Nonpolar Volatile Organic Compounds Research Articles

3D monolithic composites TiO2/HKUST-1/RGO@melamine foam with improved surface mass transfer for efficient photocatalytic degradation of toluene gas

Currently, photocatalytic technology mostly uses powdered TiO2 catalysts, which are not conducive to recycling, limit the contact between volatile organic compounds (VOCs) and the photocatalyst, and result in lower mass transfer efficiency in gas-solid reactions. Meanwhile, TiO2 catalysts including the electrospun TiO2 nanofibers with hydrophilic surfaces are not favorable for the infiltration and adsorption of non-polar VOCs. To solve these problems, in this work, the monolithic composites TiO2/HKUST-1/RGO@melamine foam (named MRTH) with improved surface mass transfer composed of metal-organic framework (HKUST-1), graphene oxide (GO) and electrospun TiO2 nanofibers was designed. The metal-organic framework HKUST-1 plays a role in promoting the adsorption of toluene, while the reduced graphene oxide (RGO) facilitates the infiltration of non-polar molecules on the surface of the composite and has better electron transport capability. A type II heterojunction between the electrospun TiO2 nanofibers and HKUST-1 formed in the monolithic composites suppresses the recombination of electron-hole pairs and extends their lifespan. Comparing with the bare electrospun TiO2 nanofibers, the MRTH foam composites exhibit a wider light absorption range, hydrophilic and oleophobic properties and a higher separation efficiency of photogenerated carriers. In 90 min of dark adsorption, the removal rate of toluene over MRTH-8 was 52.32 %, while under irradiation by xenon lamp for 150 min, the removal rate over MRTH-8 reached 90.15 %. The amount of monolithic foam composites can also be easily adjusted in the reactor to achieve the best possible removal of the contaminant. The prepared composite materials have been characterized in detail, and the possible mechanisms have also been discussed. The foam composites prepared in this work have high catalytic activity and gas-solid reaction mass transfer efficiency, so they have wide practical application prospects in the field of VOCs abatement.

Anti-competitive adsorption of gaseous benzene on hydrophilic microporous carbon in humid conditions

The adsorption capture of ambient volatile organic compounds (VOCs) is of practical importance for air quality management. Herein, unique anti-competitive adsorption behavior of benzene on a hydrophilic activated carbon (Procarb-900 (P900)) is evidenced in the presence of competing components (e.g., formaldehyde (FA) and/or moisture). Contrary to general expectations, the adsorption capacity of 10 Pa benzene (QB) onto P900 (30 mg) at the 99 % breakthrough level improves from 144.8 to 187 mg g−1 as the relative humidity (RH) increases from 0 to 25 %. Such pattern is maintained at 183.9 mg g−1 even at the relatively high RH of 50 %. Furthermore, QB exhibits a remarkable increase of 56.1 % (to 226.0 mg g−1) in the binary phase (100 ppm benzene plus 50 ppm FA) relative to its single phase (144.8 mg g−1). The kinetic studies confirm the occurrence of anti-competitive adsorption of benzene under humid conditions with the unusual decrease in rate constants at the elevated RHs (i.e., 25 and 50 %). The thermodynamic studies suggest the exothermic nature of benzene adsorption onto P900. The hydrophilicity of P900's outer surface promotes the preferential adsorption of polar FA and water vapor over non-polar benzene, which deforms the activated carbon texture and lowers the pore size distribution (PSD). The narrow PSD enhances benzene uptake in the complex systems due to the confinement effect. Overall, this study offers insights into the unique anti-competitive adsorption of non-polar VOCs (e.g., benzene) on hydrophilic microporous adsorbents in the presence of potential interferences such as polar water vapor and FA. These findings offer a guideline for the practical implementation of adsorption techniques for gaseous VOCs in humid conditions.

