High Concentrations Of Toluene Research Articles

In situ synthesis of porous metal-organic frameworks NH2-UiO-66 on tea stem biochar and application in odours adsorption

Multiple odour nuisance in livestock farming is a notorious problem that has a significant impact on the living environment of surrounding communities. Adsorbents based on metal-organic framework (MOF) materials show great promise for controlling odour pollution, as they offer a high specific surface area, a controllable structure and an abundance of active sites. However, the MOF formation process is prone to problems such as pore clogging or collapse and reduced porosity, which limits its further application. In this study, a series of odour adsorbents were prepared by in situ growth of NH2-UiO-66 on tea stem biochar (TSBC) using a hydrothermal method and named UiO (Zr)-TSBCx. The physical and chemical properties and composition of UiO (Zr)-TSBCx have been systematically characterized using SEM, TEM, XRD, FT-IR, N2 adsorption-desorption and XPS. The release of odours from the pig farm effluent was monitored using in-situ continuous Proton-Transfer-Reaction Mass Spectrometry (PTR-MS), and the obtained primary compositions were tested for further adsorption. In dynamic adsorption experiments focused on butyric acid, UiO (Zr)-TSBC2 showed a high adsorption capacity of 3.99 × 105 μg/g and exceptional structural stability. UiO (Zr)-TSBC2 showed variable adsorption efficiencies for different odorous gases, with the best performance for the removal of ammonia, toluene and butyric acid. It also demonstrated the ability to rapidly mitigate instantaneous high concentrations of hydrogen sulfide (H2S), methanethiol and toluene resulting from agitation. Additionally, based on the relationship between the adsorption amount and the structural characteristics of the adsorbent as well as the nature of the odours, a possible adsorption mechanism of UiO (Zr)-TSBC2 for a variety of odours released from pig farm effluent was proposed. This work demonstrates a novel approach to promote deodorization applications in livestock and poultry farming environments by the in-situ growth of NH2-UiO-66 on biochar prepared from tea stem.

Exploring the rate-control step of toluene oxidation over the novel octahedral Pt/Mn3O4 catalyst with stable low-temperature catalytic performance via in situ DRIFTS

The high efficiency and stability of catalysts are crucial for their practical application in toluene oxidation. Herein, a novel octahedral Pt/Mn3O4-110 catalyst with excellent structural stability was synthesized and 100 % toluene conversion can be achieved at low-temperature 160 °C. XRD and Raman results indicated that the structure of Pt/Mn3O4-110 can be well maintained after 120 h on-stream reaction, the resistance to H2O (3 or 5 vol%) and high concentration toluene (3000 ppm)/CO2 (5 vol%) tests. In situ DRIFTS comparative studies between Pt/Mn3O4-110 and Pt/Mn3O4-100 (30 % toluene conversion at 160 °C) samples demonstrated that the rate-control steps of toluene oxidation on Pt/Mn3O4-110 and Pt/Mn3O4-100 were both the further oxidation of benzoate species in the presence of gas-phase oxygen, while the transformation of benzaldehyde to benzoate species was the rate-control step on Pt/Mn3O4-100 in the absence of gas-phase oxygen. The weaker Mn-O bonds, richer oxygen vacancies and higher mobility of oxygen species on Pt/Mn3O4-110 sample than that of Pt/Mn3O4-100 are beneficial for the easier release of lattice oxygen from the surface of catalyst and then participated in toluene oxidation via Mars-van Krevelen mechanism, contributing to easier oxidation of benzaldehyde to benzoate species and formation of formic acid and bicarbonate species.

Modelling and prediction of toluene adsorption saturation basing on characteristic values of activated carbons

Herein, the association between the dynamic adsorption capacity of toluene and several important characteristic values on activated carbon (AC) samples was investigated by multidimensional linear regression. Among the characteristic values, the carbon tetrachloride (CTC) adsorption value has demonstrated relatively stronger correlation with the toluene adsorption capacity on AC samples with diverse sources and forms, particularly in exposure to high-concentration toluene. Notably, the relevance of the toluene adsorption capacity to the CTC value could also be extended to a series of other porous adsorbents, which proved the wide applicability of CTC value in characterizing the adsorption behaviors. Based on these results, a mathematical and visual model was then established to predict the toluene adsorption saturation under different conditions (inlet concentration, adsorption time, initial CTC value, etc.) on diverse AC samples, of which the accuracy has later been verified by experimental data. As such, a fast and accurate estimation of the adsorption behaviors over AC samples, and possibly other porous adsorbents, was realized.

