Kinetics of carbon dioxide sorption by the composite material K2CO3 in Al2O3

The kinetics of the CO₂ sorption by a composite sorbent K₂CO₃ in Al₂O₃ was studied in a gradientless adsorber at 295 K. The order of the sorption rate with respect to the CO₂ concentration was found to be n = 1.04 ± 0.07. The sorption rate constants were evaluated for sorbent grains of various sizes between 0.25 and 2.1 mm. It was shown that the rate constant is proportional to the grain reciprocal radius. The dynamic capacity was obtained as a function of the CO₂ concentration. The maximum sorption capacity was found to be 83 mg of CO₂ per 1 g of the sorbent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selective electrochemical molecular recognition of benzenediol isomers using molecularly imprinted TiO2 film electrodes

In this paper, selective recognition of benzenediol isomers was studied using molecularly imprinted TiO₂ film formed on a graphitic electrode. The imprinting process was investigated in detail using IR. The electrode process for p-hydroquinone follows a E_rC_r mechanism. The cavities formed by p-phthalic acid have good selectivity toward p-hydroquinone among the isomers. The complex ratio between p-hydroquinone and binding sites was estimated to be 1:2 with an apparent equilibrium constant of 2.98×10⁶ l² mol⁻². For o-hydroquinone and m-benzenediol, the ratio decreased to 1:1 with an apparent equilibrium constant of 1.20×10³ and 1.35×10³ l mol⁻¹. The apparent complexing ratio and equilibrium constants could shed some insight on the nature of isomeric selectivity of the recognition sites with respect to different isomers of benzenediol. The cavities designed by o-phthalic acid present good selectivity toward o-hydroquinone.     

Nonenzymatic electrochemical glucose sensor based on MnO2/MWNTs nanocomposite

In this communication, an amperometric glucose biosensor based on MnO₂/MWNTs electrode was reported. MnO₂ was homogeneously coated on vertically aligned MWNTs by electrodeposition. The MnO₂/MWNTs electrode displayed high electrocatalytic activity towards the oxidation of glucose in alkaline solution, showing about 0.30 V negative shift in peak potential with oxidation starting at ca. −0.20 V (vs. 3 M KCl–Ag/AgCl) as compared with bare MWNTs electrode. At an applied potential of +0.30 V, the MnO₂/MWNTs electrode gives a linear dependence (R = 0.995) in the glucose concentration up to 28 mM with a sensitivity of 33.19 μA mM⁻¹. Meanwhile, the MnO₂/MWNTs electrode is also highly resistant toward poisoning by chloride ions. In addition, interference from the oxidation of common interfering species such as ascorbic acid, dopamine, and uric acid is effectively avoided. The MnO₂/MWNTs electrode allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensor.     

Kinetics of Mn2O3 digestion in H2SO4 solutions

The kinetics of Mn₂O₃ digestion in various H₂SO₄ solutions (0.5-2.0 M) and at various temperatures (ambient to 80 °C) to form solid γ-MnO₂ and soluble Mn(II) have been examined using X-ray diffraction. Using a modified first-order Avrami expression to describe digestion kinetics, rate constants in the range 0.02-0.98 h⁻¹ were found for Mn₂O₃ disappearance, and 0.03-0.42 h⁻¹ for γ-MnO₂ formation, with higher H₂SO₄ concentrations and temperatures leading to faster conversion rates. Also, for a particular set of experimental conditions, the rate of γ-MnO₂ formation was always slower than Mn₂O₃ disappearance. This was interpreted in terms of the solubility and stability of the soluble Mn(III) intermediated formed during the digestion. Activation energies for Mn₂O₃ dissolution and γ-MnO₂ formation were also determined.     

Interrupted thermal desorption of TiH2

Structural changes of commercial TiH₂ were studied using interrupted temperature desorption spectroscopy and X-ray diffraction techniques to understand the mechanism of its degradation under non-equilibrium conditions. Rapid cooling on different stages of temperature-programmed heating allowed to study the intermediate phase compositions that evolve upon cooling from the high-temperature phase βTi(H). The phase transformation sequence is described as a number of consecutive reactions corresponding to the observed desorption peaks. Phases δTiH_2−x, γTiH, and the solid solution αTi(H) were found to be intermediates in the TiH₂ → αTi transformation when the latter is interrupted. Additional evidence for the thermodynamic stability of γTiH is given.     

