Common Volatile Organic Compounds Research Articles

Enhanced ethanol sensing response of nanostructured Ce-doped CuO thin films

CuO based thin films doped with Ce concentrations varying from 0 to 8 mol% were prepared by chemical spray pyrolysis. X-ray diffraction analysis revealed bandgap modulation which is dependant on Ce doping and also showed perservation of the single phased monoclinic CuO structure for all the films after doping indicating successful substitution of Ce4+ ions in host matrix. SEM and AFM microscopy showed changes in morphology as Ce doping was increased. And this appeared to have a significant role on the ethanol sensing capabilities of the thin films which were measured at different working temperatures. Good gas sensing stability and maximum response was observed for the 4% Ce thin film. The sensing device was found to be more responsive towards ethanol than other common volatile organic compounds such as methanol, acentronile, ammonia and acetone. The response and recovery times for the sensing suggest a chemosorbption mechanism.

A Miniaturized Quartz Crystal Microbalance (QCM) Measurement Instrument Based on a Phase-Locked Loop Circuit

The quartz crystal microbalance (QCM) has been widely used in laboratory settings as an analytical tool for recognizing and discriminating biological and chemical molecules of interest. As a result, recent studies have shown there to be considerable attention in practical applications of the QCM technique beyond the laboratory. However, most commercial QCM instruments are not suitable for off-laboratory usage. For field-deployable applications and in situ detection, the development of a portable QCM measurement system achieving comparable performance to benchtop instruments is highly desired. In this paper, we describe the development of a fully customizable, miniaturized, battery-powered, and cost-efficient QCM system employing a phase-locked loop (PLL) electronic circuit-based QCM measurement system. The performance of this developed system showed a minimum frequency resolution of approximately 0.22 Hz at 0.1 s measurement time. This novel, miniaturized system successfully demonstrated an ability to detect two common volatile organic compounds (VOCs), methanol and dichloromethane (DCM), and the obtained results were comparable to responses from a commercially available benchtop instrument.

Development of a headspace-gas chromatography/mass spectrometry method based on matrix-matched calibration for evaluating VOC content, characterization, source, and risk in RO membrane

Analytical method has been developed to determine volatile organic compounds (VOCs) in reverse osmosis (RO) membrane using headspace-gas chromatography/mass spectrometry (HS-GC/MS). The operating parameters, including incubation temperature, incubation time and the choice of matrix modifier, were investigated. The existence of matrix effect was evaluated and the VOC-free RO membrane was selected as the best material for developing matrix-matched calibration curve. At these optimized operating conditions, the established method was found to perform well — giving good linearity (r > 0.996), allowing for consistent repeatability (<9.5%), making possible high levels of VOC recoveries (84.7%–123%) and satisfactory detection limits (3.44–748 μg/kg). The method was applied to determining thirty-seven common VOCs for RO membrane. Toluene and N,N-dimethylformamide were the most abundant VOCs in measured samples, with average contents of 90 087 μg/kg and 249 957 μg/kg respectively. In addition, a range of other common compounds, including acetone, dichloromethane, hexane, chloroform, 1,2-dichloroethane, benzene, chlorobenzene, ethylbenzene, xylene, and styrene, were also found with content between N.D.—112 419 μg/kg in detection rate between 40%–100%. The analysis of VOC distribution provides further substantial evidence that the solvents used during the production of the RO membrane frequently are the main source of VOCs in commercial RO membrane. Our experiments proved that, of these VOCs, four compounds, dichloromethane, chloroform, 1,2-dichloroethane, and toluene, were hardly removed by pre-washing. The relationship between the content of VOCs in RO membrane and their corresponding concentration in filtrated water shows a highly positive correlation and the safety limit values for these four compounds are evaluated as 2.6 × 102–3.8 × 105 μg/kg, but more accurate and completed guideline values should be formulated to guarantee the RO membrane quality.

