Study on the adsorption characteristics of aqueous caffeine solutions on macroporous resins with hydrogen-bonding interactions

Abstract

The adsorption characteristics of caffeine on six macroporous resins have been investigated. The results show that the resin with hydroxyl groups (XDA-200) offer better adsorption/ desorption capacity than other resins, and its adsorption kinetics fit a pseudo- second-order model. The adsorption process is a type of fast adsorption, and multiple adsorption mechanisms controlled the rate of adsorption. The isothermal equilibrium curve of caffeine adsorbed onto XDA-200 show a good fit to the Freundlich model, and thermodynamics tests show that the process is exothermic and spontaneous. The absolute value of enthalpy is 14.347 kJ/mol, which is in the range of the adsorption enthalpy related to hydrogen-bonding interactions. XPS and FTIR analyses also verify the existence of hydrogen-bonding interactions.