Toluene Degradation Efficiency Research Articles

Fabrication of core–shell Fe3O4@SiO2/graphite catalyst to improve the charge separation for enhanced photocatalytic toluene oxidation

Magnetite (Fe3O4) has been regarded as a potential photocatalyst for VOCs degradation. Nevertheless, the magnetism of Fe3O4 always leads to the aggregation of particles, which is adverse for gaseous VOCs degradation. Meanwhile, the fast charge recombination of Fe3O4 seriously limits the photocatalytic activity. Herein, a layer of SiO2 was coated on the surface of Fe3O4, and Fe3O4@SiO2 particles were combined with graphite to prepare the core–shell catalyst for photocatalytic toluene oxidation. Fe3O4@SiO2/G catalyst showed the toluene degradation efficiency of 85.09%, which was 3.2 and 1.3 times than those of Fe3O4 and Fe3O4/G. The coating of SiO2 prevented the aggregation of Fe3O4 and greatly enhanced the specific surface area. Experimental and theoretical calculation proved that the existence of SiO2 promoted the spatial charge separation and inhibited the charge recombination, resulting in the generation of abundant reactive oxygen species. These findings offered an insight into the catalyst design for photocatalytic VOCs oxidation.

Enhanced photocatalytic degradation of toluene on surface C- and CN-modified TiO2 microspheres

Surface modified TiO2 materials are widely used in photocatalytic environmental purification processes. The employment of solution might exert a discernible influence on the catalyst. In this study, we incorporated tetrahydrofuran (THF) and pyrrolidine (PY) during the hydrolysis of titanium butoxide (TBOT) to modify the surface of TiO2, successfully synthesizing surface C-modified TiO2 (THF-TiO2) and surface CN-modified TiO2 (PY-TiO2) catalysts. The assistance of THF and PY not only reduced agglomeration, but also increased the specific surface area of both catalysts, leading to the exposure of more active sites in TiO2 during the photocatalytic degradation of toluene. When compared to the unsatisfactory degradation of toluene (80%) and CO2 mineralization efficiencies (40–45 %) observed using unmodified TiO2, the synthesized THF-50-TiO2 and PY-1-TiO2 microspheres demonstrated enhanced toluene degradation efficiency to 100 % and 99.8 %, respectively, and improved mineralization efficiencies to 76 % and 80 % after 120 min of ultraviolet irradiation. The experimental data and characterization results indicate that the surface-modified carbon species in THF-50-TiO2 facilitate the acceleration of electron-hole pair separation and suppress recombination. In contrast, partial nitrogen species introduced into the surface lattice of PY-1-TiO2 narrow its band gap and induce a visible light response. Overall, this study provides two methods to modify the surface of TiO2, which can be applied to prepare outstanding photocatalysts for possible application in the degradation of volatile organic compounds (VOCs) present in the air. Furthermore, it has been confirmed that solution have a significant impact on the catalyst.

Efficient activation of the Co/SBA-15 catalyst by high-frequency AC-DBD plasma thermal effects for toluene removal

Dielectric barrier discharge (DBD) plasma excited by a high-frequency alternating-current (AC) power supply is widely employed for the degradation of volatile organic compounds (VOCs). However, the thermal effect generated during the discharge process leads to energy waste and low energy utilization efficiency. In this work, an innovative DBD thermally-conducted catalysis (DBD-TCC) system, integrating high-frequency AC-DBD plasma and its generated thermal effects to activate the Co/SBA-15 catalyst, was employed for toluene removal. Specifically, Co/SBA-15 catalysts are closely positioned to the ground electrode of the plasma zone and can be heated and activated by the thermal effect when the voltage exceeds 10 kV. At 12.4 kV, the temperature in the catalyst zone reached 261 °C in the DBD-TCC system, resulting in an increase in toluene degradation efficiency of 17%, CO2 selectivity of 21.2%, and energy efficiency of 27%, respectively, compared to the DBD system alone. In contrast, the DBD thermally-unconducted catalysis (DBD-TUC) system fails to enhance toluene degradation due to insufficient heat absorption and catalytic activation, highlighting the crucial role of AC-DBD generated heat in the activation of the catalyst. Furthermore, the degradation pathway and mechanism of toluene in the DBD-TCC system were hypothesized. This work is expected to provide an energy-efficient approach for high-frequency AC-DBD plasma removal of VOCs.