Boosting room-temperature ppb-level NO2 sensing over reduced graphene oxide by co-decoration of α-Fe2O3 and SnO2 nanocrystals

As promising sensing materials, reduced graphene oxide (RGO)-based nanomaterials have drawn considerable attention in the fields of gas monitoring owing to their low operating temperature. However, constructing RGO-based room-temperature gas sensors possessing ppb-level limit of detection with high sensitivity remains challenging. In this work, a series of highly sensitive NO2 sensors were fabricated using α-Fe2O3 and SnO2 co-decorated RGO hybrids (designated as α-Fe2O3/SnO2-RGO) as sensing materials. They were rationally synthesized by a one-pot hydrothermal method. Compared to SnO2 modified RGO hybrids (SnO2-RGO with bandgap of 3.88 eV), the bandgap energy of α-Fe2O3/SnO2-RGO hybrids (3.53 eV) was reduced by adding α-Fe2O3; the narrower bandgap facilitated the sensing materials to release more electrons and form more oxygen ions at room temperature. Besides, the high carrier migration of RGO, which served as continuous phase, identical structure with ultrasmall particle size of α-Fe2O3 and SnO2 (about 3–6 nm), and abundant chemisorbed oxygen species on the surface (20.8%) of the sensing materials, as well as their suitable bandgap (3.53 eV) in the sensing materials, significantly improved NO2 response at room temperature. Among the sensors fabricated, α-Fe2O3/SnO2-RGO-15-based NO2 sensor had the highest response of 7.4 with a short response time of 59 s towards 1 ppm NO2; it could even reach a response of 2.6 towards 100 ppb NO2. Notably, α-Fe2O3/SnO2-RGO-15 sample has excellent capability to recognize NO2, where the response value (7.4) towards 1 ppm NO2 is about 7 times higher than that of 100 ppm ammonia and common volatile organic compounds (formaldehyde, toluene, ethanol and acetone). Such NO2 sensor has superior repeatability with negligible response deviation towards 1 ppm NO2 for four reversible cycles. This makes it to have a great potential application in the field of NO2 detection.

Assessment of Volatile Organic Compounds Removal in Kuwait Wastewater Treatment Plants

This study presents the results of an analysis of the most common Volatile Organic Compounds (VOCs) in wastewater samples from one of the largest wastewater treatment plants in Kuwait. Samples from four different locations (plant influent, aeration tank inlet, aeration tank, and plant effluent) were collected weekly and were analyzed for toluene, benzene, xylene, 1, 3, 5 trimethylbenzene, dichloromethane and chloroform. The results showed that all the selected VOCs were detected except benzene. The average concentrations of VOCs that entered the treatment plant were as follows: chloroform 0.22 ± 0.03 μg/mL, dichloromethane 0.18 ± 0.05 μg/mL, toluene 0.08 ± 0.01 μg/mL, O-Xylene 0.03 μg/mL, M-Xylene 0.01 μg/mL, P-Xylene 0.02 μg/ml, and 1,3,5-trimethylbenzene 0.02 μg/mL. The concentration of VOCs during the treatment processes decreased for all the selected VOCs (treatment efficiency &gt;98%), except chloroform, which has increased. The disinfection process in the treatment plant might have generated byproducts (such as chloroform) which could have increased chloroform concentration. In conclusion, all of the analyzed VOCs in this study were lower than the maximum level of VOCs in treated wastewater.

Hydrothermal synthesis of Siliceous Beta Zeolite by an inorganic cation-driven strategy and its crystallization mechanism

Siliceous Beta zeolite and its metal-containing counterparts are effective adsorption and catalysis materials. To develop facile and efficient synthesis strategy would facilitate their large-scale production and application. Herein, we report the fluoride-free hydrothermal synthesis of siliceous Beta achieved by an inorganic cation-driven strategy. It is found that the types of inorganic cations are more critical than anions in determining the product phase. Inorganic cations with smaller sizes (such as Li+, Na+ and Mg2+) facilitate the synthesis of siliceous Beta, while the larger ones (such as K+, Ca2+ and NH4+) tend to give rise to impurity or amorphous materials. Crystallization mechanism investigation based on the Na+-added system revealed that inorganic cations can effectively promote the fast polymerization of SiO2 colloids at the initial stage. The crystallization occurs on the polymerized composites, yielding siliceous Beta with high solid yield. The resultant material is well characterized, which possesses few framework defects, high hydrophobicity and large adsorption uptake for toluene (one of the common volatile organic compounds). Breakthrough experiments further evidence the dynamic toluene adsorption capacity of the material is 24% higher than that of siliceous Beta synthesized by fluoride route.