TiO2 nanotube, nanowire, and rhomboid-shaped particle thin films fixed on a titanium metal plate

Titanium dioxide thin films having various nanostructures could be formed by various treatments on sodium titanate nanotube thin films approximately 5 μm thick fixed on titanium metal plates. Using an aqueous solution with a lower hydrochloric acid concentration (0.01 mol/L) and a higher reaction temperature (90 °C) than those previously employed, we obtained a hydrogen titanate nanotube thin film fixed onto a titanium metal plate by H⁺ ion-exchange treatment of the sodium titanate nanotube thin film. Calcination of hydrogen titanate nanotube thin films yielded porous thin films consisting of anatase nanotubes, anatase nanowires, and anatase nanoparticles grown directly from the titanium metal plate. H⁺ ion-exchange treatment of sodium titanate nanotube thin films at 140 °C resulted in porous thin films consisting of rhomboid-shaped anatase nanoparticles.     

The structure and ordering of ε-MnO2

The presence of ε-MnO₂ as a major component of electrolytic manganese dioxide (EMD) has been demonstrated by a combined X-ray diffraction/transmission electron microscopy (TEM) study. ε-MnO₂ usually has a partially ordered defect NiAs structure containing 50% cation vacancies; these vacancies can be fully ordered by a low temperature (200 °C) heat treatment to form a pseudohexagonal but monoclinic superlattice.Numerous fine-scale anti-phase domain boundaries are present in ordered ε-MnO₂ and cause extensive peak broadening and a massive shift of a very intense, 0.37 nm superlattice peak. This suggests a radically different explanation of the ubiquitous, very broad ∼0.42 nm peak (∼21-22° 2θ, CuKα radiation) in EMDs, which heretofore has been attributed to Ramsdellite containing numerous planar defects. This work confirms the multi-phase model of equiaxed EMDs proposed by Heuer et al. [ITE Lett. 1(6) (2000) B50; Proc. Seventh Int. Symp. Adv. Phys. Fields 92 (2001)], rather than the defective single-phase model of Chabre and Pannetier [Prog. Solid State Chem. 23 (1995) 1] and Bowden et al. [ITE Lett. 4(1) (2003) B1].     

Selective water sorbents for multiple applications, 4. CaCl2 confined in silica gel pores: Sorption/desorption kinetics

This paper presents experimental data on water sorption/desorption kinetics on composite SWS-1L and SWS-1S materials, bulk aqueous CaCl₂ solutions and pure KSKG silica gel. Desorption kinetic curves are measured in the temperature range of 328–363 K at different vapor pressures. First order kinetics is found for both SWS materials and the bulk aqueous solution with the apparent activation energies of the water desorption equal to 23.5 kJ/mol and 48.6 kJ/mol, respectively. The difference in the kinetic behavior of the bulk and disperse systems is discussed.     

Efficient preparation of nanocrystalline anatase TiO2 and V/TiO2 thin layers using microwave drying and/or microwave calcination technique

This study has demonstrated that the synthesis of TiO₂ and V/TiO₂ thin layers may be significantly improved and extended if microwave energy is employed during the drying and/or calcination step. Thin nanoparticulate titania layers were prepared via the sol-gel method using titanium n-butoxide as a precursor. As prepared films were then analyzed by means of various characterization techniques (Raman spectroscopy, UV/Vis, AFM, XPS) in order to determine their functional properties. The photocatalytic activities of prepared layers were quantified by the decoloring rate of Rhodamine B. All thermal treatments in microwave field were done in the same manner, by using an IR pyrometer in the microwave oven and monitoring the temperature of the heating. Nevertheless the microwave and thermally prepared materials were different. This in turn may lead to differences in their functional and also photocatalytic properties.     

