Nonpolar Gases Research Articles

A Rapid Method for the determination of Dehydrated alcohol (Ethanol) content in Clobetasol propionate foam by Non-polar Capillary Gas chromatography

Clobeatsol propionate foam is a topical class 1 corticosteroid used to treat itching and inflammatory arthritis on the skin occurred by allergic reactions, psoriasis and eczema. In the pharmaceutical aerosol products, Dehydrated alcohol (Ethanol) is the primary ingredient and its concentration level in the formulation composition plays a significant role in the regulation of aerosol rate, droplet shape and particle size. It can also act as solubilizer for active pharmaceutical ingredient, topical disinfectant and skin permeation enhancer. Hence accurate assay of Ethanol is a crucial quality control component. A simple and rapid gas chromatography method was developed to quantify Ethanol content in Clobetasol propionate foam drug product using fused silica glass tube non-polar capillary column (HP-5, 30 m, 0.53 mm, 1.5 µm). Ethanol in the sample was diluted with methanol after adding suitable amount of internal standard, the isopropyl alcohol solution.The developed method is precise, linear and accurate in the range of 5 mg/mL to 15 mg/mL of nominal concentration of ethanol i.e. 10 mg/mL . The presented method has an advantage of a very quick gas chromatographic separation (less than 16 min) and therefore is highly suitable for in-process and stability analysis of Ethanol content in Clobetasol propionate foam drug product.

A Database of Experimentally Derived and Estimated Octanol–Air Partition Ratios (KOA)

Equilibrium partition coefficients or partition ratios are a fundamental concept in physical chemistry, with wide applications in environmental chemistry. While comprehensive data compilations for the octanol–water partition ratio and the Henry’s law constant have existed for many years, no comparable effort for the octanol–air partition ratio (KOA) exists. Considering the increasing use of KOA in understanding a chemical’s partitioning between a wide variety of organic phases (organic phases in atmospheric particles, plant foliage, polymeric sorbents, soil organic matter, animal tissues, etc.) and the gas phase, we have compiled all KOA values reported in the published literature. The dataset includes more than 2500 experimentally derived values and more than 10 000 estimated values for KOA, in total covering over 1500 distinct molecules. The range of measured log10 KOA values extends from −2 to 13. Many more measured values have been reported in the log10 KOA range from 2 to 5 and from 6 to 11 compared to the range from 5 to 6, which is due to the complementary applicability range of static and dynamic measurement techniques. The compilation also identifies measured data that are judged not reliable. KOA values for substances capable of undergoing strong hydrogen bonding derived from regressions with retention times on nonpolar gas chromatographic columns deviate strongly from values estimated by prediction techniques that account for such intermolecular interactions and should be considered suspect. It is hoped that the database will serve as a source for locating existing KOA data and for the calibration and evaluation of new KOA prediction techniques.

Ag/AgCl as an efficient plasmonic photocatalyst for greenhouse gaseous methane oxidation

In this work, quasi-cube Ag/AgCl plasmonic photocatalyst was synthesized by a simple co-precipitation method and in situ photo-reduction process. The synthesized Ag/AgCl shows high efficiency and good stability in the complete oxidation of nonpolar greenhouse gas methane under the simulated sunlight irradiation. Systematic experiments and finite-difference time-domain (FDTD) simulated calculations were employed to explore the reasons for the appreciable performance improvement, and results showed that the surface plasmonic resonance (SPR) effect of Ag nanoparticles can generate strong electric field which would induce the polarization of methane molecules, hence enhancing the adsorption of methane. This work provides a new idea for exploration of other plasmonic photocatalysts in the field of nonpolar gaseous molecules photo-oxidation.

Functionalized Imidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids for Gas Sensors: Solubility of H2, O2 and SO2

Gas solubilities of non-polar (hydrogen and oxygen) and polar (sulphur dioxide) gases in a set of functionalized alkyl imidazolium ionic liquids with the bis(trifluoromethylsulfonyl)imide ([NTFf2]−) anion are reported between 303 and 333 K at 1 bar. The alkyl side-chains in the imidazolium cations include different functional groups, such as –OH, –CN and benzyl; their effects on gas solubilities were studied. The solubility decreases with temperature for all gases, as expected for an exothermic dissolution. Sulphur dioxide is by far the most soluble gas, with mole fractions between 0.29 and 0.41 in the ionic liquids at 313 K and 1 bar, approximately 2–3 orders of magnitude higher than the two other gases studied. Oxygen is generally more soluble in the ionic liquids than hydrogen with mole fractions ranging from 9 × 10−4 to 21 × 10−4 and 5 × 10−4 to 15 × 10−4 at 313 K and 1 bar for oxygen and hydrogen, respectively. In the case of hydrogen, the solubility increases when the molar volume of the ionic liquid increases, whereas for oxygen, the presence of polar groups in the cation causes a reduction in the solubility. None of the three gases is chemically absorbed in the ionic liquids.

