Structural characteristics and photocatalytic activity of ambient pressure dried SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> aerogel composites by one-step solvent exchange/surface modification

An ambient pressure synthesis of SiO₂/TiO₂ binary aerogel was prepared through the low-cost precursors of titanium tetrachloride (TiCl₄) and sodium silicate (Na₂O·nSiO₂). After gelation, solvent exchange and surface modification were performed simultaneously and the modified gel was finally dried under ambient pressure. Microstructural analyses by transmission electron microscope (TEM) indicate that fabricated SiO₂/TiO₂ aerogel composite shows similar sponge-like nanostructure as silica aerogel, and the Brunauer–Emmett–Teller (BET) analysis shows that the specific surface area of the composite reaches 605 m²/g, and the average pore size is 9.7 nm. Such binary aerogel exhibits significant photocatalytic performance in this paper for treating model pollutant of methyl orange (MO), and the decolorizing efficiency of MO is detected as 84.9% after 210 mins exposure to UV light irradiation. Degraded gel suspends in the water so as to separate from solution for reuse, and after 4 times recycling, 70% degradation efficiency can be easily reached when composite catalyzed system is exposed for 210 mins under UV irradiation.     

Erosion Resistance of CaO-AI203-SiO2 System Glass-Ceramics

The erosion resistance tests were used to research the erosion wear behavior of CaO-Al2O3-SiO2 system glass-ceramic. With the orthogonal test method, the factors thai affect the erosion wear of CaO-Al2O3-SiO2 system galss-ceramic such as pacticles property, impact angle, impact time, size of particles were discussed. The results show that erosion rate rises along a straight line at the early period of erosion wear. With the impact time increased, the erosion rate deviates from original staight line, tendency of the erosion rate increases, With the size of paricle increased , it will have more kinetic energy, the erosion rate of the surface of glass-ceramics ploate rises.     

Construction of amperometric glucose biosensor based on <Emphasis Type="Italic">in-situ</Emphasis> fabricated hierarchical meso-macroporous SiO<Subscript>2</Subscript> modified Au film electrodes

Gold nanoparticles (GNPs) modified hierarchical meso-macroporous (HMMP) SiO₂ layer on the surface of Au film electrode was developed as a novel enzyme immobilization matrix for biosensors construction. HMMP SiO₂-Au bilayer film electrodes were in-situ fabricated with magnetron sputtering process and templating method. The as-prepared HMMP SiO₂ films were characterized by SEM, TEM, and cyclic voltammetry (CV). The modified layer of HMMP SiO₂ has interconnected pore channels, and the sizes of macropores and mesopores are about 330 nm and 9 nm, respectively. The HMMP SiO₂ modified gold film electrodes not only have no diffusion barrier for electrochemical probes, but also exhibit good electrochemical properties. In addition, the activity and stability of the immobilized enzyme can be commendably retained in HMMP SiO₂. The biosensor exhibits an excellent bioelectrocatalytic response to glucose with a linear range of 1.0×10^-4 M-1.0×10^-2 M, high sensitivity of 18.0 μA·mM^-1·cm^-2, as well as good reproducibility and stability.     

Mechanical characteristics of SiO<Subscript>2</Subscript> electrets

1μm SiO₂ layer was thermally grown on silicon wafer. Negative and positive charging of SiO₂ layer was performed by means of corona method at room temperature. By controlling grid voltage, we have obtained uniformly charged SiO₂ with surface potential from −500 to +200 V. With certain electric field, the electrostatic force between charged SiO₂ is investigated. Experimental results indicate that attraction not only exists between charged SiO₂ with different polarity, but also exists between charged SiO₂ with the same polarity, and no repulsion has been observed. The attractive force is related to both surface potential difference of charged SiO₂ and the uniformity of the electric field. Based on the experiment, the attractive force is supposed to be caused by polarization when two charged SiO₂ wafers are close.     

Double-layer modification of water-based aluminum with SiO<Subscript>2</Subscript> and polyacrylic acid by sol-gel process and in situ polymerization

A double-layer aluminum consisting of an aluminum core and a shell of SiO₂ and polyacrylic acid was synthesized. This modified aluminum was used to improve the corrosion resistance and dispersive property of aluminum in waterborne media. TEM, FTIR, XPS, and EDX determination showed that PAA and SiO₂ were coated on the surface of aluminum. Evolved hydrogen detection showed that the corrosion resistance of composite particle had been markedly improved. Maximum corrosion inhibition efficiency of SiO₂ coated aluminum (SiO₂@Al) was 95.1% while that of double-layer coated aluminum (PAA/SiO₂@Al) was 98.8%. Meanwhile, polyacrylic acid layer improved the agglomeration of aluminum significantly. According to the dispersibility test, the particle size of 50% volume fraction [d(0.5)] of aluminum, SiO₂@Al and PAA/SiO₂@Al were 42, 53, and 34 μm, respectively.     