Redistribution reactions of heteroleptic barium iodide derivatives: Synthesis and structures of trans-BaI2(DME)(triglyme), cis-BaI2(DME)(tetraglyme) and [Ba(tetraglyme)2]I2 · C7H8

The reaction between BaI₂ · 2H₂O and NaHFIP [HFIP = OCH(CF₃)₂] in a 1:1 stoichiometry gave the heterometallic compound NaBaI₂(HFIP)(H₂O)(THF)_0.5 (1). Attempts to recrystallize 1 in the presence of N- or O-donor ligands lead to redistribution reactions. Barium iodide adducts such as BaI₂(DME)₃ (2), trans-BaI₂(DME)(triglyme) (3) and cis-BaI₂(DME)(tetraglyme) (4) were isolated with DME as solvent. A similar behavior was observed for the reaction between BaI₂ · 2H₂O and NaTFA (TFA = O₂CCF₃) in a 1:1 stoichiometry in THF, and [Ba(tetraglyme)₂]I₂ · C₇H₈ (6) was isolated in the presence of excess tetraglyme. All compounds have been characterized by elemental analysis, IR and ¹H NMR as well as single crystal X-ray studies for 3, 4 and 6. Compounds 3 and 4 are covalent adducts with eight- and nine-coordinate barium, respectively. Compound 6 is an ionic compound where two tetraglyme ligands wrap the 10-coordinate barium cation in a helical fashion. The presence of DME actually allows the coordination number of barium in the mixed-ligand adducts 3 and 4 to be tuned. The average Ba–O bond lengths (2.80 for 3 to 2.87 Å for 6) reflect the coordination number of the metal. The same observation is valid for the average Ba–I bond distance, 3.442 for 3 vs. 3.536 Å for 4.     

Synthesis and Structural Characterization of Manganese Carbonyl Incorporated Polyoxomolybdate （n-Bu4N）2 [Mo6O16（OCH3）2 {HOCH2C（CH2O）3}2 {Mn（CO）3}2]

The polyoxoanion incorporated {Mn（CO）3^＋} complex, （n-Bu4N）2[Mo6O16（OCH3）2{HOCH2C（CH2O）3}2·{Mn（CO）3}2]（1）, has been synthesized by the reaction of （n-Bu4N）4[Mo8O26] with Mn（CO）5Br in methanol, in the presence of C（CH2OH）4. The complex 1 has been characterized by IR, UV-Vis, X-ray single crystal diffraction, and TG. Crystal data for the complex 1：C25H48MnMo3NO16 （1）, Triclinic Pi, a=0.9405（3） nm, b=1.3351（4） nm, c=1.5455（4） nm, α=103.206（5）°, β=102.165（5）°, γ=100.784（5）°, V=1.7896（9） nm^3, Z=2, R1=0.0703, wR2= 0.1495. The structure analysis of complex 1 shows that the complex consists of two tetrabutylammonium cations and a polyoxomolybdate anion that incorporates two fac-Mn（CO）3^＋ units. The anion of complex 1 can be considered as the dimer of two rhomb-like anions by sharing of two comers.     

Hydrate film growth at the interface between gaseous CO2 and sodium chloride solution

Greenhouse gas CO₂ has become a serious problem for human beings. The hydrate technology has been considered as a possible approach to sequester CO₂. In this work, the lateral growth rates of a CO₂ hydrate film in aqueous NaCl solutions of different concentrations were measured by means of suspending a single gas bubble in liquid. The results show that the film growth rates depended on not only the driving force, but also the NaCl concentration, and the film growth rates decreased with the increasing NaCl concentration. The simple relationship v_f∝ΔT ^5/2 could be used to correlate the hydrate film growth rate of a CO₂ + NaCl + water system by introducing a NaCl concentration-dependent coefficient. The film thickness was investigated experimentally and evaluated theoretically; the results show that it became thicker at a higher NaCl concentration when the temperature and pressure were specified. In addition, a series of interesting phenomena, such as the occurrence of double hydrate films, were displayed and discussed. Supported by the National Natural Science Foundation of China (Grant Nos. 20676145 & U0633003) and the Program for New Century Excellent Talents in University (Grant No. NCET-07-0842)     

