Photocatalytic decomposition of gaseous acetone using TiO2 and Pt/TiO2 catalysts

Metallic platinum was photodeposited on TiO₂ particles, and morphological characteristics of the Pt/TiO₂ catalyst were determined. The dispersion of metallic platinum was uniform and did not alter the morphology of the TiO₂ particles. However, absorbance of the Pt/TiO₂ catalyst for light with wavelength more than 400 nm was significantly improved by the addition of metallic platinum. Gaseous acetone was decomposed in an annular photoreactor coated with TiO₂ or Pt/TiO₂ catalysts using a UV or a fluorescent lamp as light source. The decomposition of acetone with the application of a UV lamp was obviously enhanced for experiments conducted with Pt/TiO₂ catalyst. Decomposition of acetone was promoted considerably with increasing oxygen concentration for experiments conducted with oxygen less than 50,000 ppmv, yet the decomposition of acetone was kept relatively constant for experiments conducted with oxygen above 50,000 ppmv. On the basis of the mass balance for carbon species, the amount of organic intermediates formed for experiments conducted under various conditions was found to be minimal. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 209–216, 2008     

Photocatalytic oxidation of gaseous trichloroethylene by UV/TiO2 process

Summary The objective of this study was to investigate the reaction behavior of the photocatalytic oxidation of gaseous trichloroethylene (TCE) using titanium dioxide at room temperature. The experiments were carried out under various humidity levels and oxygen contents of carrier gas in an annular photoreactor. Experimental results indicated that the factors affecting the photocatalysis of TCE by UV/TiO₂ process are carrier gases and humidity. It was found that increasing the relative humidity in inlet gas flow under low humidity could improve the decomposition of trichloroethylene and the mineralization of organic intermediates at an irradiation UV light intensity of 2.82 W m^-2 by UV/TiO₂ process. The photocatalytic kinetics of gaseous trichloroethylene can be described by the Langmuir-Hinshelwood rate equation.     

Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel

Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO₂ problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO₂ was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers, was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO₂ photocatalyst was used under a light intensity of 10 W/cm². When mixed oxide, TiO₂–SiO₂, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO₂–SiO₂ photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight, its photoactivity was significantly enhanced. Finally, CO₂ photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed.     

Decomposition of Toluene and Acetone in Packed Dielectric Barrier Discharge Reactors

The influences of TiO₂ catalytic material and glass pellet packing on the decomposition efficiency of toluene and acetone in air by dielectric barrier discharge (DBD) reactors were experimentally investigated in this study. The effects of both packing materials on the formation of byproducts such as CO and CO₂ were also evaluated. Experimental results indicate that the introduction of glass materials into the plasma zone of a wire-tube reactor would improve the decomposition efficiency of toluene and acetone compared to a nonpacked reactor. The apparent decomposition rate constant of a glass packed-bed reactor was 4.5–4.8 times greater than that of a nonpacked reactor. The results also indicate that the decomposition rate constant of toluene was approximately 2.6 times higher than that of acetone no matter which type reactor was utilized. The application of TiO₂ coated pellets in DBD reactors will enforce the hydrocarbon byproducts to further be oxidized to CO₂, notwithstanding, it will not significantly improve the performance of the reactors in the decomposition of toluene and acetone, and in the formation of CO. The results show that the best selectivity of CO₂ for acetone decomposition in a TiO₂ coated pellets packed-bed reactor was approximately 40% higher than that in a glass packed-bed reactor.     

