Photocatalytic Degradation Of Gaseous Toluene Research Articles

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.

Reduced Graphene Oxide-TiO<sub>2</sub> Nanocomposite Facilitated Visible Light Photodegradation of Gaseous Toluene

The photocatalytic degradation of gaseous toluene was investigated on TiO2 nanoparticles coated on reduced graphene oxide. Reduced graphene oxide-TiO2 composite (RGO-TiO2) was synthesized via two step processes. The prepared RGO-TiO2 composite was characterized using SEM, XRD, and UV-visible spectra. A significant increase in light absorption to visible light was observed by RGO-TiO2 compared with that of pure TiO2 nano particles. The photocatalytic degradation efficiency of the RGO-TiO2 composite was much higher than that of the P25 TiO2, 95% and 40% respectively. In our investigated conditions, the initial concentration, flow rate and relative humidity had significant influences on the photocatalytic degradation of gaseous toluene. The most efficiency was recorded at the 0.3 ppm concentration, 1L/min flow rate and 30% relative humidity. We believe that this TiO2 based composite material can be effectively used as a highly active and stable photocatalyst to remove various indoor air pollutants especially gaseous toluene. The photocatalytic degradation efficiencies of toluene increased slowly below 20% relative humidity and then decreased as the relative humidity increased further. The main reason of enhanced photocatalytic property might be the strong electron transfer ability, and the increased adsorption capacity of RGO sheets in the composites as well as the retarded charge recombination rate contributed by the energy level of the two materials. We believe that this TiO2 based composite material can be effectively used as a highly active and stable photocatalyst to remove various gaseous pollutants.

Physiochemical properties of n-n heterostructured TiO2/Mo-TiO2 composites and their photocatalytic degradation of gaseous toluene

The composite TiO2/Mo-TiO2 were prepared by a modified sol-gel method. The prepared catalysts were characterized by X-ray diffraction, BET analysis, SEM, X-ray photoelectron spectroscopy, and UV–vis diffused reflectance spectroscopy techniques. The structural characterization results demonstrated that Mo was successfully doped into the TiO2 lattice and caused slight changes in the physiochemical properties. The UV–vis DRS showed a red shift of the adsorption edge to the visible region. The photocatalytic decomposition efficiencies of the catalysts were examined with toluene as a typical VOC in a continuous flow reactor. The photocatalytic activity of the n-n heterogeneous TiO2/Mo-TiO2 was greater than that of pure TiO2 and Mo-TiO2, and the catalyst containing a Mo/Ti mole ratio of 2.5% exhibited optimum photocatalytic properties. In general, a relative humidity of 35%, a higher oxygen content, a lower initial toluene concentration, and a higher UV intensity were beneficial for toluene decomposition.

Photocatalytic degradation of gaseous toluene by using TiO2 nanoparticles immobilized on fiberglass cloth

Abstract Photocatalytic properties of titanium dioxide have been exploited for various purposes, including the photocatalytic purification of air, where an immobilized catalyst is preferred over a dispersed one as it has much higher application value. In this work, we have investigated the photocatalytic degradation of toluene on titania nanoparticles immobilized on fiberglass cloth. The progress of the reaction was monitored using a self-constructed photoreactor equipped with UVA lamps. Commercially available P25 and PC500 powder catalysts were successfully immobilized on fiberglass cloth by a “sol suspension” procedure. The prepared photocatalysts were characterized by scanning electron microscopy (SEM), UV–vis-NIR diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FT-IR). The highest photocatalytic degradation performance was obtained for the PC500 catalyst followed by a 1:1 mixture of P25 and PC500 and the lowest performance was observed in case of the P25 immobilized catalyst. The highest degradation rate of PC500 can be ascribed to its smallest particle size and highest surface area in comparison to others.

TiO2 Nanotubes with Open Channels as Deactivation-Resistant Photocatalyst for the Degradation of Volatile Organic Compounds.

