Highly monodispersed mesoporous, heterojunction ZnO@Au micro-spheres for trace-level detection of NO2 gas

- Mesoporous ZnO@Au heterojunction microspheres were developed using two-step facile chemical method that can be used as a high performance, low temperature NO2 gas sensor.
- Structural studies reveal the existence of defects with high degree of crystallinity and chemisorbed oxygen species.
- Mesoporous ZnO@Au heterojunction microspheres establish enhanced gas sensing performance at 250 °C compared to pristine ZnO microspheres (400 °C).
- Enhancement in sensor properties was observed due to the presence of Au nanoclusters on the surface of ZnO microspheres which resulted in the formation of Schottky contacts at the interfaces leading to sensitization effects.
- The mesoporous heterojunction material found to be selective towards NO2 gas and found to be highly stable in nature.

Highly monodispersed, mesoporous ZnO@Au heterojunction micro-spheres have been successfully synthesized using a two-stage facile chemical method and their surface bound NO2 sensing properties were explored. Room temperature Photoluminescence (RTPL) reveal the presence of high degree of oxygen defects and zinc interstitials for the pristine ZnO mesoporous-spheres and a drastic reduction in PL intensity of the ZnO@Au heterojunction mesoporous-spheres pointing towards the utilization of surface defects for the Au cluster growth, facilitating electron transfer process between ZnO and Au. NO2 gas sensor property analysis of the ZnO@Au mesoporous-spheres showed an extraordinary sensitivity and selectivity at a lower operating temperature of 250 °C than pristine ZnO mesoporous-spheres (450 °C). The enhanced sensing behavior of the ZnO@Au heterojunction mesoporous-spheres can be ascribed to the synergetic effect of Au nanoclusters at the heterojunctions which acts as spill-over zone for the physisorption mediated sensing process and the inherent high surface area and surface defects.

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