Determining the fatty acids, polar and non-polar volatile organic compounds of the veterinary preparation “Trametin Plus”

For the prevention and treatment of associated gastrointestinal and respiratory diseases of growing stock, a new veterinary preparation “Trametin Plus” is proposed. This drug is obtained from fungi-xylotrophs using biotechnology methods. The properties of such preparations depend on bioactive substances included in their composition.Available publications present miscellaneous information on the lipogenesis features and fatty acids composition synthesized by wood-destroying fungi. In this work, we study the qualitative and quantitative composition of fatty acids and analyze volatile polar and non-polar organic compounds of “Trametin Plus”. The total concentration of fatty acids was found to be 70 µg/g, with 50.0% being free acids and 50.0% being their esters. Squalene was established to be the most dominant non-polar volatile component. Concerning the minor non-polar volatile components of “Trametin Plus”, these are amino acids with a low molecular weight, such as glycine, arginine and β-alanine. The analysis confirms the multicomponent composition of the preparation, which accounts for its diverse biological properties, namely antibacterial, antiviral, antioxidant and immune-boosting activity. These properties determine the high health-promoting efficacy of the studied veterinary preparation.

Volatile Organic Compounds Adsorption Capacities of Zeolite/Activated Carbon Composites Formed by Electrostatic Self-Assembly.

Activated carbon (AC) is a broad-spectrum adsorbent but is flammable and has low adsorption capacities for polar and/or high-boiling volatile organic compounds (VOCs), while zeolites exhibit high thermal stability but poor adsorption of macromolecular and nonpolar VOCs. In this study, zeolite/AC composites were synthesized with the aim of obtaining broad-spectrum, efficient, and safe adsorbents for VOCs. Dimethyldiallylammonium chloride (DDA)-modified AC was used as a carrier for an in situ hydrothermal reaction enabling assembly with zeolites due to electrostatic attraction. Interface models were constructed for their phases, which revealed the binding force and simulated the binding process. The adsorption and flame resistance of the composites were evaluated. The results showed that DDA effectively modified AC to give it a long-lasting positive charge in solutions. High-silicon and pure-silicon zeolites exhibited low negative charges or were even neutral; it was difficult to combine with the modified AC via electrostatic attractions. Instead, LTA zeolites with high aluminum contents and negative charges were used, and the seed-induction method was used. Ethanol and ultrasonic dispersion were used to prevent agglomeration of the seeds and modified AC powder, so they were self-assembled electrostatically. Moreover, the crystallization time was extended and composites with high zeolite loadings were successfully prepared. According to the model calculation, the binding energy between the zeolite and AC before and after the DDA modification were 324.97 and 1076.46 kcal mol-1, respectively, and the distance between them was shortened by 2.7 Å after DDA treatment. As a result, AC and zeolite combined more closely and exhibited a stronger binding energy. The adsorption capacity for highly polar dichloromethane was improved by zeolite loading on the AC, and the bed penetration time was doubled. However, impregnation with inorganic sodium enhanced the reactivities of the organic components in the composite, and the ignition point was slightly reduced. Furthermore, the electrostatic self-assembly method can expand to prepare the LTA zeolite/columnar AC composite from shaped AC, greatly improving its application prospects.

Biomass Derived, Hierarchically Porous, Activated Starbons® as Adsorbents for Volatile Organic Compounds.

The use of potassium hydroxide activated Starbons® derived from starch and alginic acid as adsorbents for 29 volatile organic compounds (VOCs) was investigated. In every case, the alginic acid derived Starbon® (A800K2) was found to be the optimal adsorbent, significantly outperforming both commercial activated carbon and starch derived, activated Starbon® (S800K2). The saturated adsorption capacity of A800K2 depends on both the size of the VOC and the functional groups it contains. The highest saturated adsorption capacities were obtained with small VOCs. For VOC's of similar size, the presence of polarizable electrons in lone pairs or π-bonds within non-polar VOCs was beneficial. Analysis of porosimetry data suggests that the VOC's are being adsorbed within the pore structure of A800K2 rather than just on its surface. The adsorption was completely reversible by thermal treatment of the saturated Starbon® under vacuum.