Regulation of TiO2/ZSM-5 catalyst for enhanced photocatalytic toluene oxidation: Intensified light absorption, charge separation and toluene adsorption

TiO2 has been widely studied in photocatalytic VOCs oxidation but its photocatalytic activity is still unsatisfied due to poor visible light absorption, serious charge recombination and weak toluene adsorption. Herein, a composite catalyst (TiO2/ZSM-5) was constructed between TiO2 and hierarchical ZSM-5 by ball milling for photocatalytic toluene oxidation. The optimal composite catalyst exhibited the toluene degradation efficiency of 91.08 %, which was 2.7 and 1.3 times than those of TiO2 and TiO2/commercial ZSM-5. It showed that the strong interaction between TiO2 and hierarchical ZSM-5 was established via the formation of Ti-O-Si bond, which decreased the band gap from 3.08 to 0.55 eV when compared with TiO2 and was helpful for the enhanced charge separation. In addition, the mesoporous volume of hierarchical ZSM-5 was regulated by a dual-template method, making the mesoporous volume increased from 0.23 to 0.38 cm−3 g−1 when compared with TiO2/commercial ZSM-5, which improved the toluene adsorption capacity from 0.12 to 0.16 cm−3 g−1. DFT calculation further indicated that the energy barrier of toluene oxidation and ring-opening reaction was reduced in the presence of hierarchical ZSM-5. This work provided a new catalyst design method to improve the photocatalytic activity by the synergy action of TiO2 and ZSM-5.

Efficient toluene degradation using Bacillus subtilis biofilm-supported Mn–Ce/zeolite catalysts

This study investigated a new approach for synthesizing Bacillus subtilis biofilm-supported Mn–Ce/zeolite catalysts for the degradation of gaseous toluene. Four different metal oxide nano-catalysts (ZMn, ZMnCe-10%, ZMnCe-20%, and ZMnCe-30%) were synthesized with varying ratios of manganese (Mn) and cerium (Ce) on zeolite nanoparticles. TEM, SEM, XRD, BET, XPS, and EDX mapping were used to examine these four samples, as well as simple zeolite. Based on these analyses, the catalytic activity of the prepared samples ZMn, ZMnCe-10%, ZMnCe-20%, and ZMnCe-30% for the complete oxidation of toluene and toluene intermediate products were tested with Non-thermal plasma (NTP) technology in a dielectric barrier discharge (DBD) reactor. Among all, ZMnCe-20% showed the highest toluene degradation efficiency (89%) at low concentrations (200 ​ppm) and humidity (>50%). Later, highly efficient and hydrophobic nano-biocatalysts were prepared by combining B. subtilis biofilm wild-type (WT) and engineered B. subtilis biofilm EPS with ZMnCe-20% catalyst. EPS is the main component found in biofilm matrix and plays a key role in influencing properties such as biofilm stability, electron transfer, surface roughness and hydrophobicity. Compared to WT B. subtilis biofilm, EPS overexpressed B. subtilis biofilm showed stronger growth and development on ZMnCe-20% nanocatalyst. Moreover, the NTP system packed with ZMnCe-20%/biofilm (EPS+) nano-biocatalyst exhibited the highest toluene degradation activity (99%) with (83%) CO2 selectivity, (up to 50%) reduction in NOx concentration and complete ozone decomposition at (250 ​ppm) toluene concentrations and increased humidity (>90%). High-energy electrons generated in the NTP system break the C–H and C–C bond between the rings of the toluene molecule, forming several byproducts which are later reacted with active radical species such as O, OH, and O3 and further converted into final degradation products (CO2 and H2O). The results demonstrated successful biofilm development and growth on the ZMnCe-20% catalyst with advanced features such as superhydrophobicity, H2O resistance, improved surface roughness, and electron generation. In short, the study's approach combines bioengineering and material science to develop sustainable nano-biocatalysts for removing VOCs in industrial and environmental settings.

