Wenqian Yan

Bio: Wenqian Yan is an academic researcher from Nanjing Tech University. The author has contributed to research in topics: Aerogel & Adsorption. The author has an hindex of 2, co-authored 6 publications receiving 18 citations.

Thermal and Mechanical Performances of the Superflexible, Hydrophobic, Silica-Based Aerogel for Thermal Insulation at Ultralow Temperature.

Abstract: A superflexible hydrophobic silica-based aerogel (FHSA) was prepared via a facile sol-gel process and ambient pressure drying method. The FHSA was treated at different temperatures varying from -196 to 450 °C to evaluate its thermal and mechanical performances. The evolutions of the physical property, hydrophobicity, microstructure, pore structure, and chemical structure of the FHSA with the various treatment temperatures were investigated comprehensively. The structure of the FHSA did not show an obvious change after treatment in the liquid nitrogen. The bulk density of the FHSA increased from 0.047 to 0.077 g cm-3 when the thermal treatment temperature increased from 25 to 450 °C. The specific surface area and pore volume of the FHSA increased with the treatment temperature owing to the decomposition of the organic moieties. The Fourier transform infrared spectra showed that the methyl groups in the FHSA had excellent thermostability up to 400 °C. The water contact angles of the FHSA after treatment at -196, 25, 200, 300, 350, 400, and 450 °C were 131, 151, 162, 150, 132, 119, and 34°, respectively. The thermal conductivity of the FHSA at a low temperature of -10 °C was 0.022 W m-1 K-1. The reversible deformation rate of the FHSA was more than 80% within 100 compression cycles. After treatment in liquid nitrogen, the reversible deformation rate of the FHSA remained at 50%. The synthesis method of the FHSA is simple, the resulting FHSA showed good performance both in thermostability and flexibility, and it is promisingly applied for thermal insulation and sealing in ultralow-temperature environments.

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

Abstract: 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.

Preparation of the novel B4C–SiC composite aerogel with high compressive strength and low thermal conductivity

Abstract: A novel B4C–SiC composite aerogel is synthesized using nano boron carbide suspension, 3-aminopropyltriethoxysilane (APTES), and resorcinol–formaldehyde (RF) as precursors through the sol–gel route and carbothermal reduction process. The effects of different B/Si molar ratios and calcination temperatures on the physical chemistry properties of B4C–SiC composite aerogels are investigated. The addition of the B4C phase is beneficial for improving the comprehensive properties of composite aerogel. The results show that the compressive strength of B4C–SiC composite aerogel is as high as 3.05 MPa. The specific surface area can reach 692.81 m2/g, which ensures that it has a thermal insulation capacity under elevated temperatures. After heat-treated at 1650 °C for 3 h, the thermal conductivity of carbon fiber mat reinforced composite aerogel is 0.058 W/m K (25 °C). This composite aerogel material has great application prospects in the field of high temperature insulation.

Metal Oxide Gas Sensors For Detecting NO2 in Industrial Exhaust Gas: Recent Developments

Abstract: NO2 is an oxidizing gas, which is considered to be the most dangerous and most toxic gas that should be controlled. Because of the advantages of high sensitivity, selectivity, stability and fast response/recovery speed, the chemical resistance sensor is used as a NO2 gas sensor. This article reviews the NO2 gas sensor based on metal oxides. Firstly, the hazards of NO2 and the major disadvantages of chemiresistive sensors based on metal oxides were discussed. Then, different sensitive materials of chemical resistance sensors were discussed, including metal oxides (MO), conductive polymers and carbon-based materials. Finally, the NO2 gas sensors based on metal oxide (including ZnO, NiO, CuO, SnO2, WO3) were discussed from the aspects of morphology, preparation method, modification, doping and composite.