Degradation Of Gaseous Toluene Research Articles

A High-Performing Nanostructured Ir Doped-TiO2 for Efficient Photocatalytic Degradation of Gaseous Toluene

TiO2-based photocatalysts still have some limitations such as large bandgap and low surface area, leading to low efficiency in the photocatalytic degradation of VOCs and limiting it to use in sunlight. Here we report that the nanostructured Ir-doped TiO2 as an efficient photocatalyst generates an excellent risk-reduction material of gaseous toluene. We have succeeded in developing a nanostructured Ir-doped TiO2 and initially found that excellent efficient photocatalytic VOC decomposition can be achieved in our materials The nanostructured Ir-doped TiO2 was synthesized by a one pot, low temperature hydrothermal process with different ratios of Ir doped into the TiO2. It exhibited a high surface area, uniformly spherical morphology of 10–15 nm. Its activity for the photocatalytic degradation of gaseous toluene exhibited up to 97.5% under UV light. This enhancement could be explained by iridium doping which created a high concentration oxygen vacancy and changed the recombination rate of the photogenerated charge carriers. More generally, our study indicates a strategic way to develop the novel nanostructured material for numerous applications.

Ce-Doped Perovskite-Type Catalyst Derived from Ti-Bearing Blast Furnace Slag for Photocatalytic Degradation of Gaseous Toluene Under Visible Light

Ce-Doped Perovskite-Type Catalyst Derived from Ti-Bearing Blast Furnace Slag for Photocatalytic Degradation of Gaseous Toluene Under Visible Light

Mesoporous SmMnO3/CuMnOx catalyst for photothermal synergistic degradation of gaseous toluene

Mesoporous SmMnO3/CuMnOx catalyst was prepared by a two-step method using flaky CuMnOx with high specific surface and excellent catalytic ability as the carrier, which was further applied to photothermal synergistic degradation of gaseous toluene. Quantitative analysis of O2-TPD and H2-TPR showed that SmMnO3/CuMnOx exhibited abundant of the surface oxygen species and oxygen vacancies content, which enabled it to convert free oxygen to lattice oxygen more quickly during the reaction, and thus improving the reaction process. I-t and photoluminescence experiments demonstrated the improvement of photogenerated electron and hole separation ability of SmMnO3/CuMnOx catalyst. UV–Vis analysis manifested the full spectral range of absorption. XPS analysis verified the unequal positions of valence band of the two materials, which can facilitate the separation of photogenerated electrons from holes and improve the ability of better electron transfer. SmMnO3/CuMnOx catalyst has higher adsorbed oxygen content and light absorption capacity, which is beneficial to the catalytic oxidation. In situ DRIFTs proved that the oxidation reaction on the catalyst followed the Mars-van Krevelen redox cycle. The VOCs test found that SmMnO3/CuMnOx composite catalyst is with lower onset reaction temperature (T90 = 190 °C, T90, corresponding to 90% conversion) and good mineralization (100% at 275 °C).

A vertically configured photocatalytic-microbial fuel cell for electricity generation and gaseous toluene degradation

A vertically configured photocatalytic-microbial fuel cell (photo-MFC) is developed by combining a nanodiamond-decorated ZnO (ZnO/ND) photocathode with a bioanode. The system can effectively couple the light energy with bioenergy to enhance the degradation of volatile organic compounds (VOCs) and boost electricity output. Results show that the composite system exhibits increased performance for toluene removal (60.65%), higher than those of individual parts (ZnO/ND-photocatalysis: 37.16%, MFC: 17.81%). Furthermore, its electrochemical performance is dramatically increased. The peak power density of 120 mW/m2 and the current density of 1.07 A/m2 are generated under light illumination, which are about 1.57-fold and 1.37-fold higher than that under dark (76 mW/m2, 0.78 A/m2), respectively. Microbial community analysis demonstrates Proteobacteria and Firmicute are dominant phyla, implying they play important roles on accelerating the extracellular-electron transfer and toluene degradation. In addition, the underlying mechanism for toluene degradation in the photo-MFC system is preliminary explored. Our results suggest that the photo-MFC has great potential for simultaneous treatment of VOCs with energy recovery.

