Equilibrium and kinetics of 5-aminosalicylic acid adsorption by halloysite

• Published in: Microporous and mesoporous materials 2008-02, Vol.108 (1), p.112-116
• Main Authors: Viseras, M.T., Aguzzi, C., Cerezo, P., Viseras, C., Valenzuela, C.
• Format: Article
• Language: English
• Subjects: 5-Aminosalicylic acid; Adsorption; Chemistry; Colloidal state and disperse state; Equilibrium; Exact sciences and technology; General and physical chemistry; Halloysite; Kinetics; Porous materials; Surface physical chemistry
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2007.03.033

This paper investigates equilibrium, kinetics and thermodynamic aspects of the adsorption of 5-amino salicylic acid [5-ASA], an anti-inflammatory agent, onto halloysite, a mesoporous polymorph of kaolin appearing as hollow nanotubes with diameters typically smaller than 100 nm and lengths ranging from 500 nm to over 1 μm. Kinetic and equilibrium studies were performed in aqueous medium at different temperatures and drug concentrations. The amounts of 5-ASA retained by the clay was evaluated by UV spectroscopy. Mathematical treatment of the data was performed following Valenzuela et al. [C. Valenzuela-Calahorro, A. Navarrete-Guijosa, M. Stitou, E. Cuerda-Correa, Colloids Surf. A: Physicochem. Eng. Aspects 224 (2003) 135–147], and thermodynamic parameters were then calculated by using the Eyring equation. The overall adsorption process of 5-ASA onto halloysite was explained as the result of two separate processes. Initial rapid adsorption of 5-ASA (specific adsorption rates between 10.0 and 12.3 s −1) on the external halloysite surface (ΔH = 7.59 kJ/g) was followed by slow adsorption (specific adsorption rates between 0.2 and 0.4 s −1) of the drug inside the phyllosilicate pores (ΔH = 42.28 kJ/g). Adsorption experiments showed that promising delivery systems may be designed by supporting 5-ASA onto halloysite.