间接电氧化媒质Ce4+/Ce3+的循环与再利用

设计了一种适用于间接电氧化合成反应,中试规模的填充式隔膜电解槽.该电解槽以铜板为阴极,PbO2/Ti石墨颗粒填充电极为阳极,电解液[0.16mol/L Ce2(SO4)3,1.5 mol/L H2SO4]采用外循环的方式控制其温度为30～50℃,在50A/m2的电流密度下电解,获得大于80%的电流效率.讨论了电极材料、电流密度、电解液温度、Ce3+浓度和循环次数等对电流效率的影响.其中Ce3+浓度是限制电流密度和影响电流效率的主要因素;电解液在间接电氧化对甲氧基甲苯反应中连续循环使用20次,仍然保持高于85%的电流效率;PbO2/Ti石墨颗粒填充电极使用寿命超过6个月.     

Influence of aromatic reactants and products involved in the two stage electrochemical oxidation on the voltammetric behaviour of Ce(IV)/Ce(III) redox couple

The redox behaviour of the Ce(IV)/Ce(III) couple in 1.0 M nitric acid, 1.0 M sulfuric acid, 1.0 M perchloric acid and in different concentrations of methane sulfonic acid was investigated on a glassy carbon electrode using cyclic voltammetry. Quasi reversible redox behaviour with low E _p value of 200 mV and below were observed in 1.0 M sulfuric acid and high concentrations of methane sulfonic acid. Anionic complexes apparently exist in this media. The reactants and products involved in the indirect oxidations are found to influence cerous/ceric redox behaviour in 2.0 M methane sulfonic acid in three distinct ways: (i) in the presence of cerous methane sulfonate organic compounds such as toluene, benzaldehyde and naphthaquinone do not exhibit substantial inhibitive effects; (ii) compounds such as p-xylene and p-tolualdehyde exhibit some inhibitive effect at higher concentrations; and (iii) compounds like naphthalene, p-ethoxy toluene and p-ethoxy benzaldehyde exhibit a fairly high level of inhibitive effect.     

Cr2O7^2-／Cr^a＋和Ce^4＋／Ce^3＋电解液作媒质间接合成对甲氧基苯甲醛

在高剪切混合乳化机搅拌下，通过对Cr2O7^2-／Cr^a 和Ce^4 ／Ce^3 两种媒质间接合成对甲氧基苯甲醛槽外反应的研究，得到合成对甲氧基苯甲醛的优选条件分别为：原料配比n(Cr2O7^2-)：n(p-CH3O-C6H4-CH3)=1：6，反应温度80℃，反应时间10min，对甲氧基苯甲醛反应收率90．5％：原料配比n(Ce^4-)：n(p-CH3O-C6H4-CH3)=1：1，反应温度30℃，反应时间6min，对甲氧基苯甲醛反应收率97．1％。结果表明，Ce^4 ／Ce^3 做媒质产品时．空效率较低，这是Ce^4 ／Ce^3 媒质存在的本质缺陷：而Cr2O7^2-/Cr^3 做媒质产品时一空效率提高近2倍，显著地增加产品的产量，提高了经济效益。     

Electrochemical behaviour of galena (PbS) in aqueous nitric acid and perchloric acid solutions

The electrochemical reactions of natural n-type PbS in nitric and perchloric acid solutions have been studied using cyclic voltammetry, SEM and XPS. Several oxidation stages, which differ in their electrode kinetics, surface topography and sulfide phase composition, particularly Pb/S ratios and the state of sulfur, were demonstrated. The quantities of surface sulfate and thiosulfate were rather low at PbS oxidized in HNO₃ solutions, even at high potentials. The magnitude of the reoxidation peaks of cathodically formed products, primarily Pb⁰, was found to increase as the electrodissolution of PbS on the preliminary positive-going sweep was hindered. It is proposed that the predominant donor-like defects in the disordered reaction layers limit the concentration and mobility of holes, thus inhibiting PbS oxidation and promoting metallic lead deposition in the course of potential cycling. The model developed as an alternative to the traditional explanations uses the concept of negative correlation energy centres resembling those in non-crystalline chalcogenide semiconductors.     

