Volatile Organic Compound Vapors Research Articles

Gallium and indium nanomaterials for environmental protection

Recent advances in preparation and use of gallium and indium nanoparticles and nanocomposites are briefly presented. The following applications of the obtained materials are outlined: (i) Preparation of sensors for measuring in air of gaseous pollutants (carbon monoxide, nitrogen dioxide, hydrogen sulfide, ammonia, ozone, hydrogen), vapours of volatile organic compounds (methanol, ethanol, butanol, acetone, liquefied petroleum gas), and humidity, including the basics of the sensing mechanism; (ii) removal of water pollutants by photocatalysis and/or adsorption. Finally, conclusions are drawn about the potential of gallium and indium nanoparticles and nanocomposites and the further studies needed to achieve the implementation of these materials in the real life.

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Nanoscale light–matter interactions in metal–organic frameworks cladding optical fibers

The utilization of refractive index (RI) change due to guest-host interactions between the guest volatile organic compound vapor and porous metal-organic frameworks (vapor-MOF interactions) is promising in photonic vapor sensors. Therefore, the study of light-matter interactions in nanoporous metal-organic frameworks (MOFs) is fundamental and essential for MOF-based photonic devices. In this work, the manipulation of light in MOFs to investigate the vapor-MOF interactions by using optical fiber devices is demonstrated. The vapor-MOF interactions and the light-vapor interactions (light in MOFs to sense the RI changes resulting from the vapor-MOF interactions) are investigated. The cladding mode is excited by a long-period fiber grating (LPFG) for evanescent field sensing in a ZIF-8 sensitive coating. The experimental results combining quantum chemical calculations and optical simulations reveal the relationships between the microscopic energy of vapor desorption, RI changes and evanescent field enhancement in ZIF-8 during the vapor-MOF interactions. With exceptionally large RI changes, the evanescent field of cladding mode in ZIF-8 is greatly enhanced to sense the vapor-MOF interactions. As a proof-of-concept, a LPFG sensor with ZIF-8 coating showed a high sensitivity of 1.33 pm ppm-1 in the linear range from 9.8 ppm to 540 ppm for the sensing of ethanol vapor. The investigation of light-matter interactions in ZIF-8 provides a useful guideline for the design and fabrication of MOF-based optical waveguide/fiber sensors.

Метод конкурирующих реакций в исследовании процессов удаления паров ненасыщенных органических соединений в воздухе под действием плазмы импульсного разряда

To study the efficiency of the removal of vapors of volatile organic compounds from air flows when processed by a plasma of pulsed discharges, a method of competing reactions is proposed. Using a compound with known parameters in the model mixture, it is possible to estimate similar parameters of other compounds using a chromatographic method of analysis that does not have a high temporal resolution. By the example of styrene and methyl methacrylate vapors, it was shown that for unsaturated compounds their relative reactivity in the discharge plasma correlates well with the ratio of the rate constants of their reactions with ozone.

Adsorption Characteristics of Volatile Organic Compounds on Used Coffee Grounds Based on the Breakthrough Curves

We investigated the adsorption characteristics of volatile organic compounds (VOCs) on the surface of coffee beans after extraction (coffee grounds). Temperature-controllable adsorption equipment of VOC vapor was manufactured, and nitrogen gas containing about 100 ppm of VOC vapor was introduced into a coffee extraction residue. The air in the downstream was analyzed with a gas chromatograph equipped with a flame ionization detector over a period of time. A breakthrough curve was obtained from the analysis of values and time, and the adsorbed amount of each volatile organic compound on the coffee grounds was calculated from a graphical integration of the breakthrough curve. Fourteen VOCs were tested, and the adsorbed amount tended to increase with increases in the boiling point of the VOCs. It was also found that the adsorbed amount of methanol and toluene was affected by the water content in the coffee grounds used in the experiment.

