The sensing performances of gas sensors must be improved and diversified to enhance quality of life by ensuring health, safety, and convenience. Metal–organic frameworks (MOFs), which exhibit an extremely high surface area, abundant porosity, and unique surface chemistry, provide a promising framework for facilitating gas‐sensor innovations. Enhanced understanding of conduction mechanisms of MOFs has facilitated their use as gas‐sensing materials, and various types of MOFs have been developed by examining the compositional and morphological dependences and implementing catalyst incorporation and light activation. Owing to their inherent separation and absorption properties and catalytic activity, MOFs are applied as molecular sieves, absorptive filtering layers, and heterogeneous catalysts. In addition, oxide‐ or carbon‐based sensing materials with complex structures or catalytic composites can be derived by the appropriate post‐treatment of MOFs. This review discusses the effective techniques to design optimal MOFs, in terms of computational screening and synthesis methods. Moreover, the mechanisms through which the distinctive functionalities of MOFs as sensing materials, heterostructures, and derivatives can be incorporated in gas‐sensor applications are presented.
The H2S sensing characteristics of SnO2 thin films loaded with CuO were found to be much improved by reducing the film thickness. A 40-nm-thick film showed sensitivity as high as 20000 and 2000 to 1.5 and 0.3 ppm H
2
S in air, respectively, at 200° C, while the rate of response to 0.3 ppm H
2
S was rather slow.
The oxygen partial pressure dependence of current in CuOIZnO heterocontact has been investigated to confirm its humidity sensing mechanism. A CuO/ZnO heterocontact was fabricated by physically pressing the sintered disks of CuO and ZnO, and its current was measured at various oxygen partial pressures under wet and dry conditions at room temperature.The current of the heterocontact was strongly dependent on oxygen partial pressure only at forward bias and wet atmosphere. Such a phenomenon originates from the humidity sensing mechanism, i.e., electrolysis of water physisorbed at the vicinity of the heterocontact. The current measurement under air with ammonia water vapor also provided one more evidence for the electrolysis function of the heterocontact. gen partial pressure up to about 0.01 atm and then decreased smoothly. The maximum current change from the N2 to 02 atmosphere was large by about a factor of 100.
Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (particle size 3 nm) by a spin‐coating method and subjected to calcination at different temperatures up to 800°C for 30 min. The grain size of SnO2 was found to be far smaller than those obtained from the SnO2 sol‐derived powder under the same calcination conditions. The suppression of grain growth of SnO2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO2 grain size remained as small as 6 nm after calcination at 800°C. It is suggested that the SnO2 grains in the ultrathin film deposited on the substrate are restrained from moving and coalescing with each other, resulting in the suppression of grain growth.
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