K+掺杂LiNi1/3Co1/3Mn1/3O2材料的制备及电化学性能研究

锂离子电池正极材料LiNi_1/3Co_1/3Mn_1/3O₂具有放电比容量大、热稳定性好、成本低、安全性能好等优点,但其倍率性能有待进一步提升。本文采用水热法制备了K⁺掺杂LiNi_1/3Co_1/3Mn_1/3O₂材料LNCM-xK。通过X射线衍射谱、场发射扫描电镜和X射线光电子能谱表征LNCM-xK的形貌和结构,通过电化学工作站和蓝电测试系统测试其电化学性能。结果表明:K⁺掺杂能有效降低阳离子混排程度,改善LiNi_1/3Co_1/3Mn_1/3O₂材料的电化学性能,其中当x=0.125时K⁺掺杂LiNi_1/3Co_1/3Mn_1/3O₂样品(LNCM-0.125K)阳离子混排程度最低;LNCM-0.125K样品电化学性能最佳,0.2 C下50次循环后容量保持率为96.15%;在不同电流密度(0.2 C,0.5 C,1 C,2 C,5 C)下进行倍率性能测试,连续充放电30次后LNCM-0.125K样品容量保持率为97.00%。     

Photoluminescence and energy transfer of efficient and thermally stable white-emitting Ca9La(PO4)7:Ce3+, Tb3+, Mn2+ phosphors

The development of novel single-component white-emitting phosphors with high thermal stability is essential for improving the illumination quality of white light-emitting diodes. In this work, we synthesized a series of Ce³⁺, Tb³⁺, Mn²⁺ single- and multiple-doped Ca₉La(PO₄)₇ (CLPO) phosphors with β-Ca₃(PO₄)₂-type structure by the simple high-temperature solid-state reaction. The crystallization behavior, crystal structure, surface morphology, photoluminescence performance, decay lifetime and thermal stability were systematically investigated. The PL spectra and decay curves have evidenced the efficient energy transfer from Ce³⁺ to Tb³⁺ and from Ce³⁺ to Mn²⁺ in the CLPO host, and corresponding energy transfer efficiency reaches 41.8% and 54.1%, respectively. The energy transfer process of Ce³⁺→Tb³⁺ and Ce³⁺→Mn²⁺ can be deduced to the resonant type via dipole-dipole and dipole-quadrupole interaction mechanism, and corresponding critical distance were determined to be 12.23 and 14.4 Å, respectively. Based on the efficient energy transfer, the white light emission can be successfully achieved in the single-component CLPO:0.15Ce³⁺, 0.10Tb³⁺, 0.04Mn²⁺ phosphor, which owns CIE chromaticity coordinates of (0.3245, 0.3347), CCT of 5878 K, internal and external quantum efficiency of 84.51% and 69.32%. Especially, compared with the emission intensity at 25 °C, it still remains 98.5% at 150 °C and 92.0% at 300 °C. Based on these results, the single-component white light emission phosphor CLPO:0.15Ce³⁺, 0.10Tb³⁺, 0.04Mn²⁺ is a potential candidate for UV-converted white LEDs.     

Thin-Layer Chromatography of Metal Ions in Formic Acid Medium on Impregnated and Unimpregnated Silica Gel G: Semiquantitative Determination of Fe3+, Cd2+, Th4+, Al3+, Zn2+, UO2+ 2, VO2+, Ce4+, and Ni2+

Abstract

The adsorption behavior of metal ions in the formic acid-sodium formate system using unimpregnated as well as impregnated silica gel G as thin layers has been studied. A remarkable result of this study is the dramatic selectivity of impregnated silica gel G thin layers when compared to the corresponding unimpregnated silica gel G thin layers. This impregnation effect provides us with a new adsorbent phase which is sufficiently stable in the formic acid-sodium formate medium. Some important ternary separations have been achieved on silica gel G thin layers. Al³⁺, Ni²⁺, Fe³⁺, and Pb²⁺ have been qualitatively separated from mixtures of other ions. Cu²⁺ has been selectively separated on impregnated silica gel G thin layers. The semi-quantitative determination of nine metal ions on impregnated silica gel G layers has also been attempted.     

