Preparation of highly crystalline NiO meshed nanowalls via ammonia volatilization liquid deposition for HS detection.

Novel NiO meshed nanowalls, with characteristics of open geometry, porosity, single crystal and highly crystalline framework, are grown in situ on different substrates (including AlO tube, glass slide, ITO, stainless steel mesh, nickel foam and carbon cloth) via a simple ammonia volatilization liquid deposition process at room temperature and a postcalcination treatment. The calcination temperature can strongly influence the pore size and crystallinity of the product, leading to different gas-sensing performances. The product that obtained at 700 °C (NiO-700) has the advantage in the combination of the largest pore size and high crystallinity, and shows the highest response to HS gas. In 0.01-100 ppm HS gas, the NiO-700 meshed nanowalls based sensor can give evident and reversible response signals at a low optimal operating temperature of 50 °C, the response towards 100 ppm HS can reach to 137.3, the detection limit is as low as 10 ppb. Furthermore, the sensor also exhibits excellent selectivity, repeatability, anti-humidity and long-term stability for HS detection. The results of gas chromatograph-mass spectrometry (GC-MS) and infrared gas analysis (IRGA) reveal that the HS gas can be oxidized to SO after interacting with NiO-700 meshed nanowalls material. Therefore, the possible HS sensing mechanism should be proposed as: HS gas molecules undergo a redox reaction with adsorbed oxygen anion on the surface of NiO-700 meshed nanowalls to form SO; meanwhile, the electrons restricted by adsorbed oxygen return to the bulk and recombine with the holes, resulting in a decrease in effective carrier concentration of holes and thus generating a change in resistance.