Preparation and adsorption property of phenyltriethoxysilane modified SiO2 aerogel

The hydrophobic silica aerogel (SiO₂ aerogel) was prepared by in situ polymerization sol-gel method and ethanol supercritical drying, with tetraethoxysilane (TEOS) as silica source, phenyltriethoxysilane (PTES) as modifier, ethanol as solvent and ammonia as catalyst. The effects of n(PTES)/n(TOES) were investigated on gel time, structure, and hydrophobicity. The SiO₂ aerogel was measured by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The effects of n(PTES)/n(TOES) were also studied on adsorption property of pentane, hexane, heptane, octane, benzene, toluene, o-xylene, nitromethane, nitroethane, and nitrobenzene. The adsorption intensity of SiO₂ aerogel was compared with that of activated carbon. The results show, with the increasing of n(PTES)/n(TOES), the surface area, pore volume, and pore size of SiO₂ aerogel decreased, gel time and hydrophobicity increased, and the contact angle could be 154° with n(PTES)/n(TOES)=0.7. The adsorption intensity of SiO2 aerogel with n(PTES)/n(TOES)=0.5 was bigger than that of activated carbon with an average 5.84 times of 10 organic liquid. The adsorption intensity of aerogel with n(PTES)/n(TOES) =0.1 was the best one in all samples with the average 8.33 times compared with that of activated carbon.     

Synthesis and photocatalytic property of the ZrO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> pillared laponite

The ZrO2/TiO2 pillared laponite (Ti-Zr-lap) photocatalysts were prepared with intercalation reaction by supercritical fluid drying (SCFD),and characterized by XRD,TEM,SEM and BET surface area analysis,and the photocatalytic properties of Ti-Zr-lap were investigated by degradation of azo dye acid red B (ARB).The results showed that the ZrO2/TiO2 pillared structures in laponite could be formed,with the mass fraction of (Zr4++Ti4+)/laponite (Xm) increasing,the basal spacing and the BET surface area of Ti-Zr-lap significantly increased.The Ti-Zr-lap used as photocatalyst had the advantages of stable and porous layered structure,large surface area with the anatase type TiO2.Compared with the Ti-Zr-lap dried by air drying,the Ti-Zr-lap dried by SCFD showed better photocatalytic property which was very close to that of P25 TiO2.Using the Ti-Zr-lap as photocatalyst with the optimum Xm of 0.16 and the calcination temperature of 500 ℃,under the conditions of the initial concentration of ARB 20 mg/L,photocatalyst concentration of 1.5 g/L and irradiation time 60 min,the decoloring rate of ARB could achieve 98.3%,indicating that the Ti-Zr-lap had excellent photocatalytic property.     

Improved visible transparency of SIO<Subscript>2</Subscript>/ZNO:AL /CEO<Subscript>2</Subscript>-TIO<Subscript>2</Subscript>/SIO<Subscript>2</Subscript> multilayer films with high UV absorption and infrared reflection rate

New visible transparent, UV absorption, and high infrared reflection properties have been realized by depositing multilayer SiO₂/ZnO: Al/CeO₂-TiO₂/SiO₂ films onto glass substrates at low temperature by radio frequency magnetron sputtering. Optimum thickness of SiO₂, ZnO: Al (ZAO) and CeO₂-TiO₂ (CTO) films were designed with the aid of thin film design software. The degree of antireflection can be controlled by adjusting the thickness and refractive index. The outer SiO₂ film can diminish the interference coloring and increase the transparency; the inner SiO₂ film improves the adhesion of the coating on the glass substrate and prevents Ca²⁺, Na⁺ in the glass substrate from entering the ZAO film. The average transmittance in the visible light range increases by nearly 18%-20%, as compared to double layer ZAO/CTO films. And the films display high infrared reflection rate of above 75% in the wavelength range of 10-25 μm and good UV absorption (> 98%) properties. These systems are easy to produce on a large scale at low cost and exhibit high mechanical and chemical durability. The triple functional films with high UV absorption, antireflective and high infrared reflection rate will adapt to application in flat panel display and architectural coating glass, automotive glass, with diminishing light pollution as well as decreasing eye fatigue and increasing comfort.     