Enhancing air treatment through controlled fabrication of transition metal-doped titanium dioxide nanocomposites for photocatalytic toluene degradation

Rapid industrial growth and urbanization have resulted in a significant rise in environmental pollution issues, particularly indoor air pollutants. As a result, it is crucial to design and develop technologies and/or catalysts that are not only cost-effective but also promising high performance and practical applicability. However, achieving this goal has been so far remained a challenging task. Herein, a series of transition metal M − TiO2 (M = W, Fe, Mn) nanocrystals was prepared for photocatalytic degradation of volatile organic compounds (VOCs), i.e., toluene. Of the nanocomposites tested, W–TiO2 showed significantly improved photocatalytic activity for VOC degradation under UV irradiation compared to the others. In particular, the optimized W dopant amount of 0.5 wt% resulted in the outstanding degradation performance of toluene (96%) for the obtained W–TiO2(0.5%) nanocomposite. Moreover, W–TiO2(0.5%) nanocomposite exhibited good stability for 32 h working under high toluene concentration (10 ppm) compared to the pristine TiO2. The current work demonstrates the potential usage of M − TiO2 nanocrystals, particularly W–TiO2(0.5%), as a promising photocatalyst for efficient VOCs degradation.

Self-assembly of MOFs-like materials by Zn2+ and histidine functionalized graphene quantum dots for the efficient removal of VOCs simulants

Volatile organic compounds (VOCs) in the field of printing and packaging, have caused great harm to the environment. Therefore, the removal of volatile organic compounds (VOCs) is a hot topic, and metal-organic frameworks (MOFs) and graphene quantum dots (GQDs) have been applied in this field. However, improving the removal efficiency of different VOCs by using the two kinds of materials is still a great challenge. Herein, ZIF-8 like materials of Zn-His-GQDs were prepared by assembling Zn2+ and histidine functionalized GQDs (His-GQDs) in this work. The morphologies, structure and adsorption performances of Zn-His-GQDs were investigated. These results showed that mesoporous Zn-His-GQDs with a specific surface area of 63.3 m2·g−1 had similar structure to ZIF-8. When the content of Zn-His-GQDs was 200 mg, the equilibrium adsorption capacity for toluene solution of 500 mg·L−1 and ethyl acetate solution of 1600 mg·L−1 was 350 mg·L−1 and 669.44 mg·L−1, respectively. Due to channel filling, cation-π interaction, π-π interaction, hydrogen bond and high surface energy, Zn-His-GQDs exhibited a relative high removal efficiency for high concentration of toluene and ethyl acetate. The removal rate of Zn-His-GQDs on toluene and ethyl acetate after five cycles remained 59.80 % and 36.75 %, respectively. Moreover, this kind of MOFs like materials maintained stable structure during the adsorption in different pH solutions. Therefore, as-prepared Zn-His-GQDs with excellent adsorption performances for typical VOCs simulants in this work have potential application in the treatment of VOCs in the field of printing and packaging.

Decorating {0 0 1} TiO2 nanosheets on hydrophobic NaY zeolite: An efficient deactivation-resistant photocatalyst for gaseous toluene removal

Photocatalysis is regarded as a promising in situ air purification technology for the removal of volatile organic compounds. However, the deactivation of photocatalysts remains a serious issue that needs to be addressed. Herein, we report a novel dual-functional photocatalyst (TiO2@HYZ) with spatially separated catalytic sites and adsorption sites, which has been obtained by combining hydrophilic {001} TiO2 nanosheets with hydrophobic NaY zeolite. TiO2@HYZ showed excellent photocatalytic activity for the degradation of gaseous toluene under UV irradiation in humid air. The optimized TiO2@HYZ-2 (containing 45.7 wt% TiO2) achieved 96.6% toluene removal and 87.4% mineralization within 120 min. The specific reaction rate constant of TiO2@HYZ-2, pristine TiO2 and P25 normalized by the unit amount of TiO2 during the photocatalytic degradation process were calculated to be 0.481, 0.230 and 0.250 min−1 g−1, respectively. Moreover, TiO2@HYZ-2 showed superior durability, maintaining stable performance over repeated toluene degradation processes, even at high toluene concentration, whereas pristine TiO2 incurred severe deactivation with increasing number of photocatalysis cycles. The significantly enhanced activity and anti-deactivation property was attributed to a synergistic effect between HYZ and TiO2 in the catalyst structure, which strengthened the adsorption of toluene on HYZ and facilitated effective separation of photoexcited charge carriers on TiO2, thus avoiding the deposition of degradation intermediates on the active sites and simultaneously improving mineralization. This work provided a new perspective for the design of efficient and deactivation-resistant photocatalysts for air pollution remediation.

