Photocatalytic Degradation Of Toluene Research Articles

Thick film titania on glass supports for vapour phase photocatalytic degradation of toluene, acetone, and ethanol

Thick film titania photocatalysts (50–100 μm, Degussa P-25 TiO 2) coated on two types of soda glass supports viz. beads (TiO 2/B) and Rasching rings (TiO 2/R) were tested in vapour phase photodegradation of toluene (63–383 g m −3), acetone (116–1161 g m −3), and ethanol (116–1161 g m −3) in a batch recirculation photoreactor at 60–70 °C. The concentrations of the substrates were 10- to 100-fold higher than those reported previously in similar investigations. The films were characterized by using SEM for morphology and EDX for elemental composition and mapping. Further, the effects of water vapour and shape and packing of the glass supports on the photodegradation kinetics were examined. The TiO 2 films on both the glass supports demonstrated high activity for photodegradation of toluene, acetone, and ethanol according to first-order kinetics. The apparent rate constants ( k a ) were found to vary from 1.48 × 10 −2 to 9.4 × 10 −3 g m −3 min −1 for the photodegradation of toluene on both TiO 2/B and TiO 2/R; 5.57 × 10 −2 to 1.29 × 10 −2 g m −3 min −1 for TiO 2/B and 6.70 × 10 −2 to 1.17 × 10 −2 g m −3 min −1 for TiO 2/R for acetone; and 2.14 × 10 −1 to 1.96 × 10 −2 g m −3 min −1 and 7.25 × 10 −2 to 3.51 × 10 −2 g m −3 min −1 using TiO 2/R for ethanol photodegradation. The efficient photodegradation of higher concentration of toluene, acetone, and ethanol was attributed to (i) availability of more amounts of active sites on the thick TiO 2 films for adsorption of VOCs, (ii) their photodegradation within ‘photoactive zone’ constituting outer surface layer of thick TiO 2 coating and (iii) higher reactor temperature. The SEM and EDX data suggest migration of sodium ions across glass/TiO 2 interface into ‘photoactive zone’ of the thick TiO 2 layers did not occur. The TiO 2/R appear to show better efficiency in comparison with TiO 2/B because their packing in the reactor allows for better illumination of catalysts surface.

Gas phase photocatalytic oxidation of toluene using highly active Pt doped TiO 2

Platinum doped TiO 2 materials were studied for the gas phase photocatalytic degradation of toluene. Platinum deposition was achieved by photodeposition method over TiO 2 prepared by means of a sol–gel route. The effect of sulphuric acid pretreatment on the further platinisation process has been extensively studied. From the wide structural and surface analysis of the catalysts an interesting synergetic effect has been demonstrated. The previous sulphate treatment over TiO 2 leads to improved dispersion of the Pt which presents a lower aggregation and homogeneous cluster size. This fact, together with the adequate control of anatase structural and surface parameter due to the sulphate treatment, renders a good photocatalytic performance for toluene oxidation reaction. The highest reaction rates and CO 2 selectivities have been obtained for Pt–S–TiO 2 samples.

Spray-hydrolytic synthesis of highly photoactive mesoporous anatase nanospheres for the photocatalytic degradation of toluene in air

Mesoporous titania nanospheres with high specific surface area and good photocatalytic activity were fabricated on a large scale by a simple spray-hydrolytic method at 90°C. The as-prepared TiO2 spherical powders were characterized by X-ray diffraction, N2 adsorption–desorption measurements, field emission scanning electron microscope, transmission electron microscopy, UV–visible diffuse reflectance spectra and photocurrent measurements. The photocatalytic activity was evaluated by photocatalytic decomposition of toluene in air. The effects of calcination temperatures on the microstructures and photocatalytic activity of the TiO2 powders were investigated and discussed. The results revealed that a large amount of mesoporous titania nanospheres could spontaneously form by self-assembly of countless tiny TiO2 primary nanoparticle during the spray hydrolysis at 90°C. The calcination temperature exhibited a strong effect on the microstructures and photocatalytic activity of the prepared titania. The 400°C-calcined sample showed the highest photocatalytic activity and was about two times higher than that of Degussa P25. At 600°C, the photocatalytic activity decreased because of the destruction of bimodal mesoporous structure of the titania and the drastic decrease of specific surface areas.

