Adsorption Kinetics and Thermodynamics Characteristics of Expanded Graphite for Poly(vinyl alcohol)

Abstract

In the present study, expanded graphite processing of an expanded volume of 400 mL/g is prepared through chemical oxidation intercalation and its adsorption kinetics and thermodynamics characteristics for poly(vinyl alcohol) with polymerization degree of 1750 in aqueous solution is investigated. We studied the influence of initial poly(vinyl alcohol) concentration, temperature and ionic strength on adsorption capacity. Langmuir constants and Gibbs free energy change (DGº) are calculated according to the experimental data. Kinetic studies are carried out with a series of poly(vinyl alcohol) concentration under different temperatures and the data are simulated with pseudo first-order and second-order kinetic model, respectively. Thermodynamic study indicates that ionic strength has no obvious influence on the equilibrium adsorbance. Adsorption isotherm of expanded graphite for poly(vinyl alcohol) with a polymerization degree of 1750 is type I; 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 increase with the increasing of temperature. Adsorption activation energy of expanded graphite for poly(vinyl alcohol) with a polymerization degree of 1750 is less than 20 kJ mol^-1, physical adsorption is the major mode of the overall adsorption process.