Thermal annealing to influence the vapor sensing behavior of co-continuous poly(lactic acid)/polystyrene/multiwalled carbon nanotube composites

With the main purpose of being used as vapor leakage detector, the volatile organic compound (VOC) vapor sensing properties of conductive polymer blend composites were studied. Poly(lactic acid)/polystyrene/multi-walled carbon nanotube (PLA/PS/MWCNT) based conductive polymer composites (CPCs) in which the polymer components exhibit different interactions with the vapors, were prepared by melt mixing. CPCs with a blend composition of 50/50 wt% resulted in the finest co-continuous structure and selective MWCNT localization in PLA. Therefore, these composites were selected for sensor tests. Thermal annealing was applied aiming to maintain the blend structure but improving the sensing reversibility of CPC sensors towards high vapor concentrations. Different sensing protocols were applied using acetone (good solvent for PS and PLA) and cyclohexane (good solvent for PS but poor solvent for PLA) vapors. Increasing acetone vapor concentration resulted in increased relative resistance change (Rrel) of CPCs. Saturated cyclohexane vapor resulted in lower response than nearly saturated acetone vapor. The thermal annealing at 150 °C did not change the blend morphology but increased the PLA crystallinity, making the CPC sensors more resistant to vapor stimulation, resulting in lower Rrel but better reversibility after vapor exposure.

Model compound mixtures for studying the main trends of volatile organic compounds conversion in processes of air cleaning by pulsed discharges

To study the process of removing volatile organic compounds (VOCs) vapors from air flow by the action of pulsed discharge plasma, it is proposed to use specially selected model mixtures of components. The components of these mixtures are in equal conditions, which makes it possible to measure the relative reactivity with high accuracy without using high-speed analysis techniques. Using three groups of the mixtures, it was shown that substances with different functional groups react with different components of the discharge plasma. Multifunctional VOCs react with active forms of nitrogen and oxygen. Halogenated compounds are mainly removed due to electron attachment processes, and unsaturated compounds are removed by reaction with ozone.

Temporal variability of chlorinated volatile organic compound vapor concentrations in a residential sewer and land drain system overlying a dilute groundwater plume

Some subsurface sewer and land drain networks will facilitate the migration of chlorinated volatile organic compounds (CVOCs) from dissolved contaminant groundwater plumes to indoor air. As this vapor intrusion (VI) pathway has only recently been documented, guidance for evaluating it, including recommendations for timing, frequency, duration and location for vapor sampling in subsurface piping networks is non-existent. To address this gap, a three-year investigation of CVOC concentrations from land drains, storm drains, and sanitary sewers was undertaken in a neighborhood overlying a large-scale dissolved chlorinated VOC (CVOC) groundwater plume. Vapor sampling included the collection of grab (time-discrete) samples from up to 277 manholes, hourly grab sampling from three manhole locations, and 24-h duration collection during week-long sampling from 13 land drain and sewer manholes. The spatial distribution of vapor and water concentrations and the temporal variations in the vapor values observed in this study suggest that week-long vapor sampling conducted at different times of the year and with samples collected at manhole locations overlying and outside a dissolved plume might be needed to ensure robust VI pathway assessment at other sites. These findings are expected to be of relevance to regulatory agencies involved in the development of current or future VI pathway assessment guidance.

Development of VOCs gas sensor with high sensitivity using colorimetric polymer nanofiber: a unique sensing method

A challenge for sensors detecting ultralow amount of volatile organic compounds (VOCs) in form of solvent or gas for reliable sampling and large surface area to volume ratio of sample must be studied. In this study, polydiacetylene (PDA)/ Polyurethane (PU) nanofibers web was manufactured using polydiacetylene, which was characterized by colorimetric. The manufactured nanofibers were exposed to volatile organic compounds (VOCs) solvents and gases to examine color changes and to monitor the reaction rate by manufacturing films under the same conditions. When PDA/PU nanofibers were exposed to VOCs solutions and vapors, color alteration was occurred from blue to red, which enabling the VOCs detection. In addition, the colorimetric response (CR) is high in the nonpolar and aprotic solvents, and lower in the lower the polarity of the solvent.. This colorimetric response (CR) is expected to enable qualitative analysis between solvents. Also, it was confirmed that nanofibers have higher sensitivity and faster reaction rate than films due to changes in color of nanofibers and films. The PDA/PU nanofibers developed through this study are expected to be available as colorimetric sensors for VOCs detection through rapid colorimetric response.

Ultrasensitive Detection of Volatile Organic Compounds by a Freestanding Aligned Ag/CdSe-CdS/PMMA Texture with Double-Side UV-Ozone Treatment.

