Gas-phase Concentrations Research Articles

Detection and identification of Criegee intermediates from the ozonolysis of biogenic and anthropogenic VOCs: comparison between experimental measurements and theoretical calculations.

Ozonolysis of alkenes is a key reaction in the atmosphere, playing an important role in determining the oxidising capacity of the atmosphere and acting as a source of compounds that can contribute to local photochemical “smog”. The reaction products of the initial step of alkene-ozonolysis are Criegee intermediates (CIs), which have for many decades eluded direct experimental detection because of their very short lifetime. We use an innovative experimental technique, stabilisation of CIs with spin traps and analysis with proton transfer reaction mass spectrometry, to measure the gas phase concentration of a series of CIs formed from the ozonolysis of a range of both biogenic and anthropogenic alkenes in flow tube experiments. Density functional theory (DFT) calculations were used to assess the stability of the CI-spin trap adducts and show that the reaction of the investigated CIs with the spin trap occurs very rapidly except for the large β-pinene CI. Our measurement method was used successfully to measure all the expected CIs, emphasising that this new technique is applicable to a wide range of CIs with different molecular structures that were previously unidentified experimentally. In addition, for the first time it was possible to study CIs simultaneously in an even more complex reaction system consisting of more than one olefinic precursor. Comparison between our new experimental measurements, calculations of stability of the CI-spin trap adducts and results from numerical modelling, using the master chemical mechanism (MCM), shows that our new method can be used for the quantification of CIs produced in situ in laboratory experiments.

Broad spectrum infrared thermal desorption of wipe-based explosive and narcotic samples for trace mass spectrometric detection.

Wipe collected analytes were thermally desorbed using broad spectrum near infrared heating for mass spectrometric detection. Employing a twin tube filament-based infrared emitter, rapid and efficiently powered thermal desorption and detection of nanogram levels of explosives and narcotics was demonstrated. The infrared thermal desorption (IRTD) platform developed here used multi-mode heating (direct radiation and secondary conduction from substrate and subsequent convection from air) and a temperature ramp to efficiently desorb analytes with vapor pressures across eight orders of magnitude. The wipe substrate experienced heating rates up to (85 ± 2) °C s-1 with a time constant of (3.9 ± 0.2) s for 100% power emission. The detection of trace analytes was also demonstrated from complex mixtures, including plastic-bonded explosives and exogenous narcotics, explosives, and metabolites from collected artificial latent fingerprints. Manipulation of the emission power and duration directly controlled the heating rate and maximum temperature, enabling differential thermal desorption and a level of upstream separation for enhanced specificity. Transitioning from 100% power and 5 s emission duration to 25% power and 30 s emission enabled an order of magnitude increase in the temporal separation (single seconds to tens of seconds) of the desorption of volatile and semi-volatile species within a collected fingerprint. This mode of operation reduced local gas-phase concentrations, reducing matrix effects experienced with high concentration mixtures. IRTD provides a unique platform for the desorption of trace analytes from wipe collections, an area of importance to the security sector, transportation agencies, and customs and border protection.

Organophosphate Ester Flame Retardants and Plasticizers in the Global Oceanic Atmosphere.

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers and have been detected ubiquitously in the remote atmosphere. Fourteen OPEs were analyzed in 115 aerosol phase samples collected from the tropical and subtropical Atlantic, Pacific, and Indian Oceans during the MALASPINA circumnavigation campaign. OPEs were detected in all samples with concentrations ranging from 360 to 4400 pg m-3 for the sum of compounds. No clear concentration trends were found between the Northern and Southern hemispheres. The pattern was generally dominated by tris(1-chloro-2-propyl) phosphate (TCPP), although tri-n-butyl phosphate (TnBP) had a predominant role in samples close to continents and in those influenced by air masses originating in continents. The dry deposition fluxes of aerosol phase ∑14OPE ranged from 4 to 140 ng m-2 d-1. An estimation of the OPE gas phase concentration and gross absorption fluxes by using three different sets of physical chemical properties suggested that the atmosphere-ocean diffusive exchange of OPEs could be 2-3 orders of magnitude larger than dry deposition. The associated organic phosphorus inputs coming from diffusive OPE fluxes were estimated to potentially trigger up to 1.0% of the reported primary production in the most oligotrophic oceanic regions. However, the uncertainty associated with these calculations is high and mostly driven by the uncertainty of the physical chemical properties of OPEs. Further constraints of the physical chemical properties and fluxes of OPEs are urgently needed, in order to estimate their environmental fate and relevance as a diffusive source of new organic phosphorus to the ocean.

