Peculiarities of the electrochemical behavior of polyaniline synthesized in the presence of Ce3+ cations

Polyaniline (PANI) is synthesized in the potentiostatic pulse mode from an electrolyte containing Ce³⁺ sulfate. The electrochemical behavior of PANI and PANI-Ce is studied in electrolytes with and without cerium cations. The data on the relaxation and the effect of electrochemical cycling on the magnitude and behavior of the electrochemical capacitance are shown. After the cathodic reduction in the presence of Ce³⁺ rare-earth cations, the PANI relaxation proceeds faster and the specific electrochemical capacitance is almost completely retained at long-term electrochemical cycling.     

Electrochemical properties of polyaniline film doped by Ce3+ cation

Electrochemical Synthesis (ES)of polyaniline (PAni) is carried out in the presence in electrolyte (1 M H₂SO₄) of cerium (III) sulfate under potentiostatic and potentiodynamic modes. It is shown that Ce³⁺ cations in electrolyte catalyze ES, i.e. accelerate both ES variants. The obtained polymers were characterized using the scanning electron microscopy (SEM) technique and also on the basis of the calculation of electrochemical characteristics. Relaxation in PAni polymers doped by the Ce³⁺ cation occurs several times faster than in proton-doped PAni. The minimum change in ΔE and E is observed in polymers doped by Ce³⁺ cations during the electrochemical cycling of PAni and PAni-Ce at high rates.     

One‐pot synthesis of polyaniline doped with transition metal ions using H2O2 as oxidant

Polyanilines (PANIs) doped with Zn²⁺ and Cu²⁺ were synthesized by H₂O₂ oxidative polymerization of aniline in the presence of corresponding metal chloride in solution. The products were characterized by elemental analysis, UV‐Vis‐NIR, FTIR and Raman spectroscopies. Scanning electron micrograph was employed to examine the morphology of PANIs fabricated in the presence of different transition metals. Experimental results showed that transition metal ions had been successfully incorporated into the polymer, and there was a strong interaction between the transition metal ions and the PANI chains. The electrical conductivity of PANI doped with Zn²⁺ and Cu²⁺ is 0.37 and 0.21 S/cm, respectively, which is higher than that of HCl doping PANI corresponding to 0.052 S/cm. The cyclic voltammetric study has indicated that incorporation of metal ions in PANI backbone results in increasing of specific capacitance compared to that of HCl doping PANI. Copyright © 2014 John Wiley & Sons, Ltd.     

Monodisperse Mesocrystals of YF3 and Ce3+/Ln3+ (Ln=Tb,Eu) Co‐Activated YF3: Shape Control Synthesis,Luminescent Properties,and Biocompatibility

A family of monodisperse YF₃, YF₃:Ce³⁺ and YF₃:Ce³⁺/Ln³⁺ (Ln=Tb, Eu) mesocrystals with a morphology of a hollow spindle can be synthesized by a solvothermal process using yttrium nitrate and NH₄F as precursors. The effects of reaction time, fluorine source, solvents, and reaction temperature on the synthesis of these mesocrystals have been studied in detail. The results demonstrate that the formation of a hollow spindle‐like YF₃ can be ascribed to a nonclassical crystallization process by means of a particle‐based reaction route in ethanol. It has been shown that the fluorine sources selected have a remarkable effect on the morphologies and crystalline phases of the final products. Moreover, the luminescent properties of Ln³⁺‐doped and Ce³⁺/Ln³⁺‐co‐doped spindle‐like YF₃ mesocrystals were also investigated. It turns out that Ce³⁺ is an efficient sensitizer for Ln³⁺ in the spindle‐like YF₃ mesocrystals. Remarkable fluorescence enhancement was observed in Ce³⁺/Ln³⁺‐co‐doped YF₃ mesocrystals. The mechanism of the energy transfer and electronic transition between Ce³⁺ and Ln³⁺ in the host material of YF₃ mesocrystals was also explored. The cytotoxicity study revealed that these YF₃‐based nanocrystals are biocompatible for applications, such as cellular imaging.     

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.     

