Characterization of an adsorbent prepared from maize waste and adsorption of three classes of textile dyes

In the past years, investigations have been accomplished in order to evaluate both inexpensive and alternative materials as potential adsorbents for pollutants and colored compounds. A novel adsorbent SOMAP, prepared from maize waste, was activated and characterized under the aspect of its reproducible employment using elemental analysis, thermogravimetry, porosimetry and adsorption of different dyes from solution. In the pretreated samples, the nitrogen content and the concentration of carboxylic groups was smaller than in the washed adsorbent. No major differences in the porosity of the pretreated and non-pretreated adsorbent were observed. The adsorption capacity was evaluated against basic (basic blue BB41), reactive (reactive black RB5) and acid (methyl orange MO) dyes. The adsorption equilibrium in batch experiments was more slowly reached in the case of the reactive and acid dyes. The affinity upon the dyes graded according the series: MO < RB5 < BB41, and the desorption efficiency increased in the inverse order. The adsorption equilibrium was examined in terms of absolute adsorption isotherms for SOMAP and two different lots of the treated material, and was fitted according to Henry, Langmuir and Freundlich models of adsorption for a quantitative evaluation. ATR/IR spectra provided information about the interaction sites and orientation of the adsorbed dyes. Determination of the adsorption equilibrium concentrations was accomplished by two independent analytical methods, i.e. HPLC and VIS spectrophotometry.