Design of cellular structure of graphene aerogels for electromagnetic wave absorption

Tungsten oxide (WO 3 ) with different morphologies (nanorods, spheres, sea urchins and flowers) were synthesized by a hydrothermal method. Among them, the WO 3 based gas sensor with sea urchin morphology (WO 3 -3) exhibits excellent sensitivity, selective and ultrafast response to acetone in the concentration range of 2–5000 ppm at 200 ℃. The response of WO 3 -3 sensor to 100 ppm acetone can reach 29.7 and the response time is ultrafast (3 s), which makes the sensors a promising candidate for practical applications. As temperature is one of the important factors that affect the sensor performance, we also investigated the effects of temperature on the as-prepared WO 3 structures using Raman spectroscopy. Changes in the spectra measured for the different WO 3 structures were seen over a temperature range from 60 to 200 ℃. Raman spectra were also measured for the WO 3 -3-based sensor exposed to air and acetone at room temperature and the optimum working temperature. The temperature studies using Raman spectroscopy expanded our understanding of the interactions between the gas and gas sensing materials in the WO 3 -based sensors. The excellent sensing properties of the WO 3 -3-based sensors is attributed to the special, urchin-shaped structure as well as the oxygen activity and oxygen vacancy regulation in these materials. • The sea urchins-like WO 3 sensor shows ultrafast response (3 s) to 100 ppm acetone. • In-situ Raman technique was used to analysis acetone detection. • As temperature increased, a redshift occurs in the Raman spectrum of WO 3 . 

Sea urchins-like WO3 as a material for resistive acetone gas sensors

NO2 detection and redox capacitance reaction of Ag doped SnO2/rGO aerogel at room temperature

Boosting room-temperature ppb-level NO2 sensing over reduced graphene oxide by co-decoration of α-Fe2O3 and SnO2 nanocrystals

To develop high-performance microwave absorption materials with the features of lightweight, thin thickness, broad bandwidth, and strong absorption, an ultralight Ni3S2@N, S-codoped graphene aerogel with a density of 13.5 mg/cm3 has been fabricated by the use of metal-organic frameworks (MOFs) to directly initiate the gelation of graphene oxide strategy. In such a strategy, dual-functional 1D Ni-MOF nanorods not only act as the gelation agent but also afford the doping elements (N and S) originated from the organic species and the precursor for metal sulfide. Due to the synergistic effects of good impedance matching and multiple losses, the optimal reflection loss (RL) of as-prepared Ni3S2@N, S-codoped graphene aerogel reaches −46.9 dB at 17.1 GHz with only 2.0 mm and ultralow filling content (1.75 wt%). The maximum effective absorption bandwidth (EAB) reaches 6.3 GHz (11.7–18.0 GHz) at 2.38 mm, covering the whole Ku band. Moreover, the value of EAB with the RL less than −30 dB can be tuned to 12.2 GHz (5.8–18 GHz) at the absorber thickness ranging from 1.9 to 5.0 mm. This work provides insight for rational design and fabrication of multicomponent-containing graphene aerogels, showing the potential application in lightweight and high-performance microwave absorption.

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Ultralight MOF-Derived Ni3S2@N, S-Codoped Graphene Aerogels for High-Performance Microwave Absorption

An acidified SnO2/rGO aerogel (ASGA) is an attractive contributor in ethanol gas sensing under ultralow concentration because of the sufficient active sites and adsorption pores in SnO2 and the rGA, respectively. Furthermore, a p-n heterojunction is successfully constructed by the high electron mobility between ASP and rGA to establish a brand-new bandgap of 2.72 eV, where more electrons are released and the surface energy is decreased, to improve the gas sensitivity. The ASGA owns a specific surface area of 256.1 m2/g, far higher than SnO2 powder (68.7 m2/g), indicating an excellent adsorption performance, so it can acquire more ethanol gas for a redox reaction. For gas-sensing ability, the ASGA exhibits an excellent response of Ra/Rg = 137.4 to 20 ppm of ethanol at the optimum temperature of 210 °C and can reach a response of 1.2 even at the limit detection concentration of 0.25 ppm. After the concentration gradient change test, a nonlinear increase between concentration and sensitivity (S-C curve) is observed, and it indirectly proves the chemical adsorption between ethanol and ASGA, which exhibits charge transfer and improves electron mobility. In addition, a detailed energy band diagram and sensor response diagram jointly depict the gas-sensitive mechanism. Finally, a conversed calculation explains the feasibility of the nonlinear S-C curve from the atomic level, which further verifies the chemical adsorption during the sensing process.

Yiming Liu

Papers

Chemical Surface Adsorption and Trace Detection of Alcohol Gas in Graphene Oxide-Based Acid-Etched SnO2 Aerogels.