Stability and Thermodynamics of Glutamic Acid Complexes with Cerium(III) and Yttrium(III)

Stepwise stability constants of the complexes of glutamic acid with cerium(III) and yttrium (III) have been determined by the Calvin-Bjerrum pH titration technique as used by Irving and Rossotti in aqueous solution at 25° and 45°C. The values of log β₂ for cerium complexes are: 9.75 (μ = 0.1), 9.57 (μ = 0.2), 9.38 (μ = 0.3) at 25°C; and 10.90 (μ = 0.1), 10.74 (μ = 0.2), 10.64 (μ = 0.3) at 45°C. The log β₂ values for yttrium complexes at μ = 0.1 are 9.98 and 9.77 at 25° and 45°C respectively. The values of log β₂ (μ = 0.0) for cerium complexes are 10.21 and 11.24 at 25° and 45°C respectively. The increasing ionic strength of the medium decreases the stabilities of cerium complexes which are also more stable at 45° than 25°C whereas yttrium complexes are less stable at 45°C. The values of AH and ΔS are positive for cerium complexes whereas in the case of yttrium complexes, the values of ΔH are negative and those of ΔS are positive.     

Low-Temperature Synthesis and Characterization of Mixed Sodium Cerium(III) Hexa-Aluminate

Two forms of sodium cerium(III) mixed hexa-aluminate were prepared at temperature as low as 1270°C, i.e., 300°C lower than those reported previously, and characterized by X-ray diffraction techniques. These compounds are formed by thermal treatment, under argon, of an amorphous organometallic precursor obtained by the "citric acid method". During the synthesis, the 3+ oxidation state of cerium is retained at all temperatures.     

Preparation and Properties of Tricyclopentadienyl Cerium (IV) Chloride and Bisindenyl Cerium (IV) Dichloride

The reactions of dipyridinium cerium (IV) hexachloride with tetracyclopentadienyl cerium or sodium cyclopentadienide and tetraindenyl cerium or sodium indenide in tetrahydrofuran yield tricyclopentadienyl cerium (IV) chloride and bisindenyl cerium (IV) dichloride. Infrared spectra, thermal stabilities and other characteristics of the compounds have been studied.     

Synthesis,Ion Exchange Properties,and Applications of Amorphous Cerium(III) Tungstosilicate

Abstract

A novel hetropolyacid-based cation exchanger cerium(III) tungstosilicate was synthesized in amorphous form by mixing tungstosilisic acid (TSA) solutions to cerium(III) nitrate solutions at different Ce:TSA ratios. The materials were precipitated from the liquid phase by raising the pH of the solutions using sodium hydroxide. The produced ion exchange powders were characterized using powder X-ray diffractometry, thermogravimetry, infrared spectrometry, inductively coupled plasma and atomic absorption elemental analysis. The materials which were dried at 50°C were found to be stable in water, dilute acids, alkaline solutions, and high temperature up to 1000°C. The Ion exchange properties of the synthesized samples were studied by measuring the distribution coefficients (K_d) for 29 metal ions in demineralized water and nitric acid media. On the basis of K_d values, some quantitative separations such as Co²⁺-Pb²⁺, Cr³⁺-Zr⁴⁺, and Mo⁶⁺- W⁶⁺ are achieved on their columns.     

New Process for the Preparation of Monodispersed, Spherical Silica Particles

A new method is presented for preparing highly monodispersed silica particles using a two-stage semibatch/batch hydrolysis reaction of Si(OC₂H₅)₄. The slower rate of hydrolysis of the tetraethylorthosilicate (TEOS) that occurred during the semibatch process resulted in larger silica particles with a higher yield and narrower size distribution. This was in direct contrast to the batch process. In addition, the ability of four different mixed processes to produce silica particles with good packing density, narrower particle-size distribution, and higher yield were evaluated. These were batch/batch (B-B), batch/semibatch (B-S), semibatch/batch (S-B), and semibatch/semibatch (S-S) processes. The S-S system produced the largest particles with the highest yields. The size of the silica particles obtained by the S-B method decreased with increasing reaction time, while the particles obtained by the B-S process had the best particle-size distribution and packing density. In conclusion, a mixed batch/semibatch system was the best way to produce an extremely narrow particle-size distribution and a good packing density.     