Exogenous electron transfer mediator enhancing gaseous toluene degradation in a microbial fuel cell: Performance and electron transfer mechanism

Effective electron transfer (ET) between microorganisms and electrodes is essential for the toluene degradation and power generation in a microbial fuel cell (MFC). In this work, the neutral red, with excellent electrochemical reversibility and compatible redox potential as NADH/NAD+, was selected as electron mediator to boost the performance of the MFC. Experimental results revealed that, with the 0.5 μM neutral red, the removal efficiency and coulombic efficiency of the gaseous toluene powered MFC was increased by ~19% and ~400%, respectively. However, further increase in neutral red concentration resulted in a decreased in removal efficiency and coulombic efficiency, which was attributed by the toxicity of neutral red to the microbes. The microbial community analysis indicated that, with the dosage of the neutral red, the dominated bacteria shifted from Geobacter to Ignavibacteriales, resulting in a high coulombic efficiency. With the further increase in the neutral red, the amount of Ignavibacteriales gradually decreased and thus the coulombic efficiency declined at a high neutral red concentration. Based on the cyclic voltammetry analysis, an electron transport pathway involving neutral red, cytochromes, and OMCs in neutral red mediated MFC was proposed. Overall, the dosage of neutral not only enhanced the electron transfer but also induced the growth of the exoelectrogens, and thus significantly improve the MFC performance.

Fast electron transfer and enhanced visible light photocatalytic activity of silver and Ag2O co-doped titanium dioxide with the doping of electron mediator for removing gaseous toluene

Volatile organic compounds (VOCs) can influence air quality and threaten human health; however, the development of an effective method to remediate toxic VOCs is still remain challenge. Herein, a novel silver and Ag2O co-doped TiO2 with fast electron transfer modified by nitrogen doping carbon dots was prepared via a facile chemical precipitation-reduction method. Under 50 min of visible light irradiation, the novel photocatalyst exhibited approximately 50% gaseous toluene degradation efficiency, which was ca. 9.7 times and 2.2 times higher than that of bare TiO2 and silver and Ag2O co-doped TiO2, respectively. Importantly, the photocatalyst also showed a stable structure and good recycling ability after 400 min of photocatalytic degradation with little amount of NCDs. Besides, the up-conversion effect of NCDs could emit high-energetic light and thus generate more e−-h+ pairs, which could facilitate the SPR effect of Ag and thus showed strong visible light response because of the localized surface plasmon resonance (LSPR) excitation. Thus, the excellent photocatalytic performance could attribute to the synergetic effect of up-conversion effect of NCDs and SPR effect of silver which could both facilitate charge carriers separation and improve visible-light response. Finally, a possible mechanism for the excellent photocatalytic activity was proposed, in which the active species including ·O2−, ·OH and h+ were generated and contributed to photocatalytic process. The successful fabrication of DACT provides a potential strategy for the treatment of VOCs in practical applications.

The filtration and degradation mechanism of toluene via microwave thermo-catalysis ceramic membrane

A series of ceramic membranes for toluene filtration and degradation were prepared by impregnation. The filtration and degradation of gaseous toluene was investigated during microwave thermo-catalysis in the continuous flow mode. The results showed that the ceramic membranes with components of Cu, Mn, Ce oxides were active in the filtration and degradation of toluene. The active ingredients uniformly existed in spinel form of Cu, Mn and Ce oxides with different valence, and the load distribution was also correlated with its surface morphology and specific surface area. Under the optimal conditions of toluene concentration of 697 ± 54 mg m−3, gas flow rate of 200 mL min−1 and microwave power of 500 W, the membrane with three loading times of active components showed excellent retaining property, catalytic activity and structural stability. After 10 consecutive cycles (2100 min in total), the maximum removal efficiency of toluene was 85%. Based on total volatile organic compounds (TVOC) analysis, removal efficiency of TVOC was maintained at 94%. Toxicity analysis indicated that most of the possible intermediate products generated in the degradation process had relatively less impact on the environment than that of toluene. Results demonstrated a new way to design catalytic ceramic membranes that can retain and degrade VOCs during filtration and microwave thermo-catalysis process.