Adsorption and desorption of a mixture of volatile organic Compounds: Impact of activated carbon porosity

Cyclic adsorption–desorption on activated carbon is typically used to control volatile organic compound (VOC) emissions from automotive paint booths. In this study, the impact of activated carbon porosity on adsorption–desorption performance was investigated using a mixture of industrially relevant surrogate VOCs (alcohol, ester, ketone, glycol ether, aromatic hydrocarbons, n-alkane) as a feed stream. Three commercially available beaded activated carbons (BACs) with similar chemical properties (e.g., surface oxygen content) but different structural properties (e.g., surface area, pore volume, microporosity) were used, allowing for isolating the effect of carbon porosity on competitive adsorption. Effluent streams during adsorption and desorption were analyzed by gas chromatography-mass spectrometry (GC–MS) and flame-ionization detector (FID). Overall, BACs with higher total pore volume achieved higher VOC uptake and longer adsorption breakthrough time. For adsorption and desorption kinetics, however, BACs with a higher share of mesopores showed faster kinetics in both cases. Overall, VOCs with higher boiling points, larger molecular weights, and/or lower polarity displaced VOCs with lower boiling points, smaller molecular weights, and/or higher polarity, via competitive adsorption, with this phenomenon being more apparent in mesoporous BACs. Traces of high-boiling-point, nonpolar VOCs were retained on all BACs at the end of the desorption step, owing to strong physical adsorption. Closure analysis based on gravimetric measurements was consistent with GC–MS results obtained during adsorption and desorption. The findings have important implications for industrial applications, indicating that the adsorber should be designed to ensure effective control of different VOCs with varying adsorption affinities.

Room Temperature Humidity Tolerant Xylene Sensor Using a Sn-SnO2 Nanocomposite

Xylene is one of the representative indoor pollutants, even in ppb levels, that affect human health directly. Due to the non-polar and less reactive nature of xylene, its room temperature detection is challenging. This work demonstrates a metallic tin-doped Sn-SnO2 nanocomposite under controlled pH conditions via a simple solvothermal route. The Sn nanoparticles are uniformly distributed inside the SnO2 nanospheres of ∼70 nm with a high specific surface area of 118.8 m2/g. The surface of the Sn-SnO2 nanocomposite exhibits strong affinity toward benzene, toluene, ethylbenzene, and xylene (BTEX) compared to other polar volatile organic compounds (VOCs) such as ethanol, acetone, isopropyl alcohol, formaldehyde, and chloroform tested in this study. The sensor's response is highest for xylene among BTEX molecules. Under ambient room temperature conditions, the sensor exhibits a linear response to xylene in the 1-100 ppm range with a sensitivity of ∼255% at 60 ppm within ∼1.5 s and recovers in ∼40 s. The sensor is hardly affected by humidity variations (40-70%), leading to enhanced reliability and repeatability under dynamic environmental conditions. The meso and microporous nanosphere morphology act as a nanocontainer for non-polar VOCs to diffuse inside the nanostructures, providing easy accessibility. The metallic Sn increases the affinity for less reactive xylene at room temperature. Thus, the nanocatalytic Sn-SnO2 nanocomposite is an active gas/VOC sensing material and provides an effective solution for sensing major indoor pollutants under humid conditions.

Spectral comparison of nanoporous silica-adsorbed organic molecules with gaseous and liquid states using a new waveguide technology

Nanoporous materials play an important role in many applications including separations and sensing, therefore understanding surface interactions, molecular adsorption, and nanoconfinement phenomena are important. Here we use near-infrared spectroscopy to measure spectra of volatile organic compounds (VOCs) adsorbed inside a nanoporous silica waveguide and compare to the spectral features of the VOCs’ gas and liquid phase spectra. The 10 mm long nanoporous waveguide has a transparent optical window between 1200 and 2200 nm that allows sensitive near-infrared measurements of a range of polar and non-polar VOCs. For the non-polar compounds, the spectra of the molecules adsorbed in the nanopores have similar spectral features to those of the gas molecules in free space. However, for the polar compounds, there are more prominent spectral similarities between the adsorbed molecules and their corresponding liquid spectra. Interestingly, we also observed that the 10 mm path length porous waveguide was capable of sensing gas concentration at least one order of magnitude lower compared to a 400 mm path length conventional gas-cell. The novel optical waveguide allows for sensitive measurement in the near-infrared, demonstrating a strong potential to be used as a tool to study adsorption in nanoporous materials and as a gas sensor.

