Effect of nitrogen functional groups on competitive adsorption between toluene and water vapor onto nitrogen-doped spherical resorcinol-formaldehyde resin-based activated carbon

To elucidate the effect of nitrogen functional groups on the competitive adsorption of toluene and water vapor, a series of N-doped resorcinol-formaldehyde resin-based activated carbons using g-C₃N₄ as the nitrogen source were prepared, which possessed different N contents (1.29-6.14%). The competitive adsorption characteristics and mechanisms were investigated by characterizations, dynamic adsorption experiments, adsorption isotherms, and density functional theory calculations. Results showed that the normalized toluene adsorption capacity under 50 RH% was consistent with the N content, revealing that nitrogen functional groups can enhance the competitive adsorption for toluene under a humid atmosphere. Adsorption isotherms analysis suggested that nitrogen functional groups can not only accelerate the adsorption of toluene but also improve the hydrophobicity of carbon surface. Competitive adsorption mechanisms were ascribed to π-π interactions and electrostatic interactions. Specifically, graphitic-N and pyridinic-N enhance competitive adsorption for toluene through reinforced π-π interactions with toluene and weakened electrostatic interactions with water molecule. However, pyrrolic-N improve the competitive adsorption, which is principally attributed to enhanced π-π interactions with toluene. Furthermore, it was found that the reusability of activated carbon could be improved by nitrogen functional groups. This study provides theoretical hints to develop volatile organic compound adsorbents in the presence of water vapor.

PM2.5-mediated photochemical reaction of typical toluene in real air matrix with identification of products by isotopic tracing and FT-ICR MS

The sight into photoconversion of toluene, a ubiquitous typical pollutant, attentively by the involvement of PM2.5 in the real air environment is crucial for controlling haze pollution. Compared with the large-size PM2.5 on normal day (PM2.5-ND), the PM2.5 on haze day (PM2.5-HD) formed of small particle agglomerates featured greater oxidation capability, evidenced by the valence distribution of sulfur species. Notably, PM2.5-HD had abundant O₂^-• and •OH and participated in the photochemical reaction of toluene, giving it a greater toluene conversion with a first-order kinetic rate constant of 0.4 d^-1 on haze day than on normal day (0.2 d^-1). During the toluene photoconversion, isotopic labelling traced small molecules including benzene and newfound pentane, ethylbenzene, 1,3,8-p-menthatriene and 4-methyl-1-pentanone benzene that could be formed by methyl breakage, ring opening, fragmentation reforming and addition reaction of toluene. Given ADMET properties, 1,3,8-p-menthatriene was assigned high priority since it had poor metabolism, low excretion and severe toxicity, while benzene and 4-methyl-1-pentanone benzene should also be noticeable. FT-ICR MS results indicated that toluene could create multiple macromolecular products that are more sensitive to SOA generation in haze air matrix with broader carbon number and O/C, more oxygenated substitution with CHO/CHON occupying by 81.4%, lower DBE_average at 4.66 and higher OS_C‾ at -1.60 than normal air matrix. Accordingly, a photochemical reaction mechanism for toluene in real air atmosphere was proposed. The stronger oxidation property of PM2.5 not only facilitated toluene to generate small molecules but also boosted the conversion of intermediates to oxygenated macromolecular products, contributing to the formation of SOA.

Effects of thermal aging on the electronic and structural properties of Pt-Pd and toluene oxidation activity

Catalytic oxidation is a feasible method for remediating volatile organic compounds (VOCs), due to its lower energy consumption and mineralization of VOCs into H₂O and CO₂. Noble metal-based catalysts are preferred for the catalytic oxidation of VOCs because of their superior activity, but they are usually deactivated by thermal aging which sinters the metal particles. Here, we report that Pt-Pd/Al₂O₃ thermally aged at 700-900 °C in air showed enhanced catalytic activity for toluene oxidation in humid conditions. There were electronic and structural changes in the thermally aged Pt-Pd/Al₂O₃, as confirmed by numerous analyses. Both Pt and Pd existed in a metallic rather than oxidized state without additional reduction steps. The noble metal particles were assembled to form Pt-Pd alloy, in the form of isolated Pd atoms surrounded by Pt atoms. This specific alloy structure was found to be crucial to the observed enhancement in catalytic toluene oxidation at low temperature.

