Fig. 2: Formation and distribution of polydopamine on HNTs.

a Particle size distributions—as deduced from dynamic light scattering of a dopamine solution after different polymerization times with and without halloysite nanotubes (HNTs); b time evolution of the particle size during polydopamine growth in the presence and absence of HNTs; c BJH pore size distribution; d TGA graphs for HNTs after different exposure times to the dopamine solution and e time evolution of the polydopamine mass deposited on the HNT surface during polymerization. All error bars indicate the standard deviation of the experiments. Scanning transmission electron microscope (STEM) dark-field image and EDS elemental mapping images for HNT after f 1 h, g 4 h, and h 24 h of polydopamine polymerization. The carbon signal in the left bottom corner of f is due to the carbon grid that was used as support for the nanotubes. The difference in the intensity of the constituent elements of HNTs is due to the fact that these images were taken on different nanotubes that may have different numbers of layers.