Synthesis of the porous NiO/SnO2 microspheres and microcubes and their enhanced formaldehyde gas sensing performance

Porous NiO/SnO2 microspheres and microcubes were obtained using a facile chemical solution route combined with a subsequent calcination process. The morphologies and crystal structures of the products were comprehensively characterized via X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric-differential thermal analysis, and Brunauer-Emmett-Teller N2 adsorption-desorption analyses. The process of inducing porosity began with the NiSn(OH)6 precursors formed by the co-precipitation of the metal ions from the aqueous solution. Thermal decomposition of the precursors led to an intimate mixture of cubic phase NiO and tetragonal phase SnO2 and formed the porous NiO/SnO2 microspheres and microcubes. The gas-sensing properties of the as-prepared porous NiO/SnO2 microspheres and microcubes for toxic volatile organic compounds (VOCs), such as formaldehyde, ethanol, benzene, methanol, acetone, and toluene, were investigated. Compared with other VOCs gases, the porous NiO/SnO2 microsphere and microcube sensors exhibited a high response to formaldehyde. As for the porous NiO/SnO2 microsphere sensor, the detection limit of formaldehyde was approximately 0.13 ppm (signal-to-noise ratio, S/N = 3). The relationship between the gas-sensing performance and the microstructure of the porous NiO/SnO2 micro/nanomaterials was also discussed.