- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Effects of Protonation, Hydroxylamination, and Hydrazination of g-C3N4 on the Performance of Matrimid?/g-C3N4 Membranes
摘要： One of the challenges to continue improving polymeric membranes properties involves the development of novel chemically modified fillers, such as nitrogen-rich 2-D nanomaterials. Graphitic carbon nitride (g-C3N4) has attracted significant interest as a new class of these fillers. Protonation is known to afford it desirable functionalities to form unique architectures for various applications. In the work presented herein, doping of Matrimid? with protonated g-C3N4 to yield Matrimid?/g-C3N4 mixed matrix membranes was found to improve gas separation by enhancing the selectivity for CO2/CH4 by up to 36.9% at 0.5 wt % filler doping. With a view to further enhancing the contribution of g-C3N4 to the performance of the composite membrane, oxygen plasma and hydrazine monohydrate treatments were also assayed as alternatives to protonation. Hydroxylamination by oxygen plasma treatment increased the selectivity for CO2/CH4 by up to 52.2% (at 2 wt % doping) and that for O2/N2 by up to 26.3% (at 0.5 wt % doping). Hydrazination led to lower enhancements in CO2/CH4 separation, by up to 11.4%. This study suggests that chemically-modified g-C3N4 may hold promise as an additive for modifying the surface of Matrimid? and other membranes.
关键词： carbon nitride,O2/N2,Matrimid? 5218,CO2/CH4,gas separation,mixed matrix membrane
更新于2025-09-23 15:23:52
-
Differential Column Measurements Using Compact Solar-Tracking Spectrometers
摘要： We demonstrate the use of compact solar-tracking Fourier transform spectrometers (Bruker EM27/SUN) for differential measurements of the column-averaged dry-air mole fractions of CH4 and CO2 within urban areas. Using Allan variance analysis, we show that the differential column measurement has a precision of 0.1% for XCO2 and XCH4 using an optimum integration time of 10 min, which corresponds to standard deviations of 0.04 ppm, and 0.2 ppb, respectively. The sensor system is very stable over time and after relocation across the continent. We report tests of the differential column measurement, and its sensitivity to emission sources, by measuring the downwind minus upwind column gradient ?XCH4 across dairy farms in the Chino California area and using the data to verify emissions reported in the literature. Spatial column gradient ratios ?XCH4/?XCO2 were observed across Pasadena within the Los Angeles basin, indicating values consistent with regional emission ratios from the literature. Our precise, rapid measurements allow us to determine significant short-term variations (5-10 minutes) of XCO2 and XCH4, and to show that they represent atmospheric phenomena. Overall, this study helps establish a range of new applications for compact solar-viewing Fourier transform spectrometers. By accurately measuring the small differences in integrated column amounts across local and regional sources, we directly observe the mass loading of the atmosphere due to the influence of emissions in the intervening locale. The inference of the source strength is much more direct than inversion modeling using only surface concentrations, and less subject to errors associated with small-scale transport phenomena.
关键词： compact solar-tracking spectrometers,urban emissions,differential column measurements,CH4,CO2
更新于2025-09-23 15:21:21
-
A fibered near-infrared laser heterodyne radiometer for simultaneous remote sensing of atmospheric CO2 and CH4
摘要： The performance of an all fibered near-infrared laser heterodyne radiometer (NIR-LHR) is demonstrated in ground-based solar occultation mode. A 1 × 2 fiber optical switch is employed as an alternative modulator to traditional chopper, which makes the system more stable and compact. Two distribute feedback (DFB) lasers centered at 1.6 μm and 1.65 μm, are employed as local oscillators to probe absorption lines of CO2 and CH4, respectively. After data processing and retrieval, column-averaged abundances and the mixing ratio of atmospheric CO2 and CH4 are determined based on the measurement of over six months in our laboratory (Hefei, China, 31.9°N 117.16°E). Finally, the results are validated by comparison with the GOSAT results during the same time period. The reported all fibered laser heterodyne radiometer in this manuscript has great potential to be a portable and high spectral resolution instrument for atmospheric remote sensing of multi-component gases.
