Low-temperature ozone treatment for carbon nanotube template removal: improving the template-based ALD method

This work addresses the production of standalone ceramic nanotubes by the template-based ALD method at low temperature. Nitrogen-doped multiwalled carbon nanotubes (CNTs) were coated with ZnO. Afterward, the template removal was evaluated by two different approaches: using oxidation in dry air or in an ozone-rich atmosphere. The samples treated by the two different methods were analyzed by XRD, TEM, SAED, and Raman spectroscopy. The dry air atmosphere requires high temperatures (similar to 700 degrees C) for a complete CNT removal; at that temperature, the ZnO tubular shape is completely collapsed due to recrystallization. Under ozone atmosphere, the template can be removed at temperatures as low as 85 degrees C; this temperature is lower than the ALD preparation temperature (120 degrees C). The ozone treatment maintains the tubular shape of the ZnO nanostructures. Photocatalytic activity of the ZnO samples was evaluated using the photo-oxidation of Amaranth as probe reaction, showing a higher activity the ZnO nanotubes obtained from the low-temperature ozone treatment than the high-temperature processed materials. The use of ozone for the template removal reinforces the template-based ALD method to produce inorganic nanotubes.