Study of Hydrogen Adsorption on Pt/WO_3-ZrO_2 through Pt Sites

The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO3- ZrO2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WOa-ZrO2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr. The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K. The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures, indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms, the spillover of hydrogen atoms onto the surface of the WO3-ZrO2 catalyst, the diffusion of spiltover hydrogen atom over the surface of the WO3-ZrO2 catalyst, and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site. The rate determining step was the spillover with the activation energy of 12.3 kJ/mol. The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion. The activity of Pt/WO3-ZrO2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.

Effect of iridium loading on HZSM-5 for isomerization of n-heptane

The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Bro¨nsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.

All the Fundamental Massless Fermion Fields in Superstring Theory: A Rigorous Analysis

A systematic rigorous analysis of both massless fermion fields in the mass spectra of superstring theory is carried out. Our interest is in dynamical aspects of these fields. An explicit novel expression for the propagator of the massless Rarita-Schwinger field (the gravitino), in the mass spectrum involving massless fermions in superstring theory in 10 dimensions, is derived. The analysis is carried in the presence of a non-constrained external source so that the full expression of the propagator emerges. The number of associated degrees of freedom is also obtained. We work in a Coulomb-like gauge. The massless Dirac field (the dilatino), the other massless fermion field in the mass spectra of superstring theory in 10 dimensions, is first investigated to this end.

Preparation and characterization of In and Cu co-doped ZnS photocatalysts for hydrogen production under visible light irradiation

In this work, a new photocatalyts In(0.1),Cu(x)-Zn S(x = 0.01, 0.03, 0.05) is successfully synthesized using simple hydrothermal method. The physical and chemical properties of the In and Cu co-doped Zn S photocatalyst were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), diffuse reflectance UV-visible spectroscopy(DR UV-visible) and photoluminescence spectroscopy(PL). The photocatalytic activity of the as-prepared In and Cu co-doped Zn S for hydrogen production from water with Na_2SO_3 and Na_2S as sacrificial agent under visible light irradiation(λ ≥ 425 nm) was investigated. The presence of co-dopants facilitated the separation of electron-hole as well as increases the visible light absorption. The absorption edge of the co-doped Zn S photocatalyst shifted to longer wavelength as the amount of Cu increases. This indicates that the absorption properties depended on the amount of Cu doped. The photocatalytic activity of single doped In(0.1)-Zn S was significantly enhanced by co-doping with Cu under visible light irradiation. The highest photocatalytic activity was observed on In(0.1),Cu(0.03)-Zn S with the hydrogen production rate of 131.32 μmol/h under visible light irradiation.This is almost 8 times higher than single doped In(0.1)-ZnS.

Carbon Dioxide Fixation Method for Electrosynthesis of Benzoic Acid from Chlorobenzene

Carbon dioxide fixation technique was developed as an alternative dechlorination method of chlorobenzenes. Electrolysis of chlorobenzene was carried out in a one-compartment cell fitted with an aluminium anode and a platinum cathode. Electrolysis in N, N-dimethylformamide （DMF） solution containing 0.1 M of tetrapropylammonium bromide （TPAB） at 0 ℃, 100 ml/min of CO2 flow rate and 120 mA/cm^2 of current density was found to be the optimum conditions of this electrocarboxylation, which gave 72% yield of benzoic acid from chlorobenzene. These conditions were then applied to 1,2-dichlorobenzene and 1,3-dichlorobenzene in order to convert them to their corrcsponding benzoic acids.

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

The influences of thermal annealing on the structural and optical features of radio frequency（rf） magnetron sputtered self-assembled Ge quantum dots（QDs） on Si（100） are investigated.Preferentially oriented structures of Ge along the（220） and（111） directions together with peak shift and reduced strain（4.9%to 2.7%） due to post-annealing at 650 ℃ are discerned from x-ray differaction（XRD） measurement.Atomic force microscopy（AFM） images for both pre-annealed and post-annealed（650 ℃） samples reveal pyramidal-shaped QDs（density - 0.26×10^11 cm^-2） and dome-shape morphologies with relatively high density - 0.92×10^11 cm^-2,respectively.This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity.The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role.The observed red-shift - 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing,and is related to the effect of quantum confinement.Furthermore,the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots.Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart.An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes.A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established.Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

Synthesis and mesomorphic properties of Schiff base esters possessing terminal chloro substituent

A homologous series of Schiff base esters,4-chlorobenzylidene-4'-n-alkanoyloxyanilines,containing even number of carbons at the end groups of the molecules(C_(n-1)H_(2n-1)COO-,n=4,6,8,10,12,14,16) were synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC) and polarizing optical microscopy(POM).It was found that the end groups of the molecules had an effect on the mesomorphic properties.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy exhibited monotropic smectic phase.The higher members in this homologous series were enantiotropic smectogens.