Catalytic oxidation of toluene by manganese oxides: Effect of K+ doping on oxygen vacancy

Alkali metal potassium was beneficial to the electronic regulation and structural stability of transition metal oxides. Herein, K ions were introduced into manganese oxides by different methods to improve the degradation efficiency of toluene. The results of activity experiments indicated that KMnO4-HT (HT: Hydrothermal method) exhibited outstanding low-temperature catalytic activity, and 90% conversion of toluene can be achieved at 243°C, which was 41°C and 43°C lower than that of KNO3-HT and Mn-HT, respectively. The largest specific surface area was observed on KMnO4-HT, facilitating the adsorption of toluene. The formation of cryptomelane structure over KMnO4-HT could contribute to higher content of Mn3+ and lattice oxygen (Olatt), excellent low-temperature reducibility, and high oxygen mobility, which could increase the catalytic performance. Furthermore, two distinct degradation pathways were inferred. Pathway Ⅰ (KMnO4-HT): toluene → benzyl → benzoic acid → carbonate → CO2 and H2O; Pathway ⅠⅠ (Mn-HT): toluene → benzyl alcohol → benzoic acid → phenol → maleic anhydride → CO2 and H2O. Fewer intermediates were detected on KMnO4-HT, indicating its stronger oxidation capacity of toluene, which was originated from the doping of K+ and the interaction between KOMn. More intermediates were observed on Mn-HT, which can be attributed to the weaker oxidation ability of pure Mn. The results indicated that the doping of K+ can improve the catalytic oxidation capacity of toluene, resulting in promoted degradation of intermediates during the oxidation of toluene.

Excellent degradation of toluene by non-thermal plasma coupled with M-BTC MOF（M=Mn, Cu, Ce）

In view of the unsatisfactory synergy between plasma technology and catalyst, a series of M-BTC MOFs (M=Mn, Cu, Ce) were introduced to couple with non-thermal plasma using for toluene degradation. M-BTC MOFs containing multi-carboxylic groups were successfully synthesized and presented the excellent crystallinity, morphology and thermal stability. DBD-catalysis systems presented the more excellent toluene degradation performance than single DBD alone system. Due to the porous structure and the multivalent form of manganese, the highest toluene degradation efficiency of 96.27%, the energy efficiency of 22.32 g/kW·h, the CO2 selectivity of 53.5% and the mineralization degree of 70.17% were acquired for DBD coupled with Mn-BTC under SED of 766.35 J/L. Besides, DBD/Mn-BTC had the lowest ozone and NOx production. Moreover, the toluene degradation mechanism was analyzed by plasma emission spectra analysis, XPS spectra and GC-MS diagram analysis. It indicated plasma discharge can produce abundant free radicals and reactive species to decompose toluene firstly, and the residual toluene and intermediates in the gas can be then adsorbed on Mn-BTC and further oxidized by metal active species. Furthermore, more reactive oxygen species will be generated by activating ozone through Mn-BTC, which was beneficial for toluene degradation.

New Pt/TiO2/Ti2Fe2O7 nanocomposite using sugarcane bagasse agro-waste for photodegradation of toluene gas pollutant under sunlight

An eco-friendly and economical hydrothermal carbonization route is applied to prepare Pt-C hard template from sugarcane bagasse agro-waste, and then synthesize new Pt/TiO2/Ti2Fe2O7 nanocomposites. Pt-C was prepared by utilizing the sugarcane bagasse. Spheres of Pt-C were obtained by hydrothermal technique at 180 °C for 6 h. TiO2 nanoparticles with mixed anatase/rutile phases were synthesized by calcination at 700 °C and confirmed by XRD patterns. The elemental composition and surface morphology of Pt/TiO2/Ti2Fe2O7 nanocomposite were evaluated by using FEEM equipped with EDX. The particle size and shape were determined by HRTEM. FTIR analysis was also performed and the diffuse reflection spectrum (DRS) was carried out. N2 adsorption was utilized to establish the textural characters. The results of photocatalytic test exhibited that the percentage of degradation efficiency of toluene using Pt/C and Pt/TiO2 was 23% and 25%, respectively, as compared to ˃ 95% for Pt/TiO2/Ti2Fe2O7 under visible light, almost 4 times enhancement.