Photochemical method for removing methane interference for improved gas analysis

Abstract. The development of laser spectroscopy has made it possible to measure minute changes in the concentrations of trace gases and their isotopic analogs. These single or even multiply substituted species occur at ratios from percent to below parts per million and contain important information concerning trace gas sources and transformations. Due to their low abundance, minimizing spectral interference from other gases in a mixture is essential. Options including traps and membranes are available to remove many specific impurities. Methods for removing CH4, however, are extremely limited as methane has low reactivity and adsorbs poorly to most materials. Here we demonstrate a novel method for CH4 removal via chlorine-initiated oxidation. Our motivation in developing the technique was to overcome methane interference in measurements of N2O isotopic analogs when using a cavity ring-down spectrometer. We describe the design and validation of a proof-of-concept device and a kinetic model to predict the dependence of the methane removal efficiency on the methane concentration [CH4], chlorine photolysis rate JCl2, chlorine concentration [Cl2] and residence time tR. The model was validated by comparison to experimental data and then used to predict the possible formation of troublesome side products and by-products including CCl4 and HCl. The removal of methane could be maintained with a peak removal efficiency &gt;98 % for ambient levels of methane at a flow rate of 7.5 mL min−1 with [Cl2] at 50 ppm. These tests show that our method is a viable option for continuous methane scrubbing. Additional measures may be needed to avoid complications due to the introduction of Cl2 and formation of HCl. Note that the method will also oxidize most other common volatile organic compounds. The system was tested in combination with a cavity ring-down methane spectrometer, and the developed method was shown to be successful at removing methane interference.

Volatile Profile Survey of Five Apple Varieties Grown in Southwest Colorado from Juice to Finished, Dry-Hopped Cider

The volatile organic compounds (VOCs) produced during cider fermentation, maturation, and dry hopping greatly impact enjoyment of the final product. To investigate the effect of apple variety on VOC development in cider, five apple varieties were picked from two orchards in southwest Colorado. Each apple variety was juiced, fermented with Lalvin QA23 Saccharomyces cerevisiae, dry-hopped with Citra hops, and analyzed separately alongside non-dry hopped controls. The aroma attributes of these historical southwest Colorado apples have never been explored, and few studies have chemically profiled the aromas of dry-hopped cider. A total of 73 VOCs were identified using headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) from fruit juice to cider. Ethyl esters, acetate esters, higher alcohols, and terpenes were the major aroma contributors observed in dry-hopped cider. The identity and concentrations of VOCs varied greatly between apple varieties, with only 24 common VOCs detected in all samples studied. This indicates the importance of apple variety choice in tuning the aroma profile of the finished cider. This method can be used to more effectively evaluate orchard or cider production treatments on cider quality. This case study also provides practical information for cider makers seeking to improve the quality of their products through consideration of fruit variety and dry hopping. Supplemental data for this article is available online at https://doi.org/10.1080/03610470.2021.2013645 .

The variability of volatile organic compounds in the indoor air of clinical environments

The development of clinical breath-analysis is confounded by the variability of background volatile organic compounds (VOCs). Reliable interpretation of clinical breath-analysis at individual, and cohort levels requires characterisation of clinical-VOC levels and exposures. Active-sampling with thermal-desorption/gas chromatography-mass spectrometry recorded and evaluated VOC concentrations in 245 samples of indoor air from three sites in a large National Health Service (NHS) provider trust in the UK over 27 months. Data deconvolution, alignment and clustering isolated 7344 features attributable to VOC and described the variability (composition and concentration) of respirable clinical VOC. 328 VOC were observed in more than 5% of the samples and 68 VOC appeared in more than 30% of samples. Common VOC were associated with exogenous and endogenous sources and 17 VOC were identified as seasonal differentiators. The presence of metabolites from the anaesthetic sevoflurane, and putative-disease biomarkers in room air, indicated that exhaled VOC were a source of background-pollution in clinical breath-testing activity. With the exception of solvents, and waxes associated with personal protective equipment (PPE), exhaled VOC concentrations above 3 µg m−3 are unlikely to arise from room air contamination, and in the absence of extensive survey-data, this level could be applied as a threshold for inclusion in studies, removing a potential environmental confounding-factor in developing breath-based diagnostics.