Comparison of Automated Extraction Techniques for Volatile Analysis of Whole Milk Powder.

Volatile profiling of whole milk powder is valuable for obtaining information on product quality, adulteration, legislation, shelf life, and aroma. For routine analysis, automated solventless volatile extraction techniques are favored due their simplicity and versatility, however no single extraction technique can provide a complete volatile profile due to inherent chemical bias. This study was undertaken to compare and contrast the performance of headspace solid phase microextraction, thermal desorption, and HiSorb (a sorptive extraction technique in both headspace and direct immersion modes) for the volatile analysis of whole milk powder by gas chromatography mass spectrometry. Overall, 85 unique volatiles were recovered and identified, with 80 extracted and identified using a non-polar gas chromatography column, compared to 54 extracted, and identified using a polar gas chromatography column. The impact of salting out was minimal in comparison to gas chromatography column polarity and the differences between the extraction techniques. HiSorb extracted the most and greatest abundance of volatiles, but was heavily influenced by the number and volume of lactones extracted in comparison to the other techniques. HiSorb extracted significantly more volatiles by direct immersion than by headspace. The differences in volatile selectivity was evident between the techniques and highlights the importance of using multiple extraction techniques in order to obtain a more complete volatile profile. This study provides valuable information on the volatile composition of whole milk powder and on differences between extraction techniques under different conditions, which can be extrapolated to other food and beverages.

A metal-organic framework for C2H2/CO2 separation under highly humid conditions: Balanced hydrophilicity/hydrophobicity

Metal-organic frameworks (MOFs) intended for C2H2/CO2 separation should possess high C2H2/CO2 adsorption selectivity and large C2H2 adsorption capacity. Here we report the scalable synthesis of a cage-interconnected microporous MOF (JNU-2). Dynamic column breakthrough experiments on JNU-2 manifest a C2H2-capture capacity of 3.08 mmol g−1 for an equimolar C2H2/CO2 mixture at 298 K and 1 bar, exceeding the benchmark materials such as UTSA-74a and FeNi-M’MOF. Meanwhile, the selectivity factor was estimated to be ca. 1.5 for JNU-2 and consistent with the increasing flow rate. Theoretical calculations confirm that the surface of the JNU-2 framework enables preferential binding of C2H2 over CO2via multiple C–H···O, C–H···N, and π-complexation interactions. More importantly, JNU-2 retains its C2H2/CO2 separation capacity under highly humid conditions. Although the equilibrium adsorption of H2O is much higher than those of C2H2 and CO2, kinetic studies reveal that the diffusion of C2H2 and CO2 in JNU-2 is more than two orders of magnitude faster than that of H2O. A balanced hydrophobicity/hydrophilicity of the MOF framework surface might be the key to achieving large adsorption capacity for nonpolar gas molecule while minimizing the competition of water vapor adsorption.

An equation of state based on the intermolecular potential and the radial distribution function to estimate the virial coefficients by using PvT chaotic data

We derive a new equation of state (EOS) for any non-polar, polar or quantum gas and any intermolecular potential through an approximation of the radial distribution function based on the Ornstein-Zernike equation. Such EOS is applied to estimate the virial coefficients B and C using two approaches. On one hand, B and C are directly computed from the proposed EOS considering the Mie potential for neon and water steam, which leads to values in very good agreement with the experimental data. On the other hand, the proposed EOS is applied in the context of a thermodynamic model to estimate B and C by fitting the simulated chaotic PvT data at an almost constant temperature. Such estimations of B and C are compared with the experimental values, which allows elucidating if B and C have a significant contribution on the virial equation at the considered pressures and temperatures. This methodology is applied to nitrogen and helium4 considering the intermolecular potentials of Mie, Morse, Kihara and Buckingham. For the considered gases and intermolecular potentials, the calculated values of B and C are in very good agreement with experimental data in a wide range of pressures and temperatures.