Photodegradation of EDTA using Fenton’s reagent: a pilot-scale study

The presence of ethylenediaminetetraacetic acid (EDTA) in decontamination wastes can cause complexation of cations resulting in interferences in their removal by various treatment processes, for example chemical precipitation, ion exchange, etc., and can negatively affect the quality of the final form of the waste. Advanced oxidation processes using ozone, H₂O₂, ultrasonics (US), ultraviolet (UV) light, Fenton’s reagent (Fe(II) + H₂O₂), alone or in combination, are regarded as possible methods of clean and ecologically safe remedial treatment for the degradation of organics. In this study, the development of a column photoreactor (15 L) and a shallow-tank photoreactor (100 L) was carried out at the Centralised Waste Management Facility, Kalpakkam, India. Pilot-scale (batch) studies of the photocatalytic degradation of EDTA (20,000 mg/L) using UV + Fenton’s reagent in these reactor geometries were attempted. The effect of the power of the UV radiation on the kinetics of photodegradation of EDTA (20,000 mg/L) was studied using the column photoreactor. The shallow-tank reactor was used to study the photodegradation of EDTA (20,000 mg/L) using UV radiation, visible radiation, and sunlight. The successful use of sunlight as a source of energy and its greater effectiveness than UV radiation in the treatment of EDTA are presented.     

Abatement of volatile organic compounds using an annular photocatalytic reactor: Study of gaseous acetone

Photocatalytic oxidation of organic compounds in gas phase appears to be a promising process for remediation of polluted air. In the present work, the photocatalytic degradation of acetone, which is a typical pollutant of indoor air, was investigated by using an annular photoreactor. After a modelling by a cascade of elementary continuously stirred tank reactor, the annular photoreactor was assimilated to a plug flow reactor (PFR). No transfer limitation (external and internal) has been demonstrated for this reactor with the fibreglass photocatalytic support. The influence of several kinetic parameters has been studied such as pollutant concentration, incident light irradiance, contact time and humidity content. The Langmuir–Hinshelwood model has been verified for acetone. It can be noticed that no by-products have been detected by FID suggesting almost total mineralization. The possible minor gaseous by-products have been accumulated into a mixture of ethanol–liquid nitrogen at −50 °C then a sample of it has been injected into a GC/MS for analysis. A mechanistic pathway is then proposed for the photocatalytic degradation of acetone.     

Novel photoreactors for heterogeneous photocatalytic wastewater treatment

Heterogeneous photocatalysis is an effective treatment method for removal of toxic pollutants from industrial wastewaters. A novel, thin film slurry photoreactor was evaluated in this work for its effectiveness in removing phenol. The efficiency of parameters, initial phenol and catalyst concentrations and the light intensity on phenol removal was studied. The reactor performed well giving near complete removal of phenol even at a higher concentration of 500 mg/l.     

Glutamate production from CO2 by Marine CyanobacteriumSynechococcus sp.

A photobioreactor was constructed in the form of a Perspex column 900 mm tall with an internal diameter of 70 mm. The reactor volume was 1.8 L and the light source consisted of a metal-halide lamp to reproduce sunlight. Light was distributed through the culture using a new type of optical fiber that diffuses light out through its surface, perpendicular to the fiber axis. A cluster of 661 light-diffusing optical fibers (LDOFs) pass from the light source through the reactor column (60-cm culture depth) and are connected to a mirror at the top of the reactor. This biosolar reactor has been used for the production of glutamate from CO₂ by the marine cyanobacterium Synechococcus sp. NKBG040607. We present here details of the construction of the biosolar reactor and characterization of its properties. The effect of light intensity on glutamate production was measured. Carbon dioxide-to-glutamate conversion ratios were determined at different cell densities: the maximum conversion ratio (28%) was achieved at a cell density of 3x10⁸ cells/mL. A comparison of glutamate production using the LDOF biosolar reactor described here with production by batch culture using free or immobilized cells showed that use of an optical-fiber biosolar reactor increased glutamate-production efficiency 6.75-fold. We conclude that as a result of its high surface-to-volume ratio (692/m) increased photoproduction of useful compounds may be achieved. Such a system is generally applicable to all aspects of photobiotechnology.     

Methodology for studying oxidation of organic species in solution

A photoreactor was developed to study products of photochemical oxidation in a wide range of organic compounds. Analysis of the products from the reactor were used to determine the extent of mineralization of the organic material, to characterize any intermediate compounds formed, and to obtain information on the decomposition mechanism. Appropriate methods for separation and characterization include LC, UV spectrophotometry, gas chromatography/mass spectrometry, total organic carbon, and total inorganic carbon. The uses of the reactor are described for the photocatalytic decomposition of phenol and of its major decomposition intermediates 1,2- and 1,4-dihydroxybenzene.     

