Synthesis and enhanced gas-sensing properties of ultralong NiO nanowires assembled with NiO nanocrystals

NiO crystallites based nanowires with different aspect ratios have been synthesized by a hydrothermal reaction of NiCl2 with NaC2O4 and H2O in the presence of ethylene glycol (EG) and subsequent annealing at 400 °C in air. Control over the aspect ratios of NiC2O4·2H2O precursor nanowires in the range of 11–1050 was achieved by adjusting the hydrothermal reaction temperature and time. The formation of the NiC2O4·2H2O nanowires results from the selective adsorption of EG molecules on ( 1   0   1 ¯ ) , ( 1 ¯   0   1 ) , (0 1 0) and ( 0   1 ¯   0 ) prismatic faces of NiC2O4·2H2O with a monoclinic structure. The gas-sensing performance of the as-prepared NiO nanowires with different aspect ratios was investigated towards toluene, ethanol, acetone, triethylamine and methanol. It was found that the gas-sensing performance was improved with an increase on the aspect ratios of NiO nanowires.