Typical Volatile Organic Compounds Research Articles

Dynamic Adsorption Model Fitting Studies of Typical VOCs Using Commercial Activated Carbon in a Fixed Bed

The adsorption behaviors of five typical volatile organic compounds (VOCs) onto one commercial activated carbon (CAC) in a fixed bed were investigated in this study. The selected CAC as a model adsorbent has a high surface area of 1099.74 m2 g−1. Moreover, five kinds of typical VOCs, including acetone, ethyl acetate, propyl acetate, butyl acetate, and isopropanol, were chosen as the target pollutants. The adsorption capacities of the above VOCs were 289.8, 389.4, 443.7, 467.4, and 474.3 mg g−1, respectively. The adsorption data were fitted by using two dynamic adsorption models (Boltzmann and Yoon-Nelson) and four kinetic models (pseudo-first-order, pseudo-second-order, Elovich and Banham adsorption rate equation). Compared to other models, the Boltzmann model and the Banham adsorption rate equation could well fit the data of the selected sorption periods. These observations indicated that the fixed bed has a small effect of the mass transfer resistance and a high utilization for the adsorbent. Meanwhile, the Banham adsorption rate equation also could well predict the real condition and the maximum adsorption capacity of the adsorbent. Therefore, the present study clarified the adsorption dynamic behaviors of the selected VOCs onto the CAC in a fixed bed. We believe that the finding of this work is helpful to optimize the design of dynamic adsorption system for the removal of VOCs.

Adsorption mechanisms of different volatile organic compounds onto pristine C2N and Al-doped C2N monolayer: A DFT investigation

Volatile organic compounds (VOCs) are a class of air pollutants which seriously affect the ecological environment and threaten human health. Adsorption of VOCs is considered as a promising technology for VOCs enriching, separation and utilization. In this work, density functional theory (DFT) calculations are employed to investigate the adsorption properties of typical VOCs molecules onto C2N monolayer and Al-doped C2N system due to the huge specific surface and porous structure of newly-reported holey two-dimensional C2N. The results demonstrate that three typical VOCs: formaldehyde, benzene and trichloroethylene, can be absorbed onto pristine C2N monolayer with weak adsorption energy, while the adsorption ability can be improved with the formation of a strong chemical bond. Especially for the formaldehyde molecule, the best adsorption capacity on the Al-doped C2N surface with adsorption energy of −2.754 eV, nearly 5 times larger than the pristine C2N system. The PDOS analysis and electronic distribution results also show that doped Al atom can act as a bridge to link VOCs molecules with C2N monolayer and strengthen their interaction, which can significantly enhance the adsorption capacity. Therefore, Al doped C2N monolayer is demonstrated to be a promising adsorbent for VOCs enriching and utilization.

Effect of gold loading on ceria-zirconia support in total oxidation of VOCs

0.20, 0.37, 0.83, 1.55 and 3.35 wt.% of gold was impregnated on Ce0.5Zr0.5O2 prepared by sol-gel method. Systematic characterizations of gold catalysts by atomic emission spectroscopy, N2 physisorption, X-ray powder diffraction, H2 chemisorption, transmission electron microscopy, temperature programmed reduction by hydrogen and measurement of oxygen storage capacity allowed detailed monitoring of their characteristics. Subsequently, the catalytic performance and selectivity in the oxidation of selected volatile organic compounds (VOCs) was studied and linked to the physicochemical properties. The study revealed that depending on VOC type, an improvement in catalytic performance with increasing gold loading can be observed despite of gold sintering to large agglomerates during the preparation of catalysts.

Efficacy of Various Preservatives on Extending Shelf Life of Vacuum-Packaged Raw Pork during 4°C Storage