Experimental and numerical study of flame stability in a rotary flow reversal reactor with ultra-lean toluene/air mixture

A rotary flow reversal reactor with a fixed packed bed and rotary intake is established to study the combustion stability with ultra-lean toluene/air mixture. The experimental results show that the stable temperature distribution in the packed bed is vertically graded and circumferentially uniform with bottom rotary intake. The three-dimensional numerical simulation using sliding grid technology on the combustion process is presented. The effects of intake toluene concentration, axial velocity and circumferential rotation speed on the combustion stability are analyzed numerically. High intake toluene concentration or feed axial velocity will decrease the propagation velocity of the flame front and raise the peak temperature and the maximum reaction rate to achieve a quasi-steady state finally. However, the intake rotation speed has little effect on the combustion process. The work will enrich the investigation of flame stability during the filtration combustion of ultra low-calorific value gas.

Application of Co-Mn-Al sheet-like metal oxide catalysts in the liquid phase conversion of toluene to benzaldehyde

The main problems of liquid-phase oxidation of methylarenes to benzaldehydes are that the catalytic reaction rate is slow, benzaldehydes are easily over-oxidized to form benzoic acids, and a large amount of solvent is required. These problems make it difficult to realize the liquid phase catalytic oxidation of methylarenes to benzaldehydes in industrial production. Here, we report the catalytic oxidation of toluene to form benzaldehyde, by using N-hydroxyphthalimide (NHPI) as the radical catalyst, sheet-like Co-Mn-Al oxides (CMA-n) as the redox catalyst, and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as the solvent. CMA-n/NHPI was found to be highly active in catalyzing the oxidation of toluene to benzaldehyde. The use of HFIP as the solvent prevents the over-oxidation of benzaldehyde to benzoic acid. In addition, the reaction proceeded at a high concentration of toluene. The conversion rate of toluene reached 5826 μmol g−1 h−1, and the generation rate of benzaldehyde reached 4049 μmol g−1 h−1.

Study on catalytic degradation of toluene by copper manganese composite oxide

AbstractHerein, Cu–Mn catalysts were used to study the catalytic oxidation system of toluene, revealing the optimal preparation conditions for catalytic oxidation of toluene and the effects of other factors on catalytic performance (oxygen concentration, toluene concentration, temperature, humidity, space velocity). The as‐synthesized Cu2Mn1Ox exhibited the best catalytic activity and stability. The BET, XRD, and O2‐TPD results indicated that the synthesized Cu2Mn1 catalyst can effectively form the Cu1.4Mn1.6O4 phase at the optimal calcination temperature (500–600°C) and accelerate the toluene degradation at 220°C. Although water vapor can promote the progress of catalytic reactions, excessive water vapor tends to form competitive adsorption at active sites, inhibiting the progress of catalytic reactions. In addition, oxygen concentration plays a key role in catalytic reactions. Based on the results, it was found that at lower oxygen concentrations or higher toluene concentrations, the catalyst was easy to react with toluene to generate Cu and MnO, resulting in catalyst deactivation.

Investigation of high-concentration toluene degradation by DBD plasma under different operating parameters

This paper studies the degradation effect of high-concentration toluene in dielectric barrier discharge (DBD) plasma under different operating conditions. The degradation efficiency and energy yield (EY) were comprehensively evaluated by a response surface method under different operating parameters (discharge powers, gas flow rate, and initial concentrations) in the DBD plasma system. The results showed that the EY and degradation efficiency could reach 22.17 g kWh−1 and 72.3% when discharge power, initial concentration, and gas flow rate were 5.49 W, 1374.5 ppm, and 529.5 ml min−1, respectively. Furthermore, a mineralization effect was also analyzed related to different operating parameters. When the gas flow rate was 600 ml min−1 and the initial concentration was 2500 ppm, the CO x selectivity could reach 98.5%. Through analysis of the effect of oxygen content in the background gas on high-concentration toluene degradation, it was found that oxygen content had a significant effect on the formation of oxygen-containing active substances. Emission spectra showed that normal air discharge occurred in the discharge space of the DBD plasma, and nitrogen-containing active substances were generated. Therefore, active substances containing oxygen and nitrogen played an important role in DBD plasma degradation of high-concentration toluene.

