Electron spin resonance linewidths of Co2+ in magnesium oxide

Electron spin resonance linewidths of Co²⁺ in single-crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Co²⁺ concentration from 310 to 9900 ppm. In contrast to the behaviour expected from dipolar broadening, the experimental peak-to-peak linewidth for the octed hyperfine lines were about twelve to fifty times less than the calculated dipolar linewidths according to temperature and concentrations. The peak-to-peak linewidths as determined experimentally increase from 0.8 mT at 310 ppm Co²⁺ to 4.0 mT at 9900 ppm Co²⁺ at a polar angle _H= O° and at 20 K. Peak-to-peak linewidths independent of polar angle but strongly dependent on temperature and slightly dependent on concentrations were observed. The ratio of moments M ₄ ^1/4 /M ₂ ^1/2 derived from the experimental data lay between 1.35 to 1.44 and the lineshapes were markedly Lorentzian in the range of temperature measured. The data suggest that Co²⁺ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined, after exchange energy, over the whole concentration range examined and that the exchange energy whose values lay between 6 and 77 GHz, varied linearly with concentration.     

Analysis of transmission spectra for large ratio of emission-to-absorber linewidths: extension of differential absorption lidar analysis for finite laser linewidths

A simple algorithm is presented for the analysis of transmission spectra provided by a lidar with an emission linewidth that is comparable with or larger than the absorption features of interest. The spreading of line shapes as seen by the lidar precludes use of the classical differential absorption lidar (DIAL) approach. However, it is assumed that, as with the DIAL method, small spectral intervals exist where single absorbers are dominant, and an inversion process for the transmission over such intervals is carried out for the absorber concentration. A second-stage algorithm based on singular-value decomposition is also provided to improve further the concentration estimates. An example situation for use of the algorithms is included wherein the objective is to estimate the concentration of a known trace gas in a composite transmission spectrum in the mid-infrared, where the dominant absorbers are water vapor and methane.     

Clustering and electron spin resonance linewidths in Fe/MgO

Electron spin resonance linewidths and integrated intensities for the 1/2 –1/2 transition of Fe³⁺ in cubic sites in single-crystal MgO have been examined at 9 GHz between 293 and 90 K for iron concentrations between 100 and 12 900 ppm. Very little of the iron is present in cubic sites as isolated Fe³⁺ ions. It is suggested that this is partly caused by clustering, even at extremely low concentrations. The measured linewidths, which agree well with those reported previously, have been analysed in terms of Kittel and Abrahams' dipolar broadening theory. The highest measured Fe³⁺ concentrations give linewidths comparable with those predicted, but for most samples the measured linewidths are considerably broader than those calculated. This broadening may be caused by interactions with the undetected iron, which accounts for the major fraction. There is no evidence for exchange narrowing of the Fe³⁺ lines for the range of concentrations examined.     

Liquid-in-Aerogel Porous Composite Allows Efficient CO2 Capture and CO2/N2 Separation

The pursuit of efficient CO₂ capture materials remains an unmet challenge. Especially, meeting both high sorption capacity and fast uptake kinetics is an ongoing effort in the development of CO₂ sorbents. Here, a strategy to exploit liquid-in-aerogel porous composites (LIAPCs) that allow for highly effective CO₂ capture and selective CO₂/N₂ separation, is reported. Interestingly, the functional liquid tetraethylenepentamine (TEPA) is partially filled into the air pockets of SiO₂ aerogel with left permanent porosity. Notably, the confined liquid thickness is 10.9–19.5 nm, which can be vividly probed by the atomic force microscope and rationalized by tailoring the liquid composition and amount. LIAPCs achieve high affinity between the functional liquid and solid porous counterpart, good structure integrity, and robust thermal stability. LIAPCs exhibit superb CO₂ uptake capacity (5.44 mmol g⁻¹, 75 °C, and 15 vol% CO₂), fast sorption kinetics, and high amine efficiency. Furthermore, LIAPCs ensure long-term adsorption–desorption cycle stability and offer exceptional CO₂/N₂ selectivity both in dry and humid conditions, with a separation factor up to 1182.68 at a humidity of 1%. This approach offers the prospect of efficient CO₂ capture and gas separation, shedding light on new possibilities to make the next-generation sorption materials for CO₂ utilization.     

