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Applied Catalysis B, Environmental (v.94, #3-4)
TiO2 photocatalyst for indoor air remediation: Influence of crystallinity, crystal phase, and UV radiation intensity on trichloroethylene degradation by Valeria Puddu; Hyeok Choi; Dionysios D. Dionysiou; Gianluca Li Puma (pp. 211-218).
Nanocrystalline TiO2 photocatalysts prepared through a simple sol–gel process followed by calcination at 100–800°C were evaluated for the decomposition of trichloroethylene (TCE) in simulated indoor air. Catalysts made of pure anatase, anatase/rutile mixture and pure rutile with crystal sizes of 5.8–75.8nm and surface areas of 4.3–498m2/g were immobilized as thick films on borosilicate glass and installed in a gas-phase, flat-plate photocatalytic reactor. Pure anatase TiO2 treated at 300–600°C exhibited higher activity than commercial TiO2 (P-25) under UV-A radiation with intensity of 5.1, 14.0 and 20.8W/m2. Conversely, pure rutile and mixed phase TiO2 materials showed significantly lower activity. The photocatalytic activity of fully grown anatase TiO2 with crystal size of 27nm was up to three-fold higher than that of P-25 despite exhibiting lower surface area. The increase in the crystallinity of anatase TiO2 upon calcination overcame the depreciation in its structural properties (decrease in surface area and porosity) for the decomposition of TCE. The dependence of the TCE oxidation rate on the intensity of the incident radiation in the range 5.2–20.8W/m2 was found to be first-order for the samples containing a rutile phase (including P-25) and 0.75-order for the sample containing pure anatase suggesting that “absorbed” photons are more effectively used when a rutile phase is present. However, less number of incident photons are absorbed by samples with pure rutile compared to samples with pure anatase. The crystallographic properties of TiO2 over its structural properties were found to be essential factors which determined the higher photocatalytic activity of TiO2 anatase for the photocatalytic decomposition of TCE. Rate equations for the photocatalytic oxidation of TCE over TiO2 films derived from an elementary reaction mechanism and with explicit effect of the incident photon flux were correlated with the catalyst properties.
Keywords: Indoor air treatment; Titanium dioxide; Photocatalysis; Trichloroethylene; Degussa P-25; Crystal phase; Anatase; Rutile; UV radiation intensity
FTIR spectroscopy study of the reduction of carbon dioxide on lead electrode in aqueous medium by B. Innocent; D. Pasquier; F. Ropital; F. Hahn; J.-M. Léger; K.B. Kokoh (pp. 219-224).
The electrochemical reduction of carbon dioxide at a lead electrode was studied in alkaline aqueous medium. Chronoamperometry experiments combined with in situ reflectance spectroscopic measurements were performed after bubbling CO2 in an alkaline solution up to a pH value of 8.6. Combining information from E–pH diagram which provided the predominant species in the bulk solution and the adsorbed species determined spectroscopically, the results showed the only synthesis of formate from the electroreduction of hydrogenocarbonate. The identification of the different electroactive species allowed a reaction mechanism to be proposed for the transformation of hydrogenocarbonate into formate on the lead cathode.
Keywords: Pb electrode; CO; 2; reduction; In situ; IR reflectance spectroscopy; Hydrogenocarbonate; Formate
Flow calorimetry and adsorption study of dibenzothiophene, quinoline and naphthalene over modified Y zeolites by J. Keir Thomas; Kamalakar Gunda; Peter Rehbein; Flora T.T. Ng (pp. 225-233).
The adsorptive removal of dibenzothiophene (DBT), quinoline and naphthalene in hexadecane on the zeolites, NaY, NiY and CsY, using liquid phase flow calorimetry and adsorption experiments, was studied at 30°C. NiY and CsY were prepared by the liquid phase ion-exchange method. The adsorbents were characterized by XRD, BET surface area, elemental analysis (ICP-OES) and DRIFT spectroscopic techniques. The adsorption experiments were carried out by equilibrium adsorption and flow calorimetry techniques. Modification of NaY zeolite with Ni and Cs salts resulted in the partial amorphotization of the zeolite structure which affected the adsorption properties. A higher heat of adsorption was determined for quinoline compared to DBT and naphthalene and a preferential adsorption of quinoline in a mixture containing quinoline, naphthalene and DBT was observed on NaY, NiY and CsY. The adsorption of quinoline on NiY possibly involved a direct end-on σ interaction of the Ni2+ with the lone pair of electrons of the N atom on quinoline while the adsorption of DBT and naphthalene occurs via a π interaction of the d orbitals of Ni2+ with the electrons in the aromatic rings. The equilibrium adsorption capacity of NaY was found to be the highest among the three zeolites. The decrease in the adsorption capacities of NiY and CsY appears to result mainly from the partial collapse of the zeolite structure during the ion-exchange process.
