Nonlinear Fitting for Estimation of Adsorption Equilibrium, Kinetic and Thermodynamic Parameters of Methylene Blue onto Activated Carbon

Abstract

Adsorption equilibrium, kinetics, and thermodynamics of methylene blue dye (MB) from aqueous solutions onto activated carbon (AC) synthesized from pomegranate peel was conducted in controlled batch systems. The effects of initial MB concentration, AC particle size, contact time, and temperature on adsorption were evaluated. Under the optimized conditions (i.e., contact time 120 min, pH ∼ 5, particle size 125 µm, dye concentration 20 mg/L, temperature 333 K, and 0.5 g AC/50 mL MB solution), the removal percentages can achieve ∼ 98.28%. The nonlinear method was conducted for estimating the equilibrium and kinetic parameters, where the equilibrium data were fitted to the Langmuir isotherm model. The Langmuir isotherm suggested a maximum monolayer adsorption capacity of 5.03 mg/g at 60 °C. The pseudo-second-order kinetic model provided the best fit to the experimental data compared with the pseudo-first-order. Kinetic studies showed that the adsorption equilibrium was rapidly established, with low activation energy entailed for adsorption (Ea; 15.60 kJ/mol). Thermodynamic parameters showed that the adsorption was spontaneous (−∆G° and +∆S°), endothermic (+∆H°), and favorable at ambient conditions.

Amine-Terminated Modified Succinic Acid-Magnetite Nanoparticles for Effective Removal of Malachite Green Dye from Aqueous Environment

“…Furthermore, the value of enthalpy changes also shed light on the type of adsorption mechanism, as for physisorption (∆H • < 20 kJ/mol), for electrostatic interaction (20 < ∆H • < 40 kJ/mol), and for chemisorption (80 < ∆H • < 450 kJ/mol)[71]. As in our case, the value of ∆H • was −34.76 (kJ/mol), suggesting the electrostatic interaction of MG on the MSA@TEPA surface[71,72]. The negative values of ∆S • indicate a degree of disorder of the adsorbed MG at the solid/liquid interface, which is a normal and general phenomenon.…”

Removal of Arsenic by Adsorption using Activated Carbon Derived from Zea mays

“…The linear part at the initial stage is due to film diffusion on the available surface active site; the curve part (stage II) is caused by the percolation of As(III) ions through the adsorbent pores and the plateau (stage III) declares saturation of the adsorbent surface leads to attaining equilibrium state. The increase of C values (Table-4) as 2.62, 3.65 and 4.84 for the stages I, II and III, respectively and minimized Kd values with time (0.4650, 0.2527, 0.0762 for the stages I, II and III, respectively) proves that the rate of adsorption is high at the initial stage and further reduces because of the enhancement of diffusional resistance and increase of boundary layer effect [12,[21][22][23][24][25]. Summarizing the kinetic models for the adsorption mechanism, the rate-limiting step of the adsorption mechanism is explained by the best-fit model pseudo-secondorder and intraparticle diffusion models.…”

“…Adsorption kinetic studies: To illustrate the reaction pathway between adsorbate As(III) ions and adsorbent activated carbon and the mechanism of the adsorption process, the linear and non-linear kinetic models have been employed. Largergen pseudo-first-order kinetic model explains the adsorption rate on the basis of surface active sites through diffusion and boundary layer effect [19][20][21][22]. The non-linear pseudo-first-order kinetic model is given below in eqn.…”

“…Apart from this, the intraparticle diffusion model plot in Fig. 5b suggests that the adsorption mechanism is a multistep process [21][22][23][24]. The linear part at the initial stage is due to film diffusion on the available surface active site; the curve part (stage II) is caused by the percolation of As(III) ions through the adsorbent pores and the plateau (stage III) declares saturation of the adsorbent surface leads to attaining equilibrium state.…”