Photodegradation Of Trichloroethylene Research Articles

Photocatalytic coatings with self-cleaning properties for indoor air treatment

In this work we have studied the photocatalytic and self-cleaning properties of TiO2 layers immobilized on polymeric panels, as passive elements for air treatment. In order to achieve easy scale-up technologies for the preparation of coatings, roller-coating technique was selected, comparing the results with those prepared by dip-coating. Composites were characterized by SAXRD, UV–Vis DRS spectroscopy, profilometry, N2 adsorption–desorption, SEM and AFM microscopy. The adherence of the coating was evaluated according the ASTM D3359 standard adhesive tape test. The photocatalytic properties of the materials were evaluated by the photodegradation of trichloroethylene or formaldehyde, as model volatile organic compounds, in the gas phase. The hydrophilic-hydrophobic properties were measured by studying the in-situ variation of the water contact angle with time and UV-A irradiation. Moreover, the self-cleaning properties were analyzed according to ISO 27448:2009 for oleic acid removal. Although coatings of approximately ca. 250 nm layer thickness can be prepared by both techniques, roller-coating allows the material deposition with a coral-like structure in a single and simple step. Surface roughness was promoted by roller process. The developed materials present high photocatalytic performance for the elimination of both model pollutants in the gas phase. Aging tests under outdoor conditions and Scotch tape test show the stability and resistance of the coatings. In-situ irradiation measurements show the superhydrophilic character of the coatings. Water contact angle lower than 10 ° after 300 min of UV-A irradiation was achieved for oleic acid removal. The combination of TiO2 nanoparticles with different crystal structures and sizes improves the photocatalytic performance. A correlation between the ability for pollutants degradation in gas phase and the self-cleaning properties (in-situ or oleic acid measurements) was determined.

A study on photodegradation of trichloroethylene using an optical fiber coated with different photocatalysts

In this research, optical fiber photocatalytic technology was used to treat trichloroethylene (TCE) in simulated groundwater. The study investigated the effects of various conditions on TCE treatment, including the type and modification method of photocatalyst, pH value of the solution, and pollutant concentration on the photocatalytic reaction rate and hydroxyl radical conversion rate (ROH,UV). The objective was to improve the transmission and extension of light energy using the high light-conducting properties of optical fibers. This technique is particularly useful in areas where light transmission is obstructed and can address the issues associated with traditional photocatalytic treatment methods, such as photocatalyst recovery. Soil reaction flasks were used as containers, and a LED as the experimental light source. The coated photocatalysts were analyzed for their basic characteristics using SEM/EDS, UV–Vis DRS, and XRD. In addition, p-chlorobenzoic acid (pCBA) as a hydroxyl radical (･OH) probe for kinetic study and calculation of ROH,UV. The results show that N-doped TiO2 (NT) with the addition of 10 mL NH4OH improved TCE removal efficiency at sampling point A from about 20% to 49.6%, while Ag-doped TiO2 (AT) was increased to 53.8% with the addition of 0.5 g AgNO3. These two dosages had the highest hydroxyl radical generation efficiency compared to other higher dosage conditions. However, excessive dosage can inhibit crystal formation. The study also conducted reaction rates under different pH solution environments, showing that NT had the highest reaction rate (kapp) at pH 7 and AT at pH 10. Overall, this research highlights the potential of optical fiber photocatalytic technology for TCE treatment in groundwater and provides insights into the factors that affect its efficiency.

Photocatalytic performance of highly transparent and mesoporous molybdenum-doped titania films fabricated by templating cellulose nanocrystals

In this paper, the synthesis of mesoporous Mo-doped titania films templated by cellulose nanocrystals (CNCs) and their photocatalytic performance are reported for the first time. The prepared titania composite precursors containing the CNCs and molybdenum chloride were spin-coated on indium tin oxide (ITO) glass substrate, followed by calcining at 400 °C for 1 h. X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), and UV–vis spectrometer were employed to characterize the phase composition, pore structure, morphology, and optical property of the titania films in relation to CNCs templating and Mo doping. Photocatalytic performances of the titania films were also evaluated on the photodegradation of trichloroethylene under a fluorescent light source. The Mo-doped titania films with CNCs templating were highly transparent and mesoporous, exhibiting only anatase phase, high specific surface areas ranging in 135.4 – 149.0 m2/g, and small crystallite sizes of 9.5 – 11.1 nm. The results indicate that Mo ions were successfully doped by substituting for Ti ions in the titania lattice. The Mo doping stabilized the anatase phase and also increased the surface area of the CNCs-templated titania film while decreasing the mean pore width. Notably, the visible light absorption capacity and photocatalytic activity of the CNCs-templated titania films doped with Mo were dramatically greater than those of the pure and the CNCs-templated titania films, which is ascribed to the decreased recombination rate of photoexcited charges and the increased surface area with aids of the CNCs templating and the Mo doping.