Unexpectedly acidic nanoparticles formed in dimethylamine–ammonia–sulfuric-acid nucleation experiments at CLOUD

Abstract. New particle formation driven by acid–base chemistry was initiated in the CLOUD chamber at CERN by introducing atmospherically relevant levels of gas-phase sulfuric acid and dimethylamine (DMA). Ammonia was also present in the chamber as a gas-phase contaminant from earlier experiments. The composition of particles with volume median diameters (VMDs) as small as 10 nm was measured by the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Particulate ammonium-to-dimethylaminium ratios were higher than the gas-phase ammonia-to-DMA ratios, suggesting preferential uptake of ammonia over DMA for the collected 10–30 nm VMD particles. This behavior is not consistent with present nanoparticle physicochemical models, which predict a higher dimethylaminium fraction when NH3 and DMA are present at similar gas-phase concentrations. Despite the presence in the gas phase of at least 100 times higher base concentrations than sulfuric acid, the recently formed particles always had measured base : acid ratios lower than 1 : 1. The lowest base fractions were found in particles below 15 nm VMD, with a strong size-dependent composition gradient. The reasons for the very acidic composition remain uncertain, but a plausible explanation is that the particles did not reach thermodynamic equilibrium with respect to the bases due to rapid heterogeneous conversion of SO2 to sulfate. These results indicate that sulfuric acid does not require stabilization by ammonium or dimethylaminium as acid–base pairs in particles as small as 10 nm.

Predicting the gas-phase concentration of semi-volatile organic compounds from airborne particles: Application to a French nationwide survey

Semi-volatile organic compounds (SVOCs) partition indoors between the gas phase, airborne particles, settled dust, and other surfaces. Unknown concentrations of SVOCs in the gas phase (Cg) can be predicted from their measured concentrations in airborne particles. In previous studies, the prediction of Cg depended largely on choosing a specific equation for the calculation of the particle/gas partition coefficient. Moreover, the prediction of Cg is frequently performed at a reference temperature rather than the real indoor temperature. In this paper, a probabilistic approach based on Monte Carlo simulation was developed to predict the distribution of SVOCs' Cg from their concentrations in airborne particles at the target indoor temperature. Moreover, the distribution of the particle/gas partition coefficient of each SVOC at the target temperature was used. The approach was validated using two measured datasets in the literature: the predicted Cg from concentrations measured in airborne particles and the measured Cg were generally of the same order of magnitude. The distributions of the Cg of 66 SVOCs in the French housing stock were then predicted. The SVOCs with the highest median Cg, ranging from 1ng/m3 to >100ng/m3, included 8 phthalates (DEP, DiBP, DBP, DEHP, BBP, DMP, DiNP, and DMEP), 4 polycyclic aromatic hydrocarbons (fluorene, phenanthrene, fluoranthene, and anthracene), 2 alkylphenols (4-tert-butylphenol and 4-tert-octylphenol), 2 synthetic musks (galaxolide and tonalide), tributyl phosphate, and heptachlor. The nationwide, representative, predicted Cg values of SVOCs are frequently of the same order of magnitude in Europe and North America, whereas these Cg values in Chinese and Indian dwellings and the Cg of polybrominated diphenyl ethers in U.S. dwellings are generally higher.