Fluorescent switch-on probe for carbon-centered radicals and real-time assessment of toluene degradation efficacy

Carbon-centered radicals derived from parent compounds are primary radical intermediates involved in the degradation of organic pollutants. This study presents a bifunctional probe with a fluorescent "switch-on" and radical capture functions for in situ trapping and specific detection of carbon-centered radicals. Carbon-centered radicals can be quickly trapped and they can notably turn on the 11-fold fluorescence, which enables the monitoring of unstable and short-lived carbon-centered radicals generated during toluene degradation. The proposed system was applied to assess the toluene degradation efficacy in real time. The fluorescence response was similar to that of the toluene degradation efficiency measured using high-performance liquid chromatography (HPLC). In addition, the benzyl radical was identified as the primary carbon-centered radical intermediate by high-resolution liquid chromatography-mass spectrometry (LC-MS), which provides direct evidence for the toluene degradation mechanism by thermally activated persulfate.

Investigation of hybrid plasma-catalytic degradation of toluene over FeOOH/γ-Al2O3 catalysts

In the present study, FeOOH/γ-Al2O3 catalyst was first introduced into dielectric barrier discharge (DBD) plasma-catalysis system for toluene degradation, and its catalytic performance and mechanism were studied. It was found that the toluene degradation efficiency, energy yield (EY), and COx selectivity were significantly improved in the plasma-FeOOH/γ-Al2O3 system by comparison to the plasma-only process. The ozone concentration detected in this study decreased significantly in plasma-FeOOH/γ-Al2O3 system, which could be concluded that the ozone catalytic process played an important role in the plasma-FeOOH/γ-Al2O3 system for toluene degradation. The toluene and intermediates adsorbed on the surface FeOOH catalysts could react with O* from O3 decomposition and Oads derived from oxygen vacancies, which was conducive to an improved degradation and mineralization performance. Besides, the transformation of O3 to·OH on FeOOH surface was considered as one of the main mechanisms for enhancing toluene degradation when the relative humidity of the background gas was increased from 30% to 50%. The key process parameters, including specific energy input (SEI), catalyst loading, and oxygen content of the background gas, were optimized by response surface methodology (RSM) integrated Box-Behnken design (BBD). The results showed that oxygen content of the background gas was the most significant factor affecting the degradation efficiency of toluene, while energy yield was mainly determined by SEI. The possible toluene degradation pathways in plasma-FeOOH/γ-Al2O3 system were proposed according to the identification of intermediates using GC-MS.

Synergistic mechanism of Ce-Mn in ZSM-5 carrier catalysts for catalytic oxidation of toluene

Volatile organic compounds (VOCs) are the main components of air pollutants, posing threat to the public health and the environment. In this study, a series of CeMnOx-ZF catalysts with different metal loadings were prepared from coal fly ash (CFA), and the optimal activation route of CFA to the synthesize carrier and the toluene catalytic oxidation effects by carrier catalysts were investigated. The synergistic mechanism of Ce and Mn metals in CeMnOx-ZF catalysts were investigated. The results showed that, CFA exhibited the highest activity under the pretreatment conditions of the 15% HCl mass fraction, 1.5:1 alkali/ash ratio, and 500℃ calcination temperature. Under optimized reaction conditions (600 ppm initial toluene concentration, 30000 h−1 GHSV, and 120-390℃ reaction temperature), 20 wt.% CeMnOx-ZF catalyst exhibited an extremely high toluene removal efficiency with the maximum of 99.6%. After water vapor introduction, the toluene degradation efficiency remained at a stable level, but CO2 yield increased. After 100-hour cycle test, the 20 wt% CeMnOx-ZF catalyst still exhibited a high toluene degradation efficiency (96.5%), indicating its high stability. This study provides a simple and convenient method for CFA activation and proposes a feasible strategy for designing and synthesizing high-efficiency catalysts for the degradation of VOCs.

Emission Control of Toluene in Iron Ore Sintering Using Catalytic Oxidation Technology: A Critical Review

Iron ore sintering flue gas containing large amounts of volatile organic compounds (VOCs) can form secondary photochemical smog and organic aerosols, thus posing a serious threat to human health and the ecological environment. Catalytic combustion technology has been considered as one of the most prospective strategies for VOC elimination. This paper focuses on a review of studies on catalytic removal of typical VOCs (toluene) on transition metal oxide catalysts in recent years, with advances in single metal oxides, multi-oxide composites, and supported metal oxide catalysts. Firstly, the catalytic activities of a series of catalysts for toluene degradation are evaluated and compared, leading to an analysis of the key catalytic indicators that significantly affect the efficiency of toluene degradation. Secondly, the reaction pathway and mechanism of toluene degradation are systematically introduced. Considering the site space and investment cost, the conversion of VOC pollutants to harmless substances using existing selective catalytic reduction (SCR) systems has been studied with considerable effort. Based on the current development of simultaneous multi-pollutant elimination technology, the interaction mechanism between the NH3-SCR reaction and toluene catalytic oxidation on the surface is discussed in detail. Finally, views on the key scientific issues and the challenges faced, as well as an outlook for the future, are presented. This overview is expected to provide a guide for the design and industrial application of NO/VOC simultaneous removal catalysts.