Beneficial effects of atypical antipsychotics on object recognition deficits after adolescent toluene exposure in mice: involvement of 5-HT1A receptors

Background: Inhalant (e.g. toluene) misuse by adolescents has been linked to psychosis and persistent cognitive deficits. Identifying effective strategies to improve cognitive deficits following chronic toluene misuse is critical. 5-HT_1A receptor has been proposed as a target for the treatment of cognitive deficits.Objectives: We compared the effects of antipsychotics on recognition deficits after adolescent toluene exposure in mice and elucidated the role of 5-HT_1A receptors in the cognition-improving effects of antipsychotics.Methods: Male NMRI mice (n = 279) received one injection per day of either toluene (750 mg/kg) or corn oil at postnatal days 35-39 and 42-46. Thereafter, the acute and subchronic effects of haloperidol, aripiprazole, or clozapine on toluene-induced recognition deficits were evaluated by novel object recognition test.Results: Acute administration of aripiprazole (p < .05) and clozapine (p < .01), but not haloperidol, significantly attenuated the toluene-induced recognition deficits. Pretreatment with 5-HT_1A receptor antagonist WAY -100,635 (p < .05) blocked their beneficial effects. Moreover, 5-HT_1A receptor agonist buspirone (p < .01) ameliorated the toluene-induced recognition deficits, which was reversed by WAY -100,635 (p < .001). Finally, after repeated treatment with clozapine, aripiprazole, and buspirone daily for 14 days, the impaired object recognition in toluene-exposed mice was significantly improved (p < .05) and the beneficial effects lasted for at least 2 weeks (p < .05).Conclusions: The results indicate that clozapine and aripiprazole, which display 5-HT_1A agonist properties, restored cognitive deficits in mice induced by adolescent toluene exposure. These findings suggest that these antipsychotics should be further explored as a potential treatment option for cognitive deficits in patients with psychosis associated with toluene exposure.

Systematic comparison of a biotrickling filter and a conventional filter for the removal of a mixture of hydrophobic VOCs by Candida subhashii

This work systematically compared the potential of a conventional fungal biofilter (BF) and a fungal biotrickling filter (BTF) for the abatement of a mixture of hydrophobic volatile organic compounds (VOCs). Candida subhashii was herein used for the first time, to the best of the author's knowledge, to remove n-hexane, trichloroethylene, toluene and α-pinene under aerobic conditions. C. subhashii immobilized on polyurethane foam supported steady state removal efficiencies of n-hexane, trichloroethylene, toluene and α-pinene of 25.4 ± 0.9%, 20.5 ± 1.0%, 19.6 ± 1.5% and 25.6 ± 2.8% in the BF, and 35.7 ± 0.9%, 24.0 ± 1.6%, 44.0 ± 1.7% and 26.2 ± 1.8% in the BTF, respectively, at relatively short gas residence times (30 s). The ability of C. subhashii to biodegrade n-hexane, TCE, toluene and α-pinene was confirmed in a batch test conducted in serum bottles, where a biodegradation pattern (toluene ≈ n-hexane > α-pinene > trichloroethylene) comparable to that recorded in the BF and BTF was recorded.

Association of metabolites of benzene and toluene with lipid profiles in Korean adults: Korean National Environmental Health Survey (2015-2017)

Background

Environmental exposure to benzene and toluene is a suspected risk factor for metabolic disorders among the general adult population. However, the effects of benzene and toluene on blood lipid profiles remain unclear. In this study, we investigated the association between urinary blood lipid profiles and metabolites of benzene and toluene in Korean adults.

Methods

We analyzed the data of 3,423 adults from the Korean National Environmental Health Survey Cycle 3 (2015–2017). We used urinary trans,trans-muconic acid (ttMA) as a biomarker of benzene exposure, and urinary benzylmercapturic acid (BMA) as an indicator of toluene exposure. Multivariate logistic regression analyses were performed to explore the association between blood lipid profiles and urinary metabolites of benzene and toluene. Additionally, we examined the linear relationship and urinary metabolites of benzene and toluene between lipoprotein ratios using multivariate regression analyses.

Results

After adjusting for covariates, the fourth quartile (Q4) of ttMA [odds ratio (OR) (95% confidence interval, CI = 1.599 (1.231, 2.077)] and Q3 of BMA [OR (95% CI) = 1.579 (1.129, 2.208)] were associated with an increased risk of hypertriglyceridemia. However, the Q4 of urinary ttMA [OR (95% CI) = 0.654 (0.446, 0.961)] and Q3 of urinary BMA [OR (95% CI) = 0.619 (0.430, 0.889)] decreased the risk of a high level of low-density lipoprotein cholesterol (LDL-C). Higher urinary ttMA levels were positively associated with the ratio of triglycerides to high-density lipoproteins [Q4 compared to Q1: β = 0.11, 95% CI: (0.02, 0.20)]. Higher urinary metabolite levels were negatively associated with the ratio of low-density lipoprotein to high-density lipoprotein [Q4 of ttMA compared to reference: β = -0.06, 95% CI: (-0.11, -0.01); Q4 of BMA compared to reference: β = -0.13, 95% CI: (-0.19, -0.08)].

