Preparation and characterization of cerium oxide doped TiO2 nanoparticles

A mixed oxide consisting of TiO₂ as the major phase and CeO_2−y (0<y<0.5) as the dopant phase was prepared via the sol-gel reaction of Ti(i-OC₃H₇)₃ in an aqueous solution of Ce(NO₃)₃. The resulting oxide powders with different CeO_2−y contents were all composed of nano-sized spheres. The CeO_2−y phase was identified to have retarding effect on the phase transition from anatase TiO₂ to rutile TiO₂ at calcinations temperature as high as 800 °C, which would otherwise be a thorough conversion. The CeO_2−y-TiO₂ powders could apparently shift the UV-absorption band of TiO₂ toward visible range, and there was an optimal CeO_2−y content in association with the maximum absorbance. This effect is interpreted as the existence of an n-type impurity band, due to the substitution of Ti⁴⁺ for Ce^3+/4+ at the interface between the two oxides, in the gap of TiO₂. According to X-ray photoelectron spectroscopy (XPS) investigation, the Ti element mainly existed as the chemical state of Ti⁴⁺ and the Ce oxide doping did not affect the peak position of Ti 2p. The Ce 3d spectrum of CeO_2−y-doped TiO₂ sample basically denotes a mixture of Ce^3+/4+ oxidation states giving rise to a myriad of peaks.     

The surface properties and the activities in catalytic wet air oxidation over CeO2-TiO2 catalysts

No-noble metal CeO₂-TiO₂ catalysts prepared by sol-gel method were developed and examined for catalytic wet air oxidation (CWAO) of acetic acid. The structure of the catalysts was measured by BET, SEM, XRD, XPS and DTA-TG. We investigated the effect of the interactions of Ce and Ti on the structure of CeO₂-TiO₂ catalysts. The mechanisms of the relationships between the different content of Ti and the activity of CeO₂-TiO₂ catalysts were discussed. The results showed that the average crystal size of CeO₂ decreased and the surface areas increased; the low valence of Ce³⁺ increase, and the chemisorbed oxygen slightly decreased with the increase of Ti content on the surface of CeO₂-TiO₂ catalysts. The order of the activity in CWAO of acetic acid followed: Ce/Ti 1/1 > Ce/Ti 3/1 > Ce/Ti 1/3 > Ce/Ti 5/1 > CeO₂ > TiO₂ > no catalyst. In CWAO of acetic acid, the optimal atomic ratio of Ce and Ti was 1, and the highest COD removal was over 64% at 230 °C, 5 MPa and 180 min reaction time over Ce/Ti 1/1 catalyst. The excellent activity and stability of CeO₂-TiO₂ catalysts was observed in our study.     

Different effects of cerium ions doping on properties of anatase and rutile TiO2

Pure and Ce⁴⁺ doped anatase and rutile TiO₂ were prepared by hydrothermal methods and characterized by XRD, TEM, UV-vis diffusion spectroscopy, and XPS measurements. The photocatalytic reactivity of the catalysts was evaluated by the photodegradation of Rhodamine B (RB) under ultraviolet irradiation. The photocatalytic efficiency of the rutile sample doped with an appropriate amount of Ce⁴⁺ was enhanced while all Ce⁴⁺ doped anatase samples showed a much lower activity than pure anatase. The reasons were discussed     

Preparation and characterization of visible light responsive Fe2O3-TiO2 composites

In this study we present the effects of iron oxide (Fe₂O₃) on titanium dioxide (TiO₂) in synthesising visible-light reactive photocatalysts. A Fe₂O₃-TiO₂ composite photocatalyst was synthesized from Fe₂(SO₄)₃ and Ti(SO₄)₂ by a ethanol-assisted hydrothermal method. The preparation conditions were optimized through the investigation of the effects of hydrothermal temperature and time as well as molar ratio of Ti to Fe on the photocatalytic activity. The visual, physical and chemical properties of the Fe₂O₃-TiO₂ composites were investigated. The results showed that α-Fe₂O₃ and anatase TiO₂ were present in the composites. The Fe₂O₃-TiO₂ synthesized under optimum condition consisted of mesoporous structure with an average pore size of 4 nm and a surface area of 43 m²/g. Under visible and solar light irradiation, the photocatalytic activity of optimized sample was significantly higher than that of pure TiO₂. This sample led to a photodegradation efficiency of 90% and 40% of auramine under visible light and solar light, respectively.     

