Photocatalytic Degradation Of Gaseous Toluene Research Articles

Unraveling the generation mechanism of singlet oxygen in Bi2WxMo1-xO6 solid solution and roles in photocatalytic degradation of gaseous toluene under visible-light irradiation

Photocatalytic degradation volatile organic compounds (VOCs) represent an appealing strategy since the inexhaustible solar energy and facile reaction condition. In this work, a flower-like microsphere Bi2WxMo1-xO6 solid solution photocatalysts with abundant oxygen vacancies (OVs) were prepared via HTAB-assisted hydrothermal method. The mole ratio of W and Mo atoms were regulated by adjusting the stoichiometric ratio of their precursor. The optimized Bi2W0.25Mo0.75O6 presented outstanding photocatalytic performance with 96.8% of toluene degradation rate after 180 min of irradiation under visible light (>420 nm), which was 13.76 times higher than that of pure Bi2MoO6 and 10.32 times higher than that of pure Bi2WO6, respectively. The enhanced photocatalytic activity of Bi2W0.25Mo0.75O6 was attributed to the optimized band structure and efficient separation efficiency of carriers as well as the participation of singlet oxygen (1O2) radicals. Free radical trap experiments and electron spin resonance investigations revealed that 1O2, hydroxyl radical, and holes were the predominated reactive oxygen species (ROSs) in toluene degradation. Meanwhile, the generation of 1O2 was related to abundant OVs of Bi2W0.25Mo0.75O6 solid solution. This work suggested that solid solution with abundant OVs was an effective photocatalyst to improve the VOCs degradation activity under visible-light irradiation.

Experiments and DFT investigation of microwave-assisted sol–gel method prepared S-doped g-C3N4 for enhanced photocatalytic degradation of gaseous toluene

Doping S with defects to create heterojunction-like junctions is an effective method for increasing g-C3N4 photodegradation efficiency of gaseous toluene.

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.

A compact Z-scheme heterojunction of BiOCl/Bi2WO6 for efficiently photocatalytic degradation of gaseous toluene

Construction of Z-scheme heterojunction photocatalysts with efficient electron-hole pairs separation and robust oxidation abilities is a promising strategy to decompose volatile organic compounds (VOCs). Herein, UV-light-driven BiOCl and visible-light-driven Bi2WO6 were successfully combined via a one-pot hydrothermal method and compact Z-scheme heterojunction photocatalyst BiOCl/Bi2WO6 was obtained. Owing to the similar precursors and synthesis conditions, the integrated BiOCl/Bi2WO6 heterojunction was intimate and homogenous, which resulted in the efficient separation of photogenerated carriers, and generated abundant holes (h+), hydroxyl radicals (·OH) and superoxide radicals (·O2–). The optimal BiOCl/Bi2WO6 photocatalyst (BWOCl-2), achieved by tailoring the amount of hydrochloric acid, exhibited almost 100 % of toluene degradation and excellent durability. Electron spin resonance (ESR) results revealed that h+, ·O2– and ·OH were dominant active species in the BiOCl/Bi2WO6 photocatalytic system. The degradation intermediate products were monitored by in situ Diffuse Reflection Infrared Fourier Transform spectroscopy (DRIFTS) and the possible photocatalytic mechanism was also revealed according to the band structure of BiOCl/Bi2WO6 heterojunction. This work provided a novel avenue to design an efficient homogenous heterojunction photocatalyst for the efficient degradation of VOCs under sunlight.

Highly efficient visible-light-driven photocatalytic degradation of gaseous toluene by rutile-anatase TiO2@MIL-101 composite with two heterojunctions

The construction of heterophase junctions by rutile-anatase TiO2 is considered an effective strategy for toluene degradation, but the photogenerated electron utilization is still insufficient. In this study, the formation of type-II heterojunction by the encapsulation of Materials of Institut Lavoisier (MIL-101) by anatase is performed, and then the heterophase junction is further constructed to improve the catalytic performance of the photocatalyst. The enhancement of photocatalytic performance depends on the encapsulation of MIL-101 by anatase, the light absorption capacity of anatase, and the contact area of two heterojunctions. Photogenerated electrons are transferred to oxygen vacancies of anatase and promoting the generation of oxygen-containing radicals. The material certifies the synergistic effect of the heterophase junction and heterojunction design and provides a theoretical basis for application in the degradation of volatile organic compounds.