Betaboltz: A Monte-Carlo simulation tool for gas scattering processes

We present an open-source code for the simulation of electron and ion transport for user-defined gas mixtures with static uniform electric and magnetic fields. The program provides microscopic interaction simulation and is interfaced with cross-section tables published by LXCat[1]. The framework was validated against drift velocity tables available in literature obtaining an acceptable match for atomic and non-polar molecular gases with spherical symmetry. The code is written in C++17 and is available as a shared library for easy integration into other simulation applications. Program summaryProgram Title: BetaboltzCPC Library link to program files:https://doi.org/10.17632/hjhx8bj45c.1Licensing provisions: LGPL v3Programming language: C++17Nature of problem: Simulations of electron and ion transport in arbitrary gas mixture under static uniform electric and magnetic fields.Solution method: Particle motion using classical and relativistic equation via interaction sampling using Monte-Carlo techniques.Additional comments including restrictions and unusual features: At the time of writing only static uniform electromagnetic fields are supported. However, the implementation of arbitrary fields can be added given an analytical solution is available. A custom XML format for cross-section was developed, because full compatibility with LXCat [1] XML format was not possible. Cross-section databases in the new format are available in the download section of the LXCat site [2].

Two-Dimensional Nanomaterials for Wearable Breath Sensors

There has been considerable effort to develop wearable electronics from life-supporting devices for solders to fashion accessories such as smartwatches. The research of gas sensor has also attempted to adapt wearables with the power of nanotechnology. On the wearable platform, miniature gas sensors will provide real-time information about the atmosphere to protect each personnel from possible hazardous chemical attacks. In addition, wearable gas sensor can be facilitated to monitor human’s breath as medical applications. [1] One of the important factors to develop wearable gas sensors is to operate at room temperature with excellent sensing performance. Recently, two-dimensional (2D) nanostructured materials have been highlighted as new sensing materials due to their working ability at low temperatures. Unlike conventional metal oxides, 2D materials such as graphene are able to work at room temperature with comparable gas response to NO2 gas. However, insufficient sensing performance, such as sluggish recovery and low gas response, need to be developed. [2] As one attempt to enhance performance, 2D material was hybridized with metal oxide. By incorporating two nanostructured materials, synergistic effect, which comes from benefits of each material, can improve sensing performance. [3] Another novel innovation is the introduction of newly discovered 2D materials. 2D transition metal carbides and/or carbonitrides (called MXenes) are a new family of 2D materials. The vast diversity in a combination of constituent elements and ordered structure in MXenes offers future possibilities to find out a new generation of sensing materials with their superior performance. [4, 5]In this study, different types of 2D nanostructured materials and their hybrids were investigated for the breath analysis of various volatile compounds. Graphene oxide (GO) was incorporated with TiO2 nanoparticles, and the composite was photo-reduced under UV irradiation. Room temperature gas sensing was carried out against various VOC gases, and sensing performance was evaluated by comparing with pure GO. With the tailored hetero-junction at the interfaces of GO and TiO2, the composite can identify ethanol, methanol, and acetone, and its gas response was enhanced. In addition, we introduced new 2D nanostructured materials, MXenes including Ti3C2Tx and V2CTx. 2D V2CTx gas sensors showed excellent gas-sensing performance in terms of high response toward non-polar gases. Compared to the sensing properties of Ti3C2Tx MXene, 2D V2CTx sensor showed higher selectivity and long-term stability. The comparative results suggest that the modification of ordered structure and constituent elements of MXenes play a pivot role in the interaction between analyte and MXenes leading to an extensive change designed to detect individual compounds. [5, 6]References[1] Patel, S., Park, H., Bonato, P., Chan, L., & Rodgers, M. (2012). A review of wearable sensors and systems with application in rehabilitation. Journal of Neuroengineering and Rehabilitation, 9(1), 21.[2] Choi, S. J., & Kim, I. D. (2018). Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electronic Materials Letters, 1-40.[3] Meng, F. L., Guo, Z., & Huang, X. J. (2015). Graphene-based hybrids for chemiresistive gas sensors. TrAC Trends in Analytical Chemistry, 68, 37-47.[4] Yu, X. F., Li, Y. C., Cheng, J. B., Liu, Z. B., Li, Q. Z., Li, W. Z., ... & Xiao, B. (2015). Monolayer Ti2CO2: a promising candidate for NH3 sensor or capturer with high sensitivity and selectivity. ACS Applied Materials & Interfaces, 7(24), 13707-13713.[5] Lee, E., VahidMohammadi, A., Prorok, B. C., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2017). Room Temperature Gas Sensing of Two-Dimensional Titanium Carbide (MXene). ACS Applied Materials & Interfaces, 9(42), 37184-37190.[6] Lee, E., VahidMohammadi, A., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2019). Two-Dimensional Vanadium Carbide MXene for Gas Sensors with Ultrahigh Sensitivity Toward Nonpolar Gases. ACS Sensors, 4, 1603-1611.

