Mineralization Of Toluene Research Articles

D-band center modulated water molecule adsorption and activation towards highly photocatalytic toluene mineralization

Photocatalysis is a promising strategy for deep purification of low-concentration toluene, driving by hydroxyl radicals (•OH) with potent oxidation capacity. Unfortunately, •OH evolution from H2O activation is a thermodynamically unfavorable process and suffers from the low utilization efficiency of photoexcited holes. Herein, a novel strategy to tailor the d-band center of perovskite BaSnO3 via heteroatom Zn substitution is proposed, aiming at optimizing the H2O adsorption configuration and efficiently activating H2O to yield •OH. The upshifted d‐band center mediated by the incorporation of Zn improves the adsorption capacity of H2O molecule, and directly determines the H2O adsorption configuration. Meanwhile, the dual transport channels of electron-hole accelerate O-H band fracture and lower the energy barrier for hole transfer to OH, allowing for efficient H2O activation. The optimized catalyst shows a 3-fold activity in toluene mineralization compared to commercial TiO2. This work sheds substantial light on H2O activation and environmental catalyst design.

Surface oxygen vacancies induced by cu-doping in hexagonal ZnMn2O4 nanoplates for high efficiency photothermocatalytic oxidation of toluene

The exploitation of efficient and stable photothermal catalyst for the deep mineralization of volatile organic compounds (VOCs) is crucial and challenging. Herein, a photothermal catalyst with abundant oxygen defects was prepared for the first time via Cu-doped ZnMn2O4 hexagonal nanoplate. Experimental characterization results reveal that Cu doping enhances not only the ZnMn2O4 defect contents but also the light absorption and thermal conversion ability of ZnMn2O4. Compared to the undoped ZnMn2O4 (ZMO), the ZnMn2O4 with optimal Cu doping amount (ZMO-4Cu) exhibits excellent photothermal catalytic performance (94% toluene conversion and 87% toluene mineralization) and good resistance to low concentration SO2 under full-spectrum light irradiation. Experimental characterizations and theoretical calculations jointly demonstrated that the oxygen vacancies of ZMO-4Cu surface are more conducive to the adsorption of O2, effectively reduce the oxygen dissociation energy of ZMO-4Cu, thus generating abundant active oxygen species and improving the photothermal catalytic activity for toluene oxidation. In situ IR experiments disclosed that photothermal catalysis is more conducive to the toluene deep oxidation than thermal catalysis. This work provides new insights for the design of high efficiency photothermal catalysis for the deep oxidation of VOCs.

Efficient photothermal mineralization of toluene over MnCo2O4 with different exposed facets: Revealing the role of oxygen vacancy and photo-/thermo- synergistic mechanism

Modulating oxygen vacancies through facet engineering is a potential strategy to enhance activity of photo-/thermo- synergistic catalysis for toluene mineralization. Hence, we synthesized MnCo2O4 catalysts with exposed {01−1} facets (MCO-R), {1−1−2} facets MCO-S), and {1−10} facets (MCO-C), in which the MCO-R with the highest oxygen vacancy concentration exhibited the highest toluene conversion (95.8 %) and CO2 yield (85.5 %) under the full-spectrum light irradiation. The results of various characterizations and DFT calculations confirmed that the oxygen vacancy could accelerate the activation of lattice oxygen and molecule oxygen, thereby enhancing the photothermal catalytic toluene activity of MnCo2O4. Meanwhile, the results of performance evaluations identified that the efficient photothermal mineralization activity of toluene was induced by the photo-/thermo- synergistic catalysis. Besides, the reaction pathway studies by In-situ DRIFTS tests revealed the key role of oxygen vacancy and photo-/thermo- synergistic effects in the reaction progress of photothermal mineralization of toluene over MnCo2O4.