A highly dispersed Co–Fe bimetallic catalyst to activate peroxymonosulfate for VOC degradation in a wet scrubber

This work synthesized a highly dispersed Co–Fe bimetallic catalyst with uncalcined SBA-15 as the support, which was very efficient for PMS activation and gaseous toluene degradation in the wet scrubbing waste gas treatment system.

Enhanced photocatalytic degradation of gaseous toluene and liquidus tetracycline by anatase/rutile titanium dioxide with heterophase junction derived from materials of Institut Lavoisier-125(Ti): Degradation pathway and mechanism studies

Anatase/rutile titanium dioxide (TiO2) with heterophase junction and large Brunauer-Emmett-Teller (BET) specific surface area (50.1 m2 g−1) is successfully synthesized by calcinating Materials of Institut Lavoisier-125(Ti) (MIL-125(Ti)) with 30% O2/Ar at the temperature of 600 °C (M−O−600). Several techniques are used to examine the physicochemical, photoelectrochemical and optical properties of samples, and their photocatalytic performances are evaluated by photodegradation of gaseous toluene and liquidus tetracycline (TC) under visible light illumination. It is found that the calcination temperature has significant influence on the crystal structure and physicochemical parameters of TiO2. The weight fractions of rutile and anatase TiO2 of M−O−600 are approximately 0.7 and 0.3, which displays outstanding photocatalytic activity. Through the construction of heterophase junction, M−O−600 has better oxygen adsorption and higher density of localized states, which effectively promotes the generation of superoxide radical (·O2–) and hydroxyl radical (·OH) species. In-situ infrared spectra indicate that toluene is oxidized to benzyl alcohol, benzaldehyde and benzoic acid in turn and then oxidized to formic acid and acetic acid before eventually degraded into H2O and CO2. Gas chromatography-mass spectrometry (GC–MS) is also used to further investigate the degradation pathway of toluene. Degradation pathway and mechanism of TC are studied by liquid chromatography-tandem mass spectrometry (LC-MS). Moreover, three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs) and total organic carbon (TOC) show that TC can be effectively mineralized through a series of reactions by M−O−600 during photocatalysis.

Efficient photocatalytic degradation of gaseous toluene over F-doped TiO2/exfoliated bentonite

To solve the aggregation problem of TiO2 nanomaterials and improve the catalytic efficiency, F-doped TiO2/exfoliated bentonite (TF/EB) composite was prepared by dispersing F-doped TiO2 (TF) nanoparticles on an exfoliated bentonite (EB) using a facile sol–gel method. The exfoliated bentonite was prepared by liquid-exfoliation method from the natural bentonite (B). The prepared samples were applied for toluene degradation in gas phase under UV and visible light irradiation. The as-prepared TF/EB composite exhibited higher toluene degradation efficiency than that of pure TiO2, F-doped TiO2 and TF/B composite. Results indicated that the calcination temperature and the initial F/Ti atom ratio of reaction precursors greatly affected the photocatalytic activity towards toluene degradation. The best photocatalytic performance was obtained by the sample calcinated at 400 °C with an initial F/Ti atom ratio of 5%. The improved photocatalytic performance is ascribed to a series of benefits introduced by F-doping and exfoliation process. The presence of F- ions increases the percentage of exposedreactive {001} facets on TiO2. Moreover, F- ions incorporated into the TiO2 lattice generate oxygen vacancies and Ti3+ defects, which influence the transfer and migration of the photoinduced charge carriers and induce a visible-light photocatalytic activity. Furthermore, the electrostatic interaction of negatively charged exfoliated bentonite surface leads to a more efficient separation of charge carriers.

Visible light-induced photocatalytic degradation of gaseous toluene by Ce, S and N doped ionic liquid-TiO2

Ce, S and N doped TiO2 photocatalysts were synthesized through sol-gel method assisted by 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]). The as-prepared samples were characterized by means of Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope, X-ray diffraction, pore structure, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopic. The photodegradation of gaseous toluene was further investigated at visible light. Ionic liquid-TiO2 samples expose high specific surface area (about 100 m2 g−1), which are 5 times higher than bare TiO2. The results also showed that ionic liquid-TiO2 samples, especially in the introduction of [Bmim][Cl], present rather pure crystalline anatase with smaller crystallite size, higher hydrogen groups on surface and wider visible absorption bands. Moreover, tri-doped IL-TiO2 has superior photocatalytic degradation of gaseous toluene due to the above-mentioned characteristics, which is 5.7 times higher than bare TiO2.