Keywords: Desulfurization; Adsorption capacity; Modified zeolites; Flow calorimetry; Heat of adsorption; Quinoline; Dibenzothiophene; Naphthalene
Preparation and photodegradation activity of high aspect ratio rutile TiO2 single crystal nanorods by Chunrong Xiong; Xiangyun Deng; Jianbao Li (pp. 234-240).
Well faceted TiO2 nanorods with a regular geometric configuration were hydrothermally prepared by chemical modification of TiCl4 by ethylene glycol to slow down the reactivity of the precursor toward water. XRD patterns revealed that the as made products were pure rutile. The nanorods were highly crystalline and had an elongated prismatic shape. They grew in the [001] direction and have an aspect ratio of ∼45. The rod size can also be tailored via recipe modification. Ag loaded TiO2 was achieved upon exposure of the rutile nanorods to UV light in AgNO3 aqueous solution. The photocatalytic activities of the pure and Ag loaded TiO2 nanorods were evaluated by the photodegradation of phenol and methylene green (MG).
Keywords: Rutile TiO; 2; High aspect ratio; Well faceted; Single crystal nanorods
Facile preparation of high performance visible light sensitive photo-catalysts by Hyeong Jin Yun; Hyunjoo Lee; Ji Bong Joo; Nam Dong Kim; Mi Yeong Kang; Jongheop Yi (pp. 241-247).
Since the conversion of solar energy to electric or chemical forms is essential for achieving a sustainable society, the development of novel photo-catalytic materials is a subject of considerable interest. Here we report on the facile synthesis of a visible light sensitive photo-catalyst by doping a large amount of carbon into TiO2 nanoparticles. The findings show that carbon is clearly incorporated into the TiO2 framework, as evidenced by TPO, XANES, and EXAFS. The photo-catalytic activity of the carbon-doped TiO2 is increased by more than 4 times, compared to commercial TiO2 P25 for the degradation of phenol under irradiation by white light. Additionally, we observed for the first time that the carbon-doped TiO2 shows catalytic activity under irradiation by visible light at wavelengths longer than 600nm. The synthetic method developed in this study is very simple, and doping level of carbon can be easily controlled by changing the synthetic conditions used.
Keywords: Carbon doping; TiO; 2; Nanoparticle; Visible light; Photo-catalyst
Dependence of photocatalytic activities upon the structures of Au/Pd bimetallic nanoparticles immobilized on TiO2 surface by Yoshiteru Mizukoshi; Kazuhisa Sato; Toyohiko J. Konno; Naoya Masahashi (pp. 248-253).
Bimetallic nanoparticles with a Au-core/Pd-shell structure were prepared and successfully immobilized on a TiO2 surface using sonochemical method. When immobilizing the core/shell structured bimetallic nanoparticles with a Au/Pd molar ratio of 25/75, TiO2 showed the highest activity for the photochemical H2 evolution from ethanol aqueous solution. The activities of other two types of photocatalysts with the same Au/Pd molar ratio, TiO2 immobilizing the mixture of Au and Pd monometallic nanoparticle, and TiO2 immobilizing Au/Pd random alloy nanoparticles wherein Au and Pd atoms homogeneously located, were also evaluated. The dependence of the photocatalytic activities on the nanostructures of the immobilized bimetals was confirmed.
Keywords: Photocatalyst; Promotional effect; Sonochemistry; Nanostructure
Low temperature H2-SCR over platinum catalysts supported on Ti-containing MCM-41 by Landong Li; Peng Wu; Qing Yu; Guangjun Wu; Naijia Guan (pp. 254-262).