Competitive and Synergistic Adsorption of Mixtures of Polar and Nonpolar Gases in Carbonaceous Nanopores.

Most adsorption applications involve mixtures, yet accurate predictions of the adsorption of mixtures remain challenging, in part due to the inability to account for the interplay between adsorbate-adsorbate and adsorbate-adsorbent interactions. This study involves a comprehensive Monte Carlo simulation of the adsorption of two groups of mixtures (namely, supercritical and subcritical ones) in carbon nanopores and quantifies Henry's constants, isotherms, energetics, and density distributions in the pores. When interadsorbate interactions are negligible (e.g., in supercritical mixtures such as mixtures of nonpolar gases), adsorbates behave like ideal gases and the adsorption isotherm can be predicted with the ideal adsorbed solution theory (IAST). However, when interadsorbate interactions become significant, IAST fails. This study reveals that (1) in mixtures of polar and nonpolar gases, the stronger intermolecular interaction for the polar constituent leads to synergistic adsorption that causes the nonpolar adsorbate to desorb and (2) for mixtures of polar gases, such as ethanol and water, the adsorbate-adsorbate interactions are so dominant that the unfavorable adsorbate-adsorbent interactions are overcome, such that water adsorbs onto the hydrophobic adsorbent. The competitive and synergistic interactions highlighted here are expected to be valuable in enhancing gas separations.

Crystallite structure of Palm shell Activated Carbon/MgO and Its Influence on Carbon Monoxide and Carbon Dioxide Adsorption

Gas emission of the motor vehicle is a major contributor to climate change, with a total of 14% emission annually, and the best potential option for reducing pollution is using the adsorption method. Magnesium oxide (MgO) has been proven as an effective adsorbent for liquid and gases. The impregnation of MgO on porous structure increases the affinity toward nonpolar gases, which is one of the purposes of this study. The crystallite structure is also a key factor that determines the adsorption capacity of activated carbon (AC). However, deeper analysis is needed in the activated carbon crystallite structure represented by d002 (aromatic layer), Lc (crystallite height), and La (crystallite diameter) on the adsorption of motor vehicle gas emissions. Three types of palm shell-based activated carbon were tested in this experiment. The results showed that activated carbon made using the two-step method and the AC/MgO produced surface structure with a d002 value of 0.33 nm and 0.32 nm, respectively. The impregnation of MgO on AC showed changes in surface structure and affected its crystallinity. The ability to adsorb CO2 and CO by AC/MgO increase up to 80% and 88%, respectively.

Revisiting the extraction and dehydration of ethanol by the hot propane process

Conventional liquid extraction is not a suitable separation method for the recovery and dehydration of ethanol and other light alcohols from aqueous solutions. Condensed non-polar gases like propane and CO2 looked promising as potential solvents. The favorable effect of temperature on the alcohol distribution coefficient of condensed propane led to the development of the hot propane process (HPP) for extraction and dehydration of alcohols. The dehydration of the alcohols took place in the solvent recovery column, thanks to the water entrainment effect of propane. Earlier pilot plant studies confirmed the process feasibility. In the present work, we design mixtures of propane + CO2 and phase conditions that fulfill the key properties of the HPP: (1) good alcohol distribution coefficient in the high-pressure extractor and (2) adequate water entrainment effect in the solvent recovery column.

