The catalysis of photoelectrochemical reactions: I. The catalytic action of large gold islands on photoelectrochemical reactions at n-TiO2 electrode

Large gold islands were deposited on n-TiO₂ single crystal electrode by sputtering, photo-reduction and electrodeposition. Photoelectrochemical behaviors of Au-coated semiconductor electrode and pure Au electrode were measured in H₂SO₄ solution and acidic solution containing Fe^2+/3+. From the analysis of these polarization curves it was found that the contact between gold particles and semiconductor surface is mainly ohmic in nature. The catalytic behaviors of gold islands on the competitive photo-oxidation of Ce³⁺ and water were studied by using the RRDE with interchangeable disc. It was proved that gold particles in the form of large islands could only catalyse dark (electrochemical) reaction, but not the photo-electrochemical reaction.     

Enhancing Photoactivity of TiO2(B)/Anatase Core–Shell Nanofibers by Selectively Doping Cerium Ions into the TiO2(B) Core

Cerium ions (Ce³⁺⁾ can be selectively doped into the TiO₂(B) core of TiO₂(B)/anatase core–shell nanofibers by means of a simple one‐pot hydrothermal treatment of a starting material of hydrogen trititanate (H₂Ti₃O₇) nanofibers. These Ce³⁺ ions (≈0.202 nm) are located on the (110) lattice planes of the TiO₂(B) core in tunnels (width≈0.297 nm). The introduction of Ce³⁺ ions reduces the defects of the TiO₂(B) core by inhibiting the faster growth of (110) lattice planes. More importantly, the redox potential of the Ce³⁺/Ce⁴⁺ couple (E°(Ce³⁺/Ce⁴⁺)=1.715 V versus the normal hydrogen electrode) is more negative than the valence band of TiO₂(B). Therefore, once the Ce³⁺‐doped nanofibers are irradiated by UV light, the doped Ce³⁺ ions—in close vicinity to the interface between the TiO₂(B) core and anatase nanoshell—can efficiently trap the photogenerated holes. This facilitates the migration of holes from the anatase shell and leaves more photogenerated electrons in the anatase nanoshell, which results in a highly efficient separation of photogenerated charges in the anatase nanoshell. Hence, this enhanced charge‐separation mechanism accelerates dye degradation and alcohol oxidation processes. The one‐pot treatment doping strategy is also used to selectively dope other metal ions with variable oxidation states such as Co^2+/3+ and Cu^+/2+ ions. The doping substantially improves the photocatalytic activity of the mixed‐phase nanofibers. In contrast, the doping of ions with an invariable oxidation state, such as Zn²⁺, Ca²⁺, or Mg²⁺, does not enhance the photoactivity of the mixed‐phase nanofibers as the ions could not trap the photogenerated holes.     

Self-assembly and photoelectric properties of cerium complexes with 3, 4, 9, 10-perylenetetracarboxylic acid on nanocrystalline TiO2 films

Self-assembled (SA) films (PMP, M = Ce³⁺ or Ce⁴⁺) of 3,4,9,10-perylenetetracarboxylic acid (PTA) on nanocrystalline TiO₂ films with Ce³⁺ or Ce⁴⁺ as a bridge were fabricated and characterized with UV-Vis, IR, and XPS synchrotron radiation photoelectron spectroscopy (SRPES) which gave the HOMO energy levels for the SA films. It was shown that thin-layer sandwich-type solar cells based on these SA films possess good properties for photoelectric conversion. While PTA-loaded TiO₂ electrode (P) generated 26.9% of incident monochromatic photon-to-electron conversion efficiency (IPCE), PMP-sensitized TiO₂ electrodes yielded 55.8% and 39.1% for Ce⁴⁺ and Ce³⁺ respectively. PMP films can be considered as a kind of complexes whose HOMO energy levels were proved to be higher than that of film P, which is one of the major reasons for the increase in IPCE from film P to film PMP.     

