Semiconductor‐photocatalyzed degradation of carboxylic acids: Enhancement by particulate semiconductor mixture

Degradation of oxalic acid on particulate TiO₂, ZnO, CuO, Bi₂O₃, In₂O₃, and Nb₂O₅ under UV‐A light exhibits first‐order kinetics, and the degradation rates increase linearly with the photon flux. All the oxides show sustainable photocatalytic activity, and the photonic efficiencies of degradation of oxalate are very much lower than those of the acid. The ease of degradation of carboxylic acids is the following: formic > oxalic > acetic > citric. Intimate mixtures of two different particulate semiconductors kept under suspension and at continuous motion exhibit higher photocatalytic activity, revealing interparticle charge transfer. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 716–726, 2009     

Investigation of thermal decomposition of yttrium–aluminum-based precursors for YAG phosphors

Three types of precursors were prepared using the wet-chemical synthesis route, starting from yttrium?Ceuropium?Caluminum nitrate solution and different precipitating agents (urea, oxalic acid, and ammonium carbonate). The precursors were fired at 1200?°C in nitrogen atmosphere in order to obtain europium-doped yttrium aluminate Y₃Al₅O₁₂:Eu³⁺ phosphor with garnet structure (YAG:Eu). The processes involved in the thermal decomposition of precursors and their composition were put in evidence using thermal analysis (TG?CDTA) and FT-IR spectroscopy. The GA?CDTA curves possess typical features for basic-oxalate, -nitrate, and -carbonates as formed with oxalic acid, urea, and ammonium carbonate, respectively. Correlation between the thermal decomposition steps, mass loss, and composition of gases evolved during the thermal treatment was established using TG?CDTA?CFT-IR coupling. It was found that the different composition of precursors reflects on the luminescent characteristics of the corresponding phosphors. Urea and ammonium carbonate lead to the formation of YAG type phosphors, with garnet structure and specific red emission. As for the oxalic acid, this precipitating agent generates a non-homogeneous powder that contains yttrium oxide as impurity phase. This phosphor is a mixture of Y₂O₃:Eu³⁺, Y₄Al₂O₉:Eu³⁺, and Y₃Al₅O₁₂:Eu³⁺ that explain the relative higher emission intensity.     

Use of composites based on boron nitride in combined photocatalytic process for generation of hydrogen and degradation of soluble organic substances

Possibility of using composites based on boron nitride in combined photocatalytic processes for degradation of soluble organic substances and generation of hydrogen was examined. The hydrogen evolution rate and output capacity of the composites under study in release of hydrogen from aqueous solutions of formic and oxalic acids and hydrazine under irradiation with visible and UV light were evaluated. It is shown that the highest efficiency of generation of molecular hydrogen is achieved in photodecomposition of hydrazine and oxalic acid with a composite whose phase composition includes iron and a set of semiconductor carbides (Fe₃C, MgC₂, Al₄C₃, SiC).     

Total Oxidation of Propene and Toluene on Copper/Yttrium Doped Zirconia

The catalytic oxidation of propene and toluene has been investigated on pure ZrO₂, pure Y₂O₃, and ZrO₂ doped with 1, 5, and 10 mol % Y₂O₃ in the presence or absence of copper (0.5, 1, and 5 wt%). A synergetic effect has been detected since ZrO₂ and Y₂O₃ exhibit significantly lower activities than the mixed oxides. The higher surface areas, related to structural change from mononoclinic (ZrO₂) to tetragonal (ZrO₂–;;Y₂O₃), partly explained the higher activity of ZrO₂–;;Y₂O₃. However, it has been shown that the number of anionic vacancies, created by the substitution of Zr⁴⁺ by Y³⁺, in yttria-stabilized zirconia solids depends on the yttrium contents. Their effect on propene and toluene oxidation activity is significant. The anionic vacancies should induce better activity of the ZrO₂—5 mol % Y₂O₃ catalyst with or without copper, which presents the higher number of Zr³⁺ species. This support should favor the formation of CuO particles, which should be the most active catalytic sites in the studied reaction.     