Conclusion

Benzene and toluene metabolites were significantly and positively associated with hypertriglyceridemia. However, urinary ttMA and BMA levels were negatively associated with high LDL-C levels. These findings suggest that environmental exposure to benzene and toluene disrupts lipid metabolism in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-14319-x.

Short- and long-term effects of chronic toluene exposure on recognition memory in adolescent and adult male Wistar rats

Abuse of toluene-containing volatile inhalants, particularly among youth, is of significant medical and social concern worldwide. Teenagers constitute the most abundant users of toluene and the majority of adult abusers of toluene started as teenagers. Although the euphoric and neurotoxic effects of acute toluene have been widely studied, lasting effects of chronic toluene exposure, especially in various age groups, have not been well investigated. In this study, we used adolescent and adult male Wistar rats to evaluate the short- and long-term effects of chronic toluene on various behaviors including cognitive function. Daily exposure to toluene (2000 ppm) for 40 days (5min/day) resulted in age-dependent behavioral impairments. Specifically, adolescent animals showed recognition memory impairment the day after the last exposure, which had normalized by day 90 post- exposure, whereas such impairment in adult animals was still evident at day 90 post-exposure. Our data suggest that age-dependent responses should be taken into consideration in interventional attempts to overcome specific detrimental consequences of chronic toluene exposure.

Surface analysis of sequential semi-solvent vapor impact (SAVI) for studying microstructural arrangements of poly(lactide-co-glycolide) microparticles

Biodegradable poly(lactide-co-glycolide) (PLGA) microparticles have been used as long-acting injectable (LAI) drug delivery systems for more than three decades. Despite extensive use, few tools have been available to examine and compare the three-dimensional (3D) structures of microparticles prepared using different compositions and processing parameters, all collectively affecting drug release kinetics. Surface analysis after sequential semi-solvent impact (SASSI) was conducted by exposing PLGA microparticles to different semi-solvent in the liquid phase. The use of semi-solvent liquids presented practical experimental difficulties, particularly in observing the same microparticles before and after exposure to semi-solvents. The difficulties were overcome by using a new sequential semi-solvent vapor (SSV) method to examine the morphological changes of the same microparticles. The SASSI method based on SSV is called surface analysis of semi-solvent vapor impact (SAVI). Semi-solvents are the solvents that dissolve PLGA polymers depending on the polymer's lactide:glycolide (L:G) ratio. A sequence of semi-solvents was used to dissolve portions of PLGA microparticles in an L:G ratio-dependent manner, thus revealing different structures depending on how microparticles were prepared. Exposing PLGA microparticles to semi-solvents in the vapor phase demonstrated significant advantages over using semi-solvents in the liquid phase, such as in control of exposure conditions, access to imaging, decreasing the time for sequential exposure of semi-solvents, and using the same microparticles. The SSV approach for morphological analysis provides another tool to enhance our understanding of the microstructural arrangement of PLGA polymers. It will improve our comprehensive understanding of the factors controlling drug release from LAI formulations based on PLGA polymers.

Yttrium-modified Co3O4 as efficient catalysts for toluene and propane combustion: Effect of yttrium content

A series of Y-modified cobalt oxides with various Y/(Co+Y) molar ratios (0.25 %, 0.5 %, 1 %, 3 % and 5 %) were prepared to study the effect of Y content on toluene and propane combustion. The characterization of the catalysts revealed that proper Y incorporation resulted in smaller crystallite sizes, larger specific surface areas, more oxygen vacancies and weaker Co-O bonds. As such, the Y-modified Co₃O₄ showed enhanced low-temperature reducibility, boosted oxygen mobility and better catalytic activity. However, excess Y (> 1 %) aggregates on the surface of Co₃O₄ and forms yttrium carbonate species, hindering the catalyst activity. A volcano-type relationship between the Y content and the catalytic activity was established. The optimal catalyst 1 % Y-Co (with Y/(Co+Y) molar ratio of 1 %) exhibited toluene oxidation rate of 24 nmol g^-1 s^-1 at 220 °C and propane oxidation rate of 69 nmol g^-1 s^-1 at 180 °C. Besides, 1 % Y-Co presented perfect cycling stability and long-term durability in propane oxidation. Regarding its low cost, high efficiency and good stability, 1 % Y-Co is a promising catalyst for the practical elimination of hydrocarbon emissions.