Sorption Kinetics and Sequential Adsorption Analysis of Volatile Organic Compounds on Mesoporous Silica.

Adsorption-desorption behaviors of polar and nonpolar volatile organic compounds (VOCs), namely, isopropanol and nonane, on mesoporous silica were studied using optical reflectance spectroscopy. Mesoporous silica was fabricated via electrochemical etching of silicon and subsequent thermal oxidation, resulting in an average pore diameter of 11 nm and a surface area of approximately 493 m2/g. The optical thickness of the porous layer, which is proportional to the number of adsorbed molecules, was measured using visible light reflectance interferometry. In situ adsorption and desorption kinetics were obtained for various mesoporous silica temperatures ranging from 10 to 70 °C. Sorption as a function of temperature was acquired for isopropanol and nonane. Sequential adsorption measurements of isopropanol and nonane were performed and showed that, when one VOC is introduced immediately following another, the second VOC displaces the first one regardless of the VOC's polarity and the strength of its interaction with the silica surface.

The co-adsorption potential of metal–organic framework/activated carbon composites against both polar and non-polar volatile organic compounds in air

Adsorbents with high surface area and diverse functional groups are regarded as an effective option to deal with volatile organic compounds with different polarities. Herein, a metal–organic framework-199 (MOF-199 (prototypical Cu-MOF))/powdered activated carbon (PAC) composite (MOF-199@PAC) was fabricated and utilized to simultaneously treat multiple VOC system consisting of both non-polar (i.e., benzene) and polar VOCs (i.e., methyl ethyl ketone (MEK)). Kinetic and isotherm models combined with density functional theory simulations were also employed to address the adsorption mechanism of different VOCs onto the MOF-199@PAC composite (e.g., relative to pristine PAC and MOF-199). The overall results suggest that the MOF-199@PAC composite should be used efficiently for the adsorptive removal of polar (e.g., MEK) and non-polar VOCs (e.g., benzene) on its surface with the aid of abundant π-π conjugated sites and polar groups, respectively.

Ultra-fast detection and monitoring of cancerous volatile organic compounds in environment using graphene oxide modified CNT aerogel hybrid gas sensor

Ultra-fast detection of cancerous volatile organic compounds (VOCs) by carbon nanotube aerogel (CNT aerogel)-graphene oxide (GO) hybrid network has been studied in this paper. VOCs, especially non-polar compounds are difficult to detect due to their low electronegativity. A homogenous GO solution was drop cast on CNT aerogel film, both developed in-house, to obtain the CNT aerogel-GO composite. The CNT aerogel contains multi-directional porous CNT webs providing a stable and compact platform for GO adsorption. The loading concentration of GO and O/C ratios were optimized to obtain a highly sensitive CNT aerogel-GO hybrid sensor. The hybrid sensor could detect a range of non-polar VOCs like benzene, hexane, toluene, cyclohexane, and chlorobenzene with a limit of detection around 70 ppb. The optimized CNT aerogel-GO hybrid sensor showed 3 times better sensing performance than the bare CNT aerogel sensor. The principal component analysis (PCA) plot showed discrimination in all the VOCs as they all were distinct and spread over all four quadrants, indicating highly selective behavior of the sensor. Chemical and structural analysis by X-ray photoelectron spectroscopy and Raman spectrum showed that the oxygen loading could change the sp2 structure, making it ideal for sensing applications. The electron micrography images confirm the uniformity of the GO layer on the CNT aerogel. It is concluded that the concomitant formation of the CNT-GO junction can achieve better interaction and charge transfer during hybrid sensor fabrication. Subsequently, a sensitive, fast and durable CNT aerogel-GO hybrid sensor can be obtained for detection and continuous monitoring of cancerous VOCs.

