SiO2 Modification Research Articles

全无机ZnO纳米棒/SiO2电致发光器件的研究

全无机ZnO纳米棒/SiO₂电致发光器件的研究

Improvement in Ti-porcelain bonding by SiO2 modification of titanium surface through cast method

This study aimed to improve Ti-porcelain bonding strength through SiO2 modifications. Wax patterns were coated with SiO2 mixed with tetraethoxy silane (group C), patterns without coating were used as controls and subdivided into sandblasting group (group S) and polishing group (group P). Castingsurfaces were analyzed with XRD, while Ti-ceramic interfaces were characterized using SEM/EDS. Metal-ceramic specimens were tested in three point bending, and characterizations were also analyzed with SEM/EDS of porcelain debonding surfaces. In group C, SiO2 and Ti5Si3 phases were observed; SEM micrograph showed that Ti-porcelain had a compacted interface, and EDS maps of the interface illustrated the diffusion of Si, Al, and Sn to Ti, and cohesive fracture within the bonding agent. The bond strength of group C was 39.04±5.0 MPa, which was 15% higher than that of group S and 32% higher than that of group P. SiO2 coating could improve Ti-porcelain bond strength.

Capacitance Improvement and Electrochemical Characteristics of Silica-Coated Carbon Electrodes for Capacitive Deionization Application

Silicon oxides were coated on the surface of activated carbon powders (ACPs) by the sol-gel reaction in order to improve the capacitance of ACP electrodes for capacitive deionization application. The electrochemical characteristics of SiO2-coated carbon electrodes were studied by using cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS), and zeta potential measurement. The coating of SiO2 on the surface of ACPs was effective to enhance the specific capacitance due to the reduction in the diffusion resistance of ions and to the improvement in the propagation of the ac signal into the electrode pores. The zeta potential of ACPs was decreased with increasing the SiO2 content, which indicated that more adsorption sites for ions are formed. Consequently, the specific capacitance of SiO2-coated carbon electrodes showed a linear relation with the zeta potential value. In terms of the capacitance, the optimized SiO2 content was about 1.0 mmol SiO2 per unit carbon mass, and then the specific capacitance was improved about 34% of the pure ACP electrode. From a CDI unit cell test, it was confirmed that the SiO2 modification could improve the desalination efficiency about 10%.

The Effect of the Coating Layer and the Doped Ion Concentration on the Dielectric Properties of SiO<sub>2</sub>-PANI Electrorheological Fluid

The silicon dioxide particles are coated by polyaniline (PANI) under low temperature, and the doped ion concentration in PANI was adjusted by ammonia with different pH. The dielectric properties of PANI/SiO2 eletrorheological (ER) fluids are measured by impedance analyzer. The results indicated that the dielectric increment and relaxation frequency of ER fluid were enhanced after surface modification of SiO2, which are positive to the ER effect. Moreover, the pH of ammonia can change the relaxation frequency of ER fluid, which can improve the response ability of ER fluid to electric field.

Study on Preparation and Properties of Nano-Modified Polypropylene

The printing and packaging properties of ordinary Polypropylene (PP) materials were modified by self-made nanometer silicon dioxide (SiO2) and the effects of different SiO2 proportion were investigated. The results showed that SiO2 modification not only greatly increased the mechanic properties of PP but also improved its universal performance including polarity, ink adhesion and solvents residual and therefore enable PP materials better meet the requirement for food packaging industry.

High refractive index modification of SiO2 created by femtosecond laser nanostructuring

By comparing simulations with experiment, we show that the effective refractive index of fused SiO2 can be locally reduced by (1.8 ± 0.2)% by femtosecond laser nanostructuring. We create a microlens of material containing a planar array of nanocracks embedded inside fused silica and probe how it refracts or absorbs light as a function of pulse energy. The self-generated microlens lowers the peak light intensity by deflecting the light around the focus. We obtain the refractive index by simulating the beam transport using the 3D wave equation in conjunction with the measured dimensions of the modified material.

Highly active and stable catalytic performance on phosphorous-promoted Ru/Co/Zr/SiO2 Fischer–Tropsch catalyst

A novel doubly promoted Ru/Co/ZrP/SiO2 catalyst with zirconium–phosphorous species (ZrP) reveals high activity and stability on Fischer–Tropsch synthesis (FTS). The surface modification of SiO2 with ZrP species containing appropriate amount of phosphorous component, has an effect on the suppression of cobalt particle aggregation during FTS reaction. The spatial confinement of cobalt particles in ZrP matrix could be significantly enhanced when P/(Zr + P) molar ratio is around 0.13 (CoZrP(0.5)).

Synthesis, Crystal Structure and Properties of Na2MnO2

AbstractNa2MnO2 was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn2O3, NaN3 and NaNO3) were heated in an appropriate regime up to 390 °C and annealed at this temperature for 20 h, in specially designed silver containers. As the most prominent feature, the crystal structure of Na2MnO2 (C2/c, Z = 12, a = 12.5026(9), b = 12.1006(9), c = 6.0939(4) Å, β = 117.94(0)°, 1556 independent reflections, R1 = 3.83 % (all data)) forms a three dimensional framework polyanion of corner sharing MnO4‐tetrahedra. The connectivity pattern of the tetrahedral building units corresponds to the moganite structure, a rare SiO2 modification. According to measurements of the magnetic susceptibility in the temperature range from 2 to 750 K, Na2MnO2 shows antiferromagnetic ordering below 250 K. Evaluation of the high temperature data employing the Curie‐Weiss law revealed a magnetic moment of μeff = 5.93 μB, confirming the presence of divalent manganese.