Structure and optical properties of cerium(III)-doped PbWO4 micro-crystals synthesized by a facile wet chemical method

Cerium(III) doped PbWO₄ micro-crystals with different doping contents were synthesized via a facile wet chemical method in air atmosphere at room temperature. X-ray diffraction patterns of as-synthesized powders revealed that these micro-crystals were pure scheelite PbWO₄, without any impurities such as Ce₂(WO₄)₃ and PbO, and Ce³⁺ could enter into Pb²⁺ sites, which would induce the formation of lead vacancies in the PbWO₄ crystal lattice. The UV–vis diffuse reflection spectra, Raman spectra and photoluminescence (PL) spectra of doped and pure PbWO₄ micro-crystals were studied in detail, which indicated that optical properties of doped PbWO₄ were greatly changed. The adsorption edge of Ce(III)-doped PbWO₄ micro-crystals would shift toward high wavelength (red-shift) with gradually increasing Ce³⁺ doping concentration. It shows an obvious decrease in blue emission band which made the shape of the whole emission band remodeled with the Ce³⁺ doping.     

Unique Spectral Overlap and Resonant Energy Transfer between Europium(II) and Ytterbium(III) Cations: No Quantum Cutting

Samples of the Ca₃Sc₂Si₃O₁₂ (CSS) host singly doped with Eu²⁺ or Yb³⁺, doubly doped with Eu²⁺ and Yb³⁺, and triply doped with Ce³⁺, Eu²⁺ and Yb³⁺ were synthesized by a sol–gel combustion process under reducing conditions. Unlike previous reports of Eu²⁺→Yb³⁺ energy transfer in other systems, the energy transfer is resonant in the CSS host and the transfer efficiency reaches 100 % for lightly doped samples. The transfer mechanism is multipolar rather than electron transfer for the sample compositions employed herein. The emission intensity of Yb³⁺ is further enhanced by co‐doping with Ce³⁺ in addition to Eu²⁺. The quantum efficiencies of the doped materials range between 9 % and 93 %.     

A Polyaniline-Deposited Nonplatinum Metal as a Potentiometric Sensor—An Inexpensive Alternate to Conventional Platinum for Some Potentiometric Redox Reactions

For the purpose of employing an inexpensive alternative to conventional platinum for use by upper-division as well as graduate students, polyaniline (PANI)-deposited stainless steel (SS) and mild steel (MS) electrodes are described as indicator electrodes for potentiometry and potentiometric titrations of some redox reactions. PANI is deposited on the nonplatinum metal by electrochemical polymerization of aniline using cyclic voltammetric technique. Alternate methods to produce the PANI electrodes are also suggested. The electrodes respond to concentration changes of hydroquinone (H₂O), Fe²⁺/Fe³⁺, and [Fe(CN)₆]^4–/[Fe(CN)₆]^3– in HCL electrolytes, and the potential variation with concentration follows the Nernst relationship. Under identical experimental conditions, the response time of the PANI/SS, PANI/MS, and Pt electrodes for a change in concentration of Fe³⁺ in a mixed electrolyte of Fe²⁺ and Fe³⁺ is found to be about 20 s. Neutralization reaction of HC1 versus NaOH, redox reaction of Fe²⁺ and Ce⁴⁺, and redox reaction of Fe²⁺ and KMnO₄ in several concentrations in the range from 1 mM to 100 mM are carried out using the PANI/SS, PANI/MS, and Pt indicator electrodes. The performance of the PANI/SS and PANI/MS electrodes is as good as that of the Pt at all concentration levels of the titrations. The electrodes can be reused for several titrations by storing them in an acid electrolyte for a long period of time. Thus, the conventional inert Pt or Au can be substituted for by using a PANI-deposited nonplatinum reactive metal as a potentiometric sensor for redox titrations.     

Cerium luminescence in nd perovskites

The luminescence of Ce³⁺ in perovskite (ABO₃) hosts with nd⁰ B-site cations, specifically Ca(Hf,Zr)O₃ and (La,Gd)ScO₃, is investigated in this report. The energy position of the Ce³⁺ excitation and emission bands in these perovskites is compared to those of typical Al³⁺ perovskites; we find a Ce³⁺ 5d¹ centroid shift and Stokes shift that are larger versus the corresponding values for the Al³⁺ perovskites. It is also shown that Ce³⁺ luminescence quenching is due to Ce³⁺ photoionization. The comparison between these perovskites shows reasonable correlations between Ce³⁺ luminescence quenching, the energy position of the Ce³⁺ 5d¹ excited state with respect to the host conduction band, and the host composition.     