Photocatalytic oxidation of volatile organic compounds (VOCs) in air using ultraviolet light-emitting diodes (UV-LEDs)

The aim of this study was to experimentally investigate the application of ultraviolet light-emitting diodes (UV-LEDs) for removing volatile organic compounds (VOCs) from air. For this purpose, a 365 nm UV-LED and a photocatalyst were used in a batch reactor to study the photocatalysis of toluene as the representative pollutant. It was demonstrated that combining reduced graphene oxide (rGO) with titanium dioxide (TiO2) and immobilizing the catalyst on the porous substrate could significantly improve the photocatalytic activity compared with the pristine TiO2 catalyst on a solid substrate. Photocatalyst deactivation was also studied by running cyclical tests. The photocatalytic crystal structure remained intact, but catalytic activity declined more than 80% after five consecutive photocatalytic tests for treating relatively high toluene concentrations. The adsorbed intermediates of toluene photocatalysis, such as benzoic acid, benzaldehyde, and benzyl alcohol, were identified, and the deactivation mechanism was proposed. It was shown that the deactivated photocatalyst can be effectively regenerated by UV-LED irradiation of 38.5 mW/cm2 irradiance within two hours. Overall, it was concluded that the UV-LED with a TiO2 on porous support provides an effective method for practical air purification applications.

Effects of indoor exposure to low level toluene on neural network alterations during working memory encoding

ObjectiveWhile high concentrations of toluene are known to affect multiple human organ systems, research concerning the influence of immediate, short-term exposure to toluene indoors and at low concentrations is scarce. Here, we studied effects of indoor toluene exposure on neural network alterations during working memory (WM) encoding. MethodsA total of 23 healthy college students were recruited. All participants were situated in a closed environmental chamber with a full fresh air system. Each participant was subjected to four exposure experiments with different toluene concentrations (0, 17.5, 35, and 70 ppb, named Group A, B, C and D, respectively), with at least one week between each experiment. WM Behavioral and 19-channel electroencephalogram (EEG) recordings in a pre-set environmental chamber were conducted simultaneously during each toluene exposure experiment. Neural networks relevant to WM encoding were visualized analyzing the obtained data. Results1. No significant difference in WM behavioral performance among the four groups was found. However, a significant increase in whole brain neural network functional connectivity was noted, especially in the frontal region.2. An outflow directional transfer function (DTFoutflow) revealed higher frontal region values among Group D (the 70 ppb group) as compared to Group A, B and C (the0, 17.5 ppb and 35 ppb groups, respectively), although no differences in frontal region DTFinflow values among the four groups were noted.3. The DTFFZ-F7, DTFFZ-T5, DTFFZ-P4, DTFFZ-P3, DTFFP2-O2, DTFP3-T4, DTFP3-F4, DTFP4-CZ and DTFP4-T4 values of Group D were found to be higher as compared to those of Group A and B. Furthermore, DTFFZ-F7 and DTFP4-T4 values of Group C were higher as compared to those of Group A. The DTFFZ-F7 values of Group D were higher as compared to those of the Group C. ConclusionShort-term toluene exposure significantly influences neural networks during cognitive processes such as WM encoding, even at low concentration.

Enhanced catalytic performance and reduced by-products emission on plasma catalytic oxidation of high-concentration toluene using Mn-Fe/rGO catalysts

