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Applied Catalysis B, Environmental (v.89, #3-4)

Editorial Board (pp. i).

Contents (pp. co4).

IFC Editorial Board (pp. co2).

Contents Continued (pp. i-ii).

A novel synthesis of carbon-coated anatase nanocrystals showing high adsorption capacity and photocatalytic activity by Yu-Chuan Hsu; Huang-Ching Lin; Chien-Wei Lue; Yi-Ting Liao; Chia-Min Yang (pp. 309-314).

Anatase nanocrystals coated with thin and uniform carbon layer have been prepared directly by using molecular precursors of titanium tetrachloride as a titanium source and fructose as a carbon source in benzyl alcohol. The anatase nanoparticles thus prepared possess high crystallinity, and the carbonaceous species from the dehydrated sugar coat the nanoparticles and transform to uniform and thin carbon layer with graphitic nature. The thus prepared carbon-coated anatase nanocrystals exhibit fast adsorption of methylene blue with high capacity, and they also catalyze the photodecomposition of the dye with greatly enhanced activity. The synthesis route provides rational control over the properties of carbon-coated anatase nanocatalysts for practical applications.

Keywords: Anatase nanocrystals; Carbon coating; Dye adsorption; Methylene blue photodecomposition

The effects of regeneration-phase CO and/or H₂ amount on the performance of a NO_X storage/reduction catalyst by Meshari AL-Harbi; William S. Epling (pp. 315-325).

The effects of regeneration-phase CO and/or H₂, and their amounts as a function of temperature on the trapping and reduction of NO_X over a model and a commercial NO_X storage/reduction catalyst have been evaluated. Overall, for both catalysts, their NO_X removal performance improved with each incremental increase in H₂ concentration. For the commercial sample, using CO at 200°C, beyond a small amount added, was found to decrease performance. The addition of H₂ to the CO-containing mixtures resulted in improved performance at 200°C, but the presence of the CO still resulted in decreased performance in comparison to activity when just H₂ was used. With the model sample, the presence of CO resulted in very poor performance at 200°C, even with H₂. The data suggest that CO poisons Pt sites, including Pt-catalyzed nitrate decomposition. At 300°C, H₂, CO, and mixtures of the two were comparable for trapping and reduction of NO_X, although with the model sample H₂ did prove consistently better. With the commercial sample, H₂ and CO were again comparable at 500°C, but mixtures of the two led to slightly improved performance, while yet again H₂ and H₂-containing mixtures proved better than CO when testing the model sample. NH₃ formation was observed under most test conditions used. At 200°C, NH₃ formation increased with each increase in H₂, while at 500°C, the amount of NH₃ formed when using the mixtures was higher than that when using either H₂ or CO. This coincides with the improved performance observed with the mixtures when testing the commercial.

Keywords: NO; _X; reduction; NO; _X; storage; Vehicle emissions

Mechanism of heterogeneous catalytic ozonation of nitrobenzene in aqueous solution with modified ceramic honeycomb by Lei Zhao; Jun Ma; Zhizhong Sun; Huiling Liu (pp. 326-334).

The degradation efficiencies of nitrobenzene in aqueous solution were investigated by semi-continuous experiments in the processes of ozone alone, ozone/ceramic honeycomb (CH) and ozone/modified ceramic honeycomb (MCH). MCH with 1.0% Mn and 0.5% Cu had more pronounced catalytic ability than CH to accelerate the degradation of nitrobenzene, to increase the utilization efficiency of ozone, to improve the concentrations of hydrogen peroxide (H₂O₂) formation and hydroxyl radical (OH) initiation, and to enhance the removal efficiency of TOC. The modification process of CH with the metals enhanced the density of surface hydroxyl groups, which determines the initiation ofOH from ozone decomposition and the generation of intermediate species on heterogeneous catalytic surface, yielding the acceleration of the degradation of nitrobenzene in aqueous solution. Possible reaction mechanism of ozone with heterogeneous catalytic surface in aqueous solution was proposed, and the formation mechanism of H₂O₂ andOH was also discussed according to the combined reactions in heterogeneous and homogeneous catalytic systems.

Keywords: Heterogeneous; Catalytic ozonation; Ceramic honeycomb; Nitrobenzene; Degradation; Surface hydroxyl groups; Initiation; Hydroxyl radical (; OH)

The Effect of nitric oxide on the photocatalytic oxidation of small hydrocarbons over titania by Stephen Poulston; Martyn V. Twigg; Andrew P. Walker (pp. 335-341).

The catalytic UV photo-oxidation of NO in the absence and presence of ethane, ethene, propane, propene, and n-butane over TiO₂ in the presence of excess oxygen was studied in the temperature range 21–150°C. It was confirmed in our system that in the absence of hydrocarbon NO was photocatalytically oxidised by oxygen to NO₂ over TiO₂ and was strongly absorbed. Both NO and hydrocarbon could be simultaneously photo-converted with the conversion varying considerably with both NO and hydrocarbon concentration and the nature of the hydrocarbon. In some instances the presence of NO in the feed gas enhanced hydrocarbon oxidation via reactions involving NO₂ that is a powerful oxidant. The extent of this effect depended on the relative strengths of adsorption on TiO₂ of the reactants and products. To reduce surface coverage of hydrocarbon most reactions were run at 150°C, and it was shown that at this temperature NO x adsorbed on titania could be reduced by photogenerated hydrocarbon surface species to N₂O and N₂ under these conditions. The formation of N₂ was confirmed using¹⁵NO with helium as carrier gas. By contrast, at room temperature in the presence of propene NO was converted to NO₂.

Keywords: Photocatalysis; Titania; TiO; ₂; Hydrocarbon oxidation; Propene; Propane; Ethane; Ethene; Butane; NO; x; reduction

Photodegradation of chloroacetic acids over bare and silver-deposited TiO₂: Identification of species attacking model compounds, a mechanistic approach by Hajnalka Czili; Attila Horváth (pp. 342-348).

Photocatalytic degradation of chloroacetic acids (ClAAs) over various bare and silver-deposited Degussa P25 TiO₂ particles was studied. Adsorption measurements carried out using TiO₂ photocatalysts of different origin demonstrated significant dependence of the adsorption efficiency on the nature of semiconductor particles and on the number of chlorine atoms of the substrate. Irradiation of the reaction mixtures containing monochloroacetic acid (MCA), dichloroacetic acid (DCA) and trichloroacetic acid (TCA), respectively, over P25 titania were performed under anaerobic and aerobic conditions. The progress of photocatalysis was followed by measuring the substrate concentration, the total organic carbon content (TOC) and the concentration of the chloride ion in the liquid phase of reaction mixtures. Opposite trends in the photodecomposition rate of the substrates were obtained for aerobicvMCA≈vDCA>vTCA and for anaerobic experimentsvTCA>vDCA>vMCA, respectively. The evolved CO₂ was also measured under aerobic photodecomposition of DCA. Important role of hydroxyl radicals in the photomineralization of mono- and dichloroacetic acid was confirmed by using coumarin (COU) as a hydroxyl radical scavenger and oxalic acid as an efficient scavenger for holes. Silver deposition onto the TiO₂ surface enhanced the efficiency of the semiconductor by a factor of 4 for the photooxidation of TCA and by a factor of 1.4 for DCA and MCA.

Keywords: Heterogeneous photocatalysis; TiO; ₂; Silver-deposited TiO; ₂; Chloroacetic acids; Coumarin; Hydroxyl radicals

Controlled modification of Pt/Al₂O₃ for the preferential oxidation of CO in hydrogen: A comparative study of modifying element by Shailesh K. Jain; Eleanor M. Crabb; Lesley E. Smart; David Thompsett; Andrew M. Steele (pp. 349-355).

The catalytic performance of a series of Pt/Al₂O₃ catalysts, modified with Cr, Mn, Fe, Co, Ni, Cu and Sn, has been tested for the preferential oxidation of CO in hydrogen. The promoters were deposited onto the surface of a 5wt.% monometallic Pt/Al₂O₃ catalyst using a controlled surface approach, to give a nominal promoter:Pt surface atomic ratio of 1:2 (corresponding to typically 0.15–0.25wt.% of the promoting metal). The aim of this approach was to selectively create the Pt-promoter oxide interfacial sites considered to be important for the non-competitive dual-site mechanism proposed for such promoted catalysts. In this mechanism the promoting oxide is believed to act as an active oxygen provider, providing oxygen for the oxidation of the CO on the Pt. The catalysts were characterised using TEM, EDX, ICP-AES and CO chemisorption and results suggest that the promoter was successfully deposited on to the Pt surface. Even at the low loadings of promoter used, significant enhancement was observed in the catalytic performance of the PROX reaction in a simulated reformate mixture, for the Fe- and Co-promoted catalysts in particular (and to a lesser extent the Mn, Sn, Cu- and Ni-promoted catalysts), highlighting the successful preparation of the Pt-promoting metal oxide interfacial sites. The Mn-promoted catalyst, however showed no enhancement in the absence of water suggesting that the form of the promoting metal oxide may be particularly important for promotion of Pt for the PROX reaction.