Inexpensive and easily replicable precipitation of CuO nanoparticles for low temperature carbon monoxide and toluene catalytic oxidation

Herein CuO nanoparticles (NPs) with nanostructures were prepared by precipitation method using hydrate copper sulfate (CuSO₄.5H₂O) and sodium hydroxide followed by heat treatment at 400 °C. The as-prepared CuO NPs with nanostructures were investigated using X-ray diffraction (XRD), Fourier Transformed Infra-red spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), X-ray photochemical spectroscopy (XPS), Energy dispersive spectroscopy (EDS), and Ultra-violet-visible (UV-vis) spectroscopy. In order to evaluate the reducibility, temperature programmed reduction (H₂-TPR) was applied. More importantly, CuO NPs was successfully tested as catalyst towards the total conversion of carbon monoxide (CO) and toluene (C₇H₈). Both XRD and Raman analysis as well as FTIR show that the sample exhibited a monoclinic spinel structure. SEM images indicate that CuO NPs are well-covered by grains size exhibiting homogeneous morphology composed of very fine interconnected particles with an apparent porosity. The sample was made up of Cu and O, according to the XPS and EDS measurements. The band gap energy obtained from optical property analysis is ∼2.65 eV. The catalytic performances of CuO NPs can be assigned to the combined effects of crystal structure, morphology, surface oxygen mobility, redox property and the higher specific surface area (∼87 m²/g). More precisely XPS and H₂-TPR data suggests that, the conversion of CO and C₇H₈ over CuO NPs follows a Mars-van Krevelen type mechanism. More importantly CuO NPs catalysts is reusable and exhibited good stability in the prolonged isothermal test. Thus, CuO NPs is confirmed as an efficient and inexpensive catalysts for CO and C₇H₈ conversion at low temperatures.

In2S3 nanoflakes grounded in Bi2WO6 nanoplates: A novel hierarchical heterojunction catalyst anchored on W mesh for efficient elimination of toluene

Toxic toluene can be completely oxidized in CO₂ and H₂O with novel three-dimensional (3D) In₂S₃@Bi₂WO₆ hierarchical crystals under visible light. Dense and uniform In₂S₃ nanoflakes are rooted in Bi₂WO₆ nanoplates which intercross with each other and are anchored on a pliable tungsten mesh. This leads to the construction of a stable and porous interface for adsorbing and decomposing target gaseous toluene. The firm contact between In₂S₃ and Bi₂WO₆ initiates the formation of a built-in electric field that helps in channeling the photogenerated electrons in Bi₂WO₆ CB to quench the holes in₂S₃ VB. This results in highly capable electrons and holes, as well as notable increase in the yields of •O₂^- and •OH. 99.7% of toluene is removed and 93.4% is converted to CO₂ when it is degraded in simulated air. This validates its remarkable efficacy in detoxifying toluene.

Study on the synergy effect of MnOx and support on catalytic ozonation of toluene

MnO_x has received widespread attention in low-temperature catalytic oxidation of VOCs, however, the synergy effect of MnO_x and support on the VOCs catalytic ozonation were rarely studied. In this study, five different MnO_x/X (X: MCM-41, 13X, ZSM-5, HY, USY) were synthesized and found their support greatly affect the catalytic oxidation activity. MnO_x/MCM-41 presents the largest specific surface area, pore volume and unique surface morphology, and thereby provides more sites for MnO_x loading and VOCs adsorption. Moreover, MnO_x/MCM-41 presents a high proportion of Mn³⁺, which helps to enhance the ion exchange capability, and thus promotes the regeneration of oxygen vacancies. Furthermore, a part of Mn was proved to be introduced into the MCM-41 lattice, which can promote the electron transfer between the active components and the support, and thereby effectively improve the surface electronic properties of the catalyst. The toluene catalytic experiments showed that MnO_x/MCM-41 exhibited the best catalytic activity, presenting complete degradation of O₃ and VOCs at room temperature. In addition, 5 wt%MnO_x/MCM-41 exhibited better catalytic activity than other loading, and its higher surface oxygen species endowed it with strong water resistance and stability. In-situ DRIFTs indicated that toluene was initially oxidized into benzyl alcohol during the adsorption process, and then decomposed to intermediate products (benzaldehyde, phenolate, etc.) during the catalytic ozonation process, and finally oxidized to carbon dioxide. In conclusion, the supply of loading sites and the improvement of interfacial electron transfer are the manifestations of the synergy between the support and MnO_x, leading to the promotion of the catalytic ozonation of VOCs.