A series of Ti-containing MCM-41 were prepared by isomorphously substitution, wet impregnation and mechanical mixing. Ti-containing MCM-41 materials, together with reference Si–MCM-41, were characterized by means of XRD, TEM and low temperature N2 adsorption/desorption. The nature of Ti species on Ti-containing MCM-41 was analyzed by means of UV–vis and Raman spectroscopy. Pt catalysts supported on Si–MCM-41 and Ti-containing MCM-41 were studied for the selective catalytic reduction of NO by hydrogen in excess oxygen. Particular attention was paid to the promotion effect of different Ti species on the catalytic activity for H2-SCR and the origin thereof. Pt/Ti–MCM-41 prepared by wet impregnation with the Ti/Si ratio of 0.6 exhibited the best activity and ca. 89% NOx conversion as well as ca. 79% N2 selectivity, could be achieved at 140°C with a feed stream containing 1000ppm NO, 5000ppm H2, 6.7% O2 at a high GHSV of 80,000h−1. Moreover, Pt–Ti–MCM-41 exhibited good duration and good tolerance to co-existing 20ppm SO2 or 50ppm CO, which demonstrated its potential for future applications.
Keywords: NO selective reduction; Hydrogen; Pt; Ti–MCM-41
Unpredictable photocatalytic ability of H2-reduced rutile-TiO2 xerogel in the degradation of dye-pollutants under UV and visible light irradiation by Carlos A. Páez; Dirk Poelman; Jean-Paul Pirard; Benoît Heinrichs (pp. 263-271).
A series of H2-reduced TiO2 xerogels of low specific surface area was prepared by the sol–gel process. The gels were dried, calcined in air at various temperatures (400, 500, 700°C) and then reduced at 400°C under hydrogen flow (H2-HTR treatment). The materials were characterized by X-ray diffraction, transmission electron microscopy (TEM) and UV/Visible diffuse reflectance spectroscopy, and their texture was determined by nitrogen adsorption–desorption. IR spectroscopy was used to study to what extent samples were reduced. The effects of the calcination/H2-HTR treatments on the adsorption of methylene blue (MB) in aqueous solution and on the photocatalytic degradation of MB and crystal violet (CV) under UV and visible light irradiation were also evaluated. Results showed predictable modifications in the physicochemical properties caused by the annealing of TiO2 xerogel at high temperature (700°C), such as a total anatase-to-rutile phase transition and a considerable loss of specific surface area from 260 to 2m2g−1. However, the higher degree of reduction exhibited by the rutile-TiO2 lattice led to unpredictable photocatalytic activity for the dye conversion under UV and visible light irradiation. The loss of specific surface area of the rutile-TiO2 sample was compensated by the increase in the affinity of this sample for the dye. Under UV light, the rutile-TiO2 xerogel obtained at 700°C showed a similar level of photoactivity as the one obtained with anatase-TiO2 xerogels obtained by calcination at 400 and 500°C. On the other hand, under visible light, unlike anatase-TiO2 xerogels, the rutile-TiO2 xerogel showed a dye photoconversion rate per external surface area that was up to 40 times higher than the one obtained with commercial Degussa P25 TiO2.
Keywords: Reduced TiO; 2; Rutile; Dye photodegradation; Visible irradiation
Study on highly visible light active Bi2O3 loaded ordered mesoporous titania by Sajjad Shamaila; Ahmed Khan Leghari Sajjad; Feng Chen; Jinlong Zhang (pp. 272-280).
The well-defined two-dimensional (2D) hexagonal mesoporous nanocrystalline anatase TiO2 was synthesized by the nonhydrolytic evaporation-induced co-assembly (EISA) of non-ionic amphiphilic triblock-copolymer template, titanium tetrachloride and tetrabutyl titanate. The ordered mesoporous TiO2 (M-TiO2) was loaded with different % of Bi2O3 using the wet impregnation method. For comparison Degussa P25 impregnated with Bi2O3 was also prepared. The samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy, photoluminescence spectra (PLS), Fourier transform infrared spectra (FT-IR), N2 adsorption–desorption (BET) and X-ray photoelectron spectroscopy (XPS) techniques. XRD and Raman spectra showed the pore wall was composed of anatase. 1.0% Bi2O3 loaded M-TiO2 revealed the well-ordered mesostructure. UV–vis diffuse reflectance spectroscopy measurements showed an extension of light absorption into the visible region. PLS analysis indicated that the electron–hole recombination rate have been effectively inhibited when Bi2O3 was loaded with ordered M-TiO2. The photo oxidation efficiency was evaluated by methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) degradation under visible illumination. The samples loaded with different % of Bi2O3 showed higher photocatalytic activity than M-TiO2 and Bi2O3 loaded P25. The catalyst exhibited high activity due to the Bi2O3-photosensitization and well-ordered 2D pore structure. The ordered mesoporous channels facilitate mass transport of the organic pollutants. TiO2 could extend the spectral response from UV to visible region because of Bi2O3-photosensitization which make the Bi2O3 loaded M-TiO2 photocatalyst visible light responsive.
