Heterostructural coaxial nanotubes of CNT@Fe2O3 via atomic layer deposition: effects of surface functionalization and nitrogen-doping

This study attempted to synthesize onedimensional (1D) coaxial nanotubes of Fe2O3 based on carbon nanotubes (CNT@Fe2O3) via atomic layer deposition (ALD) using ferrocene and oxygen as precursors. Results disclosed that undoped CNTs were suitable for the ALD of Fe2O3 (ALD-Fe2O3) only if they were chemically functionalized, due to their inert surface nature. It was further demonstrated that the effects of both covalent and non-covalent methodologies were limited in functionalizing undoped CNTs, leading to random and non-uniform deposition of Fe2O3. In sharp contrast, it was found that, as an alternative, nitrogen-doped CNTs (N-CNTs) contributed uniform and tunable ALD-Fe2O3, due to their active surface nature induced by incorporated N atoms. Consequently, various 1D heterostructural coaxial nanotubes were obtained with well-controlled growth of Fe2O3 on N-CNTs. For a better understanding, the underlying mechanisms were explored based on different N-doping configurations. In addition, high-resolution transmission electron microscopy and X-ray diffraction jointly demonstrated that as-deposited Fe2O3 is single-phase crystalline a-Fe2O3 (hematite). The as-synthesized heterostructural coaxial nanotubes of CNT@Fe2O3 may find great potential applications in photocatalysis, gas-sensing, and magnetic fields.