Toluene degradation in air/H2O DBD plasma: A reaction mechanism investigation based on detailed kinetic modeling and emission spectrum analysis

Non-thermal plasma (NTP) is emerging as an attractive method for decomposing volatile organic compounds (VOCs). In this paper, to study toluene degradation mechanism in air/H2O dielectric barrier discharge (DBD) plasma, optical emission spectrometry (OES) was employed to in-situ monitor active species in plasma, with the permanent degradation products being detected by on-line mass spectrometry under various operations. A detailed kinetic model of NTP with incorporation of non-constant electron filed and thermal effects has also been established. A toluene degradation efficiency > 82% could be achieved at P = 115 W, Cin, toluene = 1000 ppm. The relative spectrum intensity of excited OH, O, H and N2 (A3Σ+u) increased with increase of discharge power and was decreased at higher gas flowrates. Toluene degradation was mainly induced by oxidation of OH and O at afterglow stage, while part of toluene was decomposed by attack of electrons and reactive particles N2 (A3Σ+u) in discharge stage. A toluene degradation pathway has been proposed as: toluene→benzyl→benzaldehyde→benzene→phenoxy→cyclopentadiene→polycarbenes/alkynol→CO2/H2O. Benzoquinone, benzaldehyde, cyclopentadiene and cyclopentadienyl are supposed to be important intermediates for the ring-opening of toluene. Clarification of toluene degradation behaviors at discharge and afterglowing stage could provide new insights for plasma-catalytic process in future.

OPTIMIZING THE STRUCTURAL CHARACTERISTICS OF DRAFT TUBE IN A SPOUTED BED REACTOR FOR BEST PHOTOCATALYTIC DEGRADATION OF TOLUENE AND CO2 SELECTIVITY USING RESPONSE SURFACE METHODOLOGY

In this study, toluene degradation efficiency and carbon dioxide (CO2) selectivity in a spouted bed reactor with a porous draft tube were optimized using the response surface methodology. For this purpose, titanium dioxide (TiO2) was used as a catalyst for photocatalytic degradation of gaseous toluene in a dynamic mode under ultraviolet (UV) irradiation. The influence of draft tube parameters' (including height, diameter, gap, and porosity) on toluene degradation efficiency and CO2 selectivity (as the response variables) was investigated by central composite design. Analysis of variance (ANOVA) was applied to evaluate the significance of the variables' effects and the interaction between them. Results showed that maximum toluene degradation efficiency of 78.1 % and maximum CO2 selectivity of 88.7 % were obtained at 1.99 cm draft tube height, 1.3 cm draft tube diameter, 1.3 cm gap, and 60 % draft tube porosity. The highest F-values indicated that the gap is the most important variable affecting the toluene degradation efficiency and CO2 selectivity, while the draft tube diameter is the second important variable. The results of experiments at optimal levels of parameters with three replications showed a maximum toluene degradation efficiency of 78.8% (SD= 0.62) and maximum CO2 selectivity of 89.1 % (SD= 0.46). The study revealed that the spouted bed reactor with a porous draft tube has a good stability for volatile organic compounds (VOCs) degradation and mineralization.