Keywords: PROX; Platinum; Promoted catalysts

Fe-zeolites as catalysts for chemical oxidation of MTBE in water with H₂O₂ by R. Gonzalez-Olmos; U. Roland; H. Toufar; F.-D. Kopinke; A. Georgi (pp. 356-364).

The heterogeneous catalytic wet oxidation of methyl tert-butyl ether (MTBE) with hydrogen peroxide, catalyzed by the iron-containing zeolites Fe-ZSM5 and Fe-Beta, was studied at ambient conditions and pH 7. The kinetics of MTBE degradation could be well-fitted to a pseudo-first-order model. Using Fe-ZSM5, the dependence of the reaction rate constant on hydrogen peroxide and catalyst concentration was determined. Furthermore, the formation and oxidation of tert-butyl alcohol and tert-butyl formate as intermediates of MTBE oxidation were studied. A comparison of the reaction rates of MTBE, trichloroethylene and diethyl ether in the Fe-ZSM5/H₂O₂ system revealed that adsorption plays a positive role for the degradation reaction.Comparing the two types of Fe-containing zeolites applied in this study, Fe-Beta showed a lower catalytic activity for H₂O₂ decomposition and also MTBE degradation. However, in terms of utilization of H₂O₂ for MTBE degradation Fe-Beta is advantageous over Fe-ZSM5. This could be explained by the stronger adsorptive enrichment of MTBE on the Fe-Beta zeolite. This study shows that Fe-containing zeolites are promising catalysts for oxidative degradation of MTBE by H₂O₂.

Keywords: MTBE; Zeolites; Fenton; Advanced oxidation processes; Adsorption; Kinetics

Cobalt oxide species supported on SBA-15, KIT-5 and KIT-6 mesoporous silicas for ethyl acetate total oxidation by Tanya Tsoncheva; Ljubomira Ivanova; Jessica Rosenholm; Mika Linden (pp. 365-374).

Cobalt oxide modified SBA-15, KIT-5 and KIT-6 mesoporous silicas with different pore size/pore entrances have been synthesized by a conventional wet impregnation method using cobalt nitrate as the precursor. The modified materials were characterized by N₂-physisorption, XRD, TEM-EDX, XPS, FT-IR, UV–vis and TPR-TG with hydrogen. Their catalytic activities in total oxidation of ethyl acetate were evaluated. A good correlation was observed between the catalytic activity, and the presence of spinel-type Co₃O₄ in the materials. Supports with larger mesopores facilitated the formation of such easily reducible spinel particles. However, the interconnectivity of the mesopores and the uniformity of the channel dimensions also had an influence on the catalytic activity, implying that mass-transfer effects, especially in the case of supports with cage-like mesopores.

Keywords: SBA-15; KIT-5; KIT-6; Mesoporous silicas; Ethyl acetate combustion; Co; ₃; O; ₄

Preparation, characterization and catalytic properties of carbon nanofiber-supported Pt, Pd, Ru monometallic particles in aqueous-phase reactions by Carmen Diaz Taboada; Jurka Batista; Albin Pintar; Janez Levec (pp. 375-382).

Carbon nanofibers (CNF) synthesized by catalytic chemical vapor deposition (CVD) method were used to prepare supported platinum, palladium and ruthenium monometallic (2.0wt.%) catalysts by means of incipient-wetness impregnation method. The CNF support and catalysts were characterized by X-ray powder diffraction (XRD), nitrogen adsorption/desorption isotherms, volumetric chemisorption of hydrogen, temperature-programmed reduction (H₂-TPR) and scanning electron microscopy (SEM). Solids were tested in catalytic wet-air oxidation (CWAO) of phenol aqueous solution (180–240°C and 10.0bar of oxygen partial pressure) carried out in a continuous-flow trickle-bed reactor. Trends of phenol and total organic carbon (TOC) conversion demonstrate that the CNF support and CNF-Pt catalyst did not exhibit constant activity for CWAO of phenol. A decrease of catalyst activity, detection of carbon dioxide in the off-gas stream while examining catalyst stability and significant textural changes observed, provide an evidence that under net oxidizing reaction conditions gasification of the CNF support occurs. The prepared catalysts were also tested in liquid-phase thermal decarboxylation of formic acid in inert atmosphere (60–220°C). Among solids examined, the CNF-Pd exhibited the highest activity. At the employed conditions, no decomposition of the CNF support was observed during the thermal decarboxylation of formic acid.

Keywords: Carbon nanofibers; Noble metal catalysts; Characterization; Catalytic wet-air oxidation; Liquid-phase thermal decarboxylation; Heterogeneous catalysis; Trickle-bed reactor

Effect of sulphur poisoning on perovskite catalysts prepared by flame-pyrolysis by Ilenia Rossetti; Olga Buchneva; Cesare Biffi; Riccardo Rizza (pp. 383-390).

ABO₃ perovskite-like catalysts are known to be sensitive to sulphur-containing compounds. Possible solutions to increase resistance to sulphur are represented by either catalyst bed protection with basic guards or catalyst doping with different transition or noble metals. In the present workLa(1−x)A′xCoO3,La(1−x)A′xMnO3 andLa(1−x)A′xFeO3, with A′=Ce, Sr and x=0, 0.1, 0.2, either pure or doped with noble metals (0.5wt% Pt or Pd), were prepared in nano-powder form by flame-pyrolysis. All the catalysts were tested for the catalytic flameless combustion of methane, monitoring the activity by on-line mass spectrometry. The catalysts were then progressively deactivated in operando with a new procedure, consisting of repeated injection of some doses of tetrahydrothiophene (THT), usually employed as odorant in the natural gas grid, with continuous analysis of the transient response of the catalyst. The activity tests were then repeated on the poisoned catalyst. Different regenerative treatments were also tried, either in oxidising or reducing atmosphere.Among the unsubstituted samples, higher activity and better resistance to poisoning have been observed in general with manganites with respect to the corresponding formulations containing Co or Fe at the B-site. The worst catalyst showed LaFeO₃, from both the points of view of activity and of resistance to sulphur poisoning. La_0.9Sr_0.1MnO₃ showed, the best results, exhibiting very high activity and good resistance even after the addition of up to 8.4mg of THT/g of catalyst. Interesting results were attained also by adding Sr to Co-based perovskites. Sr showed a first action by forcing Mn or Co in their highest oxidation state, but, in addition, it could also act as a sulphur guard, likely forming stable sulphates due to its basicity. Among noble metals, Pt doping proved beneficial in improving the activity of both the fresh and the poisoned catalyst.

Keywords: Methane; Catalytic combustion; Sulphur poisoning; Perovskite-like catalysts

N₂O decomposition over K-promoted Co-Al catalysts prepared from hydrotalcite-like precursors by Hongkui Cheng; Yanqiang Huang; Aiqin Wang; Lin Li; Xiaodong Wang; Tao Zhang (pp. 391-397).

N₂O decomposition was investigated over a series of K-promoted Co-Al catalysts. The activity tests showed that doping with K greatly enhanced the catalytic activity of the Co-Al catalyst, and the enhancement was critically dependent on the amount of K and the calcination temperature. When the catalyst had a K/Co atomic ratio of 0.04 and was calcined at 700–800°C, a full N₂O conversion could be reached at a reaction temperature of 300°C. Moreover, even under the simultaneous presence of 4% O₂ and 2.6% water vapor, such high-temperature treated K/Co-Al catalyst exhibited high reactivity and stability, with the N₂O conversion remaining at a constant value of 92% over 40h run at 360°C. In contrast, non-doped Co-Al catalyst showed a severe activity loss under such reaction conditions. A combination of characterization techniques was employed to reveal the promoting role of K and the effect of calcination temperature. The results suggest that doping with K increases the electron density of Co and weakens the Co–O bond, thus promoting the activation of N₂O on the Co sites and facilitating the desorption of oxygen from the catalyst surface. High-temperature calcinations made the desorption of O₂ proceed more readily.