The Effect of Sulfate Ion on the Isomerization of n-Butane to iso-Butane

The effect of sulfate ion （SO4^2-） loading on the properties of Pt/SO4^2-ZrO2 and on the catalytic isomerization of n-butane to/so-butane was studied. The catalyst was prepared by impregnation of Zr（OH）4 with H2SO4 and platinum solution followed by calcination at 600 ℃. Ammonia TPD and FT-IR were used to confirm the distribution of acid sites and the structure of the sulfate species. Nitrogen physisorption and X-ray diffraction were used to confirm the physical structures of Pt/SO4^2-ZrO2. XRD pattern showed that the presence of sulfate ion stabilized the metastable tetragonal phase of zirconia and hindered the transition of amorphous phase to monoclinic phase of zirconia. Ammonia TPD profiles indicated the distributions of weak and medium acid sites observed on 0.1 N and 1.0 N sulfate in the loaded catalysts. The addition of 2.0 N and 4.0 N sulfate ion generated strong acid site and decreased the weak and medium acid sites. However, the XRD results and the specific surface area of the catalysts indicated that the excessive amount of sulfate ion collapsed the structure of the catalyst. The catalysts showed high activity and stability for isomerization of n-butane to iso-butane at 200 ℃ under hydrogen atmosphere. The conversion of n-butane to iso-butane per specific surface area of the catalyst increased with the increasing amount of sulfate ion owing to the existence of the bidentate sulfate and/or polynucleic sulfate species （（ZrO）2SO2）, which acts as an active site for the isomerization.

Germanium nanoislands grown by radio frequency magnetron sputtering: Annealing time dependent surface morphology and photoluminescence

Structural and optical properties of ～ 20 nm Ge nanoislands grown on Si（100） by radio frequency （rI） magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600 ℃ for 30 s, 90 s, and 120 s are performed to examine the influence of annealing time on the surface morphology and photoluminescence properties. X-ray diffraction spectra reveal prominent Ge and GeO2 peaks highly sensitive to the annealing time. Atomic force microscope micrographs of the as-grown sample show pyramidal nanoislands with relatively high-density （～ 10^11 cm^-2）. The nanoislands become dome-shaped upon annealing through a coarsening process mediated by Oswald ripening. The room temperature photoluminescence peaks for both as-grown （～ 3.29 eV） and annealed （～ 3.19 eV） samples consist of high intensity and broad emission, attributed to the effect of quantum confinement. The red shift （～ 0.10 eV） of the emission peak is attributed to the change in the size of the Ge nanoislands caused by annealing. Our easy fabrication method may contribute to the development of Ge nanostructure-based optoelectronics.

Structural and Optical Behavior of Germanium Quantum Dots

Controlled growth,synthesis,and characterization of a high density and large-scale Ge nanostructure by an easy fabrication method are key issues for optoelectronic devices.Ge quantum dots(QDs)having a density of~1011 cm^(-2) and a size as small as~8 nm are grown by radio frequency magnetron sputtering on Si(100)substrates under different heat treatments.The annealing temperature dependent structural and optical properties are measured using AFM,XRD,FESEM,EDX,photoluminescence(PL)and Raman spectroscopy.The effect of annealing is found to coarsen the Ge QDs from pyramidal to dome-shaped structures as they grow larger and transform the nanoislands into relatively stable and steady state configurations.Consequently,the annealing allows the intermixing of Si into the Ge QDs and thereby reduces the strain energy that enhances the formation of larger nanoislands.The room temperature PL spectra exhibits two strong peaks at~2.87 eV and~3.21 eV attributed to the interaction between Ge,GeO_(x) and the possibility of the presence of QDs core-shell structure.No reports so far exist on the red shift~0.05 eV of the strongest PL peak that results from the effect of quantum confinement.Furthermore,the Raman spectra for the pre-annealed QDs that consist of three peaks at around~305.25 cm^(-1),409.19 cm^(-1) and 515.25 cm^(-1) are attributed to Ge-Ge,Ge-Si,and Si-Si vibration modes,respectively.The Ge-Ge optical phonon frequency shift(~3.27 cm^(-1))associated with the annealed samples is assigned to the variation of shape,size distribution,and Ge composition in different QDs.The variation in the annealing dependent surface roughness and the number density is found to be in the range of~0.83 to~2.24 nm and~4.41 to~2.14×10^(11)cm^(-2),respectively.