Synergistic effects of octahedral TiO2-MIL-101(Cr) with two heterojunctions for enhancing visible-light photocatalytic degradation of liquid tetracycline and gaseous toluene

The photocatalytic performance of TiO2 is severely restricted by its low photocatalytic activity and high charge-carrier recombination rate. In order to overcome these defects, a novel octahedral TiO2-MIL-101(Cr) (T-MCr) photocatalyst with type-II heterojunction and surface heterojunction is prepared by growth of TiO2 particles on MIL-101(Cr) via optimizing the synthesis conditions. The physicochemical, optical and photoelectrochemical properties of the samples are characterized utilizing several techniques, and its photocatalytic activity for liquid tetracycline and gaseous toluene degradation is evaluated under visible light irradiation. Particularly, the T-MCr-60 shows the outstanding photocatalytic activity. The improved photocatalytic performance of T-MCr-60 is ascribed to strong interfacial contact between (0 0 1) facets, (1 0 1) facets, and MIL-101 and the synergistic effects of two heterojunctions promoting efficient charge transfer. The possible photocatalytic mechanisms involving pollutants degradation pathway and charge transfer mechanisms during the process of pollutants degradation is also discussed.

The high selectivity for benzoic acid formation on Ca2Sb2O7 enables efficient and stable toluene mineralization

The selectivity for different intermediates in VOCs degradation process may lead to different reaction paths, which determines the overall pollutant degradation efficiency. In this work, Ca2Sb2O7 shows a superior photocatalytic activity and stability in gaseous toluene degradation as compared to P25. To shed light on the mechanism of efficient and stable toluene degradation, particularly the role of selectivity for intermediates during the reaction process, the theoretical and experimental approaches were closely combined. Owing to the promoted charge transfer between the absorbents (such as O2, H2O, toluene and other intermediates) and Ca2Sb2O7, both the ROS generation and principal intermediates adsorption are significantly enhanced, which leads to a high selectivity for benzoic acid formation. That is confirmed by in suit DRIFTS and theoretical calculations. Enhanced generation of benzoic acid on Ca2Sb2O7 surface could improve the efficiency of toluene ring-opening and over-all degradation due to lower energy barrier for toluene transformation into benzoic acid. Thus, this could enable efficient and stable degradation of toluene and prevent the catalyst from deactivation. This work provides new insight into the mechanistic understanding of photocatalytic VOCs degradation reaction.

Plasma-photocatalytic degradation of gaseous toluene using SrTiO3/rGO as an efficient heterojunction for by-products abatement and synergistic effects

In this study, toluene degradation was studied in a combined plasma-photocatalytic system using the SrTiO3/rGO as photocatalyst. The photocatalyst was combined with Non-Thermal Plasma (NTP) to improve the performance of NTP in terms of increased toluene removal efficiency (RE) and lower by-products formation. SrTiO3/rGO was synthesized through the simple hydrothermal method and characterized by XRD, FESEM-EDX, UV–vis DRS, and FTIR. Toluene degradation was performed in dynamic mode taking into account the effects of gas flow rate, toluene concentration, relative humidity (RH), and discharge power on the toluene RE. Interactions between the process parameters and optimization of the toluene removal in the plasma-photocatalytic system were investigated by central composite design (CCD). Results showed that Maximum RE of 100 % was obtained at 0.3 L/min flow rate, 61 % RH, 100 ppm initial concentration, and 291 w discharge power. An excellent synergistic effect was observed by combining the NTP with SrTiO3/rGO so that the toluene RE in the NTP-Photocatalytic system at 187.5 w discharge power was almost equal to RE obtained at 292 w discharge power in the NTP alone system. The introduction of SrTiO3/rGO also removed the organic by-products (benzaldehyde, benzoic acid, formic acid, and acetic acid) produced by NTP and improved the CO2 selectivity.