Keywords: N; ₂; O decomposition; Alkali metal; Potassium; Hydrotalcite

Aerosol-assisted flow synthesis of B-doped, Ni-doped and B–Ni-codoped TiO₂ solid and hollow microspheres for photocatalytic removal of NO by Yu Huang; Wingkei Ho; Zhihui Ai; Xiao Song; Lizhi Zhang; Shuncheng Lee (pp. 398-405).

In this study, highly effective B-doped, Ni-doped and B–Ni-codoped TiO₂ microspheres photocatalysts were directly synthesized via an aerosol-assisted flow synthesis method. The resulting samples were characterized by XRD, SEM, TEM, UV–vis diffuse reflectance spectroscopy, nitrogen adsorption and XPS. The characterizations revealed hollow microspherical structure of the B-doped and B–Ni-codoped TiO₂ photocatalysts, while the Ni-doped and undoped TiO₂ products consisted of solid microspheres. It was found that the boron dopant was partially embedded into the interstitial TiO₂ structure, existing in the form of Ti–O–B structure. The band gap was enlarged after the boron doping. However, both Ni-doped and B–Ni-codoped TiO₂ samples showed obvious red shift in their absorption edges because of the Ni doping. The photocatalytic activities of these samples were evaluated on the photocatalytic removal of NO under simulated solar light irradiation. All the aerosol-assisted flow synthesized samples had much higher photocatalytic activities than P25 and the doped TiO₂ microspheres exhibited enhanced photocatalytic activity than the undoped counterparts. More interestingly, the B–Ni-codoped TiO₂ photocatalyst possessed superior photocatalytic activity to the as-prepared single doped TiO₂ products. The enhanced photocatalytic activity was explained and the formation mechanisms of hollow and solid microspheres were also proposed on the basis of characterizations. We think this general method may be easily scaled up for industrial production of highly active microspherical photocatalysts for efficient NO removal under simulated solar light irradiation.

Keywords: TiO; ₂; Photocatalysis; Doped; NO removal; Ni; B; Aerosol-assisted flow synthesis

Enhancement of the photocatalytic reactivity of TiO₂ nano-particles by a simple mechanical blending with hydrophobic mordenite (MOR) zeolite by Masato Takeuchi; Junichi Deguchi; Manabu Hidaka; Shiro Sakai; Kyoungja Woo; Pyuck-Pa Choi; Jong-Ku Park; Masakazu Anpo (pp. 406-410).

The photocatalytic oxidation of gaseous acetaldehyde with O₂ on commercial TiO₂ nano-particles could be successfully enhanced by a simple mechanical blending with a high-silica mordenite (MOR) zeolite, the surface of which showed high hydrophobic properties. When the TiO₂ nano-particles of ca. 5–20wt% were mixed with the MOR zeolite powders in an agate mortar for only 5min, the blended TiO₂/MOR samples showed higher photocatalytic reactivity as compared to the pure TiO₂ nano-particles. Since the high-silica zeolite powders are highly transparent in UV light regions, the incident UV light is effectively irradiated onto the whole part of the TiO₂ nano-particles without any loss of light intensity. Furthermore, the siliceous MOR zeolite powders effectively adsorb the gaseous acetaldehyde molecules and supply them onto the surfaces of the blended TiO₂ nano-particles, resulting in an enhancement of the photocatalytic reactivity.

Keywords: Photocatalytic oxidation of gaseous acetaldehyde; TiO; ₂; nano-particles; High-silica mordenite zeolites having hydrophobic character; Mechanical blending

Palladium and platinum catalysts supported on carbon nanofiber coated monoliths for low-temperature combustion of BTX by S. Morales-Torres; A.F. Pérez-Cadenas; F. Kapteijn; F. Carrasco-Marín; F.J. Maldonado-Hódar; J.A. Moulijn (pp. 411-419).

In this work carbon nanofiber (CNF)-coated monoliths with a very thin, homogeneous, consistent and good adhered CNF layer were obtained by means of catalytic decomposition of ethylene on Ni particles.The catalytic behaviour of Pt and Pd supported on the CNF-coated monoliths was studied in the low-temperature catalytic combustion of benzene, toluene and m-xylene (BTX) and compared with the performance of Pt and Pd supported on γ-Al₂O₃ coated monoliths.The catalysts supported on CNF-coated monoliths were the most active, independent of the metal catalyst or the type of the tested aromatic compound. TPD experiments showed that the γ-Al₂O₃ phase retained important amounts of the water molecules produced during the reaction. When water vapour was supplied to the reactant flow, the activity of Pd catalysts decreased much stronger than the Pt ones, and the activity of the Pt catalysts supported on the γ-Al₂O₃ was more affected than that of the catalysts supported on CNF.BTX combustion reactions seem to be catalyzed by Pt and Pd through different kinetic mechanisms, explaining why Pt catalysts always were more active than the Pd ones deposited on the same type of support. Pd catalyzed combustion of benzene is strongly inhibited by oxygen and by water.Catalysts supported on CNF-coated monoliths showed a selectivity to burn benzene better than toluene or m-xylene, attributed to a better aromatic-CNF surface interaction.

Keywords: Carbon nanofibers; Coating; Monolithic catalysts; BTX combustion; Platinum; Palladium

Preparation of copper-containing mesoporous manganese oxides and their catalytic performance for CO oxidation by Y. Hasegawa; K. Fukumoto; T. Ishima; H. Yamamoto; M. Sano; T. Miyake (pp. 420-424).

Copper-containing mesoporous manganese oxides were prepared by the sol–gel method. The samples obtained were characterized by XRD, N₂ adsorption–desorption, ICP, CO-TPD, redox measurement and XPS. After calcination at 300°C, amorphous structure was shown by XRD for all the samples. All the samples had mesopores of about 6nm and high surface areas of 170–230m²g⁻¹. Using these samples as catalysts, CO oxidation was carried out as a model reaction. Copper-containing mesoporous manganese oxide prepared by the sol–gel method showed a very high activity. On the other hand, copper-supported manganese oxide prepared by the impregnation method using copper sulfate showed a low activity. Differences in activities were correlated with the mobility of lattice oxygen.

Keywords: Manganese oxide; Mesoporous; CO oxidation; Lattice oxygen; Copper

Photoelectric catalytic degradation of methylene blue by C₆₀-modified TiO₂ nanotube array by Jie Lin; Ruilong Zong; Mi Zhou; Yongfa Zhu (pp. 425-431).

Fullerene (C₆₀)-modified TiO₂ nanotube array (TNA) was prepared by the electrophoresis deposition technique. The as-prepared samples showed the high efficiency for the photoelectric catalytic (PEC) degradation of nonbiodegradable azodyes methylene blue (MB). The highest PEC activity of C₆₀-modified TNA (TNA/C₆₀) was achieved at a lower bias potential (4.0V), which was 2.3 times of the highest activity of TNA at 5.0V. The high PEC activity came from the synergetic effect between C₆₀ and TiO₂, which promoted the charge separation, influenced the charge distribution of the electrical double layer and reduced the impedances of the Helemholtz and depletion layers. Moreover, the oxidation of MB was a quick process during the PEC degradation, and the process began with the oxidation of the dimethylamino group, which was different from the photocatalytic (PC) process began with the oxidation of S atom; MB was mineralized completely during PEC degradation.

Keywords: Photoelectrical catalysis; Fullerene; TiO; ₂; nanotube array; Methylene blue

Adsorption and oxidation of PCP on the surface of magnetite: Kinetic experiments and spectroscopic investigations by Xiaofei Xue; Khalil Hanna; Mustapha Abdelmoula; Nansheng Deng (pp. 432-440).

The oxidation of pentachlorophenol (PCP) on the surface of magnetite used as heterogeneous catalyst has been investigated under various experimental conditions (initial substrate concentration, H₂O₂ dose, solid loading and temperature) at neutral pH and correlated with the adsorption behavior. The surface reactivity of magnetite was evaluated by conducting the kinetic study of both H₂O₂ decomposition and PCP oxidation experiments. The occurrence of the optimum values of H₂O₂ and magnetite concentrations for the effective degradation of PCP could be explained by the scavenging reactions with H₂O₂ or iron oxide surface. The surface interactions with PCP in the absence and the presence of oxidant can be well described by Langmuir and Langmuir–Hinshelwood models, respectively. All batch experiments indicate that Fenton-like oxidation of PCP was controlled by surface mechanism reaction and the species compete with each other for adsorption on a fixed number of surface active sites. The apparent degradation rate was dominated by the rate of intrinsic chemical reactions on the oxide surface rather than the rate of mass transfer. Raman analysis suggested that the sorbed PCP was removed form magnetite surface at the first stage of oxidation reaction. The mineralization determined by TOC abatement was completed after 7 d, while total dechlorination was achieved at 4 d treatment time. The first reaction of PCP oxidation should be the dechlorination since 90% of chloride was formed at the first 30h corresponding to the total disappearance of parent compound. All X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and chemical analyses showed that the magnetite catalyst exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle.