Growth of Ge/Si(100) Nanostructures by Radio-Frequency Magnetron Sputtering: the Role of Annealing Temperature

Surface morphologies of Ge islands deposited on Si(100) substrates are characterized and their optical properties determined.Samples are prepared by rf magnetron sputtering in a high-vacuum chamber and are annealed at 600℃,700℃ and 800℃ for 2 min at nitrogen ambient pressure.Atomic force microscopy,field emission scanning electron microscopy,visible photoluminescence (PL) and energy dispersive x-ray spectroscopy are employed.The results for the annealing temperature-dependent sample morphology and the optical properties are presented.The density,size and roughness are found to be strongly influenced by the annealing temperature.A red shift of ~0.29 eV in the PL peak is observed with increasing annealing temperature.

Negative effect of Ni on PtHY in n-pentane isomerization evidenced by IR and ESR studies

Ni/PtHY with different Ni loadings was prepared by impregnating HY with hexachloroplatinic acid solution and Ni2＋/N,N-dimethylformamide solution. An increase in the Ni loading decreased the crystallinity, specific surface area and meso-micropores of the catalysts. Ni interacted with hydroxyl groups to produce IR absorption bands at 3740-3500 cm-1, Increasing Ni loadings resulted in a decrease in the intensities of the broad bands at 3730-3500 cm-1 and the sharp band at 3740 cm-1 with simultaneous development of new absorbance band at 3700 cm-1 that was attributed to （-OH）Ni. The acidity of the samples did not significantly change with Ni loadings up to 1.0 wt%, which indicated that Ni mostly interacts with non-acidic silanol groups （terminal- and structural-defect OH groups）. The presence of Ni decreased the activity of PtHY toward the isomerization of n-pentane because of a decrease in the number of active protonic-acid sites that formed from molecular hydrogen. IR and ESR studies confirmed that Pt facilitated the formation of protonic-acid sites from molecular hydrogen, whereas Ni, even when combined with Pt, didn＇t exhibit such ability. The absence of protonic-acid sites from molecular hydrogen significantly decreased the yield of iso-pentane and markedly increased the cracking products.

A Note on the Invariance Properties and Conservation Laws of the Kadomstev–Petviashvili Equation with Power Law Nonlinearity

First,we studied the invariance properties of the Kadomstev–Petviashvili equation with power law nonlinearity.Then,we determined the complete class of conservation laws and stated the corresponding conserved densities which are useful in finding the conserved quantities of the equation.The point symmetry generators were also used to reduce the equation to an exact solution and to verify the invariance properties of the conserved flows.

Tunable Multi Wavelength by Pulse Signal Modulation in Laser Pumping of EDFA

This report is aimed to present the result of experimental setup of the erbium-doped fiber amplifier (EDFA) with modulated pulse signal by laser pumping at wavelength 980 nm. The amplified spontaneous emission (ASE) from EDFA has multi wavelength and the spacing of wavelength can be controlled by controlling the pulse width of laser pumping. The result in this experiment shows that the feasibility of using EDFA system can generate the multi wavelength of all of C-Band spectrum. The pulse signal, for modulated laser pumping, is observed ranging from 10 to 100 Hz and the wavelength spacing can be tuned from 14.7 nm to 14.9 nm.

The Explicit Pure Vector Superfield in Gauge Theories

An explicit expression of the pure vector superfield is derived in gauge theories in the Wess-Zumino gauge. A pure vector superfield means that the theta independent part of the superfield transforms as a Lorentz vector. This is to be contrasted with the so-called general scalar superfield, whose theta independent part is a scalar, as well as with the known spinor superfield, whose theta independent part is a spinor, which both contain a vector field. In contrast to the latter two superfields, the action of supersymmetric gauge theories follows directly from the theory of a pure vector superfield from a so-called D-term. As the construction of a supersymmetric gauge theory of Yang-Mills vector Bosons, is more naturally generated out of a pure vector supersfield and not of a scalar or a spinor, the importance of a pure vector superfield cannot be overemphasized.