Uncontrolled bacterial growth and metabolic activities are responsible for the short shelf life of raw pork. Culture-independent analysis by 16S ribosome cDNA could reveal viable bacteria in raw pork. This study investigated microbial growth and volatile organic compounds of raw pork supplemented with various preservatives. Vacuum-packaged raw pork was stored at 4°C, after soaking in solutions of potassium sorbate, ε-poly-l-lysine, kojic acid (KA), or sodium diacetate, individually. Spoilage of raw pork was monitored by determining pH and total volatile basic nitrogen, whereas bacterial growth was determined by culture-dependent and culture-independent analyses. Data indicated that all the preservatives were able to inhibit bacterial growth and extend the shelf life of pork. High-throughput sequencing of 16S ribosome cDNA indicated that Pseudomonas was inhibited under vacuum conditions, whereas facultative anaerobes ( Acinetobacter, Photobacterium, Brochothrix, and Myroides) were the most active genera in the spoiled pork. Photobacterium was further inhibited by each preservative. The inhibition of Acinetobacter, Photobacterium, and Myroides could be responsible for the extended shelf life of vacuum-packaged pork; they were effectively inhibited by KA, which also induced the longest shelf life. Moreover, 19 types of volatile organic compounds were detected. 3-Methylbutanol, 3-methylbutanol acetate, 2-butanone, toluene, benzeneacetaldehyde, dimethyl trisulfide, and acetoin were associated with spoilage. Furthermore, KA is a potential preservative in raw pork; because no phenol was detectable within 35 days, excessive intake of phenol induced by preservatives was avoided.

Photolysis and photooxidation of typical gaseous VOCs by UV Irradiation: Removal performance and mechanisms

Photodegradation by ultraviolet irradiation (UV) is increasingly applied in volatile organic compound (VOC) and odor gas treatments. In this study, 27 typical VOCs, including 11 hydrocarbons and 16 hydrocarbon derivatives, at 150–200 ppm in air and nitrogen gas were treated by a laboratory-scale UV reactor with 185/254 nm irradiation to systematically investigate their removal and conversion by UV irradiation. For the tested 27 VOCs, the VOC removal efficiencies in air were within the range of 13%–97% (with an average of 80%) at a retention time of 53 s, which showed a moderate positive correlation with the molecular weight of the VOCs (R = 0.53). The respective contributions of photolysis and photooxidation to VOC removal were identified for each VOC. According to the CO2 results, the mineralization rate of the tested VOCs was within the range of 9%–90%, with an average of 41% and were negatively correlated to the molecular weight (R = −0.63). Many of the tested VOCs exhibited high concentration particulate matters in the off-gases with a 3–283 mg/m3 PM10 range and a 2–40 mg/m3 PM2.5 range. The carbon balance of each VOC during UVirradiation was analyzed based on the VOC, CO2 and PM10 concentrations. Certain organic intermediates and 23–218 ppm ozone were also identified in the off-gases. Although the UV technique exhibited a high VOC removal efficiency, its drawbacks, specifically low mineralization, particulate matters production, and ozone emission, must be considered prior to its application in VOC gas treatments.

Prediction of ethylene and propylene release during coal pyrolysis with modified CPD model

The well-known CPD model (chemical percolation model for devolatilization) is further developed to simulate typical volatile organic compounds (ethylene and propylene) release during coal pyrolysis. A look-up table of ethylene corresponding to the extent of light gas release is constructed and added to the light gas sub-model. With the updated CPD model, the mass fractions of the released ethylene from the flash pyrolysis experiments in a Currie Point pyrolyzer are successfully predicted for a set of coals under different pyrolysis temperatures. The results suggest that, the predicted ethylene yields are accurate when the coal is located in the vicinity of the reference coal in the interpolation mesh and the secondary reactions are insignificant. The predicted release of ethylene during the pyrolysis of an anthracite coal and a bituminous coal using a tube furnace also compares well with the available experimental data. It reveals that as long as the temperatures of coal/char particles are estimated accurately, the prediction of the ethylene mass fraction can be applied to a wider range of heating rates. In addition, the propylene is estimated based on the time-resolved profiles obtained from an online single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) and the main pyrolysis products acquired from an offline gas chromatograph/mass spectrometry (GC/MS). Accordingly, the prediction of propylene is carried out. The consistent yields of ethylene and/or propylene at identical pyrolysis temperatures, regardless of coal types, indicate that the evolution of these light gases is insensitive to coal type. When the ratio of the final mass fraction between ethylene and propylene is fixed to be 1.1, the predicted release profiles of these compounds correlate well with the published experimental data, indicating the effectiveness of the modified CPD model.

Research on Volatile Organic Compounds From Bacillus subtilis CF-3: Biocontrol Effects on Fruit Fungal Pathogens and Dynamic Changes During Fermentation.