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

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.

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.

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.

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.

Surface modification of (001) facets dominated TiO2 with ozone for adsorption and photocatalytic degradation of gaseous toluene

This study investigated the positive effect of surface modification with ozone on the photo-catalytic performance of anatase TiO2 with dominated (001) facets for toluene degradation. The performance of photocatalyst was tested on a home-made volatile organic compounds degradation system. The ozone modification, toluene adsorption and degradation mechanism were established by a combination of various characterization methods, in situ diffuse reflectance infrared fourier transform spectroscopy, and density functional theory calculation. The surface modification with ozone can significantly enhance the photocatalytic degradation performance for toluene. The abundant unsaturated coordinated 5c-Ti sites on (001) facets act as the adsorption sites for ozone. The formed Ti–O bonds reacted with H2O to generate a large amount of isolated Ti5c-OH which act as the adsorption sites for toluene, and thus significantly increase the adsorption capacity for toluene. The outstanding photo-catalytic performance of ozone-modified TiO2 is due to its high adsorption ability for toluene and the abundant surface hydroxyl groups, which produce very reactive OH· radicals under irradiation. Furthermore, the O2 generated via ozone dissociation could combine with the photogenerated electrons to form superoxide radicals which are also conductive to the toluene degradation.

Ozone-assisted photocatalytic degradation of gaseous toluene from waste air stream using silica-functionalized graphene oxide/ZnO coated on fiberglass: performance, intermediates, and mechanistic pathways

The present study focused on the potential of an ozone-assisted photocatalytic process using the catalyst silica-functionalized graphene oxide/ZnO coated on fiberglass (Si-GO/ZnO-FG) in the removal of toluene from waste air stream. Here, a comparative examination was performed in terms of toluene removal efficiency in the photocatalytic process (UV/Si-GO/ZnO-FG) and photocatalytic ozonation (O3/UV/Si-GO/ZnO-FG). The gaseous intermediates resulting from degradation of toluene by different processes were analyzed using GC-MS. The results of this study indicated that with the addition of ozone to the UV/Si-GO/ZnO-FG process, toluene removal increased significantly from 76.18 to 87.8%. The reason for this incremental efficiency can be explained by the fact that with the addition of ozone, the production rate and the extent of hydroxyl radical (OH•) production grow significantly; thereby, more pathways are developed for toluene degradation. The major byproducts in toluene oxidation by photocatalytic and photocatalytic ozonation processes include formic acid, acetic acid, benzyl alcohol, benzaldehyde, p-cresol, hydroquinone, and benzoic acid. Given the intermediates and the dominant oxidants detected in the aforementioned process, the possible toluene degradation pathway by the utilized process was suggested.

In situ FTIR spectra investigation of the photocatalytic degradation of gaseous toluene over a novel hedgehog-like CaFe2O4 hollow-structured materials

A novel hedgehog-like CaFe2O4 hollow microspheres was successfully fabricated by a simple template-assisted method with post-heat treatment. Especially, the hollow architecture was assembled by the nanorods, the surface areas could reach 111.5 m2·g−1. Due to the enhanced light scattering by the hollow architecture, the effective charges separation by the assembled nanorods and the strong catalytic oxidizing performances by the Fe-base spinel material, the hedgehog-like CaFe2O4 catalysts showed marvelous catalytic performance for gaseous toluene degradation. Besides, by in situ FTIR technique, the degradation mechanism of gaseous toluene was clarified clearly based on the detected intermediates and final products in real time.

Nanodiamond-decorated ZnO catalysts with enhanced photocorrosion-resistance for photocatalytic degradation of gaseous toluene

Photocatalytic degradation of indoor volatile organic compounds (VOCs) is considered as one of a promising strategy for resolving indoor pollution problems. Zinc oxide has been widely used in photocatalysis. However, the photocorrosion of ZnO restrains its further application. Herein, we decorated ZnO with nanodiamonds to solve the photocorrosion problem of ZnO for photocatalytic degradation of gaseous toluene. The photocorrosion-resistance of nanodiamond-decorated ZnO catalysts was enhanced. It was demonstrated that after the decoration of nanodiamonds, the optical absorption and transient photocurrent were effectively increased, while the photoluminescence intensity and electrochemical impedance were greatly reduced, indicating that nanodiamonds decoration not only improved the light adsorption for ZnO, but also promoted the charge transfer and eventually enhanced the photocatalytic oxidation efficiency of toluene. We hope that this work could propose possible ways to relieve the photocorrosion of ZnO semiconductor in the photocatalytic application and provide new insights into the degradation of gaseous pollutants.