High-concentration toluene is refractory to mineralize and must be controlled. The synergistic catalytic degradation of toluene with dielectric barrier discharge (DBD) results in the creation of large quantities of O3 and NOx. In this study, reduced graphene (rGO)-based catalysts with Mn and Fe (Mn-Fe/rGO) were recommendable. The effect of Mn-Fe/rGO catalysts on DBD oxidation of toluene was studied by changing Mn-Fe molar ratios and total loading. We investigated the performance of Mn-Fe/rGO catalysts on DBD oxidation of toluene by varying the Mn-Fe molar ratios and the total loading. The Mn-Fe molar ratio was 3:1, loading was 10 wt%, maximum toluene conversion was 85%, and COx selectivity was as high as 69.8%. When energy density (ED) was 598.25 J/L and toluene concentration was 657.14 mg/m3, toluene conversion, COx selectivity, O3 conversion, NO2 conversion, and NO conversion were 85.6%, 68.9%, 82.5%, 68.2%, and 64.3%, respectively. Analyzing the gas chromatography-mass spectrometric (GC-MS) data and determining the tail gas mechanism, it was found that toluene ring-opening was synergistic between active substances and Mn-Fe/rGO catalysts. Ferromanganites not only promoted the ring-opening degradation of toluene, but also had a positive effect on O3 conversion and NOX conversion. They consume aldehydes and NOX, produce O·and N·, and thus facilitate the mineralization process. This study provides new insights into plasma catalytic oxidation of high-concentration organic pollutants.

Insights into the superior performance of mesoporous MOFs-derived Cu[sbnd]Mn oxides for toluene total catalytic oxidation

A novel approach is developed to synthesize a series of flower like CuMn oxides catalysts for toluene removal with high efficiency. The optimal catalyst (i.e., 1Cu1Mn-450 prepared by calcination of Cu1Mn1-ptcda MOFs with Cu/Mn molar ratio of 1:1 by 450 °C) maintains 100% toluene removal for 54 h in the presence of steam (5.0 Vol%) at 210 °C. Besides, 1Cu1Mn-450 displays superior catalytic activity at high WHSV and high toluene concentrations. The relationships between textural, structural, and toluene catalytic performance are analyzed by various characterization techniques. Due to strong low-temperature reducibility, mobility of active oxygen, high average oxidation states (AOS) of Mn, mobility of active oxygen, as well as oxygen storage capacity at low temperatures, 1Cu1Mn-450 exhibits excellent activity and stability of toluene oxidation. The toluene oxidation was in the following pathway of toluene → alkoxide → benzoate → phenolate → maleic anhydride → short-chain carboxylates → CO2 and H2O. The breakage of CO in benzoate or CC in benzene ring is proved to be the rate-controlled step according to in situ DRIFTS. These findings can provide a feasible method to desigin transition metal oxide catalysts for large-scale industrial applications.

Effects of Co-Addition of Au and CuO to Macroporous SnO2 Microspheres on Their Acetone and Toluene Sensing Properties As Thick Film Sensors

