XAFS investigation of [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][AuCl<Subscript>4</Subscript>]<Subscript>2</Subscript> and its thermolysis products

Thermolysis of double complex salt [Pd(NH₃)₄][AuCl₄]₂ has been studied in helium atmosphere from ambient to 350 °C. The XAFS of Pd K and Au L₃ edges and thermogravimetry measurements have been carried out to characterize the intermediates and the final product. In the temperature range 115–160 °C the complex is decomposed to form Pd(NH₃)₂Cl₂ and AuCl_4−x N _x species with x ranging from 2 to 3. Subsequent heating of the intermediate up to 300 °C leads to the total loss of NH₃. The Au–Cl and Au–Au bonds form the local environment of Au at the stage of decomposition while only four chlorine atoms are around Pd. At the temperature of 330 °C the Au and Pd nanoparticles as well as residues of palladium chloride are detected. The final product consists of separated Au and Pd nanoparticles.     

Low Temperature Plasma Assisted Catalytic Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> in Simulated Marine Diesel Exhaust

Plasma Assisted Catalytic Reduction (PACR) of NO _x has been investigated at laboratory scale for gas stream compositions representative of marine diesel exhausts. PACR NO _x reduction in excess of 90% was measured at 350°C, a plasma specific energy of 60 J/l and two NO _x concentrations (1,200 and 1,800 ppm). PACR NO _x reduction of over 50% was measured for simulated marine engine conditions at 250°C, 60 J/l and 1,200 ppm NO _x . The performance under these conditions could be increased, achieving a peak of ∼74% NO _x reduction, although at a relatively high plasma power. Water, present in diesel exhaust, was shown to inhibit the poisoning effects of fuel sulphur using SO₂ as a representative exhaust component. The PACR system performance demonstrated tolerance to simulated fuel sulphur levels of up to 1% for the duration of the tests. PACR performance was also shown to be sensitive to the amount of hydrocarbon reductant used.     

Effect of heat treatment on electrochromic properties of TiO<Subscript>2</Subscript> thin films

Electrochromic titanium oxide (TiO₂) films were deposited on ITO/glass substrates by chemical solution deposition (CSD). The stock solutions were spin-coated onto substrates and then heated at various temperatures (200–500 °C) in various oxygen concentrations (0–80%) for 10 min. The effects of the processing parameters on the electrochromic properties of TiO₂ films were investigated. X-ray diffraction measurements demonstrated that the amorphous TiO₂ films were crystallized to form anatase films above 400 °C. The electrochromic properties and transmittance of TiO₂ films were measured in 1 M LiClO₄–propylene carbonate (PC) non-aqueous electrolyte. An amorphous 350 nm-thick TiO₂ film that was heated at 300°C in 60% ambient oxygen exhibited the maximum transmittance variation (ΔT%), 14.2%, between the bleached state and the colored state, with a ΔOD of 0.087, Q of 10.9 mC/cm², η of 7.98 cm²/C and x in Li _x ClO₄ of 0.076 at a wavelength (λ) of 550 nm.     

Reactivity of C<Subscript>3</Subscript>-C<Subscript>8</Subscript> alkanes with nitronium ions in sulfuric acid

We have determined the parameters of the Arrhenius equation (E, log A) for reactions between \textNO₂⁺ {\text{NO}}_2^{+} ions and C₃-C₈ alkanes in HNO₃–93 wt.% H₂SO₄ solutions at 277–353 K, and we have also estimated the activation parameters E _j , log A _j for secondary and tertiary C—H bonds of these alkanes. We show that the following compensation relations are satisfied: E = 2.3R βlog A + C with isokinetic temperature β = 360 ± 65 K, and also E _j =2.3Rβ _j log A _j  + C _j , for secondary C—H bonds, β₂ =300 ± 60, and for tertiary C—H bonds, β₃ =310 ± 50.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

Simultaneous removal of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and SO<Subscript>2</Subscript> by low-temperature selective catalytic reduction over modified activated carbon catalysts