Volatile organic compounds (VOCs) are organic chemicals having a high vapor pressure at room temperature. Chronic exposure to VOC vapor can be potentially dangerous to human health. In this study, we build a high-performance freestanding aligned Ag/CdSe-CdS/poly(methyl methacrylate) (PMMA) texture to detect VOC vapors. The insight of this new VOC-sensing material is based on electrospinning techniques, ultraviolet (UV)/ozone treatments, and nano-optics. The incorporation of CdSe-CdS core-shell quantum rods (QR) and silver nanocrystals in the PMMA nanofibers amplifies the polarization response of long rods in VOC detection, thus increasing the sensitivity of VOC-sensing materials. Further, the uniaxial aligned Ag/QR/PMMA sensing material was treated by UV-ozone etching to increase surface absorption. The advanced double-sided UV-ozone etching on the uniaxial aligned Ag/QR/PMMA efficiently enhanced the extinction changes of VOCs. Two categories of solvents, typical VOCs and alcoholic VOCs, were put into practical tests for the Ag/QR/PMMA VOC-sensing materials. The Ag/QR/PMMA reached the detection limit for 100 ppm butanol within 1 min. The freestanding aligned Ag/CdSe-CdS/PMMA texture is a newly designed nanocomposite device for environmental risk monitoring. It can be accepted by the market compared to the other highly sensitive commercial VOC-sensing materials.

Enhanced response of hydrogenated Fe2O3 nanostructured materials to volatile organic compound vapors and gas sensing mechanism

We demonstrated a new approach to increasing response of Fe2O3 nanoparticles and sea urchin-like nanostructures towards methanol, ethanol, formaldehyde, acetone, triethlamine and n-Butylamine by increasing number of surface Fe atoms having dangling bonds through hydrogenation. The surface Fe atoms having dangling bonds are believed to serve as the reactive atoms for sensing reaction, thus, a gas sensing mechanism at atomic and molecular level is presented for the first time. The surface unsaturated active Fe atoms can adsorb oxygen molecules, produce electrons and catalyze the chemical reaction of the adsorbed oxygen with target gas. Hydrogenation may be a universal approach to increasing gas sensing performances of metal oxides. The gas sensing mechanism can deepen comprehending electron transfer during the gas sensing process and offer guidance to design the gas sensing materials with higher performances.

A wide range sensor of a 3D mesoporous silica coated QCM electrodes for the detection of volatile organic compounds

A quartz crystal microbalance (QCM) electrode coated with high surface area mesoporous silica KIT-6 films was designed as a sensor for the detection of a wide range of volatile organic compounds (VOCs) such as aliphatic alcohols, aliphatic amines, benzene and toluene at room temperature. A thin film of KIT-6 coating on Au-electrode of QCM was prepared by a simple drop-coating approach. The mesoporous silica KIT-6 was characterized with transmission electron microscope (TEM), low-angle X-ray difraction (XRD), Fourier transform infrared spectrocsopy (FT-IR) and N2 sorption isotherm. The frequency shifts (Δf) of the QCM coated with mesoporous silica KIT-6 films were measured as a function of time after injection of different VOCs vapors. Δfs were found to be increased linearly with the injected chemical vapor concentration. The results definitely showed an enhanced detection sensitivity and a fast response of the QCM sensor. The sensor showed an unusual high sensitivity and selectivity for amine compounds and the equilibrium was achieved within few seconds. The adsorption kinetics and relaxation time of methanol and ethanol vapors were carefully studied.

Detection and Discrimination of Volatile Organic Compounds using a Single Film Bulk Acoustic Wave Resonator with Temperature Modulation as a Multiparameter Virtual Sensor Array.

This paper describes the detection and discrimination of volatile organic compounds (VOCs) using an e-nose system based on a multiparameter virtual sensor array (VSA), which consists of a single-chip temperature-compensated film bulk acoustic wave resonator (TC-FBAR) coated with 20-bilayer self-assembled poly(sodium 4-styrenesulfonate)/poly(diallyldimethylammonium chloride) thin films. The high-frequency and microscale FBAR multiparameter VSA was realized by temperature modulation, which can greatly reduce the cost and complexity compared to those of a traditional e-nose system and can allow it to operate at different temperatures. The discrimination effect depends on the synergy of temperature modulation and the sensing material. For proof-of-concept validation purposes, the TC-FBAR was exposed to six different VOC vapors at six different gas partial pressures by real-time VOC static detection and dynamic detection. The resulting frequency shifts and impedance responses were measured at different temperatures and evaluated using principal component analysis and linear discriminant analysis, which revealed that all analytes can be distinguished and classified with more than 97% accuracy. To the best of our knowledge, this report is the first on an FBAR multiparameter VSA based on temperature modulation, and the proposed novel VSA shows great potential as a compact and promising e-nose system integrated in commercial electronic products.

