Development of Novel Polyamide-Imide/DES Composites and Their Application for Pervaporation and Gas Separation.

Novel polymer composites based on polyamide-imide Torlon and deep eutectic solvent (DES) were fabricated and adapted for separation processes. DES composed of zinc chloride and acetamide in a ratio of 1:3 M was first chosen as a Torlon-modifier due to the possibility of creating composites with a uniform filling of the DES through the formation of hydrogen bonds. The structure of the membranes was investigated by scanning electron microscopy and X-ray diffraction analysis; thermal stability was determined by thermogravimetric analysis and mass spectrometry. The surface of the composites was studied by determining the contact angles and calculating the surface tension. The transport properties were investigated by such membrane methods as pervaporation and gas separation. It was found that the inclusion of DES in the polymer matrix leads to a significant change in the structure and surface character of composites. It was also shown that DES plays the role of a plasticizer and increases the separation performance in the separation of liquids and gases. Torlon/DES composites with a small amount of modifier were effective in alcohol dehydration, and were permeable predominantly to water impurities in isopropanol. Torlon/DES-5 demonstrates high selectivity in the gas separation of O2/N2 mixture.

Borehole diameter shrinkage rule considering rheological properties and its effect on gas extraction.

To study the shrinkage rule of borehole diameter and its effect on gas extraction, a visco-elastoplastic model for boreholes considering strain softening and the dilatancy characteristic was established to obtain the expressions of the coal stress, variation in diameter, and pressure relief range. The stress distribution and pressure relief effect of the boreholes in soft and hard coal seams were comparatively analyzed. The shrinkage rule of the borehole diameter was studied. The reasons for the rapid reduction in the extraction concentration of the borehole in soft coal seams were described. A technology of improving the gas extraction effect in soft coal seams was developed. The research results showed that the radius of the plastic softening zone is 0.405 m for a borehole in a soft coal seam and 0.224 m for that in a hard coal seam. This indicates that the borehole in a soft coal seam has a better pressure relief effect. The boreholes in both hard and soft coal seams will incur a shrinkage phenomenon; however, the soft coal seam has low strength and a weak ability to resist damage, and thus the surrounding coal will have a more intense creep deformation, leading to an instability failure during a short period of time and thus, a blocking of the extraction channel, thereby causing a rapid reduction in the gas extraction concentration. The borehole in a hard coal seam also shows a shrinkage phenomenon, but remains in a stable state without a blockage; thus, high-concentration gas can be extracted from this borehole for a long period of time. The geo-stress and coal strength are the two main factors controlling the amplitude of borehole shrinkage. From an increase in stress, the borehole in a hard coal seam shows a more intense creep deformation in a deep mine, which may lead to blockage. The key to improving the gas extraction effect in soft coal seams is to maintain a smooth extraction channel. The full screen pipe is installed through the drill pipe to retain an extraction channel, leading to an average gas extraction increase from 0.043 m3/min to 0.12 m3/min, an increase of 2.77 times. These research results are consistent with actual production, and can provide theoretical guidance for determining the gas extraction parameters.

Key Applications and Potential Limitations of Ionic Liquid Membranes in the Gas Separation Process of CO2, CH4, N2, H2 or Mixtures of These Gases from Various Gas Streams.

Heightened levels of carbon dioxide (CO2) and other greenhouse gases (GHGs) have prompted research into techniques for their capture and separation, including membrane separation, chemical looping, and cryogenic distillation. Ionic liquids, due to their negligible vapour pressure, thermal stability, and broad electrochemical stability have expanded their application in gas separations. This work provides an overview of the recent developments and applications of ionic liquid membranes (ILMs) for gas separation by focusing on the separation of carbon dioxide (CO2), methane (CH4), nitrogen (N2), hydrogen (H2), or mixtures of these gases from various gas streams. The three general types of ILMs, such as supported ionic liquid membranes (SILMs), ionic liquid polymeric membranes (ILPMs), and ionic liquid mixed-matrix membranes (ILMMMs) for the separation of various mixed gas systems, are discussed in detail. Furthermore, issues, challenges, computational studies and future perspectives for ILMs are also considered. The results of the analysis show that SILMs, ILPMs, and the ILMMs are very promising membranes that have great potential in gas separation processes. They offer a wide range of permeabilities and selectivities for CO2, CH4, N2, H2 or mixtures of these gases. In addition, a comparison was made based on the selectivity and permeability of SILMs, ILPMs, and ILMMMs for CO2/CH4 separation based on a Robeson's upper bound curves.

