Effects of acid activation on the halloysite nanotubes for curcumin incorporation and release

Halloysite nanotubes (HNT) are natural aluminum silicate clays with a hollow tubular structure and chemical formula of Al2Si2O5(OH)•2H2O. The selectivity of its surface allows different types of treatments in order to improve some of its properties, such as pore volume and surface area, as well enabling the incorporation and release of drugs and bioactive compounds, such as curcumin, in a more efficient way. In this work, the HNT have undergone an acid treatment to incorporate curcumin. From the analysis of FTIR, TEM, XRD, SEM-EDS and nitrogen adsorption / desorption it was possible to suggest that activation with HCl on the nanotubes made it possible to obtain an increase in the specific surface area, in the volume of pores and in the lumen diameter, preserving the tubular structure of these materials. This process favored the incorporation of curcumin (Cur), which had a higher incorporation efficiency value of 77.42 ± 1.92% and an antioxidant activity of 75.91 ± 0.94%, and consequently 80% release after 90 min. With this study of in vitro release, TEM and TGA, it was possible to reveal that the incorporation of curcumin occurred in the lumen (diameter ≈ 23 nm) through electrostatic interactions between Al3+ and Cur−. In addition, the curcumin was partially adsorbed on the HNT pores surface, where a shift in Tonset of 15 °C was found for a lower temperature and an increase of 12 nm in the external diameter. These results indicate that acid activation in HNT favored the incorporation and release of Cur, which allows us to suggest the possibility of investigating the use of HNTA-C in the biomedical area, as in the treatment with antioxidant compounds. [Display omitted] •Curcumin was incorporated into halloysite nanotubes (HNT) after acid activation.•HNT were characterized by physical-chemical, thermal and morphological analysis.•Acid activation allowed to increase the specific surface area and pore volume of HNT.•Acid treatment favored the incorporation and release of curcumin in HNT.•The curcumin release mechanism of HNTA-C follows the Fickian diffusion model.