Photocatalytic Degradation Of Trichloroethylene Research Articles

Pd@Bi2Ru2O7/BiVO4 Z-Scheme Heterojunction Nanocomposite Photocatalyst for the Degradation of Trichloroethylene.

Photocatalytic degradation of chlorinated persistent organic pollutants is a very challenging process due to the high redox potential of the C-Cl bond that requires wide band gap catalysts that are activated under UV light. Designing a Z-scheme heterojunction between visible light-activated metal oxides with compatible band gaps enables these redox potentials. Herein, we report the design of a pyrochlore/Aurivillius Z-scheme heterojunction to enhance the photocatalytic activity of BiVO4 for the degradation of trichloroethylene. We prepared Bi2Ru2O7/BiVO4 heterostructured photocatalysts by a controlled hydrothermal approach. Upon optimizing the Bi2Ru2O7 ratio to 1.0 wt %, the heterostructured photocatalyst demonstrated enhanced activity in the degradation of trichloroethylene (TCE) under simulated sunlight irradiation compared to bare BiVO4 and Bi2Ru2O7, respectively. Decorating the surface of the catalyst with palladium nanodomains to create the Pd@Bi2Ru2O7/BiVO4 nanocomposite showed a substantial increase in the photocatalytic degradation of TCE. The material characterization indicated that the architecture of the material provides a synergy of enhancing the redox potential of the photocatalyst and improving the charge carrier dynamics. Furthermore, the photoelectrochemical characterization confirmed that the dual heterojunctions in the Pd@Bi2Ru2O7/BiVO4 nanocomposite resulted in improved interfacial charge carrier transfer and enhanced the electron/hole separation efficiency compared to the nonpalladized catalysts. This work provides a promising approach for band gap engineering of visible light photocatalysts for the degradation of halogenated persistent organic pollutants.

In-situ observation of photocatalysis of gaseous trichloroethylene using a fourier transform infrared in the presence of a visible light responding homemade oxynitride doped TiO2 under blue LED and violet LED irradiations

A visible light responding TiO2 photocatalyst was prepared by the hydrolysis of TiCl4 with ammonia. Its structures were characterized to anatase with doping of oxynitride by XRD and XPS followed by drying and heat treatment at 400 °C for 2 h (TiON400). The primary particle size observed by TEM was ~10 nm, and the BET surface area was 320 m2/g. Photocatalytic degradation of trichloroethylene (TCE) over TiON400 under blue light emitting diode (BLED) and violet light emitting diode (VLED) irradiation was tested using a Fourier transform infrared (FTIR) spectrometer. The collected FTIR spectra verified the decrease in TCE concentration and the formation of intermediates such as dichloroacetyl chloride (DCAC) and COCl2 during the photocatalysis of TCE. It is concluded that in-situ FTIR analysis can be a useful and reliable tool to evaluate the photocatalytic performance of materials. A new ISO standard for photocatalysis testing method with FTIR analysis under ultraviolet, visible, or violet irradiation is possible to propose.

Evaluation of the photocatalytic performance of construction materials for urban air depollution

The photocatalytic degradation of trichloroethylene and nitric oxide (model volatile organochloride and inorganic compounds) by two commercial TiO2-based cementitious materials at the laboratory scale was studied. TiO2 P25 was selected as the benchmark photocatalyst. The materials were characterized by N2 adsorption–desorption, TGA, SEM–EDX, and XRD, and the hydrophobic/hydrophilic nature of the cement surface was determined through contact angle measurements. Preliminary photoactivity tests in which a glass plate was covered with photocatalytic material were performed. Moreover, the photocatalytic activities of asphalt plates (approximately 1 cm thick) covered with either of the photoactive cementitious materials were also evaluated. A notable improvement in the photocatalytic activity from the first to the second photocatalytic run was observed because sample conditioning with airflow and UV-A irradiation led to the elimination of species (carbonates) that were adsorbed at active TiO2 sites, ensuring stability under operating conditions. The cementitious samples completely photooxidized the organochloride compound but presented reduced photoefficiency for nitric oxide oxidation. The results obtained when the materials were deposited on glass and asphalt showed the crucial influences of the sample loading and the nature of the substrate on nitric oxide photooxidation. Using TiO2 P25 led to the complete conversion of nitric oxide but also to the formation of a large amount of nitrogen dioxide. On the other hand, one of the photoactive asphalts exhibited a nitric oxide conversion rate of 32%, which was lower than that achieved with pure TiO2-P25, but using this material did not lead to the release of nitrogen dioxide. When tested according to the ISO 22197-1:2007 standard, the selected photocatalytic asphalt removed 29% of the NO and 22% of the NOx under more demanding operating conditions.

