NiO doped SnO2 p–n heterojunction microspheres: preparation, characterisation and CO sensing properties

Abstract

We successfully synthesised pure and NiO doped SnO2 p–n heterojunction microspheres with different doping levels via a facile and environment friendly hydrothermal route. The crystalline structures, surface morphologies, element components and valences of the as synthesised nanostructures were characterised by means of X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy respectively. SnO2 based planar chemical gas sensors were fabricated from the as prepared samples, and their sensing performances towards carbon monoxide (CO) were systematically investigated. Compared with pure SnO2 sensor, NiO doped SnO2 microsphere sensors exhibit obviously enhanced CO sensing properties, such as higher gas response, lower operating temperature etc. It might be attributed to the p–n heterojunctions formed between p-type NiO and n-type SnO2 interfaces, further increasing the amount of absorbed oxygen ions and decreasing the activation energy of catalytic oxidation. The 3 at-%NiO doped SnO2 sensor demonstrates the highest response, quick response and recovery speed, good reproducibility and prominent stability against CO gas at an operating temperature of 260°C among the four sensors.