Synergetically Selective Toluene Sensing in Hematite-Decorated Nickel Oxide Nanocorals

The decoration of p-type nickel oxide (NiO) with n-type hematite (α-Fe2O3) to achieve vertically ordered 1D nanostructures is an attractive strategy to enhance gas sensing properties. Herein, the authors report a facile method for α-Fe2O3 decoration of the whole surface of vertical NiO nanorods. An NiO/Fe heterostructure is deposited in multiple steps using a glancing angle deposition method, which is followed by the oxidation of Fe into α-Fe2O3. Thermally agglomerated α-Fe2O3 nanoparticles are uniformly distributed on the whole surface of the NiO nanorods. Due to the α-Fe2O3 decoration, the NiO nanorods exhibit a coral-like rough surface and, more interestingly, their preferential crystallographic orientation changed from (111) to (200). Compared to bare NiO nanorods, the α-Fe2O3-decorated NiO nanocorals exhibit a 45.4 times higher response to 50 ppm toluene (C7H8) at 350 °C. Their theoretical detection limit for C7H8 is calculated to be ≈22 ppb. The observed unprecedented synergetic effects of α-Fe2O3-decorated NiO nanocorals for the extremely selective C7H8 sensing, as well as their facile synthetic route, establish a new perspective on heterostructured metal oxide 1D nanostructures for selective gas sensing.