Effect of the factors on the mixture of toluene and chlorobenzene degradation by non-thermal plasma

Toluene (TOL) and chlorobenzene (CB), as typical representatives of VOCs and CVOCs, respectively, widely exist in various industries. The synergistic degradation experiment of TOL and CB was carried out in NTP reactor, and compared with the treatment of TOL or CB. Meanwhile, the effects of the mixture concentration ratio, gas velocity and the catalyst (0.4 Ru-1.0 Ce /TiO2/cordierite) on the degradation of TOL and CB were also investigated. The experimental results suggested that the 45.6% of degradation efficiency and 14.4% of CO2 selectivity of TOL was higher than that of 39.6% and 11.5% of CB at 14 kV. Compared with the NTP alone, the degradation efficiency of TOL was increased by 20.8% in the mixture systems, while CB was inhibited and decreased by 21.3%. The kinetic analysis also proved this phenomenon. The concentration ratio of TOL and CB had little effect on the degradation efficiency and CO2 selectivity. Higher gas velocity reduced the degradation efficiency and CO2 selectivity of the mixture. Meanwhile, the degradation efficiency and CO2 selectivity were greatly improved through the catalyst. Furthermore, the ozone concentration near 0 mg m−3 at 22 kV, and the results of ozone demonstrated that the formation and degradation of ozone were not only related to the temperature of the reaction system, but also related to the type, concentration and gas velocity of pollutants. Finally, the possible degradation pathways of two aromatic VOCs in the process of plasma degradation were proposed and discussed.

Toluene degradation using plasma-catalytic hybrid system over Mn-TiO2 and Fe-TiO2.

This paper proposed a hybrid system that combined dielectric barrier discharge plasma with catalysis (DPC) for toluene degradation. To improve the performance of DPC, photocatalysts TiO2 were doped by Mn and Fe, respectively. All prepared photocatalysts were characterized using UV-Visual DRS., SEM, XPS, BET, and XRD. The effects of the doping ratio, AC frequency, electric field intensity, gas flow rate, and initial concentration on toluene degradation efficiency, ozone decomposition capacity, and COx selectivity have been investigated. The best doping ratios of Mn and Fe were both 1.0 at%. The increase of electric field intensity in the range of 6.9-10.3kV/cm could favor the synergism for DPC significantly, but the ascending of AC Frequency failed to do that. Fe-DPC showed slightly better performance than Mn-DPC in degradation efficiency and COx selectivity, while Mn-DPC was ahead of Fe-DPC for the ozone decomposition. Mn-DPC and Fe-DPC both could maintain the high toluene degradation efficiency, when gas flow rate and initial concentration increase from 2.5 to10.1cm/s and from 700 to 2300mg/cm3, respectively.

Basic magnesium chloride whisker photocatalytic materials: Synthesis and toluene degradation efficiency

This study brings a novel magnesium oxychloride cement-based photocatalytic material. Basic magnesium chloride whisker (BMCW) was modified by nano-SiO2 to improve the loading capacity of TiO2 photocatalyst. Then, TiO2 was supported in BMCW/SiO2 to form the basic magnesium chloride whisker photocatalytic materials (BMCWPM). The effects of pH values and TiO2 supporting concentrations on physio-chemical properties and photocatalytic performance were investigated in detail. As TiO2 hydrosol pH value is about 7.55, the loaded BMCWPM has the best degradation efficiency on gaseous toluene. BMCWPM synthesized with 5 % TiO2 supporting concentration shows the best photocatalytic efficiency of unit TiO2, also shows an excellent photocatalytic cyclic stability, the photocatalytic degradation efficiency and reaction rate of gaseous toluene are exceeding 55 % and 22.7*10−7 mol/m2 min, respectively. This study provides a kind of photocatalytic material with high efficiency and durability, which is expected to apply in wall decoration materials for air purification.

Catalytic conversion and DFT analysis of post DDBD-catalysis system for degradation of toluene, ethyl acetate and acetone with different metal-oxides catalysts