We synthesized ordered TiO2 nanotubes (TNT) and compared their photocatalytic activity with that of TiO2 nanoparticles (TNP) film during the repeated cycles of photocatalytic degradation of gaseous toluene and acetaldehyde to test the durability of TNT as an air-purifying photocatalyst. The photocatalytic activity of TNT showed only moderate reduction after the five cycles of toluene degradation, whereas TNP underwent rapid deactivation as the photocatalysis cycles were repeated. Dynamic SIMS analysis showed that carbonaceous deposits were formed on the surface of TNP during the photocatalytic degradation of toluene, which implies that the photocatalyst deactivation should be ascribed to the accumulation of recalcitrant degradation intermediates (carbonaceous residues). In more oxidizing atmosphere (100% O2 under which less carbonaceous residues should form), the photocatalytic activity of TNP still decreased with repeating cycles of toluene degradation, whereas TNT showed no sign of deactivation. Because TNT has a highly ordered open channel structure, O2 molecules can be more easily supplied to the active sites with less mass transfer limitation, which subsequently hinders the accumulation of carbonaceous residues on TNT surface. Contrary to the case of toluene degradation, both TNT and TNP did not exhibit any significant deactivation during the photocatalytic degradation of acetaldehyde, because the generation of recalcitrant intermediates from acetaldehyde degradation is insignificant. The structural characteristics of TNT is highly advantageous in preventing the catalyst deactivation during the photocatalytic degradation of aromatic compounds.

Photocatalytic degradation of gaseous toluene over bcc-In2O3 hollow microspheres

In this work, the body-centered cubic indium oxide (bcc-In2O3) hollow microspheres were prepared via a P123-assisted solvothermal process. The structural properties of samples were investigated by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV–visible diffusive reflectance spectroscopy, and nitrogen adsorption-desorption isotherms. The photocatalytic effects of degrading gaseous toluene were evaluated by gas chromatography and in situ Fourier transform infrared (FTIR) spectra under a irradiation of a 500W high pressure xenon lamp. The results indicated that the as-prepared bcc-In2O3 hollow microspheres exhibited a high degradation efficiency towards toluene within a short reaction time. Besides, the preliminary mechanism therein was inferred with the aid of in situ FTIR and electron spin-paramagnetic resonance techniques to understand the degradation process.

Effect of surface modification with H2S and NH3 on TiO2 for adsorption and photocatalytic degradation of gaseous toluene

This study investigates the effects of surface modification with H2S and NH3 respectively on the photocatalytic activity of TiO2 for toluene degradation. Surface modification with H2S was observed to enhance the adsorption of toluene and promote the degradation rate at the start of photocatalytic degradation, while that with NH3 inhibited the adsorption of toluene but enhanced the photocatalytic activity for the toluene degradation. By a combination of in situ DRIFTS and other characterization methods, the adsorption mechanism and relationship between surface structure and photocatalytic activity were proposed. For TiO2–H2S, the sulfhydryl group, which is formed from the dissociation of H2S molecules, could easily interact with toluene. The low photocatalytic activity may be caused by the inhibition of the regeneration of surface hydroxyl groups, poor generation of O2− radicals and accumulation of highly stable intermediates. For TiO2–NH3, steric hindrance serves as interference to the adsorption of toluene, while the abundant surface hydroxyl groups are possibly conducive to the degradation of toluene.

Photocatalytic degradation of gaseous toluene with multiphase TixZr1−xO2 synthesized via co-precipitation route

In the present work, the multiphase TixZr1−xO2 particles containing cubic-phase ZrO2 were fabricated via co-precipitation route. The mole ratios of Ti and Zr elements were controlled by three levels: Ti/Zr=7/3 (maximum), Ti/Zr=5/5 (medium), and Ti/Zr=3/7 (minimum). The materials prepared were characterized by using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. For the maximum usage of solar power with fabricated catalysts, elimination of gaseous toluene was chosen as a model to evaluate the performances under visible light. The results indicated that the degradation efficiency of toluene was about 80% after 6h reaction using Ti0.3Zr0.7O2 as the photocatalyst. On the other hand, the multiphase TixZr1−xO2 (x=0.7 or 0.5) photocatalysts showed significant enhancement in the activity, compared with the commercial TiO2 (Degussa P25). The enhanced performances of TixZr1−xO2 might be attributed to the lower charge recombination rate of photoinduced electron–hole pairs. In addition, some intermediates (the benzaldehyde and benzoic acid) and final product (CO2) adsorbed on the surface of the particles were also detected by using in situ Fourier transform infrared (FTIR) spectroscopy.

