mg $g^{-1}$ and from 6.80 to 49.22 mg $g^{-1}$ for 298, 308 and323 K, respectively. The monolayer adsorption capacity ($q_m$) of PSP was determined to be 56.18, 64.94, 95.24 mg $g^{-1}$ for298, 308 and 323 K, respectively. Thermodynamic parameters for free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) ofthe separation process were determined as -1737,1 J $mol^{-1}$, 14.776 kJ $mol^{-1}$ and 55,413 J$mol^{-1}$, respectively. The negative values of $Delta G^o$showed that this separation process was endothermic and natural. Theresults of the present study demonstrated that PSP can be used as an alternative material in dye removal.