College of Chemical Science and Engineering, Tongji University, Shanghai 200092, P. R. China
Abstract:
In the solution adsorption experiment, different adsorption mode has been observed for aqueous ethanol and aqueous n-butanol, respectively. However, it is difficult to make an adjustment by the profiles of σ-c relationship. Choosing the experimental conditions improperly will give wrong results. Since there is no consistency between the Gibbs adsorption isotherm and Langmuir adsorption isotherm, the experimental data should not be fitted by using any algebraic equations or physical models. The data fitting for this experiment should be carried out according to the following steps:fitting the σ-lnc curve manually, making it monotonic and smooth; retrieving more data from this fitting curve, and re-plotting the σ-lnc curve; calculating the first derivatives at these data points (i.e., (∂σ/∂lnc)T); calculating surface adsorptions by Gibbs adsorption isotherm, Γ=-(∂σ/∂lnc)T/RT. As for the calculation of the cross-section area for the solute molecule, the effect of concentration of bulk solution (i.e., c) on the surface molecular density should be taken into account.
