Electrochemical and Molecular Assessment of Quinones as CO2-Binding Redox Molecules for Carbon Capture

The complexation and decomplexation of CO2 with a series of quinones of different basicity during electrochemical cycling in dimethylformamide solutions were studied systematically by cyclic voltammetry. In the absence of CO2, all quinones exhibited two well-separated reduction waves. For weakly complexing quinones, a positive shift in the second reduction wave was observed in the presence of CO2, corresponding to the dianion quinone-CO2 complex formation. The peak position and peak height of the first re-duction wave were unchanged, indicating no formation of complexes between the semiquinones and CO2. The relative heights of both reduction waves remained constant. In the case of strongly complexing quinones, the second reduction wave disappeared while the peak height of the first reduction wave approximately doubled, indicating that the two electrons transferred simultaneously at this potential. The observed voltammograms were rationalized through several equilibrium arguments. Both weakly and strongly complexing quinones underwent either stepwise or concerted mechanisms of oxidation and CO2 dissociation depending on the sweep rate in the cyclic voltammetric experiments. Relative to stepwise oxidation, the concerted process requires a more positive electrode potential to remove the electron from the carbonate complexes to release CO2 and regenerate the quinone. For weakly complexing quinones, the stepwise process corresponds to oxidation of the uncomplexed dianion and accompanying equilibrium shift, while for strongly complexing quinones the stepwise process would correspond to the oxidation of mono(carbonate) dianion to the complexed semiquinone and accompanying equilibrium shift. This study provides a mechanistic interpretation of the interactions that lead to the formation of quinone-CO2 complexes required for the potential development of an energy efficient electrochemical separation process and discusses important considerations for practical implementation of CO2 capture in the presence of oxygen with lower vapor pressure solvents.

Linking diffuse radiation and ecosystem productivity of a desert steppe ecosystem

Radiation components have distinct effects on photosynthesis. In the desert steppe ecosystem, the influence of diffuse radiation on carbon fixation has not been thoroughly explored. We examined this diffusion and its effect on ecosystem productivity was examined during the growing season from 2014 to 2015 on the basis of eddy covariance measurements of CO2 exchange in a desert steppe ecosystem in northwest China. Our results indicated that the gross ecosystem production (GEP) and diffuse photosynthetically active radiation (PARdif) peaked when the clearness index (CI) was around 0.5. The maximum canopy photosynthesis (Pmax) under cloudy skies (CI < 0.7) was 23.7% greater than under clear skies (CI ≥ 0.7). When the skies became cloudy in the desert steppe ecosystem, PARdif had a greater effect on GEP. Additionally, lower vapor pressure deficits (VPD ≤ 1 kPa), lower air temperatures (Ta ≤ 20 °C), and non-stressed water conditions (REW ≥ 0.4) were more conducive for enhanced ecosystem photosynthesis under cloudy skies than under clear skies. This may be due to the comprehensive effects of VPD and Ta on stomatal conductance. We concluded that cloudiness can influence diffuse radiation components and that diffuse radiation can increase the ecosystem production of desert steppe ecosystems in northwest China.

Frost-free zone on macrotextured surfaces

Numerous studies have focused on designing functional surfaces that delay frost formation or reduce ice adhesion. However, solutions to the scientific challenges of developing antiicing surfaces remain elusive because of degradation such as mechanical wearing. Inspired by the discontinuous frost pattern on natural leaves, here we report findings on the condensation frosting process on surfaces with serrated structures on the millimeter scale, which is distinct from that on a conventional planar surface with microscale/nanoscale textures. Dropwise condensation, during the first stage of frosting, is enhanced on the peaks and suppressed in the valleys, causing frost to initiate from the peaks, regardless of surface chemistry. The condensed droplets in the valley are then evaporated due to the lower vapor pressure of ice compared with water, resulting in a frost-free zone in the valley, which resists frost propagation even on superhydrophilic surfaces. The dependence of the frost-free areal fraction on the geometric parameters and the ambient conditions is elucidated by both numerical simulations based on steady-state diffusion and an analytical method with an understanding of boundary conditions independent of surface chemistry. We envision that this study would provide a unified framework to design surfaces that can spatially control frost formation, crystal growth, diffusion-controlled growth of biominerals, and material deposition over a broad range of applications.