Cellulose-Based Carbon Molecular Sieve Membranes for Gas Separation: A Review.

In the field of gas separation and purification, membrane technologies compete with conventional purification processes on the basis of technical, economic and environmental factors. In this context, there is a growing interest in the development of carbon molecular sieve membranes (CMSM) due to their higher permeability and selectivity and higher stability in corrosive and high temperature environments. However, the industrial use of CMSM has been thus far hindered mostly by their relative instability in the presence of water vapor, present in a large number of process streams, as well as by the high cost of polymeric precursors such as polyimide. In this context, cellulosic precursors appear as very promising alternatives, especially targeting the production of CMSM for the separation of O2/N2 and CO2/CH4. For these two gas separations, cellulose-based CMSM have demonstrated performances well above the Robeson upper bound and above the performance of CMSM based on other polymeric precursors. Furthermore, cellulose is an inexpensive bio-renewable feed-stock highly abundant on Earth. This article reviews the major fabrication aspects of cellulose-based CMSM. Additionally, this article suggests a new tool to characterize the membrane performance, the Robeson Index. The Robeson Index, θ, is the ratio between the actual selectivity at the Robeson plot and the corresponding selectivity-for the same permeability-of the Robeson upper bound; the Robeson Index measures how far the actual point is from the upper bound.

Deep Physical-Chemical Purification of Gas Medium in Artificial Ecosystems.

The results of experiments on application of a newly developed facility for oxidation of volatile organic compounds on a platinum catalyst are presented. The feasibility of using this method in artificial ecosystems as a whole and in mass exchange of closed biological-technical life support systems in particular is shown. The possibility of deep purification of gas emitted from the reactor of physical-chemical processing of organic wastes is demonstrated. Wheat growing experiment on using the facility for oxidation of volatile organic compounds in a sealed chamber was performed. No adverse effect of probable toxic oxidation products on wheat plants during a 4-day experiment was determined.

Covalent Organic Frameworks in Separation.

In the wake of sustainable development, materials research is going through a green revolution that is putting energy-efficient and environmentally friendly materials and methods in the limelight. In this quest for greener alternatives, covalent organic frameworks (COFs) have emerged as a new generation of designable crystalline porous polymers for a wide array of clean-energy and environmental applications. In this contribution, we categorically review the merits and shortcomings of COF bulk powders, nanosheets, freestanding thin films/membranes, and membranes on porous supports in various separation processes, including separation of gases, pervaporation, organic solvent nanofiltration, water purification, radionuclide sequestration, and chiral separations, with particular reference to COF material pore size, host-guest interactions, stability, selectivity, and permeability. This review covers the fabrication strategies of nanosheets, films, and membranes, as well as performance parameters, and provides an overview of the separation landscape with COFs in relation to other porous polymers, while seeking to interpret the future research opportunities in this field.

Biotechnology progress for removal of indoor gaseous formaldehyde.

Formaldehyde is a ubiquitous carcinogenic indoor pollutant. The treatment of formaldehyde has attracted increasing social attention. Over the past few decades, an increasing number of publications have reported approaches for removing indoor formaldehyde. These potential strategies include physical adsorption, chemical catalysis, and biodegradation. Although physical adsorption is widely used, it does not really remove pollution. Chemical catalysis is very efficient but adds the risk of introducing secondary pollutants. Biological removal strategies have attracted more research attention than the first two methods, because it is more efficient, clean, and economical. Plants and bacteria are the common organisms used in formaldehyde removal. However, both have limitations and shortcomings when used alone. This review discusses the mechanisms, applications, and improvements of existing biological methods for the removal of indoor gaseous formaldehyde. A combination strategy relying on plants, bacteria, and physical adsorbents exhibits best ability to remove formaldehyde efficiently, economically, and safely. When this combination system is integrated with a heating, ventilation, air conditioning, and cooling (HVAC) system, a practical combined system can be established in formaldehyde removal. Multivariate interactions of biological and non-biological factors are needed for the future development of indoor formaldehyde removal. KEY POINTS: • Indoor gaseous formaldehyde removal is necessary especially for new residence. • Biological removal strategies have attracted increasing research attentions. • Combined system of plants, bacteria, and physical adsorbents exhibits best efficiency. • Integrated device of biological and non-biological factors will be potential practical.

Two-Dimensional Membranes: New Paradigms for High-Performance Separation Membranes.