Synthesis and Characterization of Hyperbranched Polyurethane Hybrids Using Tetraethoxysilane (TEOS) As Cross-Linker

Organic−inorganic hybrid coatings were derived from a hydroxyl-terminated hyperbranched polyester, 3-isocyanatopropyl triethoxysilane (ISPTES), and then cross-linked with various percentages of SiO2. This system was able to cross-link by hydrolysis of a tetraethoxysilane group in room temperature and humid conditions and then at 120 °C for 12−14 h, forming a three-dimensional hybrid structure, where the organic and inorganic phases were bonded covalently. The main focus of this work was to study the change of properties of the coating with SiO2 modification. These hybrid coatings were also characterized by using NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamical mechanical thermal analyzer (DMTA), thermal analysis (TGA), and tensile strength.

Organic Modification of SiO2 and Its Influence on the Properties of Co-Based Catalysts for Fischer–Tropsch Synthesis

Abstract SiO2 was modified by various organic groups before the impregnation of the cobalt precursor. These modified supports and the corresponding catalysts were characterized by IR spectroscopy, X-ray diffraction, and temperature-programmed reduction. The results showed that the organic modification of SiO2 reduced the surface silanol (Si–OH) concentration of the SiO2 support, suppressed the interaction between cobalt and silica, enhanced the reduction of the supported cobalt, and thus increased the catalytic activity of Co catalysts for Fischer–Tropsch synthesis. Moreover, SiO2 modified by different organic groups had different surface silanol concentration because of the steric hindrance, and the catalytic activity increased with the decrease of surface silanol concentration.

Nonlinear rheological behavior of silica filled solution‐polymerized styrene butadiene rubber

AbstractThe reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO2) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO2 causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO2 hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007

Photocatalytic activity of surface modified TiO2/RuO2/SiO2 nanoparticles for azo-dye degradation

SiO2/RuO2 modified high surface area titania dioxide nanoparticles prepared by hydrogen reduction were examined for their catalytic properties towards the photodegradation of methyl orange (MO), a common water pollutant in the textile industry. The modified materials present enhanced photocatalytic activity and can decompose the MO faster than the unmodified TiO2. Results showed that doping with RuO2 only offered a marginal benefit over TiO2 alone. On the other hand, modification of TiO2with RuO2 and SiO2 resulted in a marked increase in the rate constant and the photodegradation efficiency. These results are consistent with the unique structural, morphologoical and surface characteristics of the composite titania dioxide/ruthenium dioxide/silicon dioxide materials. The lower the average particle size and roughness of the materials, the higher the percentage of photodecomposition and the rate constant. The surface doping and modification effects thus appears synergetic to the charge separation process and the photocatalytic results are explained on the basis of the mechanism that involves efficient separation of electron–hole pairs induced by the silicon dioxide particles. This enhances the ability of the modified TiO2 particles to effectively capture protons. Results also show that the modified nanoparticles can be used repeatedly over a long time without loss of efficiency.

Structural modification of C-doped SiO2 induced by swift heavy ion irradiations

Thermally grown amorphous SiO2 samples were implanted at room temperature (RT) with 120keV C-ions to a dose ranging from 1.0×1016 to 8.6×1017C ions/cm2, then irradiated at RT with 950MeV Pb, 345 or 1754MeV Xe ions to a fluence in the region from 1.0×1011 to 3.8×1012 ions/cm2, respectively. The irradiated samples were investigated using micro-FTIR and micro-Raman spectroscopes. It was found that new chemical bonds such as Si–C, CC(O), CC and Si(C)–O–C bonds formed significantly in the C-doped SiO2 films after heavy ion irradiations. The evolution of Si–O–C bonds and possible mechanism of structural modification in C-doped SiO2 induced by swift heavy ion irradiations were discussed.

Synthesis of Nano‐Sized TiO2 Colloidal Sol and Its Optical Properties

Nano‐sized TiO2 sol was prepared through a wet synthesis process. The synthesis procedure involved hydrolysis of TiCl4, acid treatment, and a SiO2 surface‐modifying process. Before surface modification, the TiO2 suspension was treated with acid to remove Na ions, soluble TiO2, and other impurities. The acid treatment of a TiO2 suspension at a higher temperature was proved to be useful for effective SiO2 modification. The colloidal sol provided high transparency in visible light as well as excellent UV‐shielding properties. Surface modification of TiO2 particles with SiO2 greatly improved both the dispersing stability in neutral pH and the photostability of TiO2 colloidal sol.