The chemical synthesis of conductive polyaniline doped with dicarboxylic acids

The chemical polymerization of aniline was carried out in media containing different linear dicarboxylic acids with the use of oxidants such as K₂Cr₂O₇, KMnO₄, K₂S₂O₈, KIO₃ and FeCl₃. The highest yield and the conductivity were observed with K₂Cr₂O₇. The yield and the conductivity of the polyaniline (PAn) synthesized were observed to decrease in the order of oxalic acid > malonic acid > succinic acid > glutaric acid > adipic acid > phthalic acid. The solubility tests carried out in solvents such as DMF, DMSO and NMP showed that the larger the dopant molecule, the higher is the solubility of polyaniline. The PAn synthesized was characterized by measurements of conductivity, intrinsic viscosity, density and FTIR, UV-VIS and TGA techniques.     

Photoelectrochemistry in particulate systems. 5. Visible light-induced polymerization of 1-vinylpyrene in semiconductor suspensions

Photoelectrochemical polymerization of 1-vinylpyrene has been achieved in a semiconductor photocatalyst suspension under visible light irradiation (λ > 480 nm). Bandgap excitation of CdS, CdSe or Fe₂O₃ led to the oxidation of 1-vinylpyrene, which initiated the polymerization process. A 25–47% yield of poly(1-vinylpyrene) could be obtained upon irradiation of these semiconductor photocatalyst suspensions with 1-vinylpyrene in acetonitrile. Dependence of the polymer yield on various experimental conditions is described.     

Influence of support on resistance to carbon-deposition of catalyst for CH4, CO2 with O2 to synthesis gas

In the reaction of catalytic oxidation of CH₄, CO₂ with O₂ to synthesis gas, carbon-deposition is an important factor for deactivation. By adding different oxides to Ni/Al₂O₃ catalyst, its resistance to carbon-deposition was improved. The experimental results indicate that the order of resistance to carbon-deposition is as follows: Ni/CaO-Al₂O₃>Ni/MgO-Al₂O₃>Ni/ TiO₂-Al₂O₃ > Ni/CeO₂-Al₂O₃>Ni/La₂O₃-Al₂O₃>Ni/Y₂O₃-Al₂O₃>Ni/Fe₂O₃-Al₂O₃>Ni/Al₂O₃. The catalysts were characterized by CO₂-TPD, O₂-TPD and XPS methods. Here the relation between the order of resistance to carbon-deposition and performance of catalyst is discussed.     

Thermogravimetric study of the nonstoichiometric regions in the Y-Ba-Cu-O system

The paper presents the results of studies on thermal reduction and oxidation of the nonstoichiometric phases from the Y-Ba-Cu-O in air.The thermogravimetric (TG, DTA) experiments were performed in air in order to establish the ranges of stoichiometry and temperature of oxidation and reduction of YBa₂Cu₃O_x, YBa₄Cu₃O_x, YBa₅Cu₂O_x and Y₃Ba₈CusO_x.It has been found, that at 950°C in air there are four oxygen deficient ternary cuprates: YBa₂Cu₃O_6.02, YBa₄Cu₃O_8.01, YBa₅Cu₂O_8.35, Y₃Ba₈Cu₅O_16.45 and stoichiometric Y₂BaCuO₅. When these nonstoichiometric cuprates are cooled slowly to room temperature in air they oxidize to the following compositions: YBa₂Cu₃O_6.98, YBa₄Cu₃O_8.97, Y₃Ba₈Cu₅O₁₈ and YBa₅Cu₂O_8.97.This work has been supported by the CPBR 6.6.64 research programme.     

Two-Layer Nano-Oxide Composite Films on Fe-18Cr Alloys

A two-layer film composed of a reactive element (RE) oxide (ZrO₂, Y₂O₃, CeO₂, or La₂O₃) and aluminum oxide (Al₂O₃) was prepared on the surface of Fe-18Cr alloys by an electrochemical process combined with sintering. High-resolution field emission scanning electron microscopy (FE-SEM) was used to characterize the two-layer film, which showed nanostructure. SEM, EDS and mass gain measurement were used to study the oxidation resistance of the film on Fe-18Cr alloy. It is proved that this kind of film is effective in protecting the substrate from oxidation. The results also indicated that the two-layer film possesses superior oxidation resistance than a single Al₂O₃ film. The mechanisms accounting for such effects have been discussed.     