Gas hydrate and free gas estimation from seismic analysis offshore Chiloé island (Chile)

In this study one seismic section offshore Chiloe Island was analyzed to better define the seismic character of the hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration and relate it to the geological features. The velocity model allowed us to recognize two important layers that characterize hydrate- and free gas-bearing sediments above and below the BSR respectively: one located above the BSR, characterized by high velocity (1,800-2,200 m/s) and a second one, below the BSR, characterized by low velocity (1,600-1,700 m/s). A weak reflector at about 100 m below the BSR marks the base of the second layer. AVO analysis and offset stack sections confirming that the reflector interpreted as BGR is related to free gas presence in the pore space. The velocity field is affected by lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the sector. Here, the highest gas hydrate and free gas concentrations were calculated, obtaining 9.5% and 0.5% of total volume respectively. A variable BSR depth (from 300 to 600 mbsf) can be justified supposing a variable geothermal gradient (from 25 to 45 °C/km).

Ambient Gas-Particle Partitioning of Tracers for Biogenic Oxidation.

Exchange of atmospheric organic compounds between gas and particle phases is important in the production and chemistry of particle-phase mass but is poorly understood due to a lack of simultaneous measurements in both phases of individual compounds. Measurements of particle- and gas-phase organic compounds are reported here for the southeastern United States and central Amazonia. Polyols formed from isoprene oxidation contribute 8% and 15% on average to particle-phase organic mass at these sites but are also observed to have substantial gas-phase concentrations contrary to many models that treat these compounds as nonvolatile. The results of the present study show that the gas-particle partitioning of approximately 100 known and newly observed oxidation products is not well explained by environmental factors (e.g., temperature). Compounds having high vapor pressures have higher particle fractions than expected from absorptive equilibrium partitioning models. These observations support the conclusion that many commonly measured biogenic oxidation products may be bound in low-volatility mass (e.g., accretion products, inorganic-organic adducts) that decomposes to individual compounds on analysis. However, the nature and extent of any such bonding remains uncertain. Similar conclusions are reach for both study locations, and average particle fractions for a given compound are consistent within ∼25% across measurement sites.

Kinetics and reaction pathways of total acid number reduction of cyclopentane carboxylic acid using subcritical methanol

Abstract Cyclopentane carboxylic acid (CPCA) is a model compound of Naphthenic acids (NAs). This objective of this paper is to discover total acid number (TAN) reduction kinetics and pathways of the reaction between CAPA and subcritical methanol (SubC-MeOH). The experiments were carried out in an autoclave reactor at temperatures of 180-220°C, a methanol partial pressure (MPP) of 3 MPa, reaction times of 0-30 min and CPCA initial gas phase concentrations of 0.016-0.04 g/mL. TAN content of the samples were analyzed using ASTM D 974 techniques. The reaction products were identified and quantified with the help of GC/MS and GC-FID respectively. Experimental results reveal that TAN removal kinetics followed first order kinetics with an activation energy of 13.97 kcal/mol and a pre-exponential factor of 174.21 s-1. Subcritical methanol is able to reduce TAN of CPCA decomposing CPCA into new compounds such as cyclopentane, formaldehyde, methyl acetate and 3-pentanol.

Diffusion of CO2 in Large Crystals of Cu-BTC MOF.

Carbon dioxide adsorption in metal-organic frameworks has been widely studied for applications in carbon capture and sequestration. A critical component that has been largely overlooked is the measurement of diffusion rates. This paper describes a new reproducible procedure to synthesize millimeter-scale Cu-BTC single crystals using concentrated reactants and an acetic acid modulator. Microscopic images, X-ray diffraction patterns, Brunauer-Emmett-Teller surface areas, and thermogravimetric analysis results all confirm the high quality of these Cu-BTC single crystals. The large crystal size aids in the accurate measurement of micropore diffusion coefficients. Concentration-swing frequency response performed at varying gas-phase concentrations gives diffusion coefficients that show very little dependence on the loading up to pressures of 0.1 bar. The measured micropore diffusion coefficient for CO2 in Cu-BTC is 1.7 × 10(-9) m(2)/s.

