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Surface engineering techniques can be used to develop high-performance gas sensing materials and advance the development of sensors. In this study, we improved the gas sensing performance of two-dimensional (2D) WO3 nanoplates by combining surface Zn modification and the in situ formation of ZnWO4/WO3 heterojunctions. Introducing Zn atoms by surface modification can reconstruct the atomic surface of 2D WO3 nanoplates, creating additional active sites. This allowed for the preparation of various types of ZnWO4/WO3 heterojunctions on the surface of the WO3 nanoplates, which improved the selectivity and sensitivity to the target gas triethylamine. The sensor exhibited good gas sensing performance for triethylamine even at low operating temperatures and strongly resisted humidity changes. The ZnWO4/WO3 material we prepared demonstrated a nearly threefold improvement in the triethylamine (TEA) response, with a gas sensing responsivity of 40.75 for 10 ppm of TEA at 250 °C. The sensor based on ZnWO4/WO3 has a limit of detection (LOD) for TEA of 200 ppb in practical measurements (its theoretical LOD is even as low as 31 ppb). The method of growing ZnWO4 on the surface of WO3 nanoplates using surface modification techniques to form surface heterojunctions differs from ordinary composites. The results suggest that the in situ construction of surface heterojunctions using surface engineering strategies, such as in situ modifying, is a practical approach to enhance the gas sensing properties and resistance to the humidity changes of metal oxide materials. [ABSTRACT FROM AUTHOR]

Bimetallic oxides are becoming a widely attended gas-sensing material in recent years for their good thermal and chemical stability, especially as their highly flexible composition allows for tunable properties. In this work, a hierarchical nanostructured rocksalt solid solution Ni0.7Zn0.3O with hollow porous microspheres has been first prepared by deriving the microspheres from Zn/Ni-based metal–organic frameworks. These nanostructured Ni0.7Zn0.3O spheres were constructed with a nanosized shell (about 100 nm), which consisted of 15–30 nm nanoparticles. This nanostructured morphology provided a high special surface area that is an advantage for enhancing gas-sensing properties. The gas sensor based on these nanostructured Ni0.7Zn0.3O hollow spheres has presented a high sensitivity and selectivity toward aniline at a low concentration of about 500 ppb (S = 63%) at 300 °C, and the response/recovery speed is very fast (less than 15 s). This hierarchical nanostructured rocksalt NixZn(1–x)O solid solution proposes an excellent selective and sensitive gas-sensing material for detecting aniline. Moreover, this method for preparing rocksalt NixZn(1–x)O solid solution can be widely used to design and synthesize bimetallic oxides with hollow and hierarchical nanostructures. [ABSTRACT FROM AUTHOR]

• Stannate spinel oxide Co 2 SnO 4 was firstly adopted for gas sensing showed excellent properties. • The TEA sensing properties was highly improved by the stannate spinel structure and Co2+ ion. • The modification of the morphology of Co 2 SnO 4 can result in the improvement of selectivity. The spinel oxides are identified as the highly promising materials for gas sensing application due to their good thermal stability, low cost and nice sensitivity. The spinel oxide nanocomposites of Co 3 O 4 /SnO 2 and Co 2 SnO 4 /SnO 2 were prepared by the co-precipitation method, and their gas sensing characteristics were investigated in this work. Compared with the Co 3 O 4 /SnO 2 nanocomposites, the sensor based on Co 2 SnO 4 /SnO 2 nanocomposites exhibited significantly enhanced response and selectivity performance toward triethylamine (TEA). The response of the Co 2 SnO 4 /SnO 2 composites is about 45.9 to 100 ppm TEA at 270 °C, which was almost 4 times higher than that of Co 3 O 4 /SnO 2 nanocomposites. The excellent performance of the Co 2 SnO 4 /SnO 2 composites can be attributed to the catalytic ability of divalent Co2+ cation located in octahedral sites in spinel structure, which results in enhanced gas absorption and catalytic performance. [ABSTRACT FROM AUTHOR]