Adjusting Ag0 on oxygen-deficient Ag/MnO2 through electronic metal-support interaction to enhance mineralization of toluene in post-plasma catalytic system

While nonthermal plasma (NTP) technology exhibits notable efficacy in removing volatile organic compounds (VOCs), its practical application is impeded by a restricted carbon dioxide (CO2) selectivity. In this work, Ag-loaded α-MnO2 nanorods with strong electronic metal-support interaction (EMSI) were synthesized to enhance the mineralization of toluene in post-plasma system (PPC). EMSI was constructed between Ag species and MnO2 by anchoring Ag on hydroxyl groups. Increasing Ag loading facilitated the generation of oxygen vacancies, which promoted electron transfer from MnO2 to Ag sites, reinforcing EMSI and favoring the formation of Ag0. The results showed that the 3% Ag-loaded α-MnO2 nanorods exhibited better activity than bare MnO2, with a remarkable boost in CO2 selectivity to 77.5%, far exceeding the 33% CO2 selectivity of MnO2. It was concluded that both oxygen vacancies and Ag0 affected the toluene conversion by enhancing the conversion of ozone (O3) to reactive oxygen species (ROS). Through in-situ DRIFTS, it was found that Ag0 transformed O3 to a higher concentration of atomic oxygen (O*), capable of degrading organic intermediates to CO2. Additionally, Ag0 facilitated the direct ring-opening of adsorbed toluene. This research introduces a novel method for designing catalysts with EMSI to improve the mineralization of VOCs.

Unveiling the activity difference cause and ring-opening reaction routes of typical radicals induced degradation of toluene

This study employs five UV-AOPs (PMS, PDS, H2O2, NaClO and NaClO2) to produce radicals (•OH, SO4•-, ClO•, O2•- and 1O2) and further comparatively studies their activity sequence and activity difference cause in toluene degradation. The toluene mineralization efficiency as a descending order is 73 % (UV-PMS) > 71 % (UV-PDS) > 70 % (acidified-UV-NaClO) > 55 % (UV-H2O2) > 36 % (UV-NaClO) > 35 % (UV-NaClO2); that of conversion efficiency is 99 % (acidified-UV-NaClO) > 95 % (UV-PMS) > 90 % (UV-PDS) > 74 % (UV-H2O2) > 44 % (UV-NaClO) > 41 % (UV-NaClO2). Acidic pretreatment significantly boosts the reactivity of UV-NaClO. ESR combined with radical quenching tests reveals the radicals’ generation and evolution, and their contribution rates to toluene conversion, i.e. ClO• > SO4•- > O2•- > 1O2 > •OH. Theoretical calculations further unveil the ring-opening reaction routes and the nature of the activity difference of different radicals. The minimum energy required for ring-opening reaction is 116.77, 150.63, 168.29 and 191.92 kJ/mol with respect to ClO•, SO4•-, 1O2 and •OH, and finding that the ClO•-HO• pair is the best for toluene mineralization. The difficulty for eliminating typical VOCs by using UV-AOPs method is determined as toluene > chlorobenzene > benzene > ethyl acetate.

Enhanced mineralization capacity for photocatalytic toluene degradation over Ag3PO4/TiO2: the critical role of oxygen vacancy

Mesoporous disk-like Ag3PO4/TiO2 heterojunctions with rich oxygen vacancies using MIL-125(Ti)-derived TiO2 as support were prepared for photocatalytic degradation toward toluene. The low amount of Ag3PO4 into Ag3PO4/TiO2-10 (1.7 wt% Ag3PO4) greatly improved the toluene mineralization capacity up to 95 %, which was much higher than that of the TiO2 alone (41.3 %). In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) directly verified that the benzene ring was opened rapidly by the Ag3PO4/TiO2-10, while intermediate (like benzaldehyde and benzoic acid) accumulation occurred using pristine TiO2 as photocatalyst. It was demonstrated that Z-scheme heterojunction was formed between Ag3PO4 and TiO2, in which the photo-induced electrons were transferred from conduction band (CB) of the Ag3PO4 to valence band (VB) of the TiO2 under photoexcitation, boosting the generation of reactive oxygen species and inhibiting the photocorrosion of Ag3PO4. Interestingly, quantitative structure-activity relationship suggested that oxygen vacancies as crucial active sites both activated molecular oxygen and captured the photo-induced electrons to form •O2− that dominated in toluene mineralization. This work proved that the construction of Z-scheme heterojunction between MIL-125(Ti)-derived TiO2 and Ag3PO4 solved the inactivation of TiO2 and photocorrosion of Ag3PO4 in photocatalysis, highlighting the role of oxygen vacancy in determining the active species and mineralization degree for photocatalytic toluene elimination.