Preparation of photocatalytic Fe2O3-TiO2 coatings in one step by metal organic chemical vapor deposition

There are two major difficulties in the TiO₂ liquid-solid photocatalytic system: effective immobilization of the TiO₂ particles; and improving the catalytic activity under visible light. To simultaneously solve these two problems, Fe₂O₃-TiO₂ coatings supported on activated carbon fiber (ACF), have been prepared in one step by a convenient and efficient method—metal organic chemical vapor deposition (MOCVD). XRD results revealed that Fe₂O₃-TiO₂ coatings mainly composed of anatase TiO₂, α-Fe₂O₃ phases and little Fe₂Ti₃O₉. The pore structure of ACF was preserved well after loading with Fe₂O₃-TiO₂ coatings. UV-vis diffuse reflectance spectra showed a slight shift to longer wavelengths and an enhancement of the absorption in the visible region for Fe₂O₃-TiO₂ coatings, compared to the pure TiO₂ sample. A moderate Fe₂O₃-TiO₂ loading (13.7 wt%) was beneficial to mineralizing wastewater because the intermediates could be adsorbed onto the surface of photocatalyst following decomposition. The stable performance revealed that the Fe₂O₃-TiO₂ coatings were strongly adhered to the ACF surface, and the as prepared catalysts could be reused showing potential application for wastewater treatment.     

Surface state of TiO2 treated with low ion energy plasma

The effect of low pressure radio frequency (rf) plasma treatment on TiO₂ surface states has been studied using X-ray photoelectron spectroscopy. Three different oxidation states of oxygen in untreated TiO₂ powder were observed, which suggests the existence of adsorbed water and carbon on the surface. The ratio of oxygen to titanium (O/Ti) was decreased for the low ion dose plasma treated samples due to desorption of water from the surface. In the case of Ti 2p about 20% of surface states were converted to Ti³⁺ 2p_3/2 state after plasma treatment with a very good stability, whereas untreated TiO₂ remained mostly as Ti⁴⁺ state. A rapid decrease in the ratio of carbon to titanium (C/Ti) at TiO₂ surface was also observed after plasma treatment and more than 90% of carbon atoms were removed from the surface. Therefore, the plasma treatment of TiO₂ has advantages to surface carbon cleaning, increasing O⁻ and Ti³⁺ surface states, hence improving the activity of TiO₂ for different environmental, energy and biological applications.     

Eu3+掺杂的Sr2CeO4发光材料的光致发光研究

利用高温固相反应法制备了Eu³⁺掺杂的Sr₂CeO₄样品,并对其吸附水前后的光谱特性进行了研究.结果发现,对于刚制备的Sr_2-xEu_xCeO_4+x/2样品, 在Ce⁴⁺—O^2-的电荷迁移激发中,只有强激发带(～35700cm^-1)与Eu³⁺离子间存在能量传递,而弱激发带 (～29400cm^-1)只是引起Ce⁴⁺—O^2-的电荷迁移发射;在Sr_2-xEu_xCeO_4+x/2样品吸附水后,Eu³⁺的线状吸收跃迁强度显著增加, Ce⁴⁺—O^2-两个激发带均向Eu³⁺离子传递能量. Ce⁴⁺—O^2-强激发带通过交换作用向Eu³⁺离子传递能量,而弱激发带与Eu³⁺离子间的能量传递机理是非辐射多极子近场力的相互作用. 关键词： 2-xEu_xCeO_4+x/2')" href="#">Sr_2-xEu_xCeO_4+x/2 发光性质 能量传递 吸附水     

Synchrotron radiation photoelectron spectroscopy study of metal-oxide thin film catalysts: Pt-CeO2 coated CNTs

The interaction of Pt with CeO₂ layers was investigated by using high resolution hard X-ray photoelectron spectroscopy. Pt doped CeO₂ layers were deposited simultaneously by rf-magnetron sputtering on a SiO₂/Si substrate and carbon nanotubes (CNTs) grown on a carbon diffusion layer of a polymer membrane fuel cell. In the case of the CNT support photoelectron spectra showed the formation of ionic platinum rich cerium oxide with Pt^2+,4+ species, and with the Pt²⁺/Pt⁴⁺ ratio strongly dependent on the amount of platinum. Ce reveals 4+/3+ mixed valent character with Ce³⁺ concentration increasing with Pt content. In the case of the SiO₂/Si substrate the film revealed Ce⁴⁺ and Pt⁴⁺ species only.     