Scaling Up of a Photoreactor for Formic Acid Degradation Employing Hydrogen Peroxide and UV Radiation

A model for scaling up a homogeneous photoreactor was developed and experimentally verified in a pilot‐plant‐size apparatus. The procedure is exemplified by the oxidation of dilute aqueous HCOOH solutions with UV radiation (254 nm) and H₂O₂. First, the kinetic model and the kinetic parameters of the HCOOH degradation were obtained in a well‐stirred, small, batch flat‐plate photoreactor (volume=70 ml). The method employed in the analysis of the experimental results yielded reaction‐rate expressions for HCOOH and H₂O₂ that were independent of the reactor configuration. These kinetic equations and the corresponding kinetic constants were then used in a mathematical, fully deterministic model of a continuous‐flow, 2‐m‐long, annular reactor (0.0065 m² of cross section for flow) operating in a laminar‐flow regime to predict exit concentrations of HCOOH. Irradiation was provided in both cases by two different types of germicidal lamps. No additional experiments were made to adjust the reactor‐model parameters. Theoretical predictions from the representation of the reactor performance obtained were compared with experimental data furnished by experiments in the much‐larger‐size, cylindrical‐flow reactor. Results showed good agreement for the range of variables explored; they corresponded to expected operating conditions in water streams polluted with low concentrations of organic compounds.     

Acceleration of Acetone Destruction Process under Synergistic Action of Photocatalytic Oxidation and Barrier Discharge

Separate and joint work of photocatalytic oxidation based on TiO₂ and surface barrier discharge as a source of active oxygen and UV radiation is investigated for acetone vapors destruction under ambient air conditions. Experiments were carried out in a 404 l airtight Plexiglas chamber and used five different combinations of photocatalyst, barrier discharge and ultraviolet irradiation under identical initial concentration (∼170 ppm) of acetone. It is shown for the synergistic action of photocatalytic method and barrier discharge that the initial rate of acetone decomposition per watt of input power increases in more than 1.5 times compared to photocatalytic oxidation. Under operation of plasma of barrier discharge, intermediate products are formed such as CO, acetic acid, acetaldehyde and methane nitrate (CH₃NO₃). These products are not detected for photocatalytic oxidation. Some interesting features of kinetics of acetone decomposition and formation of intermediate products with participation of barrier discharge are revealed.     

UV/H2O2工艺湿法脱除燃煤烟气中NO的研究

在自行设计的内置紫外光-鼓泡器中，利用UV/H₂O₂高级氧化工艺湿法脱除燃煤烟气中的NO气体。主要对紫外光强度、H₂O₂初始浓度、NO初始浓度以及烟气总流量对NO脱除效率的影响进行了考察。研究结果表明，在实验范围内，NO脱除效率随着紫外光强度和H₂O₂初始浓度的增加而增加，但当达到一定值后，NO脱除效率的增加幅度均变得相对平缓；NO脱除效率随着NO初始浓度以及烟气总流量的增加呈近似线性减小。通过离子色谱对液相离子产物进行了定性与定量检测，并对NO中的氮元素进行了物料平衡计算，在此基础上对NO脱除路径与产物形态进行了理论分析。
     

Study on the Relationship between the Emission of Chlorine and UV/VIS Sensitive Organic Matter from Heating MSWI Baghouse Ash: Using an Optical UV/VIS Spectrometer as the On‐Line Monitoring Sensor