Effect of 2-MeIM/Zn Molar Ratio on CO2 Permeability of Pebax/ZIF-8 Mixed Matrix Membranes

The impact of controlling molar ratio of ZIF-8 precursors on Pebax 1657 and Pebax 2533 based Mixed Matrix Membranes (MMMs) on the CO2 permeability and CO2 /N2 ideal selectivity was investigated. Three types of ZIF-8 were synthesized by controlling molar ratio of 2-methylimidazole and zinc nitrate hexahydrate as 2/1, 8/1, and 32/1. The SEM images and XRD patterns of ZIF-8 showed that particle sizes and crystallinity peaks were decreased as molar ratio of ZIF-8 increased. The CO2 permeability of Pebax MMM was improved by filling with the ZIF-8 particles compared to the pure Pebax. At equivalent temperatures, the highest CO2 permeability was shown in Pebax 1657/ZIF-8 with the ZIF8 precursors’ molar ratio of 32/1 and Pebax 2533/ZIF-8 with the molar ratio of 2/1. As molar ratio of ZIF-8 precursors increases, CO2 permeability of Pebax 1657 was increased by excessive sorption of CO2 by imidazolium ions in ZIF-8, whereas CO2 permeability of Pebax 2533 was decreased by decreasing pore size and particle size of ZIF-8. The CO2 permeability was higher in Pebax 2533/ZIF-8 compared to Pebax 1657/ZIF-8, because Pebax 2533 has more concentrations of polar groups in the polymer matrix than Pebax 1657. However, the CO2 /N2 ideal selectivity was higher in Pebax 1657/ZIF-8 compared to Pebax 2533/ZIF-8 because diffusivity of Pebax 1657 compared to Pebax 2533 is lower for nonpolar gases, such as N2 , and the solubility is higher for polarizable gases like CO2 . As increasing temperature, Pebax/ZIF-8 MMMs showed enhancement of CO2 and N2 permeability but decreased in CO2 /N2 ideal selectivity.

Artificial neural network modelling for solubility of carbon dioxide in various aqueous solutions from pure water to brine

Predicting the solubility of CO2 in various aqueous solutions, such as pure water, brackish water, saline water and brine, has become increasingly important because of the interdisciplinary significance of carbon dioxide solubilization, particularly in the energy and environmental fields. Despite experimental difficulties, the solubility of CO2 in various aqueous solutions of single and multi-salt was measured under limited conditions for specific purposes. In this study, artificial neural network (ANN) model was applied to the solubility data of CO2 (2406 experimental data) in salt-dissolved solutions over a wide range of pressures (0.92–712.31 bar), temperatures (273.15–473.65 K), concentrations of electrostricted water molecules (0–90.12 mol/kgw), and overall mole fractions of dissolved salts (0–25.39 mol%), including supercritical condition of CO2. Compared with the conventional thermodynamic models using many parameters, the accuracy of ANN model with only four input variables was comparable for salt solutions and even feasible for brine-rock systems. While the average of the absolute relative deviation of the thermodynamic model with respect to CO2 solubility data in pure water and single-salt solution (1556 data of total 2406 data) was 5.44 %, that of the developed ANN model for the corresponding data was 4.90 %. The developed ANN model presented the capability of dimensional extrapolation in the prediction of CO2 solubility in salt solutions without over-fitting when the thermodynamic-based input variable was used. The model for the solubility prediction of non-polar gases in salt solutions could be a useful approach in complex salt solutions under a wide range of temperature and pressure.

Refractive index measurement of nonpolar rarefied gas in quantum vacuum metrology standard

为进一步提高真空量值的复现性和准确性, 最新研究采用量子技术实现对真空量值的测量与表征. 该方法利用Fabry-Perot谐振腔实现腔内气体折射率的精密测量, 并反演出气体密度, 进而获得对应的真空量值, 其中气体折射率的测量是影响真空量值准确性的关键. 本文基于第一性原理, 利用从头计算理论计算了在已知压力和温度条件下的氦气折射率, 给出腔内气体压力与折射率关系的表达式, 并利用基于Fabry-Perot激光谐振腔的真空测量装置, 通过双腔谐振激光拍频精确测量了充气前后谐振激光频率的变化, 测出了氦气折射率, 并分析了测量不确定度. 将理论计算值与实验测量值进行了对比分析, 得出了制约准确度提高的主要因素, 并提出了修正方法.