CFD Evaluation of In Situ Probe Techniques for Catalytic Honeycomb Monoliths

Collecting spatially resolved gas phase concentration profiles in catalytic monoliths by applying suction probe techniques has become an important tool for understanding the reaction sequence and for optimizing the design of structured catalysts. The impact of the capillary on the data is investigated by means of computational fluid dynamics (CFD) simulations using the exemplary cases of catalytic partial oxidation of methane over rhodium and oxidation of carbon monoxide over palladium. The influence of a suction probe inside a rectangular channel of a monolith on flow field and concentration profiles are discussed. Four different configurations were investigated: probe in center or corner of the channel with insertion from upstream or downstream in each case. If the capillary is located in the corner of the channel, the influence on the data is negligible. For a position in the center, a noticeable impact was observed. A simple analytical model can predict the reduction of the mass flux due to the insertion of the probe. The worst case exhibits a reduction >50 %. The measuring error is dependent on the direction of insertion of the capillary into the channel (upstream or downstream). Additionally, axial diffusion plays a significant role. For any interpretation of the data, the influence of the probe on the measured data has to be considered. The quantification of the error requires three-dimensional CFD simulations.

Multi-year air monitoring of legacy and current-use brominated flame retardants in an urban center in northeastern China

The occurrence and temporal trends of polybrominated diphenyl ethers (PBDEs) and non-PBDE brominated flame retardants (NBFRs) were investigated in an urban atmosphere of Northeast China in consecutive six years (2008–2013). Among all chemicals, BDE-209, l,2,5,6,9,10-hexabromocyclododecane (HBCD), and decabromodiphenylethane (DBDPE) were the three most dominant compounds. During the period, the levels of pentabromodiphenyl ethers in the gas-phase and octabromodiphenyl ethers in the particle-phase significantly decreased, while the levels of BDE-209 and NBFRs increased in either the gas-phase or particle-phase. Ambient temperature was the most significant variable that influenced the gas-phase and particle-phase concentrations of BFRs, followed by wind speed and relative humidity. A stronger temperature dependence of the atmospheric concentrations was found for lower mass BFRs. Gas-particle partitioning studies suggested PBDEs in the urban atmosphere of Northeast China were at steady-state. Steady-state equation can also well describe the partitioning behavior for NBFRs, suggesting that the atmospheric partitioning behaviors of NBFRs were similar to those of PBDEs.

Determination of Atmospheric PCB Level Variations in Continuously Collected Samples.

Polychlorinated biphenyls (PCBs) were measured in ambient air samples (n=48) that were collected for a 2- to 3-day period in each season (winter, spring, summer, fall) of 2013. The samples were collected on the Campus of Uludag University, which is in a semirural region. The samples were collected using a high-volume air sampler. The gas and particle phase concentrations of 87 PCB congeners (Σ87PCB) were measured in these samples. The average gas and particle phase concentrations of the Σ87PCB were calculated to be 293±257 and 52±56ng/m(3), respectively. However, the results of short-term measurements showed that the variation among the measurements in the gas phase was up to 39-fold and up to 84-fold in the particle phase. These results demonstrated that the ambient air PCB concentrations were not stable and changed dramatically on a daily basis. Therefore, it was clear that a small number of samples could not be representative of the entire region. Furthermore, the obtained concentrations showed differences that depended on the meteorological conditions and long distance transportation. The sampling indicated that PCB homologues with 3 or 4 chlorines were dominant.