Dechlorination and photodegradation of trichloroethylene by Fe/TiO2 nanocomposites in the presence of nickel ions under anoxic conditions

The removal of priority pollutants by nanocomposites has recently received much attention. In the present study, the dechlorination as well as photodegradation of trichloroethylene (TCE) by the combination of nanoscale zerovalent iron (NZVI) with Degussa P-25 TiO2 (Fe/TiO2 nanocomposites) in the presence of nickel ions under anoxic conditions were studied. The Fe/TiO2 nanocomposites were synthesized by a novel and simple method using polyethylene glycol and sodium borohydride as the cross-linker and reducing agent, respectively. Scanning electron microscopy (SEM) images showed that the NZVI was spherical with the average particle size of 60±5nm. Electron-probe microanalysis elemental maps showed that the distribution of Fe and Ti in nanocomposites was uniform. The Fe/TiO2 nanocomposites exhibited excellent ability in dechlorination as well as photodegradation of TCE in the presence of nickel ions. Ethane was found as the major end product of TCE in both dark and photocatalytic reactions, depicting that hydrodechlorination was the major reaction mechanism. In addition, the dechlorination of TCE by Fe/TiO2 nanocomposites followed the pseudo-first-order kinetics and the rate constant (kobs) for TCE dechlorination was (1.3±0.1)×10−2h−1, which was higher than that by NZVI alone ((7.4±0.2)×10−3h−1). The photodegradation efficiency of TCE by Fe/TiO2 nanocomposites was enhanced in the presence of nickel ions under illumination of UV light at 365nm. The kobs for TCE photodegradation increased 6.0–11.6 times when Fe/TiO2 was illuminated with UV light in the presence of nickel ions. A rapid and complete dechlorination of TCE by Fe/TiO2 nanocomposites was observed after 7 cycles of injection in the presence of nickel ions and UV light, indicating the stability of nanocomposites towards TCE dechlorination.

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.

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.

The photodegradation of trichloroethylene with or without the NAPL by UV irradiation in surfactant solutions

The photodegradation of trichloroethene (TCE) with or without nonaqueous phase liquids (NAPL) by ultraviolet irradiation in surfactant solutions was examined in this study. The photodecay of TCE was studied at monochromatic 254 nm UV lamps. The effects of the type of surfactants, initial surfactant concentrations, pH levels and NAPL concentrations were examined to explore the photodecay of TCE. All the photodegradation of TCE followed pseudo-first-order decay kinetics at various conditions. It was found that Brij 35 overdose and higher initial pH levels may retard or inhibit the photodecay of TCE, mainly due to protons, intermediate generation and change of surfactant structure in the processes. The optimal condition for TCE photodecay was suggested based on the analysis of kinetics data, from which the reaction mechanism of TCE in the presence of NAPL form was also studied. In general, the reactions of TCE in micellar solution and NAPL pool can be considered as independent pathways due to the low molecule diffusion between the two phases.

Degradation of trichloroethylene by photocatalysis in an internally circulating slurry bubble column reactor

The effects of initial trichloroethylene (TCE) concentration, recirculating liquid flow rate and gas velocity on photodegradation of TCE have been determined in an internally circulating slurry bubble column reactor (0.15 m-ID × 0.85 m-high). Titanium dioxide (TiO 2) powder was employed as a photocatalyst and the optimum loading of TiO 2 in the present system is found to be approximately 0.2 wt%. The stripping fraction of TCE by air flow increases but photodegradation fraction of TCE decreases with increasing the initial TCE concentration, recirculating liquid flow rate and gas velocity. The average removal efficiency of TCE is found to be approximately 97% in an internally circulating slurry bubble column reactor.

UV Photolysis of Trichloroethylene: Product Study and Kinetic Modeling

Direct UV photolysis of trichloroethylene (TCE) in dilute aqueous solution generated chloride ions as a major end product and several reaction intermediates, such as formic acid, di- and monochloroacetic acids, glyoxylic acid, and, to a lesser extent, mono- and dichloroacetylene, formaldehyde, dichloroacetaldehyde, and oxalic acid. Under prolonged irradiation, these byproducts underwent photolysis, and a high degree of mineralization (approximately 95%) was achieved. TCE decays through the following major pathways: (1) TCE + h nu --> ClCH=C*Cl + Cl*; (2) TCE (H2O) + h nu --> ClCH(OH)-CHCl2; (3) TCE + h nu --> HC[triple bond]CCl + Cl2; (4) TCE + h nu --> ClC[triple bond]CCl + HCl; (5) TCE + Cl* --> Cl2HC-C*Cl2. A kinetic model was developed to simulate the destruction of TCE and the formation and fate of byproducts in aqueous solution under irradiation with polychromatic light. By fitting the experimental data, the quantum yields for the four photolysis steps were predicted as phi(1) = 0.13, phi(2) = 0.1, phi(3) = 0.032, and phi(4) = 0.092, respectively. The reaction mechanism proposed for the photodegradation of TCE accounts for all intermediates that were detected. The agreement between the computed and experimental patterns of TCE and reaction products is satisfactory given the complexity of the reaction mechanism and the lack of photolytic kinetic parameters that are provided in the literature.