The Co-Adsorption Potential of Metal-Organic Framework/Activated Carbon Composites Against Both Polar and Non-Polar Volatile Organic Compounds in Air

The Co-Adsorption Potential of Metal-Organic Framework/Activated Carbon Composites Against Both Polar and Non-Polar Volatile Organic Compounds in Air

The control on adsorption kinetics and selectivity of formaldehyde in relation to different surface-modification approaches for microporous carbon bed systems

It is perceived that surface modification of microporous carbon is an efficient option to remove light-weight volatile organic compounds (VOCs) like formaldehyde (FA). To adjust textural characteristics with surface functionalities of amine/sulfur and amino-silane, the commercial activated carbon (AC) was treated with dicyandiamide/thiourea (AC-M) and N-[3-(trimethoxysilyl)propyl]ethylenedia (AC-S), respectively, by thermal/microwave-assisted solvothermal methods. The adsorption performance of honeycomb air filters packed with different bed heights of AC-M/-S adsorbents (e.g., 1.38 ± 0.05, 6.36 ± 0.06, 7.99 ± 0.04, and 10.93 ± 0.04 mm) was evaluated (relative to commercial AC-based filters) towards the adsorption removal of FA (10 Pa) in both single and binary mixtures with benzene (at 10 Pa). . Based on the partition coefficient and kinetic metrics, the AC-M/-S based filters showed higher efficacy for FA capture than commercial AC filter with increasing bed height (e.g., ≥ 7.99 ± 0.04 mm) to reflect the increased number of Lewis acid/base active sites on the bed surface. At the highest bed height (10.93±0.04 mm), AC-S was far superior with significantly enhanced selectivity of FA (by 20 times) over benzene with the accelerated mass transfer and acid-base surface interactions at the gas-solid interface. In contrast, AC-M outperformed commercial ACs for benzene adsorption from the binary gas mixture (breakthrough time (τ-value) of 683 min) with the aid of the improved surface porosity (71.8%) through the modification process. The kinematic data also confirmed that the adsorption affinity of modified AC-M/-S adsorbents was unaffected by the feed gas composition (single or binary phase) at the initial BT region. It thus supports the key role of surface modification technique on the enhanced adsorptivity of aldehyde and/or aromatic VOCs. This study is expected to help expand our basic knowledge on the interplay between surface/textural characteristics of modified AC and fixed-bed height to control the adsorptivity of air filter for efficient trapping of FA in either single or mixed phases with non-polar VOCs (like benzene).

Method for Accurate Quantitation of Volatile Organic Compounds in Urine Using Point of Collection Internal Standard Addition.

A method to achieve accurate measurement of unmetabolized volatile organic compounds (VOCs) in urine was developed and characterized. The method incorporates a novel preanalytical approach of adding isotopically labeled internal standard (ISTD) analogues directly to the collection container at the point of collection to compensate for analyte loss to the headspace and the collection container surfaces. Using this approach, 45 toxic VOCs ranging in water solubility and boiling point were evaluated and analyzed by headspace solid-phase microextraction/gas chromatography–mass spectrometry. Results show that urine VOCs could be equally lost to the container headspace as to the container surface suggesting similarity of these two regions as partition phases. Surface adsorption loss was found to trend with compound water solubility. In particular, with no headspace, more nonpolar VOCs experienced substantial losses (e.g., 48% for hexane) in a standard 120 mL urine cup at concentrations in the low- and sub-ppb range. The most polar VOCs evaluated (e.g., tetrahydrofuran) showed no significant loss. Other commonly practiced methods for urine sample collection and analysis such as aliquoting, specimen freezing, and use of surrogate ISTD were found to significantly bias results. With this method, we achieved errors ranging from −8.0 to 4.8% of spiked urine specimens. Paired urine and blood specimens from cigarette smokers were compared to assess this method.

