Highly Sensitive, Temperature-Independent Oxygen Gas Sensor Based on Anatase TiO2 Nanoparticle Grafted, 2D Mixed Valent VO x Nanoflakelets.

Herein, we report a facile approach for the synthesis of TiO2 nanoparticles tethered on 2D mixed valent vanadium oxide (VO x/TiO2) nanoflakelets using a thermal decomposition assisted hydrothermal method and investigation of its temperature-independent performance enhancement in oxygen-sensing properties. The material was structurally characterized using XRD, TEM, Raman, DSC, and XPS analysis. The presence of mixed valent states, such as V2O5 and VO2 in VO x, and the metastable properties of VO2 have been found to play crucial roles in the temperature-independent electrical conductivity of VO x/TiO2 nanoflakelets. Though pristine VO x exhibited characteristic semiconductor-to-metal transition of monoclinic VO2, pure VO x nanoflakelets exhibited poor sensitivity toward sensing oxygen. VO x/TiO2 nanoflakelets showed a very low temperature coefficient of resistance above 150 °C with improved sensitivity (35 times higher than VO x for 100 ppm) toward oxygen gas. VO x/TiO2 nanoflakelets exhibited much higher response, faster adsorption and desorption toward oxygen as compared to pristine VO x beyond 100 °C, which endowed the sensor with excellent temperature-independent sensor properties within 150-500 °C. The faster adsorption and desorption after 100 °C led to shorter response time (3-5 s) and recovery time (7-9 s). The results suggest that 2D VO x/TiO2 can be a promising candidate for temperature-independent oxygen sensor applications.