Photocatalytic Degradation of Toluene in the Gas Phase: Relationship between Surface Species and Catalyst Features

Photocatalytic activity of both commercial and homemade samples was tested for the degradation of toluene in the gas phase by using two different irradiation sources, UV and solar. The role played by humidity in affecting the final toluene degradation was discussed. Catalyst deactivation (due to the high toluene level, 1000 ppm) and subsequent regeneration, by washing with water, were analyzed. Highest degradations and corresponding kinetic constants were achieved in the case of the anatase/brookite composite samples, while the commercial ones (including P25 Degussa) showed lower efficiency. Various adsorbed aromatic species (benzoic acid, the major surface product hydroquinone, benzylic alcohol, benzaldehyde, and cresols) obtained by washing the exhaust catalysts were analyzed by HPLC. Parallel results were achieved by Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The presence of different photodegradation surface species for the various photocatalysts suggests the occurrence of different reaction pathways, depending on the fine physicochemical features of the specific TiO2 adopted in the reaction.

Characterization and photocatalytic activities of C, N and S co-dopedTiO2 with 1D nanostructure prepared by the nano-confinement effect

A novel method was developed for preparing high specific surface area(156.2 m2 g−1)one-dimensional TiO2 nanostructures co-doped with C, N and S by the nano-confinement effect. Anonmetal doping source (thiourea) was first intercalated into the inner space ofH-titanate nanotubes prepared by the hydrothermal method, and then calcined at450 °C for 2 h in air. The as-prepared C, N and S co-dopedTiO2 nanowires exhibited high visible light and enhanced UV–vis activities in photocatalyticdegradation of toluene in the gas phase. The samples were characterized by x-raydiffraction, transmission electron microscopy, high-resolution transmissionelectron microscopy, fast Fourier transform analysis, x-ray photoelectronspectroscopy, UV–vis diffuse reflectance spectra and photoluminescence. The resultsindicated that the anatase nanowires grew along the [101] direction. DopingTiO2 nanowires with C, N and S could not only broaden the light adsorption spectra into thevisible region (400–600 nm), but also inhibit the recombination of photo-inducedcarriers. A mechanism is proposed to elucidate the nano-confinement effect ofH-titanate nanotubes in the formation of C, N and S co-doping. Based onthis mechanism, the effect of C, N and S co-doping on the band structure ofTiO2 nanowires is also discussed.

Photocatalytic degradation of toluene over doped and coupled (Ti,M)O2 (M = Sn or Zr) nanocrystalline oxides: Influence of the heteroatom distribution on deactivation

In this work, we have studied the photocatalytic oxidation (PCO) of toluene over Sn- and Zr-doped TiO2, and coupled TiO2/SnO2 and TiO2/ZrO2 catalysts. The TiO2 sample doped with Sn (8% of metal ions) is composed by the anatase and rutile phases of TiO2, while the Zr-doped sample (same dopant content) contains only the anatase phase. The coupled photocatalysts are formed, in addition to the phases present in their doped counterparts, by a segregated MO2 phase (M: Sn or Zr). For the photocatalytic degradation of toluene, higher rates in the stationary state are obtained with the coupled catalysts with respect to the doped ones and the TiO2 references (both synthetic and Degussa P25). In the case of the coupled photocatalysts, these higher rates are due to the absence of the deactivation that does occur for the rest of samples. Fresh and used photocatalysts have been studied by FTIR and EPR spectroscopies and by solid/liquid extraction in methanol, followed by GC/MS analysis. The obtained results lead us to conclude that, while structural and electronic modifications, due to the guest cations, are responsible for the high activity of doped samples observed in previous studies for a reaction not causing catalyst deactivation (methylcyclohexane PCO), other factors are crucial for the PCO of toluene. For this reaction, there is a relationship between surface water, adsorbed intermediates and resistance to deactivation, and thus the modifications in the amount and arrangement of surface water molecules caused by the second oxide may be the cause of the high degradation rate obtained with the coupled TiO2/SnO2 and TiO2/ZrO2 photocatalysts.