Keywords: Fenton-like; Oxidation; Adsorption; Magnetite; Mineralization

Boosting TiO₂-anatase antimicrobial activity: Polymer-oxide thin films by Anna Kubacka; Manuel Ferrer; María L. Cerrada; Cristina Serrano; Manuel Sánchez-Chaves; Marta Fernández-García; Alicia de Andrés; Rafael J. Jiménez Riobóo; Fernando Fernández-Martín; Marcos Fernández-García (pp. 441-447).

TiO₂ incorporation into an isotactic polypropylene (iPP) polymeric matrix was achieved via a straightforward and cost-effective melting process using laboratory-made nanometric anatase-TiO₂ and an industrial polymer. The structural characteristics of the resulting nanocomposite thin films as a function of the inorganic component content were examined using wide and small angle X-ray scattering (WAXS/SAXS) and vibrational Raman spectroscopy. Electron scanning and transmission microscopy (SEM/TEM) studies were also performed to provide evidence of the nanometric dispersion of the oxide within the polymer matrix, showing the presence of average aggregates of ca. 80nm. TiO₂ incorporation into the iPP renders self-sterilized nanocomposite films upon light excitation, the activity of which was tested against Gram negative ( P. aeruginosa) and positive ( E. faecalis) bacteria. TiO₂ displays maximum activity for a sample containing a 2wt.% of anatase-TiO₂ irrespective of the microorganism nature. The antimicrobial activity of the nanocomposite films is significantly enhanced with respect to that of the oxide alone. This key fact is interpreted on physical basis with the help of a complete optical (UV–vis and photoluminescence) and electron paramagnetic resonance (EPR) characterization.

Keywords: Titania; Anatase; Nanocomposites; Thin films; Biocide; Germicide; Disinfection

Degradation of atrazine using metalloporphyrins supported on TiO₂ under visible light irradiation by Gilma Granados-Oliveros; Edgar A. Páez-Mozo; Fernando Martínez Ortega; Corinne Ferronato; Jean-Marc Chovelon (pp. 448-454).

The photocatalytic activity of tetra(4-carboxyphenyl)porphyrin with different metal centers (Fe(III), Cu(II), Zn(II) and metal-free), adsorbed on TiO₂ surface has been investigated by carrying out the photodegradation of atrazine in aqueous solution and under visible light irradiation. Under this condition, no photocatalytic activity was found meaning that anion superoxide (which was evidenced by photodegradation of luminol) is not sufficiently oxidant to degrade atrazine. However by adding hydrogen peroxide in the solution, a degradation of atrazine was observed. Under this condition, the maximum photocatalytic activity was obtained using Cu(II) porphyrin as photosensitizer (82% of degradation after 1h of irradiation). The influence of H₂O₂ concentration has been studied. It has been found that in the range 0.015–0.05molL⁻¹ the higher the concentration the higher the rate of degradation, whereas for higher H₂O₂ concentrations, the rate of degradation leveled off. Intermediate products were identified using high performance liquid chromatography-Diode Array Detector (HPLC-DAD) and GC–MS and a mechanism of degradation was proposed.

Keywords: Dye-sensitized TiO; ₂; Atrazine degradation; Metalloporphyrins; Visible light irradiation

Tungsten carbide as electrocatalyst for the hydrogen evolution reaction in pH neutral electrolyte solutions by Falk Harnisch; Gustav Sievers; Uwe Schröder (pp. 455-458).

In this communication we demonstrate that tungsten carbide, WC, is a promising electrocatalyst for the hydrogen evolution reaction in pH neutral electrolytes. In a systematic investigation of mixed catalysts containing different fractions of WC, W₂C, W and WO₂ we show that the performance of the catalyst is proportional to its WC content, whereas W₂C, W and WO₂ play only a minor role. The relationship between WC content and electrocatalytic activity indicates that hydrogen evolution and oxidation are related to similar surface sites preferentially formed on WC. In contrast to anodic conditions, the cathodic polarization diminishes corrosion processes and thus increases the long term stability.

Keywords: Biofuel cells; Microbial fuel cells; Microbial electrolysis cell; Hydrogen evolution reaction; Electrocatalysis; Tungsten carbide

Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe³⁺ using a boron-doped diamond electrode by Elena Guinea; Francesc Centellas; José Antonio Garrido; Rosa María Rodríguez; Conchita Arias; Pere-Lluís Cabot; Enric Brillas (pp. 459-468).

This paper reports a comparative study on the anodic oxidation of 2.5l of 50mgl⁻¹ TOC of formic, oxalic, acetic, pyruvic or maleic acid in 0.1M Na₂SO₄ solutions of pH 3.0 with and without 1.0mM Fe³⁺ as catalyst in the dark or under solar irradiation. Experiments have been performed with a batch recirculation flow plant containing a one-compartment filter-press electrolytic reactor equipped with a 20cm² boron-doped diamond (BDD) anode and a 20cm² stainless steel cathode, and coupled to a solar photoreactor. This system gradually accumulates H₂O₂ from dimerization of hydroxyl radical (OH) formed at the anode surface from water oxidation. Carboxylic acids in direct anodic oxidation are mainly oxidized by direct charge transfer and/orOH produced on BDD, while their Fe(III) complexes formed in presence of Fe³⁺ can also react withOH produced from Fenton reaction between regenerated Fe²⁺ with electrosynthesized H₂O₂ and/or photo-Fenton reaction. Fast photolysis of Fe(III)-oxalate and Fe(III)-pyruvate complexes under the action of sunlight also takes place. Chemical and photochemical trials of the same solutions have been made to better clarify the role of the different catalysts. Solar photoassisted anodic oxidation in presence of Fe³⁺ strongly accelerates the removal of all carboxylic acids in comparison with direct anodic oxidation, except for acetic acid that is removed at similar rate in both cases. This novel electrochemical advanced oxidation process allows more rapid mineralization of formic, oxalic and maleic acids, without any significant effect on the conversion of acetic acid into CO₂. The synergistic action of Fe³⁺ and sunlight in anodic oxidation can then be useful for wastewater remediation when oxalic and formic acids are formed as ultimate carboxylic acids of organic pollutants, but its performance is expected to strongly decay in the case of generation of persistent acetic acid during the degradation process.

Keywords: Carboxylic acids; Electrochemical degradation; Fenton reaction; Solar irradiation; Mineralization

Photocatalytic activity of boron-modified TiO₂ under visible light: The effect of boron content, calcination temperature and TiO₂ matrix by Adriana Zaleska; Ewelina Grabowska; Janusz W. Sobczak; Maria Gazda; Jan Hupka (pp. 469-475).

Our research examines the photoactivity under visible light ( λ>400nm) and surface properties (BET surface area, UV–vis absorption properties, chemical composition and crystal structure) of boron-modified TiO₂. B–TiO₂ photocatalysts were prepared by surface impregnation procedure using boric acid triethyl ester (BATE) as a boron precursor. The photocatalytic activity of obtained powders in visible light was estimated by measuring the decomposition of phenol (0.21mmol/dm³) in aqueous solution. The effect of boron content, calcination temperature and titanium dioxide source used during preparation procedure on photoactivity was investigated. The degradation of phenol indicated that the photoactivity under visible light strongly depended on preparation manner of B–TiO₂ photocatalysts. The highest photoactivity was observed for the sample obtained by impregnation with 2wt.% of BATE and calcinated at 400°C. Phenol degradation rate, in the presence of these samples, equaled to 3.0μmoldm⁻³min⁻¹. The mode of BATE binding to TiO₂ surface is discussed.

Keywords: Titanium dioxide; Boron-modified TiO; ₂; Visible light photocatalysis

Transient analysis of oxygen storage capacity of Pt/CeO₂–ZrO₂ materials with millisecond- and second-time resolution by Evgenii V. Kondratenko; Yoshiyuki Sakamoto; Kohei Okumura; Hirofumi Shinjoh (pp. 476-483).