Synthesis and structure of three manganese oxalates: MnC2O4·2H2O, [C4H8(NH2)2][Mn2(C2O4)3] and Mn2(C2O4)(OH)2

Three manganese oxalates have been hydrothermally synthesized, and their structures determined by single-crystal X-ray diffraction. MnC₂O₄·2H₂O (I) is orthorhombic, P2₁2₁2₁, , , , , Z=4, final R, R_w=0.0832, 0.1017 for 561 observed data (I>3σ(I)). The one-dimensional structure consists of chains of oxalate-bridged manganese centers. [C₄H₈(NH₂)₂][Mn₂(C₂O₄)₃] (II) is triclinic, , , , , α=81.489(2)°, β=81.045(2)°, γ=86.076(2)°, , Z=1, final R, R_w=0.0467, 0.0596 for 1773 observed data (I > 3σ (I)). The three-dimensional framework is constructed from seven coordinate manganese and oxalate anions. The material contains extra-framework diprotonated piperazine cations. Mn₂(C₂O₄)(OH)₂ (III) is monoclinic, P2₁/c, , , , β=91.10(3)°, , Z=1, final R₁, wR2=0.0710, 0.1378 for 268 observed data (I>2σ (I)). The structure is also three dimensional, with layers of MnO₆ octahedra pillared by oxalate anions. The hydroxide group is found bonded to three manganese centers resulting in a four coordinate oxygen.     

Preparation and crystal structure of [Bi3I(C4H8O3H2)2(C4H8O3H)5]2Bi8I30 containing the novel polynuclear [Bi8I30] anion

Preparation and crystal structure of the novel compound [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ are reported. The title compound is prepared by heating of BiI₃ and diethylene glycol at 413 K in a sealed quartz glass tube filled with argon. Deep red single crystals are grown and applied to perform X-ray powder diffraction and X-ray single-crystal diffraction measurements. The compound crystallizes triclinic with space group P-1: Z=2, a=13.217(1) Å, b=15.277(1) Å, c=22.498(1) Å, α=84.33(1), β=73.18(1), γ=67.48(1). [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ comprises the novel polynuclear [Bi₈I₃₀]⁶⁻ anion and [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]³⁺ as the cation. Cation as well as the anion can be assumed to represent intermediates between solid BiI₃ and BiI₃ completely dissolved in diethylene glycol.     

Chemical solution deposited silver tantalate niobate, Ag x (Ta0.5Nb0.5)O3? y , thin films on (111)Pt/Ti/SiO2/(100)Si substrates

Silver tantalate niobate films are candidates for temperature stable microwave dielectrics. In this work, a chemical solution deposition synthesis method was developed for Ag _x (Ta_0.5Nb_0.5)O_3−y films on Pt-coated Si substrates. Stable solutions with a range of silver stoichiometries were prepared using 2-methoxyethanol and pyridine as solvents, from AgNO₃ and Nb and Ta ethoxide precursors. It was extremely difficult to prepare phase-pure perovskite films of Ag(Ta_0.5Nb_0.5)O₃ on Pt-coated Si subtrates; instead a mixture of perovskite and natrotantite phases was identified. Such mixed phase films had dielectric constant ɛ _r and dielectric loss tanδ values ranging from 200±20 to 270±25 and 0.006±0.002 to 0.002±0.001 at 100 kHz, respectively, depending on the firing temperature. For Ag₂(Ta_0.5Nb_0.5)₄O₁₁, Ag_0.8(Ta_0.5Nb_0.5)O_2.9, Ag_0.85(Ta_0.5Nb_0.5)O_2.925 and Ag_0.9(Ta_0.5Nb_0.5)O_2.95 films, mainly the natrotantite phase was observed. The ɛ _r values of these films were between 70±10 and 130±15 with tan δ values of 0.008±0.002 at 100 kHz.     