Individual CdS-covered aerographite microtubes for room temperature VOC sensing with high selectivity

The synthesis of new nanomaterials with a large surface-to-volume ratio is of high interest for sensing applications, and especially for gas sensors with high performances. In this work, a thin layer of CdS is deposited onto tubular graphitic/aerographite microstructures using RF magnetron sputtering for further integration into sensing devices using a FIB/SEM system. The quality of the deposited layers as well as microstructural features were analyzed by transmission electron microscopy and energy dispersive X-ray spectroscopy. The gas sensing measurements at room temperature demonstrated the excellent sensing properties towards vapors of volatile organic compounds (VOCs), such as ethanol, acetone, 2-propanol and n- butanol. The superior properties were attributed to the nanometer thickness (20–30 nm) and high surface-to-volume ratio of CdS thin layers as a result of the tubular structure of wrinkled Aerographite (AG). This causes a big number of gas sensitive potential barriers between particles, resulting in a high sensor response. This makes mesoporous graphitic/aerographite microtubes ideal construction blocks for the formation of hybrid materials and for their use in gas sensing applications. The presented strategy can be also applied to other materials with high performance gas sensing properties.

Volatile organic compound vapor detection with responsive microgel-based etalons

Optical sensors (etalons) composed of poly(N-isopropylacrylamide) (pNIPAm)-based microgels have been developed for detecting volatile organic compound (VOC) vapors such as hexane, cyclohexane, chloroform, petroleum ether and tetrahydrofuran (THF). PNIPAm-based microgels were synthesizedandcharacterized, and etalons were subsequently fabricated, which exhibited visual color and multipeak reflectance spectra. The color change of etalons in response to VOC vapor exposure was evaluated by bubbling the vapors through water containing the etalon, and the shift in the reflectance peak position monitored. The results showed that the etalons were able to respond to the VOC vapor by changing their color, as evidenced by a shift in the position of the reflectance peak. Dynamic light scattering data showed that the microgels dissolved in solutions composed of the respective VOCs exhibit sizes that vary with VOC type and concentration, which leads to the optical response observed for the microgel-based etalons. The results showed that the etalons were most responsive to THF, which we conclude is a result of cononsolvency of the microgels in THF/water mixtures. With the setup used here, we could detect 1.27 mM THF vapor in 4 min, although the limit of detection, and detection time, can be tuned by changing the experimental conditions. Finally, we showed that individual etalons can be used at least 3 times to detect THF vapor without a loss in etalon function, which suggests that the etalons can be used multiple times for detecting VOC vapors.

Bioinspired Flexible Volatile Organic Compounds Sensor Based on Dynamic Surface Wrinkling with Dual-Signal Response.

Living systems can respond to external stimuli by dynamic interface changes. Moreover, natural wrinkle structures allow the surface to switch dynamically and reversibly from flat to rough in response to specific stimuli. Artificial wrinkle structures have been developed for applications such as optical devices, mechanical sensors, and microfluidic devices. However, chemical molecule-triggered flexible sensors based on dynamic surface wrinkling have not been demonstrated. Inspired by human skin wrinkling, herein, a volatile organic compound (VOC)-responsive flexible sensor with a switchable dual-signal response (transparency and resistance) is achieved based on a multilayered Ag nanowire (AgNW)/SiOx /polydimethylsiloxane (PDMS) film. Wrinkle structures can form dynamically in response to VOC vapors (such as ethanol, toluene, acetone, formaldehyde, and methanol) due to the instability of the multilayer induced by their different swelling capabilities. By controlling the modulus of PDMS and the thickness of the SiOx layer, tunable sensitivities in resistance and transparency of the device are achieved. Additionally, the proximity mechanism of the solubility parameter is proposed, which explains the high selectivity of the device toward ethanol vapor compared with that of other VOCs well. This stimuli-responsive sensor exhibits the dynamic visual feedback and the quantitative electrical signal, which provide a novel approach for developing smart flexible electronics.

Zinc ferrite based gas sensors: A review

Abstract Flammable, explosive and toxic gases, such as hydrogen, hydrogen sulfide and volatile organic compounds vapor, are major threats to the ecological environment safety and human health. Among the available technologies, gas sensing is a vital component, and has been widely studied in literature for early detection and warning. As a metal oxide semiconductor, zinc ferrite (ZnFe2O4) represents a kind of promising gas sensing material with a spinel structure, which also shows a fine gas sensing performance to reducing gases. Due to its great potentials and widespread applications, this article is intended to provide a review on the latest development in zinc ferrite based gas sensors. We first discuss the general gas sensing mechanism of ZnFe2O4 sensor. This is followed by a review of the recent progress about zinc ferrite based gas sensors from several aspects: different micro-morphology, element doping and heterostructure materials. In the end, we propose that combining ZnFe2O4 which provides unique microstructure (such as the multi-layer porous shells hollow structure), with the semiconductors such as graphene, which provide excellent physical properties. It is expected that the mentioned composites contribute to improving selectivity, long-term stability, and other sensing performance of sensors at room or low temperature.

