Investigation of dyes adsorption by materials obtained from spent coffee grounds
Abstract
The subject of the research is spent coffee grounds and their adsorption capacity. The main purpose of the research is modifying coffee wastes by hydrogen peroxide for obtaining sorbents of high efficiency, which are suitable for water purification from dyes. Properties of original coffee wastes and the samples obtained by a treatment with one molar hydrogen peroxide solution are compared in the article.
Adsorption capacity of the samples towards methylene blue and congo red was determined by static method. Dyes concentration in the solutions was determinened spectrophotometrically. The point of zero charge was determined by immersion technique using the procedure adapted to plant sorbents. Specific surface area of original and modified samples was determined by means of sorption of ethylene glycol monoethyl ether. For an estimation of functional groups of the sorbent surfaces IR-spectroscopy was applied.
The treatment with hydrogen peroxide was shown to lead to an increase of specific surface area of the sorbent. The nature of functional groups didn’t change essentially after the treatment. Kinetic curves of adsorption were analyzed using conventional models of diffusion and chemical kinetics. Sorption of both dyes was found to occur in mixed diffusion regime and could be satisfactorily described by pseudo-second order equation. Adsorption isotherms of methylene blue and congo red were analyzed. Isotherms for both original and modified sorbents were demonstrated to fit Langmuir model. The results obtained can be applied in the processes of water purification. The conclusion was made that sorbents obtained from spent coffee grounds are prospective materials with high sorption capacity towards both to cationic and anionic dyes.
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References
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