*2.5. Characterization of Nanoparticles*

Field emission transmission electron microscopy (TEM, Tecnai G2 F30 S-Twin) was used to photograph the morphological differences between HNTs and etched HNTs. The nanoparticles were first dispersed in an ethanol solution ultrasonically for 5 min, and then dropped on the surface of the copper grid to be observed after drying.

The change in the porous structure of the nanoparticles was measured by the Micromeritics ASAP2020 system. Before the experiment, the sample was vacuum degassed at 250 ◦C for 8 h. The specific surface area and pore size distribution of the sample were determined according to the Brunauer Emmett Teller (BET) method and the Barret-Joyner-Halenda (BJH) method, respectively.