Comparison of multi-valent manganese oxides (Mn4+, Mn3+, and Mn2+) doping in BiFeO3-BaTiO3 piezoelectric ceramics

Different manganese oxides-doping effects were compared in piezoceramic BiFeO₃-BaTiO₃ system. 0.67Bi_1.05(Fe_0.99Mn^x_0.01)O₃-0.33BaTiO₃ (valence state x = 4+, 3+, and 2+) ceramics were prepared via a solid-state reaction process followed by furnace-cooling (FC) or water-quenching (WQ) process. For the FC ceramics, the direct piezoelectric sensor coefficient (d₃₃) was almost independent of valence state of doped Mn, while d₃₃ depended on the fraction of Fe³⁺/Fe²⁺ in WQ ceramics. The d₃₃ value was highest for the donor Mn⁴⁺-doped ceramic, among the FC ceramics, with 175 pC/N. However, acceptor-doping with Mn²⁺ prevented the transition of Fe ion valence state from 3+ to 2+ in the WQ ceramics, the Mn²⁺-doped WQ ceramic showed the largest d₃₃ of 313 pC/N and converse piezoelectric actuator coefficient, d₃₃^* of 352 pm/V, with high Curie phase transition temperature (482 °C).     

聚丙烯酸改性凹土对Pb2+、Ni2+和Cr3+的选择性吸附

通过凹土的表面功能化开发高性能低成本的吸附材料,采用溶液聚合法在其表面接枝聚丙烯酸,制备出聚丙烯酸/凹土吸附材料(PAA/ATP),系统考察了PAA/ATP对Pb²⁺、Ni²⁺和Cr³⁺三元混合体系的吸附性能。结果表明:PAA/ATP复合吸附材料的有机物接枝率为14.1%,其结构中出现聚丙烯酸的特征官能团;PAA/ATP吸附Pb²⁺的动力学符合拟二级动力学,即化学吸附是速率控制步骤,说明PAA/ATP对Pb²⁺的吸附是一个有化学作用的过程,吸附过程与Pb²⁺和吸附剂PAA/ATP表面官能团之间的电子转移或电子共用有关;PAA/ATP对Pb²⁺的吸附符合Langmuir吸附等温模型;PAA/ATP对Pb²⁺、Ni²⁺和Cr³⁺的竞争吸附能力依次为Pb²⁺ > Cr³⁺ > Ni²⁺,即对Pb²⁺具有较好的选择性吸附。     

Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Gas phase esterification of acetic acid with ethanol over MoO3 supported on AlPO4 and the effect of modification with phosphomolybdic acid and Ce4+ ions

A series of AIPO₄–MoO₃ (APM) systems with various molybdena loadings (5–50) mol %, same modified with phosphomolybdic acid (PMA) and cerium ions, were prepared by an impregnation method and calcined at 400 °C, except for the samples modified with PMA which were calcined at 350 °C for 4 h. The catalysts were characterized by TG/DTG, XRD, IR spectroscopy, N₂ adsorption and electrical conductivity measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of isopropyl alcohol. The catalytic esterification of acetic acid with ethanol was carried out in a convention fixed bed reactor. The results clearly revealed that the catalyst with a composition of 10 mol % MoO₃ (APM10) was the most active and selective catalyst for the production of ethyl acetate. Moreover, the yield of ethyl acetate increases on addition of PMA into APM10 while it decreases on the addition of Ce⁴⁺ ions. These results were correlated with structure, semiconductivity and the acid–base properties of the prepared catalysts. Copyright © 2003 Society of Chemical Industry     

Optimization of Ce3+ concentration and Y4MgSi3O13 phase in Mg2+-Si4+ Co-doped Ce: YAG ceramic phosphors

As a promising replacement for nitride red phosphors, Ce: Y₃(Mg_1.8Al_1.4Si_1.8)O₁₂ (Ce: YMASG) ceramic phosphors have attracted significant attention recently for their advantages in inorganic encapsulation and massive red-shifting of Ce³⁺ emission. In this work, Ce: YMASG with different doping concentrations of Ce³⁺ and Al₂O₃, was fabricated by vacuum sintering to investigate its effects on the elimination of the impurity phase and the enhancement of the luminescent properties of white light-emitting diodes (w-LEDs). It was discovered that the emission wavelength redshifts from 592 to 606 nm as the Ce³⁺ concentration increases, while at 450 K, the emission intensity deteriorates from 0.47 to 0.36 of its initial value. The Rietveld analysis revealed the presence of an impurity phase of Y₄MgSi₃O₁₃ with a concentration of 17.021 wt% in Ce: YMASG. With the introduction of Al₂O₃, the impurity phase was eliminated from the matrix completely, the emission peak shifted to a shorter wavelength, and the thermal stability was greatly improved. When the correlated color temperature was controlled at around 3000 K in the packaged w-LEDs, the commission international de l'éclairage (CIE) chromaticity coordinates shifted toward the bottom left corner of the diagram with increasing concentration of Ce³⁺. Conversely, the luminous efficiency (LE) increased from 36 lm/W to 58.6 lm/W as the concentration of Al₂O₃ increased from 0 to 10 wt%, which demonstrated the application prospect of the fabricated phosphor in warm w-LEDs.     

