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Langmuir-Blodgett Films
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
The monolayer that results from introducing amphiphilic molecules to the water-air interface was traditionally called a two-dimensional gas due to the expected large distances between the molecules. However, it is quite clear now that amphiphiles self-organize at the air-water interface even at relatively low surface pressures.8–11 For example, Shih et al. showed X-ray diffraction data from a monolayer of heneicosanoic acid spread on a 0.5 mM CaCl2 solution at zero pressure.12 Once the barrier starts moving and compresses the molecules, the surface pressure (π) increases and the area per molecule (A) decreases. The surface pressure, which is the force per unit length of the barrier (in newtons/meter, or dyn/cm), is π == σ “σ, where σ0 is the surface tension of pure water and cr is that of the water covered with a monolayer. Because we know the total number of molecules and the total area that the monolayer occupies, we can calculate the area per molecule (Å2) and construct a π-A isotherm that describes the surface pressure as a function of the area per molecule.3,4Figure 22.2 presents a schematic π-A isotherm for a phospholipid of fatty acid. This isotherm is rich in information on stability of the monolayer at the water-air interface, the reorientation of molecules in the two-dimensional system, phase transitions, and conformational transformations.
Slow pyrolysis of biomass: effects of effective hydrogen-to-carbon atomic ratio of biomass and reaction atmospheres
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Min Wang, Sheng-Li Zhang, Pei-Gao Duan
The molecular compositions of HPO were identified using a LECO®4D Pegasus two-dimensional gas chromatograph with a time-of-flight mass spectrometer (GC × GC-TOF/MS). Oil solution samples were prepared by diluting 0.2 g of oil with dichloromethane to 1 g and were injected into the GC installed with two columns. The sample injection volume was 1 µL at a split ratio of 10:1. The inlet temperature was 300°C. The 1st column was a nonpolar Rtx®-5SilMS with dimensions of 30 m length × 0.25 mm ID × 0.25 μm film thickness installed in the main oven. The 2nd column was an Rxi®-17 MS with dimensions of 1.10 m length × 0.10 mm ID × 0.10 μm film thickness installed in the second oven. The first-dimension column was initially held at 40°C for 4 min. The temperature was ramped to 300°C at 4°C/min and held isothermally for 4 min. The second-dimension column was initially held at 45°C for 4 min. The temperature was ramped to 305°C at 4°C/min and held isothermally for 4 min. The modulation period, the hot-pulse duration, and the cool time between stages were set to 5, 0.6, and 1.9 s, respectively. The transfer line to the TOFMS detector source was operated at 280°C. The ion source temperature was 250°C with a filament bias voltage of 70 eV. The data acquisition rate was 100 spectra/s for the mass range of 35 to 500 amu. The detector voltage was 1500 V. LECO ChromaTOF® software recorded and analyzed data with spectral identification provided by the NIST library. The accuracy and sensitivity of the MS detector were calibrated and tested using perfluorotributylamine (PFTBA) and hexachlorobenzene (HCB), respectively.
A study on the reaction mechanism of microwave pyrolysis of oily sludge by products analysis and ReaxFF MD simulation
Published in Environmental Technology, 2022
Yanjun Wen, Wenxuan Li, Yingshen Xie, Zhiwen Qin, Meixia Gu, Tianli Wang, Yingfei Hou
The TG-DTG analysis of OS was carried out on a TGA2 thermal gravimetric analyzer produced by Mettler Toledo (Switzerland). Nitrogen (99.99%) was used as carrier gas at a rate of 50 ml/min. The temperature raised from 30℃ to 1000℃ at a rate of 10℃/min. The GC analysis of gas from OS pyrolysis was carried out on gas chromatograph (Agilent 7890B, America). Hydrogen (99.999%) was used as carrier gas. The oil from OS pyrolysis was analyzed by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-MS). The gas chromatography part is Agilent 7890 B gas chromatography, equipped with a two-stage four-nozzle heat modulator, and the mass spectrometry part is LECO Pegasus 4D time-of-flight mass spectrometer. Compared with ordinary GC-MS analysis, GC×GC-MS analysis has higher separation capacity, peak capacity, high resolution, and more precise qualitative and quantitative analysis capability. GC×GC-MS fully improves the degree of separation and identification of organic compounds in complex mixtures and solves the problem that complex mixtures are difficult to be separated and identified. The XRD analysis of residue from OS pyrolysis was carried out on D8 Advance X-ray diffractometer (Bruker, Germany).
Polycyclic musks in the environment: A review of their concentrations and distribution, ecological effects and behavior, current concerns and future prospects
Published in Critical Reviews in Environmental Science and Technology, 2021
Jianv Liu, Wenying Zhang, Qixing Zhou, Qingqin Zhou, Yu Zhang, Linfang Zhu
Method detection limits (MDLs) below 32 ng/L have been successfully applied to real samples with no significant differences. HHCB and AHTN are chiral substances, and several tertiary production impurities are isomers. If all stereoisomers and enantiomers are considered, tandem mass spectrometry cannot overcome the obstacle of having to separate approximately 30 peaks with similar mass spectra. To solve this problem, comprehensive two-dimensional gas chromatography (GCxGC) was applied. Relić et al. (2017) assessed the state of waters in Belgrade regarding pollution with musk compounds using comprehensive orthogonal two-dimensional gas chromatography with mass spectrometry (GCxGC/TOF-MS) as the final analytical method. GCxGC/TOF-MS was also used to determine a group of high-priority EOCs in wastewater and river water (Gomez, Herrera, Sole, Garcia-Calvo, & Fernandez-Alba, 2011), including six synthetic musk fragrances, and excellent results were obtained for the separation efficiency and musk compound identification. GCxGC has great power in the detection of PCMs and could be further developed and applied widely (Hu et al., 2011).