The dynamic changes of the levels of volatile organic compounds (VOCs) produced by Bacillus subtilis CF-3 and their biocontrol effects on common fungal pathogens were researched in this study. The results showed that the VOCs in 24-h fermentation liquid (24hFL) of B. subtilis CF-3 inhibited mycelial growth of Botrytis cinerea, Colletotrichum gloeosporioides, Penicillium expansum, Monilinia fructicola, and Alternaria alternata, with a mean inhibition rate of 59.97%. The inhibitory effect on M. fructicola and C. gloeosporioides was the highest; they were therefore selected as target fungal pathogens for further experiments. Based on headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS), 74 potential VOCs were identified during the fermentation: 15 alcohols, 18 ketones, 4 pyrazines, 4 esters, 10 acids, 5 phenols, 3 hydrocarbons, 3 amines, 2 aldehydes, 5 ethers, and 5 other components. At different fermentation times, the type and content of VOCs were different. Most of the potential VOCs (62 VOCs) were identified in the 48hFL. The inhibition rates of all VOCs reached their peaks (73.46% on M. fructicola and 63.63% on C. gloeosporioides) in the 24hFL. Among the identified VOCs, 2,4-di-tert-butylphenol, 1-octanol, and benzothiazole showed significant positive correlations with the rates of M. fructicola and C. gloeosporioides inhibition. Benzoic acid and benzaldehyde showed a significant positive correlation with the rates of M. fructicola inhibition, and anisole and 3-methylbutanal showed a significant positive correlation with the rates of C. gloeosporioides inhibition. In vitro, 2,4-di-tert-butylphenol showed a strong inhibitory effect on both M. fructicola and C. gloeosporioides. In vivo, benzothiazole showed the strongest inhibitory effect on the mycelial extensions of both M. fructicola and C. gloeosporioides, which also led to an increased rate of healthy fruit. The results of the present study clarified that 2,4-di-tert-butylthiophenol and benzothiazole are key inhibitory VOCs produced by B. subtilis CF-3.

Efficient photocatalytic degradation of gaseous N,N-dimethylformamide in tannery waste gas using doubly open-ended Ag/TiO2 nanotube array membranes

Gaseous N,N-dimethylformamide (DMF), typical volatile organic compound exhausted from manufacturing factories, may damage the health of workers under long-term exposure even at low levels. The defined geometry, porous surface and highly ordered channels make the free-standing anodic TiO2 nanotube (TiNT) arrays particularly suitable for applications of practical air purification by flow-through photocatalysis. In the present work, crystallized doubly open-ended Ag/TiNT array membranes were designed and prepared by employing a lift-off process based on an anodization-annealing-anodization-etching sequence, followed by uniform Ag nanoparticles decoration. For the photocatalytic degradation of gaseous DMF at low concentration levels close to that found in realistic pollutant air, an analytical methodology for the monitoring and determination of degradation process was developed based on the coupling of headspace sampling with gas chromatography mass spectrometry (HS-GC-MS). The doubly open-ended Ag/TiNT arrays exhibited higher removal efficiency of gaseous DMF from air compared with conventional bottom-closed Ag/TiNT arrays and pure bottomless TiNT arrays. These results indicated that the photocatalytic properties of TiNT arrays were improved with the open-bottom morphology and the Ag nanoparticles decoration. Based on the analysis with GC-MS and high performance ion chromatography (HPIC), it was found that demethylation is the main pathway of DMF degradation in photocatalytic reactions. Furthermore, decontamination of actual polluted tannery waste gas collected in leather factory proved that the photocatalysis on doubly open-ended Ag/TiNT array membrane is an efficient way and a promising application to treat air contaminated by DMF despite the complexity of various volatile organic compounds.

Characteristics of Volatile Organic Compounds Released from Various Types of Decorative Particleboards

Abstract Surface finishes change the characteristics of volatile organic compounds (VOCs) released from wood-based panels. This research studied the effects of different finishes on the VOCs released from particleboard (18 mm thick). Various materials, such as polyvinyl chloride (PVC), melamine paper, and water-based paint, were compared with unfinished particleboard. A 1-m3 climate chamber and gas chromatography–mass spectroscopy were used to examine the types and rates of release and the percentages of various VOCs released by decorative particleboard over 28 days. By comparing the characteristics of VOCs released from unfinished particleboard, the effects of different surface finishes were determined. The VOC substances of concern released from particleboards were analyzed by their type and concentration until they reached a state of equilibrium on day 28. Results showed that none of the surface finishes changed the variety of total VOC (TVOC) released from particleboard, but they had a prominent influence on the rate of TVOC released, especially in the early stages. Acrylic water-based paint increased the TVOC release rate from the particleboard, whereas the PVC and melamine finishes decreased the rate. Surface finishing greatly influences the concentration of various VOCs. Although the same types of VOCs were released by the various finished particleboards, they each had different release rates and different variations in their release-rate tendencies. Surface finishing can change the percentages of various VOC components, so that the amounts were different depending on the finish, and different types of VOCs were controlled better by certain types of finishes.