Photodegradation of acetone vapor by carbon dots decorated TiO2 catalyst: effects of experimental conditions

Being one of the most common volatile organic compounds (VOCs), acetone can be found in everyday products and high doses of acetone pose harmful effects on human health. Photocatalytic oxidation has captured the attention as an alternative feasible and cost-effective technology in treating VOCs. This study mainly focused on the photocatalytic performance of carbon dots (CDs) decorated TiO2 prepared using the microwave-assisted method in degrading acetone in a continuous flow under UVA irradiation at room temperature with various experimental conditions (initial concentrations, water contents and flow rates). The presence of carbon dots on the surface of TiO2 had improved the removal efficiency of the photocatalyst and maintained a good overall performance throughout the experiments. Significantly, the prepared CDs/TiO2 exhibited sustainable performance under the change of water contents which usually significantly impacts the performance of photocatalysts in general.

Rational design of a novel two-dimensional porous metal-organic framework material for efficient benzene sensor

As a common volatile organic compound, benzene (C6H6) exists in home decoration pollution gas widely, which causes great harm to the environment and human health. Therefore, it is necessary to rationally design advanced materials with high selectivity to detect and capture C6H6. Herein, combined with the d-band center theory and cohesive energy, a new two-dimensional metal-organic framework material, Ni-doped hexaaminobenzene-based coordination polymer (Ni-HAB-CP) is designed, and its application potential as a C6H6 sensor are systematically investigated by using first principles calculation. The result shows that Ni-HAB-CP has a strong adsorption for C6H6 without any additional method. In addition, Ni-HAB-CP can maintain good conductivity before and after adsorption, and C6H6 can be easily desorbed from the surface of Ni-HAB-CP by charge control. Moreover, the I-V curve calculated by Atomistix Toolkit (ATK) reveals that Ni-HAB-CP has high sensitivity and selectivity to C6H6. Hence, Ni-HAB-CP is expected to be used as a potential material for a highly efficient and recyclable C6H6 sensor in the future. The calculation and analysis methods used in this paper could provide a certain theoretical basis and reference for the future research of gas sensors.

Sago cycas-based hierarchical-structured porous carbon for adsorption of acetone vapour: preparation, characterization and performance.

The porous structure and oxygen-containing functional groups of carbon materials play important roles in the adsorption of volatile organic compounds (VOCs). In this study, hierarchical-structured porous carbons (HSPCs) with a large specific surface area and abundant oxygen-containing functional groups were prepared from sago cycas without a template or post-processing for acetone (one of the most common VOCs) adsorption. The micropore volume (0.41-1.15 cm3 g-1) and oxygen-containing functional groups (0.3-1.92 mmol g-1) of HSPCs were manipulated by adjusting the activation temperature. Static adsorption data showed that the HSPC activated at 600 °C (HSPC-600) was superior for acetone adsorption, and a maximum adsorption capacity of 3.75 mmol g-1 was achieved at 25 °C and 0.1 kPa. Breakthrough curves and cyclic adsorption-desorption tests demonstrated the dynamic adsorption capacity and regeneration performance of HSPC-600 were excellent as well. The adsorption isotherms were well described by Langmuir and Langmuir-Freundlich models, indicating the adsorption of acetone on HSPCs is a monolayer adsorption process. Due to electrostatic interaction, hydrogen bond and van der Waals forces between acetone molecules and oxygen-containing functional groups, the adsorption capacity of HSPCs for acetone was significantly improved at low relative pressure. This study may provide a peculiar insight into the development of high-performance acetone adsorbent.

The Proof-of-Concept: The Transformation of Naphthalene and Its Derivatives into Decalin and Its Derivatives during Thermochemical Processing of Sewage Sludge

One solution for sewage sludge (SS) management is thermochemical treatment due to torrefaction and pyrolysis with biochar production. SS biochar may contain toxic volatile organic compounds (VOCs) and polyaromatic hydrocarbons (PAHs). This study aimed to determine the process temperature’s influence on the qualitative PAHs emission from SS-biochar and the transformation of PAHs contained in SS. SS was torrefied/pyrolyzed under temperatures 200–600 °C with 1 h residence time. The headspace solid-phase microextraction (SPME) combined with gas chromatography and mass spectrometry (HS-SPME-GC-MS) analytical procedure of VOCs and PAHs emission was applied. The highest abundance of numerous VOCs was found for torrefaction ranges of temperature. The increase of temperatures to the pyrolytic range decreased the presence of VOCs and PAHs in biochar. The most common VOCs emitted from thermally processed SS were acetone, 2-methylfuran, 2-butanone, 3-metylbutanal, benzene, decalin, and acetic acid. The naphthalene present in SS converted to decalin (and other decalin derivatives), which may lead to SS biochar being considered hazardous material.