Photocatalytic degradation of gaseous toluene and ozone under UV254+185 nm irradiation using a Pd-deposited TiO2 film

Abstract This study investigated the effects of palladium nanoparticles (Pd NPs) that were deposited onto a TiO 2 film on the simultaneous removal of toluene and ozone byproduct during 254 nm ultraviolet and 185 nm vacuum ultraviolet (VUV) irradiation. The uniform Pd NPs that were deposited onto the TiO 2 film via an electrostatic method showed a high activity for toluene and ozone conversion. Pd NPs with the smallest mean size (1.9 ± 0.7 nm) exhibited the highest turnover frequency (TOF). However, the Pd–TiO 2 film prepared with an immersion time of 10 min exhibited the highest activity for both toluene and ozone conversion because of the relatively small size and high density of the as-deposited Pd NPs. Compared with the direct VUV photolysis and the TiO 2 /VUV photocatalytic processes, the Pd–TiO 2 /VUV process exhibited a better performance in degrading toluene over a range of concentrations with a short retention time (5.7 s), and 90% of the ozone generated by 185 nm VUV was simultaneously decomposed. In addition, approximately 94.1% of the converted toluene was mineralized into CO 2 and CO, and only a small amount of degradation intermediates, such as benzaldehyde and formic acid, were detected in the Pd–TiO 2 /VUV process with a total yield less than 2%.

Mechanism Study of Photocatalytic Degradation of Gaseous Toluene on TiO2 with Weak-Bond Adsorption Analysis Using In Situ Far Infrared Spectroscopy

The development of far infrared spectroscopy offers a powerful method for comprehensive study in adsorption structure and photocatalytic degradation mechanism of photocatalysis. This study presented an improved in situ diffuse reflectance infrared Fourier transform spectroscopy technique in far infrared region for investigation of weak-bond adsorption and photocatalytic degradation of gaseous toluene on the surface of TiO2. It was found that toluene tends to be adsorbed on the hydroxyl group via three possible sites, the ortho-, meta-, and para-adsorption site, instead of ipso-structure. The methyl group of toluene is consumed first during the process of toluene photocatalytic degradation. Based on these, a reaction route for the photocatalytic degradation of gaseous toluene on TiO2 surface was proposed.

Rapid degradation of toxic toluene using novel mesoporous SiO2 doped TiO2 nanofibers

Toluene is a typical volatile organic compound (VOC), which is harmful to human. The novel mesoporous TiO2 composite fibers with optimal SiO2 content were fabricated via electrospinning the relevant gel precursor, and were characterized by XRD, SEM, TEM, TG–DTA, UV–vis, and BET surface analysis, respectively. Through photocatalytic degradation of gaseous toluene with these nanostructured fibrous catalysts, it has shown that 10% silica doped TiO2 nanofibers displayed the highest degradation rate among a lot of titania fibers with different silica content, and whose reaction rate is two-fold enhancement than Degussa P25. What is more, it is easy to fix and recycle nanofibrous catalysts. Furthermore, the degradation pathway of cleaning toluene has been verified based on GC–MS detection.

Photocatalytic degradation of gaseous toluene by using immobilized titania/silica on aluminum sheets

The aim of this study was to prepare a highly active immobilized titania/silica photocatalyst and to test its performance in situ toward degradation of toluene as one of the major toxic indoor contaminants. In this work, two different titania layers immobilized on Al sheets were synthesized via low temperature sol-gel method employing presynthesized highly active titania powders (Degussa P25 and Millennium PC500, mass ratio 1:1): (a) with a silica/titania binder and a protective layer and (b) without the binder. The photocatalysts were characterized by X-ray diffraction, nitrogen sorption measurements, scanning electron microscopy (SEM), infrared spectroscopy, and UV-vis diffuse reflectance spectroscopy (DRS). The in situ photocatalytic degradation of gaseous toluene was selected as a probe reaction to test photocatalytic activity and to verify the potential application of these materials for air remediation. Results show that nontransparent highly photocatalytically active coatings based on the silica/titania binder and homogeneously dispersed TiO(2) powders were obtained on the Al sheets. The crystalline structure of titania was not altered upon addition of the binder, which also prevented inhomogeneous agglomeration of particles on the photocatalyst surface. The photoactivity results indicate that the adsorption properties and photocatalytic activity of immobilized photocatalysts with the silica/titania binder and an underlying protective layer were very effective and additionally, they exhibited considerably improved adhesion and uniformity. We present a new highly photocatalytically active immobilized catalyst on a convenient metallic support, which has a potential application in an air cleaning device.

