Facile synthesis of α-MnO₂ micronests composed of nanowires and their enhanced adsorption to Congo red

Abstract

In this paper, α-MnO₂ micronests composed of nanowires were fabricated via a hydrothermal reaction of MnSO₄·H₂O and K₂S₂O₈ solutions. The α-MnO₂ micronests were demonstrated to have a higher adsorption capacity than γ-MnO₂ microspheres due to their large specific surface area. The amount of Congo red adsorbed per unit weight of α-MnO₂ micronests increased significantly from 114 to 282 mg·g^-1 with concentration of Congo red solution increasing from 50 to 200 mg·L^-1, but it had a little change with temperature. Kinetics, isotherms and thermodynamics for the adsorption of Congo red on α-MnO₂ micronests were examined. The adsorption process followed the pseudo-second-order kinetics with good correlation. The experimental data were analyzed by Langmuir and Freundlich models, and equilibrium data fitted the Langmuir isotherm very well with maximum monolayer adsorption capacity of 625 mg·g^–1 at 22 °C. The adsorption was spontaneous and endothermic according to thermodynamic studies. The experimental results indicate that α-MnO₂ micronests possess a high adsorption capacity and could be employed as a replacement of traditional sorbents.

Key words： MnO₂; Congo red; adsorption; kinetics; isotherm; thermodynamics

Acknowledgements

The authors are grateful to the financial supports of the National Natural Science Foundation of China (Grants Nos. 20976033, 21176054 and 21271058), the Fundamental Research Funds for the Central Universities (2010HGZY0012) and the Education Department of Anhui Provincial Government (TD200702).

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