Keywords: Ordered mesoporous anatase; Bi; 2; O; 3; Visible light; Photocatalysis; MO; 2,4-DCP
Preferential CO oxidation in hydrogen-rich stream over an electrochemically promoted Pt catalyst by A. de Lucas-Consuegra; A. Princivalle; A. Caravaca; F. Dorado; C. Guizard; J.L. Valverde; P. Vernoux (pp. 281-287).
We have conducted a study on the preferential CO oxidation in hydrogen-rich stream (PROX) coupling catalysis and electrochemistry, i.e., by using an electrochemical catalyst (Pt/K-βAl2O3). It was shown that PROX activity and selectivity of a Pt catalyst can be strongly enhanced by electrochemical pumping of potassium ions from the solid electrolyte support. The observed promotional effect was attributed to a decrease in the CO and H2 chemisorption and to an increase in the O2 chemisorption which led to a relative increase in the CO oxidation reaction vs. the H2 oxidation. The electrochemical promotion allowed decreasing the operating temperature window of the Pt catalyst and attenuating the inhibiting effect of H2 on both catalytic activity and selectivity. In addition some of the catalytic results were supported by in situ electrochemical characterization techniques such as cyclic voltammetry and open circuit potential measurements. Finally a very interesting permanent NEMCA effect was shown. It demonstrated the high stability of the formed promoting species and the potential for a further development of NEMCA effect in PROX real configurations.
Keywords: Electrochemical promotion; NEMCA effect; PROX; Preferential oxidation; Selective CO oxidation
Kinetics and mechanism of advanced oxidation processes (AOPs) in degradation of ciprofloxacin in water by Taicheng An; Hai Yang; Guiying Li; Weihua Song; William J. Cooper; Xiangping Nie (pp. 288-294).
Fluoroquinolones and their metabolites are found in surface and ground waters, indicating their ineffective removal by conventional water treatment technologies. Advanced oxidation processes (AOPs) are alternatives to traditional water treatments. They utilize free radical reactions to directly degrade fluoroquinolones. This work reports absolute rate constants for the reaction of ciprofloxacin with several free radicals,OH,N3 and SO4− as well as hydrated electrons. Pulsed radiolysis experiments showed thatOH,N3 and eaq− reacted quickly with ciprofloxacin, with bimolecular reaction rate constants of (2.15±0.10)×1010, (2.90±0.12)×1010 and (2.65±0.15)×1010M−1s−1, respectively, while the SO4− radical appeared not to react with ciprofloxacin. Transient spectra were observed for the intermediate radicals produced by hydroxyl and azide radical reactions. Moreover, ciprofloxacin can be degraded rapidly using a typical advanced oxidation process, TiO2 photocatalysis, with half-lives of 1.9–10.9min depending upon pH values. Seven degradation products were elucidated by LC/MS/MS analysis, and the degradation mechanism of ciprofloxacin was also tentatively proposed by combining the experimental evidence with theoretical calculations of frontier electron densities. The calculations suggest that the addition of a hydroxyl radical to ciprofloxacin and photo-hole direct attack is two predominant reaction pathways.
Keywords: Ciprofloxacin; Advanced oxidation processes; Photocatalytic; Kinetics; Mechanism
Effect of calcination temperature on morphology and photoelectrochemical properties of anodized titanium dioxide nanotube arrays by Jiaguo Yu; Bo Wang (pp. 295-302).
Highly ordered TiO2 nanotube arrays are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and calcination temperatures exhibit a great influence on their architectures and photoelectrochemical properties.Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures. The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation. The production of hydroxyl radicals (OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule. The transient photocurrent response is measured by several on–off cycles of intermittent irradiation. The results show that low temperatures (below 600°C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca. 600°C. At 800°C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed. The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600°C) due to the enhancement of crystallization. Especially, at 600°C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures. With further increase in the calcination temperature from 600 to 800°C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas.
