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In this work, the synthesized Co 3 O 4 /NiCo 2 O 4 /CC is a layered structure, which was prepared by a feasible method of hydrothermal reaction, thermal annealing of ZIF-67 template and other thermal treatment. This novel structure is based on carbon cloth, and Co 3 O 4 hollow nanocubes as semiconductor material grow in situ on nanowire arrays. Under the condition of different temperatures and different concentrations of ethanol, the response of the gas sensor based on Co 3 O 4 /NiCo 2 O 4 was studied. The result shows high sensitivity, good linear relationship and excellent response-recovery properties. And its high sensitivity is demonstrated with a maximum response up to 35 at 180 °C and 200 ppm. The sensor performs well in gas sensitivity thanks to the structure of the material. Large specific surface area, high porosity and fast electronic transport channel between Co 3 O 4 and CC are all important reasons. Accordingly, this method of preparing the novel hierarchical structure can improve the gas sensitive performance. This work would provide a reference for further research on the application of Co 3 O 4 MOF-derived structure in gas sensitive. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is one of the main harmful gas in agricultural greenhouse. Its concentration can effectively reflect the health status of plants in agricultural greenhouse. In this paper, the adsorption characteristics of SO 2 on modified graphene-based were studied in comparison. The adsorption models of epoxy grouped graphene (G-O), palladium doped graphene (Pd-G) and epoxy and palladium co-doped graphene (Pd-G-O) to SO 2 were established based on the first-principles, analyzing in terms of adsorption energy, density of states, orbitals, charge density and desorption time of the adsorption models. The results showed that Pd-G-O exhibited strong chemisorption with adsorption energy of -1.237 eV. Furthermore, three modified graphene-based sensing materials were prepared via the redox method in this paper, and their crystal morphology and chemical elemental composition were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The response performance of the graphene-based sensor to SO 2 was tested by a gas-sensitive testbed. The test results confirmed that the response of the Pd-G-O sample to 50 ppm SO 2 at room temperature was 10.5 (1.567 and 1.235 times than that of G-O, Pd-G). Pd-G-O provides theoretical basis and experimental support for the development of a highly sensitive and fast response sensor for the detection of harmful gases in agricultural greenhouse. [ABSTRACT FROM AUTHOR]

It is of great significance to monitor internal faults of transformer and ensure its normal and safe operation. Usually, acetylene (C 2 H 2) is considered as the characteristic gas caused by discharge failure in transformer. Using gas sensor technology to analyze dissolved gases in transformer oil is an important strategy. Recently, metal oxide semiconductor (MOS) heterojunctions with tailored microstructures have been developed to fabricate high quality gas sensors for gas detection. In this paper, hierarchical flower-like NiO/ZnO heterostructures assembled with 2D nanosheets have been synthesized by a facile hydrothermal method and calcination process. Noticeably, the introduction of different contents of NiO (3.0 at%, 5.0 at% and 10.0 at%) leads to different assembly manners of the building nanosheets into hierarchical flower-like structures, thus affecting the gas performances. Given this, a variety of microscopic characterization methods were used to observe and compare the differences in the structures and morphologies of the composites. Through the gas sensing test, it was found that the 5.0 at% NiO-modified ZnO based sensor exhibited superior sensing performances to C 2 H 2 compared with that of others. The enhanced properties may be attributed to the formation of p-n heterojunctions as well as high porosity of the nanosheets. This promising approach is versatile for the applications of high-quality gas sensors. [ABSTRACT FROM AUTHOR]

Acetylene (C 2 H 2) gas concentration is a key parameter in transformer monitoring. In current work, the selective acetylene sensors which based on flower-like ZnO structures with NiO nanoparticles were successfully fabricated. The NiO–ZnO composites were synthesized by two-step hydrothermal method. And various of characterization analyses had been applied to the exploration of crystal structure and the p-n heterojunction. According to the systematic gas sensitivity tests, the response of NiO–ZnO (5%) to 50 ppm C 2 H 2 was 15.23 at 200 °C whereas the response of pure ZnO was 4.1 in the same condition. In addition, the response value of NiO–ZnO (5%) to 50 ppm C 2 H 2 was 3.6 times to 50 ppm H 2. Such a good gas-sensing property of NiO–ZnO composites is due to p-n heterojunction and high catalytic activity of NiO. [ABSTRACT FROM AUTHOR]