Two-dimensional (2D) materials with atomic thicknesses have aroused great interest as promising building blocks for the preparation of ultrathin 2D membranes. These 2D membranes can exhibit unprecedentedly high separation permeance owing to their ultrasmall membrane thicknesses and superior selectivity because of their size-selective nanopores and/or nanochannels. Until now, a large number of 2D membranes with good performance have been reported, highlighting the potential of these novel membranes for efficient liquid and gas separations. Summarized in this review are the latest advances in 2D membranes, with a special focus on industrially attractive separation processes, fabrication methods of laminar membranes, choices of membrane materials, designs of membrane structures, and unique membrane transport properties. Opportunities and challenges of 2D membranes for commercial applications are also briefly discussed.

Insights into the Gas Adsorption Mechanisms in Metal-Organic Frameworks from Classical Molecular Simulations.

Classical molecular simulations can provide significant insights into the gas adsorption mechanisms and binding sites in various metal-organic frameworks (MOFs). These simulations involve assessing the interactions between the MOF and an adsorbate molecule by calculating the potential energy of the MOF-adsorbate system using a functional form that generally includes nonbonded interaction terms, such as the repulsion/dispersion and permanent electrostatic energies. Grand canonical Monte Carlo (GCMC) is the most widely used classical method that is carried out to simulate gas adsorption and separation in MOFs and identify the favorable adsorbate binding sites. In this review, we provide an overview of the GCMC methods that are normally utilized to perform these simulations. We also describe how a typical force field is developed for the MOF, which is required to compute the classical potential energy of the system. Furthermore, we highlight some of the common analysis techniques that have been used to determine the locations of the preferential binding sites in these materials. We also review some of the early classical molecular simulation studies that have contributed to our working understanding of the gas adsorption mechanisms in MOFs. Finally, we show that the implementation of classical polarization for simulations in MOFs can be necessary for the accurate modeling of an adsorbate in these materials, particularly those that contain open-metal sites. In general, molecular simulations can provide a great complement to experimental studies by helping to rationalize the favorable MOF-adsorbate interactions and the mechanism of gas adsorption.

Fabrication of hybrid thin film based on bacterial cellulose nanocrystals and metal nanoparticles with hydrogen sulfide gas sensor ability.

The nanocrystalline structures of bacterial cellulose (BC) are described as "environmentally friendly green nanomaterials". Bacterial cellulose (BC) was produced from Gluconacetobacter xylinus in pellicle form with a large bundle of fibers were acid hydrolyzed to obtain bacterial cellulose nanocrystals (BCNCs). The H2SO4 acid-hydrolyzed BCNCs were evaluated for their smallest crystallite size and hydrodynamic size, highly negative ζ-potential value, and the highest specific surface area to interact with metallic nanoparticles. Hybrid thin film of BCNCs based surface-loaded silver nanoparticles (AgNPs) and alginate-molybdenum trioxide nanoparticles (MoO3NPs) was developed for hydrogen sulfide (H2S) gas sensor. Sensor characteristics were investigated as well as its response with H2S gas. The film was successfully detected H2S gas. The color of the film changed by the shift of oxidation number of MoO3NPs. Once activated by AgNPs, MoO3NPs was readily reduced to a colored sub-oxide by atomic hydrogen that produced and received from reaction of H2S gas.

Covalent organic frameworks for separation applications.

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with highly tuneable structures and functionalities. COFs have been proposed as ideal materials for applications in the energy-intensive field of molecular separation due to their notable intrinsic features such as low density, exceptional stability, high surface area, and readily adjustable pore size and chemical environment. This review attempts to highlight the key advancements made in the synthesis of COFs for diverse separation applications such as water treatment or the separation of gas mixtures and organic molecules, including chiral and isomeric compounds. Methods proposed for the fabrication of COF-based columns and continuous membranes for practical applications are also discussed in detail. Finally, a perspective regarding the remaining challenges and future directions for COF research in the field of separation has also been presented.

Removal of toluene vapor in the absence and presence of a quorum-sensing molecule in a biotrickling filter and microbial composition shift.