A sustainable Decision Support System for soil bioremediation of toluene incorporating UN sustainable development goals

Decision Support System (DSS) is a novel approach for smart, sustainable controlling of environmental phenomena and purification processes. Toluene is one of the most widely used petroleum products, which adversely impacts on human health. In this study, Fusarium Solani fungi are utilized as the engine of the toluene bioremediation procedure for the monitoring part of DSS. Experiments are optimized by Central Composite Design (CCD) - Response Surface Methodology (RSM), and the behavior of the mentioned fungi is estimated by M5 Pruned model tree (M5P), Gaussian Processes (GP), and Sequential Minimal Optimization (SMOreg) algorithms as the prediction section of DSS. Finally, the control stage of DSS is provided by integrated Petri Net modeling and Failure Modes and Effects Analysis (FMEA). The findings showed that Aeration Intensity (AI) and Fungi load/Biological Waste (F/BW) are the most influential mechanical and biological factors, with P-value of 0.0001 and 0.0003, respectively. Likewise, the optimal values of main mechanical parameters include AI, and the space between pipes (S) are equal to 13.76 m³/h and 15.99 cm, respectively. Also, the optimum conditions of biological features containing F/BW and pH are 0.001 mg/g and 7.56. In accordance with the kinetic study, bioremediation of toluene by Fusarium Solani is done based on a first-order reaction with a 0.034 s-1 kinetic coefficient. Finally, the machine learning practices showed that the GP (R2 = 0.98) and M5P (R2 = 0.94) have the most precision for predicting Removal Percentage (RP) for mechanical and biological factors, respectively. At the end of the present research, it is found that by controlling seven possible risk factors in bioremediation operation through the FMEA- Petri Net technique, efficiency of the process can be adjusted to optimum value.

A high-performance and stable Cu/Beta for adsorption-catalytic oxidation in-situ destruction of low concentration toluene

Finding a cost-effective treatment to remove of low concentrations of volatile organic compounds (VOCs) is still a challenge. In this study, a Cu/Beta material was developed for in situ adsorption-catalytic oxidation of low concentrations of toluene. The results showed that the addition of Cu enhanced the adsorption and catalytic oxidation of toluene by Beta zeolite. Cu7/Beta with a Cu⁺ ratio of close to 50% performed best. The high adsorption of Cu7/Beta was mainly attributed to the abundant Cu⁺ species and the micro-mesoporous structure of the Beta zeolite, and the high catalytic oxidation was attributed to the lattice oxygen in the uniformly dispersed CuO. Finally, the adsorption intermediates and reaction pathways in the catalytic oxidation of toluene were clarified using XPS and DRIFTS spectra. This work provides new strategies for the development of efficient and stable adsorption-catalytic oxidation in situ destruction materials.

[Acute toluene, xylene and ethylbenzene poisoning leads to neurological sequelae: a case report]

This article reports a poisoning case after occupational exposure to toluene, xylene, and ethylbenzene for 3 days. The main clinical manifestation of the patient was consciousness disorder. After dehydration, cerebral awakening, anti-epileptic and anti-myoclonic treatment, the patient had secondary epilepsy and cerebellar ataxia for a long time. According to diagnostic criteria, the patient was diagnosed with occupational acute chemical poisoning (severe) , occupational acute chemical poisoning sequelae. It is suggested that the clinical awareness of benzene compound poisoning should be strengthened, early diagnosis and early treatment should be carried out to improve the prognosis of patients.

Quenching-induced surface modulation of perovskite oxides to boost catalytic oxidation activity

Quenching is a powerful method for modulating surface structures of metal oxide nanocatalysts to achieve high catalytic oxidation activities, but it is still challenging. Herein, a catalyst of ultrafine Co₃O₄ nanoparticles decorated on Co-doped LaMnO₃ (Co₃O₄/LaCo_xMn_1-xO₃) is synthesized via one-step quenching perovskite-type LaMnO₃ nanocatalyst into an aqueous solution of cobalt nitrate, which exhibits significantly improved catalytic performance with toluene (1000 ppm) conversion of 90% at 269 °C under the gas hourly space velocity of 72000 mL g^-1 h^-1. The high catalytic activity correlates with large surface area, abundant oxygen vacancies and good reducibility. Furthermore, density functional theory calculations disclose that Co doping and interfacial effect of Co₃O₄/LaCo_xMn_1-xO₃ can achieve lower C-H bond activation energy. These findings provide a unique and effective route towards surface modification of nanocatalysts.

