In this work, three-dimensional (3D) hierarchical In2O3@SnO2 core–shell nanofiber (In2O3@SnO2) was designed and successfully prepared via a facile electrospinning and further hydrothermal methods. Vertically aligned SnO2 nanosheets uniformly grown on the outside surface of In2O3 nanofibers were clearly observed by field emission scanning electron microscopy. Besides, hierarchical core–shell nanostructure of In2O3@SnO2 was characterized by elemental maps using scanning transmission electron microscopy. The formaldehyde (HCHO) sensing performances of pure In2O3 nanofibers, SnO2 nanosheets, and In2O3@SnO2 core–shell nanocomposite were compared, and the In2O3@SnO2 nanocomposite possessed highest response value, fast response/recovery speed, best selectivity, and lowest HCHO detection limit. Specifically, the response value (R a/R g) of the In2O3@SnO2 nanocomposite reached 180.1 toward 100 ppm of HCHO gas, which was near 9 and 6 times higher than that of the pure In2O3 nanofibers (R a/R g = 19.7) and pure SnO2 nanosheets (R a/R g = 33.2), respectively. In addition, the gas sensor showed instantaneous response/recovery time (3/3.6 s) toward 100 ppm of HCHO at the optimal operation temperature of 120 °C. More importantly, the detection limit toward HCHO gas was as low as 10 ppb (R a/R g = 1.9), which could be used for trace HCHO gas detection. The excellent sensing properties of the In2O3@SnO2 were attributed to the synergistic effect of large specific surface areas of SnO2 nanosheet arrays, abundant adsorbed oxygen species on the surface, unique electron transformation between core–shell heterogeneous materials, and long electronic transmission channel of SnO2 transition layer. This work provides an efficient route for the preparation of novel hierarchical sensitive materials.
In this article, we demonstrated an extremely high-sensitivity formaldehyde (HCHO) gas sensor, where the graphene oxide (GO) in situ modified two-dimensional (2D) SnO2 nanosheets with in-plane mesopores were utilized as the sensing materials. The sensor response (R a/R g) was larger than 2000 toward 100 ppm HCHO at 60 °C. In addition, the selectivity for detecting HCHO was excellent against other interferences including ethanol, acetone, methanol, toluene, ammonia, water, etc. The outstanding sensing performance of 2D mesoporous GO/SnO2 nanosheets was attributed to the synergism of the sensitizer effect of GO, large surface areas of 2D nanostructure, suitable particle size, and abundant in-plane mesopores. The high sensitivity, high selectivity, and low working temperature of the sensor reported here endowed it a great potential in selective detection of HCHO. Meanwhile, the design and synthesis of GO/SnO2 nanocomposites will provide new paradigms in the future development of HCHO-sensitive materials.
In this work, we reported a formaldehyde (HCHO) gas sensor with highly sensitive and selective gas-sensing performance at low operating temperature based on graphene oxide (GO)@SnO 2 nanofiber/nanosheets (NF/NSs) nanocomposites. Hierarchical SnO 2 NF/NSs coated with GO nanosheets showed enhanced sensing performance for HCHO gas, especially at low operating temperature. A series of characterization methods, including X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) were used to characterize their microstructures, morphologies, compositions, surface areas and so on. The sensing performance of GO@SnO 2 NF/NSs nanocomposites was optimized by adjusting the loading amount of GO ranging from 0.25% to 1.25%. The results showed the optimum loading amount of 1% GO in GO@SnO 2 NF/NSs nanocomposites not only exhibited the highest sensitivity value (R a /R g = 280 to 100 ppm HCHO gas) but also lowered the optimum operation temperature from 120 • C to 60 • C. The response value was about 4.5 times higher than that of pure hierarchical SnO 2 NF/NSs (R a /R g = 64 to 100 ppm). GO@SnO 2 NF/NSs nanocomposites showed lower detection limit down to 0.25 ppm HCHO and excellent selectivity against interfering gases (ethanol (C 2 H 5 OH), acetone (CH 3 COCH 3 ), methanol (CH 3 OH), ammonia (NH 3 ), methylbenzene (C 7 H 8 ), benzene (C 6 H 6 ) and water (H 2 O)). The enhanced sensing performance for HCHO was mainly ascribed to the high specific surface area, suitable electron transfer channels and the synergistic effect of the SnO 2 NF/NSs and GO nanosheets network.Molecules 2020, 25, 35 2 of 15 sensitivity, poor selectivity and/or relatively high optimum operation temperature. Hence, designing and developing gas sensors with high sensibility, excellent selectivity and lower optimum operation temperature is urgent and important.Graphene is a typical two-dimensional (2D) sheet of sp 2 bonded carbon with excellent electronic applications. Due to its unique physical and chemical properties, many efforts have been carried out on the application of graphene as sensing elements [12]. These advantages, including its high conductivity, large surface area and low electrical noise, make it a promising platform for preparing new sensors [13][14][15]. In order to prepare a new gas sensor with high sensing performance, low operation temperature and excellent selectivity, the combination of graphene and metal oxide semiconductors is a new strategy to enhance sensing performance compared to pure sensing materials [16]. Gaikwad et al. have reported a NH 3 gas sensor based on Polyaniline/Graphene Oxide (PANI/GO) by nanoemulsion method [17]. Sun et al. have synthesized rGO/ZnSnO 3 composites as a sensing material for detecting HCHO gas by a facile solution-based self-assembly synthesis method [18]. Rong et al. have prepared microstructures of SnO 2 @rGO nanocomposites for HCHO detection by facile thermal treatment ...
Future renewable energy supply and a cleaner Earth greatly depend on various crucial catalytic reactions for the society. Atomically dispersed metal site electrocatalysts (ADMSEs) have attracted tremendous research interest and are considered as the next-generation promising oxygen reduction reaction (ORR) electrocatalysts due to the maximum atom utilization efficiency, tailorable catalytic sites, and tunable electronic structures. Despite great efforts have been devoted to the development of ADMSEs, the systematic summary for design principles of high-efficiency ADMSEs is not sufficiently highlighted for ORR. In this review, the authors first summarize the fundamental ORR mechanisms for ADMSEs, and further discuss the intrinsic catalytic mechanism from the perspective of theoretical calculation. Then, the advanced characterization techniques to identify the active sites and effective synthesis methods to prepare catalysts for ADMSEs are also showcased. Subsequently, a special emphasis is placed on effective strategies for the rational design of the advanced ADMSEs. Finally, the present challenges to be addressed in practical application and future research directions are also proposed to overcome the relevant obstacles for developing high-efficiency ORR electrocatalysts. This review aims to provide a deeper understanding for catalytic mechanisms and valuable design principles to obtain the advanced ADMSEs for sustainable energy conversion and storage techniques.
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