Rapid cationic dye adsorption on polyphenol-extracted coffee grounds-A response surface methodology approach

The Box-Behnken design under the response surface methodology (RSM) with five interacting parameters (adsorbent dose, initial dye concentration, time of agitation, initial solution pH and time of the adsorbent microwave activation) was employed to interpret the adsorption characteristics of cationic dye onto polyphenol-extracted coffee grounds in water solutions. Experimental results indicated that coffee ground is excellent low-cost biosorbent with dye removal ability more than 95% for a very short time (under conditions of 250 mg/L initial dye concentration and 15 g/L of adsorbent dose). The maximum adsorption capacity was 36.82 mg/g, whereby the adsorption rate was very fast (around 15 min). Batch mode experiments and kinetic regression results showed that the adsorption process was more accurately represented by a pseudo second-order model. Freundlich isotherm model was superior to the Langmuir isotherm model. FT-IR studies revealed that adsorption process was due to adsorption mediated by different functional groups present on the coffee surface. (C) 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.