A simple method for determining the speed of oxygen release from Pt/CeO₂–ZrO₂ materials is proposed. We determined the speed of oxygen release from three differently prepared Pt(1wt%)/CeO–ZrO₂ catalysts by two methods: the method employing temporal analysis of products (TAP) reactor with CO, O₂, and CO₂ pulsed gases, and a conventional method with CO and O₂ switch gases. Strong CO₂ adsorption precluded correct analysis of oxygen release speed, when it was determined from the amount of CO₂ formed. Therefore, instead of the amount of CO₂ formed, we suggested the t_max value, defined as the position of maximal intensity of CO₂ transient responses obtained upon low-intensity (10¹⁵–10¹⁶ molecules) CO pulsing in the TAP reactor. Shorter the t_max value, higher the rate of oxygen release, because the temperature dependence of the t_max determined in the present study resembles the previous results of oxygen release analysis [T. Tanabe, A. Suda, C. Descorme, D. Duprez, H. Shinjoh, M. Sugiura, Stud. Surf. Sci. Catal. 138 (2001) 135].

Keywords: Oxygen storage capacity; Mechanism; TAP; Platinum; Ceria

A new synthesis of a highly dispersed and CO tolerant PtSn/C electrocatalyst for low-temperature fuel cell; its electrocatalytic activity and long-term durability by Dong-Ha Lim; Dong-Hyeok Choi; Weon-Doo Lee; Ho-In Lee (pp. 484-493).

An effective method is developed for preparing highly dispersed and nano-sized PtSn/C electrocatalysts synthesized by borohydride reduction and subsequent hydrothermal treatment. From the XRD patterns, the Pt(220) peak of the PtSn/C catalysts shift slightly to lower 2 θ values with increasing Sn content, compared with that of the Pt/C catalyst, suggesting the alloy formation. Based on the HR-TEM, the PtSn nanoparticles show average particle sizes of approximately 2.3nm on the carbon surface, which is consistent with XRD data. The XPS result shows that the slight shift in the bulk metallic Pt(0) to higher binding energies is attributed to a significant contribution from the metal-support interaction and the nano-size effect. The methanol and CO oxidations on the PtSn/C catalysts occur at lower potentials as compared to the commercial Pt/C catalyst. This result suggests that Sn has the ability to promote the oxidation of adsorbed CO at lower potentials. In the single-cell and accelerated durability tests, the 3Pt1Sn/C catalyst shows higher performance under a pure H₂ and CO-containing H₂ gases and better durability under a 0.5M H₂SO₄ solution than the commercial Pt/C catalyst, due to the coexistence of PtSn alloys and Sn oxides.

Keywords: PtSn/C electrocatalysts; Borohydride reduction and hydrothermal treatment; Methanol oxidation; CO tolerance; Long-term durability; Low-temperature fuel cell

Effect of TiO₂ particle size on the photocatalytic reduction of CO₂ by K. Kočí; L. Obalová; L. Matějová; D. Plachá; Z. Lacný; J. Jirkovský; O. Šolcová (pp. 494-502).

Pure TiO₂ anatase particles with a crystallite diameters ranging from 4.5 to 29nm were prepared by precipitation and sol–gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis and scanning electron microscopy (SEM) and tested in CO₂ photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14nm. The observed optimum particle size is a result of competing effects of specific surface area, charge–carrier dynamics and light absorption efficiency.

Keywords: CO; ₂; reduction; TiO; ₂; Photocatalysis; Size effect

Carbon nanotubes/titanium dioxide (CNTs/TiO₂) nanocomposites prepared by conventional and novel surfactant wrapping sol–gel methods exhibiting enhanced photocatalytic activity by Bin Gao; George Z. Chen; Gianluca Li Puma (pp. 503-509).

In this work, a conventional sol–gel method was used to prepare CNTs/TiO₂ nanocomposites with different carbon loading in the range up to 20% CNTs/TiO₂ by weight. The bare CNTs (multi-walled), and the composites were characterized by a range of analytical techniques including TEM, XRD, BET and TGA–DSC. The results show the successful covering of the CNTs with discrete clusters of TiO₂ and bare CNTs surfaces which after annealing at 500°C led to mesoporous crystalline TiO₂ (anatase) clusters. The photocatalytic activities of the nanocomposites were monitored from the results of the photodegradation of methylene blue (MB). The optimum CNTs/TiO₂ ratio in the composites prepared by conventional sol–gel method was found to be in the range from 1.5% to 5% by weight under the experimental conditions investigated. The maximum increase in activity was found to be 12.8% compared to the pure TiO₂ sample.In contrast, the synthesis of CNTs/TiO₂ nanocomposites by a novel surfactant wrapping sol–gel method [B. Gao, C. Peng, G.Z. Chen, G. Li Puma, Appl. Catal. B: Environ. 85 (2008) 17.] led to a uniform and well-defined nanometer-scale titania layer on individual CNTs. The nanocomposites were found to enhance the initial oxidation rate of methylene blue by onefold compared to the pure TiO₂ sample. This larger degree of rate enhancement is attributed to the supporting role of the CNTs and surface properties prepared by this novel modified sol–gel method.

Keywords: Carbon nanotubes; Titanium dioxide; Photocatalysis; Nanocomposite; Surfactant; Wrapping; Sol–gel

Effect of continuous addition of H₂O₂ and air injection on ferrioxalate-assisted solar photo-Fenton degradation of Orange II by J.M. Monteagudo; A. Durán; I. San Martín; M. Aguirre (pp. 510-518).

An experimental study based on ferrioxalate-assisted solar photo-Fenton (SPFox) process shows how non-biodegradable azo dye Orange II (OII) solutions degradation can be enhanced or slowed down by continuous addition of hydrogen peroxide and air injection depending on operation conditions. The decoloration and mineralization of dye solution has been carried out in a solar Compound Parabolic Collector (CPC). An optimization study was done by using Multivariate Experimental Design including the following variables: flow rate of H₂O₂, air flow rate, pH and initial concentrations of Fe(II) and oxalic acid. The efficiency of photocatalytic degradation was determined from the analysis of color and Total Organic Carbon (TOC). Experimental data were fitted using neural networks (NNs) which allow the simulation of the process for any value of variables in the studied experimental range. The results reveal that the continuous addition of H₂O₂ improves the photocatalytic efficiency since the scavenger effect of peroxide is minimized. On the other hand, this system permits the use of a ferrous concentration below the discharge legal limit (2ppm) being bubbling of air not necessary in that conditions. In addition, oxalic acid can be used to pH adjustment, reducing the operation costs of Fe removal, chemicals and electric power. Under the optimal conditions, 100% decoloration of dye solution can be reached by using both processes (SPFox with H₂O₂ addition at the beginning or along the reaction) but with different reaction rates. However, the efficiency of TOC removal was higher in the SPFox process with continuous addition of H₂O₂ (95% TOC removal in SPFox system with continuous addition of peroxide versus 80% TOC removal in SPFox system when peroxide is added at the beginning of the reaction). Molecular and/or radical reaction pathway was studied by conducting the reaction in the presence and absence of tert-butylalcohol.

Keywords: Orange II; Ferrioxalate; Photo-Fenton; Neural networks; CPC

Phenol degradation by Fenton's process using catalytic in situ generated hydrogen peroxide by Mohammad S. Yalfani; Sandra Contreras; Francesc Medina; Jesus Sueiras (pp. 519-526).

The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6h corresponding to the termination of 100mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300ppm H₂O₂ displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45°C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts.

Keywords: Phenol degradation; Fenton's process; Hydrogen peroxide; In situ generation; Palladium; Formic acid

Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3−_xTi_xO₄ (0≤ x≤0.78) at neutral pH values by Shijian Yang; Hongping He; Daqing Wu; Dong Chen; Xiaoliang Liang; Zonghua Qin; Mingde Fan; Jianxi Zhu; Peng Yuan (pp. 527-535).

In this work, a series of Fe3−_xTi_xO₄ (0≤ x≤0.78) was synthesized using a new soft chemical method. The synthetic Fe3−_xTi_xO₄ were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures.Then, decolorization of methylene blue (MB) by Fe3−_xTi_xO₄ in the presence of H₂O₂ at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC),¹³C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe3−_xTi_xO₄ in the presence of H₂O₂ was promoted remarkably with the increase of Ti content in Fe3−_xTi_xO₄ due to the enhancement of both adsorption and degradation of MB on Fe3−_xTi_xO₄.

Keywords: Fe; 3−; _x; Ti; _x; O; ₄; Adsorption; Degradation; Mineralization; Zero-order kinetic rate constant

Repression of photoreactivation and dark repair of coliform bacteria by TiO₂-modified UV-C disinfection by Chii Shang; Lok Man Cheung; Chiu-Man Ho; Minzhen Zeng (pp. 536-542).

