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Adsorption thermodynamics and kinetics of expanded graphite for oxamine blue GN

Xiu-Yan Pang, Li-Juan Xu, Rui-Nian Lin, Qiu-Li Chen

In order to investigate the adsorption thermodynamic and kinetic characteristics of expanded graphite (EG) for oxamine blue GN, EG was prepared with 50 mesh crude graphite after chemical oxidation intercalation of potassium permanganate and vitriol. The adsorbent was characterized by expanded volume, specific surface area and pore cubage. In thermodynamic study, adsorption isotherm and free energy change (⊿G°) were detected and calculated, respectively. Influence of pH on absorbency and adsorbance, and impact of ion strength on adsorbance were investigated. In kinetic study, adsorption model and rate-limiting step for the adsorption process were discussed, adsorption rate and activation energy are calculated. Results illustrate: adsorption of oxamine blue GN on EG is a spontaneous process, and adsorption isotherm is type I. The presence of salts and the proper adjustment of pH would improve adsorption capacity. Kinetic studies show that the kinetic data can be well described by the pseudo second-order kinetic model. The internal diffusion appears to be the ratelimiting step for the adsorption process.