ESR Studies of Uncomplexed and Complexed HO2 Radical Formed in the Reaction of H2O2 with Ce4+, Fe2+ and Ti3+ Ions

Excess of H₂O₂ reacting in 0.5N HClO₄ with Ce⁴⁺, Ti³⁺ and Fe²⁺ yields the uncomplexed HO₂ radical. This radical gives a broad ESR signal with a line width of 27±1 gauss and a g-value of 2.0140±0.0015. The HO₂ radical forms a complex with excess of Ce³⁺ which gives an ESR spectrum with a linewidth of 1.3±0.1 gauss and a g-value of 2.0180±0.0005. The equilibrium between complexed [Ce³⁺‥HO₂] and uncomplexed HO₂ was studied. Two complexes are formed between HO₂ and [Ti⁴⁺…H₂O₂]. These complexes give two ESR signals with a linewidth of 0.7 ± 0.1 and 0.5± 0.1 gauss and g-value of 2.0140± ± 0.0005 and 2.0120± 0.0005 respectively.     

腐殖酸协同Mn2+催化臭氧氧化降解五氯苯酚

研究了向Mn2+催化臭氧氧化体系中添加少量腐殖酸对PCP去除效率的影响。结果表明:腐殖酸与Mn2+在催化臭氧氧化降解PCP过程中存在着明显的协同效应。在ρ(PCP)=30 mg/L,n(HA)∶n(PCP)值为3.18的条件下,氧化反应30 min,PCP去除率高达98.63%。分别向Mn(Ⅱ)/O3+HA、Mn(Ⅱ)/O3、O3+HA及单独臭氧氧化体系中加入.OH自由基抑制剂叔丁醇后,各个氧化体系中PCP的降解效率均受到了不同程度的抑制。实验结果表明,Mn(Ⅱ)/O3+HA氧化降解PCP以自由基的氧化为主,其拟一级反应表观速率常数为0.133 min-1,分别是Mn(Ⅱ)/O3及单独臭氧氧化体系的1.87、8.31倍。     

Enhanced Luminescence of Ca14Mg2Si8O28+δN4−δ:Eu2+Phosphors by Codoping Ce3+, Mn2+ for White LEDs and Their Energy‐Transfer Mechanism

The Eu²⁺, M‐codoped(M = Ce³⁺, Mn²⁺) phosphor powders were prepared by a solid‐state reaction. The addition of Ce³⁺ in the Eu²⁺ sites in partially nitridated bredigite‐structure phosphor(CMSN) remarkably enhances the luminescent intensity by ~180% through sensitized luminescence. Dual band emission was observed for Eu, Mn‐codoped CMSN through energy transfer from Eu²⁺ to Mn²⁺. Ce³⁺–Eu²⁺ and Eu²⁺–Mn²⁺ energy‐transfer mechanism was investigated through decay profile analysis using Inokuti–Hirayama model and energy‐transfer parameters are determined. Interaction mechanism was identified as dipole–dipole interaction. In addition, phosphor in glass plates was prepared using the phosphor and its feasibility in white LED application was studied and is presented.     

Optical properties of Er3+ and Yb3+/Er3+-doped NaF-Na2SO4-Al(PO3)3 fluoro-sulfo-phosphate glasses

Fluoro-sulfo-phosphate (FPS) glass is of current interest as potential material for laser application due to its good glass-forming ability, thermal, and chemical stability as well as the complicated local environment for incorporated species. Herein, the physical and luminescent properties of Er³⁺ and Yb³⁺/Er³⁺-doped FPS glasses vs S/F ratio are investigated comprehensively. The low melting temperature (750°C) leads to fewer ingredients evaporation and easier operation. The sulfate addition depolymerizes the structure of FPS glasses, leading to either monotonic or nonmonotonic variations of physical properties, while no deterioration in thermal and limited one in chemical stability is caused. The addition of sulfate also modifies the local structure around optical active species and thus, leading to higher emission cross section (1.52 × 10⁻²⁰ cm²), effective linewidth (68.4 nm), figure of merit (5.61 × 10⁻²³ s cm²), gain bandwidth (102.44 × 10⁻²⁷ cm³), and energy-transfer microparameters (51.87 × 10⁻³⁹ cm⁶/s), implying high possibility to serve as 1.5 μm laser application.     

