Synthesis and utilization of β-cyclodextrin modified chitosan for the adsorption of aspirin

Abstract

Chitosan is a very versatile substance in terms of its usage. It has a number of uses ranging from agricultural to medicinal usage. In adsorption study, chitosan is a very promising material as it can be used to adsorb a variety of waste such as dyes, metal ions and pharmaceutical. This particular ability can be attributed to the presence of amino and hydroxyl group in its molecules. However, these reactive groups tend to form hydrogen bond with each other and greatly reduces the adsorption efficiency of chitosan. A lot of research have been done in order to improve the adsorption efficiency of chitosan. One of the methods used is by modifying the surface of chitosan with another chemical. In this study, chitosan was modified with ß-cyclodextrin by using impregnation method. The response for this study was the removal of aspirin in an aqueous solution. This study was conducted to synthesize and characterize chitosan modified with ß-cyclodextrin, to determine the adsorption performance of the adsorbent for aspirin removal and analyze the adsorption mechanism of the adsorbent for aspirin removal. Chitosan was modified without using any harmful and hazardous chemical. The ß-cyclodextrin was initially dissolved in distilled water before being mixed with the chitosan. After 30 minutes of mixing, the resulting solid was filtered and dried at 60 °C before being subjected to adsorption study. The characterization of the adsorbents was conducted using Fourier transform infrared spectroscopy, point of zero charge, carbon, hydrogen, nitrogen and sulphur analysis, Field emission scanning electron microscopy and Brunauer-Emmett-Teller analysis. The adsorption kinetics were studied using the pseudo-first and pseudo-second order kinetic model and Elovich equation. The adsorption isotherm was studied using the Freundlich, Langmuir, Temkin and Dubinin-Radushkevich isotherm model. The adsorption thermodynamics was determined by studying the changes in enthalpy, changes in standard entropy and Gibbs free energy. The result shows an improvement in adsorption capacity when chitosan was modified with ß-cyclodextrin. The maximum adsorption capacity of chitosan was 236.97 mg/g while the maximum adsorption capacity for ß-cyclodextrin modified chitosan was 359.87 mg/g which is an increase of 51%. The best condition for the removal of aspirin is 10 minutes of contact time, pH 3, 30 ºC temperature, 500 mg/L initial concentration of aspirin and 0.05 g of adsorbent. The results of the model fitting showed that the adsorption of aspirin onto the adsorbent occurs via physical adsorption.