Coupling of bioelectrochemical toluene oxidation and trichloroethene reductive dechlorination for single-stage treatment of groundwater containing multiple contaminants

Bioremediation of groundwater contaminated by a mixture of aromatic hydrocarbons and chlorinated solvents is typically challenged because these contaminants are degraded via distinctive oxidative and reductive pathways, thus requiring different amendments and redox conditions. Here, we provided the proof-of-concept of a single-stage treatment of synthetic groundwater containing toluene and trichloroethene (TCE) in a tubular bioelectrochemical reactor, known as a "bioelectric well". Toluene was degraded by a microbial bioanode (up to 150 μmol L^-1 d^-1) with a polarized graphite anode (+0.2 V vs. SHE) serving as the terminal electron acceptor. The electric current deriving from microbially-driven toluene oxidation resulted in (abiotic) hydrogen production (at a stainless-steel cathode), which sustained the reductive dechlorination of TCE to less-chlorinated intermediates (i.e., cis-DCE, VC, and ETH), at a maximum rate of 500 μeq L^-1 d^-1, in the bulk of the reactor. A phylogenetic and functional gene-based analysis of the "bioelectric well" confirmed the establishment of a microbiome harboring the metabolic potential for anaerobic toluene oxidation and TCE reductive dechlorination. However, Toluene degradation and current generation were found to be rate-limited by external mass transport phenomena, thus indicating the existing potential for further process optimization.

Mechanistic insights into ball milling enhanced montmorillonite modification with tetramethylammonium for adsorption of gaseous toluene

Montmorillonite is widely used for pollutants adsorption due to its porous structure and low price. However, the low specific surface area and small porosity limit its application in gas adsorption field. In this study, montmorillonite was organically modified using a facile dry ball milling method by tetramethylammonium bromide. The adsorption behaviour of toluene as a model VOC compound on organic montmorillonite was systematically investigated through adsorption breakthrough curves, adsorption kinetics and isotherms. After modification by ball milling, the specific surface area of ball milling with tetramethylammonium bromide for montmorillonite modification (BMTMt) was increased from 20.6 m²/g to 186.4 m²/g, and the microporosity proportion was up to 47%. Dynamic adsorption experiments showed that the best performance of BMTMt for toluene (55.9 mg/g) was 6 times higher than that of original montmorillonite (8.8 mg/g). Compared with the water bath preparation method, ball milling method promoted the intercalation of tetramethylammonium bromide into the layers of montmorillonite, resulting in a higher proportion of micropores. Density functional theory calculations indicated that the interaction between tetramethylammonium bromide and montmorillonite was mainly electrostatic forces, and the enhanced adsorption performance for toluene was mainly through microporous filling. BMTMt was proved to be a promising adsorbent for VOCs removal.

Long-term degradation of toluene and phenol in soil: Identification of transformation products and pathways via HRMS-based suspect and non-target screening

In this study, the long-term fate of toluene and phenol in the soil was investigated, and the transformation products (TPs) and pathways of these compounds were studied by a high resolution mass spectrometry (HRMS)-based suspect and non-target screening approach for the first time, and 9 and 12 transformation products were identified for toluene and phenol, respectively in the lab-exposed soil samples. Salicylaldehyde, 4-hydroxybenzaldehyde, and benzaldehyde were identified in toluene-contaminated field soil samples for the first time, and the main mechanisms involved in the biodegradation and detoxification of toluene and phenol in soil were oxidation, carboxylation, dehydroxylation, and ring fission amongst others. 2-oxoglutarate, TP165-A, TP165-B, TP172, and TP195 were identified as novel phenol transformation products, while salicylaldehyde, 2-oxoglutarate, TP165-A, and TP165-B were identified as novel toluene transformation products, providing new possible evidence for additional degradation pathways, which could give new insights into the fate of toluene and phenol during the natural attenuation process in the environment. Finally, salicylaldehyde, 4-OH-benzaldehyde, and 4-OH-benzoic acid which were detected at Level 1 identification confidence were suggested as indicator chemicals of toluene and phenol exposure in the contaminated field.