Analysis on Ambient Volatile Organic Compounds and their Human Gene Targets

Although some ambient Volatile Organic Compounds (VOCs) have been recognized to influence human health, the functional basis and underlying molecular mechanisms remain obscure. Here, the ambient VOCs and corresponding human genes response to the VOCs (HGRV) were analyzed integratedly from several aspects. (1) Firstly, through identifying composition and connectivity of functional groups within VOCs, we found that there is significant bias in the co-occurrence patterns among the top five frequent groups (respectively methyl, carbon-carbon double bond, benzene ring, chlorine and ethylene). For instances, co-occurrence of chlorine and benzene are considerably frequent, whereas the connection between chlorine and methyl/ethylene occurred rarely. (2) Then, by examining the screened HGRV, it was unveiled that four genes (respectively, IL6, BCL2, FOS and PTGS2) may act as “hub/hotspots” in response to VOCs. And four types of VOCs (respectively, Acetaldehyde, Butyraldehyde, Formaldehyde and Styrene) were found to be shared stimulators of the hubs. (3) Moreover, three dominant function categories were detected, respectively, response to lipopolysaccharide, response to molecule of bacterial origin and response to oxidative stress. (4) Further, the results disclosed that three most significant pathways are IL-17 signaling pathway, TNF signaling pathway and Rheumatoid arthritis. These three most significantly enriched pathways in HGRV are primarily associated with immune diseases and cancer. (5) Subsequently, by analyzing the diseases potentially associated with HGRV, the results revealed that 50 kinds of diseases might be significantly associated with HGRV. Among them, top 3 significant diseases are Immune system diseases, Cancers and Allergies and autoimmune diseases respectively. And these top 3 diseases might be induced by 13 common VOC species, such as Benzene, Chlorobenzene and Formaldehyde. Thus, the above findings could be useful for advancing our understanding of mechanisms related to diseases by VOCs exposure and development of control strategies to limit their damage or attenuate their sequelae.

Phosphorus deficiency inducing volatile organic compounds from <i>Microcystis aeruginosa</i> and their effects on <i>Chlamydomonas reinhadtii</i>

为了揭示磷（P）营养缺乏对蓝藻释放挥发性有机化合物（VOCs）的影响及其对其他藻类的化感作用，以形成蓝藻水华的主要种类铜绿微囊藻（Microcystis aeruginosa）为材料，在无P培养条件下对其释放的VOCs进行分析，同时测定VOCs对莱茵衣藻（Chlamydomonas reinhardtii）生长、光合色素含量和光合性能的影响.结果表明，采用无P培养基培养铜绿微囊藻24 h后，其释放的VOCs种类和含量均明显增加，与标准培养基培养相比，VOCs总释放量增加了73.4%，并出现7种新化合物.将铜绿微囊藻释放的VOCs通入莱茵衣藻溶液中，在标准培养基中铜绿微囊藻释放的VOCs对莱茵衣藻生长无显著影响，而无P条件下释放的VOCs则明显抑制莱茵衣藻生长，其响应指数（RI）为-0.25.此外，莱茵衣藻光合色素含量、光系统Ⅱ（PSⅡ）最大光化学量子产量（Fv/Fm）、有效光化学量子产量、光化学淬灭系数（qP）和光合电子传递速率（ETR）也明显降低，而非光化学淬灭系数（NPQ）则明显升高，其RI为0.26.由此可见，蓝藻在富营养化水体中大量繁殖以及P自身沉降特性导致的P缺乏会促进蓝藻释放VOCs，同时这些VOCs在保持蓝藻营养竞争优势和水体藻类多样性减少中具有化感抑制作用.;In order to uncover the effects of phosphorus (P) nutrition deficiency on volatile organic compounds (VOCs) released from cyanobacteria and their allelopathic effects on other algae in freshwater bodies, the VOCs from Microcystis aeruginosa that is the main species of cyanobacterial bloom in non-P medium were analyzed, and their effects on Chlamydomonas reinhardtii cell growth, photosynthetic pigment content and photosynthetic abilities were determined in this study. The VOC types and emission amount increased after M. aeruginosa cells were kept in non-P medium for 24 h, with the increase of 73.4% of the total emission amount in contrast to that in normal medium. Meanwhile, 7 new compounds appeared. There was no significant difference in C. reinhardtii growth after the algal cells were exposed to the VOCs from M. aeruginosa in normal medium. However, C. reinhardtii growth was markedly inhibited by the VOCs from M. aeruginosa in non-P medium, with the response index (RI) of -0.25. Meanwhile, the photosynthetic pigment content, maximum quantum yield of photosystem Ⅱ (PSⅡ) photochemistry (Fv/Fm), effective quantum yield in PSⅡ photochemistry, coefficient of photochemical quenching (qP) and apparent electron transport rate through PSⅡ (ETR) in C. reinhardtii also reduced remarkably, while non-photochemical dissipation of absorbed light energy (NPQ) increased significantly, with the RI of 0.26. Therefore, P deficiency caused by cyanobacteria mass propagation and P sedimentation in eutrophicated water might induce cyanobacteria releasing abundance of VOCs, which might play allelopathic inhibitory roles in cyanobacteria keeping advantages for nutrition competition and the reduction of algal biodiversity in water bodies.