Photocatalytic degradation of trichloroethylene over BiOCl under UV irradiation

In this study, BiOCl samples were synthesized under different pH values and characterized by XRD, SEM, UV‐vis DRS, BET, photoelectrochemical measurement and PL. The photocatalytic performances of the as‐prepared samples were evaluated through the decomposition of trichloroethylene (TCE) under UV irradiation. The influences of several parameters such as solution pH and common inorganic anions on TCE removal were investigated. Results indicated that BiOCl‐0.6 exhibited better photocatalytic performance than BiOCl‐6.0 because of its higher migration ability of photo‐induced carrier. The photocatalytic degradation of TCE over BiOCl‐0.6 followed pseudo first‐order kinetics and appeared to be more efficient in acidic solution than in alkaline. TCE was almost completely dechlorinated in 120 minutes. The inhibiting effect of naturally occurring anions was in the order of HCO3‐ >SO42‐ >NO3‐, while Cl‐ exhibited a dual effect. Moreover, BiOCl‐0.6 exhibited superior reusability after three cycles of repetition tests.

Photocatalytic degradation of trichloroethylene on platinum ion-doped TiO2 under visible light irradiation

Porous platinum ion-doped TiO2 (Pt–TiO2) was prepared by a sol–gel method and demonstrated to have superior photocatalytic activity for the photodegradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation from a xenon lamp equipped with 422-nm cut-off filter. Kinetic studies were performed to clarify the effect of the doping amounts, space times, VL intensity, and mole fractions of TCE, O2, and H2O on the degradation of TCE. Under ultraviolet (UV) irradiation, the photocatalytic activity of Pt–TiO2 was the same as that of TiO2, indicating that the doped Pt ion did not act as a recombination center for the photogenerated holes and electrons. Based on the kinetic data and reaction products, we conclude that the photocatalytic degradation of TCE on Pt–TiO2 under VL irradiation proceeds similarly to TiO2 under UV irradiation. We also performed the photocatalytic degradation of TCE at the space time of 7.5 × 107 g s mol−1 in a tubular reactor packed with the Pt–TiO2 pellets which are more suitable than the Pt–TiO2 powder for the practical remediation of the contaminated gas. TCE was completely degraded, i.e. 100% conversion was achieved under VL irradiation but only a small quantity of CO2 was formed with the stoichiometric ratio of [CO2]formed/[TCE]degraded of ca. 0.33. By switching the gas stream containing TCE to humid air, more CO2 was formed, indicating that the dichloroacetates accumulated on the Pt–TiO2 surface are photodegradable to CO2 under VL irradiation.

In-situ synthesis of nanofibers with various ratios of BiOClx/BiOBry/BiOIz for effective trichloroethylene photocatalytic degradation

In this work, BiOClx/BiOBry/BiOIz (x+y+z=1) composite nanofibers were prepared through electrospinning and the sol-gel methods. Photocatalytic degradation of trichloroethylene (TCE) by BiOClx/BiOBry/BiOIz/PAN nanofibers was systematically investigated via gas chromatography (GC). Optimum photocatalytic activity was achieved with BiOCl0.3/BiOBr0.3/BiOI0.4 fibers under solar light irradiation. X-ray photoelectron spectroscopy (XPS) peaks due to CO and CO were observed at 286.0 and 288.3eV, respectively, it indicated that the BiOClx/BiOBry/BiOIz mixture had been successfully doped on the polyacrylonitrile (PAN) fibers. Furthermore, X-ray diffraction (XRD) results also confirmed that we had synthesized the as-prepared composite nanofibers successfully. Photocatalytic activities of BiOCl0.3/BiOBr0.3/BiOI0.4 were up to 3 times higher than the pure BiOCl, BiOBr and BiOI samples, respectively.

Photocatalytic degradation of trichloroethylene in a continuous annular reactor using Cu-doped TiO2 catalysts by sol–gel synthesis

In this work, we present the capability to address sustainability at the molecular level for Green Chemistry. Cu-doped (up 0.5wt%) TiO2 catalysts were prepared by sol–gel, calcined at 500°C supported on quartz tubes, and placed into a continuous annular reactor to degrade a trichloroethylene (TCE)/air mix in moist stream. To understand how the Cu content affects the photocatalytic activity of the modified catalyst, the deposited and calcined washcoat on the quartz materials was characterized. The powder catalysts were also characterized to correlate their properties with their behavior on the quartz tubes and in the tests using a continuous photocatalytic reactor. A Langmuir–Hinshelwood kinetic model that considers two active sites (one for active TCE molecules and the other for active H2O molecules) was fitted to the reaction data. The catalyst doped with 0.2wt% Cu showed the best performance in the degradation tests. Notably, this catalyst differed from the other three with 0, 0.05 and 0.5wt% Cu because it had the lowest Eg and uniform porosity. The activation energy and adsorption thermodynamic property constants demonstrated that 0.2wt% Cu content favored the mobility of both molecules, while 0.5 wt% Cu strongly obstructed the active sites through bonding with water.