Application of MCM-48 with large specific surface area for VOCs elimination: synthesis and hydrophobic functionalization for highly efficient adsorption

MCM-48 molecular sieve with a large specific area (1470.87 m²/g) was hydrothermally synthesized for VOCs elimination by the adsorption method. The dynamic adsorption behaviors of toluene on this material were evaluated via breakthrough curves under both dry and wet conditions. A high toluene adsorption capacity of 171.13 mg/g was observed under dry conditions; however, in the presence of water vapor (20% RH), the adsorption capacity greatly decreased to 58.88 mg/g due to the competitive occupation of adsorption sites between water molecules and toluene molecules. To improve the affinity to toluene, functionalized MCM-48 materials were obtained by the co-condensation method and grafting method, respectively. It was found that co-M48(1:5)-100/48 sample by co-condensation method presents the highest dynamic adsorption capacity at both dry condition (194.62 mg/g) and 20% RH (122.42 mg/g), which has a significant advantage in the same type of adsorbent. This could be ascribed to the conjugated π-electrons effect between aromatic rings of phenyl groups uniformly distributed in MCM-48 skeleton and toluene molecules, which was qualitatively confirmed by FTIR. Moreover, cycle tests confirmed that this adsorbent possesses superior stability. The Yoon-Nelson model was successfully employed to describe the dynamic adsorption behavior of toluene over the organofunctionalized MCM-48 adsorbents, and the adsorption force of toluene was explained. Finally, a diagram describing the effect of different functionalization methods on the hydrophobicity and organophilicity of MCM-48 was given for a better understanding.

Simultaneous removal of gaseous benzene and toluene with photocatalytic oxidation process at high temperatures under UVC irradiation

Organic air pollutants represent many different pollutants, including persistent toxic organics and volatile organic compounds (VOC). The VOC group includes about 150 different compounds, the majority of which are considered harmful and toxic to human health. Considering all these features, the removal of VOC is of great importance. According to the Industrial Air Pollution Control Regulation, VOCs in flue gases are classified, and the limit value for the most dangerous group is specified as 20 mg/m³ according to the degree of damage. From past to present, many different removal technologies have been developed and continue to be developed. Removal of pollutants at low concentrations by conventional methods is more inadequate than those above certain concentrations. Photocatalytic oxidation (PCO) is one of the technologies used for VOC removal recently. It has been determined that many different organic pollutants can be removed with this method. Within the scope of this study, the removal of benzene and toluene pollutants, which are two important VOCs frequently encountered in flue gases, by the photocatalytic oxidation method has been studied under UVC irradiation. In this study, a new photocatalyst by doping silver (Ag), a noble metal, and nickel (Ni), one of the transition metals, on TiO₂ nanoparticles was developed and a laboratory-scale reactor system was designed. Many experiments were carried out by changing the system parameters such as ambient temperature (120 °C, 150 °C, 180 °C), humidity (25% and 50%), and percentage of Ag and Ni doping on TiO₂ (0.5%, 1%, 2.5%, %5) and the most successful conditions for the removal of benzene and toluene contaminants were tried to be determined based on the results obtained. When all experiments carried out within the scope of this study were considered, the average removal efficiency for benzene was found as 89.33%, while the average removal efficiency for toluene was 88.23%. According to the obtained results, the most suitable conditions for the simultaneous removal of benzene and toluene pollutants with photocatalytic oxidation method under UVC light were determined as 120 °C temperature, 25% humidity, and 0.5% doping photocatalyst.

Exposure to benzene, toluene and polycyclic aromatic hydrocarbons in Nunavimmiut aged 16 years and over (Nunavik, Canada) - Qanuilirpitaa 2017 survey

There are numerous volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that Inuit may be exposed to from combustion, cooking, heating, vehicle exhaust, active and passive smoking and other local sources of contaminants such as oil spills or open-air burning in landfills. To better assess the levels of exposure to these non-persistent chemicals, we measured a suite of benzene, toluene (two VOCs) and PAHs metabolites in pooled urine samples from youth and adults aged 16 years old and over who participated in the Qanuilirpitaa? 2017 Inuit Health Survey (Q2017), a population health survey conducted in Nunavik. A cost-effective pooling strategy was established and 30 different pools from individual urine samples (n = 1266) were created by grouping individual urine samples by sex, age groups and regions. To assess smoking and exposure to second-hand smoke, cotinine levels were measured in individual urine samples. We found that benzene, toluene, all detected PAHs metabolites and cotinine levels were significantly higher in Q2017 compared to adults in the Canadian Health Measure Survey Cycle 4 (2014-2015) or the general U.S population (2015-2016). Moreover, mean levels of one benzene metabolite, S-phenylmercapturic acid, and several PAHs metabolites, 1-naphthol, 2-and 3-hydroxyfluorene, and 4- and 9-hydroxyphenanthrene, known to be associated with smoking habits, were higher in Q2017 compared to reference values (RV₉₅) established for non-smokers in the general Canadian population. Furthermore, benzene and PAHs metabolites were all correlated with cotinine levels. Our results suggest that the high smoking prevalence in Nunavik is an important contributor to the elevated benzene and PAHs exposure. Other local sources may add to that exposure, although we were not able to account for their contribution. These data highlight the importance of regional and community efforts for reducing smoking and to encourage smoke-free homes in Nunavik, while continuing to investigate and reduce other possible local sources of exposure to benzene, toluene and PAHs.