Controlling of meso- and macro-porous structure of semiconductor metal oxide particles used as sensor materials is of primary importance in improving their gas response properties. To date, we could improve H2 and NO2 response properties of SnO2 [1] and In2O3 [2] thick film sensors by the introduction of macropores into these oxide particles, by employing ultrasonic spray pyrolysis (USP) of the oxide precursor solution containing polymethylmethacrylate (PMMA) microspheres as a template. We also demonstrated the usefulness of the Au loading on macroporous In2O3 (pr-In2O3) and the PdOx-CuOx loading on pr-WO3 in improving NO2 [3] and methylmercaptan [4] response properties, respectively.By the way, toluene and acetone are typical organic solvents used widely in many fields, but are very toxic and hazardous gases to be detected and then eliminated by suitable methods form the viewpoint of our safe and reliable life. In addition, the patients suffering from lung cancer and diabetes are known to release high concentrations of toluene and acetone, respectively. Therefore, the development of gas sensors capable of detecting these gases sensitively and selectively may offer a new and non-invasive diagnostic method of these diseases.In the present study, attempts were made to improve acetone and toluene response properties of thick film sensors fabricated by pr-SnO2 microspheres prepared by the USP method. Effects of the CuO addition to pr-SnO2 microspheres (pr-(CuO-SnO2)) and the additive methods of different amounts of Au to pr-(CuO-SnO2) microspheres on their response properties to both two gases have been examined.The aqueous solution containing 5.0×10-3 mol of SnCl4･5H2O and 3.2 g of PMMA microspheres (ca. 70 nm in size) per 100 mL of deionized water was used as the base precursor solution. The precursor mists were carried into the electronic furnace heated at 1,100°C to prepare pr-SnO2 microspheres. In preparing pr-(xCuO-SnO2) and pr-(yAu-xCuO-SnO2) (x and y: the additive amounts in wt% per the SnO2 weight), appropriate amounts of CuCl2･2H2O and HAuCl4･4H2O were added to the base precursor solution. Besides, an appropriate amount of Au was loaded on pr-(xCuO-SnO2) by a conventional impregnation method. Thick film sensors (10 - 15 mm in thick) were fabricated by screen printing of the slurry of thus-prepared pr-SnO2-based microspheres on an alumina substrate equipped with a pair of Pt electrodes, and their sensing properties to 20–100 ppm acetone, toluene and ethanol were measured in the temperature range of 300–500°C in air. The gas response is defined as the ratio of the sensor resistance value in air (Ra) to that in a sample gas (Rg). The sensors thus fabricated are referred to as the abbreviations of sensor materials.Figure 1 shows FE-SEM photographs of pr-SnO2-based microspheres prepared. All kinds of microspheres are confirmed to show similar porous structure formed by the thermal decomposition and evaporation of PMMA microspheres contained in the mists of the precursor solutions, except for 3.0Au/pr-(2.0CuO-SnO2). The appearance of 3.0Au/pr-(2.0CuO-SnO2) microspheres indicates partial filling of the loaded Au inside of the pores especially for the outermost surface of macroporous microspheres. Figure 2 shows variations in response to 100 ppm acetone of pr-SnO2-based sensors with operating temperature. The order of sensor resistance value in air was pr-(3.0Au-2.0CuO-SnO2) ³ pr-(2.0CuO-SnO2) > pr-(5.0Au-2.0CuO-SnO2) > 5.0Au/pr-(2.0CuO-SnO2) > 3.0Au/pr-(2.0CuO-SnO2) > pr-SnO2 at 350°C. Although the physicochemical states of Au and CuO in pr-(5.0Au-2.0CuO-SnO2) are not clarified yet, the addition of CuO to pr-SnO2 resulted in an increase in sensor resistance in air, due to the formation of p-n heterojunction in the macroporous microspheres. In contrast, the Au addition to or the Au loading on pr-(2.0CuO-SnO2) led to a decrease in sensor resistance. Among the sensors tested, pr-(3.0Au-2.0CuO-SnO2) showed the largest response to 100 ppm acetone at 350°C. Therefore, high sensor resistance in air is one important factor for the largest acetone response, but the added Au in pr-(3.0Au-2.0CuO-SnO2) is considered to accelerate the reaction of acetone with chemisorbed oxygen effectively. The smaller acetone response observed with 3.0Au/pr-(2.0CuO-SnO2) is considered to arise from the decrease in reaction site, as is confirmed by Fig. 1 d). The detailed gas response properties of these sensors, including those to toluene and ethanol, the latter is a possible interference gas in detecting acetone and toluene, will be reported in the presentation.[1] K. Hieda, et al., Sens. Actuators B, 133(1), 144-150 (2008).[2] T. Hyodo, et al., Sens. Actuators B, 187, 495-502 (2013).[3] T. Ueda, et al., Front. Mater., 6, 1-10 (2019).[4] N. Tammanoon, et al., ACS Appl. Mater. Interfaces, 2020, 12, 41728-41739 (2020). Figure 1

Alternations in neural oscillation related to attention network reveal influence of indoor toluene on cognition at low concentration.

Despite accumulative literature reporting negative impacts of high-concentration toluene, cognitive effects of toluene at low concentration are still unclear. Twenty-two healthy college students were exposed in a closed environmental chamber to investigate the influence of indoor toluene on cognitive performance and brain activity. During each toluene exposure condition (0ppb, 17.5ppb, 35 ppb, and 70 ppb), attention network test and electroencephalogram (EEG) recording were synchronously performed after 4-hour toluene exposure. Characteristic neural oscillation patterns in three attention networks were compared between four groups. The statistical analyses indicated that short-term exposure to toluene had no significant impact on behavioral performance of attention network. However, there was a significant increase in the power of theta and alpha band of executive network and orienting network in the whole brain, especially in frontal region when exposed to toluene. Besides, no significant difference was observed in alerting network. The alternations in neural oscillation demonstrated that more effort was required to accomplish the same tasks when exposed to toluene. The present study revealed that short-term exposure to toluene affected brain activity of attention network even at low concentration, which provided a theoretical basis for the development of safer evaluation methods and standards in the future.