Toluene is highly toxic and mutagenic, and it is generally used as an industrial solvent. Thus, toluene removal from air is necessary. To solve the problem of reducing high toluene concentrations with a short gas retention time (GRT), a quorum-sensing molecule [N-(3-oxododecanoyl)-L-homoserine lactone] (OHL) was added to a biotrickling filter (BTF). In this study, a BTF was used to treat synthetic and natural waste gases containing toluene. An extensive analysis was performed to understand the removal efficiency, removal characteristics, and bacterial community of the BTF. The addition of 20 µM OHL to the BTF significantly improved toluene removal, and more than 99.2% toluene removal was achieved at a GRT of 0.5 min when natural waste gas containing toluene (590-1020 ppm or 2.21-3.83 g m-3) was introduced. The maximum inlet load for toluene was 337.9 g m-3 h-1. Moreover, the BTF exhibited satisfactory adaptability to shock loading and shutdown operations. Pseudomonadaceae (33.0%) and Comamonadaceae (26.3%) were predominant bacteria in the system after a 98-day operation. These bacteria were responsible for toluene degradation. The optimal moisture content and low pressure drop for system operations demonstrated that the BTF was energy and cost efficient. Therefore, processing through a BTF with OHL is a favorable technique for toluene treatment.

A pursuit to design highly sensitive fullerene-based sensors: adsorption and dissociation phenomenon of toxic sulfur gases on B40 fullerene.

The adsorption phenomenon of toxic sulfur gases namely H2S and SO2 on B40 fullerene is scrutinized utilizing density functional theory-non-equilibrium Green's function (DFT-NEGF) regime. Adsorption of gas molecules is considered at both the hexagonal and heptagonal rings of the fullerene and adsorption energies, charge transfer, electron charge densities, density of states, transmission spectra, molecular energy spectra; Eigen states, HOMO-LUMO gap, current voltage curve, and differential conductance are premeditated. It is inferred that H2S molecule is physisorbed on the heptagonal ring of the fullerene while it is dissociative-chemisorbed on the hexagonal ring. SO2 dissociates into SO and O species on adsorption on both the hexagonal and heptagonal rings. From the transmission spectra and DOS analysis, LUMO dominant transmission is noticed in all the devices except the one formed with heptagonal ring adsorption of H2S which favors HOMO-dominated transmission. From the I-V curve and differential conductance investigation, different conductance values are noticed for all the junctions, thus proving that B40 is an efficient material to be engaged in sensing toxic sulfur gases.

Recent Advances in Graphene Oxide Membranes for Gas Separation Applications.

Graphene oxide (GO) can dramatically enhance the gas separation performance of membrane technologies beyond the limits of conventional membrane materials in terms of both permeability and selectivity. Graphene oxide membranes can allow extremely high fluxes because of their ultimate thinness and unique layered structure. In addition, their high selectivity is due to the molecular sieving or diffusion effect resulting from their narrow pore size distribution or their unique surface chemistry. In the first part of this review, we briefly discuss different mechanisms of gas transport through membranes, with an emphasis on the proposed mechanisms for gas separation by GO membranes. In the second part, we review the methods for GO membrane preparation and characterization. In the third part, we provide a critical review of the literature on the application of different types of GO membranes for CO2, H2, and hydrocarbon separation. Finally, we provide recommendations for the development of high-performance GO membranes for gas separation applications.

Combined calorimetric gas- and spore-based biosensor array for online monitoring and sterility assurance of gaseous hydrogen peroxide in aseptic filling machines.

A combined calorimetric gas- and spore-based biosensor array is presented in this work to monitor and evaluate the sterilization efficacy of gaseous hydrogen peroxide in aseptic filling machines. H2O2 has been successfully measured under industrial conditions. Furthermore, the effect of H2O2 on three different spore strains , namely Bacillus atrophaeus, Bacillus subtilis and Geobacillus stearothermophilus, has been investigated by means of SEM, AFM and impedimetric measurements. In addition, the sterilization efficacy of a spore-based biosensor and the functioning principle are addressed and discussed: the sensor array is convenient to be used in aseptic food industry to guarantee sterile packages.

Peptide Nanotube Encapsulated Enzyme Biosensor for Vapor Phase Detection of Malathion, an Organophosphorus Compound.