Isotype Heterojunction-Boosted CO2 Photoreduction to CO

Photocatalytic conversion of CO2 to high-value products plays a crucial role in the global pursuit of carbon-neutral economy.Junction photocatalysts,such as the...     

Exploration of CO2 emission reduction pathways: identification of influencing factors of CO2 emission and CO2 emission reduction potential of power industry

Clean Technologies and Environmental Policy - Low-carbon development of China's power sector is the key to achieving carbon peaking and carbon neutrality goals. Based on the logarithmic mean...     

Interactions between reducing CO2 emissions, CO2 removal and solar radiation management

We use a simple carbon cycle-climate model to investigate the interactions between a selection of idealized scenarios of mitigated carbon dioxide emissions, carbon dioxide removal (CDR) and solar radiation management (SRM). Two CO(2) emissions trajectories differ by a 15-year delay in the start of mitigation activity. SRM is modelled as a reduction in incoming solar radiation that fully compensates the radiative forcing due to changes in atmospheric CO(2) concentration. Two CDR scenarios remove 300 PgC by afforestation (added to vegetation and soil) or 1000 PgC by bioenergy with carbon capture and storage (removed from system). Our results show that delaying the start of mitigation activity could be very costly in terms of the CDR activity needed later to limit atmospheric CO(2) concentration (and corresponding global warming) to a given level. Avoiding a 15-year delay in the start of mitigation activity is more effective at reducing atmospheric CO(2) concentrations than all but the maximum type of CDR interventions. The effects of applying SRM and CDR together are additive, and this shows most clearly for atmospheric CO(2) concentration. SRM causes a significant reduction in atmospheric CO(2) concentration due to increased carbon storage by the terrestrial biosphere, especially soils. However, SRM has to be maintained for many centuries to avoid rapid increases in temperature and corresponding increases in atmospheric CO(2) concentration due to loss of carbon from the land.     

Rechargeable Al–CO2 Batteries for Reversible Utilization of CO2

The excessive emission of CO₂ and the energy crisis are two major issues facing humanity. Thus, the electrochemical reduction of CO₂ and its utilization in metal–CO₂ batteries have attracted wide attention because the batteries can simultaneously accelerate CO₂ fixation/utilization and energy storage/release. Here, rechargeable Al–CO₂ batteries are proposed and realized, which use chemically stable Al as the anode. The batteries display small discharge/charge voltage gaps down to 0.091 V and high energy efficiencies up to 87.7%, indicating an efficient battery performance. Their chemical reaction mechanism to produce the performance is revealed to be 4Al + 9CO₂ ? 2Al₂(CO₃)₃ + 3C, by which CO₂ is reversibly utilized. These batteries are envisaged to effectively and safely serve as a potential CO₂ fixation/utilization strategy with stable Al.     

Photocatalytic transformation of CO2 to CH4 and CO on acidic surface of TiO2 anatase

Recently, many studies have demonstrated that carbon dioxide can be converted to methane on TiO₂ surface by a photocatalytic process. We show that such a photo-reduction can be significantly affected by the presence of an acidic proton in powder samples of titania. Using in situ absorption gas-phase rovibrational spectroscopic detection of CH₄, CO and CO₂, we demonstrate that proton enhancement positively affects transformation of intermediate derivatives to methane during the photo-irradiation process via several reactions in which the electron transfer inside titania is coupled to oxygen transfer to the Ti³⁺ centers of TiO₂ structure. The yield of CH₄ or CO depends on the surface conditioning of titania: the formation of CH₄ is boosted by a presence of adsorbed HCl, while the formation of CO is boosted by adsorbed H₂SO₄.     

CO2与气调保鲜

通过CO2在气调保鲜中的实际应用,说明CO2等气体在对蔬菜、水果、鱼肉类及其制品等的保鲜中的作用,并已越来越受到重视,同时强调CO2等气体质量对气调保鲜的重要性。     

二氧化碳制冷技术

CO2作为一种天然工质，是目前CFCs工质替代的一个重点研究方向。根据CO2作为制冷剂的相关热物理和化学性质及CO2制冷循环，说明采用CO2作制冷剂、采用跨临界循环的优越性。介绍CO2制冷循环系统关键设备——压缩机、膨胀机、气体冷却器／蒸发器的研究进展情况，并对采用CO2作制冷剂的汽车空调、热泵系统的应用进行综述，指出今后研究的发展方向。