Electronic structure,magnetic properties,and mixed valence character of Ce2Ni3Si5 from first principles calculations

Cerium intermetallic compounds exhibit anomalous physical properties such as heavy fermion and Kondo behaviors. Here, an ab initio study of the electronic structure, magnetic properties, and mixed valence character of Ce₂Ni₃Si₅ using density functional theory (DFT) is presented. Two theoretical methods, including pure Perdew–Burke–Ernzerhof (PBE) and PBE + U , are used. In this study, Ce³⁺ and Ce⁴⁺ are considered as two different constituents in the unit cell. The formation energy calculations on the DFT level propose that Ce is in a stable mixed valence of 3.379 at 0 K. The calculated electronic structure shows that Ce₂Ni₃Si₅ is a metallic compound with a contribution at the Fermi level from Ce 4f and Ni 3d states. With the inclusion of the effective Hubbard parameter (U _eff), the five valence electrons of 5 Ce³⁺ ions are distributed only on Ce³⁺ 4f orbitals. Therefore, the occupied Ce³⁺ 4f band is located in the valence band (VB) while Ce⁴⁺ 4f orbitals are empty and Located at the Fermi level. The calculated magnetic moment in Ce₂Ni₃Si₅ is only due to cerium (Ce³⁺) in good agreement with the experimental results. The U _eff value of 5.4 eV provides a reasonable magnetic moment of 0.981 for the unpaired electron per Ce³⁺ ion. These results may serve as a guide for studying present mixed valence cerium‐based compounds. © 2017 Wiley Periodicals, Inc.     

Silicotungstic acid modified Ce‐Fe‐Ox catalyst for selective catalytic reduction of NOx with NH3: Effect of the amount of HSiW

The HSiW(x)/Ce‐Fe catalysts were used to research the effect of silicotungstic acid contents on the catalytic activity in the selective catalytic reduction of NO_x with NH₃. Doping different contents of silicotungstic acid affected surface species and redox property as well as the catalytic activity. With the increasing amount of HSiW (x = 5%, 10% and 20%), the redox reaction between Fe³⁺/Fe²⁺ and Ce⁴⁺/Ce³⁺ enhanced, which could improve the ratio of Ce³⁺ and Fe³⁺. And then, more Ce³⁺ increased the ratio of chemisorbed oxygen (O_α). Besides, the type and strength of acid sites over HSiW(_x)/Ce‐Fe was affected by the HSiW contents. These factors facilitated the catalytic performance. Thus, the NO_x conversion of HSiW(x)/Ce‐Fe(x = 20%) was higher than 90%, which maintained in a wide temperature range between 200 and 400 °C.     

The hydrolysis of the cerium(III) ion,Ce3+, in aqueous perchlorate solutions at 50°C

The hydrolysis equilibria of the Ce³⁺ ion have been studied at 50°C by measuring, with a glass electrode, the hydrogen ion concentration of Ce(ClO₄)₃ solutions. The Ce(III) concentration ranged from 0.1 to 1 m, while the ClO⁻₄ level was kept constant at 3 m by adding LiClO₄. Solutions containing hydrolysed species, in which at the most 0.4% of the Ce³⁺ can be transformed into reaction products without the formation of a precipitate, were prepared by constant-current coulometry. The potentiometric data have been explained in terms of Ce(OH)²⁺, Ce₂(OH)⁵⁺ and Ce₃(OH)⁴⁺₅ complexes. Their formation constants in the inert 3 m LiClO₄ medium are reported.     

Chemie der Seltenerdmetalle, 19. Mitt.: Dissoziation des Ce(III)-succinats im sauren Gebiet

Zusammenfassung Die Dissoziation von Ce₂ Suc ₃·3 H₂O^** in Perchlorsäure-Lösungen wurde verfolgt und die Dissoziationskonstanten der Succinationen: (CeSuc)⁺ und (CeSuc ₂)^– unter Benützung einer Löslichkeitsmethode in 1m-NH₄ClO₄-Lösung bei 25°C bestimmt. Die Löslichkeitsprodukte von Ce₂ Suc ₃: [Ce³⁺]²[Suc ^2–]³, [CeSuc ⁺]²[Suc ^2–], [CeSuc ⁺][CeSuc ₂ ^–] wurden bestimmt.

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The dissociation of Ce₂ Suc ₃·3H₂O in perchloric acid solutions was investigated. The dissociation constants of the succinate ions (CeSuc)⁺ and (CeSuc ₂)^– were determined inM-NH₄ClO₄ at 25° using a solubility method and the solubility products of Ce₂ Suc ₃, i. e. [Ce³⁺]²[Suc ^2–]³, [CeSuc ⁺]²[Suc ^2–], [CeSuc ⁺][CeSuc ₂ ^–] measured.

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18. Mitt.:R. Pastorek, Lanthantartrate im neutralen und alkal. Bereich. Mh. Chem.99, 676 (1968).     