In this study the baghouse ash (fly ash) from municipal solid waste incineration (MSWI) plants was heated in a fixed bed reactor, from 25 °C to 800 °C. An optical fiber UV/VIS spectrometer was employed as the real‐time monitor to probe the emission behaviors of organic compounds. A two‐dimensional (2D) correlation technique was used to specify organic matter existing in exhausted gas. Three adsorbents, including water, acetone and cyclohexane, were used to adsorb the organic and molecular chlorine in the gas emitted from the reactor. Concentrations of molecular chlorine (Cl₂), total organic carbon (TOC), and total inorganic carbon (TIC) in these adsorbents were analyzed to evaluate the reactions occurring in fly ash. We have found that generation temperatures of molecular chlorine were found mainly at 200 °C and 750 °C, which are attributed to the dechlorination of chlorinated‐organic compounds and vaporization of heavy metal chlorides, respectively. 2D correlation UV/VIS spectra are useful to extract valuable information from the one‐dimensional UV/VIS of emitted gas. The identified organic species would be diethyl‐amine, dibenzo‐p‐dioxin, thioxanthone, 1,4‐dichloro‐anthraquinone, benzene, 1‐naphthalene azo, azulene, dibenzanthrone, 1‐chloro‐4‐notroso‐benzene and 4‐nitro‐toluene. The emission behaviors of dibenzo‐p‐dioxin, thioxanthone, azulene and dibenzanthrone were reported, and we concluded that the chlorine emission is almost always earlier than the release of these UV/VIS‐sensitive organic compounds.     

Combinatıon of a Box-Behnken design technique with response surface methodology for optimization of the photocatalytic mineralization of C.I. Basic Red 46 dye from aqueous solution

The photodegradation of an industrial azo dye C.I Basic Red 46 was examined in a fixed-bed photoreactor using UV-lamps simulated to the solar irradiation. In our photodecolorization study, the UV/TiO₂ process was optimized using the Box-Behnken approach to evaluate the synergistic effects of three independent parameters (initial concentration of the dye, flow rate, and UV intensity) on mineralization effectiveness. The response surface methodology was in good promise with the prediction model (coefficients of determination of decolorization and mineralization were R²_Dec = 0.997 and R²_TOC = 0.994, respectively). The effects of the factors could be estimated from a second–order polynomial equation and student’s t-test. The optimal parameters of decolorization and mineralization were as follows: initial concentration of colorant 25 mg L⁻¹, rate of fluid flow 0.3 L min⁻¹, and ultraviolet light intensity 38.1 W m⁻². The decolorization and mineralization removal efficiency under these optimal conditions were 100% and 57.63% respectively. These results indicate that optimization using response surface methodology, based on the Box-Behnken approach, is an excellent tool for determining the optimal conditions, and the process can be easily extrapolated for a specific treatment of real waste water containing the azo dye C.I Basic Red 46. Also, the intermediates that were produced during photodegradation process of Basic Red 46 were determined by GC/MS.     

Photocatalytic degradation of 4-chlorophenol: A mechanistically-based model

The photocatalytic degradation of 4-CP was mathematically modelled using the mechanistic insights and data presented in an earlier study [1]. The solution and surface concentrations of reacting species were calculated by solving a system of differential equations that account for oxidation reactions of dissolved and adsorbed species, adsorption and desorption, reduction of oxygen, and hole-electron recombination. The differential equations were integrated over discrete time-periods and annular regions of the photoreactor. The resulting model predicts the trends observed in studies in other laboratories using different experimental apparati. Using the model it is possible to predict effects of reactor geometry, TiO₂ loading, light intensity, and mixing on the course of TiO₂ photocatalytic oxidation. The model verifies the importance of surface reactions, and reveals the need to better understand the fate and role of oxygen in TiO₂ photocatalytic systems.     

Photochemistry in Photonic Crystal Fiber Nanoreactors

We report the use of a liquid‐filled hollow‐core photonic crystal fiber (PCF) as a highly controlled photochemical reactor. Hollow‐core PCFs have several major advantages over conventional sample cells: the sample volume per optical path length is very small (2.8 nL cm^?1 in the fiber used), long optical path lengths are possible as a result of very low intrinsic waveguide loss, and furthermore the light travels in a diffractionless single mode with a constant transverse intensity profile. As a proof of principle, the (very low) quantum yield of the photochemical conversion of vitamin B₁₂, cyanocobalamin (CNCbl) to hydroxocobalamin ([H₂OCbl]⁺) in aqueous solution was measured for several pH values from 2.5 to 7.5. The dynamics of the actively induced reaction were monitored in real‐time by broadband absorption spectroscopy. The PCF nanoreactor required ten thousand times less sample volume compared to conventional techniques. Furthermore, the enhanced sensitivity and optical pump intensity implied that even systems with very small quantum yields can be measured very quickly—in our experiments one thousand times faster than in a conventional cuvette.     

