A low temperature formaldehyde gas sensor based on hierarchical SnO/SnO2 nano-flowers assembled from ultrathin nanosheets: Synthesis, sensing performance and mechanism

[Display omitted] •Hierarchical SnO/SnO2 nano-flowers were successfully synthesized through a nanosheets self-assembly route under a mild hydrothermal environment.•The gas sensor constructed from SnO/SnO2 hierarchical nanostructure materials exhibited remarkably enhanced gas response toward formaldehyde at 120 °C with high gas selectivity and very low limit of detection.•A reasonable gas-sensing mechanism was proposed according to nanostructure characteristic, specific surface area, oxygen vacancy defect, p-n junction and so on. Here we report a hierarchical flower-like SnO/SnO2 gas sensing material for detecting formaldehyde vapor at a low temperature. It was rationally designed and successfully synthesized via a one-step hydrothermal route. The crystal phase, defects, element composition and morphology of the obtained samples were characterized in detail by XRD, FESEM, TEM, Raman, PL, and XPS. The characterized results reveal that hierarchical SnO/SnO2 nano-flowers are assembled from ultrathin nanosheets with about 9–11 nm in thickness. Gas sensing performance shows that the sensor based on SnO/SnO2 nano-flowers has crucial advantages for formaldehyde detection, such as low operating temperature (120 °C), excellent selectivity, short response time (7 s), high response value (80.9) and low detection limitation (8.15 ppb). The excellent gas responses of the sensor can be attributed to its unique hierarchical microstructure (for decrease of Rg and increase of Ra) and p-n junction between SnO and SnO2 (for increase of Ra). Finally, the sensing mechanism of the prepared was proposed in detail.