Efficiency of the Vehicle Cabin Air Filters for Removing Black Carbon Particles and BTEX from the Air Intake

A laboratory study was conducted to evaluate 11 vehicular cabin filters (including electrostatic filters) in removing fine particles. Two filters with charcoal were also evaluated to understand their usefulness in removing five common volatile organic compounds, including benzene, toluene, ethylbenzene, and xylene isomers (BTEX). Filters were found to show considerably different particle filtration efficiencies (FE). Electrostatic filters were found to provide 20–60% better FE across all particle diameters (6–520 nm). For 6 nm particles, FE from 78 to 94% were observed (from the worst to the best filters), while at 520 nm, FE varied from 35 to 60%. The best group of filters provided 44–46% FE for capturing the most penetrating particles (100–300 nm), while the worst group of filters provided only 10–11% FE. The filtration behavior of nominal filters was typically stable (with respect to particle number, black carbon, and particulate matter mass) over the course of 1–2 years of usage. The benefits of the electrostatic filters were significant, but such advantages were observed to gradually dissipate over the course of about 1 year; by then, the electrostatic filter becomes no different compared to a nominal filter in terms of filtration behavior. Charcoal filters showed variabilities in removing BTEX, and removal efficiencies varied from 11 to 41%.

Identification of volatile biomarkers for high-throughput sensing of soft rot and Pythium leak diseases in stored potatoes

Soft rot and Pythium leak are postharvest storage diseases of potato tubers that can cause substantial crop losses in the US. This study focused on detecting volatile organic compounds (VOCs) associated with rot inoculated tubers during storage (up to 21 days) using headspace solid-phase microextraction (SPME) coupled to gas chromatography (GC) with mass spectrometry (MS) and flame ionization detector (FID) analysis. Russet Burbank and Ranger Russet tubers were inoculated with the rot pathogens. Static sampling with 50 min trapping time followed by GC–MS and GC–FID analysis identified 23 and 30 common VOCs from the pathogen inoculated tubers. Overall, n,n–dimethylmethylamine, acetone, 1–undecene, and styrene, occurred frequently and repeatability in inoculated samples based on GC–MS analysis, with the latter two found using GC–FID analysis as well. Identification of such biomarkers can be useful in developing high-throughput VOC sensing systems for early disease detection in potato storage facilities.

Nickel-Oxide Based Thick-Film Gas Sensors for Volatile Organic Compound Detection

In this paper, we report on the development of a highly sensitive and humidity-tolerant metal-oxide-based volatile organic compound (VOC) sensor, capable of rapidly detecting low concentrations of VOCs. For this, we successfully fabricated two different thicknesses of nickel oxide (NiO) sensors using a spin-coating technique and tested them with seven different common VOCs at 40% r.h. The measured film thickness of the spin-coated NiO was ~5 μm (S-5) and ~10 μm (S-10). The fastest response and recovery times for all VOCs were less than 80 s and 120 s, respectively. The highest response (Rg/Ra = 1.5 for 5 ppm ethanol) was observed at 350 °C for both sensors. Sensors were also tested in two different humidity conditions (40% and 90% r.h.). The humidity did not significantly influence the observed sensitivity of the films. Furthermore, S-10 NiO showed only a 3% drift in the baseline resistance between the two humidity conditions, making our sensor humidity-tolerant compared to traditional n-type sensors. Thus, we propose thick-film NiO (10 μm) sensing material as an interesting alternative VOC sensor that is fast and humidity-tolerant.