Synthesis of mesoporous silica-embedded TiO<Subscript>2</Subscript> loaded with Ag nanoparticles for photocatalytic hydrogen evolution from water splitting

Ag loaded mesoporous silica-embedded TiO₂ nanocomposites were successfully synthesized via two different routes, including one-pot solvothermal method and solvothermal-chemical reduction method, both using Titanium (IV) n-butoxide (Ti(OC₄H₉)₄) as a precursor, formic acid as a solvent and reducing agent, silver nitrate as a silver source and tetraethyl silicate (TEOS) as a stabilizer. The transmission electron microscopic (TEM) images showed that silica-embedded anatase TiO₂ sample exhibited approximately rhombic shape and Ag nanoparticles could be embedded into the nanocomposites or deposited on the surface with high dispersion. The N₂ adsorption-desorption isotherms indicated that the silica-embedded anatase TiO₂ had obvious mesoporous structure with a BET specific surface area of 203.5 m²·g^-1. All Ag loaded silica-embedded TiO₂ composites showed a higher photocatalytic H₂-generation activity from water splitting under simulative solar light irradiation than that of TiO₂ products. The maximum H₂ production rate (6.10 mmol·h^-1·g^-1) was obtained over 2% Ag/silica-embedded TiO₂ nanocomposites (2% Ag/MST) prepared by solvothermal-chemical reduction method, which was 20 times that achieved on the silica-embedded TiO₂ sample. The enhanced photocatalytic H₂-evolution activity of Ag loaded mesoporous silica-embedded TiO₂ nanocomposites can be attributed to the multi-function of surface Ag co-catalyst, mesoporous structure, and embedding of silica.     

SiO2 Aerogels Prepared with Ambient Pressure Drying and Its Properties

SiO₂ aerogels were produced from tetraethyl orthosilicate (TEOS) as silicon resources, ethanol as solvent and watery HCl or ammonia by sol-gel method and surface modification at ambient pressure. Scanning electronic microscopy,Fourier transform infrared spectrometer (FT-IR),pore size distribution measurement, packing density and some other experiment methods were used to characterize the morphology and pore structure and other properties of the silica aerogels. The results show that the silica aerogels have a typical nano-porous microstructure with hydrophobic property. It was discovered that SiO₂ aerogels have better properties when the preparation condition is as following: the watery HCl concentration is 1%, the aging reagent is CH₃CHOHC₄H₉, the aging time is 20d, the volume concentration of trimethylchlorosilane (TMCS) in hexane is 6% and the surface modification time is 24h.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@PAM@NTA-Ni<Superscript>2+</Superscript> Magnetic Composite Nanoparticles for Highly Specific Separation of His-tagged Proteins

A facile approach has been developed to synthesize Fe₃O₄@PAM (polyacrylamide) nanoparticles (NPs) with carboxyl groups on the surfaces by copolymerization with acrylamide and acrylic acid in Fe₃O₄ NPs aqueous suspension. Nitrilotriacetic acid (NTA) was conjugated to the magnetic NPs via well-known carboniimide chemistry using EDC and NHS. The Ni²⁺ ions loaded on the surface of NPs provide abundant docking sites for immobilization of His-tagged green fluorescent proteins (His-tagged GFP). The high magnetic property of Fe₃O₄@PAM@NTA-Ni²⁺ allows an easy separation of the NPs from solution under an external magnetic field, with high His-tagged protein binding capacity (42 μg protein/mg of NPs). The NPs can be recycled for at least four times without significant loss of binding capacity to proteins. These materials show great potential to separate His-tagged protein with low-cost purification at industrial scale.     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Employing SiO<Subscript>2</Subscript> buffer layer to improve adhesion of the frequency-doubled antireflection coating on LBO

Frequency-doubled antireflection coatings simultaneously effective at 1064 nm and 532 nm were deposited on the lithium triborate (LiB₃O₅ or LBO) crystals using the electron beam evaporation method. Comparing with the sample without buffer layer, it is found that the adhesion of the sample with buffer layer of SiO₂ between coating and LBO substrate is improved significantly from 137.4 mN to greater than 200 mN. And the laser-induced damage threshold is increased by 20% from 15.1 J/cm² to 18.6 J/cm². The strengthening mechanism of adhesion of the buffer layer of SiO₂ is discussed by considering full plastic indentation and shear theory.     

Modification of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles by L-dopa or dopamine as an enzyme support

Fe3O4 magnetic nanoparticles were prepared by co-precipitation of Fe^2＋ and Fe^3＋ in an ammonia solution, and its size was about 36 nm measured by an atomic force microscope. Fe3O4 magnetic nanoparticles were modified by L-dopa or dopamine using sonication method. The analysis of FTIR clearly indicated the formation of Fe-O-C bond. Direct immobilization of trypsin （EC： 3.4.21.4） on Fe3O4 magnetic nanoparticles with L-dopa and dopamine spacer was investigated using glutaraldehyde as a coupling agent. No significant changes in the size and magnetic property of the three kinds of magnetic nanoparticles linked with or without trypsin were observed. The existence of the spacer molecule on magnetic nanoparticles could greatly improve the activity and the storage stability of bound trypsin through increasing the flexibility of enzyme and changing the microenvironment on nanoparticles surface compared to the naked magnetic nanoparticles.     