Synergistic oxidation of toluene through bimetal/cordierite monolithic catalysts with ozone

Toluene treatment has received extensive attention, and ozone synergistic catalytic oxidation was thought to be a potential method to degrade VOCs (violate organic compounds) due to its low reaction temperature and high catalytic efficiency. A series of bimetal/Cord monolithic catalysts were prepared by impregnation with cordierite, including MnxCu5−x/Cord, MnxCo5−x/Cord and CuxCo5−x/Cord (x = 1, 2, 3, 4). Analysis of textural properties, structures and morphology characteristics on the prepared catalysts were conducted to evaluate their performance on toluene conversion. Effects of active component ratio, ozone addition and space velocity on the catalytic oxidation of toluene were investigated. Results showed that MnxCo5−x/Cord was the best among the three bimetal catalysts, and toluene conversion and mineralization rates reached 100 and 96% under the condition of Mn2Co3/Cord with 3.0 g/m3 O3 at the space velocity of 12,000 h−1. Ozone addition in the catalytic oxidation of toluene by MnxCo5−x/Cord could efficiently avoid the 40% reduction of the specific surface area of catalysts, because it could lower the optimal temperature from 300 to 100 °C. (Co/Mn)(Co/Mn)2O4 diffraction peaks in XRD spectra indicated all the four MnxCo1−x/Cord catalysts had a spinel structure, and diffraction peak intensity of spinel reached the largest at the ratio of Mn:Co = 2:3. Toluene conversion rate increased with rising ozone concentration because intermediate products generated by toluene degradation might react with excess ozone to generate free radicals like ·OH, which would improve the toluene mineralization rate of Mn2Co3/Cord catalyst. This study would provide a theoretical support for its industrial application.

Nickel foam based monolithic catalyst supporting transition metal oxides for toluene combustion: Experimental and theoretical study of interfacial synergistic oxidation and water resistance

Composite oxides obtained by calcining layered double hydroxides (LDHs) were used to construct a functional hydrolysis interface. Using nickel foam (NF) as a carrier, LDH was produced on the surface of this monolithic catalyst. The original morphology was retained after calcination. NF provided better thermal conductivity for catalytic combustion than conventional cordierite carriers. The clear phase interface between the different mixed metal oxides (CuxCo3-xFe-MMO/NF) promoted oxidation and hydrolysis during toluene combustion. Physicochemical investigations were performed using XRD, SEM, TEM, H2-TPR, ESR, and XPS. GC–MS, in situ DRIFT, H2O-TPD, and DFT were also used to explore the deep hydrolysis mechanism. The dissociation of water to form the surface *OH was the main hydrolysis process owing to the existence of the Cu-Co functional interface, with the largest energy emission (0.56 eV from DFT calculations). This hydrolysis process also altered the toluene degradation pathway, as confirmed by the in situ DRIFTS and GC/MS results, which guaranteed significant stability of the Cu1Co2Fe-MMO/NF catalyst in a highly humid environment and the removal efficiency and mineralization of toluene were both >90 % below 270 °C. This monolithic catalyst exhibits excellent water resistance and the toluene conversion rate remained stable at 90 % without any attenuationhas >40 h, which provides potential utility in the combustion of volatile organic compounds in high-humidity industrial streams.

