Synthesis of uniform porous NiO nanotetrahedra and their excellent gas-sensing performance toward formaldehyde

Porous tetrahedron-like NiO nanostructures composed of primary nanoparticles have been successfully synthesized via a facile two-step method for the first time. The tetrahedron-like Ni(HCO3)2 precursor was firstly prepared by a solvothermal reaction with the assistance of PVP using a mixture of ethylene glycol and distilled water as the solvent. The porous NiO products were then obtained by annealing the precursor at different temperatures. Some characterization including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) was performed to obtain structural and morphological information about the as-prepared NiO products. The NiO products obtained by annealing at 400 °C and 500 °C were porous tetrahedron-like particles composed of primary nanoparticles with size increasing with annealing temperature, while the NiO products obtained by annealing at 600 °C were collapsed into irregular nanoparticles. The gas-sensing properties of the three NiO samples were evaluated and the sensors exhibit high sensitivity, good selectivity and stability towards HCHO at 250 °C. The sensitivity of the three samples follows the sample sequence S500 > S400 > S600 due to the combined effect of specific surface area, pore size and defects in the nanocrystals.