Effect of NOx and RH on the secondary organic aerosol formation from toluene photooxidation

The secondary organic aerosol (SOA) formation mechanism and physicochemical properties can highly be influenced by relative humidity (RH) and NOx concentration. In this study, we performed a laboratory investigation of the SOA formation from toluene/OH photooxidation system in the presence or absence of NOx in dry and wet conditions. The chemical composition of toluene-derived SOA was measured using Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). It was found that the mass concentration of toluene decreased with increasing RH and NOx concentration. However, the change of SOA chemistry composition (f₄₄, O/C) with increased RH was not consistent in the condition with or without NOx. The light absorption and mass absorption coefficient (MAC) of the toluene-derived SOA only increased with RH in the presence of NOx. In contrast, MAC is invariant with RH in the absence of NOx. HR-ToF-AMS results showed that, in the presence of NOx, the increased nitro-aromatic compounds and N/C ratio concurrently caused the increase of SOA light absorption and O/C in wet conditions, respectively. The relative intensity of CHON and CHO_xN family to the total nitrogen-containing organic compounds (NOCs) increased with the increasing RH, and be the major components of NOCs in wet condition. This work revealed a synergy effect of NOx and RH on SOA formation from toluene photooxidation.

Removal of toluene and SO2 by hierarchical porous carbons: a study on adsorption selectivity and mechanism

The coal combustion produces a large amount of pollutants such as organic compounds pollutants (such as VOCs, SVOCs) and conventional pollutants (such as SO₂, NOx) which need to be controlled in coal-fired plants. Currently, there have been mature emission control technologies for conventional pollutants in coal-combustion flue gas. The complicated conditions of flue gas will have great effects on the property of VOCs adsorbents. Thus, high-quality adsorbents with great adsorption properties and selectivity of VOCs are urgently needed. In this work, a biomass-derived hierarchical porous carbon (HPC-A) with high adsorption capacity (585 mg/g) and great selectivity of toluene was proposed. Analyses through the competitive adsorption tests between toluene and SO₂ indicated that the pore size distributions of adsorbents dominate the adsorption capacity and selectivity. The ultramicropores (< 0.7 nm) determine the SO₂ adsorption capacity and promote the SO₂ adsorption selectivity, while the micropores of 0.7 ~ 2 nm and mesopores are beneficial for toluene adsorption. Intriguingly, the SO₂ molecules can promote the toluene adsorption kinetics on hierarchical porous carbons through occupying ultramicropores when competitive adsorption. Besides, we indicated the mechanism of adsorption capacity, selectivity, and kinetics of toluene and SO₂, and great reusability of HPC-A was found through toluene cyclic adsorption tests. The HPC-A could be a potential adsorbent for VOCs removal from coal-combustion flue gas.

Wall losses of oxygenated volatile organic compounds from oxidation of toluene: Effects of chamber volume and relative humidity

Vapor wall losses can affect the yields of secondary organic aerosol. The effects of surface-to-volume (S/V) ratio and relative humidity (RH) on the vapor-wall interactions were investigated in this study. The oxygenated volatile organic compounds (OVOCs) were generated from toluene-H₂O₂ irradiations. The average gas to wall loss rate constant (k_gw) of OVOCs in a 400 L reactor (S/V = 7.5 m^-1) is 2.47 (2.41 under humid conditions) times higher than that in a 5000 L reactor (S/V = 3.6 m^-1) under dry conditions. In contrast, the average desorption rate constant (k_wg) of OVOCs in 400 L reactor is only 1.37 (1.20 under humid conditions) times higher than that in 5000 L reactor under dry conditions. It shows that increasing the S/V ratio can promote the wall losses of OVOCs. By contrast, the RH effect on k_gw is not prominent. The average k_gw value under humid conditions is almost the same as under dry conditions in the 400 L (5000 L) reactor. However, increasing RH can decrease the desorption rates. The average k_wg value under dry conditions is 1.45 (1.27) times higher than that under humid conditions in the 400 L (5000 L) reactor. The high RH can increase the partitioning equilibrium timescales and enhance the wall losses of OVOCs.