Surface acoustic wave (SAW) sensor for volatile organic compounds (VOCs) detection with calix[4]arene functionalized Gold nanorods (AuNRs) and silver nanocubes (AgNCs)

Abstract The detection of chemicals in gas-phase has been employed in a wide variety of applications, including indoor air quality and environmental monitoring, chemical and biochemical processing, and medical diagnostics such as lung cancer screening. In this study, gold nanorod (AuNR) and silver nanocube (AgNC) molecules were functionalized with thiol (S- terminal) containing Calix[4]arene and were investigated for their molecular recognition properties on surface acoustic wave (SAW) transducer device surfaces. These novel sensing materials on transducer SAW device were investigated for the detection of polar (acetone, ethanol, chloroform, and humidity) and nonpolar (n-hexane, toluene, isoprene) volatile organic compounds (VOCs), among which are key markers for disease diagnosis, such as toluene present in exhaled breath of lung cancer patients. Sensor responses were discussed under various concentration levels in terms of selectivity, sensitivity, limit of detection, and response time. After AuNR and AgNC modification with Calix[4]arene, sensitivity of sensors has reached up to six to eight-fold higher than the individual responses, with a selectivity towards chloroform and toluene, respectively.

Activated carbon fibers via reductive carbonization of cellulosic biomass for adsorption of nonpolar volatile organic compounds

Reductive carbonization of cellulosic fibers via nano-sized nickel catalyst in the presence of hydrogen was examined for production of activated carbon fibers (ACFs). The results showed that 99.5 % of oxygen originally presented in the biomass was removed as measured by using X-ray Photoelectron Spectroscopy (XPS), with over 63 % carbon in form of reductive species. Such reductive ACFs demonstrated high adsorption capacities for non-polar volatile organic compounds (VOCs). Particularly, the reductive ACFs absorbed benzene at a capacity that was 8 times higher than traditionally prepared carbon fibers. That can be attributed to both the reductive surface chemistry and morphology generated by the activity of the nanocatalysts. The unique network structure of the ACFs also provided a fine conductivity, that made it possible for efficient material regeneration via electrothermal desorption. The absorbed VOCs could be completely released within 1 min upon application of a moderate electrical current, and the regenerated materials could regain 100 % of its adsorption capacity even after repeated adsorption and desorption cycles. This work demonstrated for the first time the use of nanocatalyst-assisted reductive carbonization in manipulating surface properties of bio-based carbon materials, promising the production of a new class of carbon materials for industrial applications including air quality control, gas separation, and fuel storage.

Enhancing mixed toluene and formaldehyde pollutant removal by Zamioculcas zamiifolia combined with Sansevieria trifasciata and its CO2 emission.

Indoor air pollutants comprise both polar and non-polar volatile organic compounds (VOCs). Indoor potted plants are well known for their innate ability to improve indoor air quality (IAQ) by detoxification of indoor air pollutants. In this study, a combination of two different plant species comprising a C3 plant (Zamioculcas zamiifolia) and a crassulacean acid metabolism (CAM) plant (Sansevieria trifasciata) was used to remove polar and non-polar VOCs and minimize CO2 emission from the chamber. Z. zamiifolia and S. trifasciata, when combined, were able to remove more than 95% of pollutants within 48h and could do so for six consecutive pollutant's exposure cycles. The CO2 concentration was reduced from 410 down to 160ppm inside the chamber. Our results showed that using plant growth medium rather than soil had a positive effect on decreasing CO2. We also re-affirmed the role of formaldehyde dehydrogenase in the detoxification and metabolism of formaldehyde and that exposure of plants to pollutants enhances the activity of this enzyme in the shoots of both Z. zamiifolia and S. trifasciata. Overall, a mixed plant of Z. zamiifolia and S. trifasciata was more efficient at removing mixed pollutants and reducing CO2 than individual plants.

Innovative Approach to Photo-Chemiresistive Sensing Technology: Surface-Fluorinated SnO2 for VOC Detection.