A series of multiphase metal-oxide catalysts (MnOx/γ-Al2O3, CuOx/γ-Al2O3, FeOx/γ-Al2O3, CeOx/γ-Al2O3 and LaOx/γ-Al2O3) were prepared for plasma-catalyst degradation of multicomponent volatile organic compounds (VOCs, such as toluene, acetone and ethyl acetate). The results reveal that the degradation efficiency (DE) of acetone, toluene and ethyl acetate in the DDBD system can be arranged as follows: Mn2O3/γ-Al2O3> Fe2O3/γ-Al2O3> CuO/γ-Al2O3> CeO2/γ-Al2O3> La2O3/γ-Al2O3> γ-Al2O3, and the highest DE (49.5% for acetone, 93.3% for toluene and 79.8% for ethyl acetate) is obtained in Mn2O3/γ-Al2O3+double dielectric barrier discharge (DDBD) system at specific input energy (SIE) of 700 J/L. Compared with the other catalysts, Mn2O3/γ-Al2O3 also exhibits the most significant inhibitory effect on the production of ozone (O3). On the other hand, CeO2/γ-Al2O3 and La2O3/γ-Al2O3 catalysts display different catalytic selectivity. Both catalysts can slightly raise the DE of VOCs and remarkably facilitate VOCs' mineralization. The carbon balance (CB) is increased by 30.2% and 38.8%, and the CO2 selectivity (SCO2) is raised by 70.5% and 11.9% in the CeO2/γ-Al2O3+DDBD system and La2O3/γ-Al2O3+DDBD system at SIE of 700 J/L, respectively. To further understand the catalytic effect of the catalysts, the adsorption of O3 on different catalysts was simulated by a DFT model. According to the results of the DFT model, it is found that the adsorption energy of other metal oxides seems to be used as a reference for catalytic effect to a certain extent except CeO2. The higher the absolute values of adsorption energy, the higher the improvement of VOCs degradation efficiency by catalyst.

Reactive species production and toluene degradation in an expanded streamer discharge plasma induced by a floating plate electrode

In this work, a novel positive pulsed wire-plate-wire (w-p-w) streamer discharge reactor is developed by introducing a floating plate electrode based on the previous wire-wire (w-w) reactor to attain a larger plasma propagation and improve the toluene degradation performance. The streamer propagation characteristics, distribution of·OH, toluene degradation efficiency, and process efficiency of reactive species production of the w-p-w reactor were studied and found to be highly related to the position of the floating plate electrode. ICCD images show that an intensive negative streamer can be generated from the ground electrode in the w-p-w reactor, which differs from the corona-like negative discharge in the w-w reactor. The position of the floating electrode decides the distance of the positive discharge (d+) and the negative discharge (d-), subsequently affecting the reactive species production and toluene degradation of the w-p-w reactor. When the d+ /d- reaches 1:1 where a relatively symmetrical and even distribution of·OH is achieved over the discharge gap, the toluene degradation efficiency and CO2 selectivity is 17% and 14% respectively higher than that of the w-w reactor at 230 J/L. According to a kinetic model including competition by the reaction intermediates, the highest process efficiency of reactive species production is obtained when d+ /d-= 1:1 in the w-p-w reactor, consistent with its superior toluene degradation performance. FTIR results indicate that the types of toluene degradation byproducts are not affected by the insertion of the floating electrode, however, a more thorough toluene degradation can be achieved in the w-p-w reactor.

Co3O4@Zn-BTC MOF as a novel nano-photocatalyst for degradation of toluene from ambient air

ABSTRACT The present work aimed to synthesise and utilise a novel Co3O4@Zn-BTC Metal-Organic Framework (MOF) photocatalyst to decompose toluene in a dynamic stream under visible light. Nano-catalyst was prepared by a simple and facile solvothermal procedure and was characterised via various techniques included of PXRD, FE-SEM, TEM, BET, UV-VIS with DRS, and FT-IR. To optimise the effects of process parameters, namely relative humidity, toluene input concentration and flow rate on toluene degradation efficiency, the process was modelled using response surface methodology based on central composite design (RSM-CCD). RSM-CCD approach developed a quadratic polynomial model with R2 = 0.9989, adjusted R2 = 0.9980 and p-value <0.001. The optimal values of the input variables based on the obtained model were found to be 20 ppm vapour concentration, 30% RH and 15 ml/min. Under this condition, 40% Co3O4@Zn-BTC MOF showed the highest photocatalytic efficiency (64.1%) in toluene mineralisation compared to other photocatalysts (40% > 60% > 20% > 10% Co3O4@Zn-BTC > Zn-BTC). Among the studied variables, humidity (%) had the greatest efficacy on the decomposition efficiency of toluene. These outcomes could be attributed to the assembly of Co3O4 nanoparticles with Zn-BTC to form a heterogeneous structure of Co3O4@Zn-BTC MOF that expands the light absorption in the visible scope. The findings also demonstrated that the 40% Co3O4@Zn-BTC MOF photocatalyst possesses excellent stability in long-term exposure to toluene removal. Also, any by-products at the output of the photocatalytic system were not detected by GC-MS. The study shows promising ability of the MOF in photocatalytic oxidation of toluene and provides valuable information for further practical applications of the system in air purification.