Study of Complex Formation between Kryptofix 21 with La<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> Cations in Some Binary Mixed Non-Aqueous Solvents Using the Conductometric Method

The complexation reactions between La³⁺, Y³⁺ and Ce³⁺ cations with the macrocyclic ligand, kryptofix 21, were studied in methanol-acetonitrile (MeOH-AN) and methanol-methylacetate (MeOHMeOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most solvent systems, the kryptofix 21 forms a 1: 1 [M: L] complex with La³⁺, Y³⁺ and Ce³⁺ metal cations, but in the case of Y³⁺ cation in pure methylacetate, in addition of formation of a 1: 1 [ML] complex, 1: 2 [ML₂] and 1: 3 [ML₃] complexes are formed in solution. In the case of Ce³⁺cation, a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed in this solvent system at all studied temperatures. The electrical conductance data in acetonitrile, show that a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed between the ligand and La³⁺ and Ce³⁺ metal cations at different temperatures. The stability constants of the 1: 1 [ML] complexes were determined using the conductometric data and a computer program, GENPLOT. A non-monotonic relationship was observed between log_{K f} of the 1: 1 complexes with the composition of the binary solvent solutions which was discussed in term of solvent-solvent interactions and also preferential solvation of the metal cations and the ligand in solutions. The selectivity order of the ligand for the metal cations in MeOH–AN and MeOH–MeOAc binary solvent solutions, at 25°C was found to be: Y³⁺ > La³⁺ > Ce³⁺ and La³⁺ > Y³⁺ > Ce³⁺, respectively. The values of the standard thermodynamic quantities (ΔH _c ^° and ΔS _c ^° ) for formation of the 1: 1 complexes were obtained from temperature dependence of the stability constans of the complexes and the results show that the thermodynamics of the complexation reactions between kryptofix 21 and La³⁺, Y³⁺ and Ce³⁺ cations, is affected by the nature and composition of the mixed solvents systems.     

Preparation and luminescence properties of Ce and/or Tb doped LaPO4 nanofibers and microbelts by electrospinning

Ce³⁺ and/or Tb³⁺ doped LaPO₄ nanofibers and microbelts have been prepared by a combination method of sol-gel process and electrospinning. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low voltage cathodoluminescence (CL) and time-resolved emission spectra as well as kinetic decays were used to characterize the resulting samples. SEM and TEM results indicate the as-formed precursor fibers and belts are smooth, and the as-prepared nanofibers and microbelts consist of nanoparticles. The doped rare-earth ions show their characteristic emission under ultraviolet excitation, i.e. Ce³⁺ 5d-4f and Tb³⁺⁵D₄-⁷F_J (J=6-3) transitions, respectively. The energy transfer process from Ce³⁺ to Tb³⁺ in LaPO₄:Ce³⁺, Tb³⁺ nanofibers was further studied by the time-resolved emission spectra. Under low-voltage electron beam excitation, LaPO₄:Ce³⁺, Tb³⁺ microbelt phosphors have a higher intensity than that of nanofiber phosphors.     

A novel blue fluorescent chemosensor for metal cations and protons,based on 1,8‐naphthalimide and its copolymer with styrene

A new blue emitting 2‐allyl‐6‐(2‐dimethylaminoethyloxy)‐benzo[de]isoquinoline‐1,3‐dione, bearing an allylic group has been designed and synthesized. Bulk radical copolymerization has been carried out in order to prepare a fluorescent copolymer, based on styrene. The main photophysical characteristics of the monomeric and polymeric fluorophores have been investigated both in the absence and presence of metal cations and protons. It has been found that the monomeric naphthalimide can be used as a sensor for protons and Zn²⁺, Ni²⁺, Ce³⁺, Cu²⁺, Co²⁺, Ag⁺ cations. The polymeric fluorophore has been shown to be a selective chemosensor for Cu²⁺ cations. Copyright © 2006 John Wiley & Sons, Ltd.     