Effect of SiO2 on the Preparation and Properties of Pure Carbon Reaction Bonded Silicon Carbide Ceramics

Effect of SiO₂ content and sintering process on the composition and properties of Pure Carbon Reaction Bonded Silicon Carbide (PCRBSC) ceramics prepared with C−SiO₂ green body by infiltrating silicon was presented. The infiltrating mechanism of C−SiO₂ preform was also explored. The experimental results indicate that the shaping pressure increases with the addition of SiO₂ to the preform, and the pore size of the body turned finer and distributed in a narrower range, which is beneficial to decreasing the residual silicon content in the sintered materials and to avoiding shock off, thus increasing the conversion rate of SiC. SiO₂ was deoxidized by carbon at a high temperature and the gaseous SiO and CO produced are the main reason to the crack of the body at an elevated temperature. If the green body is deposited at 1800°C in vacuum before infiltration crack will not be produced in the preform and fully dense RBSC can be obtained. The ultimate material has the following properties: a density of 3.05–3.12 g/cm³, a strength of 580±32MPa and a hardness of (HRA)91–92.3. WU Qi-de: Born in 1949 This work was financially supported by the Key Research Project of the China (No. 96-A10-01-07) and the Key Research Project of the Wuhan (20001001003)     

Crystallization and Electrical Properties of （Ba0.4Pb0.3）Sr0.3TiO3 Thin Film by Pulsed Laser Deposition

（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.     

Dispersing and doping of BaTiO<Subscript>3</Subscript> powder by adsorption

Dispersing and doping of BaTiO3 powder by adsorption method were investigated. Ultrafine BaTiO3 powders were dispersed in the aqueous with ammoniumized citrate （NHa-CA） or ammoniumized citric lanthanum chelate （NH4-La-CA） as dispersant by ultrasonic bath. Better dispersion of BaTiO3 slurry was obtained in the aqueous with NH4-La-CA than that of NH4-CA when the mass ratio of citric acid （CA） to BaTiO3 was less than 0,007. The pH value hardly affects the dispersion property of BaTiO3 suspension dispersed by NH4-La-CA. BaTiO3 powder could be well dispersed （median size D50=0.45 μm） and also doped with high uniformity of added components by adsorbing citric acid chelate on surface. Compared with solid mixing, better microstructure and properties of La/Mn codoped ceramics were obtained by adsorption method.     

Effect of diatomite additive on the mechanical and dielectric properties of porous SiO<Subscript>2</Subscript>-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite ceramics

Porous SiO₂-Si₃N₄ composite ceramics with high porosity and excellent mechanical properties were fabricated by pressureless-sintering at relatively low temperature of 1 500 °C using diatomite as pore forming agent. The effects of diatomite on flexural strength, fracture toughness, shrinkage, porosity and phase transformation of the porous ceramics were investigated in detail. Compared with that of the ceramic without adding diatomite, the porosity of the ceramic with 10% diatomite is increased by about 27.4%, the flexural strength and fracture toughness reaches 78.04 MPa and 1.25 MPa·m^1/2, respectively. As the porosity increases, the dielectric constant of porous SiO₂-Si₃N₄ ceramic decreases obviously from 3.65 to 2.95.     

Microstructures and fatigue-free properties of the La<Superscript>3+</Superscript> and Nd<Superscript>3+</Superscript> doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by modified sol-gel technique

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were fabricated on Pt/TiO₂/SiO₂/Si (100) substrates by a modified sol-gel technique. X-ray diffraction indicated that these films were of single phase with random polycrystalline orientations. The surface morphologies of the films were observed by scanning electron microscope, showing uniform, dense films with grain size of 50–100 nm. Well-saturated hysteresis loops of the films were obtained in metal-ferroelectric-metal type capacitors with Cu top electrodes at an applied voltage of 400 kV/cm, giving the remanent polarization (2P _r) and coercive field (2E _c) values of the films of 25.1 μC/cm² and 203 kV/cm for BLT, and 44.2 μC/cm² and 296 kV/cm for BNT, respectively. Moreover, these capacitors did not show fatigue behaviors after up to 1.75×10¹⁰ switching cycles at the test frequency of 1 MHz, suggesting a fatigue-free character. The influences of the La³⁺ and Nd³⁺ doping on the properties of the films were comparatively discussed. Supported by the National Key Basic Research and Development Program of China (Grant No. 2006CB932305) and the Natural Science Foundation of Hubei Province, China (Grant No. 2004ABA082)     

Enhanced Ferroelectric Polarization in Laser-ablated Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films by Controlling Preferred Orientation

Polycrystalline Bi₄Ti₃O₁₂ thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO₂/Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi₄Ti₃O₁₂ thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm², respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm²) was obtained for the Bi₄Ti₃O₁₂ thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi₄Ti₃O₁₂ films.