关键词： Atmospheric remote sensing,CO2,Laser heterodyne radiometer,Near-infrared,CH4
更新于2025-09-19 17:13:59
-
Simultaneous Measurements of Soil CO and CH Fluxes Using Laser Absorption Spectroscopy
摘要： We present a method of simultaneously measuring soil CO2 and CH4 fluxes using a laser-based cavity ring-down spectrometer (CRDS) coupled to an automated non-steady-state chamber system. The differential equation describing the change in the greenhouse gas (GHG) mixing ratio in the chamber headspace following lid closure is solved for the condition when a small flow rate of chamber headspace air is pulled through the CRDS by an external pump and exhausted to the atmosphere. The small flow rate allows calculation of fluxes assuming linear relationships between the GHG mixing ratios and chamber lid closure times of a few minutes. We also calibrated the chambers for effective volume (Veff) and show that adsorption of the GHGs on the walls of the chamber caused Veff to be 7% higher than the geometric volume, with the near-surface soil porosity causing another 4% increase in Veff.
关键词： automated non-steady-state chamber system,soil CO2 and CH4 fluxes,laser absorption spectroscopy,cavity ring-down spectrometer
更新于2025-09-16 10:30:52
-
Enhanced CH4 sensitivity of porous nanosheets-assembled ZnO microflower by decoration with Zn2SnO4
摘要： In recent years, design and synthesis of heterostructured nanomaterials with high gas-sensing performance for detection of flammable and toxic gases has attracted much research interest. In this paper, pristine and Zn2SnO4-decorated ZnO microflowers with the size about 2?5 μm and assembled by porous nanosheets of about 15 nm in thickness were successfully synthesized via a simple solvothermal method and subsequent calcination process. The methane (CH4) sensing properties of the prepared Zn2SnO4/ZnO were investigated and compared with that of the pure ZnO counterpart. It was found that after decorating with a small amount of Zn2SnO4, the ZnO sensor showed an improved gas sensing properties to CH4. At optimum operating temperature of 250 oC, the sensor based on SZ2 (Zn2SnO4/ZnO composite with the optimal Zn2SnO4 contend) shows a response as high as 27.2 to 1000 ppm CH4, which is about 3.2 times higher than that of SZ0 (pristine ZnO) sensor. Meanwhile, the SZ2 sensor also shows a fast response and recover characteristic, low detection limit (1.48 ppm), good repeatability and long-term stability. The Zn2SnO4/ZnO heterostructures related CH4 sensing mechanism was discussed.
关键词： CH4,Zn2SnO4,Hierarchical structures,Gas sensor,Heterostructures
更新于2025-09-12 10:27:22
-
Enhanced photocatalytic carbon dioxide reforming of methane to fuels over nickel and montmorillonite supported TiO2 nanocomposite using monolith photoreactor
摘要： Conversion of carbon dioxide (CO2) and methane (CH4) to fuels using photo-technology is a cleaner pathway compared to thermal reforming, since its uses only light irradiations, while producing valuable chemicals. In this study, structured nickel (Ni) and montmorillonite (MMT) supported TiO2 composite, synthesized by a sol-gel method, was tested for photocatalytic reduction of CO2 using fixed-bed and monolith photoreactors. The performance of structured nanocatalyst was evaluated using CO2-H2 system via photocatalytic reverse water gas shift (RWGS) reaction and CO2-CH4 system via photocatalytic dry reforming of methane (DRM). Using photocatalytic RWGS, CO was detected as the main products, while the performance of Ni-MMT/TiO2 composite was expressively higher than using MMT/TiO2 and TiO2 catalysts. This was obviously due to larger surface area by MMT dispersion and hindered charges recombination rate by Ni. Similarly, using DRM, H2 and CO were the main products, while their selectivity was greatly dependent on the initial CH4/CO2 molar feed ratios. At a lower CH4/CO2 ratio, more CO was produced, while a higher feed ratio promoted H2 production. This shows, composite catalyst was more favorable for CO2 adsorption, while CH4 was competitively adsorbed during photo-catalysis process. Comparatively, Ni-MMT/TiO2 catalyst reveals higher photo-activity and selectivity in a monolith photoreactor than using fixed-bed reactor under the same operating conditions. This enhanced photoactivity was due to higher photonic flux with enlarged active surface area due to monolithic support and efficient sorption process. The stability of Ni/TiO2 dispersed MMT for CO and H2 production via DRM process sustained in cyclic runs using monolithic support. Hence, using Ni/MMT modified TiO2 catalyst and monolith photoreactor, CO2 and CH4 can efficiently be converted to renewable fuels under light irradiations and would be a great benefit to the environment.
关键词： Photo-technology,Ni/TiO2,Dry reforming of CH4,Monolith photoreactor,Montmorillonite,CO2 reduction
更新于2025-09-04 15:30:14