In this work, SnO₂ hollow microspheres functionalized with different incorporated amounts of Pt@Co₃O₄ complex catalyst were innovatively designed by using an MOF template. The results show that sensor based on the optimal incorporated amount of Pt@Co₃O₄ not only greatly enhances the response value of SnO₂ to formaldehyde (R_air/R_formaldehyde = 4240 toward 100 ppm) but also decreases the low detection limit (50 ppb), which is quite outstanding compared with other SnO₂-based formaldehyde sensors. Further analysis proves that the content of oxygen vacancy and chemisorbed oxygen and the catalytic effect of ultra-small Pt play the key roles in improving the formaldehyde sensing performance. Meanwhile, this present work demonstrates that oxide semiconductors functionalized with the derivatives of MOF templated catalysts may lead to the discovery of new material systems with outstanding sensing performance.

The acetone-sensing performance of BiFeO₃ is related to structural phase transformation, morphology and band gap energy which can be modulated by rare-earth ions doping. In this work, Bi_1−xEr_xFeO₃ nanoparticles with different amounts of Er doping were synthesized via the sol-gel method. The mechanism of Er doping on acetone-sensing performance of Bi_1−xEr_xFeO₃ (x = 0, 0.05, 0.1 and 0.2) sensors was the focus of the research. The optimal working temperature of Bi_0.9Er_0.1FeO₃ (300 °C) was decreased by 60 °C compared to BiFeO₃ (360 °C). The Bi_0.9Er_0.1FeO₃ sample demonstrated the optimal response to 100 ppm acetone (43.2), which was 4.8 times that of pure BFO at 300 °C. The primary reason, which enhances the acetone-sensing performance, could be the phase transformation induced by Er doping. The lattice distortions induced by phase transformation are favorable to increasing the carrier concentration and mobility, which will bring more changes to the hole-accumulation layer. Thus, the acetone-sensing performance of Bi_0.9Er_0.1FeO₃ was improved.

Carbon monoxide (CO) is one of the most toxic gases to human life. Therefore, the effective monitoring of it down to ppb level is of great significance. Herein, a series of In₂O₃ nanofibers modified with Au or Pd species or simultaneous Au and Pd species have been prepared by electrospinning combined with a calcination process. The as-obtained samples are applied for the detection of CO. Gas-sensing investigations indicate that 2 at% Au and 2 at% Pd-co-modified In₂O₃ nanofibers exhibit the highest response (21.7) to 100 ppm CO at 180 °C, and the response value is ~8.5 times higher than that of pure In₂O₃ nanofibers. More importantly, the detection limit to CO is about 200 ppb with a response value of 1.23, and is obviously lower than that (6 ppm) of pure In₂O₃ nanofibers. In addition, the sensor also shows good stability within 19 days. These demonstrate that co-modifying In₂O₃ nanofibers with suitable amounts of Pd and Au species might be a meaningful strategy for the development of high-performance carbon monoxide gas sensors.

We demonstrate the highly sensitive and fast response/recovery gas sensors for detecting isopropanol (IPA), in which the Au-nanoparticles-modified ZnO (Au@ZnO) nanofilms act as the active layers. The data confirm that both the response and the response/recovery speed for the detection of IPA are significantly improved by adding Au nanoparticles on the surface of ZnO nanofilms. The gas sensor with an Optimum Au@ZnO nanofilm exhibits the highest responses of 160 and 7 to the 100 and 1 ppm IPA at 300 °C, which indicates high sensitivity and a very low detecting limit. The sensor also exhibits a very short response/recovery time of 4/15 s on the optimized Au@ZnO nanofilm, which is much shorter than that of the sensor with a pure ZnO nanofilm. The mechanisms of the performance improvement in the sensors are discussed in detail. Both the electronic sensitization and the chemical sensitization of the ZnO nanofilms are improved by the modified Au nanoparticles, which not only regulate the thickness of the depletion layer but also increase the amount of adsorbed oxygen species on the surfaces. This work proposes a strategy to develop a highly sensitive gas sensor for real-time monitoring of IPA.