Adsorption Kinetics and Thermodynamics Characteristics of Expanded Graphite for Polyethylene Glycol
In the present study, expanded graphite (EG) is prepared with 50 mesh crude graphite through chemical oxidation and its adsorption kinetic and thermodynamic characteristics for Polyethylene glycol (PEG) with different molecular weight (MW) in aqueous solution is investigated. We study the influence of initial PEG concentration, temperature, pH and ionic strength on adsorption capacity. Langmuir constants and Gibbs free energy change (ΔG°) are calculated according to experimental data, respectively. Thermodynamic study indicates that all the equilibrium adsorbance increase with the rise in ionic strength. However, solution acidity does not have an obvious effect. Adsorption of EG for PEG with different MW is all types and PEG molecule lies flat on EG surface. Adsorption processes are all spontaneous. Kinetic studies show that the kinetic data can be delineated by pseudo second-order kinetic model. Second-order rate constants and the initial adsorption rate rise with the increasing of temperature and half-adsorption time decreases with the increasing of temperature. The adsorption activation energy of each PEG is less than 30 kJ mol-1, physical adsorption is the major mode of the overall adsorption process.