Modeling the Effect of Relative Humidity on Adsorption Dynamics of Volatile Organic Compound onto Activated Carbon.

A two-dimensional heterogeneous mathematical model was developed and validated to study the effect of relative humidity on volatile organic compound (VOC) adsorption onto activated carbon. The dynamic adsorption model consists of the macroscopic mass, momentum, and energy conservation equations and includes a multicomponent adsorption isotherm to predict the competitive adsorption equilibria between VOC and water vapor, which is described by an extended Manes method. Experimental verifications show that the model predicted the breakthrough profiles during competitive adsorption of the studied VOCs (2-propanol, acetone, n-butanol, toluene, 1,2,4-trimethylbenzene) at relative humidity range 0-95% with an overall mean relative absolute error (MRAE) of 11.8% for dry (0% RH) conditions and 17.2% for humid (55 and 95% RH) conditions, and normalized root-mean-square error (NRMSE) of 5.5 and 8.4% for dry and humid conditions, respectively. Sensitivity analysis was also conducted to test the robustness of the model in accounting for the impact of relative humidity on VOC adsorption by varying the adsorption temperature. Good agreement was observed between the experimental and simulated results with an overall MRAE of 12.4 and 7.1% for the breakthrough profiles and adsorption capacity, respectively. The model can be used to quantify the impact of carrier gas relative humidity during adsorption of contaminants from gas streams, which is useful when optimizing adsorber design and operating conditions.

Fabrication of Thin Films of Phosphonated Calix[4]Arene Bearing Crown Ether and Their Gas Sensing Properties

Calix[4]arenes bearing phosphate and crown ether groups are shown to hold considerable promise as the active layer in volatile organic compound (VOC) vapor sensor. Its chemical sensing selectivity and sensitivity can be altered by different alkyl side chains. These organic architectures were successfully deposited by the spin coating method on gold-coated glass surfaces. Surface plasmon resonance technique was used for VOCs detection to evaluate the chemical-sensing properties of these calix[4]arene derivatives. Spun thin films of calix[4]arene derivatives were exposed to a variety of VOC vapors, and the resonance angles changes of these films were recorded for the specific analyte vapors, such as chloroform, carbon tetrachloride, dichloromethane, ethanol, benzene, and toluene. Measurements were made at room temperature, and the responses were found to be fast and appeared to be completely reversible. The sensing results showed similar response patterns, and our data strongly indicate that response of used thin films of calix[4]arene derivatives to chloroform is much higher than those of any other VOCs used with the values of 0.47 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , 1.042 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , and 1.952 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> (% / ppm) for the compounds 1, 2, and 3, respectively. Furthermore, gas sensing interaction mechanisms of the thin films were evaluated in terms of the molar volumes, dipole moments, and refractive indexes of the analyzed gas molecules.

Competitive adsorption equilibrium modeling of volatile organic compound (VOC) and water vapor onto activated carbon

In this study, the Potential theory-based Manes method was used to describe competitive multicomponent adsorption of VOC and water vapor onto activated carbon. The thermodynamically consistent method was extended to water-miscible VOCs using a Raoult’s law-like relation. The method uses as input the pure single-component adsorption isotherms, which were obtained from the modified Dubinin-Radushkevich (MDR) model for VOCs and the Qi-Hay-Rood (QHR) model for water vapor. The MDR model was applicable for the studied VOCs (2-propanol, acetone, n-butanol, toluene, 1,2,4-trimethylbenzene) with an overall r2 value of 0.998. The QHR isotherm provided a good description for water vapor adsorption on activated carbon with 0.999 r2 value. Experimental validation tests revealed that the multicomponent adsorption isotherm model predicted the VOC adsorption capacity during competitive adsorption with water vapor with an overall mean relative absolute error (MRAE) of 1.9% for non-polar VOCs and 5.2% for polar VOCs. These results are encouraging, as they indicate a good agreement between modeled and experimental results. Hence, the model can potentially be integrated with dynamic adsorption models to optimize adsorber design and operation or model adsorption kinetics.