Investigation on mechanism of photocatalytic activity enhancement of nanometer cerium-doped titania

A series of Ce-TiO₂ are prepared by the sol-gel process with ammonium cerium(IV) nitrate and tetra-n-butyl titanium as raw materials and characterized with XRD, TEM, DRS, and XPS. The aberrance (0.355) of anatase(1 0 1) plane of 0.1% Ce/TiO₂ increases compared to that of TiO₂. Cerium is found to be present as a mixture of Ce^3+/4+ oxidation states, that is, the oxidation state of some cerium in Ce-TiO₂ has changed after calcination. Ce/TiO₂ yields a large red shift compared to TiO₂. Moreover, the reflectance decreases in the visible region after cerium doped on TiO₂, and the lower the reflectance the higher the activity. Cerium appears to enhance the photocatalytic activity of Ce/TiO₂ by suppressing electron-hole recombination with electron trapping at Ce⁴⁺. 0.1% Ce/TiO₂ shows highest activity for the degradation of aqueous suspension of formaldehyde.     

Synthesis and characteristics of natural zeolite supported Fe-TiO2 photocatalysts

Natural zeolite supported Fe³⁺-TiO₂ photocatalysts were synthesized for the sake of improving the recovery and photocatalytic efficiency of TiO₂. The as-prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Methyl orange was used to estimate the photocatalytic activity of the samples. The results showed that zeolite inhibited the growth of TiO₂ crystallite sizes. The Fe³⁺ concentration played an important role on the microstructure and photocatalytic activity of the samples. The iron ions could diffuse into TiO₂ lattice to the form Fe-O-Ti bond and gave TiO₂ the capacity to absorb light at lower energy levels. The photocatalytic activity of the samples could be enhanced as appropriate dosages of Fe³⁺ were doped.     

Sn interaction with the CeO2(1 1 1) system: Bimetallic bonding and ceria reduction

A tin layer 0.8 nm thick was deposited onto the CeO₂(1 1 1) surface by molecular beam deposition at a temperature of 520 K. The interaction of tin with cerium oxide (ceria) was investigated by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and resonant photoelectron spectroscopy (RPES). The strong tin-ceria interaction led to the formation of a homogeneous bulk Ce-Sn-O mixed oxide system. The bulk compound formation is accompanied by partial Ce⁴⁺ → Ce³⁺ reduction, observed as a giant 4f resonance enhancement of the Ce³⁺ species. CeO₂ and SnO₂ oxides were formed after oxygen treatment at 520 K. The study proved the existence of strong Ce-Sn interaction and charge transfer from Sn to the Ce-O complex that lead to a weakening of the cerium-oxygen bond, and consequently, to the formation of oxygen deficient active sites on the ceria surface. This behavior can be a key for understanding the higher catalytic activity of the SnO_x/CeO_x mixed oxide catalysts as compared with the individual pure oxides.     

掺杂CeO2的75TeO2-25Nb2O5-5ZnO飞秒激光诱导瞬态光栅的研究

用泵浦探测技术研究了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO玻璃在飞秒激光诱导的瞬态光栅多级自衍射。从拉曼和吸收光谱中研究了玻璃的结构特性，并证明了此玻璃中存在Ce3+离子。这种瞬态光栅起因于光克尔效应，并通过Ce3+离子中1S0?1F3电子能级跃迁形成的激发态粒子数光栅而改善，一级衍射信号的转换效率可达到11%。这些实验结果显示了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO飞玻璃在全转换开关中具有广泛应用。     

A new synthetic pathway of Sr2CeO4 phosphor and its characterization

A blue-white emitting Sr₂CeO₄ phosphor was synthesized via a simple sol-gel poly vinyl alcohol (PVA)-complexing process using strontium nitrate and cerium nitrate as raw materials. The samples were characterized by TG/DTA, XRD, FTIR, SEM and photoluminescence spectroscopy. The X-ray diffraction study confirms the structure of the system to be orthorhombic. The emission spectra when excited at 267 nm peaks at ∼470 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ion. The Commission International de l'Eclairage (CIE) co-ordinates for the Sr₂CeO₄ sample were also calculated.     