Degradation of Trichloroethylene Using Allophane–Titania Nanocomposite Supported on Porous Filter

Abstract The allophane–titania composites were prepared on a macroporous filter. The allophane particles were dispersed in a titania sol, in which the filter was irradiated by ultrasonic waves, and then the resulting deposit on the filter was heated. During the photocatalytic degradation of trichloroethylene, the composite containing a small amount of allophane improved the adsorption ability of the titania and inhibited emission of the intermediate, phosgene. The appropriate UV irradiation intensity also inhibited the phosgene emission due to an effective adsorption–degradation relay.

Photocatalytic degradation of trichloroethylene in aqueous phase using nano-ZNO/Laponite composites

The feasibility of nano-ZnO/Laponite composites (NZLc) as a valid alternative to TiO2 to mineralize trichloroethylene (TCE) without difficulties for recovery of photocatalysts was evaluated. Based on the experimental observations, the removal of TCE using NZLc under UV irradiation was multiple reaction processes (i.e., sorption, photolysis, and photocatalysis). Sorption of TCE was thermodynamically favorable due to the hydrophobic partitioning into crosslinked poly vinyl alcohol, and the adsorption onto high-surface-area mineral surfaces of both ZnO and Laponite. The degradation efficiency of TCE can be significantly improved using NZLc under UV irradiation, indicating that ZnO-mediated heterogeneous photocatalytic degradation occurred. However, the degradation efficiency was found to vary with experimental conditions (e.g., initial concentration of TCE, loading amount of NZLc, the intensity of light and initial solution pH). Although the removal of TCE by NZLc was found to be a complex function of sorption, photolysis, and photocatalysis, the photocatalytic degradation of TCE on the surface of ZnO was critical. Consequently, developed NZLc can be applied as a valid alternative to suspended TiO2 powder, and overcome drawbacks (e.g., filtration and recovery of photocatalysts) in degradation of TCE for various water resources.

Kinetics of photocatalytic degradation of trichloroethylene in aqueous colloidal solutions of TiO2 and WO3 nanoparticles

Abstract Kinetic studies on the photocatalytic degradation of trichloroethylene (TCE) were performed in TiO 2 or WO 3 aqueous sol which consisted of anatase nanocrystalline TiO 2 of ca. 3.9 nm or WO 3 spherical particles of ca. 17.6 nm. Photocatalytic activity of TiO 2 colloid is higher than that of WO 3 by a factor of 2.1. Kinetic analyses for both sols give a similar rate law containing γ value which represents a ratio of the reaction rate of the photogenerated electrons with O 2 against the total disappearance rate of the photogenerated electrons. Reaction temperature did not affect the TiO 2 photocatalysis whereas higher temperature increased the oxidation rate of TCE in the WO 3 sol. Such a difference in the temperature effect was explained in terms of the γ values. The photocatalytic degradation of TCE was enhanced by mixing the WO 3 and the TiO 2 sol and the best performance was obtained by using the mixed sol with WO 3 :TiO 2 molar ratio of 1:2. In the mixed sol, the similar temperature dependence as in the WO 3 sol was obtained. Reaction mechanism and the rate law are proposed to account for the obtained kinetic data.

Degradation of trichloroethylene using highly adsorptive allophane–TiO2 nanocomposite

A highly adsorptive allophane–TiO2 nanocomposite photocatalyst was prepared by dispersing nanoparticles of the natural clay mineral allophane into a titanium alkoxide solution by the sol–gel method. During the photocatalytic degradation of trichloroethylene using the allophane–TiO2 nanocomposite, emission of the intermediate product, phosgene, was drastically inhibited. Trichloroethylene was transformed into the intermediate products, phosgene and dichloroacetyl chloride, on the TiO2 during the UV irradiation. These compounds are rapidly adsorbed on the allophane. The compounds then gradually degraded after diffusing to the TiO2.

