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|Abstract:||Low-cost adsorbents have been investigated at the laboratory scale for the treatment of coloured effluents with different degrees of success by researchers at Department of Chemistry, Gauhati University, Guwahati, India. The dye, Methylene Blue, was adsorbed on an adsorbent prepared from mature leaves of the Neem tree (Azadirachta indica A. Juss.). A batch adsorption study was carried out with variable adsorbate concentration, adsorbent amount, pH and temperature. Ninety-three per cent of the dye could be removed by 2g of the Neem leaf powder from 1 litre of an aqueous solution containing 25mg of the dye at 300K. The adsorption followed pseudo first order kinetics with a mean rate constant of 3.73×10−3/min and an intra-particle diffusion rate constant of 6.36×10−2mg/g/min−0.5. A possible mechanism of adsorption was suggested on the basis of concurrently operating surface adsorption and pore diffusion. The experimental data yielded excellent fits with Langmuir and Freundlich isotherm equations. The Langmuir monolayer capacity had a mean value of 8.76mg/g. The adsorption of the dye was endothermic in nature (ΔH: 4.62–16.74kJ/mol) and was accompanied by an increase in entropy (ΔS: 54.22–90.23J/mol/K) and a decrease in Gibbs energy (ΔG: −10.33 to −13.62kJ/mol in the temperature range of 300–330K). The results indicated that the dye, Methylene Blue, strongly interacts with a biomass-based adsorbent, the Neem leaf powder.|
|ISSN:||0975-1092 (Online); 0972-592X (Print)|
|Appears in Collections:||NPR Vol.4(5) [September-October 2005]|
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