Variations in the structural, optical and electrochemical properties of CeO2-TiO2 films as a function of TiO2 content

Alcohol based sols of cerium chloride (CeCl₃·7H₂O) and titanium propoxide (Ti(OPr)₄) in ethanol mixed in different mole ratios have yielded mixed oxide films on densification at 500 °C. The reversibility of the intercalation/deintercalation reactions has shown electrochemical stability of the films. Addition of TiO₂ in an equivalent mole ratio manifests in producing highly transparent films with appreciable ion storage capacity. The electrochemical studies have revealed the significant role of TiO₂ in controlling the ion storage capacity of the films, as it tends to induce the disorder. In addition, the films prepared from an aged sol are observed to exhibit a much higher ion storage capacity than the films deposited using the as-prepared sol. The X-ray photoelectron spectroscopic studies have provided information on the variation of Ce⁴⁺/Ce³⁺ ratio as a function of increased TiO₂ content in the films. This study has led to a better understanding of the increased ion storage capacity with the increased TiO₂ proportion. The transmission electron microscopic study has demonstrated the presence of CeO₂ nanograins even in films, which are amorphous to X-rays. Elucidation of the structural, optical and electrochemical features of the films has yielded information on aspects relevant to their usage in transmissive electrochromic devices. The films have been found to exhibit properties that can find application as counter electrode in electrochromic smart windows in which they are able to retain their transparency under charge insertion, high enough for practical uses. Also, the fastest coloration-bleaching kinetics for the primary electrochromic electrode (WO₃) working in combination with Ce/Ti (1:1) electrode stimulates the use of latter in electrochromic windows (ECWs).     

In-situ XAS study on the Cu and Ce local structural changes in a CuO-CeO2/Al2O3 catalyst under propane reduction and re-oxidation

The redox behaviour of a CuO-CeO₂/Al₂O₃ catalyst is studied under propane reduction and re-oxidation. The evolution of the local Cu and Ce structure is studied with in-situ transmission X-ray absorption spectroscopy (XAS) at the Cu K and Ce L₃ absorption edges.CuO and CeO₂ structures are present in the catalyst as such. No structural effect on the local Cu structure is observed upon heating in He up to 873 K or after pre-oxidation at 423 K.Exposure to propane at reaction temperature (600-763 K) fully reduces the Cu²⁺ cations towards metallic Cu⁰. Quick EXAFS spectra taken during reduction show a small amount of intermediate Cu¹⁺ species. Parallel to the CuO reduction, CeO₂ is also reduced in the same temperature range. About 25% of the Ce⁴⁺ reduces rapidly to Ce³⁺ in the 610-640 K temperature interval, while beyond 640 K a further slower reduction of Ce⁴⁺ to Ce³⁺ occurs. At 763 K, Ce reduction is still incomplete with 32% of Ce³⁺.Re-oxidation of Cu and Ce is fast and brings back the original oxides.The propane reduction of the CuO-CeO₂/Al₂O₃ catalyst involves both CuO and CeO₂ reduction at similar temperatures, which is ascribed to an interaction between the two compounds.     