A visible-light-active Au-Cu(I)@Na2Ti6O13 nanostructured hybrid pasmonic photocatalytic membrane for acetaldehyde elimination

The present article reports a novel self-standing nanostructured Au-Cu(I)@Na2Ti6O13 plasmonic photocatalytic membrane, which is prepared by a hydrothermal reaction followed by a simple subsequent heat treatment process. The morphological structure, elemental composition, crystalline phases, and optical properties of the membrane were studied in detail by field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet-visible spectroscopy. Compared with that of a pure Na2Ti6O13 membrane, the Au-Cu(I)@Na2Ti6O13 membrane displayed much higher photocatalytic activity for the decomposition of acetaldehyde, a typical volatile organic compound, under visible light illumination. It was found that the photocatalytic activity of the Au-Cu(I)@Na2Ti6O13 membrane increased as the amount of Au was increased. The membrane loaded with 2.85 wt% Au showed the highest photocatalytic activity in the decomposition of acetaldehyde of the investigated materials. We found that in the photocatalyst membrane, Na2Ti6O13 acted as a support material, Au displayed plasmonic absorption, and Cu(I) behaved as a co-catalyst. The present membrane materials can avoid the self-aggregation typically observed during the course of photocatalytic reactions. As a result, they can be easily separated, recycled, and reactivated after their practical application, making these functional materials attractive for use in air cleaning applications.

Synthesis and Characterization of Co-Doped Brookite Titania Photocatalysts with High Photocatalytic Activity

Transition metal-doping could effectively extend the light response range of TiO2 photocatalysts from the ultraviolet (UV) to the visible region. Co-doped brookite titanium dioxide (Co–TiO2) photocatalysts were synthesized via the hydrothermal method with titanium tetrachloride as the raw material and cobalt chloride hexahydrate as the dopant. The prepared Co–TiO2 photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). The photocatalytic activities of Co–TiO2 photocatalysts were evaluated by photocatalytic degradation of isopropanol alcohol (IPA), a typical volatile organic compound (VOC), under visible light. The influences of different Co doping rates, initial concentrations of IPA gas and the amounts of photocatalyst addition were also studied. At the same time, the enhancement mechanism of cobalt ions as a trap for photogenerated holes was discussed. Thus, we found the optimum doping rate, initial concentration of IPA gas and amount of photocatalyst to add. The results show that the mesoporous Co–TiO2 photocatalysts possess smaller size particles, larger specific surface area, lower forbidden bandgap energy (Eg) and better photocatalytic activity than pure brookite TiO2. When the doping of Co was 7% by mass, the initial concentration of IPA gas was 1.0 × 10−6 mol/L and the addition of Co–TiO2 photocatalysts was 50 mg, the best photocatalytic activity was achieved. Furthermore, the degradation rate of IPA was up to 91%, which shows great potential for waste water treatment.

Using Structural Equation Modeling to Assess the Links between Tobacco Smoke Exposure, Volatile Organic Compounds, and Respiratory Function for Adolescents Aged 6 to 18 in the United States.