A series of modified porous activated carbon (AC) catalysts prepared by impregnation were investigated for the low-temperature (≤250°C) selective catalytic reduction (SCR) of NO _x with NH₃ with simultaneous removal of SO₂. The effects of various preparation conditions and reaction conditions on NO and SO₂ conversions were observed, such as support type, active components, copper loading, calcination temperature and presence of H₂O and O₂. The modified AC catalysts were characterized by BET, XRD, TG and TPX methods. The activity test results showed that the optimal catalyst is 15% Cu/WCSAC which can provide 52% NO conversion and 68% SO₂ conversion simultaneously at 175°C with a space velocity of 30000 h^?1, and the optimal calcination temperature was 500°C. The presence of H₂O could inhibit NO conversion and promote the SO₂ conversion. The effect of O₂ (0–5%) was evaluated, and the NO and SO₂ conversions were best when the concentration of O₂ was 3%. Research demonstrated that Cu/WCSAC catalyst was a kind of potential catalysts due to the amorphous phase, high specific areas and high active ability.     

Structure and properties of H<Subscript>8</Subscript>(PW<Subscript>11</Subscript>TiO<Subscript>39</Subscript>)<Subscript>2</Subscript>O heteropoly acid

Heteropoly acid (HPA) H₈(PW₁₁TiO₃₉)₂O·xH₂O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, ³¹P, ¹⁸³W, and ¹⁷O NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW₁₁TiO₄₀]⁵⁻ monomer stable up to pH ∼ 6. When heated (150–400)°C, I splits into H₃PW₁₂O₄₀ and, apparently, H₃PW₁₀Ti₂O₃₈ without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at ∼450°C.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

Synthesis and colour properties of pigments based on terbium-dopped Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>

The main aim of this work was to synthesize the magnesium orthostannate doped by terbium cations and tested whether these materials can be used for colouring of the different materials, e.g. organic binder and ceramic glazes. Initial composition of pigments was counted according the general formula 2MgO(1 − x)SnO₂–xTbO₂, where values of x varied from 0.1 to 0.5 in 0.1 steps. The simultaneous TG/DTA measurements of mixture containing tin oxide, magnesium carbonate hydroxide and terbium oxide showed that the formation of a new compound started at temperature 1,029 °C, but single-phase system was not prepared. Granulometric compositions of samples that were prepared by calcining at temperatures 1,300–1,400 °C are characterized by values of median (d ₅₀) in range 4–8 μm. The calcining temperature 1,500 °C caused the increase of the particle sizes at around 12 μm. The composition of sample 2MgO–1.5SnO₂–0.5TbO₂ and heating temperature 1,500 °C are the most suitable conditions for preparation of colourfully interesting pigment that can be recommended also for colouring of ceramic glazes. Especially, for colouring of decorative lead containing glaze G 07091 containing 5 wt% of PbO and 8 wt% of Al₂O₃.     

Photocatalytic removal of nitrogen oxides from air on TiO<Subscript>2</Subscript> modified with bases and platinum

The efficiency of TiO₂ (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O₂ + N₂ mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO₂, NO₃⁻), it is impossible to realize prolonged continuous removal of NO _x (NO + NO₂) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO _x adsorbed during 2-h-long irradiation. Modification of TiO₂ with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO₂ and NO₃⁻. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO₂. The SPC of the (0.5% Pt)/TiO₂ catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt⁺ and Pt²⁺, have an approximately 2 times higher SPC than unpromoted TiO₂ and ensure a much larger NO₂/NO ratio at the reactor outlet. Conversely, the samples reduced in an H₂ atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO₂ and cause no significant change in the NO₂/NO ratio.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

FTIR-ATR <Emphasis Type="Italic">in situ</Emphasis> observation on the efflorescence and deliquescence processes of Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> aerosols