Transient photocatalytic oxidation of toluene vapor via nanostructured layers prepared by sol-gel on anatase particles

Gas-phase photocatalytic degradation of toluene mixed with wet oxygen was performed in a continuous reactor using anatase nanoparticles, home-prepared by the sol-gel method combined with peptization treatments. Titanium (IV) isopropoxide was used to synthesize amorphous titania precursor, partially transformed into crystalline nanoparticles by hydrothermal or thermal treatments. The main oxidation product was carbon dioxide, but traces of benzene and benzoic acid were also detected. In order to characterize the catalysts, the evolution of titanium (IV) alkoxide to form anatase nanoparticles was studied using 1H-MAS NMR, EPR, TPD, and FTIR techniques. The results indicate that the four coordinated Ti4+ cations of the alkoxide induce the formation of amorphous aggregates of polymeric layers. The organics removal by peptization originates thin nanostructured titania layers that cover anatase particles, forming TiO2 homojunction. Photoactivity runs showed that both toluene retention and mineralization occurred at the start of irradiation, both processes exhibiting a long transient. After different times, retention stopped while mineralization reached steady-state conditions. Hydrated proton structures are considered to be the origin of both processes. Under irradiation, water photodesorption from these structures favors both the interaction of nanostructured layers with anatase particles, determining hole transfer to external surfaces and the generation of hydrated hydronium cations which, depending on the water loss, are centers able to carry out toluene mineralization or retention. After the mineralization step, photocatalytic centers must be reconstituted by recovering water, a process whose rate becomes the rate-determining one.

The Effects of Toluene Mineralization under Denitrification Conditions on Carbonate Dissolution and Precipitation in Water: Mechanism and Model

The mineralization of benzene, toluene, ethylbenzene, and xylene (BTEX) into inorganic substances by microorganisms may affect the water–rock interaction. However, few studies have quantitatively analyzed the processes. To quantitatively reveal this mechanism, in this study, nitrate and toluene were taken as the typical electron acceptor and BTEX, respectively. Based on hydro-geochemical theory, the mechanism and mathematical model were established. In addition, the model was verified with a toluene mineralization experiment. The mechanism model demonstrated that H+ was the main factor in the dissolution or precipitation of CaCO3. The mathematical model derived the equations quantitatively between the amount of toluene mineralization, CaCO3, and some biogeochemical indicators, including temperature, microbial consumption, and other major ions in groundwater. According to the model, the amount of dissolved CaCO3 increased with the increasing proportion of completely reduced nitrate. For a complete reaction, the greater the microorganisms’ consumption of toluene was, the smaller the precipitation of CaCO3. CaCO3 dissolution was a nonmonotonic function that varied with temperature and the milligram equivalent of other ions. Furthermore, the validation experiments agreed well with the mathematical model, indicating its practicality. The established model provides a tool for assessing the biodegradation of toluene by monitoring the concentration of groundwater ions.

Efficient catalytic degradation of VOCs using Mn-based hydrotalcite-like compounds coupled with non-thermal plasma

Aiming to discover a novel catalyst that exhibits a high synergistic effect with plasma technology for the degradation of volatile organic compounds (VOCs), we employed manganese-based layered double hydroxides (LDHs), which are referred to as MMn-LDHs (M=Ni, Co, Fe). Comprehensive physicochemical characterization via catalyst characterization techniques such as XRD, SEM, XPS, BET, confirmed the successful synthesis of the catalysts. These analyses revealed excellent crystallinity, distinctive lamellar structure, and remarkable thermal stability for three synthesized catalysts. The experimental results demonstrate that post non-thermal plasma (post-NTP) catalytic system has significantly improved the degradation efficiency, CO2 selectivity, and carbon balance for toluene, while notably suppressing the formation of by-products (e.g., NOx and O3) compared to the NTP alone system. Among the three MMn-LDHs, NiMn-LDHs exhibited the best performance in the post-NTP-catalytic system, achieving a toluene degradation rate of 95.87%, a CO2 selectivity of 57.41%, a carbon balance of 79.86%, and an energy efficiency of 3.19 g·kWh−1 at a specific energy density (SED) of 930.45 J/L. The catalytic degradation mechanism of toluene was proposed based on a combination of catalyst characterization techniques, plasma emission spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The findings revealed that plasma discharge generated a substantial amount of free radicals and active species, thereby promoting the decomposition of toluene. Subsequently, the residual toluene and intermediate products were adsorbed onto the catalysts, where they underwent further reacted with the abundant hydroxyl radicals and activate metal species on the catalyst surface, ultimately decomposing into CO2 and H2O. Additionally, the interaction of ozone with LDHs facilitated the generation of reactive oxygen species, consequently accelerating the decomposition of organic intermediates, formation of CO2, and the enhancement of toluene mineralization. The finding in this work offer valuable theoretical support for the plasma-catalytic degradation of VOCs.