Research on Molecular Structure and Electronic Properties of Ln3+ (Ce3+, Tb3+, Pr3+)/Li+ and Eu2+ Co-Doped Sr2Si5N8 via DFT Calculation

We use density functional theory (DFT) to study the molecular structure and electronic band structure of Sr₂Si₅N₈:Eu²⁺ doped with trivalent lanthanides (Ln³⁺ = Ce³⁺, Tb³⁺, Pr³⁺). Li⁺ was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr²⁺ by Ln³⁺. The doping of Ln lanthanide atom causes the structure of Sr₂Si₅N₈ lattice to shrink due to the smaller atomic radius of Ln³⁺ and Li⁺ compared to Sr²⁺. The doped structure’s formation energy indicates that the formation energy of Li⁺, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li⁺ doping site for double-doped lanthanide ions can be provided. In Sr₂Si₅N₈:Eu²⁺, the doped Ce³⁺ can occupy partly the site of Sr₁²⁺ ([SrN₈]), while Eu²⁺ accounts for Sr₁²⁺ and Sr₂²⁺ ([SrN₁₀]). When the Pr³⁺ ion is selected as the dopant in Sr₂Si₅N₈:Eu²⁺, Pr³⁺ and Eu²⁺ would replace Sr₂²⁺ simultaneously. In this theoretical model, the replacement of Sr²⁺ by Tb³⁺ cannot exist reasonably. For the electronic structure, the energy level of Sr₂Si₅N₈:Eu²⁺/Li⁺ doped with Ce³⁺ and Pr³⁺ appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of Sr₂Si₅N₈. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of Ce_Sr1Li_Sr1-Sr₂Si₅N₈ is from 2.42 to 2.85 eV. The energy range of 4f-CBM in Pr_Sr1Li_Sr1-Sr₂Si₅N₈ is 2.75–2.99 eV and its peak is 2.90 eV; the addition of Ce³⁺ in Eu_Sr1Ce_Sr1Li_Sr1 made the 4f energy level of Eu²⁺ blue shift. The addition of Pr³⁺ in Eu_Sr2Pr_Sr2Li_Sr1 makes part of the Eu²⁺ 4f energy level blue shift. Eu²⁺ 4f energy level in Eu_Sr2Ce_Sr1Li_Sr1 is not in the forbidden band, so Eu²⁺ is not used as the emission center.     

Chemoselective Phototransformation of CH Bonds on a Polymer Surface through a Photoinduced Cerium Recycling Redox Reaction

It is generally accepted that Ce⁴⁺ is unable to directly oxidize unreactive alkyl C?H bonds without the assistance of adjacent polar groups. Herein, we demonstrate in our newly developed confined photochemical reaction system that this recognized issue may be challenged. As we found, when a thin layer of a CeCl₃/HCl aqueous solution was applied to a polymeric substrate and the substrate subjected to UV irradiation, Ce³⁺ was first photooxidized to form Ce⁴⁺ in the presence of H⁺, and the in situ formed Ce⁴⁺ then performs an oxidation reaction on the C?H bonds of the polymer surface to form surface‐carbon radicals for radical graft polymerization reactions and functional‐group transformations, while reducing to Ce³⁺ and releasing H⁺ in the process. This photoinduced cerium recycling redox (PCRR) reaction behaved as a biomimetic system in an artificial recycling reaction, leading to a sustainable chemical modification strategy for directly transforming alkyl C?H bonds on polymer surfaces into small‐molecule groups and polymer brushes. This method is expected to provide a green and economical tool for industrial applications of polymer‐surface modification.     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation on the oxides under study occurs at higher temperatures than CO oxidation. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying a reduced number of active sites, which are Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce^{(4 + β)+} coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

Electrochemical polymerization of polyaniline doped with Zn2+ as the electrode material for electrochemical supercapacitors

Polyaniline doped with Zn²⁺ (PANI/Zn²⁺) films was synthesized by cyclic voltammetric method on stainless steel mesh substrates in 0.2 mol L^?1 aniline and 0.5 mol L^?1 sulfuric acid electrolyte with various concentrations of zinc sulfate (ZnSO₄·7H₂O). The structure and morphology of PANI and PANI/Zn²⁺ films were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques, respectively. The electrochemical properties of PANI and PANI/Zn²⁺ films were investigated by cyclic voltammetry, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy in 0.5 mol L^?1 H₂SO₄ electrolyte in a three-electrode system. The results show that the surface morphology of PANI/Zn²⁺ is more rough than that of pure PANI. The specific capacitance of the PANI/Zn²⁺ film displays a larger specific capacitance of 738 F g^?1, lower resistance, and better stability as compared with the pure PANI film. Thus, good capacitive performance demonstrates its potential superiority for supercapacitors.     

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.     