Cerium Containing Al- and Zr-Pillared Clays: Promoting Effect of Cerium (III) Ions on Structural and Catalytic Properties

Ce³⁺ containing Al- and Zr-pillared clays were prepared by co-hydrolysis and co-intercalation methods, respectively. The materials were characterized by XRD, IR and near IR techniques. The expansion in the clay lattice as a result of pillaring was confirmed from X-ray diffraction study. The basal spacing for the pillared clay materials was observed typically in the range of 18–23 Å. The IR and near IR studies were employed to show the presence of acidic and non-acidic hydroxyl groups in the pillared clays. The IR peak at 3630 cm⁻¹ corresponding to the structural hydroxyl groups was more intense in pillared clays than in the parent clay. This peak is retained even after calcination at 500^∘C. Various overtone and combination bands were observed in the NIR range of 1200–2500 nm for the pillared clay materials. Pillaring with Al- and Zr-inorganic polycations enhanced the catalytic activity of the parent clays for dehydration of cyclohexanol. The presence of Ce³⁺ ions in the pillared clays was found to influence catalytic activity and stability of the Brønsted acidic sites. The stabilizing effect of cerium ion in the pillared clays is attributed to the competitive site occupancy and prevention of octahedral migration of the catalytically active protons.     

单分散球形SiO2颗粒的制备及表征

以氨水作催化剂,采用溶胶-凝胶法制备出单分散、粒径约300～500 nm的亚微SiO2粒子.研究了氨水浓度、乙醇用量、正硅酸乙酯/水的体积比及硅烷偶联剂浓度对SiO2粒子粒径、分散度及其表面结构的影响,同时还研究了SiO2胶体粒子的稳定性能和成核生长机理.结果表明:SiO2粒子粒径随氨水浓度的增加,先增大后减小,分散度增大;且随着乙醇用量的增加,粒径减小,分散度下降.硅烷偶联剂的加入使得SiO2胶体粒子表面有机成分增多,疏水性增强,其水乳液在常温下不能长久放置,且硅烷偶联剂浓度愈高,粒子间愈容易发生黏连.     

Lanthanide(III) 1,4-Phenylenediacetate Complexes: The Relation Between the Structure and Thermal Properties

The series of isostructural lanthanide coordination polymers with the empirical formula [Ln₂(PDA)₃(H₂O)]·2H₂O, where PDA = 1,4-phenylenediacetate anion = [C₈H₈(COO)₂]^2?; Ln = La-Lu(III), and Y(III) were produced in the reaction of LnCl₃·nH₂O with ammonium salt of 1,4-phenylenediacetic acid in water solution. The compounds were characterised structurally using powder X-ray diffraction, elemental and thermogravimetric analyses as well as FT-IR spectroscopy. Thermogravimetric analyses show that in the range 60–170 °C the dehydration process occurs. The thermal stability of dehydrated compounds, Ln₂(PDA)₃ increased from about 200–350 °C in the whole series of complexes. Single-crystal X-ray diffraction analysis for the Gd(III) complex revealed that the compound crystallizes in the monoclinic P2₁/c space group with a = 21.863(2) Å, b = 10.035(1) Å, c = 13.854(1) Å, β = 91.53(1)° and V = 3,038.5(4) ų. The complex contains one-dimensional gadolinium-carboxylato chains, which are connected with the –CH₂–C₆H₄–CH₂– spacers of PDA ligand to the three-dimensional metal–organic framework.     

甲基丙烯酸铈的制备及其补强天然橡胶性能研究

制备甲基丙烯酸铈[Ce(MAA)_3],并对其补强天然橡胶(NR)性能进行研究。结果表明:Ce(MAA)_3的粒径为20μm左右;硫化后,胶料中Ce(MAA)_3的粒径明显减小,分散效果较好,与橡胶的相界面作用增强;在一定范围内,随着Ce(MAA)_3用量增大,Ce(MAA)_3补强NR硫化胶的拉伸强度和撕裂强度增大,Ce(MAA)_3用量为40份时,其补强效果较好。     

ABS/MMT纳米复合材料的制备及性能的研究

文章采用丙烯腈-丁二烯-苯乙烯(ABS)/氨基蒙脱土(MMT)进行熔融共混得到不同含量MMT的ABS/MMT纳米复合材料。用扫描电子显微镜、拉伸试验机、冲击试验机研究ABS/MMT的力学性能及断面结构。结果得出:在ABS/MMT纳米复合材料中,随着MMT含量的增加,ABS/MMT复合材料的拉伸强度呈先上升后下降,且当MMT含量在3份时性能较好,缺口冲击强度呈线性下降趋势。ABS/MMT冲击断面中,出现了许多网孔结构,橡胶粒子被蒙脱土的的片层包裹着,不能发生塑性变形,其为ABS/MMT复合材料缺口冲击强度降低的主要原因之一。     