Electrochemical characteristics of the Mn(iii)/Mn(ii) and Co(iii)/Co(ii) systems at platinum in anhydrous acetic acid solutions

The electrochemical oxidation of Mn(ii) and Co(ii) and reduction of Mn(iii) and Co(iii) at Pt in glacial acetic acid has been investigated by the rotating disc electrode technique. The diffusion coefficients of Mn(iii), Mn(ii), Co(iii) and Co(ii) ions, formal potentials and kinetic parameters of the Mn(iii)/Mn(ii) and Co(iii)/Co(ii) electrode reactions were evaluated. It was shown that the anodic oxidation of Mn(ii) and Co(ii) occurs at the surface blocked by a layer of adsorbed acetate ions. In addition, some experiments with an electrochemical quartz crystal microbalance (EQCM) were performed to explain the acetate adsorption on the surface of the polycrystalline platinum electrode.     

电氧化合成Co3+及其在对甲砜基苯甲酸制备中的应用

本文对Co3+的电氧化合成以及用作氧化对甲砜基甲苯合成对甲砜基苯甲酸进行了系统研究。研究表明，选用阳极二氧化铅、阴极铅为电极板，陶瓷膜作为阳离子交换膜，电解液浓度为C(Co2+)=0.5mol/L、C(硫酸)=4.0mol/L、C(硫酸铵)=0.15mol/L，电极间距d=2cm、电流密度J=350A/m2、电解温度t=10℃，电解液Co2+转化率可达80%，电解氧化电流效率67.5%。在进行对甲砜基甲苯的氧化时，控制电解液浓度为C(Co3+)=0.4mol/L、C(硫酸)=4.0mol/L、C(硫酸铵)=0.15mol/L，Co3+与对甲砜基甲苯的摩尔比n（Co3+）：n（对甲砜基甲苯）=6:1，反应温度30℃，反应时间30min，对甲砜基苯甲酸的收率可达97.8%，精制后纯度在98.5%以上。     

Insight into luminescent properties,energy transfer and thermal stability of NaBa4(AlB4O9)2Cl3:Ce3+, Tb3+ phosphors

A series of Ce³⁺ and Tb³⁺ singly- and co-doped NaBa₄(AlB₄O₉)₂Cl₃ (NBAC) phosphors have been synthesized via high-temperature solid state route. The crystal structure, morphology, photoluminescent properties, thermal properties and energy transfer process between Ce³⁺ and Tb³⁺ were systematically investigated. The structure refinements indicated that the phosphors based on NBAC crystallized in P42nm polar space group in monoclinic phase. The emission color could be tuned from blue (0.1595, 0.0955) to green (0.2689, 0.4334) via changing the ratio of Ce³⁺/Tb³⁺. The energy transfer mechanism of Ce³⁺/Tb³⁺ was verified to be dipole–quadrupole interaction via the examination of decay times of Ce³⁺ based on Dexter's theory. The good thermal stability showed the intensities of Ce³⁺ at 150°C were about 66.9% and 64.88% in NBAC:0.09Ce³⁺ and NBAC:0.09Ce³⁺, 0.07Tb³⁺ of that at room temperature, and the emission intensities of Tb³⁺ remained 102.41% in NBAC:0.11Tb³⁺ and 95.22% in NBAC:0.09Ce³⁺, 0.07Tb³⁺ due to the nephelauxetic shielding effect and the highly asymmetric rigid framework structure of NBAC. The maximum external quantum efficiency (EQE) of Ce³⁺ in NBAC:0.09Ce³⁺, yTb³⁺ phosphors could reach 43.38% at y = 0.13. Overall, all the results obtained suggested that NBAC:Ce³⁺, Tb³⁺ could be a promising option for n-UV pumped phosphors.