Photoreactivation and dark repair of damaged DNA can occur after some bacteria are disinfected with UV-C irradiation and thus reduce the disinfection efficiency. We have discovered that the provision of 1mg/L titanium dioxide (TiO₂) in suspension during UV-C irradiation at normal disinfection doses repressed the photoreactivation and dark repair. The repressive effect was also observed when a TiO₂-coated plate was used during UV-C exposure but removed thereafter, indicating the repressive effect does not require the presence of TiO₂ in the post-UV event. The repressive effect was consistently observed with changes of bacteria species, temperature, salinities, UV sources, doses and intensities, and with/without nutrients. The repressive effect is likely associated with the additional radical attack during UV-TiO₂ irradiation and/or formation of a small amount of stable residual oxidants (primarily hydrogen peroxide). The TiO₂-modified UV-C disinfection represents an innovative means to disinfect water. It is particularly useful in situations where additions of residual chlorine or chloramines are not allowed or not possible. Nevertheless, the TiO₂ shall be properly included, by either using the optimum dose in suspension or immobilizing it onto a surface, since too little TiO₂ cannot provide the repression while too much TiO₂ in suspension gives a detrimental effect on the UV-C disinfection.

Keywords: Inactivation; Photocatalytic; Reactivation; Regrowth; Ultraviolet

Highly active TiO2− x−_yN_xF_y visible photocatalyst prepared under supercritical conditions in NH₄F/EtOH fluid by Yuning huo; Yi jin; Jian zhu; Hexing li (pp. 543-550).

A novel N and F co-doped TiO₂ (TiO2− x−_yN_xF_y) photocatalyst is prepared by treating the TiO₂ precursor in NH₄F/ethanol fluid under supercritical conditions. During photocatalytic degradation of methylene blue under visible light irradiation, the as-prepared TiO2− x−_yN_xF_y exhibits higher activity than the undoped TiO₂, N-doped TiO₂ (TiO2−_xN_x), and F-doped TiO₂ (TiO2−_yF_y). Based on the characterizations including XRD, Raman, FTIR, TEM, PLS, UV–vis DRS, N₂ adsorption–desorption isotherms, XPS and NH₃-TPD, the synergetic promotions of N- and F-dopants incorporated into the TiO₂ lattice are discussed based on the enhanced spectral response in visible region, oxygen vacancies, and surface acidic sites. Meanwhile, the supercritical treatment also promotes the activity owing to the increase in both the surface area and the crystallization degree of anatase, and the enhanced incorporation of N- and F-dopants into the TiO₂ lattice.

Keywords: TiO; 2−; x; −; _y; N; _x; F; _y; visible photocatalyst; Supercritical treatment; NH; ₄; F/ethanol fluid; Photodegradation of methylene blue; Synergetic promoting effects

Visible light-induced photocatalytic activity of delafossite AgMO₂ (M=Al, Ga, In) prepared via a hydrothermal method by Hui Dong; Zhaohui Li; Ximing Xu; Zhengxin Ding; Ling Wu; Xuxu Wang; Xianzhi Fu (pp. 551-556).

Delafossite-structured oxides AgMO₂ (M=Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO₂>AgGaO₂>AgAlO₂. The relative high photocatalytic activity of AgInO₂ can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO₂ was proposed and its stability was also investigated.

Keywords: Hydrothermal; Delafossite; AgMO; ₂; Visible light; Photocatalytic

Photo-induced charging effect and electron transfer to the redox species on nitrogen-doped TiO₂ under visible light irradiation by Shinya Higashimoto; Masashi Azuma (pp. 557-562).

Energy levels for sub-band structures of the nitrogen-doped TiO₂ (N-TiO₂) and photo-excitation mechanism for the visible light response were investigated by photo-electrochemical and spectroscopic measurements. It was demonstrated that the photo-excitation from the N-doping level of N-TiO₂ causes the accumulation of electrons into the sub-band level at the potential energy of ca. +0.35V vs. NHE (pH 2.5) under visible light irradiation. Subsequently, electron transfer does not take place from the photo-charged N-TiO₂ under visible light irradiation into such redox species as methyl viologen (MV²⁺), H⁺, Cu²⁺ ions, but into O₂ molecules, Pt⁴⁺, Ag⁺ and Au³⁺ ions by way of the sub-band level. These findings shed light on a mechanism for the photocatalytic reactions on the N-TiO₂ under visible light irradiation.

Keywords: Nitrogen-doped TiO; ₂; Photocatalyst; Visible light; Photo-charging; Photo-electrochemistry; Charge separation; Redox potential; Electron transfer

New approaches to prepare nitrogen-doped TiO₂ photocatalysts and study on their photocatalytic activities in visible light by Mingyang Xing; Jinlong Zhang; Feng Chen (pp. 563-569).

Nitrogen-doped TiO₂ nanocatalysts were successfully synthesized by adjusting a pH range using the ammonium nitrate and ammonia water as the nitrogen source. The samples were characterized by XRD, XPS and UV-DRS. When the total amount of ammonium nitrate and ammonia water was unchanged, different pH values were modified by changing the NH₄NO₃/NH₃·H₂O ratio to prepare nitrogen-doped TiO₂. The prepared photocatalyst showed the highest photo-activity for the degradation of 2,4-dichlorophenol (2,4-DCP) under visible light when prepared at pH 5.87. XPS analysis showed the presence of nitrogen in two states doped in TiO₂. The results indicated the photocatalytic activity of N-TiO₂ is varied with the change of pH values, the amount of the nitrogen sources and water. The experimental results showed that the higher activity is due to the variation in the concentration and states of nitrogen-doped in TiO₂. In the preparation methods, the photocatalyst was treated with the hydrogen peroxide before calcination, resulting in the decrease of nitrogen doped into the lattice and the photo-degradation rate of 2,4-DCP. The results suggested that the nitrogen source could be doped into the crystal lattice only in the form of reduction state as NH₄⁺ ion during the calcination process.

Keywords: N-TiO; ₂; pH; Photocatalytic degradation; Nitrogen states

Determination and risk assessment of by-products resulting from photocatalytic oxidation of toluene by Jinhan Mo; Yinping Zhang; Qiujian Xu; Yongfa Zhu; Jennifer Joaquin Lamson; Rongyi Zhao (pp. 570-576).

The generation of harmful by-products during photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) is a bottleneck problem for the application of PCO technology in indoor environment. Toluene is a typical VOC found in indoor air. In this work, the by-products at ppb level were studied during PCO decomposition of toluene in a plate-type reactor and identified using PTR-MS (proton transfer reaction-mass spectrometry) and GC–MS (gas chromatography–mass spectroscopy). The results indicated that benzaldehyde, methanol, acetaldehyde, acetone/propionaldehyde, formic acid/ethanol and acetic acid were the main by-products in the gas phase. By adjusting the concentration of water vapor, some compounds adsorbed on the TiO₂ surface were ascertained, which resulted in the deactivation of TiO₂. They were benzoic acid, benzene, acrylaldehyde, butyraldehyde and pentanal. Some of these by-products have not been reported in the literature. Possible photocatalytic oxidation pathways of toluene were proposed. A health-related index (HRI) was introduced to assess the risk level to human health of these ppb-level by-products. It concludes that although some undesired by-products (even carcinogenic) are generated during PCO decomposition of toluene, it seems that these by-products do not have negative effects to human health because of their low concentrations.

Keywords: Photocatalytic oxidation (PCO); Volatile organic compounds (VOCs); Indoor air quality (IAQ); Toluene; PTR-MS

Self-assembly of Bi_xTi1−_xO₂ visible photocatalyst with core–shell structure and enhanced activity by Zhenfeng Bian; Jie Ren; Jian Zhu; Shaohua Wang; Yunfeng Lu; Hexing Li (pp. 577-582).

Mesoporous Bi_xTi1−_xO₂ spheres with core–shell chamber were prepared by alcoholysis under solvothermal conditions. The cross-condensation between Ti–OH and Bi–OH ensured complete incorporation of Bi-dopants into TiO₂ lattice, though Bi atom is much bigger than Ti. Meanwhile, the aggregation of titania building clusters into spheres and their subsequent reactions including dissolution and re-deposition processes lead to the hollow spheres with tunable interior structure. The Bi-doping induced strong spectral response in visible region owing to the formation of narrow intermediate energy band gaps. Meanwhile, multiple reflections within the sphere interior voids promoted the light absorbance. As a result, the as-prepared Bi_xTi1−_xO₂ spheres exhibited much higher activity than the undoped TiO₂, the Bi₂O₃/TiO₂ obtained by impregnating the TiO₂ with Bi(NO₃)₃ solution, and the Bi_xTi1−_xO₂ after being ground during photodegradation of p-chlorophenol under visible light irradiation. Meanwhile, the Bi_xTi1−_xO₂ could be used repetitively for 10 times owing to the high hydrothermal stability and the absence of Bi-leaching.