The influence of Ce3+ ions on the corrosion rate of stainless steel in acidic solutions of different pH-values

The corrosion resistance of AISI 420 stainless steel in 0.1 mol L^?1 H₂SO₄ + 0.1 mol L^?1 Na₂SO₄ solutions at different pH-values and the inhibiting effect of Ce³⁺ ions was studied using electrochemical polarization methods. The results reveal decreasing of the corrosion rate with an increasing the pH of the solution, which demonstrates the progressive protective character of the inhibitor used. At pH lower than 3.33, the corrosion inhibition was most probably a result of the competitive adsorption of Ce³⁺ with H⁺ ions on the cathodic sites of the electrode surface, and it was found to be dependent on the relative concentration of H⁺/Ce³⁺. The peroxide generated from the oxygen reduction reaction at pH 3.33 was found to be capable oxidize trivalent cerium (Ce) to the tetravalent state. As obtained hydroxide precipitates act as diffusion barrier hindering the corrosion processes, whereafter a spontaneous passivity occurs on the steel surface at this pH.     

Imaging of Oxygen Diffusion in Individual Platinum/Ce2Zr2Ox Catalyst Particles During Oxygen Storage and Release

The spatial distribution of Ce³⁺ and Ce⁴⁺ in each particle of Ce₂Zr₂O_x in a three‐way conversion catalyst system was successfully imaged during an oxygen storage/release cycle by scanning X‐ray absorption fine structure (XAFS) using hard X‐ray nanobeams. For the first time, nano‐XAFS imaging visualized and identified the modes of non‐uniform oxygen diffusion from the interface of Pt catalyst and Ce₂Zr₂O_x support and the active parts in individual catalyst particles.     

Deposition and characterisation of a porous Sn(IV) semiconductor nanofilm on boron-doped diamond

Nanofilm deposits of a porous Sn(IV) oxide are formed by anodic electrodeposition on a polished boron-doped diamond electrode immersed in an aqueous Sn²⁺ solution. Mechanically and electrochemically stable deposits of 10–15 nm thickness are formed irrespective of the Sn²⁺ concentration and mass-transport enhancement by power ultrasound. Atomic force microscopy images indicate the presence of a smooth and noncrystalline film, which is stable under ambient conditions. n-type semiconducting characteristics are observed for the aqueous solution redox couples Fe(CN)₆ ^3–/4– and Ru(NH₃)₆ ^3+/2+. However, preliminary results from voltammetric experiments indicate that the small and neutral organic molecule N,N,N′,N′-tetramethylphenylenediamine is able to diffuse through the porous film to undergo oxidation directly at the surface of the boron-doped diamond electrode. Electronic Publication     

Y2SiO5:Ce3+荧光体的基质多面体替换及其对发光性能的调控研究

荧光材料基质的结构调制对于调控发光材料的发光性能,探索固体结构-性能关系具有重要的研究意义。本文以Y2SiO5基质为模型,分别利用Si/Al和Si/P取代,以[AlO4]和[PO4]四面体替换[SiO4]四面体,设计合成了一系列组成为Y1.95Si1-xAlxO5-xFx∶0.05Ce3+(x=0.05,x=0.1,x=0.2,x=0.4,x=1)和Y1.95-yCaySi1-yPyO5∶0.05Ce3+(y=0,y=0.02,y=0.04,y=0.06,y=0.08,y=0.2)的荧光材料。结合X射线衍射、荧光光谱、荧光寿命等测试手段对其进行了表征分析。结果表明,在x≤0.2,y≤0.04时得到的产物能够保持Y2SiO5的结构特征,在一定的基质组成替换范围内,设计合成的样品Y1.95Si1-xAlxO5-xFx∶0.05Ce3+、Y1.95-yCaySi1-yPyO5∶0.05Ce3+能提高发光强度,发射光谱呈现蓝移现象。荧光寿命测试表明这两个系列的化合物中Ce3+所处的基质环境变化较小,Ce3+发光也未产生较大的变化。     

Energy Transfer from Ce3+ to Tb3+/Dy3+/Mn2+ in Ca9Ga(PO4)7 Phosphors: Synthesis,Structure and Tunable Multicolor Luminescent Properties

