Abstract
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 (pHZPC) (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 (qmax)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.
Highlights
In recent years, synthetic dyes have often been used in various industrial dyeing and printing processes
The ash content obtained in this study for activated carbon moringa pod (AMP) (2.61 %) is higher compared to those reported by Sivakumar et al.[17] (2.39 %)
It was shown that the bulk density obtained for AMP (0.64) is almost the same by those obtained from Martynia annua L. by Sivakumar et al.[17] (0.63)
Summary
Synthetic dyes have often been used in various industrial dyeing and printing processes. The textile industry is the largest consumer of synthetic dyes utilizing about 56 % of the total world dye production per annum of 7 × 105 t.1. During the textile dyeing process, released untreated effluent may contaminate water bodies which poses a great threat to aquatic organisms and the people who use these water bodies for living purposes. In a water supply system, when a concentration as low as just 1.0 mg L–1 of dye is present in the water supply, it could be dangerous for human consumption.[2]. Other effects include: toxicity to aquatic life, mutation of DNA, carcinogenicity, and damage to some vital organs in human beings, such as dysfunction of the kidneys, reproductive system, liver, brain and central nervous system.[3] Dyes possess complex aromatic structures and they may not be biodegradable
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