Keywords: Bi; _x; Ti; 1−; _x; O; ₂; visible photocatalyst; Core–shell structure; Solvothermal; Photodegradation of p-chlorophenol; Multiple reflections promoting effects

Nanowire-structured titanate with anatase titania: Characterization and photocatalytic activity by Fumiaki Amano; Taikei Yasumoto; Tamaki Shibayama; Satoshi Uchida; Bunsho Ohtani (pp. 583-589).

Nanowire-structured titanate with titanium(IV) oxide (titania) was obtained by calcination of potassium ion-containing titanate nanowires prepared through alkali treatment of titania nanoparticles. The presence of potassium ions in the as-synthesized titanate nanowires was required for maintenance of the nanowire structure under the conditions of post-heat treatment. The crystallite structure, composition, morphology, specific surface area, pore volume distribution, and optical properties were found to be dependent on the temperature at which titanate nanowires were calcined. Photocatalytic activity was examined using three probe reactions: oxidative decomposition of acetic acid in an aqueous solution, oxygen liberation from an aqueous silver sulfate solution, and hydrogen liberation from an aqueous methanol solution in the presence of hexachloroplatinic acid as a precursor of photodeposition of platinum particles. Detailed characterization and results of photocatalytic activity tests revealed that titanate crystallites greatly contributed to the photocatalytic activities of the calcined nanowires except for photocatalytic hydrogen liberation. It was found that platinum was preferentially photodeposited on anatase crystallites rather than on titanate crystallites for hydrogen liberation.

Keywords: Potassium titanate; Nanowire; Anatase; Titanium oxide; Photodegradation; Oxidative decomposition; Mineralization; Hydrogen evolution; Photodeposition

Conversion of biomass to fuel: Transesterification of vegetable oil to biodiesel using KF loaded nano-γ-Al₂O₃ as catalyst by Nezahat Boz; Nebahat Degirmenbasi; Dilhan M. Kalyon (pp. 590-596).

KF-impregnated nanoparticles of γ-Al₂O₃ were calcinated and used as heterogeneous catalysts for the transesterification of vegetable oil with methanol for the synthesis of biodiesel (fatty acid methyl esters, FAME). The ratio of KF to nano-γ-Al₂O₃, calcination temperature, molar ratio of methanol/oil, transesterification reaction temperature and time, and the concentration of the catalyst were used as the parameters of the study. A methyl ester yield of 97.7±2.14% was obtained under the catalyst preparation and transesterification conditions of KF loading of 15wt%, calcination temperature of 773K, 8h of reaction time at 338K, and using 3wt% catalysts and molar ratio of methanol/oil of 15:1. This relatively high conversion of vegetable oil to biodiesel is considered to be associated with the achieved relatively high basicity of the catalyst surface (1.68mmol/g) and the high surface to volume ratio of the nanoparticles of γ-Al₂O₃.

Keywords: Biodiesel; FAME; Heterogeneous catalyst; Nano-alumina; Potassium fluoride

Synthesis of sulfated ZrO₂/MWCNT composites as new supports of Pt catalysts for direct methanol fuel cell application by Dao-Jun Guo; Xin-Ping Qiu; Wen-Tao Zhu; Li-Quan Chen (pp. 597-601).

Sulfated zirconia supported on multi-walled carbon nanotubes as new supports of Pt catalyst (Pt–S-ZrO₂/MWCNT) was synthesized with aims to enhance electron and proton conductivity and also catalytic activity of Pt electrocatalyst in terms of larger concentrations of ionizable OH groups on surfaces. Fourier transform infrared spectroscopy analysis shows that the sample surfaces were modified with sulfate. Transmission electron microscopy results show that the Pt and sulfated ZrO₂ particles dispersed relatively uniformly on the surface of the multi-walled carbon nanotube. X-ray diffraction shows that S-ZrO₂ and Pt coexist in the Pt–S-ZrO₂/MWCNT composites and S-ZrO₂ has no effect on the crystalline lattice of Pt. Pt–S-ZrO₂/MWCNT catalyst was evaluated in terms of the electrochemical activity for methanol electro-oxidation using cyclic voltammetry, steady-state polarization experiments and electrochemical impedance spectroscopy technique at room temperature. Pt–S-ZrO₂/MWCNT catalyst show higher catalytic activity for methanol electro-oxidation compared with Pt catalyst on non-sulfated ZrO₂/MWCNT support and commercial Pt/C (E-TEK).

Keywords: Electrocatalyst; Solid superacid; Methanol oxidation; Proton conductivity; Direct methanol fuel cell

Fast adsorptive and photocatalytic purification of air from acetone and dimethyl methylphosphonate by TiO₂ aerosol by A.S. Besov; A.V. Vorontsov; V.N. Parmon (pp. 602-612).

A high concentration (1.5×10⁶cm⁻³) TiO₂ aerosol of the average particle size 0.5μm was generated by a sonic method inside 0.1m³ Plexiglas chamber and applied for the adsorptive and adsorptive-photocatalytic purification of air from vapors of acetone and chemical agents’ model dimethyl methylphosphonate (DMMP). The adsorptive capture of acetone over the TiO₂ aerosol results in establishing equilibrium adsorption state and is limited by the rate of the aerosol admission into the chamber. A model derived from the Langmuir isotherm describes well the acetone concentration vs. aerosol mass curve and allows obtaining the adsorption constant and monolayer coverage of acetone in a 10min experiment. The UV irradiation of TiO₂ aerosol accelerates dramatically the purification from acetone at the high relative humidity (RH) of the air. Increased RH of air decreases the rate of the acetone adsorption but has a little positive effect on the rate of photocatalytic oxidation of acetone over aerosol particles. The DMMP adsorption over TiO₂ aerosol is accompanied by the immediate ( τ<10s) and irreversible hydrolysis of DMMP with the formation of gas phase methanol and adsorbed methyl methylphosphonic acid. The irreversible reactive adsorption results in the very fast air purification ( τ=20–40s) due to very small diffusion distances of substrate to the TiO₂ surface in aerosol. The increase of the air RH from 4 to 37% (296K) decreases the rate of adsorption but accelerates significantly the rate of photocatalytic oxidation. The complete air purification from organic compounds within 10min is possible only with the photocatalytic oxidation because the adsorption alone does not remove methanol. The time needed for the air purification over the nanosized TiO₂ aerosol is directly determined by the rate of the aerosol generation which allows a further optimization of the TiO₂ aerosol air purification. The obtained results approve experimentally a suggestion that the photocatalytic oxidation over solid atmospheric aerosols actually takes part in the Earth atmosphere and serves as an important sink for airborne organics.

Keywords: Atmospheric chemistry; CWA; Photocatalysis; Titanium dioxide; Titania; Decontamination; Anti-terrorism; Water concentration; Gas phase; Static; Nanoparticles; Phosphoric acid; Troposphere

Efficient gas phase photodecomposition of acetone by Ru-doped Titania by Vendula Houšková; Václav Štengl; Snejana Bakardjieva; Nataliya Murafa; Václav Tyrpekl (pp. 613-619).

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by homogenous hydrolysis of TiOSO₄ in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and surface area (BET) and porosity determination (BJH). The photocatalytic activity of Ru-doped titania samples was determined in the gas phase by decomposition of acetone during irradiation at 365nm and 400nm. The Ru-doped titania samples demonstrated enhanced photocatalytic activity under visible light. Ruthenium oxide causes the anatase to rutile transformation to occur at lower temperatures and decreasing of band-gap energy of Ru-doped samples.

Keywords: TiO; ₂; Doped; RuO; ₂; Urea; Photocatalytic activity

A comparative study on the efficiency of electro-Fenton process in the removal of propham from water by Ali Özcan; Yücel Şahin; A. Savaş Koparal; Mehmet A. Oturan (pp. 620-626).

Electro-Fenton process has been widely used in the treatment of organic pollutants lately. Its oxidation efficiency mainly depends on the electrode materials. In this study, boron doped diamond (BDD), carbon sponge (CS) and platinum (Pt) electrodes were used at four different configurations as anode and cathode. The oxidation efficiencies of BDD anode and CS cathode were investigated together for the first time in the electro-Fenton process. Propham was used as the model pollutant. The obtained results indicate that the decay rate of propham and the mineralization rate of propham aqueous solutions were highest in the case of BDD and CS electrodes as expected. The obtained mineralization current efficiency (MCE) value was 81% at 100mA in the presence of 0.2mM Fe³⁺ for 30min electrolysis. The oxidative degradation intermediates of propham showed different accumulation characteristics in all configurations. The oxamic acid resisted to mineralization but it rapidly degraded in the presence of BDD anode.