A series of Ca₉Ga(PO₄)₇:Ce³⁺/Tb³⁺/Dy³⁺/Mn²⁺ phosphors with tunable color, in which Ce³⁺ acts as the sensitizer, was synthesized. Energy transfer (ET) from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺ was investigated in detail. Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ can exhibit green, yellow, and red emission, respectively. Incorporating Ce³⁺ into a Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ phosphor can remarkably promote the luminous efficiency of the Tb³⁺/Dy³⁺/Mn²⁺ ions. This enhancement originates from an efficient ET from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺. The ET was validated by luminescence spectra, decay dynamics, and schematic energy levels. Moreover, the intensity ratio of red emission of Mn²⁺ to violet emission of Ce³⁺ was analyzed based on energy-transfer and lifetime measurements. In Ce³⁺-Tb³⁺, Ce³⁺-Dy³⁺, and Ce³⁺-Mn²⁺ doped Ca₉Ga(PO₄)₇, the emitting color changed from violet to green, yellow, and red, respectively, which indicates the potential use of this new tunable phosphor in UV light-emitting diodes.     

Voltammetry with a Fluoride-Selective Electrode with Solid-Phase Reference System

Experimental results obtained in a study of the voltammetric response of an all-solid fluoride-selective electrode based on LaF₃ (Eu²⁺ 0.8 mol %), LaF₃ (Sr²⁺ 5 mol %) and CeF₃ (Sr²⁺ 5 mol %) single crystals brought in contact with Ag, Bi, and Sn metal samples are presented. The method of cathodic inversion voltammetry was applied to study the reduction of La³⁺ and Ce³⁺-cations from the rigid sublattice of solid electrolytes, which determines the threshold of the electrochemical stability of a membrane. Anodic inversion voltammetry was used to investigate the characteristics of solid-phase generation of metal fluorides at the interface between the fluoride-selective electrode and metals.     

A Porous Mooncake-Shaped Li4Ti5O12 Anode Material Modified by SmF3 and Its Electrochemical Performance in Lithium Ion Batteries

Reasonably designing and synthesizing advanced electrode materials is significant to enhance the electrochemical performance of lithium ion batteries (LIBs). Herein, a metal–organic framework (MOF, Mil-125) was used as a precursor and template to successfully synthesize the porous mooncake-shaped Li₄Ti₅O₁₂ (LTO) anode material assembled from nanoparticles. Even more critical, SmF₃ was used to modify the prepared porous mooncake-shaped LTO material. The SmF₃-modified LTO maintained a porous mooncake-shaped structure with a large specific surface area, and the SmF₃ nanoparticles were observed to be attach on the surface of the LTO material. It has been proven that the SmF₃ modification can further facilitate the transition from Ti⁴⁺ to Ti³⁺, reduce the polarization of electrode, decrease charge transfer impedance (R_ct) and solid electrolyte interface impedance (R_sei), and increase the lithium ion diffusion coefficient (D_Li), thereby enhancing the electrochemical performance of LTO. Therefore, the porous mooncake-shaped LTO modified using 2 wt % SmF₃ displays a large specific discharge capacity of 143.8 mAh g⁻¹ with an increment of 79.16 % compared to pure LTO at a high rate of 10 C (1 C=170 mAh g⁻¹), and shows a high retention rate of 96.4 % after 500 cycles at 5 C-rate.     

Hydrothermal synthesis of core-shell structured PS@GdPO<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript>/Ce<Superscript>3+</Superscript> spherical particles and their luminescence properties

Non-aggregated spherical polystyrene (PS) particles were coated with GdPO₄:Tb³⁺/Ce³⁺ phosphor layers by a conventional hydrothermal synthesis using poly(vinylpyrrolidone) (PVP) as an additive without further annealing treatment. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), as well as luminescence decay experiments were used to characterise the resulting core-shell structured PS@GdPO₄:Tb³⁺/Ce³⁺ samples. The results of XRD indicated that the PS particles were successfully coated with the GdPO₄:Tb³⁺/Ce³⁺ phosphor layers, which could be further verified by the images of FESEM. Under ultraviolet excitation, the PS@GdPO₄:Tb³⁺/Ce³⁺ phosphors show Tb³⁺ characteristic emission, i.e. ⁵D₄-⁷F_J (J = {6, 5, 4, 3}) emission lines with green emission ⁵D₄-⁷F₅ (543 nm) as the most prominent group. The core-shell phosphors so obtained have potential applications in field emission display (FED) and plasma display panels (PDP).     

