Kinetics and equilibrium study for adsorptive removal of cationic dye using agricultural waste-raw and modified cob husk

ABSTRACT

The adsorption efficiency of raw and modified cob husk to remove methylene blue (MB) dye was investigated in batch mode. The chemical modification of cob husk was done with citric acid to enhance the cationic dye removal from the aqueous solutions. Surface characterisation of the adsorbents was done through FTIR and SEM. The efficiency of raw and modified cob husk for dye removal was tested through adsorption in batch mode. The studies were carried out under optimised conditions of adsorbent dosage, dye concentration, pH and contact time. The concentration of dye before and after adsorption was estimated through spectrophotometric technique. The time taken to reach equilibrium was found to be 90 and 120 minutes for raw and modified cob husk, respectively. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were used to plot equilibrium data and slopes and intercept of respective plots were used to calculate the values of their corresponding constants. The isotherm data of cob husk and acid-modified cob husk could be best described by the Freundlich equation based on high correlation coefficient values. As a result of functionalization, the adsorption capacity of cob husk for methylene blue increased from 12.75 mgg⁻¹ to 208.3 mgg⁻¹ at 25 ֯C, respectively. Kinetic modelling of the experimental data showed that the sorption kinetics followed the pseudo-second-order kinetic model for both the adsorbents at different concentrations (25–250 mgL⁻¹). Thermodynamic studies were carried out to assess the sorption behaviour of both the adsorbents. The values of different parameters viz.∆G֯, ∆S֯and ∆H֯were calculated for both the adsorbents which showed that the sorption process was endothermic and spontaneous in nature. The results showed that modified cob husk had better adsorption capacity than the raw cob husk due to an increase in the surface area of the adsorbent by chemical modification.

KEYWORDS:

• Adsorption
• cob husk
• acid modification
• isotherm analysis
• kinetic modelling

Nomenclature

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Acknowledgments

The author acknowledges support from Head, Agricultural Chemicals Division, for providing facilities for the research work, Dr Vishal Somvanshi and Dr Gautam Chawla, Division of Nematology and the research grant provided by the Indian Agricultural Research Institute (IARI), New Delhi under the in-house research project (Project No. CRSCIARISIL2014036268).

Disclosure statement

No potential conflict of interest was reported by the author(s).