Abstract

ADEBAYO, G.B. et al. Kinetics, Thermodynamics and Isothermal Modelling of Liquid Phase Adsorption of Methylene Blue onto Moringa Pod Husk Activated Carbon. S.Afr.j.chem. (Online) [online]. 2019, vol.72, pp.263-237. ISSN 1996-840X.  http://dx.doi.org/10.17159/0379-4350/2019/v72a34.

This study focused on the liquid phase sorption of methylene blue (MB) using low cost agro-waste from moringa pod husks. Moringa pod husk was carbonized at 450 °C for 30 min, which was later activated with 0.1 M phosphoric acid. The physico-chemical properties of moringa pod activated carbon (AMP) were determined. The results of the physicochemical parameters are: moisture content (13.6 ± 0.02), ash content (2.61 ± 0.11), point of zero charge (pH_ZPC) (7.2) and bulk density (0.6 g L^-1). The sample was also characterized using Brunaeur Emmett Teller (BET), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FTIR). The BET surface area obtained for AMP is 1340.234 m² g ^-1. The effect of optimized parameters such as initial concentration, contact time, pH, adsorbent dosage, and temperature on methylene blue removal was investigated. The obtained maximum monolayer adsorption capacity value (q_max)is 9.5785 mg g^-1. The three adsorption isotherm models, namely Langmuir, Freundlich and Temkin, were employed to describe the fitness of equilibrium data. The Langmuir equation fitted the adsorbent system better with a R² value of 0.9958. The pseudo-second-order kinetic equation also fitted the data well. Thermodynamic studies showed that the AMP-MB adsorption system is spontaneous and endothermic as a negative and positive value was obtained for AG" (-0.460 KJ mol^-1) and ΔΗ" (4.482 KJ mol^-1), respectively.

Keywords : Moringa pod husks; characterization; methylene blue; adsorption kinetics; adsorption models.

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