Synthesis and Characterization of Chromium‐Doped Mesoporous Tungsten Oxide for Gas Sensing Applications

Abstract

SBA‐15 (2D hexagonal structure) and KIT‐6 (3D cubic structure) silica materials are used as templates for the synthesis of two different crystalline mesoporous WO3 replicas usable as NO2 gas sensors. High‐resolution transmission electron microscopy (HRTEM) studies reveal that single‐crystal hexagonal rings set up the atomic morphology of the WO3 KIT‐6 replica, whereas the SBA‐15 replica is composed of randomly oriented nanoparticles. A model capable of explaining the KIT‐6 replica mesostructure is described. A small amount of chromium is added to the WO3 matrix in order to enhance sensor response. It is demonstrated that chromium does not form clusters, but well‐distributed centers. Pure WO3 KIT‐6 replica displays a higher response rate as well as a lower response time to NO2 gas than the SBA‐15 replica. This behavior is explained by taking into account that the KIT‐6 replica has a higher surface area as demonstrated by Brunauer–Emmett–Teller analyses and its mesostructure is fully maintained after the screen‐printing step involved in sensors preparation. The presence of chromium in the material results in a shorter response time and improved sensor response to the lowest NO2 concentrations tested. Electrical differences related to mesostructure are reduced as a result of additive introduction.

Degradation of Methylene Blue Using Porous WO3, SiO2–WO3, and Their Au-Loaded Analogs: Adsorption and Photocatalytic Studies

“…On the other hand, upon etching, the pore diameter increased significantly due to increased porosity of the material after removal of SiO 2 . Importantly, the pure WO 3 sample had the same, if not slightly higher surface area than similar materials reported previously. , …”

“…Importantly, the pure WO 3 sample had the same, if not slightly higher surface area than similar materials reported previously. 50,51 Further changes in porosity were found for Au-loaded materials. While the surface area of Au−SiO 2 −WO 3 decreased compared to SiO 2 −WO 3 , the pore diameter increased and was larger than expected based on the characterization of the SiO 2 − WO 3 composite with no Au.…”

Synthesis of Tungsten Oxide Powders Via Thiourea‐Assisted Route: Tailoring from Hierarchical Microspheres to Mesoporously Structured Nanoparticles

“…14 On the other hand, mesoporous WO 3 replicas prepared by the mesoporous silica temple-assisted method possess higher surface areas of 48.6 m 2 /g. 6 The surface areas of our T-0 and T-122 samples are comparable with those of WO 3 synthesized without using hard templates. Moreover, the pore size distributions of the four samples, in the range of 2-100 nm, are illustrated in Fig.…”

Mesoporous three-dimensional network of crystalline WO3 nanowires for gas sensing application

“…The sensing performances of the 3D WO 3 nanowires network prepared in this work is compared favorably with that of solvothermally synthesized one-dimensional tungsten oxide nanowires [33]. Moreover, the sensor responses to NO 2 presented here are significantly superior to those of the mesoporous WO 3 particles at its optimal operating temperature of 230°C reported in the literature [15]. It is known that the gassensing mechanism of oxide materials belongs to the surface-controlled type and the gas response gets significantly influenced by the effective surface area, porosity and crystallinity and so on [27,34].…”

“…Noted that two sensor samples were fabricated under similar process conditions, and the sensing results for these two samples were found to be reproducible within an accuracy of ±5%. Comparing with the WO 3 replica templated by conventional 2D SBA-15 [15], 3D SBA-15 templated 3D WO 3 nanowires network described here exhibited much higher gas response at relatively lower optimal operating temperature. This can be attributed to the unique microstructure characteristics of stable mesopores and large surface area of the 3D nanowires network, resulted from the stable connections between the extra thin nanowires.…”