Keywords: Electro-Fenton; AOP; Hydroxyl radical; BDD; Mineralization; Propham

Effect of pretreatment and regeneration conditions of Ru/γ-Al₂O₃ catalysts for N₂O decomposition and/or reduction in O₂-rich atmospheres and in the presence of NO_X, SO₂ and H₂O by Vasilis G. Komvokis; George E. Marnellos; Iacovos A. Vasalos; Kostas S. Triantafyllidis (pp. 627-634).

The effect of the pretreatment (inert, oxidative, and reducing) of Ru/γ-Al₂O₃ catalyst on its activity and stability in the decomposition of N₂O in the absence or presence of O₂, SO₂, H₂O and NO_X was studied in the present work. Decomposition of pure N₂O was slightly enhanced by the H₂-pretreated catalyst (metallic Ru) compared to the O₂- or He-pretreated ones, owing to a cyclic oxidation–reduction pathway of metallic Ru. The observed decrease of activity by O₂ or H₂O addition was reversible compared to SO₂ which caused a strong, irreversible deactivation of the catalyst, irrespective of the type of pretreatment. This was attributed to the formation of stable sulphates, mainly those on RuO₂ surface, which could only be removed by regeneration under reducing (H₂ in He) atmosphere at temperatures of ca. 500°C. Oxidative or inert regeneration required very high temperatures (i.e. >700°C) in order to decompose these sulphates. A method of retaining N₂O conversion activity very high (≥98%) for long reaction times is suggested and is based on frequent and short-time (ca. 10min) regenerations of the catalyst under reducing atmosphere (ca. 5% H₂ in He). The effect of co-feeding various reducing agents, such as CO or C₃H₆, on the N₂O conversion activity in the presence of O₂, SO₂, H₂O and NO_X is negligible, mainly because they are oxidized at relatively low temperatures in the O₂-rich feeds used in this study.

Keywords: Nitrous oxide—N; ₂; O; Decomposition; Reduction; Ruthenium catalysts; Pretreatment; Regeneration; Combustion off-gases; CO; Propylene

Synergistic effect of TiO₂ and iron oxide supported on fluorocarbon films. Part 1: Effect of preparation parameters on photocatalytic degradation of organic pollutant at neutral pH by F. Mazille; T. Schoettl; C. Pulgarin (pp. 635-644).

Iron oxide and TiO₂ were immobilized on modified polyvinyl fluoride films in a sequential process. Synergic effects of iron oxide and TiO₂ on the polymer film were observed during the heterogeneous degradation of hydroquinone (HQ) in the presence of H₂O₂ at pH close to neutrality and under simulated solar irradiation. Within the degradation period, little iron leaching (<0.5mg/L) was observed.The surface of commercial polyvinyl fluoride (PVF) film was modified by TiO₂ under light inducing oxygen group (C–OH, CO, COOH) formation on the film surface. During this treatment, TiO₂ nanoparticles simultaneously bind to the film, leading to PVF^f–TiO₂. The possible mechanistic pathway for the TiO₂ deposition and the nature of the polymer–TiO₂ interaction are discussed. Furthermore PVF and PVF^f–TiO₂ were immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl₃, leading to PVF–Fe oxide and to PVF^f–TiO₂–Fe oxide respectively.HQ degradation and mineralization mediated by PVF^f–TiO₂, PVF–Fe oxide and PVF^f–TiO₂–Fe oxide were investigated under different conditions. Remarkable synergistic effects were observed for PVF^f–TiO₂–Fe oxide possibly due to Fe(II) regeneration, accelerated by electron transfer from TiO₂ to the iron oxide under light.

Keywords: Heterogeneous photo-Fenton; TiO; ₂; photocatalysis; Polymer surface modification; Synergistic effects; Solar detoxification

Electrocatalytic properties of diamond in the oxidation of a persistant pollutant by Elena Guinea; Francesc Centellas; Enric Brillas; Pablo Cañizares; Cristina Sáez; Manuel A. Rodrigo (pp. 645-650).

This work is focused on the study of the role of several conductive-diamond characteristics (boron doping, sp³/sp² ratio, diamond-layer thickness) on the performance of the electrolysis of enrofloxacin (as model complex-organic pollutant). Commercial lots provided by an important conductive-diamond manufacturing company have been used. Results show that enrofloxacin electrooxidation is strongly influenced by the conductive-diamond characteristics; particularly the ratio diamond/graphite carbon was found one of the most significant parameters in this process: the higher the content in diamond-carbon the greater the TOC and COD decays in the bulk electrolyses. These results have been interpreted in terms of the oxidation mechanism involved. High graphite content favours direct oxidation of the pollutant on the electrode surface and leads to the formation of many intermediates. On contrary, high diamond content seems to favour the complete oxidation of the organic to carbon dioxide, thanks to the contribution of the oxidants (hydroxyl radicals and electrogenerated reagents) present in a region close to the electrode surface. Likewise, the oxidation rate seems to be improved with increase in the concentration of boron and decrease in the thickness of the substrate layer.

Keywords: Diamond; Electrooxidation; Electrocatalytic properties; Wastewater; Persistent

Fenton-driven regeneration of MTBE-spent granular activated carbon—Effects of particle size and iron amendment procedures by Scott G. Huling; Eunsung Kan; Caleb Wingo (pp. 651-658).

Fenton-driven regeneration of spent granular activated carbon (GAC) can be used to regenerate organic contaminant-spent GAC. In this study, the effects of GAC particle size (>2mm to <0.35mm) and acid pre-treatment of GAC on Fenton-driven oxidation of methyl- tert-butyl ether (MTBE)-spent GAC were evaluated. Iron (Fe) was amended to the GAC using two methods: (1) untreated—where GAC was amended with a concentrated solution of ferrous sulfate and (2) acid pre-treatment—where GAC was amended with acid followed by sequential applications of a dilute ferrous sulfate solution. Subsequently, MTBE was amended to the GAC, followed by oxidative treatments with H₂O₂. H₂O₂ reaction and MTBE oxidation were inversely correlated with GAC particle size and were attributed to shorter intraparticle diffusion transport distances for both H₂O₂ and MTBE. Image analysis of the GAC cross-sections (i.e., prepared thin sections) revealed that the Fe amended to the GAC extended to the center of the GAC particles. Fe accumulated at higher levels on the periphery of the untreated GAC but Fe dispersal was more uniform in the acid pre-treated GAC. In the acid pre-treated GAC, conditions for MTBE oxidation were favorable and greater levels of MTBE oxidation were measured for all particle size fractions tested. Modeling and critical analysis of H₂O₂ diffusive transport and reaction indicated limited H₂O₂ penetration into large GAC particles which contributed to a decline in MTBE removal. Residual MTBE remaining on the GAC limited the quantity of MTBE that could be re-adsorbed, but no reduction in MTBE sorption capacity resulted from oxidative treatments.

Keywords: Activated carbon; Hydrogen peroxide; Iron; Methyl-; tert; -butyl ether; Oxidation

Effect of the pressure on the catalytic oxidation of volatile organic compounds over Ag/Al₂O₃ catalyst by Yi Li; Xiuli Zhang; Hong He; Yunbo Yu; Tao Yuan; Zhenyu Tian; Jing Wang; Yuyang Li (pp. 659-664).

The catalytic oxidation of volatile organic compounds (VOCs: ethanol, 1-propanol and 2-propanol) over Ag/Al₂O₃ catalyst under low and normal atmospheric pressure conditions has been studied with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). The partial oxidation intermediates of the VOCs under different pressures were identified by PIMS and their photoionization efficiency (PIE) spectra. Alkene is preferentially formed under the low pressure conditions, while aldehyde and acid are favored under the normal atmospheric pressure conditions. In addition, the low pressure conditions are more suitable for observing the active intermediates, such as ethenol, ketene and propenal. The results indicate that the pressure has a significant effect on the oxidation pathway of VOCs over Ag/Al₂O₃ catalyst.

Keywords: Silver/alumina; Volatile organic compounds; Catalytic partial oxidation; Synchrotron VUV photoionization mass spectrometry

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Applied Catalysis B, Environmental (v.89, #3-4)