Photocatalytic degradation of dichloroacetyl chloride adsorbed on TiO2

Dichloroacetyl chloride (DCAC) attracted our attention as an intermediate product of the photocatalytic degradation of trichloroethylene (TCE). The adsorption and photocatalytic reaction of DCAC on TiO2 have been investigated by FTIR spectroscopy. The influence of the surface structure of several TiO2s on the reaction mechanism was discussed in order to understand the complete degradation mechanism of TCE as well as DCAC. DCAC was transformed into dichloroacetic acid (DCAA) on the relatively hydrophobic TiO2 surface by the small amount of the water molecules weakly adsorbed on the surface. This DCAA was degraded to phosgene, CO2, and CO during UV irradiation. For the hydrophilic TiO2, DCAC was mainly transformed into the dichloroacetate anion. UV irradiation allowed this species to produce chloroform in addition to phosgene, CO2, and CO. It is suggested that DCAC easily reacts with the Ti–OH group on the hydrophilic TiO2 and forms the bidentate titanium chelate of dichloroacetate, which efficiently degrades into chloroform.

Phosgene-Free Photocatalytic Degradation of TCE and PCE Vapors with Au/TiO2

Photocatalytic oxidation of trichloroethylene (TCE) and tetrachloroethylene (PCE) in air had been carried out with TiO2 film alone and Au/TiO2 film. On the TiO2 film TCE and PCE were converted mainly into toxic COCl2, while COCl2 free TEC and PCE oxidation could be achieved with Au/TiO2.

粘土鉱物アロフェン‐酸化チタン複合体光触媒によるトリクロロエチレンの分解特性

Allophane-TiO2 composites as highly adsorptive photocatalysts were prepared by dispersing nanoparticles of the natural clay mineral, allophone, into a titanium alkoxide solution by the sol-gel method. During the photocatalytic degradation of trichloroethylene using the allophane-TiO2 composites, emission of the intermediate product, phosgene, was significantly inhibited. Trichloroethylene was transformed into the intermediate product, phosgene, on the TiO2 during the UV irradiation. This compound was rapidly adsorbed by the allophane. The compounds were gradually degraded after diffusing to the TiO2. Although the degradation rate of the trichloroethylene using the allophane-TiO2 composites was slower than that using TiO2, their activity was improved by heating at 400-500 °C.

In situ XANES studies of TiO 2/Fe 3O 4@C during photocatalytic degradation of trichloroethylene

Mainly anatase and Fe 3O 4 in the magnetic photocatalysts (TiO 2 on Fe 3O 4@C core–shell nanoparticles (TiO 2/Fe 3O 4@C)) are observed by X-ray powder diffraction (XRD) spectroscopy. The Ti K-edge least-square fitted XANES spectra of the TiO 2/Fe 3O 4@C photocatalyst indicate that the main titanium species are nanosize TiO 2 (9 nm) (77%) and bulky TiO 2 (23%). Speciation of titanium in the TiO 2/Fe 3O 4@C during photocatalytic degradation of 100 ppm of trichloroethylene (TCE) has also been studied by in situ X-ray absorption near-edge structural (XANES) spectroscopy. TiO 2 is not perturbed during the course of photocatalysis. However, it is worth to note that during photocatalytic degradation of TCE, about 33% of FeO and 67% of Fe 3O 4 are observed in the photocatalyst. It seems that the carbon layer on the TiO 2/Fe 3O 4@C photocatalysts can reduce the possibility for photoexcited electron–hole recombination as usually found on the relatively narrow bandgap of ferric oxide during photocatalysis.

Photocatalytic degradation of TCE in water using TiO 2 catalyst

Wastewater is generally released untreated into the rivers and streams in developing countries. Industrial wastewater usually contains highly toxic pollutants, cyanides, chlorinated compounds such as trichloroethylene (TCE). Ultraviolet (UV) radiation from sunlight also decomposes organic compounds by oxidation process. However, the process is less effective due to large amount of toxic effluent entering the main stream water. The solar radiation can effectively be applied to accelerate the process by using suitable catalyst for economically cleaning the major fresh water sources. This paper describes photocatalytic degradation of trichloroethylene in aqueous solution using TiO 2. Variable parameters such as initial concentration of TCE, type and concentration of TiO 2 and reaction time are investigated. The powder TiO 2 is found more effective than the sand TiO 2 for decomposing TCE. The effect of sand TiO 2 as photocatalyst is investigated at various water depths. It is observed that up to 45 mm water depth, sand TiO 2 shows photo-degradation of TCE. The degradation rate increases as the concentration of TCE is increased up to 45 μl of TCE per litre of water. Similarly the photocatalytic degradation increases with TiO 2 concentration up to 0.7 g L −1 of solution but then starts decreasing. The optimum values of TiO 2 and TCE concentration obtained are 0.7 g and 35 μl L −1 of the solution, respectively.