Keywords: TiO; 2; nanotube arrays; Calcination temperature; Photocatalytic activity; Hydroxyl radicals; Photocurrent
Photocatalytic treatment of indoor air: Optimization of 2-propanol removal using a response surface methodology (RSM) by Daniel Vildozo; Corinne Ferronato; Mohamad Sleiman; Jean-Marc Chovelon (pp. 303-310).
This paper presents an experimental design methodology for the optimization of the photocatalytic removal of 2-propanol also called isopropyl alcohol (IPA) at indoor air concentration level (ppbv). The response surface methodology (RSM) for the modelization and optimization of the photodegradation of 2-propanol in the presence of titanium dioxide was used. The effect of four different process parameters on the yield of 2-propanol mineralization was determined. Experiments were performed using an annular flow-through reactor with TiO2 as photocatalyst, 2-propanol as a volatile organic compound (VOC) model, under different ranges of relative humidity (RH: 0–60%), inlet concentration (100–700ppbv) and flow rate (100–500mLmin−1), TiO2 loading (5–20gm−2). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled with gas chromatography–mass spectrometry (ATD–GC–MS) whereas a gas chromatograph equipped with a pulsed discharge helium photoionization detector (GC–PDHID) was used for on-line measurements of CO and CO2 at ppbv level. RH was found as the principal parameter that affect significantly the mineralization and the formation of acetone, the principal reaction intermediate from the photocatalytic oxidation of 2-propanol. For example an immediate and total removal of 2-propanol at very low % of RH along with a high rate of mineralization without any by-products was found. Many strong interactions between the parameters were also found ([2-propanol]–flow rate, RH–[TiO2], [2-propanol]–RH). The model obtained ( R2=0.9965) shows a satisfactory correlation between the values of experimental data and predicted values of 2-propanol mineralization (CO2).
Keywords: Photocatalysis; TiO; 2; 2-Propanol; Indoor air; RSM
Low CO content hydrogen production from bio-ethanol using a combined plasma reforming–catalytic water gas shift reactor by Xinli Zhu; Trung Hoang; Lance L. Lobban; Richard G. Mallinson (pp. 311-317).
Bio-ethanol reforming was studied using a plasma-catalytic reactor for hydrogen production at low temperature and atmospheric pressure without diluent gas or external heating. The plasma applied was a DC pulse discharge (corona) plasma. The water gas shift (WGS) catalyst was put just below the cathode electrode. The discharge generated heat was effectively used for feed vaporization and the WGS reaction. The large amounts of CO (∼30%) in the H2 rich gas formed in plasma reforming of ethanol (H2O/ethanol=6) was successfully reduced to ∼0.8% when a Pt/TiO2 and Pt–Re/TiO2 stacked bed were used for in situ WGS catalysis with a gas hourly space velocity up to 12,000cm3g−1h−1. The resultant gases contain ∼73% H2 and ∼23% CO2, with small amounts of CO, CH4, and C2H6, that is suitable for H2 fuel cell use after residual CO removal. Stability tests with daily startup–shutdown showed both plasma and catalyst are stable. The plasma-catalytic system is promising for low CO content H2 production, and could be extended to other applications.
Keywords: Hydrogen production; Plasma; Ethanol reforming; Water gas shift; Pt–Re/TiO; 2
Modification of Rh/SiO2 catalyst for the hydrogenolysis of glycerol in water by Yasunori Shinmi; Shuichi Koso; Takeshi Kubota; Yoshinao Nakagawa; Keiichi Tomishige (pp. 318-326).
Addition of Re, Mo and W to Rh/SiO2 enhanced the catalytic activity of the glycerol hydrogenolysis using water as a solvent. The modification with Re gave the highest conversion and yield of 1,3-propanediol (1,3-PrD). The optimized Rh-ReO x/SiO2 (Re/Rh=0.5) catalyst maintained high selectivity to propanediols and suppressed C–C bond breaking even under low H2 pressure and high reaction temperature, where Rh/SiO2 is rather active to C–C bond breaking. Characterization results indicate the formation of ReO x clusters attached to the surface of Rh metal particles. This can cause the synergy between ReO x and Rh, and the glycerol hydrogenolysis proceeds on the interface between Rh metal surface and attached ReO x species.
Keywords: Glycerol; Biomass; Hydrogenolysis; Degradation; Biomass refinery