CO2 quality control in Oxy-fuel technology for CCS: SO2 removal by the caustic scrubber in Callide Oxy-fuel Project

Flue gas from Oxy-fuel combustion is enriched with CO2 and SO2. SO2 has significant impacts throughout the system. This paper primarily focuses on the operation characteristics of caustic scrubber for the removal of SO2 in Callide Oxy-fuel Project.Both gas and liquid sampling and analysis were carried out for the caustic scrubber which comprises two spray columns, the initial Quencher followed by the low pressure (LP) scrubber. Dynamic changes of gas and liquid species in two scrubbers have been obtained and several conclusions can be drawn.From gas analysis, it can be concluded that the Quencher had high capture efficiencies for SO2 (97%) and NO2 (77%), and low capture efficiencies for NO (32%). The Quencher captured most of the SO2 and NO2; the LP scrubber captured a limited amount of SO2 (1%) and NO2 (4%). Therefore, the LP scrubber is not a necessary component for capturing SO2.Liquid analysis gave consistent results with gas analysis in that the Quencher (0.011–0.037M) contained a 100 times higher concentration of Total S than that (0.0001–0.0006M) in the LP scrubber. The Total S existed in the form of S(IV) and S(VI) in the Quencher, and only in the form of S(VI) in the LP scrubber. The S(VI) ratio of 11% in the Quencher agreed with the reported 2–15% oxidation.SO2 concentration in gas phase can be correlated well with Total S in liquid, but not the effective ratio of Na+. Mass balance between gas and liquid Total S can be achieved.The long term storage of liquid samples is accompanied by pH changes and desorption of CO2 with exposure to the atmosphere. The final pH depends on the presence of HCO3−. In the presence of HCO3− in liquids, the final pH is around 8; in the absence of HCO3−, the final pH is around 4. The increase in pH to 8 is explained by desorption of CO2. The amount of CO2 desorbed is around 0.0614% of the amount of CO2 in the CPU.

Temperature dependence of the particle/gas partition coefficient: An application to predict indoor gas-phase concentrations of semi-volatile organic compounds

The indoor gas-phase concentrations of semi-volatile organic compounds (SVOCs) can be predicted from their respective concentrations in airborne particles by applying the particle/gas partitioning equilibrium. The temperature used for partitioning is often set to 25°C. However, indoor temperatures frequently differ from this reference value. This assumption may result in errors in the predicted equilibrium gas-phase SVOC concentrations. To improve the prediction model, the temperature dependence of the particle/gas partition coefficient must be addressed. In this paper, a theoretical relationship between the particle/gas partition coefficient and temperature was developed based on the SVOC absorptive mechanism. The SVOC particle/gas partition coefficients predicted by employing the derived theoretical relationship agree well with the experimental data retrieved from the literature (R>0.93). The influence of temperature on the equilibrium gas-phase SVOC concentration was quantified by a dimensionless analysis of the derived relationship between the SVOC particle/gas partition coefficient and temperature. The predicted equilibrium gas-phase SVOC concentration decreased by between 31% and 53% when the temperature was lowered by 6°C, while it increased by up to 750% when the indoor temperature increased from 15°C to 30°C.

Transdermal Detection of Low Concentrations of Hydrogen Sulfide

We report here a novel approach to measure circulating hydrogen sulfide (H2S) non‐invasively as a potential way to diagnose and monitor endothelial dysfunction and peripheral artery disease (PAD). PAD is a life‐threatening condition caused by arterial constriction and obstruction of blood flow leading to limb ischemia. Current methods to diagnose and monitor PAD lack sensitivity, result in frequent false‐negatives, and require specialized technicians. Recent studies indicate that decreased H2S production is an underlying cause of PAD. In addition, reduced plasma H2S correlates with endothelial dysfunction in untreated hypertension, diabetes, sleep apnea and other cardiovascular diseases. Conversely, excess H2S is cytotoxic causing irreversible damage to mitochondrial function. Therefore, careful monitoring of plasma H2S levels is essential to diagnose and treat vascular disease and to prevent H2S toxicity. This device was designed to measure H2S at the surface of the skin to test the hypothesis that the diffusion rate (and therefore gas phase concentration) of H2S is directly proportional to the concentration of H2S in the blood. Our results demonstrate that the device is sensitive enough to detect H2S at 10 part per billion (ppb) or lower in gas standards and in the headspace of a 3 nM solution of Na2S (H2S donor). In vitro studies used excised rat skin superfused on the subcutaneous surface with a H2S solution. H2S was detected in a stream of N2 gas flowing through a sealed chamber on the epidermal side both by GC/MS measurement and with the sensor only when the superfusing solution contained an H2S donor demonstrating that H2S diffuses through the skin. The diffusion rate of H2S through excised abdominal skin from a male Sprague‐Dawley rat is approximately 1.42×10−9 μmol/s/cm2/μM. The device also detected increases in H2S on the skin surface in anesthetized rats within seconds of intra‐venous injection of Na2S at doses that caused a fall in arterial pressure, with an estimated average diffusion rate of 4×10−8 μmol/s/cm2/μM. Therefore, this noninvasive, highly‐sensitive and portable device has the potential to transform diagnosis and monitoring of early stage PAD and to monitor H2S biosynthesis or exposure in vivo.