Bimaterial Composites via Colloidal Rolling Techniques: III, Mechanical Properties

The mechanical properties of layered Ce-TZP/Al₂O₃ composites with laminate and cellular morphologies have been investigated. The strength and toughness increase as the layer thickness decreases, and the amount of transformation in the Ce-TZP layer increases discontinuously at the laminate/cellular transition. Very high strengths (1.1 GPa) and toughnesses (16 MPa·m^1/2) have been obtained in some cases. These results indicate that the progressive refinement of layer microstructure and the disruption of planar connectivity of phases are beneficial to the mechanical performance, because they provide more stress concentrators to trigger stress-assisted transformation for toughening functions. The composites of finer microstructure, with a layer thickness of lessthan equal to20 µm, have a homogeneous hardness of 11.5 GPa, which is a considerable improvement over that of Ce-TZP alone.     

Separation of Americium (III) and Lanthanide (III) Ions using TPEN Analogs

Abstract

N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,2-ethylenediamine (TPEN) has been shown previously to exhibit a high separation factor for the separation of americium (III) and europium (III). Application of TPEN is limited due to the solubility of the material under acidic conditions (pH < 4). A variety of analogs were synthesized in this study to examine effects caused by various structural modifications in an effort to retain the selectivity of the parent compound while decreasing solubility in acidic media. Results indicate that the substitution at the ethylene linker of TPEN eliminates the ability of the compound to separate americium (III) over europium (III).     

Novel Unsymmetrical Ru(III) and Mixed-valence Ru(III)/Ru(II) Dinuclear Compounds Related to the Antimetastatic Ru(III) Drug NAMI-A

In this paper we report the stepwise preparation and the characterization of new unsymmetrical monoanionic Ru(III) dinuclear compounds, [NH(4)][{trans-RuCl(4)(Me(2)SO-S)}(mu-L){mer-RuCl(3)(Me(2)SO-S)(Me(2)SO-O)}] (L = pyz (1), pym (2)). By a similar synthetic approach we also prepared new mixed-valence Ru(III)/Ru(II) dinuclear compounds of formula [NH(4)][{trans-RuCl(4)(Me(2)SO-S)}(mu-pyz){cis,cis,cis-RuCl(2)(Me(2)SO-S)(2)(CO)}] (L = pyrazine (pyz, 3), pyrimidine (pym, 4)). Moreover, we describe the chemical behavior of compounds 1-4 in physiological solution, also after complete reduction (with ascorbic acid) to the corresponding Ru(II)/Ru(II) species. Overall, the chemical behavior of 1 and 2 after reduction resembles that of the corresponding dianionic and neutral dinuclear species, [{trans-RuCl(3)(Me(2)SO-S)}(2)(mu-L)](2-)and [{mer-RuCl(3)(Me(2)SO-S)(Me(2)SO-O)}(2) (mu-L)]. On the other hand, the mixed-valence dinuclear compounds 3 and 4, owing to the great inertness of the cis,cis,cis-RuCl(2)(Me(2)SO-S)(2)(CO)(1/2mu-L) fragment, behave substantially like the mononuclear species [trans-RuCl(4)(Me(2)SO-S)(L)](-) in which the terminally bonded L ligand can be considered as bearing a bulky substituent on the other N atom.     

Water Soluble PDCA Derivatives for Selective Ln(III)/An(III) and Am(III)/Cm(III) Separation

The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back-extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N’,N’-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic decadentate ligand called h₄tpaen. Beyond selective An/Ln extraction, the aqueous soluble h₄tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SF_Cm/Am of about 3.5.     

胶体五氧化二锑的制备及性质

以H3PO4 作为稳定剂,经双氧水氧化法制备胶体Sb2O5,对影响胶粒大小与分布的因素以及胶粒的荷电性、物相组成、光吸收特性、热稳定性进行了研究。结果表明,在 95℃、n(H3PO4 ) /n(Sb) =0 1~0 3、n(H2O2 ) /n(Sb2O3 ) >2 0条件下,制备出胶粒粒径 30nm左右的高度分散的胶体Sb2O5,胶粒表面带负电,等电点从pH=1 .85向更酸性范围移动,在 2相似文献   