Flexible catabolism of monoaromatic hydrocarbons by anaerobic microbiota adapting to oxygen exposure

Microbe-mediated anaerobic degradation is a practical method for remediation of the hazardous monoaromatic hydrocarbons (BTEX, including benzene, toluene, ethylbenzene and xylenes) under electron-deficient contaminated sites. However, how do the anaerobic functional microbes adapt to oxygen exposure and flexibly catabolize BTEX remain poorly understood. We investigated the switches of substrate spectrum and bacterial community upon oxygen perturbation in a nitrate-amended anaerobic toluene-degrading microbiota which was dominated by Aromatoleum species. DNA-stable isotope probing demonstrated that Aromatoleum species was involved in anaerobic mineralization of toluene. Metagenome-assembled genome of Aromatoleum species harbored both the nirBD-type genes for nitrate reduction to ammonium coupled with toluene oxidation and the additional meta-cleavage pathway for aerobic benzene catabolism. Once the anaerobic microbiota was fully exposed to oxygen and benzene, 1.05 ± 0.06% of Diaphorobacter species rapidly replaced Aromatoleum species and flourished to 96.72 ± 0.01%. Diaphorobacter sp. ZM was isolated, which was not only able to utilize benzene as the sole carbon source for aerobic growth and but also innovatively reduce nitrate to ammonium with citrate/lactate/glucose as the carbon source under anaerobic conditions. This study expands our understanding of the adaptive mechanism of microbiota for environmental redox disturbance and provides theoretical guidance for the bioremediation of BTEX-contaminated sites.

Boosting toluene mineralization and ozone decomposition in plasma catalytic system by regulating the oxygen vacancy over Ag-based catalyst

Incomplete mineralization and high outlet ozone concentration are two urgent issues that need to be overcome in plasma catalytic systems for the purification of volatile organic compounds (VOCs). Herein, we attempted to address these issues by coupling Ag/ZSM-5 catalyst reduced by hydrogen at different temperatures with a dielectric barrier discharge (DBD) reactor during toluene degradation. The catalyst characterization (including XRD, UV–vis, XPS, XAFS, Raman, EPR) combined with density functional theory (DFT) calculations indicated that hydrogen reduction lowered the energy between metal ions and oxygen, generating more oxygen vacancies and facilitating the transition from Ag ions to Ag0. The abundant vacancies influenced the electron properties in the adjacent atoms, making them catalytically active and thereby promoting the adsorption and activation of CO and O3. Thus, the mineralization rate and O3 decomposition performance were significantly enhanced for the hydrogen-reduced Ag/ZSM-5 catalysts. Moreover, the L-H, E-R and MVK mechanisms were first experimentally verified in plasma catalytic system by changing the background atmosphere during toluene adsorption and discharge degradation stages. This study provides insights into the rational design of highly effective catalysts in a plasma catalytic system for the removal of VOCs.