Kinetics of Hg° oxidation over a V2O5/MoO3/TiO2 catalyst: Experimental and modelling study under DeNOX inactive conditions

In this work, a kinetic study of mercury oxidation over a commercial plate-type V/Mo/Ti/O catalyst was addressed by investigating the effects of key operating variables (temperature, HCl and Hg° concentration). The study was performed under reference DeNOX-inactive conditions, that is in the absence of NOX, NH3, SOX, recognizing that surface coverage effects can greatly affect the kinetics of this complex reacting system. Aim of the work was in fact to better clarify the nature of the intrinsic reaction (in particular its temperature dependence), that, despite the increasing interest toward this reaction, is still debated with a very large scatter among observations. The experiments were performed over slabs. The combined effects of temperature and HCl concentration evidenced that the conversion of Hg° was independent from the HCl content below 300–325°C, where the reaction showed a positive temperature dependence; at higher temperature, the conversion of Hg° became highly sensitive to the HCl concentration, which determined the observed temperature dependence (negative at 2.5ppm HCl, positive at 50ppm HCl). Thus the data suggest a strong dependence of the reaction kinetics on the surface coverage of HCl.A model of the reactor cell was developed and an engineering analysis of data was performed to decouple the effects of inter-phase and intra-porous mass transfer limitations. A rate expression was derived from the formalization of a redox reaction scheme wherein a step-wise oxy-chlorination process (Hg°→HgClads→HgCl2) is assumed in line with recent theoretical findings. By assuming that the surface coverages of the HgCl intermediate and the reduced sites are negligible with respect to the coverage of free and chlorinated oxidized sites, a simple rate expression is derived which accounts for a quadratic dependence on HCl coverage and a linear dependence on the gas-phase concentration of elemental mercury (in line with the experimental evidence). The whole bulk of data could be well described, capturing the key observed trends. The activation energy of the reaction steps was found to be 14000cal/mole while the enthalpy of HCl activation was estimated at −20000cal/mole, coherently with the energetics of V-sites chlorination.

Direct and Sensitive Detection of CWA Simulants by Active Capillary Plasma Ionization Coupled to a Handheld Ion Trap Mass Spectrometer.

An active capillary plasma ionization (ACI) source was coupled to a handheld mass spectrometer (Mini 10.5; Aston Labs, West Lafayette, IN, USA) and applied to the direct gas-phase detection and quantification of chemical warfare agent (CWA) related chemicals. Complementing the discontinuous atmospheric pressure interface (DAPI) of the Mini 10.5 mass spectrometer with an additional membrane pump, a quasi-continuous sample introduction through the ACI source was achieved. Nerve agent simulants (three dialkyl alkylphosphonates, a dialkyl phosporamidate, and the pesticide dichlorvos) were detected at low gas-phase concentrations with limits of detection ranging from 1.0μg/m(3) to 6.3μg/m(3). Our results demonstrate a sensitivity enhancement for portable MS-instrumentation by using an ACI source, enabling direct, quantitative measurements of volatile organic compounds. Due to its high sensitivity, selectivity, low power consumption (<80W) and weight (<13kg), this instrumentation has the potential for direct on-site CWA detection as required by military or civil protection. Graphical Abstract ᅟ.