Photocatalytic degradation of gaseous toluene over hollow “spindle-like” α-Fe2O3 loaded with Ag

In this work, hollow “spindle-like” α-Fe2O3 nanoparticles were synthesized by a hydrothermal route. The Ag/α-Fe2O3 catalyst was prepared based on the spindle-shaped α-Fe2O3 with CTAB as the surfactant, which showed excellent photoelectric property and photocatalytic activity. The structural properties of these samples were systematically investigated by X-ray powder diffraction, scanning electronic microscopy, transmission electronic microscopy, energy-dispersive X-ray spectra, and UV–Vis diffuse reflectance spectroscopy techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage measurement. The photocatalytic performances of the Ag/α-Fe2O3 and α-Fe2O3 samples were comparatively studied in the degradation of toluene under xenon lamp irradiation by in situ FTIR spectroscopy. Benzaldehyde and benzoic acid species could be observed on the α-Fe2O3 surface rather than Ag/α-Fe2O3 surface. The results indicate that the Ag/α-Fe2O3 sample exhibited higher photocatalytic efficiency.

Photocatalytic degradation of gaseous toluene on Fe-TiO2 under visible light irradiation: A study on the structure, activity and deactivation mechanism

The Fe-TiO2 photocatalysts synthesized by a sol–gel method have the mesoporous structure with a narrow pore size distribution, large pore volume and high surface area. The incorporated Fe3+ substitutes the octahedrally coordinated Ti4+ in the TiO2 lattice to extend the absorption of TiO2 to visible light region and promote the formation of electron–hole pair. Additionally, the separation and transportation efficiency increase with the doping of Fe3+ increasing from 0.1% to 0.7%, while decreases remarkably with the doping concentration increasing from 0.7% to 1.5%. The Fe-TiO2 shows excellent photocatalytic performance for toluene degradation under visible light irradiation. The optimal Fe/Ti ratio is 0.7%. Partial deactivation of the photocatalytic activity was observed after 20 consecutive reaction runs. From the in situ DRIFTS experiment, the deactivation reason can be attributed to the formation of stable intermediates, such as benzaldehyde and benzoic acid, which occupied the active sites on the surface of the photocatalyst. The adsorbed benzaldehyde and benzoic acid can be removed with heat treatment at 653K for 3h and the deactivated photocatalyst can be regenerated completely.

Photocatalytic degradation of gaseous toluene over TiO 2–SiO 2 composite nanotubes synthesized by sol–gel with template technique

TiO 2–SiO 2 composite nanotubes were successfully synthesized by a facile sol–gel technique utilizing ZnO nanowires as template. The nanotubes were well characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, N 2 adsorption–desorption analysis and UV–vis diffuse reflectance spectroscopy. The nanotubular TiO 2–SiO 2 composite photocatalysts showed diameter of 300–325 nm, fine mesoporous structure and high specific surface area. The results indicated that the degradation efficiency of gaseous toluene could get 65% after 4 h reaction using the TiO 2–SiO 2 composite as the photocatalyst under UV light illumination, which was higher than that of P25.

Photocatalytic degradation of gaseous toluene over Ag-doping TiO 2 nanotube powder prepared by anodization coupled with impregnation method

