In this work, an ultra-low-cost and ecofriendly solvothermal strategy was employed to prepare gas-sensing materials for heterostructured p-Sb2O3/n-SnO2 nanospheres. The morphology, microstructure and other characteristics of the prepared products were comprehensively studied by several analyzers. The results show that the present SnO2 nanospheres modified with Sb2O3, exhibit exceptional mesoporous structures and high specific surface areas, as well as prominent thermal stability (only 0.02 % mass loss). For the first time, the cost-effective gas sensor based on Sb2O3/SnO2 nanospheres was fabricated, which maintained excellent gas-sensing behavior of 697 % towards 100 ppm H2 gas at operating temperature of 280 ℃, with a fast response/recovery time of 29.8/13.4 s, and the limit of detection was down to 100 ppb (S = 7.1 %). In addition, the gas sensor had quite consistency, reproducibility, long-term stability (over 40 days), and unique selectivity towards H2 gas. Investigations into a plausible gas-sensing mechanism imply that the p-n heterojunction, catalytic function of Sb2O3, mesoporous structures and high specific surface area synergistically induced the superior gas-sensing response. Undoubtedly, the present work may provide an outstanding strategy to improve H2 gas response in extremely environmental applications.

Hydrogen gas sensor based on SnO2 nanospheres modified with Sb2O3 prepared by one-step solvothermal route

We demonstrate the fabrication of free-standing inverse opals with gradient pores via a combination of electrophoresis and electroplating techniques. Our processing scheme starts with the preparation of multilayer colloidal crystals by conducting sequential electrophoresis with polystyrene (PS) microspheres in different sizes (300, 600, and 1000 nm). The critical factors affecting the stacking of individual colloidal crystals are discussed and relevant electrophoresis parameters are identified so the larger PS microspheres are assembled successively atop of smaller ones in an orderly manner. In total, we construct multilayer colloidal crystals with vertical stacking of microspheres in 300/600, 300/1000, and 300/600/1000 nm sequences. The inverse opals with gradient pores are produced by galvanostatic plating of Ni, followed by the selective removal of colloidal template. Images from scanning electron microscopy exhibit ideal multilayer close-packed structures with well-defined boundaries among different layers. Results from porometer analysis reveal the size of bottlenecks consistent with those of interconnected pore channels from inverse opals of smallest PS microspheres. Mechanical properties determined by nanoindentation tests indicate significant improvements for multilayer inverse opals as compared to those of conventional single-layer inverse opals.

https://www.mdpi.com/2079-4991/10/10/1923/pdf

Formation of Free-Standing Inverse Opals with Gradient Pores.

In this work, novel mesoporous heterostructures composed of CdS, PbS and SnO2 (CdS/PbS/SnO2) were synthesized via a green and facile treatment. Interestingly, when the CdS/PbS/SnO2 composites were assembled into sensing layer for the fabrication of H2 gas sensor for the first time, the sensor based on CdS/PbS/SnO2 exhibited more prominent gas-sensing properties than those of the CdS/SnO2 and PbS/SnO2 sensors. The CdS/PbS/SnO2 sensor showed a fast response/recovery time of 10.6/36.9 s towards 100 ppm H2 gas at 200℃, with an ultralow limit of detection of 50 ppb (17.3 %), and the sensor had a largely enhanced response of 1125.2 %, which was approximately 16.8 and 7.4 times higher than those of the CdS/SnO2 (66.8 %) and PbS/SnO2 (151.4 %) sensors. In addition, the CdS/PbS/SnO2 sensor had an outstanding selectivity towards H2 gas against other gases, reliable reversibility and long-term stability for 40 days. Such enhanced properties was mainly attributed to the large surface-to-volume ratio, which can provide abundant active sites to gas adsorbtion and diffusion in surface redox reaction. Moreover, more numerous heterojunctions of the CdS/PbS/SnO2 composites may serve as highly conductive channels to accelerate carrier transfer, thus further leading to an improved performance of the sensors. Credibly, our present work will foresee a great potential application for ppb-level H2 gas monitoring in an extreme environment.

Facile synthesis of mesoporous CdS/PbS/SnO2 composites for high-selectivity H2 gas sensor

Fabrication of a humidity-resistant formaldehyde gas sensor through layering a molecular sieve on 3D ordered macroporous SnO2 decorated with Au nanoparticles

Effect of nanoparticle-embedded 1 dimensional-nanostructures to fabricate highly sensitive and selective hydrogen gas sensors

Three-dimensionally ordered macro/mesoporous materials are known to possess a large accessible surface area with impressive permeability. In this work, we combine electrophoresis and electrodeposition to fabricate a hierarchical bi-layered inverse opaline film in which a ZnO sensing layer is stacked with an Au electrode for impressive H2 sensing activities. To enhance its responsiveness, both morphological and crystallographic properties of ZnO inverse opals are optimized using KCl as the porogen. The resulting ZnO inverse opals demonstrate a specific surface area that is three times larger over comparable ZnO inverse opals by the formation of nanoporous skeletons. In addition, the deposition bath was deliberately designed so the predominant crystallographic plane of ZnO is shifted from (10 1 - 0) to (0001) as the latter exhibits superior activity toward reducing gases. Through X-ray photoelectron spectroscopy, we show a significant increase of chemisorbed oxygen on the (0001) plane. Consequently, our hierarchical bi-layered inverse opals reveal a 500 % improvement in the sensitivity toward 15 ppm H2 under 200 °C. In short, this is the first demonstration of a vertically-arranged inverse opaline film incorporating both metal and oxide layers to function as an integrated three-dimensional gas sensor with low detection limit.

Yu-Szu Chou

Papers

A vertically integrated ZnO-based hydrogen sensor with hierarchical bi-layered inverse opals