Enhancement of solar light photocatalytic activity of TiO2-CeO2 composite by Er3+:Y3Al5O12 in organic dye degradation

The Er³⁺:Y₃Al₅O₁₂, as an upconversion luminescence agent which is able to transform the visible part of the solar light to ultraviolet light, was prepared by nitrate-citrate sol-gel method. A novel solar light photocatalyst, Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite was synthesized using ultrasonic treatment. The X-ray diffraction (XRD) and scanning election microscopy (SEM) were used to characterize the structural morphology of the Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite. In order to evaluate the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite, the Azo Fuchsine dye was used as a model organic pollutant. The progress of the degradation reaction was monitored by UV-Vis spectroscopy and ion chromatography. The key influences on the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ were studied, such as Ti/Ce molar ratio, heat-treatment temperature and heat-treatment time. Otherwise, the effects of initial dye concentration, Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ amount, solar light irradiation time and the nature of the dye on the solar light photocatalytic degradation process were investigated. It was found that the solar light photocatalytic activity of Er³⁺:Y₃Al₅O₁₂/TiO₂-CeO₂ composite was superior to Er³⁺:Y₃Al₅O₁₂/TiO₂ and Er³⁺:Y₃Al₅O₁₂/CeO₂ powder in the similar conditions.     

Electrocatalytic behaviour of citric acid at a cobalt phthalocyanine-modified screen-printed carbon electrode and its application in pharmaceutical and food analysis

Cobalt phthalocyanine-modified screen-printed carbon electrodes (CoPC-SPCEs) have been investigated as disposable sensors for the measurement of citric acid. The analyte was found to undergo an electrocatalytic oxidation process involving the Co²⁺/Co³⁺ redox couple. Calibration plots were found to be linear in the range 2 mM to 2.0 M; replicate determinations of a 5.2 mM citric acid (n = 4) solution gave a coefficient of variation of 1.43%. Additions of metal ions, such as Ag⁺, Pb²⁺, Cu²⁺, Fe³⁺ and Ca²⁺, were found not to interfere. The effects of hesperidin, cysteine, ethylenediaminetetraacetic acid (EDTA), ascorbic, formic, malic, malonic, tartaric, oxalic and trichloroacetic acids on the determination of citric acid were examined and, under the conditions employed, only oxalic acid and EDTA were found to give any significant interference. The sensors were evaluated by carrying out citric acid determinations on spiked and unspiked samples of an acid citrate dextrose (ACD) formulation, lime flesh and juice. For lime juice, recoveries were calculated to be 96.8% (% CV = 2.7%) for a sample fortified with 5% citric acid and for ACD 99.4% (%CV = 2.6%) when fortified at 2.30% citric acid. Further studies showed the possibility of determining citric acid concentrations in lime juice and fruit directly, without the need for an added electrolyte. These performance characteristics indicate that reliable data may be obtained for citric acid measurements in such samples. To our knowledge, this is the first report on the electrocatalytic oxidation of citric acid and its application using a CoPC-SPCE.     

可控粒径纳米Fe_3O_4的制备及其磁性研究

本文用空气氧化法,在可见光作用下,添加配合剂(EDTA、柠檬酸、酒石酸、谷氨酸)在室温进行了不同粒径纳米Fe3O4的制备及其磁性能研究。结果表明:在可见光作用下,随EDTA、柠檬酸、酒石酸、谷氨酸等配合剂的添加,得到纳米Fe3O4的粒径有所减小、分散性有所提高;配合剂及可见光共存时,体系反应速率得到提高,高的反应速率使纳米Fe3O4晶粒减小;控制适当的光照度和添加剂的量,室温可得到11.8~29.6nm的Fe3O4颗粒。不同粒径纳米Fe3O4分别呈现出超顺磁性、铁磁性特征。     