Sequential gas-liquid treatment for gaseous toluene degradation by Fenton’s oxidation in bubble reactors

A lab scale bubble reactor (BR) configuration was employed to evaluate the degradation of gaseous toluene by Fenton’s oxidation under semi-batch mode operation (i.e., with continuous gas bubbling in the liquid phase where organics oxidation is carried out). A parametric study was performed for evaluating the effect of Fenton’s process operating parameters, such as temperature and concentration of Fe2+ and H2O2, in the removal of toluene from the gas stream. The maximum amount of toluene transferred (0.041 mol per liter of solution) was reached when the optimal conditions ([Fe2+] = 2.5 mM, [H2O2] = 20 mM, and T = 25 ºC, at pH 3.0) were used after 120 min of reaction, yielding the highest average toluene absorption rate (5.78 × 10−6 mol/L.s). The treatment of the gas stream increased, however, the organic load in the aqueous phase, so a subsequent treatment stage of the liquid was performed. Additionally, a scale-up of the sequential gas-liquid treatment for a bubble column reactor (BCR) was carried out for several cycles, up to almost 20 h. This strategy, making use of the Fenton’s process for treating the toluene gas stream, with intermediate liquid oxidation, allowed to reach more gas treatment stages, while providing a final effluent that is non-toxic (0.0 % of inhibition of Vibrio Fischeri) and biodegradable.

Enhanced photocatalytic activity of hydrothermally synthesised SrTiO3/rGO for gaseous toluene degradation in the air: modelling and process optimisation using response surface methodology

ABSTRACT In this study, the synthesised SrTiO3 was deposited on the graphene oxide (GO) by a simple hydrothermal method. Synthesised photocatalysts were used for photocatalytic degradation of gaseous toluene in a dynamic mode under UV irradiation. Characterisation of catalysts was performed by XRD, FE-SEM, UV-vis DRS, and FTIR. Results showed that the introduction of graphene increases the removal efficiency due to its high adsorption capacity and hydrophobic property. Process parameters’ (flow rate, toluene initial concentration, and relative humidity) effects on toluene removal efficiency and the interaction between them were investigated by Central composite design (CCD). Analysis of Variance (ANOVA) was used to evaluate the significance of the variables’ effects and the interaction between them. Maximum removal efficiency (RE) of 27.2 % and 32% were obtained by bare SrTiO3 and SrTiO3/rGO, respectively. The results revealed that the relative humidity and flow rate had significant negative effects on toluene RE over both catalysts, while concentration had a significant negative effect only on the RE over bare SrTiO3. Relative humidity was the most important factor that affects the RE on both photocatalysts.

Effect of Synthesized Conditions of Cu-K-OMS-2 on Toluene Oxidation Performance

The objective of this study was to optimize synthesis conditions for the Cu-K-OMS-2 hydrothermal process. The effects of ageing temperature, ageing time and amount of copper (Cu) dopant were considered via using the Box-Behnken design (BBD) method to characterize the conditions for gaseous toluene degradation. In the models studied, the independent variables were ageing temperature (55-145ºC), ageing time (6-18 h) and amount of Cu dopant (2-6% mole). The quadratic model fitted very well with the experimental data (15 runs), which showed a higher value of R2 (0.98) and adjusted R2 (0.95), confirming that the model can explain the results successfully. Ageing temperature was found to be the only significant variable for the Cu-K-OMS-2 transformation phase, with CuO and the bixbyite phase appearing as the highest ageing temperature condition. Furthermore, the effects of ageing temperature, ageing time and amount of Cu dopant on the Cu3+/Cu2+ mole ratio were also investigated. Ageing temperature and amount of Cu dopant displayed a significant effect on both toluene removal and the Cu3+/Cu2+ mole ratio. On the other hand, ageing time was not significant for both responses. The high Cu3+/Cu2+ mole ratio led to enhancement of toluene removal. The optimized conditions for Cu-K-OMS-2 synthesis were determined as 120ºC of ageing temperature, 6 h of ageing time and 6% by mole of Cu on K-OMS-2, which removed 80% of toluene at a reaction temperature of 180ºC.

