Highly sensitive, atmospheric pressure operatable sensor based on Au nanoclusters decorated TiO₂@Au heterojunction nanorods for trace level NO₂ gas detection

A controlled synthetic strategy is established for the development of TiO₂@Au heterojunction nanorods using a facile wet-chemical method for the detection of NO₂ gas under atmospheric pressure conditions. Structural studies reveal the existence of metastable anatase phase along with thermodynamically stable rutile phase with high degree of crystallinity. The structural analysis divulges the uniform surface anchoring of Au nanoclusters onto mono-dispersed TiO₂ nanorods introducing interfacial metal–semiconductor heterojunctions. TiO₂@Au heterojunction nanorods exhibited excellent sensor performance towards trace level exposure of NO₂ gas. Owing to the interfacial electron transfer process at the heterojunction the optimum operating temperature of TiO₂@Au heterojunction nanorods determined to be 250 °C, which is much less as compared to pristine TiO₂ gas sensors (400 °C). Sensor response was found to be linear for the trace level concentration range of 0.5–5 ppm with lowest detection limit as 500 ppb. The TiO₂@Au heterojunction nanorods exhibited higher sensitivity at atmospheric pressure conditions compared to vacuum conditions because of the changes in surface O₂ adsorption properties of the heterojunction material at different oxygen partial pressure and existence of mixed phases in TiO₂ nanorods. The superior gas sensor performance of the material under atmospheric pressure conditions point towards their potential for real-time applications.