Effect of Humidity on Light-Activated NO and NO2 Gas Sensing by Hybrid Materials

Abstract

Air humidity is one of the main factors affecting the characteristics of semiconductor gas sensors, especially at low measurement temperatures. In this work we analyzed the influence of relative humidity on sensor properties of the hybrid materials based on the nanocrystalline SnO2 and In2O3 and Ru (II) heterocyclic complex and verified the possibility of using such materials for NO (0.25–4.0 ppm) and NO2 (0.05–1.0 ppm) detection in high humidity conditions (relative humidity (RH) = 20%, 40%, 65%, 90%) at room temperature during periodic blue (λmax = 470 nm) illumination. To reveal the reasons for the different influence of humidity on the sensors’ sensitivity when detecting NO and NO2, electron paramagnetic resonance (EPR) spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations were undertaken. It was established that the substitution of adsorbed oxygen by water molecules causes the decrease in sensor response to NO in humid air. The influence of humidity on the interaction of sensitive materials with NO2 is determined by the following factors: the increase in charge carrier’s concentration, the decrease in the number of active sites capable of interacting with gases, and possible substitution of chemisorbed oxygen with NO2− groups.

2D Amorphous/Crystalline a-In2O3/In2Se3 Nanosheet Heterostructures with Improved Capability for H2 and NO2 Sensing

“…In the first mechanism () proposed by Heinrich and Cox, water vapor displaces adsorbed oxygen, forming hydroxyls (OH ′ ) and releasing a vacancy (V O •• ) and e ′ . This mechanism seems to be supported by a strong reduction of the O 2 ′ /OH • radicals’ ratio in humid conditions, as recorded by EPR measurements for crystalline SnO 2 . In the second mechanism, proposed by Heiland and Kohl (6,7), either rooted (OH) O • or two terminal (OH ′ ) groups and an oxygen vacancy are formed.…”

“…This mechanism seems to be supported by a strong reduction of the O 2 ′/OH • radicals' ratio in humid conditions, as recorded by EPR measurements for crystalline SnO 2 . 62 In the second mechanism, proposed by Heiland and Kohl 63 (6,7), either rooted (OH) O…”

The Effect of Rare Earths on the Response of Photo UV-Activate ZnO Gas Sensors

“…Furthermore, electron paramagnetic resonance (EPR) spectroscopy measurements carried out by Nasriddinov et al on the surface of SNO 2 and SNO 2 /Ru confirmed that O 2 − species can be easily replaced by OH* radicals in a humid atmosphere [ 81 ].…”

Light-activated gas sensors

“…(a) Responses of SnO 2 decorated with different noble metals under UV-illumination [29] ; (b-d) ZnO with different nanostructures and (e) their gas-sensing responses [27] ; (f) TEM image showing Aunanoparticle decorated ZnO and (g) gas sensing properties of pure ZnO (red line) and Aunanoparticle decorated ZnO (black line) [28] ; (h) Response curve of hollow TiO 2 microspheres [59] ; (i) Sensing behaviors of NiO under illumination of lights with different wavelengths at room temperature [30] 表 2 带隙宽度>3.1 eV 的光激发气敏材料 NiO 372 ppb NO 2 可见光 -溶剂热 88.94% [30] ZnO 100 ppm 甲醛 365 nm -溶剂热 12.61 [27] ZnO 50 ppm NO 2 365 nm -溶剂热 15 [35] ZnO 纳米线 100 ppm 甲醛 365 nm -溶剂热 12.61 [36] ZnO 纳米棒 30 ppb 臭氧 370 nm -溶剂热 44% [37] ZnO/Au NP 6 ppm NO x 白光 100 mW/cm 2 溶剂热 78% [38] Au-ZnO 500 ppm 乙醇 白光 6 mW/cm 2 热蒸发 62 [28] ZnO/纳米 Ag 颗粒 5 ppm NO 2 470 nm 75 mW/cm 2 溶剂热 1.545 [39] TiO 2 纳米球 5 ppm 甲醛 365 nm -溶剂热 - [59] NiO@TiO 2 50 ppm 乙醚 365 nm 36 W/m 2 球磨 31.02 [31] C 量子点/NiO 30 ppm CH 4 UV -溶剂热 - 能 [40] . Ru 修饰 In 2 O 3 对(c)NO 和(d)NO 2 的气敏响应性能 [41] . Pd 修饰 WO 3 的(e)形貌及(f)对 H 2 的气敏性能 [42] .…”

“…Response of In 2 O 3 , In 2 O 3 +RuITP samples to (c) NO and (d) NO 2 in dry and humid air at room temperature [41] . (e) SEM image and (f) gas sensing properties of PdO-decorated WO 3 to H 2 [42] ;…”