The effect of the nature of the support on catalytic properties of ruthenium supported catalysts in partial oxidation of methane to syn-gas

The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was investigated. A variety of supports differed in texture and reducibility (Al₂O₃, SiO₂, TiO₂, Cr₂O₃, CeO₂ and Fe₂O₃) were used. The catalyst activity is governed by ruthenium phase formation (RuO₂ → Ru⁰), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported catalysts decreases in the order Al₂O₃ ≈ SiO₂ > Cr₂O₃ > TiO₂ > CeO₂ > Fe₂O₃. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity of CO formation were found. The selectivity of CO₂ formation (total oxidation of CH₄) under conditions of POM (a ratio of CH₄/O₂ = 2) is associated with the contribution of reducible support oxides into the catalytic performance.     

Photocatalytic Water Oxidation by a Pyrochlore Oxide upon Irradiation with Visible Light: Rhodium Substitution Into Yttrium Titanate

A stable visible‐light‐driven photocatalyst (λ≥450 nm) for water oxidation is reported. Rhodium substitution into the pyrochlore Y₂Ti₂O₇ is demonstrated by monitoring Vegard′s law evolution of the unit‐cell parameters with changing rhodium content, to a maximum content of 3 % dopant. Substitution renders the solid solutions visible‐light active. The overall rate of oxygen evolution is comparable to WO₃ but with superior light‐harvesting and surface‐area‐normalized turnover rates, making Y₂Ti_1.94Rh_0.06O₇ an excellent candidate for use in a Z‐scheme water‐splitting system.     

Phenol degradation on Pr6O11 surface under UV-A light. Synergistic photocatalysis by semiconductors

Phenol degrades on the surface of Pr₆O₁₁, an insulator, under UV-A light and the degradation rate increases linearly with phenol concentration and photon flux but decreases linearly with pH. The degradation efficiency is higher with UV-C light than with UV-A light. While TiO₂, Fe₂O₃, CuO, ZnO, ZnS, Nb₂O₅ and CdO particles individually photocatalyze the degradation each semiconductor exhibits synergistic effect, an enhanced photodegradation, when present along with Pr₆O₁₁ suggesting hole-transfer from illuminated semiconductors to phenol adsorbed on Pr₆O₁₁ during collision.     

Photomineralization of phenol on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>: synergistic photocatalysis by semiconductors

Phenol gets adsorbed on Al₂O₃ and mineralizes under UV light in the presence of dissolved O₂. The degradation exhibits first-order kinetics and its rate increases linearly with the light intensity and decreases with pH. 2,4-Diphenoxycyclohexanone and 2,6-diphenoxycyclohex-3-ene-1-ol are the intermediates of the reaction. While particulate TiO₂, ZnO, ZnS, Fe₂O₃, CuO, CdO, and Nb₂O₅ individually photocatalyze the degradation, each semiconductor exhibits synergistic photocatalysis, an enhanced photodegradation, when present along with Al₂O₃, indicating electron abstraction by illuminated semiconductors from the phenol adsorbed on Al₂O₃.     

Effect of chelating agents on catalytic performance of Cr/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dehydrogenation catalysts

Chromia/alumina (Cr₂O₃/γ-Al₂O₃) catalysts with addition of chelating agents (citric acid or oxalic acid) were prepared by the incipient impregnation method. The resulting catalysts with different citric acid (CA) or oxalic acid (OA) contents were applied to the dehydrogenation of isobutane to isobutene. The influence of chelating agents on the catalysts was investigated by means of BET, SEM, H₂-TPR, NH₃-TPD, and TG-DTG. The results showed that the Cr₂O₃/γ-Al₂O₃ catalysts with addition of CA or OA exerted slightly increase on specific surface area. The addition of the chelating agents as expected, determined a general decrease in the surface acidity. The catalysts with CA or OA have a better anti-coking ability by inhibiting the side reaction of cracking and carbon formation. The addition of CA or OA for preparing these catalysts resulted in a beneficial effect on the reducibility of the Cr species to diminish the reduction temperature. The appropriate content of chelating agents could improve dispersion of metal species in the γ-Al₂O₃ support. The catalytic activity showed an important enhancement when the metal species was impregnated in the presence of CA or OA.     