Visible light induced electron transfer process over nitrogen doped TiO 2 nanocrystals prepared by oxidation of titanium nitride

Nitrogen doped TiO 2 nanocrystals with anatase and rutile mixed phases were prepared by incomplete oxidation of titanium nitride at different temperatures. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), core level X-ray photoelectron spectroscopy (CL XPS), valence band X-ray photoelectron spectroscopy (VB XPS), UV–vis diffuse reflectance spectra (UV–vis DRS), and visible light excited photoluminescence (PL). The photocatalytic activity was evaluated for photocatalytic degradation of toluene in gas phase under visible light irradiation. The visible light absorption and photoactivities of these nitrogen doped TiO 2 nanocrystals can be clearly attributed to the change of the additional electronic (N −) states above the valence band of TiO 2 modified by N dopant as revealed by the VB XPS and visible light induced PL. A band gap structure model was established to explain the electron transfer process over nitrogen doped TiO 2 nanocrystals under visible light irradiation, which was consistent with the previous theoretical and experimental results. This model can also be applied to understand visible light induced photocatalysis over other nonmetal doped TiO 2.

Photocatalytic degradation of gaseous toluene in an ultrasonic mist containing TiO2 particles

Abstract Photocatalytic degradation of toluene gas in a mist formed by ultrasonic atomization of slurried TiO 2 was studied under various conditions. Upon irradiation at 365 nm, toluene was decomposed and mineralized by photocatalytic reaction on the mist surface or inside it. The toluene removal ratio increased as the amount of TiO 2 in the slurry was increased. Under UV 254+185 irradiation, the mineralization ratio was higher than at 365 nm. We propose that under UV 254+185 irradiation, toluene was immediately converted to water-soluble intermediates by direct photolysis and O 3 oxidation in the gas phase and that these intermediates were captured in the mist and photocatalytically mineralized to CO and CO 2 . This paper indicates a new effective utilization of ultrasonic mist and TiO 2 photocatalyst.

Synthesis, characterization and photocatalytic activity of porous manganese oxide doped titania for toluene decomposition

The present study describes the photocatalytic degradation of toluene in gas phase on different porous manganese oxide doped titanium dioxide. As synthesized birnessite and cryptomelane type porous manganese oxide were doped with titania and tested for photocatalytic decomposition of toluene in gas phase. The effects of the inlet concentration of toluene, flow rate (retention time) were examined and the relative humidity was maintained constantly. Thermal and textural characterization of manganese oxide doped titania materials were characterized by X-ray diffraction (XRD), thermogravemetry (TG), BET and TEM-EDAX studies. The aim of the present study is to synthesize the porous manganese oxide doped titania and to study its photocatalytic activity for toluene degradation in gas phase. Cryptomelane doped titania catalyst prepared in water medium [K-OMS-2 (W)] is shown the good toluene degradation with lower catalysts loading compared to commercial bulk titania in annular type photo reactor. The higher photocatalytic activity due to various factors such as catalyst preparation method, experimental conditions, catalyst loading, surface area, etc. In the present study manganese oxide OMS doped titania materials prepared by both aqueous and non-aqueous medium, aqueous medium prepared catalyst shows the good efficiency due to the presence of OH bonded groups on the surface of catalyst. The linear forms of different kinetic equations were applied to the adsorption data and their goodness of fit was evaluated based on the R 2 and standard error. The goodness to the linear fit was observed for Elovich model with high R 2 (≧0.9477) value.