Enhancement of Isobutanol and 3-Methyl-1-Butanol Production Yields in Saccharomyces Cerevisiae without Genetic Modification

Bio-based fuel produced from the renewable resources is efficiently overcome the shortcomings of fossil fuels. Several factors such as the increasing awareness on environmental problems, fossil fuel prices and the sustainability of energy has encouraged the initiative in finding another source of transportation fuels. Higher alcohols have proved to be a better candidate to replace gasoline as vehicle fuel due to characteristics of higher energy content, low solubility in water, lower vapor pressure and higher blending ability with gasoline. Biologically, isobutanol and 3-methyl-1-butanol are produced through the fermentation of renewable feedstock with microorganism. Saccharomyces cerevisiae is known to be able to produce isobutanol and 3-methyl-1-butanol titers naturally without heterologous pathways. However, the production of these alcohols by Saccharomyces cerevisiae is only in a small quantity, thus several efforts in enhancing the isobutanol and 3-methyl-1-butanol yields have been conducted. In this study, the amino acids (valine and leucine) and amino acid precursor (2-ketoisovalerate) were added into the fermentation medium prior to the fermentation. The results obtained show that the supplementation of 2-ketoisovalerate and leucine individually into the fermentation broth leads to the increased in isobutanol and 3-methyl-1-butanol titers by 3.3 folds and 1.9 folds, respectively. The combination of 2-ketoisovalerate and valine increased the isobutanol yield by 4.3 folds while the 3-methyl-1-butanol was increased by 2.5 folds when supplemented with 2-ketoisovalerate and leucine. These results portray that the isobutanol and 3-methyl-1-butanol titers can be improved by manipulating several factors which is important for future production of higher alcohols.

A comparison of spray and combustion characteristics of biodiesel (soy methyl ester, rapeseed methyl ester) with diesel

Physical properties are known to play a pivotal role in the different characteristics of spray, combustion, and emission between diesel and biodiesel. This paper reports the development and application of physical properties of diesel and biodiesel for fuel spray and combustion modeling under various conditions. An integrated numerical model has been developed based on the General Transport Equation Analysis code. The effect of turbulence in the nozzle was considered by the hybrid breakup model in the simulation, and the skeletal mechanism of diesel surrogate fuel and biodiesel surrogate fuel was used to simulate fuel oxidation. The results indicated that liquid lengths and droplet sizes are always higher for biodiesel because of its bigger surface tension and worse vaporization characteristics caused by higher critical temperature and lower vapor pressure. This phenomenon has strong influence on fuel evaporation process and results in slow evaporation rate, and this is not helpful for the mixture preparation process. The effects of ambient density, ambient temperature, and oxygen concentration on ignition delay and lift-off length of diesel and biodiesel are also analyzed and discussed. This analysis revealed that longer ignition delay usually results in longer lift-off length and biodiesel always has longer ignition delay and lift-off length compared to diesel. The flame propagation was observed to be similar for both fuels. In addition, diesel and biodiesel were employed to simulate the combustion and emission characteristics of a low-temperature combustion engine. The different combustion and NO x emission characteristics between diesel and biodiesel were observed, and the different physical properties may be the reason for these discrepancies.

Cloudiness regulates gross primary productivity of a poplar plantation under different environmental conditions

Cloud cover regulates the gross primary productivity (GPP) of forest ecosystems by changing the radiation component and other environmental factors. In this study, we used an open-path eddy covariance system and microclimate sensors installed over a poplar plantation in northern China to measure the carbon exchange and climate variables during the mid-growing seasons (June to August) in 2014 and 2015. The results indicated that the GPP of the plantation peaked when the clearness index (CI) was between 0.45 and 0.65, at which point diffuse photosynthetically active radiation (PARdif) had reached its maximum. Cloudy skies increased the maximum ecosystem photosynthetic capacity (Pmax) by 28% compared with clear skies. PARdif and soil moisture were the most and the least crucial drivers for photosynthetic productivity of the plantation under cloudy skies, respectively. The ecosystem photosynthetic potential was higher under lower vapor pressure deficit (VPD < 1.5 kPa), lower air temperature (Ta < 30 °C), and nonstressed conditions (REW > 0.4) for cloudy skies due to effects of Ta and VPD on stoma. Overall, our research highlighted the importance of cloud-induced radiation component change and environmental variation in quantifying the GPP of forest ecosystems.