A novel nanotubular TiO2-based Plug-Flow reactor for gas phase photocatalytic degradation of toluene

In this study, a novel annular plug flow reactor (PFR) with built-in nanotubular TiO2 obtained via anodizing was tested for the photocatalytic degradation of toluene. The oxide was grown directly on a titanium substrate by anodizing, as this method implies no risk of nanoparticles release in the environment during or after the photocatalytic process. Experiments were carried out in presence of an UV-A light source by modulating relative humidity, gas concentration and flow rate, to evaluate possible applications in indoor and industrial environments.The photocatalytic system demonstrated high photodegradation efficiency up to 90% for an inlet toluene concentration of 10 ppm, thus showing potential applications in mildly polluted environments, such as homes, offices and up to more severely polluted ones like offset printing plants, automobile manufacturing industries or even professional kitchens, where the exposure to cooking oil fumes is significant. In case of high toluene concentration, the initial degradation percentage falls in a range between 60 and 70%; subsequently, the instant degradation shows a gradual decrease ascribed to photocatalyst deactivation, which occurred due to the accumulation of recalcitrant by-products on the adsorption sites, thus highlighting some limitations for industrial applications when selected VOCs are present; nonetheless, the photocatalyst regained its initial activity through a simple photocatalyst reactivation process, leading to a maximum instant degradation percentage up to 90% for an inlet toluene concentration of 20 ppm.

Acute exposure to abuse-like concentrations of toluene induces inflammation in mouse lungs and brain.

Toluene is an aromatic hydrocarbon commonly abused by young adolescents for its central nervous system depressant effects. Although toluene's pharmacological effects at high concentrations are relatively well-known, few studies have assessed toluene's effects on lung and brain tissues. The present study characterized the pathological effects of acute inhaled toluene exposure in the lungs and brains of male Swiss-Webster mice (N = 68). Using a static vapor exposure chamber, mice (PND 28) received a single 30-min toluene administration (0, 1000, 2000, or 4000 ppm). Lung and brain tissues were extracted 24-h post-exposure. Histology results revealed significant changes in the morphology of lung tissue (e.g., irregular cellular architecture) with the 2000- and 4000-ppm exposures expressing greater signs of pathology than control 0-ppm exposure. Markers of immune system activity (F4/80 and Ly-6G) and cellular proliferation (Ki-67) in the lung revealed no significant differences. Additionally, brain tissues were analyzed for changes of astrogliosis (glial fibrillary acidic protein [GFAP]) and oxidative stress (glutathione peroxidase [GPx]). GFAP showed increased astrogliosis in the striatum with 2000-ppm toluene showing significantly higher expression than control (p < 0.05) and a marginal effect in the hippocampus. No other markers showed significant changes. The increased signs of inflammation and cellular damage suggest that exposure to a single high concentration of toluene, typical of abuse, is capable of producing pathology in both lung and brain tissue.

Associations between indoor VOCs and childhood asthma in Shanghai, China: an analysis stratified by frequency of window opening during night

Few studies pay attention to the possible associations between indoor VOCs and childhood asthma in Shanghai considering the effect of household ventilation. From March 2013 to December 2014, we collected air samples from 358 children's bedrooms in Shanghai, China. Information on childhood asthma, environmental exposures, and lifestyle behaviors was collected. Two-sample of Mann-Whitney U test, bivariate logistic regressions, and multiple logistic regression were used to obtain the association between VOCs and childhood asthma. Association analysis stratified by frequency of window opening during night was conducted to explore its possible effect on the target association. High concentrations of toluene and dodecane were significantly associated with childhood wheeze, and a high concentration of toluene was significantly associated with diagnosed asthma. In the bedrooms with low frequency of window opening during night, high concentrations of toluene, dodecane, and TVOC were significantly associated with childhood wheeze, and a high concentration of toluene was significantly associated with diagnosed asthma. Our results indicate that exposure to VOCs may be a risk factor for childhood asthma, especially in the bedrooms with poor ventilation during night. Family avoidance behaviors of household ventilation should be considered in the study of associations of household VOCs with childhood asthmatic symptoms.