The efflorescence and deliquescence processes of Mg(NO₃)₂ aerosol particles deposited on ZnSe substrate have been investigated through in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) technique at the molecular level. At relative humidity (RH) of ∼3%, Mg(NO₃)₂ particles existed as amorphous states. The amorphous Mg(NO₃)₂ particles were transformed into crystalline Mg(NO₃)₂ · nH₂O (n ≤ 5) with slight increasing of RH. Thermodynamically stable Mg(NO₃)₂·6H₂O crystals were gradually formed on the particle surface and started to be dissolved at the saturation point (∼53% RH). At the same time, a continuous phase transition from Mg(NO₃)₂ · nH₂O (n≤5) to Mg(NO₃)₂·6H₂O occurred on the particle surface. This led the solid particles to completely deliquesce at 76% RH, which was much higher than the saturation point of 53% RH. In the efflorescence process, Mg(NO₃)₂ droplets entered into the supersaturated region due to the gradual evaporation of water. Finally, amorphous particles were formed when RH decreased below 5%. In the FTIR-ATR spectra of the supersaturated Mg(NO₃)₂ droplets, the absorbance of the symmetric stretching vibration of NO ₃ ⁻ (v ₁- NO ₃ ⁻ ) clearly became stronger. It resulted from the continuous formation of solvent share ion pairs (SIPs), and even the contact ion pairs (CIPs) between Mg²⁺ and NO ₃ ⁻ . Supported by the Trans-Century Program Foundation for the Talents by the Ministry of Education of China, the National Natural Science Foundation of China (Grant Nos. 20073004, 20473012, and 20673010), the 111 Project (B07012), and the State Key Laboratory of Physical Chemistry for Solid Surface of Xiamen University     

Direct Mass Spectrometric Study of the Ionic Species Content of a C<Subscript>2</Subscript>HCl<Subscript>3</Subscript>/He/O<Subscript>2</Subscript> Microwave Discharge Plasma

Direct on-line studies of a C₂HCl₃/He/O₂ microwave discharge plasma made possible the evolution and detection of many unfamiliar ionic species. Numerous ionic chlorocarbons, chlorohydrocarbons, oxygenated chlorohydrocarbons, oxygenated hydrocarbon radicals, and simple hydrocarbon species were identified mass spectrometrically as by-products: C _m Cl _n (m = 1–4, 6, 8; n = 1–8), C _m H _n Cl _x (m = 1–4, 6, 7, 10; n, x = 1–6), C _m H _n Cl _x O _y (m = 1–5, 12; n = 1–7; x = 1, 2, 4, 6; y = 1–3), C _n H_2n−1O (n = 2, 3), C _m H _n (m = 2, 4, 6, 8; n = 2, 4), and so on. The studies clearly showed the presence of various unfamiliar positive ionic O-containing species such as C₂ClO₂, CCl₃CO, C₂H₂Cl₄O₂, and C₄H₂Cl₆O₃. It is apparent that positive-ion reactions play a significant role in producing many ionic species in the chemistry of C₂HCl₃ plasmas.     

Thermochemical properties of MnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Homogeneous manganocolumbite (MnNb₂O₆) was synthesized from Nb₂O₅ and MnO oxides. Powder sample was orthorhombic with unit cell parameters: α = 0.5766 nm, b = 1.4439 nm, c = 0.5085 nm and V = 0.4234 nm³. Heat capacity over the temperature range of 313–1253 K was measured in an inert atmosphere with combined thermogravimetry and calorimetry using NETZSCH STA 449C Jupiter thermoanalyzer. Melting point was 1767 ± 3 K, enthalpy of melting was 144 ± 4 kJ mol⁻¹. Experimental heat capacity of MnNb₂O₆ is fitted to polynomial C _pm = 221.46 + 3.03 · 10⁻³ T + −39.79 · 10⁵ T ⁻² + 40.59 · 10⁻⁶ T ².     