Asthma is an inflammatory airway disease that affects 22 million Americans in the United States. Research has found associations between impaired respiratory function, including asthma and increased symptoms among asthmatics, and common indoor air pollutants, including tobacco smoke exposure and volatile organic compounds (VOCs). However, findings linking VOC exposure and asthma are inconsistent and studies are of mixed quality due to design limitations, challenges measuring VOC exposure, small sample sizes, and suboptimal statistical methodologies. Because of the correlation between tobacco smoke exposure and VOCs, and associations between both tobacco smoke and VOCs with respiratory function, it is crucial that statistical methodology employed to assess links between respiratory function and individual air pollutants control for these complex relationships. This research uses Structural Equation Modeling (SEM) to assess the relationships between respiratory function, tobacco smoke exposure, and VOC exposure among a nationally-representative sample of adolescents. SEM allows for multiple outcome variables, the inclusion of both observed and latent variables, and controls the effects of confounding and correlated variables, which is critically important and is lacking in earlier studies when estimating the effects of correlated air pollutants on respiratory function. We find evidence of associations between respiratory function and some types of VOCs, even when controlling for the effects of tobacco smoke exposure and additional covariates. Furthermore, we find that poverty has an indirect effect on respiratory function through its relationships with tobacco smoke exposure and some types of VOCs. This analysis demonstrates how SEM is a robust analytic tool for assessing associations between respiratory function and multiple exposures to pollutants.

Data Reconstruction Using Subspace Analysis for Gas Classification

We propose a data reconstruction method using subspace analysis for gas classification in an electronic nose system. A noise generated by defects in sensors or by environmental factors in the process of data sampling significantly degrades data classification performance. In this paper, an electronic nose system more robust to data errors is designed by reconstructing lost or damaged values of data samples based on a statistical learning method that exploits the principal components. Diverse types of volatile organic compounds were employed in the classification experiments, which were conducted to reconstruct the lost or damaged data through the proposed method. The applied method prevented the degradation of classification performance and enhanced the discriminative power in the PCA+LDA feature space.

Methanethiol generation potential from anaerobic degradation of municipal solid waste in landfills.

Volatile sulfur compounds are the main odorants at landfills. In this study, methanethiol (CH3SH) was chosen as a typical volatile organic sulfur compound, and its generation potential was investigated during the anaerobic degradation of the organic fractions of municipal solid waste (MSW) including rice, flour food, vegetable, fish and pork, paper, cellulose textile, and yard wastes. Among the experimental wastes, gas generation was the highest in the fish and pork waste with a high CH3SH concentration of up to 2.5% (v/v). Sulfur reduction in the solid phase was mostly converted into gaseous sulfur compounds. During the whole experiment, the cumulative CH3SH generation from the fish and pork waste was 0.139Lkgdw-1, which was about 2 and 6 orders of magnitude higher than that from the other experimental wastes. The ratio of CH3SH-S to TS reduction was 31.56% in the fish and pork waste. These results would be helpful to understand the generation of volatile sulfur compounds during the anaerobic degradation of MSW and develop techniques to control odor pollution at landfills.

In-situ generation of highly dispersed Au nanoparticles on porous ZnO nanoplates via ion exchange from hydrozincite for VOCs gas sensing

The indoor volatile organic compounds (VOCs) have caught much attention because millions of people are suffering from indoor air pollution. To detect VOCs, various gas sensors with fast response, high sensitivity and high stability have been fabricated by nanocomposite technology. In this study, highly dispersed Au nanoparticles are deposited on porous ZnO nanoplates (Au@ZnO) via ion exchange method from hydrozincite [Zn5(CO3)2(OH)6] without the addition of any surfactants. By immersing hydrozincite precursors into 0.1%–5% HAuCl4 solutions and followed by annealing, several Au@ZnO sensors with size-limited Au nanoparticles are fabricated for the detection of nine types of VOCs. Comparing with pure ZnO nanoplates, the as-prepared Au@ZnO sensors show enhanced sensitivity by 2–9 times at 400°C toward all nine types of VOCs. Also, fast response/recovery time and fine repeatability in the gas-sensing tests are attained. More oxygen species and active sites to the adsorbed VOCs molecules are generated by Au@ZnO hybrids, which lead to the improvement of ZnO-based gas sensor limitation.

