Modification of halloysite nanotubes with xanthene dyes and their application in luminescent polymer nanocomposites

In this study, halloysite nanotubes (HNTs) were modified with three xanthene dyes and subsequently utilized for the fabrication of luminescent polymer nanocomposites. Two different sets of dyes (rhodamine B, rhodamine 6G, and fluorescein) were chosen because of their ability to interact differently with HNTs. Rhodamines B and 6G were adsorbed on the negatively charged external surface of HNTs due to their cationic nature, while fluorescein was infiltrated into the positively charged nano-size lumen of HNTs. The influence of the HNTs substrate on photoluminescence (PL) of the dyes in the polystyrene matrix was investigated. An enhancement in the PL intensity of fluorescein by a factor of 8 was observed upon its encapsulation into lumens of HNTs. On the other hand, the adsorption of rhodamines on HNTs led to a decrease in their PL intensity. A homogenous dispersion of the dye molecules achieved at nanoscale introduced luminescence properties in the polymer nanocomposites. The robust protocol for the modification of halloysites with organic chromophores provides a straightforward way to distribute the dye molecules in a polymer matrix and to incorporate luminescent properties into different polymer matrices.