Spectrokinetic study of the mechanism of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reduction with propylene over ZrO<Subscript>2</Subscript> in excess oxygen

It has been demonstrated by quantitative spectrokinetic measurements that, on the surface of zirconia stabilized as a tetragonal phase, the rate-limiting step of the selective catalytic reduction of nitrogen oxides (SCR of NO _x ) with propylene is the interaction of surface nitrates with C₃H₆ yielding organic nitro compounds. It is hypothesized that propylene reacts not with the nitrates themselves but with the activated complex NO₂ ^ads whose structure is intermediate between the structures of the monodentate NO₃ ^? and NO₂ species. Deep C₃H₆ oxidation exerts an adverse effect on the rate of the SCR of NO _x with propylene, and the interaction between O₂ and NO, which yields NO₂ and NO₃ ^? stimulates further nitrogen reduction to N₂. The effect of the reaction between oxygen and O₂N?C _n H _m on the NO _x reduction rate is variable and is determined by the C₃H₆/NO _x ratio. A generalized scheme of the SCR of NO _x with propylene on the surface of ZrO₂ partially stabilized as a tetragonal phase has been developed by comparing experimental data of this study and data available from the literature.     

Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

Thermal behaviour and fragility of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing zinc borophosphate glasses

Thermal behaviour of the glass series (100-x)[50ZnO-10B₂O₃-40P₂O₅]·xSb₂O₃ (x=0-42 mol%) and (100-y)[60ZnO-10B₂O₃-30P₂O₅]·ySb₂O₃ (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb₂O₃ results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously increases with increasing Sb₂O₃ content in both series and varies within the range of 6.6–11.7 ppm °C⁻¹. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb₂O₃ content the ‘fragility’ of the studied glasses increases.     

Aqueous sol–gel processing of precursor oxides for ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> synthesis

This paper describes the synthesis of ZrW₂O₈ by the use of an aqueous citrate-gel method in order to prepare a fine, pure and homogeneous oxide mixture suitable for ceramic processing. The thermal expansion coefficient thus obtained for α-ZrW₂O₈ is −10.6 × 10⁻⁶ °C⁻¹ (50–125 °C) whereas for the β-ZrW₂O₈ a value of −3.2 × 10⁻⁶ °C⁻¹ (200–300 °C) is obtained. The advantages of the use of a sol–gel method is expressed in the very homogeneous end-products. The paper describes crystallographic data, morphological structure and the thermal expansion properties of the ZrW₂O₈ material. Moreover, photoluminescence and photochromic properties specific to the precursor gel are described and analyzed. These effects support our views that the precursors show homogeneity up to nanometer level.     

Preparation and electrochemical performance of nano-structured Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for supercapacitor

Nano-structured spinel Li₂Mn₄O₉ powder was prepared via a combustion method with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O), and oxalic acid (C₂H₂O₄·2H₂O) as raw materials, followed by calcination of the precursor at 300 °C. The sample was characterized by X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy techniques. Electrochemical performance of the nano-Li₂Mn₄O₉ material was studied using cyclic voltammetry, ac impedance, and galvanostatic charge/discharge methods in 2 mol L⁻¹ LiNO₃ aqueous electrolyte. The results indicated that the nano-Li₂Mn₄O₉ material exhibited excellent electrochemical performance in terms of specific capacity, cycle life, and charge/discharge stability, as evidenced by the charge/discharge results. For example, specific capacitance of the single Li₂Mn₄O₉ electrode reached 407 F g⁻¹ at the scan rates of 5 mV s⁻¹. The capacitor, which is composed of activated carbon negative electrode and Li₂Mn₄O₉ positive electrode, also exhibits an excellent cycling performance in potential range of 0–1.6 V and keeps over 98% of the maximum capacitance even after 4,000 cycles.     

Preparation,Thermal Behaviour,and Crystal Structure of MgAl<Subscript>2</Subscript>F<Subscript>8</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>

Summary.  Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂. Received October 29, 2001. Accepted (revised) December 6, 2001