Surface interaction of WO3 nanocrystals with NH3. Role of the exposed crystal surfaces and porous structure in enhancing the electrical response

Abstract

We report on the surface interaction between NH 3 and WO 3 nanoparticles having different exposed surfaces or different porous structure, to identify the relative importance of exposed crystal surfaces, porous architecture, and specific surface area in the oxide sensing properties. WO 3 nanocrystals with tailored morphology and definite prominent surfaces were synthesized by hydrothermal reactions. In parallel, inverted opal macroporous WO 3 films have been prepared by a one-step sol-gel procedure, and WO 3 hierarchical layers have been obtained by an innovative one-step dual-templating strategy which leads to macropores and mesopores simultaneously. The performances of WO 3 samples in NH 3 sensing, indicate that high-energy surfaces result in a significant improvement of the electrical response.Enhanced porous structure and high surface area are not enough to produce high electrical response, while their synergistic combination with tailored crystal faceting appears effective. XPS survey performed on shape controlled WO 3 nanocrystals demonstrated that, upon interaction with NH 3 , oxidized nitrogen atoms represent the prevalent species on the surface of rectangular (WO 3 -RE) nanocrystals with highly exposed high-energy {020} and {002} facets. Conversely, in the case of rectangular platelets and square platelets (WO 3 -RS) with very low surface area of high-energy surfaces, N-H surface groups are predominant. These results suggest that {020} and {002} crystal surfaces provide privileged reactive sites for ammonia oxidation and therefore they play a key role in driving the sensing properties of the WO 3 layers.

Tungsten Oxide Nanoplates: Facile Synthesis, Controllable Oxygen Deficiency and Photocatalytic Activity

“…2b). The change of the morphology with annealing temperature, which is also previously reported in the literature [16,19], 2θ ≈ 23.14, 23.61 and 24.38˚, respectively, which have higher surface energy and are preferable for photocatalytic applications [9,18,20,21]. The change from orthorhombic structure to the monoclinic structure when annealing at high temperature (higher than 300˚C) was explained due to dehydration [22,23] which will be mentioned later.…”

Facile synthesis and gas sensing properties of In2O3–WO3 heterojunction nanofibers

“…Consequently, a simple method is needed to detect the concentration of acetone. In recent years, gas sensors based on metal oxide semiconductor nanomaterials, such as WO 3 [7][8][9], SnO 2 [10][11][12]40,41], ZnO [13,14], In 2 O 3 [15] and TiO 2 [16][17][18][19], have attracted much attention for the gas detection, due to its high response to the target gases and simplicity in preparation. WO 3 (Tungsten oxide) and In 2 O 3 (Indium oxide) are two kinds of great technologically important materials due to their excellent electronic, chemical and optical properties.…”

Hydrothermal preparation and supercapacitive performance of flower-like WO3·H2O/reduced graphene oxide composite

“…Tungsten trioxide (WO 3 ) and its hydrates (WO 3 ·xH 2 O, x = 0∼2), as one of the important transition metal oxides, are extensively investigated due to the promising properties and a wide spectrum of applications in gas sensors [11,12], photocatalysis [13,14], electrochromic devices [15,16], electronic devices [17], dye-sensitized solar cells [18,19], adsorbent [20] and lithium ion batteries [21,22]. The capacitive behaviors of the nanostructured tungsten oxides have been also investigated as supercapacitor electrodes [23][24][25][26][27][28][29].…”