The experimental measurements for liquid densities of n -decane and p -xylene binary mixtures were performed over the entire composition with a high-pressure vibrating-tube densimeter. The temperature ranges for the present measurement were from 293.15 K to 363.15 K and the pressures were reached to 60 MPa. The experimental uncertainty is estimated to be 0.001 with 0.95 confidence level. Experimental density values were fitted by the modified Tammann–Tait equation. The PC-SAFT equation of state and Cibulka's equation was used to predict the densities of n -decane and p -xylene and its mixtures. In addition, derived volumetric properties, such as the excess molar volumes , the isothermal compressibility , and isobaric thermal expansivity, were calculated from the experimental density data. The effects of pressure and temperature on the derived properties were also discussed.
Meng-Ya Zhu,Le-Xi Zhang,Jing Yin,Jing-Jing Chen,Li-Jian Bie,Bradley D. Fahlman
A novel organic-inorganic layered perovskite compound (C 4 H 9 NH 3 ) 2 PbI 4 has been synthesized through a simple and high-yield solution method. For the first time, this layered perovskite was used as a candidate material for gas sensors. Gas sensors based on (C 4 H 9 NH 3 ) 2 PbI 4 provided unique gas-sensing properties toward 1–800 ppm p -xylene (p-C 8 H 10 ) at the working temperature of 140 °C, including fast response, quick response-recovery, good selectivity and repeatability. The as-prepared (C 4 H 9 NH 3 ) 2 PbI 4 gas sensor can detect as low as 1 ppm concentration of p -xylene with a response of 11.8 at 140 °C. In situ diffuse reflectance Fourier transform infrared (DRFTIR) measurement shows that the p -xylene sensing mechanism can be mainly attributed to physical adsorption, which is different from other common gas-sensing metal oxides that are based on adsorption-redox-desorption mechanism.
Abstract P-xylene (p-C 8 H 10 ) is extremely harmful and dangerous to human health due to high toxicity and strong carcinogenicity. Exploring sensitive material to effectively detect p-xylene is of importance. In this paper, perovskite single crystal (C 4 H 9 NH 3 ) 2 PbI 4 has been successfully synthesized via solution method. The obtained product was analyzed by single crystal X-ray diffraction. With the space group Pbca, orthorhombic (C 4 H 9 NH 3 ) 2 PbI 4 layered perovskite structure consists of an extended two-dimensional network of corner-sharing PbI 6 octahedron. Single layer perovskite sheets of distorted PbI 6 octahedron alternated with protonated n-butylammonium cation bilayers, which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances. Density functional theory (DFT) simulations regarding the adsorption energy revealed that this organic–inorganic hybrid perovskite compound has excellent selectivity toward p-xylene compared with other gases including C 2 H 5 OH, C 6 H 6 , CH 2 Cl 2 , HCHO, CH 3 COCH 3 and C 7 H 8 . The calculation of electron density, density of states and electron density difference showed the sensing mechanism of p-C 8 H 10 is mainly derived from physical adsorption–desorption in view of electron transfer. Graphic abstract For organic–inorganic hybrid perovskite (C 4 H 9 NH 3 ) 2 PbI 4 , single layer perovskite sheets of distorted PbI 6 octahedron alternated with protonated n-butylammonium cation bilayers (a), which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances. Electron density difference calculation shows that adsorption of p-xylene molecule has an obvious effect on the electron distribution of (C 4 H 9 NH 3 ) 2 PbI 4 , results in electrically polarization as a local manner (b).
P-Xylene is a prevalent indoor hazardous volatile organic compound(VOC). A long-term exposure limit of 100 ppm for p-xylene is generally recommended. Therefore, sensitive and selective detection of trace p-xylene is crucial. This work presents a method for detecting p-xylene gas by combining terahertz (THz) metasurface sensor with a metal-organic-framework (MOF) material, copper benzene-1,3,5-tricarboxylate (HKUST-1). The sensor with double split ring resonators is fabricated using a micromachining process and characterized by a terahertz time-domain-spectroscopy (TDS) system. The test results are consistent with the simulation. Subsequently, the sensor's surface is modified using the MOF material of HKUST-1 to enhance its sensitivity to the p-xylene gas. At room temperature, the sensitivity for p-xylene gas concentrations is between 1-100 ppm .The modified sensor has a maximum response frequency shift of 14 GHz for p-xylene gas at 100 ppm. Furthermore, the specificity, repeatability and stability of the sensor are characterized. The proposed method for highly sensitive and specific detection of p-xylene gas has important reference significance for the development of other types of gas sensors.
危险品化学品经营许可证（带存储）