Transparent electronics continues to revolutionize the way we perceive futuristic devices to be. In this work, we propose a technologically advanced volatile organic compound (VOC) sensor in the form of a thin-film transparent display fabricated using fluorinated SnO2 films. A solution-processed method for surface fluorination of SnO2 films using Selectfluor as a fluorinating agent has been developed. The doped fluorine was optimized to be <1%, resulting in a significant increase in conductivity and reduction in persistent photoconductivity accompanied by a faster decay of the photogenerated charge carriers. A combination of these modified properties, together with the intrinsic sensing ability of SnO2, was exploited in designing a transparent display sensor for ppm-level detection of VOCs at an operating temperature of merely 150 °C. Even a transparent metal mesh heater is integrated with the sensor for ease of operation, portability, and less power usage. A sensor reset method is developed while shortening the UV exposure time, enabling complete sensor recovery at low operating temperatures. The sensor is tested toward a variety of polar and nonpolar VOCs (amines, alcohols, carbonyls, alkanes, halo-alkanes, and esters), and it exhibits an easily differentiable response with sensitivity in line with the electron-donating tendency of the functional group present. This work opens up the door for multiplexed sensor arrays with the ability to detect and analyze multiple VOCs with specificity.

Soil–air partitioning of volatile organic compounds into soils with high water content

Environmental contextAssessing environmental and human health impacts of chemical spills relies on information about how chemicals move across multiple environments. We measured volatile contaminants in the air above soil saturated with water to provide estimates of air concentrations of selected chemicals released to soil from an oil refinery in Texas during Hurricane Harvey. Estimated concentrations were below recommended exposure limits, even in a worst-case scenario. AbstractThe emission of volatile organic compounds (VOCs) from soil into air is affected by soil moisture dynamics, soil temperature, solar irradiance and carbon availability. The high amount of water in soil can modify its properties, which changes how VOCs interact. We conducted a comprehensive measurement of the soil–air partition coefficient (KSA) of VOCs into water-saturated soil with both low and high water contents for polar, weakly polar and nonpolar VOCs into a mineral soil (S-clay) and soil containing a high amount of organic matter (S-om) under a water-saturated condition. Partitioning of non-polar substituted aromatics (1,2-dichlorobenzene and toluene) was sensitive to the organic matter content in water-saturated soil. 1,2-Dichlorobenzene and toluene had higher affinities to S-om than to S-clay at all investigated water contents because of their strong interaction with the organic matter in soil. KSA decreased with elevated water content only for non-polar substituted aromatic VOCs. Less hydrophobic VOCs (benzene and trichloroethylene) exhibited similar partitioning into both soils by sorbing onto the air-water interface and dissolving in soil water, while the organic matter did not affect partitioning. The weakly polar and polar VOCs (methyl tert-butyl ether and 1-butanol) showed similar partitioning into both soils by dissolving in soil water while sorption to the organic matter was significant only at high soil water contents. KSA of VOCs on soil with high organic matter content correlated strongly with psat and Koa, but not on mineral soil. Estimates of the air concentrations for a subset of VOCs released from one refinery during Hurricane Harvey in 2017 in Harris County, Texas were lower than the recommended exposure limits, even under a worst-case scenario.

Adsorption materials for volatile organic compounds (VOCs) and the key factors for VOCs adsorption process: A review

Volatile organic compounds are harmful to the environment and human health. Adsorption technology has been used to VOCs abatement for over 30 years and has proven to be an effective technology. This work provides a critical review of the recent research developments of VOCs adsorption materials and the key factors controlling the VOCs adsorption process. The average specific surface area, pore volume and VOCs adsorption capacity of different adsorption materials are metal organic frameworks (MOFs) > activated carbons (ACs) > hypercrosslinked polymeric resin (HPR) > zeolites. The mechanism of VOCs adsorption in adsorbent mainly includes electrostatic attraction, interaction between polar VOCs and hydrophilic sites, interaction between non-polar VOCs and hydrophobic sites, and partition in non-carbonized portion. With the specific surface area, pore volume, and surface chemical functional groups increase and the pore size decreases, the adsorption capacity increases. The volume of narrow micropores (size < 0.7 nm) controls the adsorption of VOCs. In addition, methods of activation and surface modification for improving the adsorption capacity of VOCs are discussed. The development of targeted modified adsorption materials and new adsorption materials and reduction of production costs of adsorption materials are especially important in future research.