Preparation, characterization and photocatalytic performance of TiO2/CexZr1−xO2 toward the oxidation of gaseous benzene

Increasing environmental pollution caused by the volatile organic compounds due to their toxicity makes their removal imperative. So it is crucial to develop processes which can degrade these compounds effectively. The paper demonstrates that the photocatalytic activity of TiO₂ toward the decomposition of gaseous benzene in a batch reactor can be greatly enhanced by loading TiO₂ onto the surface of Ce_xZr_1−xO₂ (x ≥ 0.25) using sol-gel technology. This research investigated the relationship between x amount and the photocatalytic activity of TiO₂. The prepared photocatalysts were characterized by BET, XRD, UV-vis diffuse reflectance and XPS analyses. The specific surface area of photocatalyst decreases as x decreases. XRD results reveal the no peaks of titania were detected. Among the five catalysts prepared, only the binding energy values of Ti2p_3/2 of TiO₂/Ce_0.5Zr_0.5O₂ shift toward lower value. The order of photocatalytic activity is TiO₂/Ce_0.5Zr_0.5O₂ > TiO₂/Ce_0.75Zr_0.25O₂ > TiO₂/CeO₂ ≈ TiO₂/Ce_0.25Zr_0.75O₂ > TiO₂/ZrO₂ ≈ TiO₂. The mechanism role of Ceria-Zirconia mixed oxides in photocatalytic reaction was speculated.     

Synthesis of (Ca,Ce,Ce)2Ti2O7: a pyrochlore with mixed-valence cerium

Pyrochlore with mixed-valence Ce was synthesized by firing and annealing Ce(NO₃)₄, TiO₂, and Ca(OH)₂ with a stoichiometry of CaCeTi₂O₇ at 1300 °C. The product contains Ce-pyrochlore, Ce-rich perovskite, CeO₂ (cerianite), and minor CaO. Electron energy-loss spectroscopy (EELS) revealed both Ce⁴⁺ and Ce³⁺ in the Ce-pyrochlore with a Ce⁴⁺ to total Ce (Ce⁴⁺/ΣCe) of 0.80 giving . Cerium in the perovskite and cerianite is dominated by Ce³⁺ and Ce⁴⁺, respectively. High-resolution transmission electron microscope (HRTEM) images show that the boundary between Ce-pyrochlore and Ce-rich perovskite is semi-coherently bonded. The orientational relationship between the neighboring Ce-pyrochlore and Ce-rich perovskite is not random. Ce-pyrochlore (CaCeTi₂O₇) is a chemical analogue for CaPuTi₂O₇, which is a proposed ceramic waste form for deposition of excess weapons-usable Pu in geological repositories. It is postulated, based on the presence of Ce³⁺ in the Ce-pyrochlore, that neutron poisons such as Gd can be incorporated into the CaPuTi₂O₇ phase.     

Structural characteristics and morphology of SmxCe1−xO2−x/2 thin films

Effect of the deposition temperature (200 and 500 °C) and composition of Sm_xCe_1−xO_2−x/2 (x = 0, 10.9–15.9 mol%) thin films prepared by electron beam physical vapor deposition (EB-PVD) and Ar⁺ ion beam assisted deposition (IBAD) combined with EB-PVD on structural characteristics and morphology/microstructure was investigated. The X-ray photoelectron spectroscopy (XPS) of the surface and electron probe microanalysis (EPMA) of the bulk of the film revealed the dominant occurrence of Ce⁴⁺ oxidation state, suggesting the presence of CeO₂ phase, which was confirmed by X-ray diffraction (XRD). The Ce³⁺ oxidation states corresponding to Ce₂O₃ phase were in minority. The XRD and scanning electron microscopy (SEM) showed the polycrystalline columnar structure and a rooftop morphology of the surface. Effects of the preparation conditions (temperature, composition, IBAD) on the lattice parameter, grain size, perfection of the columnar growth and its impact on the surface morphology are analyzed and discussed.     

Ce4+离子在Ca2SnO4一维结构基质中的电荷迁移光谱研究

利用高温固相反应法制备了Ca₂Sn_1-xCe_xO₄和Ca_2-ySr_ySn_1-xCe_xO₄一维结构发光体. XPS结果显示 Ca₂SnO₄拥有两种结合能分别为5277 eV和5293 关键词： 2Sn_1-xCe_xO₄')" href="#">Ca₂Sn_1-xCe_xO₄ 2-ySr_ySn_1-xCe_xO₄')" href="#">Ca_2-ySr_ySn_1-xCe_xO₄ 一维结构 电荷迁移光谱     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.