Microesferas de carboximetilcelulose e carbonato de cálcio: isotermas de adsorção e cinética de liberação controlada do azul de metileno

Abstract

In this work, it was made Carboxymethylcellulose and Calcium Carbonate (CMC/CaCO3) microspheres, in which was adsorbed, as model drug, Methylene Blue (MB). The adsorption experiments was realized with MB concentration of 4, 5, 6, 7 and 8 mg/L, and at 303,15, 313,15 and 333,15 K. The amount of MB adsorbed in the microspheres was in a range of 24,5 to 37,6 %, in relation of the initial amount of MB in solution, with 552 μg/g as maximum adsorption capacity. The adsorption capacity was smaller increasing the experiment temperature. It was noted that the adsorption isotherms follow a linear tendency, indicating that the adsorption is proportional to the drug concentration in the solution. The high linear correlation coefficient indicate a good agreement of the experimental data with the mathematical models of Langmuir and Freundlich isotherms, therefore, indicating that the adsorption occurs in a monolayer and in a heterogeneous surface. The adsorption was done very fast, where at 303,15 K and with 8 mg/L of MB the equilibrium was achieved in less than 30 min., following the pseudo second order mathematical model. The positive values found for Δ G°, Δ H° and Δ S° for the drug adsorption in the matrices, indicates that the process is viable but non-spontaneous, endothermic and with a reduction of the randomness of the system. The MB release of the microspheres was done in a continuous and linear form, being well descripted by the zero order kinetics model of release, where in 7,5 hours was released about 12 % of the drug adsorbed in the matrices.