Subduction-Zone Fluids

Fluids are essential to the physical and chemical processes in subduction zones. Two types of subduction-zone fluids can be distinguished. First, shallow fluids, which are relatively dilute and water rich and that have properties that vary between subduction zones depending on the local thermal regime. Second, deep fluids, which possess higher proportions of dissolved silicate, salts and non-polar gases relative to water content, and have properties that are broadly similar in most subduction systems, regardless of the local thermal structure. We review key physical and chemical properties of fluids in two key subduction-zone contexts—along the slab top and beneath the volcanic front—to illustrate the distinct properties of shallow and deep subduction-zone fluids.

Molybdenum and boron synergistically boosting efficient electrochemical nitrogen fixation

Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide ( B-MoS 2 /CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h –1 cm –2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h –1 cm –2 . A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2 p shell for boron and 5 d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N ≡ N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO 4 photo-anode with the B-MoS 2 /CFC catalytic cathode. A catalytic electrode B-MoS 2 /CFC is established for artificial nitrogen fixation, displaying the excellent ammonia production rate of 44.09 μg h –1 cm –2 and Faradaic efficiency of 21.72% in acidic aqueous electrolyte at −0.2 V. A supposed strong-weak electron polarization pair is inferred from the different electron accepting and back-donating capacities of boron and molybdenum (2 p shell for boron and 5 d shell for molybdenum), which may facilitate the adsorption of nonpolar dinitrogen and its first protonation greatly. • A carbon fiber cloth fully grafted by boron-doped molybdenum disulfide ( B-MoS 2 /CFC) nanosheets was prepared. • An excellent ammonia production rate of 44.09 μg h –1 cm –2 was obtained in 0.1 M HCl. • A strong-weak electron polarization pair of 2 p shell for B and 5 d shell for Mo was proposed to facilitate the N ≡ N bond polarization. • A visible light driven photo-electrochemical cell for overall production of NH 3 , H 2 and O 2 from H 2 O + N 2 , was demonstrated.

Temperature, Pressure, and Concentration Derivatives of Nonpolar Gas Hydration: Impact on the Heat Capacity, Temperature of Maximum Density, and Speed of Sound of Aqueous Mixtures.

The hydrophobic effect is an umbrella term encompassing a number of solvation phenomena associated with solutions of nonpolar species in water, including the following: a meager solubility opposed by entropy at room temperature; large positive hydration heat capacities; positive shifts in the temperature of maximum density of aqueous mixtures; increases in the speed of sound of dilute aqueous mixtures; and negative volumes of association between interacting solutes. Here we present a molecular simulation study of nonpolar gas hydration over the temperature range 273.15-373.15 K and a pressure range -500 to 1000 bar to investigate the interrelationships between distinct hydrophobic phenomena. We develop a new free energy correlation for the solute chemical potentials founded on the Tait equation description of the equation-of-state of liquid water. This analytical correlation is shown to provide a quantitatively accurate description of nonpolar gas hydration over the entire range of thermodynamic state points simulated, with an error of ∼0.02 kBT or lower in the fitted chemical potentials. Our simulations and the correlation accurately reproduce many of the available experimental results for the hydration of the solutes examined here. Moreover, the correlation reproduces the characteristic entropies of hydration, temperature dependence of the hydration heat capacity, perturbations in the temperature of maximum density, and changes in the speed of sound. While negative volumes of association result from pairwise interactions in solution, beyond the limits of our simulations performed at infinite dilution, we discuss how our correlation could be supplemented with second virial coefficient information to expand to finite concentrations. In total, this work demonstrates that many distinct phenomena associated with the hydrophobic effect can be captured within a single thermodynamically consistent correlation for solute hydration free energies.