Photocatalytic degradation of trichloroethylene (TCE) over TiO 2/silica gel in a circulating fluidized bed (CFB) photoreactor

The effects of the ratio of TiO 2/silica gel, superficial gas velocity ( U g), solid circulation rate ( G s), initial trichloroethylene (TCE) concentration, wavelength of UV light, and concentrations of H 2O and O 2 on photodegradation of TCE over TiO 2/silica gel have been determined in a circulating fluidized bed (CFB) photoreactor. The TCE conversion decreases with wavelength of the UV light, the initial TCE and H 2O concentrations in the CFB reactor. The optimum concentration of O 2 for TCE degradation is found to be approximately 9 vol.% in the CFB photoreactor. The CFB photoreactor is an effective tool for high TCE degradation with efficient utilization of photon energy.

Trichloroethylene degradation by photocatalysis in annular flow and annulus fluidized bed photoreactors

The effects of trichloroethylene (TCE) gas flow rate, relative humidity, TiO 2 film thickness, and UV light intensity on photodegradation of TCE have been determined in an annular flow type photoreactor. Phosgene and dichloroacetyl chloride formation could be controlled as a function of TCE gas flow rate and photodegradation of TCE decreased with increasing relative humidity. The optimum thickness of TiO 2 film was found to be approximately 5 μm and the photocatalytic reaction rate of TCE increased with square root of UV light intensity. In addition, the effects of the initial TCE concentration, phase holdup ratio of gas and solid phases ( ε g/ ε s), CuO loading on the photodegradation of TCE have been determined in an annulus fluidized bed photoreactor. The TCE photodegradation decreased with increasing the initial TCE concentration. The optimum conditions of the phase holdup ratio ( ε g/ ε s) and CuO wt.% for the maximum photodegradation of TCE was found to be 2.1 and 1.1 wt.%, respectively. Therefore, an annulus fluidized bed photoreactor is an effective tool for TCE degradation over TiO 2/silica gel with efficient utilization of photon energy.

Photodegradation of trichloroethylene using nanometre-sized ZnO particles prepared by spray pyrolysis

Photodegradation of trichloroethylene using nanometre-sized ZnO particles prepared by spray pyrolysis

TiO 2 mediated photooxidation of trichloroethylene and toluene dissolved in fluorocarbon solvents

Titanium dioxide mediated photodegradation of trichloroethylene (TCE) and toluene dissolved in a fluorocarbon solvent (Galden® HT110) was demonstrated. The photodegradation of TCE yielded dichloroacetic acid as a major intermediate. The TCE reaction kinetics and high photoefficiency suggest autocatalysis and/or a radical chain reaction mechanism. Photooxidation of toluene is a first-order reaction. Membrane-assisted solvent extraction of TCE from water to the fluorocarbon solvent was demonstrated, and the combination of photooxidation and extraction form the basis for a novel two-stage process for the removal and destruction of organic contaminants from water.

Photocatalytic Oxidation of Chlorinated Organic Compounds Over TiO2Membrane Coated on Glass Tube

Photodegradation of trichloroethylene (TCE), as a model compound of chlorinated organic compounds, was carried out in different reaction conditions of pH, dissolved oxygen, initial concentration an...

Photodegradation of trichloroethylene in microheterogeneous aqueous systems

Hydrogen generated in situ from a water-splitting process was used to reduce trichloroethylene (TCE) to ethane in water. Two hundred and eighty-five μmol of TCE were reduced to less than 8.96 μmol within 12 hours of irradiation in a platinum catalyzed water-photolysis system. Zinc was added to the system to enhance the degradation rate. The degradation of 285 μmol TCE was completed within 2 and 5 hours with 2 and 1 g. of zinc added, respectively. The hydrogen molecule is not an effective reactive reagent for the degradation of TCE. By the addition of a catalyst such as platinum particle, the hydrogen molecule may be transformed into active hydrogen atoms or the metal bonded hydride form. The hydrogen atoms are then able to reduce TCE to hydrocarbons.