Microstructure and electrochemical properties of porous La2NiO4+δ electrode screen-printed on Ce0.8Sm0.2O1.9 electrolyte

Superfine and uniform La₂NiO_4+δ powder was synthesized by a polyaminocarboxylate complex precursor method. La₂NiO_4+δ layers were screen-printed on dense Ce_0.8Sm_0.2O_1.9 electrolyte substrates and sintered at 900–1,100 °C. The microstructure and electrochemical properties of the resulting porous electrodes were investigated with respect to sintering temperature. The results indicate a significant effect of sintering temperature on the microstructure and electrode polarization. It was found that elevating sintering temperature was favorable to the charge transfer process whereas undesired for the oxygen surface exchange process due to an increase of the grain size. Sintering at 900 °C was determined to be preferred in terms of the polarization resistance of the electrode. The porous electrode sintered at the temperature showed a fine-grained microstructure (about 200 nm) and a relatively low polarization resistance of 0.28 Ω cm² at 800 °C. This work suggests that preparing the electrode from superfine starting powder is contributive to modifying the polarization properties.     

Chemie der Seltenerdmetalle, 22. Mitt.*

Zusammenfassung Auf Grund der Löslichkeit des Ce(III)-Malonats in Perchlorsäurelösungen wurden die Dissoziationsgleichgewichte der gebildeten Komplexionen, d. h., von [CeMal ₂]^– und [CeMal]⁺ untersucht. Gleichzeitig wurden auch die Löslichkeitsprodukte des Ce(III)-Malonats, u. zw.: [Ce³⁺]² [Mal ^2–]^3**, [CeMal ⁺]² [Mal ^2–] und [CeMal ⁺] [CeMal _2–] bestimmt.

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Chemistry of the rare earth metals, XXII: Dissociation equilibria of Ce(III)-malonate in weakly acidic solution

The solubility of cerous malonate in perchloric acid solutions was investigated. The dissociation equilibria of the complex ions formed, i.e. [CeMal ₂]^– and [CeMal]⁺ were studied and the solubility products of the cerous malonates, i.e. [Ce³⁺]² [Mal ^2–]³, [CeMal ⁺]² [Mal ^2–] and [CeMal ⁺] [CeMal _2–] determined.

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21. Mitt.:R. Pastorek, Gleichgewichtskonstanten der Komplex-partikeln im sauren Bereich des SystemsLn ³⁺–H₄ Tart–KOH, Acta Univ. Palack., im Druck.     

Effects of precipitants and surfactants on catalytic activity of Pd/CeO<Subscript>2</Subscript> for CO oxidation

A series of precipitants and commercial surfactants (soft templates) were employed to synthesize mesoporous/nano CeO₂ by a hydrothermal method. As-prepared CeO₂ was impregnated with palladium and employed for low-temperature catalytic oxidation of CO. It was found that both soft templates and precipitants had significant effects on the morphology, particle size, crystallinity, and porous structure of the CeO₂, having a significant effect on the surface palladium abundance, molar ratios of surface species, and catalytic activity of the final impregnated Pd/CeO₂. Using ammonia as precipitant could facilitate increased surface palladium abundance and surface molar ratios of PdO/Pd _SMSI , Ce³⁺/(Ce³⁺ + Ce⁴⁺), and O_surface/O_lattice. The catalytic activity of the final Pd/CeO₂ catalysts could be enhanced as well. The optimal P123-assisted ammonia-precipitated Pd/CeO₂ catalyst exhibited over 99% catalytic conversion of CO at 50 °C.     

Oxidation‐State Analysis of Ceria by X‐ray Photoelectron Spectroscopy

Three different methods to determine the oxide‐phase concentration in mixed cerium oxide by hard X‐ray photoelectron spectroscopy are applied and quantitatively compared. Synchrotron‐based characterization of the O 1s region was used as a benchmark to introduce a method based on the weighted superposition of the Ce 3d spectra of the pure Ce³⁺ and Ce⁴⁺ phases, which was shown to lead to reliable and highly accurate determination of the mean oxidation state in mixed cerium oxides. The results obtained reveal a linear relation between the third distinct final state (u′′′) satellite peak intensity of the Ce⁴⁺ phase and the Ce⁴⁺ concentration by proper inclusion of Ce³⁺‐related plasmon satellite peaks, which contradicts previous claims of nonlinear behavior. In contrast, quantitative conventional peak‐fitting procedures were shown to be well suited for the Ce 2p region due to its relatively simple structure. Additional satellite features observed in the Ce 3d spectrum of CeO₂ were proposed to originate from plasmon contributions.