壳聚糖与聚乙烯醇磁性水凝胶的制备和性能研究

采用反复冷冻-融化技术(冻融)制备了Fe3O4/PVA/CS磁性水凝胶,并以相同方法制备了不交联、不掺磁的PVA/CS共混水凝胶和交联、不掺磁的PVA/CS交联水凝胶,研究对比了三类水凝胶的溶胀性能、再溶胀性能和力学性能随组分配比及冻融次数的变化行为,并研究了Fe3O4/PVA/CS磁性水凝胶的磁性能.结果表明:随着交联剂和Fe3O4的加入和冻融次数的增加,水凝胶的溶胀率减小,再溶胀速率减缓,但力学性能却呈现出增大趋势.Fe3O4/PVA/CS磁性水凝胶各个样品的磁滞回线皆剩磁很少,矫顽力很小,且剩磁和矫顽力的大小取决于Fe3O4掺量的大小,与冻融次数基本无关,随着Fe3O4掺量的增加剩磁和矫顽力都增大.     

聚甲基丙烯酸甲酯／纳米SiO2复合粒子的制备与表征

采用甲基丙烯酸-3-甲氧基硅丙酯（MPs）对分散于甲基丙烯酸甲酯（MMA）中的纳米SiO2粒子进行偶联改性，得到了表面改性的纳米SiO2单体分散液，用原位悬浮聚合方法制备了不同SiO2含量的PMMA／纳米SiO2复合粒子。通过红外光谱、透射电镜、差示扫描量热分析和热重分析等方法对制备的纳米复合粒子进行了表征，结果表明，纳米SiO2粒子在PMMA中分散良好；MMA可通过与MPS的共聚而有效地接枝到SiO2粒子表面，当SiO2含量为6．6％（质量分数，下同）、MPS用量为0．06g／gSiO2时，其接枝率可达73．8％；同时，纳米SiO2的引入可提高PMMA的耐热性能，当Si02含量为14.7％时，其玻璃化转变温度和最大热分解速率时的温度分别提高了11．8℃和18．8℃。     

Near-Infrared Emission of Lanthanide(III) Texaphyrin Complexes

Lanthanide texaphyrin derivatives containing Er³⁺, Nd³⁺, and Yb³⁺ ions exhibit near-IR emission from the f–f transition of the lanthanide ions. Both the triplet transient difference absorption spectral measurement and singlet oxygen generation measurement suggest energy transfer from the macrocyclic ligand to the lanthanide ions. Electron-transfer mechanism could also play a role in the NIR emission of Yb–Tex complex.     

Synthesis and Sintering of Cerium(III) Sulfide Powders

Cerium(III) sulfide (Ce₂S₃) powder was synthesized via the sulfurization of ceria (CeO₂) powder using carbon disulfide gas. Single-phase α-Ce₂S₃ could be formed via sulfurization at 973 K for 28.8 ks. The preparation of α-Ce₂S₃ became feasible at low temperature, in comparison to sulfurization using hydrogen sulfide gas. According to the fact that the formation of α-Ce₂S₃ was accelerated by the addition of carbon black to the CeO₂ powder, carbothermic reduction was considered to become a dominant reaction, as the temperature increased. To obtain the activation energy for the densification of β-Ce₂S₃ powder, which was prepared by vacuum heating α-Ce₂S₃, the data of densification by hot pressing was analyzed by a kinetic equation that was proposed by other researchers. As a result, the sintering behavior could be best explained by a grain-boundary-diffusion mechanism that had an apparent activation energy of 382 kJ/mol.     

Actinide(III)/Lanthanide(III) Separation Via Selective Aqueous Complexation of Actinides(III) using a Hydrophilic 2,6-Bis(1,2,4-Triazin-3-Yl)-Pyridine in Nitric Acid

i-SANEX is a process for separating actinides(III) from used nuclear fuels by solvent extraction: Actinides(III) and lanthanides(III) are co-extracted from a PUREX raffinate followed by selective back extraction of actinides(III) from the loaded organic phase. This step requires a complexing agent selective for actinides(III). A hydrophilic sulfonated bis triazinyl pyridine (SO₃-Ph-BTP) was synthesized and tested for selective complexation of actinides(III) in nitric acid solution. When co-extracting Am(III) and Eu(III) from nitric acid into TODGA, adding SO₃-Ph-BTP to the aqueous phase suppresses Am(III) extraction while Eu(III) is extracted. Separation factors in the range of 1000 are achieved. SO₃-Ph-BTP remains active in nitric acid up to 2 mol/L. As a result of this performance, buffering or salting-out agents are not needed in the aqueous phase; nitric acid is used to keep the lanthanides(III) in the TODGA solvent. These properties make SO₃-Ph-BTP a suitable candidate for i-SANEX process development.