removal of caffeine from aqueous solution using multiwall carbon nanotubes: kinetic, isotherm, and thermodynamics studies

The occurrence of contaminants in wastewaters, and their behavior during wastewater treatment and production of drinking water are key issues to re-use water resources. the present research aims to remove caffeine from aqueous solutions via adsorption technique, using multi-wall carbon nanotubes (mwcnts) as an adsorbent under different experimental conditions. the processing variables such as ph (2-12), contact time (1-30 min), initial concentration of caffeine (2-314 mg/l), temperature (25, 50, 80 °c), and adsorbent mass (0.02-0.15 g) have been investigated with equilibrium and kinetic studies on adsorption of caffeine onto mwcnts being also developed. maximum caffeine removal has been obtained at ph=7 and adsorption equilibrium has been achieved in 5 min. the use of pseudo second-order kinetic model with determination coefficient of 99.3% (r2=0.993), has made the adsorption kinetics to be well fitted. the caffeine equilibrium adsorption data have been best fitted to langmuir-freundlich model with a relatively high determination coefficient of 96.5% (r2=0.965) and maximum adsorption capacity of 35.61 mg/g of caffeine on mwcnts. the thermodynamic parameters display that the adsorption of caffeine onto mwcnts has been non-spontaneous and endothermic in nature.