Large-scale fabrication of upconversion/quantum dots photocatalyst film by a facile spin-coating method

Facile and large-scale preparation of upconversion photocatalyst films is promising for the degradation of volatile organic compounds (VOCs), major component of the landfill gas stench. Herein, a spin-assisted layer-by-layer coating method is explored to fabricate the upconversion photocatalyst film of polyethylene terephthalate (PET)/Tm/Yb-doped NaYF4 (TYN)/P25/(CdSe/CdS) QDs (PET/TYN/P25/QDs). The near-infrared light energy passes through the top QDs and P25 layers to excite TYN, and the strong upconversion emissions of UV (290, 346, and 362 ​nm) and visible (452 and 476 ​nm) light are produced and absorbed by P25/QDs for photocatalysis. In the photocatalytic degradation of gaseous toluene, the removal efficiency over the PET/TYN/P25/QDs film reaches 83% after 1 ​h of simulated sunlight irradiation, which is much higher than that (40%) of the PET/TYN/P25 film. This better photocatalytic activity is ascribed to the large absorption edge of the CdSe/CdS QDs and the efficient electron-hole pair separation in the QDs-P25 heterostructure.

Oxygen vacancies enhanced photocatalytic activity towards VOCs oxidation over Pt deposited Bi2WO6 under visible light

A novel Pt assisted self-modified Bi2WO6 composites (Pt/Bi-BWO) with high oxygen vacancies concentration was successfully fabricated via a simple in-situ NaBH4 reduction method in presence of H2PtCl6•6H2O. The Pt/Bi-BWO performed excellent photocatalytic activity on the degradation of gaseous toluene under visible light illumination. The photocatalytic reaction rate of 0.15% Pt/Bi-BWO was 2.88 times higher than that of Bi2WO6. Over 90% gas phase toluene was removed by 0.15% Pt/Bi-BWO in one hour and over 80% of which was degraded into CO2 and H2O. The Pt/Bi-BWO also performed great stability confirmed by circulating runs test. The mechanism of the promotion was explored by electron paramagnetic resonance (EPR) and DFT calculations. The produced oxygen vacancies were below conduction band (CB) of Bi2WO6, leading to a narrowed band gap. Meantime, the generated oxygen vacancies could activate O2 to enhance the production of reactive oxygen species (ROS), such as O2− and OH. In addition, the added Pt could act as electron trap to suppress the recombination of electrons-holes pairs. In a word, this work produced a novel simply made photocatalyst to remove volatile organic compounds.

Photocatalytic degradation of gaseous toluene using self-assembled air filter based on chitosan/activated carbon/TiO2

Photocatalytic filters are integrated with air purifiers and ventilation systems to remove volatile organic compounds (VOCs) from indoor air. However, the filters, generally prepared by dip or spray coating, are less stable as the deposited TiO2 NPs are prone to be blown off by treated air. In the present study, we propose a novel filter preparation method based on self-assembly of activated carbon (AC) and TiO2 on non-woven polyethylene terephthalate (PET) fabric using chitosan (CS). The prepared filter (CSAT-PET) was characterized for morphological and chemical properties which revealed the homogeneity and chemical bonding of deposited TiO2. Photocatalytic activity of the prepared filter was evaluated for toluene degradation (200–600 ppb) under dark and UV illumination. Toluene removal efficiency reached 91% over CSAT-PET, while it was only 62% over pure TiO2 filter. About 40% of toluene removal was achieved by adsorption on CSAT-PET. Furthermore, CSAT-PET showed robust performance for selected face velocity ranging from 0.5 to 1.5 m/s and, the reaction rate followed Langmuir-Hinshelwood model. FTIR study identified benzaldehyde and benzoic acid as adsorbed intermediates. A UV-induced filter regeneration partially released the adsorbed species. CSAT-PET showed consistent toluene removal and intact morphology over five degradation cycles. The Box-Behnken design (BBD) in RSM was applied to optimize the filter preparation method. The optimum values of TiO2, AC and CS loading were 38.3 g/m2, 52.6 g/m2 and 2.06% (w/v), respectively which exhibited highest removal efficiency for toluene (93%). The proposed methodology can be adapted to fabricate low-cost, stable, and reusable photocatalytic filter for air purification applications.