A Remediation Study of Soils Contaminated by Chlorinated Hydrocarbons with Mechanical Soil Aeration

Mechanical soil aeration is an effective and low cost ex-situ remediation technique suitable for large areas of volatile organic contaminated sites. To understand the effectiveness of the remediation technique, the current study remediated an abandoned industry site for a typical chlor-alkali chemical using this technology. The results showed that the technology is effective in the remediation of volatile organic compounds with a pass percentage greater than 90%. The results also showed that a lower vapor pressure or higher molecular weight with the similar concentration of pollution resulted in higher residual concentrations, which need increasing agitation frequency or machine power to promote the volatilization of pollutants. In addition, we found that the more pollution or water or organic matters (more than 1%) contained, the higher concentration of residual. These type of soils should be remediated not only by physical agitations but also by other strengthen measures and long period. The present study aims to promote the remediation of contaminated sites, especially large areas contaminated by volatile contaminants.

Synthesis and Electrochemical Properties of Rechargeable Battery Electrolyte Lithium Bis(heptafluoroisopropyl)tetrafluorophosphate

Lithium-ion secondary cell has high energy density, stable and high working voltage, wide working temperature and long working term. It is a safe and clean energy resource without pollution. At present, Lithium Hexafluorophosphate is used as conducting electrolyte lithium salt in lithium-ion secondary batteries. But Lithium Hexafluorophosphate as conducting electrolyte lithium salt has some disadvantages such as hydrolysis and instability. Lithium Bis (heptafluoroisopropyl) t-etrafluorophosphate Li [(C3F7)2PF4] was received by simons process from diisopropylchlorophosphane in this paper. As electrolyte of Li ion secondary cell, Li [(C3F7)2PF4] had lower vapor pressure than LiPF6 in the solvent in the same temperature, comparable conductivity and oxidation stability in the same concentration in room temperature. It was worth mentioning that Li [(C3F7)2PF4] has excellent stability towards hydrolysis. The synthesis process is safe and easily controlled.

Electrochemical Characterization of Lithium Bis(heptafluoroisopropyl)tetrafluorophosphate with Properties of Chemical Materials

Lithium-ion secondary cell has high energy density, stable and high working voltage, wide working temperature and long working term. It is a safe and clean energy resource without pollution. At present, Lithium Hexafluorophosphate is used as conducting electrolyte lithium salt in lithium-ion secondary batteries. But Lithium Hexafluorophosphate as conducting electrolyte lithium salt has some disadvantages such as hydrolysis and instability. Lithium Bis (heptafluoroisopropyl) t-etrafluorophosphate Li [(C3F7)2PF4] was received by simons process from diisopropylchlorophosphane in this paper. As electrolyte of Li ion secondary cell, Li [(C3F7)2PF4] had lower vapor pressure than LiPF6 in the solvent in the same temperature, comparable conductivity and oxidation stability in the same concentration in room temperature. It was worth mentioning that Li [(C3F7)2PF4] has excellent stability towards hydrolysis. The synthesis process is safe and easily controlled.

Modeling SOA formation from the oxidation of intermediate volatility <i>n</i>-alkanes

The chemical mechanism leading to SOA formation and ageing is expected to be a multigenerational process, i.e. a successive formation of organic compounds with higher oxidation degree and lower vapor pressure. This process is here investigated with the explicit oxidation model GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere). Gas phase oxidation schemes are generated for the C8–C24 series of n-alkanes. Simulations are conducted to explore the time evolution of organic compounds and the behavior of secondary organic aerosol (SOA) formation for various preexisting organic aerosol concentration (COA). As expected, simulation results show that (i) SOA yield increases with the carbon chain length of the parent hydrocarbon, (ii) SOA yield decreases with decreasing COA, (iii) SOA production rates increase with increasing COA and (iv) the number of oxidation steps (i.e. generations) needed to describe SOA formation and evolution grows when COA decreases. The simulated oxidative trajectories are examined in a two dimensional space defined by the mean carbon oxidation state and the volatility. Most SOA contributors are not oxidized enough to be categorized as highly oxygenated organic aerosols (OOA) but reduced enough to be categorized as hydrocarbon like organic aerosols (HOA), suggesting that OOA may underestimate SOA. Results show that the model is unable to produce highly oxygenated aerosols (OOA) with large yields. The limitations of the model are discussed.