Sensing and Delineating Mixed-VOC Composition in the Air Using a Single Metal Oxide Sensor

Monitoring volatile organic compounds (VOCs) places a crucial role in environmental pollutants control and indoor air quality. In this study, a metal-oxide (MOx) sensor detector (used in a commercially available monitor) was employed to delineate the composition of air containing three common VOCs (ethanol, acetone, and hexane) under various concentrations. Experiments with a single component and double components were conducted to investigate how the solvents interact with the metal oxide sensor. The experimental results revealed that the affinity between VOC and sensor was in the following order: acetone &gt; ethanol &gt; n-hexane. A mathematical model was developed, based on the experimental findings and data analysis, to convert the output resistance value of the sensor into concentration values, which, in turn, can be used to calculate a VOC-based air quality index. Empirical equations were established based on inferences of vapour composition versus resistance trends, and on an approach of using original and diluted air samples to generate two sets of resistance data per sample. The calibration of numerous model parameters allowed matching simulated curves to measured data. Therefore, the predictive mathematical model enabled quantifying the total concentration of sensed VOCs, in addition to estimating the VOC composition. This first attempt to obtain semiquantitative data from a single MOx sensor, despite the remaining selectivity challenges, is aimed at expanding the capability of mobile air pollutants monitoring devices.

Sensor activity of titanium dioxide nanotubes in relation to acetone molecules

This paper presents the theoretical study results of the possibility of acetone, common volatile organic compound (VOCs) in human respiration, with titanium dioxide nanotubes. The efficiency of interaction of the acetone molecule with the TiO2 nanotube is analyzed. Recommendations for the creation of highly sensitive sensor devices using titanium dioxide nanotubes for diagnostics of various diseases have been developed.

Design and preparation of hollow NiO sphere- polyaniline composite for NH3 gas sensing at room temperature

The accurate and rapid sensing of NH3 at room temperature is a challenging conundrum for daily life and environment protection. In this work, we have explored an intriguing material, hollow NiO sphere composited with polyaniline (labelled as h-NiO-PANI) for NH3 gas sensing, fabricated by growing PANI on the hollow NiO sphere derived from solvothermal synthesis and calcination. Ni-Cu glycerate is obtained via solvothermal synthesis, which is a universal way to produce uniform glycerate microspheres. During calcination, the hollow sphere is ingeniously designed by taking advantage of the outward adhesion from CuO to the inner core. Polymerization of aniline on the hollow spheres is beneficial for large specific surface area and gas adsorption. Impressively, the sensor based on h-NiO-PANI exhibits favorable response to NH3 (ΔR/R0=43 % for 10 ppm, 149 s in response and 257 s in recovery), which is greatly better than the counterparts (NiO-PANI and PANI). Moreover, the sensor has also shown superb anti-interference against common volatile organic compounds (VOCs), water and humidity, along with the superior repeatability in 5 cycles and long-term stability in a week, manifesting the sensor a promising candidate in daily application. The enhanced gas sensing performance is attributed to the hollow structure and construction of p-p heterojunctions between NiO and PANI.

Study on the Performance of Copper‐Manganese Composite Oxide Catalysts for Toluene

AbstractCopper‐manganese (CuMn) composite oxide catalysts were prepared for the catalytic combustion of a common volatile organic compound, namely toluene. The structural properties of the catalysts were analysed by X‐ray diffraction (XRD), Brunauer‐Emmett‐Teller (BET) theory, X‐ray photoelectron spectroscopy (XPS) and hydrogen temperature‐programmed reduction (H2‐TPR). The catalytic stability was examined after 100 h. It was found that Cu1Mn1 exhibited the highest catalytic ability when the molar ratio of Cu : Mn was 1 : 1. The removal of toluene reached 90 % at a temperature below 229 °C. It was speculated that the Cu1.5Mn1.5O4 spinel structure and CuO were formed in the catalyst. The catalyst surface area was not the main factor affecting the catalytic activity. The catalysts displayed good stability and maintained high catalytic activity for a long time. Notably, fresh catalysts contained high amounts of high‐valent Mn4+ and Cu2+ cations, which played important roles in the catalytic combustion of toluene. The cations initiated the redox process and led to the conversion of toluene to CO2 and H2O. The reduced lattice oxygen supplied from air was transformed into surface oxygen on the catalyst. The catalytic combustion of toluene in the presence of CuMn composite oxide catalysts followed the Mars‐van Krevelen mechanism.