Insight into the influence of morphology of Bi2WO6 for photocatalytic degradation of VOCs under visible light

Four kinds of Bi2WO6 with different morphology were prepared by facile hydrothermal method with different additives and pH. In the photocatalytic degradation of gaseous toluene under visible light irradiation (λ > 420 nm), the nest-like Bi2WO6 performed the best photodegradation efficiency of 100% in only 20 min, and could be reused for at least eight times without a significant loss of catalytic activity. According to the characterization techniques, including XRD, SEM, TEM, XPS, BET, UV–vis, PL and TPR, the excellent photocatalytic activity of the nest-like Bi2WO6 is ascribed to the small particle size, large photo response interval, narrow band gap, high separation efficiency of electron-hole pairs and low recombination rate of photogenerated electron holes, that result in abundant reaction active sites.

Rational design of cobalt and nitrogen co-doped carbon hollow frameworks for efficient photocatalytic degradation of gaseous toluene

In this work, the hollow Co/N co-doped carbon frameworks (Co/N-C) were successfully constructed by in situ transformation of zeolitic imidazolate frameworks (ZIF-67) through polycondensation of dopamine. The hollow and porous structure of Co/N-C was demonstrated by transmission electron microscopy (TEM). The doping and Co-N-C active sites were verified by X-ray photoelectron spectroscopy (XPS). The UV–vis diffusion reflectance spectra (UV–vis DRS) of hollow Co/N-C nanoparticles reflected a significant enhancement of optical absorption in the range of 300–800 nm. With hollow porous structure, strong optical absorption and rich Co-N-C active sites, the Co/N-C exhibited a high photocatalytic performance by using gaseous toluene as a model pollutant, and the degradation efficiency of gaseous toluene was found to be around 78.2% under mild conditions (i.e., Temperature = 273 K, Pressure = 1 atom, λ ≥ 420 nm, t = 6 h). The photocatalytic degradation process and mechanism of toluene were further investigated by in situ Fourier transform infrared (FTIR) spectroscopy, which indicated that multiple hydroxylation and benzen ring opening are both involved in the catalytic elimination processes, and the initial intermediate species including benzaldehyde and benzoic acid were firstly derived from the hydroxylation due to the hydroxyl radical followed by further oxidation into carbon dioxide and water.

Construction of ternary heterojunction CuS-CdS/TiO2 nanobelts for photocatalytic degradation of gaseous toluene

The ternary heterojunction CuS-CdS/TiO2 nanobelts (CuS-CdS/TiO2 NBs) were successfully prepared. The CuS-CdS/TiO2 NBs photocatalyst was used for the decomposition of gaseous toluene under simulated solar light irradiation. Results showed that the construction of ternary heterojunction CuS-CdS/TiO2 NBs improved the photocatalytic activity. The coupling of CuS-CdS heterojunction with TiO2 NBs promoted the absorbance in visible light region. CdS and CuS were brought in contact as a cascade structure, forming the stepwise energy level structure, which leads to the increased separation and transfer of photogenerated electrons and holes. The results demonstrated that photocatalytic degradation rate increased with increasing photocatalyst area from 16 to 40 cm2. With an increase in initial concentration, the decomposition of toluene showed a tendency to increase, however, there was an optimum concentration at 4215 ppm. The optimal flow rate and reaction temperature were around 1.5 L/min and 40 °C, respectively. After illumination of 100 min the conversion of toluene was about 88.12% and the produced CO2 was about 9353 ppm, corresponding to a mineralization ratio of 31.70%. It is hoped that our work could provide a valuable evidence for directing the rationally fabrication of ternary nanojunctions photocatalysts for environment cleanup.