A comprehensive classification method for VOC emission sources to tackle air pollution based on VOC species reactivity and emission amounts

In China, volatile organic compound (VOC) control directives have been continuously released and implemented for important sources and regions to tackle air pollution. The corresponding control requirements were based on VOC emission amounts (EA), but never considered the significant differentiation of VOC species in terms of atmospheric chemical reactivity. This will adversely influence the effect of VOC reduction on air quality improvement. Therefore, this study attempted to develop a comprehensive classification method for typical VOC sources in the Beijing–Tianjin–Hebei region (BTH), by combining the VOC emission amounts with the chemical reactivities of VOC species. Firstly, we obtained the VOC chemical profiles by measuring 5 key sources in the BTH region and referencing another 10 key sources, and estimated the ozone formation potential (OFP) per ton VOC emission for these sources by using the maximum incremental reactivity (MIR) index as the characteristic of source reactivity (SR). Then, we applied the data normalization method to respectively convert EA and SR to normalized EA (NEA) and normalized SR (NSR) for various sources in the BTH region. Finally, the control index (CI) was calculated, and these sources were further classified into four grades based on the normalized CI (NCI). The study results showed that in the BTH region, furniture coating, automobile coating, and road vehicles are characterized by high NCI and need to be given more attention; however, the petro-chemical industry, which was designated as an important control source by air quality managers, has a lower NCI.

Hygienic aspects of TiO2-mediated photocatalytic oxidation of volatile organic compounds: Air purification analysis using a total hazard index

The purification of air polluted by volatile organic compounds (VOCs) using the TiO2-mediated photocatalytic oxidation (PCO) method was analyzed from a hygienic point of view by the evaluation of the total hazard during the process. For this purpose, the photocatalytic oxidation of various VOCs, including acetone, alcohols, hydrocarbons, and heteroatomic compounds, was investigated in a static reactor using an FTIR in situ method for the identification and quantitative analysis of the reaction components in the gas phase. The change in hazards during the PCO process was calculated using two hazard indexes, the maximum hazard quotient (MHQ) and the total hazard index (THI), which include the contribution of all the reaction components and be the quantitative characteristics for the estimation of the PCO purification efficiency from a hygienic point of view. The results for all the VOCs considered showed the fundamental ability of the PCO method to decrease the hazards in polluted air. The hazard indexes depended on the UV irradiation time and the type of VOC. For VOCs that are photocatalytically oxidized without the formation of gaseous intermediates, the hazard indexes initially decreased as the concentration of the VOC decreased but then slightly increased at the end of the PCO process mainly due to the accumulation of CO, which was formed as a final by-product. The TiO2 modification with Pt was shown to completely or partially suppress CO accumulation during the PCO process and to increase the efficiency of air purification from a hazard index point of view. For the photocatalytic oxidation of VOCs that results in the formation of gaseous intermediates, the hazard may increase during the PCO process and even be much higher than the initial level because such intermediates (i.e., aldehydes, acids, and inorganic compounds) have extremely low threshold limit values. Under long-term UV irradiation, all the intermediates were completely oxidized, and the hazard levels substantially decreased compared to the initial level.

Profiling of soil volatile organic compounds after long-term application of inorganic, organic and organic-inorganic mixed fertilizers and their effect on plant growth

The complexity of soil processes involved in the production, consumption and accumulation of volatile organic compounds (VOCs) makes hard to access the overall dynamics of VOCs in the soil. In this study, the field soil, applied with inorganic (CF), organic (OF) and inorganic-organic mixed (CFOF) fertilizers for ten years was evaluated for the emission of VOCs at different temperature and moisture levels. We identified 30–50 soil emitted VOCs representing the most common soil VOCs groups by using the solid-phase microextraction (SPME) fiber and gas chromatography-mass spectroscopy. The highest total emission of VOCs was found in OF treatment, but it was non-significantly different with CF treatment. The emission of VOCs was significantly increased with the decrease in moisture contents and increase in the temperature of the soil. Among different fertilizer treatments, the emission of VOCs was significantly higher in OF treatment at 5% moisture, and in CF and OF treatments at 35°C. Further, the VOCs emitted from soil treated with CFOF showed the highest increase in plant growth while CF and OF treatments showed similar results. The VOCs were also extracted from the soil using methanol to better understand the dynamics of VOCs. The abundance of VOCs extracted from the soil was 44–61%, while the richness was 65–70% higher than the VOCs emitted from the soil in different treatments. Taken together the results of emitted and extracted VOCs from the soil, we conclude that the fertilizers are able to discriminate among the VOC patterns of soil. In addition, most of the VOCs are retained in the soil and the emission of VOCs from soil depends on the type of VOCs, soil properties and environmental conditions; however, more research is required to find out better soil VOCs analysis methods.