마이크로 연소기에서 발생하는 열 소염과 화학 소염 현상 (I) -이온 주입법을 이용한 SiOx(≤2) 플레이트 제작과 구조 화학적 분석-

Effects of surface defect distribution on flame instability during flame-surface interaction are experimentally investigated. To examine chemical quenching phenomenon which is caused by radical adsorption and recombination processes on the surface, thermally grown silicon oxide plates with well-defined defect density were prepared. Ion implantation technique was used to control the number of defects, i.e. oxygen vacancies. In an attempt to preferentially remove oxygen atoms from silicon dioxide surface, argon ions with low energy level from 3keV to 5keV were irradiated at the incident angle of 60°. Compositional and structural modification of SiO₂ induced by low-energy ArSUP+/SUP ion irradiation has been characterized by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). It has been found that as the ion energy is increased, the number of structural defect is also increased and non-stoichiometric condition of SiOSUBx/SUB(x2) is enhanced.

Photodissociation and recombination dynamics of I2 in DDR (decadodecasil 3R): Dependence on the geometry of the host matrix monitored by femtosecond time-resolved pump–probe experiments

We present polarization dependent femtosecond time-resolved pump–probe experiments on iodine molecules embedded in well-defined cages of the crystalline microporous SiO2 modification decadodecasil 3R (DDR). Inside the DDR porosils the I2 molecules reside isolated from each other in hexagonal cages of ≈350 A3. After pump excitation of the B 0+u (3Π) state, the collision induced dissociation takes place via different crossing repulsive potential curves. The surrounding cages cause the atoms to recombine. The resulting iodine molecules are prepared in their A, A′, and X states where vibrational relaxation takes place due to the collisions with the surroundings. For a better understanding of the complex dynamics, a theoretical model was developed based on the classical Langevin equation (Brownian dynamics). The simulations of the experimental data obtained from powder samples are compared with earlier calculations by Ermoshin et al. (V. A. Ermoshin, G. Flachenecker, A. Materny and V. Engel, J. Chem. Phys., 2001, 114, 8132) based on molecular dynamics modeling. Brownian dynamics simulations are also applied to polarization dependent pump–probe experiments on single crystalline I2-DDR samples. It is demonstrated, that by switching the polarization of the lasers relative to the crystal axis the predissociation process of the excited B state of I2 can be influenced. This effect can be simulated using the theoretical model.

Modified Beta Zeolite as Catalyst for Fries Rearrangement Reaction

Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH3-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO2 did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce2O3, the number of acid sites determined by NH3-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO2 modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce2O3-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce2O3 modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce2O3-modified beta zeolite.

Rb2CdSiO4: Synthesis and Crystal Structure

The new compound Rb2CdSiO4 has been synthesized from Rb2CdO2 and SiO2 in the presence of excess Rb2O (typical molar ratio 1:1:2) under Ar atmosphere in a sealed Ag container at 330°C (40d). The twinned structure has been refined from X-ray single crystal data. Rb2CdSiO4 was found to crystallize in the space group C2221 (No. 20) with a=1142.6(2) pm, b=1102.3(1) pm, c=1672.5(2) pm. The lattice constants were refined from X-ray powder data. The crystal structure can be described as a stuffed derivative of the α-cristobalite modification of SiO2.

Caging of I2 in deca-dodecasil 3R: Pump–probe experiments and molecular dynamics modeling

We present transients obtained by femtosecond time-resolved spectroscopy on I2 encapsulated in well-defined cages of the crystalline microporous SiO2 modification deca-dodecasil 3R. After pump excitation into the electronic B-state, collision-induced predissociation is observed followed by recombination into A/A′ and X states, where the molecules undergo vibrational relaxation. To explain the complex time-behavior of the transient signals, molecular dynamics simulations are performed which account for the nonadiabatic transitions in I2 and the adsorbate-framework interactions. The theoretical study shows that the total signal contains contributions from four optical transitions which are influenced by predissociation and vibrational relaxation processes. A pronounced dependence of the transient signals on the probe-laser wavelength is determined by the position of the resonance window for the optical transition.

Isolated Se6Rings in the Voids of a Weakly Interacting, Electroneutral, and Crystalline SiO2Matrix: Combined Experimental and Theoretical Study

For the first time a selenium species has been successfully trapped in the voids of an electroneutral SiO2 modification, namely, in the porosil decadodecasil 3R (DDR). Raman spectroscopy in combination with theoretical ab initio calculations at the SCF and MP2 levels of theory have been used to assign the observed spectral bands exclusively to Se6 rings with D3d symmetry. The A1g(r) and Eg(r) mode frequencies of the matrix-isolated Se6 rings are considerably higher than those of bulk Se6, suggesting that intermolecular correlations are lost for the perfectly isolated molecules in the microporous host matrix. By an EXAFS analysis of Se K-spectra, Se−Se bond lengths of 2.34 Å and next-nearest Se···Se distances of 3.61 Å are obtained, in very good agreement with the theoretical ab initio studies. EXAFS analysis in addition reveals that the interaction between the SiO2 framework and the embedded Se6 rings are weak, resulting in a novel host−guest compound with nearly unperturbed Se6 guest molecules. The crystalline electroneutral host thus acts similarly to a noble gas matrix at low temperatures.