Nanosized Ti–V mixed oxides: Effect of doping level in the photo-catalytic degradation of toluene using sunlight-type excitation

In this report we investigate the behavior of nanosized Ti–V mixed oxides with anatase structure in the photo-elimination of toluene using sunlight-type excitation. These systems were prepared by a microemulsion method and their physico-chemical properties characterized by a multitechnique approach using X-ray diffraction, electron paramagnetic resonance, Raman, and UV–vis spectroscopies. The preparation method allows the incorporation of significant amounts of vanadium in the anatase structure and two well-differentiated structural/electronic situations occur for samples having a V content below/above ca. 5at.%. The photo-activity of the Ti–V samples reached a maximum for a sample having a vanadium content of ca. 2.5at.%, which displays a reaction rate 2.3/2.7 times larger than the parent-TiO2/P25 references. The chemical/physical bases of such behavior are discussed in light of the characterization results.

Photocatalytic Degradation of Toluene in Air Using a Fluidized Bed Photoreactor

The photocatalytic degradation of toluene in air was carried out on particles ofTiO2in a photocatalytic reactor that had been developed to study the treatment of organic pollutants in a gaseous phase. Hypothetically, the fluidized bed technology of this reactor could make it possible to increase the mass transfer coefficients in comparison with those of conventional photoreactors. The photocatalytic particles used were prepared by mixingTiO2(Degussa P25) and starch in a methanol solution. The XRD and SEM results of these aggregates confirm the titanium dioxide (Degussa P25) characteristics, such as the presence of anatase on the particle surface and spongy and wrinkled morphology. Toluene concentrations varied from 0.9 to 199ppmv, and all the experiments were carried out with a flow rate of 300 NL/h. Toluene conversions from 77%to 100%were obtained in the range studied. In this work, the regeneration processes of deactivatedTiO2photocatalysts have been investigated using FT-IR and GC/MS techniques. Benzoic acid, benzaldehyde, and benzyl alcohol were the three major intermediate products identified.

Photocatalytic degradation of toluene with ozone addition

The main goal of this study is to analyze the characteristics of photodegradation and photocatalytic activation experimentally with the major parameters such as air flow rate, inlet toluene concentration, ozone concentration, UV light and bead material, etc. In particular, the effects of transmissivity of UV radiation with TiO2 coated supporter (bead material) and void fraction (bead size) on the photocatalytic degradation are estimated for TiO2/UV and O3/TiO2/UV process. In results, the experiment shows that the UV light transmissivity of 5mm glass bead becomes much higher than that of 6.5 mm alumina bead in spite of lower void fraction inducing the higher photoactivation. The conversion of toluene represents about 96% during reaction time 420 min at the toluene concentration of 100 ppm and ozone concentration of 2.5 ppm, showing a conversion rate of ozone of 95% for O3/TiO2/UV process.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe‐doped TiO2 Catalyst on Porous Nickel Sheets¶

ABSTRACTA novel continuous‐flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe‐doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X‐ray diffraction, scanning electron microscope and electric field‐induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95 % can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets¶

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

SII-3 フッ素系液体(FC)/水エマルジョン溶媒中におけるトルエンの超音波/光触媒併用分解(スペシャルセッションII(環境))

SII-3 フッ素系液体(FC)/水エマルジョン溶媒中におけるトルエンの超音波/光触媒併用分解(スペシャルセッションII(環境))

VUV Photocatalytic Degradation of Toluene in the Gas Phase

Abstract The photocatalytic degradation rate of gaseous toluene under irradiation of vacuum ultraviolet (185 nm) was 2–3 times faster than that under irradiation of 254 nm. The 185-nm VUV photolysis was greatly improved by the presence of TiO2 photocatalyst.