Hydrogen Production by Decomposition of Light Paraffins over Ni/Ca/Carbon Catalysts in the Absence or Presence of Impurities

The decomposition of light paraffins was investigated using a Ni/Ca/carbon-based catalyst and an Ag-Pd membrane-type reactor (PMR). The use of this combined system resulted in the formation of smaller amounts of methane (<10% yield) than in fixed-bed reactor systems (10–50% yield). The initial activity of CH₄ decomposition seems to be little affected by these impurities such as NO, SO₂, CO₂, and H₂O. The activity in the presence of SO₂, however, was found to be completely lost after 250 min. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photooxidative treatment of sulfurous water for its potabilization

The feasibility of potabilization of sulfurous water was investigated by photochemical oxidation processes using a batch photoreactor and a continuous-flow photoreactor, equipped with UV lamps of 1000 W and 1500 W, respectively. Additionally, two advanced processes of oxidation were applied i.e. with a use of a UV light/H2O2/air and UV light/H2O2/O3/air. These two processes were compared for their efficiency to the direct oxidation process where ozone is used in the absence of UV light. Results obtained for both advanced processes showed better oxidation than takes place by ozone in the absence of UV light. After the photooxidation processes, different processes for the absorption or precipitation of sulfates were investigated to comply with the World Health Organization (WHO) norm that demands a limit of < or =250 mg L(-1) of SO4(2-) in drinking water. Additionally, reverse osmosis was simulated using Osmonics Inc. software to predict the feasibility of lowering the salt concentration below WHO limits.     

Acrylate nanolatex via self‐initiated photopolymerization

The use of UV light to initiate emulsion polymerization processes is generally overlooked, whilst extensive literature exists on photocuring of monomer films. In this study, the unique potential of UV light to produce at ambient temperature polyacrylate latexes without initiator was exploited. Although radical initiators are utilized at low concentration, their cost, toxicity, and odor provide incentives for finding alternatives. Starting with concentrated (30 wt %) and low scattering acrylate miniemulsions (droplet diameter <100 nm), it was demonstrated that acrylate self‐initiation can promote an efficient and fast photopolymerization in micrometer‐scale reactor (spectrophotometric cell) and lab‐scale photoreactor. Herein, all kinetic, colloidal, and mechanistic aspects involved in the self‐initiation of acrylate miniemulsion were extensively examined to provide a complete picture. In particular, the effects of droplet size, initiating wavelength, optical path, and irradiance on the course of the polymerization were thoroughly discussed. A diradical self‐initiation pathway is the most likely mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1843–1853     

Characterization of an LED based photoreactor to degrade 4-chlorophenol in an aqueous medium using coumarin (C-343) sensitized TiO2

A detailed performance evaluation of a simple high intensity LED based photoreactor exploiting a narrow wavelength range of the LED to match the spectrum of a dye in a photocatalysis system is reported. A dye sensitized (coumarin-343, lambda max = 446 nm) TiO 2 photocatalyst was used for the degradation of 4-chlorophenol (4-CP) in an aqueous medium using the 436 nm LED based photoreactor. The LED reactor performed competitively with a conventional multilamp reactor and sunlight in the degradation of 4-CP. Light intensities entering the reaction vessel were measured by conventional ferrioxalate actinometry. The results can be fitted by approximate first order kinetic behavior in this system. Hydroxyl radicals were detected by spin trapping EPR, and effects of OH radical quenchers on kinetics suggest that the reaction is initiated by these radicals or their equivalents. LEDs operating at competitive intensities offer a number of advantages to the photochemist or the environmental engineer via long life, efficient current to light conversion, narrow bandwidth, forward directed output, and direct current power for remote operation. Matching light source spectrum to chromophore is a key.