Structure Sensitivity of CO Oxidation on Co3O4: A DFT Study

The reaction mechanism of CO oxidation on the Co₃O₄ (110) and Co₃O₄ (111) surfaces is investigated by means of spin‐polarized density functional theory (DFT) within the GGA+U framework. Adsorption situation and complete reaction cycles for CO oxidation are clarified. The results indicate that 1) the U value can affect the calculated energetic result significantly, not only the absolute adsorption energy but also the trend in adsorption energy; 2) CO can directly react with surface lattice oxygen atoms (O_2f/O_3f) to form CO₂ via the Mars–van Krevelen reaction mechanism on both (110)‐B and (111)‐B; 3) pre‐adsorbed molecular O₂ can enhance CO oxidation through the channel in which it directly reacts with molecular CO to form CO₂ [O₂(a)+CO(g)→CO₂(g)+O(a)] on (110)‐A/(111)‐A; 4) CO oxidation is a structure‐sensitive reaction, and the activation energy of CO oxidation follows the order of Co₃O₄ (111)‐A(0.78 eV)>Co₃O₄ (111)‐B (0.68 eV)>Co₃O₄ (110)‐A (0.51 eV)>Co₃O₄ (110)‐B (0.41 eV), that is, the (110) surface shows higher reactivity for CO oxidation than the (111) surface; 5) in addition to the O_2f, it was also found that Co³⁺ is more active than Co²⁺, so both O_2f and Co³⁺ control the catalytic activity of CO oxidation on Co₃O₄, as opposed to a previous DFT study which concluded that either Co³⁺ or O_2f is the active site.     

Chelating agents role on phase formation and surface morphology of single orthorhombic YMn2O5 nanorods via modified polyacrylamide gel route

YMn2O5nanorods were synthesized through a modified polyacrylamide gel route.The synthesis strategy in this work is based on a sol-gel process using a polyacrylamide gel method in which oxalic acid,citric acid or tartaric acid is employed as the chelating agent.In the gel routes,oxalic acid was used as a carboxyl chelating agent,while citric acid or tartaric acid was a carboxyl and hydroxyl chelating agent.The as-prepared samples were characterized by means of techniques such as X-ray powder diffraction(XRD)measurement,thermogravimetric analysis(TG),differential scanning calorimetry analysis(DSC),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),thermal expansion measurement and field-emission scanning electron microscopy(SEM)investigations.It was found that oxalic acid is the best chelating agent with Y(NO3)3·6H2O and Mn(CH3COO)2·4H2O as precursors to prepare a single orthorhombic YMn2O5nanorods at 1000°C.Scanning electron microscope observation shows that the morphology of YMn2O5powders is significantly dependent on the chelating agent.The peaks(single orthorhombic YMn2O5nanorods)at 642,600,573,546,521,493,486,468,448 and 400cm?1were observed from FTIR spectra.The phase,surface morphology and chelation mechanisms of YMn2O5samples have been discussed on the basis of the experimental results.     

同轴静电纺丝技术制备Y2O3:Eu3＋@SiO2豆角状纳米电缆与表征

采用同轴静电纺丝技术, 以氧化钇、氧化铕、正硅酸乙酯(C₈H₂₀O₄Si)、无水乙醇、PVP和DMF为原料, 成功制备出大量的Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆. 用TG-DTA, XRD, SEM, TEM和荧光光谱等分析技术对样品进行了系统地表征． 结果表明, 得到的产物为Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆, 以无定型SiO₂为壳层, 晶态Y₂O₃:Eu^3＋球为芯, 电缆直径约为200 nm, 内部球平均直径约150 nm, 壳层厚度约为25 nm, 电缆长度＞300 μm. 纳米电缆内部为球状结构, 沿着纤维长度方向有序排列, 形貌均一. Y₂O₃:Eu^3＋@SiO₂豆角状纳米电缆在246 nm紫外光激发下, 发射出Eu^3＋离子特征的波长为614 nm的明亮红光. 对其形成机理进行了初步讨论.