Effect of the Electrode Material on the Reduction of La<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> in Fluoride-Conducting Solid Electrolytes

The reduction of immobile cations La³⁺ and Ce³⁺ in fluoride-conducting solid electrolytes (FSE) LaF₃ (Eu²⁺ 0.8 mol %), LaF₃ (Sr²⁺ 5 mol %), and CeF₃ (Sr²⁺ 5 mol %) in contact with Ag, Bi, Si, La, Ce, and Sm working electrodes is studied by chronoamperometry and voltammetry with linear potential scan. Discovered is linear dependence of initial segments of potentiostatic transients of cathodic current on t ^1/2 at FSE interfaces with Ag, Bi, La, Ce, and Sm. The dependence is due to diffusion-controlled instantaneous nucleation of Ln and Ce. The La³⁺ and Ce³⁺ reduction at the FSE/Ag interface is reversible in a narrow region. The reduction and oxidation of La³⁺ and Ce³⁺ (cations of the FSE rigid lattice) at the FSE/Me (Me = La, Ce and Sm, Bi, Si) interface is irreversible and involves a chemical reaction.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 662–672.Original Russian Text Copyright © 2005 by Turaeva, Kot, Urchukova, Murin.     

A Study of Different Doped Metal Cations on the Physicochemical Properties and Catalytic Activities of Ce20M1Ox (M=Zr,Cr, Mn,Fe, Co,Sn) Composite Oxides for Nitric Oxide Reduction by Carbon Monoxide

This work is mainly focused on investigating the effects of different doped metal cations on the formation of Ce₂₀M₁O_x (M=Zr, Cr, Mn, Fe, Co, Sn) composite oxides and their physicochemical and catalytic properties for NO reduction by CO as a model reaction. The obtained samples were characterized by using N₂ physisorption, X‐ray diffraction, laser Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, inductively coupled plasma atomic emission spectroscopy, X‐ray photoelectron spectroscopy, temperature‐programmed reduction by hydrogen and by oxygen (H₂‐TPR and O₂‐TPD), in situ diffuse reflectance infrared Fourier transform spectroscopy, and the NO+CO model reaction. The results imply that the introduction of M^x+ into the lattice of CeO₂ increases the specific surface area and pore volume, especially for variable valence metal cations, and enhances the catalytic performance to a great extent. In this regard, increases in the oxygen vacancies, reduction properties, and chemisorbed O₂^? (and/or O^?) species of these Ce₂₀M₁O_x composite oxides (M refers to variable valence metals) play significant roles in this reaction. Among the samples, Ce₂₀Cr₁O_x exhibited the best catalytic performance, mainly because it has the best reducibility and more chemisorbed oxygen, and significant reasons for these attributes may be closely related to favorable synergistic interactions of the vacancies and near‐surface Ce³⁺ and Cr³⁺. Finally, a possible reaction mechanism was tentatively proposed to understand the reactions.     

Controlled synthesis and characterization of LaPO4, LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ by EDTA assisted hydrothermal method

LaPO₄, LaPO₄:Ce³⁺ and LaPO₄:Ce³⁺, Tb³⁺ particles with different morphologies and sizes have been successfully synthesized via a simple EDTA assisted hydrothermal method. The effects of the doping components, pH value, and the chelating reagent on the phases, structures and morphologies were well investigated by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Photoluminescent (PL) spectra and kinetic decays were used to characterize the fluorescent properties of the samples. The results reveal that all the samples are of high purity and assigned to the single-crystalline monoclinic structure of LaPO₄ phase. The aspects ratio of the nanostructures synthesized in acid synthetic condition is larger than those obtained in alkaline solution. Additionally, the Ce³⁺ or/and Tb³⁺ doped LaPO₄ particles show less smoother surface compared with pure LaPO₄. Furthermore, the tendency for anisotropic growth under hydrothermal conditions can be simply enhanced by selecting the chelating ligands (EDTA). The possible growth mechanism of the LaPO₄:Ln³⁺ (Ln = Ce³⁺, Tb³⁺) nanostructures has been proposed as well. Upon ultraviolet excitation, LaPO₄:Ce³⁺ and LaPO₄:Ce³⁺, Tb³⁺ phosphors show the characteristic 5d–4f emissions of Ce³⁺ and ⁵D₄–⁷F_j (j = 6–3) emission lines of Tb³⁺, respectively.