Removal of CO2 from Biogas by Using Tert-Butyl Peroxy-2-ethylhexanoate and Water

In this work, the effects of tert-butyl peroxy-2-ethylhexanoate (TBPO) and the operating conditions on the separation of CO2 from a CO2/CH4 (67.0 mol %) gas mixture based on hydrate formation have been studied through experiments. The results showed that CO2 separation was effectively achieved by adding TBPO to aqua-solutions. The content of methane in the residual gas hiked when the gas/liquid volume ratio decreased. Methane concentration in the residual gas phase was increased from 67.0% to 89.6%, obtained when the initial gas/liquid volume ratio was 2.23 by one-stage hydrate separation with 26.0 wt % TBPO at 287 K and 2 MPa. The CH4 recovery was 0.91, and the CO2 separation factor was 17.01 by adding 5.0 wt % TBPO. Through the use of a hand pump to keep pressure constant for the residual gas in the vessel to form hydrates, CH4 concentration in the residual gas phase increased to as high as 93.3%.

Gas–liquid equilibrium data for mixture gas of carbon dioxide + nitrogen in 1,2-ethanediamine + triethylene glycol aqueous solution

ABSTRACTIsothermal gas–liquid equilibrium (GLE) data were measured for the system of 1,2-ethanediamine (EDA) + triethylene glycol (TEG) + H2O + carbon dioxide (CO2) + N2 at T = 293.15, 298.15, 303.15 and 308.15 K and p = 121.74, 126.94 and 129.87 kPa with CO2 partial pressure ranging from 0 to 13.0 kPa. Measurements were carried out using a saturation method in a glass absorption apparatus, which was controlled at the constant temperature by a thermostatic circulation bath with a Beckmann thermometer. The measurement uncertainties for temperature, total pressure, CO2 concentration in the gas phase and CO2 concentration in the liquid phase were less than ±0.02 K, ±0.15 kPa, ±2.5% and ±0.6, respectively. The results indicate that the addition of TEG into the aqueous EDA solution could significantly improve the stability of EDA in CO2 absorption process, thus enhancing the performance of aqueous amine-based CO2 scrubbing.

Generalized Mechanistic Model for the Chemical Vapor Deposition of 2D Transition Metal Dichalcogenide Monolayers.

Transition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are layered materials capable of growth to one monolayer thickness via chemical vapor deposition (CVD). Such CVD methods, while powerful, are notoriously difficult to extend across different reactor types and conditions, with subtle variations often confounding reproducibility, particularly for 2D TMD growth. In this work, we formulate the first generalized TMD synthetic theory by constructing a thermodynamic and kinetic growth mechanism linked to CVD reactor parameters that is predictive of specific geometric shape, size, and aspect ratio from triangular to hexagonal growth, depending on specific CVD reactor conditions. We validate our model using experimental data from Wang et al. (Chem. Mater. 2014, 26, 6371-6379) that demonstrate the systemic evolution of MoS2 morphology down the length of a flow CVD reactor where variations in gas phase concentrations can be accurately estimated using a transport model (CSulfur = 9-965 μmol/m(3); CMoO3 = 15-16 mmol/m(3)) under otherwise isothermal conditions (700 °C). A stochastic model which utilizes a site-dependent activation energy barrier based on the intrinsic TMD bond energies and a series of Evans-Polanyi relations leads to remarkable, quantitative agreement with both shape and size evolution along the reactor. The model is shown to extend to the growth of WS2 at 800 °C and MoS2 under varied process conditions. Finally, a simplified theory is developed to translate the model into a "kinetic phase diagram" of the growth process. The predictive capability of this model and its extension to other TMD systems promise to significantly increase the controlled synthesis of such materials.