Pt/Al2O3 and Pt/Ba?Al2O3 catalysts studied by temperature programmed desorption of oxygen: Evidence for a low temperature desorbing species

For fresh and aged Pt/Al₂O₃ catalysts, TPD of oxygen is fairly well related to the noble metal surface areas and to the catalytic activity in butane combustion, whereas for aged Pt/Ba−Al₂O₃ solids, the catalytic activity is still preserved despite a tremendous sintering of the metallic phase and seems to be connected to a surface barium superoxide.     

Investigation of HfO2 doping on GeTe for phase change memory

The phase change characteristics of HfO₂ doping on GeTe thin films were investigated by X-ray photoelectron spectroscopy, X-ray diffraction patterns, scanning electron microscope, atom force microscopy, and in situ resistance-temperature measurements. It is shown that the crystallization of amorphous GeTe film could be suppressed by the incorporation of HfO₂, which had a favorable effect on the archival life stability. The activation energy for crystallization increased from 2.36 to 4.69 eV, and the temperature for 10 years data retention increased from 108 to 187 °C with the increasing concentration of HfO₂ form 0 to 12 mol%. Meanwhile, the grain size and surface roughness decreased. Phase change memory based on GeTe–HfO₂ film was fabricated and characterized. A reversible phase change could be trigged by the pulse with at least 100 ns width which was shorter than that of Ge₂Sb₂Te₅ (500 ns). The resistance ratio between amorphous and crystalline states achieved 500 times. The minimum energy necessary for RESET operation of GeTe–HfO₂ based test cell was much smaller than that of Ge₂Sb₂Te₅-based one.     

Synthesis, structure and magnetic behavior of a new three-dimensional Manganese phosphite-oxalate: [C2N2H10][Mn2(OH2)2(HPO3)2(C2O4)]

A novel manganese phosphite-oxalate, [C₂N₂H₁₀][Mn₂^II(OH₂)₂(HPO₃)₂(C₂O₄)] has been hydothermally synthesized and its structure determined by single-crystal X-ray diffraction. The structure consists of neutral manganese phosphite layers, [Mn(HPO₃)]_∞, formed by MnO₆ octahedra and HPO₃ units, cross-linked by the oxalate moieties. The organic cations occupy the middle of the 8-membered one-dimensional channels. Magnetic studies indicate weak antiferromagnetic interactions between the Mn²⁺ ions.     

水热法制纳米CeO2膜及紫外吸收性能研究

以Ce(NO3)3.6H2O和CO(NH2)2为原料,采用水热法在玻璃基质上制备了CeO2纳米膜。研究了水热温度和时间对所制备纳米CeO2薄膜的抗紫外性能的影响。采用XRD、FT-IR、SEM、UV-Vis以及自动椭圆偏振仪等测试手段对CeO2纳米膜及粉体进行了表征。结果表明,水热法制备的薄膜,最佳的水热工艺条件为水热温度130℃加热7 h。在此条件下,制备的薄膜厚度达100nm,晶型较好,膜表面平整度较高,且具有优异的可见光透过性和紫外吸收特性。     

Defect and transport properties of the NdCoO3 catalyst and sensor material

The NdCoO₃ perovskite has been investigated using a combination of atomistic simulation and experimental techniques to examine its possible use as an oxidation catalyst and/or sensor material. The sensing properties of NdCoO₃ and Nd_0.8Sr_0.2CoO₃ towards CO have been investigated by employing thin films deposited by means of radio-frequency (RF) magnetron sputtering onto polycrystalline Al₂O₃. The response of the films was monitored by performing four-probe DC-conductivity measurements. The conductivity variation induced by switching between a CO-free atmosphere (air) and a CO-rich one with the same composition of residual gas was recorded and analysed as a function of temperature; results are compared for the two samples. Simulation studies focussed on the dopant, transport and redox properties of the pure material; the results indicate that Sr and Ca on the Nd site are the most soluble dopants and that when divalent dopants are incorporated in the structure, charge compensation occurs via oxygen ion vacancies. The low activation energy for oxygen vacancy migration suggests high oxide-ion mobility through the lattice. Particular attention is paid to the electronic processes because of their importance with respect to practical applications of the material.