Amorphous/crystalline Cu1.5Mn1.5O4 with rich oxygen vacancies for efficiently photothermocatalytic mineralization of toluene

Searching a photothermal catalyst for significantly boosting photothermocatalytic mineralization of volatile organic compounds (VOCs) still remains a challenge. Herein, an amorphous/crystalline Cu1.5Mn1.5O4 catalyst with rich oxygen vacancies was firstly fabricated for photothermal mineralization of toluene. Compared to crystalline Cu1.5Mn1.5O4 samples, amorphous/crystalline Cu1.5Mn1.5O4 catalyst exhibited a more superior photothermal catalytic activity (92.3% toluene conversion and 82.9% CO2 yield) and stability. The collective experimental studies confirmed that oxygen vacancies could contribute to photothermal conversion capacity and low temperature reducibility of amorphous/crystalline Cu1.5Mn1.5O4, enhanced the activation of reactive oxygen species and the deep oxidation of toluene under full-spectrum light. In the meantime, visible light played an auxiliary role in toluene oxidation. Moreover, the possible photothermal reaction mechanism of toluene was investigated by in situ infrared spectroscopy technique. This study can provide new ideas for application of amorphous/crystalline bimetallic oxides in photothermal mineralization of VOCs.

Enhanced photocatalytic toluene oxidation on CN species modified TiO2: Nitrogen doping state and anti-inactivation mechanism

The photocatalytic oxidation of toluene is limited by low mineralization and inactivation. Cheap carbon and nitrogen (CN) species on TiO2 provides an efficient strategy. CN species from the urea calcination in situ formed on TiO2 were denoted as UTx (x = 0.5, 1, 2), and UT1 photocatalyst had the best performance of ca. 90% conversion and 85% mineralization of toluene in light (λ ≥ 400 nm, RH= 20%), with keeping for at least 720 min. The excellent activity of UT1 photocatalyst was resulted from the observed interstitial nitrogen and CN species with triple bonds. Because easily forming interstitial nitrogen resulted in isolated states and more negative VBM to generate hydroxyl radicals, and CN species with triple bonds was beneficial for transferring electrons and opening benzene rings. Therefore, quinone intermediates on UT1 were oxidized to 3-hydroxyglutaric dialdehyde and deeply mineralized, while more accumulated benzaldehyde on TiO2 led to poorer stability.

Unique S-scheme TiO2/BaTiO3 heterojunctions promote stable photocatalytic mineralization of toluene in air

Exploring stable and efficient photocatalysts to promote the photo-oxidation of volatile organic compounds (VOCs) to CO2 and H2O is crucial for air pollution control. In this research, the S-type TiO2/BaTiO3 heterojunctions synthesized by simple physical milling were developed. Compared to the pristine TiO2, it possesses the capability to suppress the production of refractory intermediates and efficiently mineralize the toluene under a wide range of humidity. Density functional theory calculations combined with experimental studies demonstrate that the directional electron transfer from BaTiO3 to TiO2 via Ti-O link bridge (Ti belongs to BaTiO3 and O belongs to TiO2) in TiO2/BaTiO3 heterojunctions can form an internal electric field (IEF). The carriers migration of TiO2/BaTiO3 under illumination is induced in an S-type trajectory by IEF, which effectively improves the carriers separation efficiency, and retains the holes and electrons with high redox potential. And the photogenerated holes and electrons react with H2O and O2 adsorbed at different locations, respectively, generating numerous reactive oxygen radicals and promoting the photocatalytic oxidation of toluene. This work could provide new insights into the development of efficient and stable photocatalysts for air purification.

Key role of •O2− in promoting deep degradation of VOCs in VUV-based process

VUV photolysis presents a simple process for VOCs degradation, while the poor mineralization rate and extensive by-products greatly limit its application. In this study, the contribution and synergy between •OH and •O2− to toluene degradation in the VUV-based process were comprehensively investigated by controlling water and oxygen in the gas flow. It was found that •OH promoted the initial degradation of toluene and macromolecular intermediates, while •O2− dominated toluene mineralization by boosting the formation of small molecules and CO2. Compared with the •OH-dominated VUV photolysis, the presence of catalyst greatly changed the degradation pathway, promoted toluene mineralization into CO2 and reduced health toxicity via promoting •O2− formation. This study originally focuses on the key role of •O2− in VOCs deep oxidation and provides an effective strategy to boost its clean mineralization via the VUV-based process.