Hierarchical flower-like WO 3 with exposed active {-112} facets synthesized using a microwave-assisted gas-liquid interfacial solvothermal method shows a superior triethylamine gas sensing performance at room temperature. • The flower-like WO 3 with exposed active {-112} facets can be controllably synthesized using a microwave-assisted method. • {-112} faceted WO 3 shows the best gas sensing response to trimethylamine at room temperature with excellent selectivity. • Our results evidence the strategy to improve the gas sensing performance of metal oxides through surface engineering. • The as-prepared gas sensor qualifies the great potential for trimethylamine practical detection and monitoring. Effective detection of triethylamine (TEA) is important for the human health and environment, while challenging. In this study, a novel hierarchical flower-like WO 3 nanomaterial was synthesized using a microwave-assisted gas-liquid interface method. The morphology and exposed facets of WO 3 nanomaterials can be manipulated through the control of the volume ratio between the water and ethylene glycol (EG) during the synthesis. Our results demonstrate that the samples prepared with water/EG ratio of 8:32 are mainly exposed {-112} facets, which have the best gas sensing response of 180.7 to 100 ppm TEA at room temperature (RT). Its superior gas sensing performance and stability are also evidenced by the short recovery speed of 72 s to 100 ppm TEA at RT. More importantly, our experiments revealed an excellent selectivity in terms to other volatile organic compounds and further confirmed by the first-principles theoretical results. The outcomes of this study suggest that the surface engineering technique is a promising approach to improve the gas sensing performance of metal oxides gas sensor and show great potential for TEA practical detection and monitoring. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The cactus-like WO 3 /Co 3 O 4 p-n junction nanocomposite was synthesized by in-situ growth on the surface of device substrate. • The number of WO 3 /Co 3 O 4 p-n junctions can be controlled by the reaction time for improving its gas property. • WO 3 /Co 3 O 4 gas sensor can detect 0.1 ppm triethylamine and show good gas sensing performance. Abstract Metal oxide heterostructures are significant materials for developing and improving various toxic gas detection sensors. However, the gas sensing performance, such as response, selectivity, stability and response/recovery time of the sensors, still need to be optimized for practical applications. Low dimensional heterostructures will improve the gas sensing performance remarkably. In this work, hierarchical cactus-like WO 3 /Co 3 O 4 nanocomposites were directly deposited on the surface of ceramic tube via a simple two-step process. The p-type Co 3 O 4 nanorods array were grown on the surface of n-type WO 3 nanosheets by using chemical bath deposition (CBD) and thus many nanoscale p-n junctions were formed which greatly improved the gas sensing performance. A response value (R a /R g) of 6.19 to 1 ppm triethylamine (TEA) was achieved at 240 ℃ by the WO 3 /Co 3 O 4 nanocomposite with the CBD deposition time of 30 min, which is 3 times higher than that of the pure WO 3 nanosheets (S r = 2.02). And the response/recovery time was about 13 s/152 s, which shows good gas sensing performance to TEA. [ABSTRACT FROM AUTHOR]

The detection of nitrogen dioxide (NO 2 ) is essential for the environment and human health. Tin dioxide (SnO 2 ) based sensors have demonstrated capabilities to detect NO 2 , while their response, response/recover speed and selectivity are not good enough for their practical applications. To address these issues, the SnO 2 nanoparticles doped with reduced graphene oxides (rGO) have been synthesized by using a facile microwave-assisted gas-liquid interfacial solvothermal method in this work. The NO 2 sensing performances have been greatly enhanced after the doping of rGO due to the improved electronic conductivity and the formation of the p-n junction in the as-synthesized SnO 2 /rGO nanocomposites. Moreover, our results demonstrate that the sensors based on the SnO 2 /(0.3%)rGO nanocomposites (with an average diameter about 10–15 nm) exhibit the best overall performance with the high response of 247.8 to 10 ppm NO 2 , fast response/recovery speed (39 s/15 s) and the excellent selectivity at the working temperature of 200 ℃. Remarkably, the SnO 2 /(0.3%)rGO sensors still exhibit a good gas sensing performance to NO 2 even at room temperature. [ABSTRACT FROM AUTHOR]