Application of a Single Model to Study the Adsorption Kinetics of Prednisolone on Six Carbonaceous Materials

Abstract

The knowledge of the adsorption processes of nonelectrolytes from liquid solution on solid materials involves the study of their kinetic and equilibrium aspects as well as the understanding of their thermodynamic functions. However, in most published papers adsorption isotherms are analyzed by using the Giles classification and other proposed equations which are either empirical or based on kinetic or thermodynamic criteria. Our opinion is that both the kinetic and the equilibrium studies must be complementary and that, in general, equations describing the adsorption isotherms come from the kinetic laws governing the different partial processes which determine the global process. These kinetic laws may be derived from single models. In this paper a single model is proposed, which makes it possible to establish a kinetic law satisfactorily fitting a great number of C (concentration) vs t (time) isotherms. This model has been applied to study the adsorption process of prednisolone by six carbonaceous materials from ethanol solution, the specific adsorption rate, and the activation thermodynamic functions being calculated. The results obtained have also been used to analyze the influence of the intraparticle diffusion on the kinetics of the process.

Application of a Single Model to Study the Adsorption Equilibrium of Prednisolone on Six Carbonaceous Materials

“…According to our own experience (2), the adsorption processes following the kinetic law [2] give rise to equilibrium isotherms that can be fitted to Eq. [3].…”

“…Then the flasks were placed in a thermostatted shaker bath (150 rpm) at 10, 20, 30, 40, and 50 • C ± 0, 1 • C for 15 days. A time of 15 days is long enough to ensure that equilibrium was reached between prednisolone adsorbed and prednisolone in solution (2). After shaking, the solutions were centrifuged and the concentration of prednisolone in the supernatant liquid was determined by UV spectrophotometry at 244 nm, the wavelength corresponding to its maximum absorbance.…”

“…In those processes studied in this paper, the kinetic law is given by Eq. [2], which yields to [3] in which C = equilibrium solution concentration of the adsorbable. n = partial reaction order relating to C (i.e., n 1 in equation [2]).…”

“…As indicated in a previous paper (2), the study of adsorbent/sorbable systems from solution provides information about the number of active sites in the solid surface, as well as about the nature and magnitude of the interactions between these active sites and the sorbed molecules. In the above-mentioned paper, 1 To whom correspondence should be addressed.…”

Mechanistic understanding of the behavior of diuron in the adsorption from water onto activated carbon

“…The uptake of diuron increases significantly with temperature in the whole range of concentration tested, thus the observed effect of temperature on the adsorption capacity of diuron does not follow the most common trend for adsorption. This apparent endothermic behaviour has been interpreted in terms of an increased planarity and diffusivity of the diuron molecules linked to the easier desolvation of diuron molecules in solution as temperature increases [10,11,27]. In a first approach, the equilibrium isotherms of Fig.…”