Unraveling reactive oxygen species-dependent toluene mineralization routes via construction of TixSn1−xO2 infinite solid solution photocatalysts

Intermediates seriously affect the reaction process and rate in terms of kinetics. However, there are few studies on the effect of reactive oxygen species on intermediates of toluene mineralization. Herein, SnO2 and TixSn1−xO2 infinite solid solution photocatalysts are prepared and the mineralization ability of Ti0.1Sn0.9O2 is 2.7 times that of SnO2. Introduction of Ti shifts the conduction band position upward, providing thermodynamic possibility for superoxide radicals formation. The sole hydroxyl radicals over SnO2 lead to the generation of benzyl alcohol; while synergetic hydroxyl radicals and superoxide radicals result in benzoic acid existed in solid solution catalysts. Theoretical calculation confirms that benzoic acid has lower ring opening barrier, thereby improving toluene mineralization ability over TixSn1−xO2. The synergetic roles of Ti and Sn in adsorption and activation of water and toluene moleculars are also proposed. This work provides new insights into reactive oxygen radicals regulation to alter intermediates and ease toluene removal.

Removal of a complex VOC mixture by potted plants-effects on soil microorganisms.

Microorganisms in the soil of potted plants are important for removal of volatile organic compounds (VOCs) from indoor air, but little is known about the subject. The aim of this study was therefore to obtain a better understanding of the effect of VOCs on the microbial community in potted plants. Hedera helix was exposed to gasoline vapors under dynamic chamber conditions for 21days and three main parameters were investigated. These were (1) removal of the target compounds heptane, 3-methylhexane, benzene, toluene, ethylbenzene, m,p-xylene, and naphthalene from the gasoline mixture; (2) toluene mineralization; and (3) bacterial abundance and bacterial community structure. H. helix was able to reduce the concentration of the target compounds in the continuously emitted gasoline by 25-32%, except for naphthalene, which was too low in concentration. The soil microcosm of gasoline exposed plants had for an initial 66h increased toluene mineralization rate compared to the soil microcosm in the soil of plants exposed to clean air. Bacterial abundance was decreased in response to gasoline exposure while bacterial community structure was changed. The change in bacterial community structure was, however, different between the two experiments indicating that several taxonomic units can degrade gasoline components. Especially the genera Rhodanobacter and Pseudonorcardia significantly increased in abundance in response to gasoline vapors. Bauldia, Devosia, and Bradyrhizobium, on the other hand, decreased.

Synergistic double doping of Co and Cu constructs multiple active sites to achieve catalyzed degradation of toluene at high humidity

Developing high water resistance, efficient, and stable, functional catalysts under practical working conditions is significant reducing and controlling VOCs (volatile organic compounds). It is a considerable challenge to elucidate the catalytic process and mechanism of VOCs degradation under the action of environmental water. In this study, CoCu-CeO2 trimetallic oxide catalysts are designed to investigate the catalytic performance in the water-toluene complex system by modulating the morphological and structural characteristics of the bimetallic at the multiphase interface. The result indicates that introducing Cu species enhances the electron transfer process from Co3+ to Co2+resulting in improved redox performance. Co species significantly promote the migration and conversion of the Cu species at the nanoscale to achieve lattice atom substitution. The bimetallic substitution enhances the ability of CeO2 to form oxygen defects. In the presence of ambient water, Co-Cu interactions inhibit the oxidation of toluene to benzaldehyde and benzoic acid by-products with enhanced mineralization of toluene. Design defects and multi-metal sites play a crucial role in the O2-H2O-toluene reaction system. The construction of this catalyst system provides scientific guidance in efficiently removing volatile organic pollutants in complex multi-media environments.