Two-Dimensional Nanomaterials for Wearable Breath Sensors

There has been considerable effort to develop wearable electronics from life-supporting devices for solders to fashion accessories such as smartwatches. The research of gas sensor has also attempted to adapt wearables with the power of nanotechnology. On the wearable platform, miniature gas sensors will provide real-time information about the atmosphere to protect each personnel from possible hazardous chemical attacks. In addition, wearable gas sensor can be facilitated to monitor human’s breath as medical applications. [1] One of the important factors to develop wearable gas sensors is to operate at room temperature with excellent sensing performance. Recently, two-dimensional (2D) nanostructured materials have been highlighted as new sensing materials due to their working ability at low temperatures. Unlike conventional metal oxides, 2D materials such as graphene are able to work at room temperature with comparable gas response to NO2 gas. However, insufficient sensing performance, such as sluggish recovery and low gas response, need to be developed. [2] As one attempt to enhance performance, 2D material was hybridized with metal oxide. By incorporating two nanostructured materials, synergistic effect, which comes from benefits of each material, can improve sensing performance. [3] Another novel innovation is the introduction of newly discovered 2D materials. 2D transition metal carbides and/or carbonitrides (called MXenes) are a new family of 2D materials. The vast diversity in a combination of constituent elements and ordered structure in MXenes offers future possibilities to find out a new generation of sensing materials with their superior performance. [4, 5]In this study, different types of 2D nanostructured materials and their hybrids were investigated for the breath analysis of various volatile compounds. Graphene oxide (GO) was incorporated with TiO2 nanoparticles, and the composite was photo-reduced under UV irradiation. Room temperature gas sensing was carried out against various VOC gases, and sensing performance was evaluated by comparing with pure GO. With the tailored hetero-junction at the interfaces of GO and TiO2, the composite can identify ethanol, methanol, and acetone, and its gas response was enhanced. In addition, we introduced new 2D nanostructured materials, MXenes including Ti3C2Tx and V2CTx. 2D V2CTx gas sensors showed excellent gas-sensing performance in terms of high response toward non-polar gases. Compared to the sensing properties of Ti3C2Tx MXene, 2D V2CTx sensor showed higher selectivity and long-term stability. The comparative results suggest that the modification of ordered structure and constituent elements of MXenes play a pivot role in the interaction between analyte and MXenes leading to an extensive change designed to detect individual compounds. [5, 6]References[1] Patel, S., Park, H., Bonato, P., Chan, L., & Rodgers, M. (2012). A review of wearable sensors and systems with application in rehabilitation. Journal of neuroengineering and rehabilitation, 9(1), 21.[2] Choi, S. J., & Kim, I. D. (2018). Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electronic Materials Letters, 1-40.[3] Meng, F. L., Guo, Z., & Huang, X. J. (2015). Graphene-based hybrids for chemiresistive gas sensors. TrAC Trends in Analytical Chemistry, 68, 37-47.[4] Yu, X. F., Li, Y. C., Cheng, J. B., Liu, Z. B., Li, Q. Z., Li, W. Z., ... & Xiao, B. (2015). Monolayer Ti2CO2: a promising candidate for NH3 sensor or capturer with high sensitivity and selectivity. ACS applied materials & interfaces, 7(24), 13707-13713.[5] Lee, E., VahidMohammadi, A., Prorok, B. C., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2017). Room Temperature Gas Sensing of Two-Dimensional Titanium Carbide (MXene). ACS applied materials & interfaces, 9(42), 37184-37190.[6] Lee, E., VahidMohammadi, A., Yoon, Y. S., Beidaghi, M., & Kim, D. J. (2019). Two-Dimensional Vanadium Carbide MXene for Gas Sensors with Ultrahigh Sensitivity Toward Nonplar Gases. ACS Sensors, 4, 1603-1611.

A constitutive model for predicting the solubility of gases in water at high temperature and pressure

In the drilling and development of gas fields, gas exhibits good solubility in drilling fluids and in the formation water under high temperatures and pressures. Therefore, the prediction of the amount of dissolved gas in water plays a vital role in the development of natural gas. In this work, the principle of equal fugacity in a gas-liquid equilibrium, a non-iterative gas solubility prediction model was established. The gas-phase fugacity coefficient was calculated by the Peng-Robinson equation of state combined with the non-random mixing rule, and the liquid phase was calculated by Henry's law. The model can predict the solubility of CO2, CH4 and C2H6 in pure water at temperatures of 273–448 K and pressures of 0–100 MPa, with an error of less than 5.5%; however, the calculation accuracy for H2S was low. It is found that the effect of moisture in the gas phase of gas-liquid equilibrium cannot be ignored. Compared with the existing mixed gas solubility experimental data, this model could accurately calculate the solubility of non-polar mixed gases, such as CO2 + CH4, and CH4 + C2H6 mixture. For the mixtures containing a polar gas, the lower the polar gas content, the smaller was the prediction error of the model for the non-polar gas in the mixture. On the contrary, the higher the content of polar gas, the larger was the deviation in the prediction of non-polar gas in the mixture, but lower was the deviation in the prediction of polar gas. Finally, the ability of Krichevsky-Kasarnovsky equation to predict the solubility of pure gas was evaluated.