Photocatalytic degradation of toluene by platinized titanium dioxide photocatalysts

A photoreactor has been set up to study the photodegradation of volatile organic compound (VOC) in situ. In the reactor, TiO2 and Pt/TiO2 photocatalysts were immobilized on to UV-transparent quartz support. Scanning electron microscope (SEM) studies and Brunauer-Emmett-Teller (BET) surface area measurements revealed that the quartz fiber support was mostly coated with catalyst with a total surface area of 4.0 +/- 0.3 m2/g. The photocatalytic activity of the photocatalysts was evaluated for the photodegradation of 160 ppm toluene-laden air. It was found that 50-70% of toluene was degraded within the first 5 min of UV illumination. Both TiO2 and Pt/TiO2 photocatalysts suffered from deactivation after 18 hours of continuous operation, and the photocatalysts' activity was significantly reduced. However, platinization doubled the photocatalyst life and delayed the onset of de-activation. The presence of moisture was found to shift the onset of catalyst de-activation to an earlier time. It is concluded that the de-activation of the photocatalyst was due to the accumulation of intermediates on the photocatalysts surface preventing the toluene being adsorbed on the photocatalyst surface for degradation.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photocatalytic oxidation of toluene on irradiated TiO 2: comparison of degradation performance in humidified air, in water and in water containing a zwitterionic surfactant

Photocatalytic degradation of toluene was carried out both in gas–solid and in liquid–solid regime by using polycrystalline samples of TiO 2 Merck and TiO 2 Degussa P25. For the gas–solid regime two types of continuous photoreactor were used, a fixed bed one of cylindrical shape and a Carberry type photoreactor, both irradiated by near-UV light. The inlet reacting mixture consisted of air containing toluene and water vapours. The influence of the gas flow rate and the presence of water vapour on the photocatalytic process was investigated. CO 2 and benzaldehyde were the toluene degradation products detected in the gas phase by using TiO 2 Merck. In the presence of water vapour this catalyst exhibited a stable activity, which greatly decreased in the absence of water vapour. On the contrary, TiO 2 Degussa P25 produced CO 2 and traces of benzaldehyde but it continuously deactivated even in the presence of water vapour. For the liquid–solid regime a batch photoreactor with immersed lamp was used. In order to increase the reaction rate, a zwitterionic surfactant, i.e. tetradecyldimethylamino-oxide, was added to the reacting mixture. A complete photo-oxidation of toluene was achieved after few hours of irradiation in the presence of both types of photocatalysts; longer irradiation times produced the photodegradation of surfactant. The main intermediates of toluene degradation were p-cresol and benzaldehyde while traces of pyrogallol and benzyl alcohol were also found. Benzoic acid, hydroquinone and trans, trans-muconic acid were detected only with TiO 2 Merck. The reaction rate was higher in the presence of the surfactant suggesting that this compound acts as a sequestration agent. An FTIR study gave information on the role played by superficial hydroxyl groups both on the onset of activity and on the deactivation process. On the basis of photoreactivity results and of FTIR investigation the differences of activity and distribution and nature of toluene degradation products are critically discussed for the three reacting systems used.

Deactivation and regeneration of titania catalyst supported on glass fiber in the photocatalytic degradation of toluene

Two titania photocatalysts supported on glass fiber (GF) were prepared by using anatase-type crystalline P25 powder and dilute titanium isopropoxide solution (DTS). Chemical compositions and characteristics of the surface of the P25/GF and DTS/GF catalysts were examined with an XPS method, and their activities in the photocatalytic degradation of toluene under UV irradiation were discussed. Although a large amount of titania was stably impregnated on glass fiber on the DTS/GF catalyst, low-temperature calcination brought about insufficient oxidation of titanium atoms resulting in a heavy deposit of carbonaceous materials. Both catalysts (P25/GF and DTS/GF) were active in photocatalytic degradation, while their catalytic activity was lowered because of the accumulation of reactant and carbonaceous materials on the surface. Hydrogen peroxide completely regenerated the deactivated P25/GF catalyst by removing contaminants. However, the activity of the used DTS/GF catalyst was considerably enhanced by exposing it to hydrogen peroxide vapor to a level higher than the fresh catalyst due to the increase in the surface concentration of active oxidizing species as well as the removal of carbonaceous materials.