Toluene-Sensing Properties of Mixed-Potential Type YSZ-Based Gas Sensors Attached with Au-Based Electrodes Prepared By a Spin-Coating Method

Introduction Exhaled breath of patients contains a higher concentration of specific gases than that of healthy people. For example, the patients suffering from lung cancer, diabetes and periodontitis release a high concentration of toluene, acetone and hydrogen sulfide and/or methyl mercaptan, respectively [1, 2]. Among various kinds of gas sensors, solid-electrolyte gas sensors have shown enhanced sensing properties to volatile organic compounds (VOCs) by optimizing the composition and/or microstructure of the sensing electrode (SE) [3]. We also reported that sensors attached with thin-film CeO2-added Au SEs (thickness: 30‒100 nm) fabricated by a spin-coating method showed large response to toluene at 500°C. In addition, the toluene response of the sensors attached with a 24 wt% CeO2-added Au SE increased with an increase in the SE thickness, and the sensor attached with the thickest SE showed the largest response [4]. In this study, effects of the change in the additive amount of CeO2 to Au SE, operating temperature, and toluene concentration on the sensing properties of the sensors were evaluated, and their sensing mechanisms were discussed. Experimental CeO2-added Au SEs were fabricated by a spin-coating method. The coating solution was prepared by the addition of Ce(NO3)3ˑ6H2O and polyvinyl alcohol into a 0.1 M HAuCl4 aqueous solution. The solution was dropped on the YSZ substrate, and it was spun at 3000 rpm for 30 s, followed by the heat treatment at 300°C. This process was repeated multiple times to increase the film thickness. Then, they were annealed at 700°C for 2 h in air. The obtained SEs were denoted as nCeO2/Au(x) SEs (n: an additive amount of CeO2, 8‒24 (wt%), x: the number of spin-coating cycle, 5–15). A Pt paste was screen-printed on the backside of the YSZ as the counter electrode (CE), and it was annealed at 700°C for 2 h in air. Sensing properties of the fabricated sensors (nCeO2/Au(x) sensors) to 50 ppm toluene in dry air were measured in a flow apparatus (gas-flow rate: 100 cm3 min−1) at 450‒550°C. The SE was exposed to a sample gas, while the CE was always exposed to dry synthetic air during gas response measurements. The open-circuit voltage between the two electrodes (E, mV) of the sensors as a sensing signal was measured with a digital electrometer, and the response (ΔE) was defined as the difference in E between in dry air and in toluene balanced with dry air. The microstructure of the sensors was observed by scanning electron microscopy (SEM; JEOL Ltd., JSM-7500F). Results and Discussion The thickness of the SEs increased with the number of spin-coating cycles, and the thickness was not affected by the additive amounts of CeO2 in the examined number of spin-coating cycles (x). Therefore, the SE thickness was controlled from 30 to 100 nm only by changing the x value [4]. Figure 1 shows response transients of the nCeO2/Au(x) sensors (n: 8, 24, x: 5, 10, 15) to 50 ppm toluene at 450 and 550°C in dry air. The E values of all the sensors negatively shifted upon exposure to toluene, but ΔE was largely affected by the SE thickness and the additive amount of CeO2 at both temperatures. ΔE of the 8CeO2/Au(x) sensors largely decreased with an increase in the thickness of SE, and the values observed at 550°C was much smaller than that at 450°C. Generally, the VOC-sensing mechanism of solid-electrolyte gas sensors can be explained on the basis of the mixed potential theory [3]. Based on the theory, the electrochemical oxidation of toluene and electrochemical reduction of oxygen simultaneously proceed at triple phase boundaries (TPBs) at the interface between SE and YSZ, when toluene diffuses in SE and reaches TPBs [5]. In addition, a certain amount of toluene is catalytically oxidized during the diffusion in SE. Therefore, the actual concentration of toluene at TPBs decreased with an increase in both the SE thickness and the operating temperature, which resulted in the largest toluene response of the 8CeO2/Au(5) sensor at 450°C among the 8CeO2/Au(x) sensors. However, ΔE of the 24CeO2/Au(x) sensors increased with an increase in the thickness of SEs at both temperatures. In addition, ΔE of the 24CeO2/Au(5) sensor at 550°C was larger than that at 450°C, while ΔE of the 24CeO2/Au(x) sensors (x: 10, 15) at 550°C was smaller than that at 450°C. This behavior probably arises from the increase in the number of active sites for electrochemical toluene oxidation in the CeO2-added Au SE. The details of the response properties and gas-sensing mechanism of these sensors will be discussed in the presentation.