Effect of inert ambient annealing on structural and defect characteristics of coaxial N-CNTs@ZnO nanotubes coated by atomic layer deposition

The structure and intrinsic defects of ZnO determine the photogeneration of electron-hole pairs. The control of these characteristics allows for improving the activity of photocatalytic nanostructures. The intrinsic defects of ZnO atomic layer deposited around carbon nanotubes, coaxial N-CNT@ZnO, and its evolution after annealing in a nitrogen atmosphere are studied. TEM showed that the coaxial N-CNT@ZnO structure is preserved up to 500 °C; some damage is seen at 600 and 700 °C. Raman and XPS reveal a low surface defect concentration for as-grown ZnO, increasing to a maximum for the 600 °C annealed sample. Cathodoluminescence shows a broad low-intensity green emission associated with oxygen vacancies of ZnO. The surface defects improved the photocatalytic degradation of amaranth dye, however, damage to the coaxial structure lowers the catalytic activity.