Crystal lattice engineering in a screw-dislocated ZnO nanocone photocatalyst by carbon doping

Abstract

Screw-dislocated ZnO nanocones exposing a greater percentage of polar {0001} facets are developed by a tailor-made CTAB-assisted hydrothermal process. A possible formation mechanism of ZnO nanocones with step edges exposing high-energy {0001} facets is explained by screw dislocated crystal growth theory. Further, ZnO nanostructures are defect-engineered by the introduction of carbon atoms into their crystal lattice. A facile synthesis route for carbon-doped zinc oxide (C:ZnO) nanostructures is proposed, in which ZnO nanostructures synthesized by a hydrothermal method are subjected to an electrospinning process, followed by calcination, to incorporate carbon as the dopant. Polyvinyl alcohol (PVA) acts as both the dopant-precursor and the spinning agent for the construction of C:ZnO nanostructures. XPS analysis confirms the incorporation of carbon atoms into the oxygen vacancies of the ZnO lattice in C:ZnO nanostructures. The increase in the lattice parameters of ZnO resulting from carbon doping is evidenced by XRD analysis. UV-visible diffuse reflectance spectroscopy (DRS) results revealed improved photogenerated charge separation in C:ZnO by the reduction of bandgap energy as a result of valence band extension to a higher energy region upon carbon-doping. C:ZnO nanostructures showed a markedly higher photocatalytic activity (97%, kinetic rate constant k = 39.57 × 10⁻³ min⁻¹) compared to undoped ZnO nanostructures (51%, k = 13.64 × 10⁻³ min⁻¹) within 90 min visible-light irradiation of methylene blue dye solution. The mechanism of photogenerated charge carrier separation and visible-light photocatalytic pathways in C:ZnO nanostructures was further elucidated. Altogether, this new-fangled simple synthesis approach for crystal lattice engineering in ZnO for enhancing its visible-light photoactivity brings both the material and the methodology well-nigh suitable for various environmental applications.