Hierarchical SnO/SnO2 nanocomposites: Formation of in situ p–n junctions and enhanced H2 sensing

Herein, we present a new approach to achieve well-defined SnO/SnO2 composites with in situ formation of p–n heterojunctions. The materials synthesized by a simple one-pot hydrothermal method were characterized in detail using powder X-ray diffraction (XRD), thermogravimetry (TGA), micro-Raman, X-ray photo electron spectroscopy (XPS), and ultra violet-diffused reflectance spectroscopy (UV-DRS). Analysis confirms the presence of mixed phases and the findings are consistent. The morphological evaluations were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The investigations reveal the self-assembly of smaller nanoparticles into hierarchical structures resembling nanorods which aggregate further to form loose cube-like morphology finally transforming into dense micro-prisms. Selected area electron diffraction (SAED) establishes the phases of these nano- and microstructures. Synthesized materials also show improved electrical properties owing to the presence of SnO/SnO2 multiple p–n heterojunctions in the bulk. The advantage is reflected in the results of gas sensing studies that indicate enhanced hydrogen gas sensing response. Significant improvement in sensor response, selectivity and sensitivity could be achieved further with incorporation of Pd. A plausible mechanism of gas sensing on the material surface based on the formation of heterojunctions is discussed.