Hybrid photocatalysts for the degradation of trichloroethylene in air

Hybrid photocatalysts based on an adsorbent SiMgOx and a photocatalyst TiO 2 were developed in a plate shape. The ceramic surface was coated with TiO 2 by the slip-casting technique. The effect of the support in the photocatalytic degradation of trichloroethylene (TCE) was analyzed by modifying TiO 2 loading and the layer thickness. Photocatalysts were characterised by N 2 adsorption–desorption, mercury intrusion porosimetry, SEM, UV–vis spectroscopy and XRD. A direct relationship between the TiO 2 content and the photocatalytic activity was observed up to three layers of TiO 2 (0.66 wt.%). Our results indicate that intermediate species generated on the TiO 2 layer can migrate through relatively long distances to react with the OH − surface groups of the support. By increasing the TiO 2 loading of the photocatalyst two effects were observed: trichloroethylene conversion is enhanced, while the efficiency of the oxidation process is decreased at expenses of increasing the selectivity to COCl 2 and dichloroacetylchloride (DCAC). The results are discussed in terms of the layer thickness, TiO 2 amount, TCE conversion and CO 2, and COCl 2 selectivity.

Photocatalytic degradation of trichloroethylene using N-doped TiO2 prepared by a simple sol–gel process

Visible-light-driven N-doped TiO2 was prepared by a simple sol–gel process using nitric acid not only as the acid catalyst of the sol–gel reaction but also as the source of nitrogen. The photocatalytic performance of the N-doped TiO2 was investigated by using FTIR spectroscopy to monitor the degradation of trichloroethylene (TCE) during UV and visible irradiation. The photocatalytic degradation of TCE was well-reproduced several times. The activity of Ti–O–N species was supported experimentally. The N-doped TiO2 was found to be responsive to visible light and was stable during repeated runs and maintained the nitrogen species and its activity for at least four months.

Influence of Catalyst Properties and Reactor Configuration on the Photocatalytic Degradation of Trichloroethylene Under Sunlight Irradiation

In this work, the influence of the reactor configuration and the characteristics of the catalysts on the photodegradation of trichloroethylene (TCE) vapors are studied under sunlight illumination. The photocatalytic activity tests were carried out using two types of continuous flow reactors: (i) a compound parabolic collector (CPC) and (ii) a simple flat reactor. Three different photocatalysts based on TiO2 were utilized: (i) commercial powders calcined at 500°C (ii) a TiO2−xNx sample synthesized by treating the commercial sample at 500°C in an NH3 gas flow, and (iii) TiO2 thin film coatings on differently shaped borosilicate glass supports prepared by a sol-gel procedure. The obtained data reveal that the photonic efficiency for the removal of TCE is quite high but slightly decreases with increasing the light intensity. The commercial TiO2 sample presents the highest efficiency while nitrogen doping seems to be slightly detrimental for photoactivity, despite the fact that certain photoresponse in the visible can be envisaged. In contrast, transparent sol-gel TiO2 coatings present the highest TCE degradation rate per mass of catalyst. Regarding the type of reactor, it is found that the use of CPCs can be advantageous, especially when dealing with high volumes of effluent and elevated concentration of TCE, although flat reactor also shows a considerable efficiency.

On the Preparation of TiO2−Sepiolite Hybrid Materials for the Photocatalytic Degradation of TCE: Influence of TiO2 Distribution in the Mineralization

Hybrid structured photocatalysts based on sepiolite, an adsorbent, and TiO2 were prepared by extrusion of ceramic dough and conformed as plates. The influence of the photocatalyst configuration was studied either by including TiO2 in the extrusion process (incorporated materials) or by coating the sepiolite plates with a TiO2 film (coated materials). The influence of the OH- surface concentration in the photocatalytic performance was studied by treating the ceramic plates at different temperatures. The samples were characterized by N2 adsorption-desorption, MIP, SEM, XRD, and UV-vis-NIR spectroscopy and tested in the photocatalytic degradation of trichloroethylene (TCE) as a target VOC molecule. Most of the catalysts presented high photoactivity, but considerable differences were observed when the CO2 selectivity was analyzed. The results demonstrate that there is a significant effect of the catalyst configuration on the selectivity of the process. An intimate contact between the sepiolite fibers and TiO2 particles for incorporated materials with a corncob-like structure favored the migration of nondesirable reaction products such as COCl2 and dichloroacetyl chloride (DCAC) to the adsorbent, reacting with OH- groups of the adsorbent and favoring the TCE mimeralization.