Effects of Eu3＋ and Dy3＋ doping or co-doping on optical and structural properties of BaB2Si2O8 phosphor for white LED applications

A series of Eu3＋ and Dy3＋ doped/co-doped as well as un-doped BaB2Si2Os phosphors were synthesized via solid state reaction method. The PL result showed typical blue and green emission from Dy3＋ and red emission from Eu3＋. The f-f transitions in- volving the lanthanide ions along with dopant site occupancy were discussed thoroughly. Phonon assisted energy transfer process was observed from Eu3＋ to Dy3＋, which enhanced the emissions of Dy3＋. Combinations of the emissions from Eu3＋ and Dy3＋ showed a possible white to red tuneable emission on the CIE diagram. The white warmth emissions of the phosphor were revealed to be ad- justable through designing the dopant concentration and excitation wavelengths. An unusual energy transfer that originated from Eu3＋ to Dy3＋ was also discovered and the energy transfer mechanism was discussed. Proposed energy transfer mechanism was investigated using luminescence decay lifetime. All the phosphor exhibited efficient excitation in the UV range which matched well with the emissions from GaN-based LED chips. This presented the BaB2Si208 phosphor as a promising candidate for white LED applications. The effects of doping on the structural properties and the optical band gap of BaB2Si208 phosphor were also discussed in this study.

Structural and luminescence studies of europium ions in lithium aluminium borophosphate glasses

Eu3＋ doped borophosphate glasses with the chemical composition 20Li2O-30Al2O3-10B2O3-40P2O5-xEu2O3（where x=0.05 mol.%, 0.1 mol.%, 1.0 mol.%, 1.5 mol.% and 2.0 mol.%） were prepared by conventional melt quenching technique. The structural and luminescence properties of the prepared Eu3＋ doped borophosphate glasses were studied and compared with reported results. The XRD pattern showed the amorphous nature of the prepared glasses. Whereas, the FTIR spectra revealed the vibrational modes in the prepared glasses. The bonding parameters（ β and ？） were calculated through the excitation spectra. Judd-Ofelt（J-O） intensity parameters were calculated from the emission spectra and were used to determine transition probability（A）, stimulated emission cross-section（σE P）, radiative lifetime（τR） and branching ratios（βexp） for the transition 5D0→7Fj（j=1, 2, 3 and 4） of Eu3＋ ions. Furthermore, the luminescence intensity ratio（R） of 5D0→7F2 to 5D0→7F1 transition was also calculated. Transition 5D0→7F2 had the highest value of stimulated emission cross-section and branching ratios and the results were comparable with the reported values. This indicated that the present glass is promising host material for Eu3＋ doped fiber amplifiers.

Morphology and Optical Properties of Self-Assembled In_(0.5)Ga_(0.5)As Quantum Dots with Different Spacer Layer Thickness

Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.

Why Matter Occupies so Large a Volume?

The paper represents a rigorous treatment of the underlying quantum theory, not just in words but providing the underlying technical details, as to why matter occupies so large a volume and its intimate connection with the Pauli exclusion principle, as more and more matter is put together, as well as of the contraction or shrinkage of ＂bosonic matter＂, upon collapse, for which the Panli exclusion is abolished. From the derived explicit bounds of integrals of powers of the particle number densities, explicit bounds on probabilities of the occurrences of the events just described are extracted. These probabilities lead one to infer the change of the ＂size＂ or extension of such matter, upon expansion or contraction, respectively, as their content is increased.

Optical behavior of self-assembled high-density Ge nanoislands embedded in SiO_2

The radio frequency magnetron sputtering method is used to prepare well-dispersed pyramidal-shaped Ge nanoislands embedded in amorphous SiO2 sublayers of various thicknesses. The estimated size and number density of Ge nanoislands in SiO2 sublayer thicknesses beyond 30 nm are approximately 15 nm and 1011 cm-2, respectively. Atomic force microscopy （AFM） reveals root mean square （RMS） roughness sensitivity as the SiO2 sublayer thickness varies from 30 to 40 nm. The formation of nanoislands with high aspect ratios is attributed to the higher rate of surface reactions between Ge adatoms and nucleated Ge islands than reactions associated with SiO2 and Ge. The Ge nanoisland polyorientation on SiO2 （50-nm thickness） is revealed by X-ray diffraction （XRD） patterns. Photoluminescence （PL） peaks of 2.9 and 1.65 eV observed at room temperature （RT） are attributed to the radiative recombination of electrons and holes from the Ge nanoislands/SiO2 and Si02/Si interfaces, respectively. The mean island sizes are determined by fitting the experimental Raman profile to two models, namely, the phonon confinement model and the size distribution combined with phonon confinement model. The latter model yields the best fit to the experimental data. We confirm that SiO2 matrix thickness variations play a significant role in the formation of Ge nanoislands mediated via the minimization of interfacial and strain energies. OCIS codes： 250.5230, 170.5660.