In this work, Ag-doping TiO 2 nanotubes were prepared and employed as the photocatalyst for the degradation of toluene. The TiO 2 nanotube powder was produced by the rapid-breakdown potentiostatic anodization of Ti foil in chloride-containing electrolytes, and then doped with Ag through an incipient wetness impregnation method. The samples were characterized by scanning electron microscope, high-resolution transmission electron microscopy, X-ray diffraction, surface photovoltage measurements, X-ray photoelectron spectroscopy and N 2 adsorption. The nanotubular TiO 2 photocatalysts showed an outer diameter of approximately 40 nm, fine mesoporous structure and high specific surface area. The photocatalytic activity of Ag-doping TiO 2 nanotube powder was evaluated through photooxidation of gaseous toluene. The results indicated that the degradation efficiency of toluene could get 98% after 4 h reaction using the Ag-doping TiO 2 nanotubes as the photocatalyst under UV light illumination, which was higher than that of the pure TiO 2 nanotubes, Ag-doping P25 or P25. Benzaldehyde species could be observed during the photocatalytic oxidation monitored by in situ FTIR, and the formed benzaldehyde intermediate during reaction would be partially oxidized into CO 2 and H 2O.

Photocatalytic degradation of gaseous toluene over ZnAl2O4 prepared by different methods: A comparative study

The development of a “green” treatment process for typical indoor pollutants such as toluene is greatly desirable. In this study, ZnAl2O4 nanoparticles were prepared via three different routes, i.e., solvothermal, citrate precursor and hydrothermal methods. Their structural properties were systematically investigated by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), energy-dispersive X-ray spectra (EDX), Brunauer–Emmett–Teller (BET), UV–vis diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The photo-induced charge separation in the samples was demonstrated by surface photovoltage (SPV) measurement. The photocatalytic performances of the ZnAl2O4 samples and nanostructured TiO2 samples were comparatively studied by the degradation of gaseous toluene under UV lamp irradiation in in situ FTIR reactor. The results indicated that the sample synthesized by facile solvothermal method exhibited about 90% photocatalytic efficiency of toluene. The toluene was mineralized into carbon dioxide and water as the major species. The photocatalytic oxidation of gaseous pollutant over UV-illuminated ZnAl2O4 is a promising technique for air purification.

FT-IR study of the photocatalytic degradation of gaseous toluene over UV-irradiated TiO2 microballs: enhanced performance by hydrothermal treatment in alkaline solution

In this study, photocatalysts of TiO2 microballls were obtained via a hydrothermal treating of commercial P25 in alkaline solution, and then characterized with SEM, XRD, BET, DRS and surface photovoltage spectroscopy (SPS) techniques. The photovoltage response of the prepared TiO2 microballs on spectrum features a quantum size effect brought about by the reduced grain size with respect to the precursor. The UV-assisted photodegradation of gaseous toluene over P25 and the prepared TiO2 microballs was monitored by an in situ infrared technique. The results demonstrated that the prepared TiO2 microballs in anatase form were more active than commercial P25 in photocatalytic oxidation of gaseous toluene. The promoted activity of the hydrothermal-treated TiO2 is attributed to the increasing specific surface area and larger band gap induced by the reduced crystallite size.

Microwave Heating Preparation of Ag-modified TiO<SUB>2</SUB> for Photocatalytic Degradation of Gaseous Toluene

Microwave Heating Preparation of Ag-modified TiO<SUB>2</SUB> for Photocatalytic Degradation of Gaseous Toluene

Mechanistic study and mutagenicity assessment of intermediates in photocatalytic degradation of gaseous toluene

Photocatalytic oxidation is a promising technique for the degradation of volatile organic compounds. However, it is necessary to clarify the genotoxicity mutagenic potential of intermediates formed during photocatalytic degradation. A gas–solid TiO 2 thin film reactor was fabricated to degrade toluene under UV irradiation. The results showed that the degradation efficiencies of toluene at a concentration of about 1500 μg L −1 reached almost 100% within 120 min of illumination. The intermediates produced during the photocatalytic degradation were identified by using gas chromatography–mass spectroscopy. Benzene was the only by-product identified in the gas phase, while small amounts of benzaldehyde and benzoic acid were detected at the TiO 2 surface. Species such as benzene and CO 2 should derive from the photo-decarboxylation of benzoic acid, produced by further oxidation of benzaldehyde. Neither the original toluene nor the gaseous intermediates produced at different times presented mutagenic activity to strains TA98 and TA100 in the presence or absence of the S9 mixture at the tested doses by using Ames assay. All of the results indicated that the effluent gas of toluene treated by photocatalysis will not cause mutagenic toxicity to humans or other organisms.