This study explores the use of a butyrylcholinesterase (BChE)-based, reversible reaction biosensor using screen-printed electrodes (SPEs) having a smaller working surface area than the single-use electrodes previously studied. Previous research demonstrated the prospective application of a single-use biosensor fabricated with an acetylcholinesterase (AChE) enzyme encapsulated in peptide nanotubes (PNTs) and enhanced with horseradish peroxidase (HRP) to detect organophosphorus compounds (OPCs) in aqueous and gas phases. In the current study, potential improvements to the biosensor are investigated. BChE-based biosensors were fabricated using PNTs, HRP, and Nafion in combination to increase the reactive surface area, enhance sensitivity, and maintain enzyme stability. Cyclic voltammetry (CV) was used along with the new modified sensor to measure malathion concentration in the gas phase. The results show that a BChE-based biosensor could reliably measure gas phase malathion concentrations between 6-25 ppbv by CV with the extent of inhibition linearly proportional to the malathion concentration (R2 = 0.941). This research demonstrated that fabricated BChE-based biosensors could be stored without cold storage requirement for up to six weeks with minimal performance degradation. Moreover, the sensor electrodes were each reused several times, and were still useable at the conclusion of the research. This research demonstrates the potential of fabricating a reusable, inexpensive biosensor that is capable of OPC detection with high sensitivity and a low detection limit without a long-term cold storage requirement.

An E-Nose for the Monitoring of Severe Liver Impairment: A Preliminary Study.

Biologically inspired to mammalian olfactory system, electronic noses became popular during the last three decades. In literature, as well as in daily practice, a wide range of applications are reported. Nevertheless, the most pioneering one has been (and still is) the assessment of the human breath composition. In this study, we used a prototype of electronic nose, called Wize Sniffer (WS) and based it on an array of semiconductor gas sensor, to detect ammonia in the breath of patients suffering from severe liver impairment. In the setting of severely impaired liver, toxic substances, such as ammonia, accumulate in the systemic circulation and in the brain. This may result in Hepatic Encephalopathy (HE), a spectrum of neuro-psychiatric abnormalities which include changes in cognitive functions, consciousness, and behaviour. HE can be detected only by specific but time-consuming and burdensome examinations, such as blood ammonia levels assessment and neuro-psychological tests. In the presented proof-of-concept study, we aimed at investigating the possibility of discriminating the severity degree of liver impairment on the basis of the detected breath ammonia, in view of the detection of HE at its early stage.

Application of Near-Infrared Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) to the Detection of Ammonia in Exhaled Human Breath.

The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of αmin = 2.3 × 10-9 cm-1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm-1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.

Removal of gaseous elemental mercury by hydrogen chloride non-thermal plasma modified biochar.

Hydrogen chloride (HCl) non-thermal plasma was applied to introduce Cl active sites on biochar prepared from sorghum straw in this study. Surface modified biochar was then placed in flue gas with typical components to investigate its elemental mercury (Hg0) capture ability. To elucidate the adsorption mechanism & binding properties, samples were characterized by N2 adsorption, scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and X-ray absorption near edge structure (XANES) analysis of Hg LIII-edge, Cl K-edge and S K-edge. Experimental results showed that HCl plasma modification successfully increased Cl active sites on biochar and greatly increased its mercury removal efficiency. Both HCl treatments (w/without plasma involvement) altered biochar's surface structure and layered structure generated. XANES spectra revealed that adsorbed-Hg on HCl-treated biochars mainly in the form of Hg+. Gaseous Hg0 was believed to heterogeneously react with chlorinated sites through electron-transfer and formed Hg2Cl2 compounds. With the presence of NO or SO2 in the system, adsorbed mercury existed on biochar mainly as Hg+. SO2 competed and inhibited the adsorption of Hg0; while NO promoted Hg0 removal capacity by increasing the active sites and enhancing the adsorption kinetics of adjacent Cl-containing sites.

Silicon nanowire arrays for the preconcentration and separation of trace explosives vapors.

Silicon nanowire (SiNW) arrays are demonstrated as a suitable platform for the preconcentration of trace nitroaromatic compounds and subsequent desorption via Joule heating of the array. Arrays are fabricated from Si wafers containing an epitaxially grown layer of low conductivity intrinsic Si sandwiched between layers of high conductivity p-type Si. Passage of current through the nanowires results in nanowire temperatures in excess of 200 °C during heating of the arrays as verified by using the temperature-dependent shift of the Si Raman band at ˜520 cm-1. Analyte vapor preconcentration and partial separation is achieved on the array at analyte concentrations nearly two orders-of-magnitude below saturated vapor concentrations at room temperature. The effects of desorption carrier gas flow rate and temperature on the ability to preconcentrate and resolve the analytes of interest are determined. 2,6-dinitrotoluene (2,6-DNT) and 2,4-dinitrotoluene (2,4-DNT) were detected at nominal vapor concentrations of 800 pptv with a 1 min sample time (1.1 ng nominal mass load) and trinitrotoluene (TNT) was detected at a nominal vapor concentration of 65 pptv with a 10 min sample time (1.1 ng nominal mass load).