Effect of TiO2 nanoparticles aggregation in silicate thin coating films on photocatalytic behavior for antifouling materials

Two types of disperser namely, a high speed agitation bead mill and a colloidal mill, were used for the dispersion behavior control of TiO₂ nanoparticles (20 nm in average primary diameter) in an aqueous suspension. A composite thin film raging in thickness from 90 to 400 nm was prepared from the coating suspension following the addition of a commercial ethyl silicate oligomer binder into the prepared suspension by means of a spray coating method. The mean aggregate size of TiO₂ nanoparticles in the aqueous suspension was found to be 80 nm and 290 nm in diameter, respectively, when using the agitated bead and colloidal milling methods. Large aggregates on the order of several hundred nanometers were found to remain in the suspension after colloidal milling. Further, a fine dispersion of TiO₂ nanoparticles in the thin film produced using the agitation bead milling process promoted the photocatalytic activity and enhanced transparency of the film for visible light. The aggregate structure of TiO₂ nanoparticles in an aqueous suspension was well maintained in the film prepared by a spray coating process.     

Photocatalytic behavior of TiO2 nanoparticles supported on porous aluminosilicate surface modified by cationic surfactant

In order to utilize the photocatalytic function of TiO₂ nanoparticles in materials manufactured from organic polymeric compounds, such as paper, resins, and textiles, TiO₂ nanoparticles supported on aluminosilicate, which contained 1, 5, and 10 wt% of TiO₂ were prepared by mixing commercial TiO₂ nanoparticles and porous aluminosilicate at pH 7 in a cationic surfactant aqueous solution. Most of the supported TiO₂ nanoparticles on the aluminosilicate surface were observed by TEM–EDS (energy depressive X-ray spectroscopy) analysis. TiO₂ nanoparticles supported on aluminosilicate reduced the formaldehyde concentration from 20 to 0 ppm after UV irradiation for 20 h; the reduction of formaldehyde concentration under UV irradiation was obviously different from that in the dark. Moreover, a paper mixed with 20 wt% of TiO₂ nanoparticles supported on aluminosilicate bleached the stains colored with cigarette tar after UV irradiation for 6 h. However, the paper maintained its initial tensile strength even after UV irradiation for 1 year; in contrast, the paper mixed with a simple dry mixture of TiO₂ powder and aluminosilicate lost approximately half of its initial tensile strength after a year. TiO₂ nanoparticles supported on aluminosilicate could exhibit photocatalytic activity without decomposing the organic polymeric compounds.     

Air detoxification with nanosize TiO2 aerosol tested on mice

A method for fast air purification using high concentration aerosol of TiO₂ nanoparticles is evaluated in a model chemical catastrophe involving toxic vapors of diisopropyl fluorophosphate (DFP). Mice are used as human model in a closed 100 dm³ chamber. Exposure of mice to 37 ppm of DFP vapor for 15 min resulted in acute poisoning. Spraying TiO₂ aerosol in 2 min after the start of exposure to DFP vapors resulted in quick removal of DFP vapors from the chamber's air. Animals did not show signs of poisoning after the decontamination experiment and exposure to TiO₂ aerosol alone. Reactive oxygen species (ROS) and antioxidant activity (AOA) of mice blood plasma were measured for animals exposed to sound of aerosol generator, DFP vapors, TiO₂ aerosol and DFP vapors + TiO₂ aerosol. Reduced ROS and increased AOA were found for mice exposure to sound, DFP and TiO₂ aerosol. Exposure to DFP and decontamination with TiO₂ nanoparticles resulted in decreased AOA in 48 h following the exposure. The results suggest that application of TiO₂ aerosol is a powerful method of air purification from toxic hydrolysable compounds with moderate health aftermaths and requires further study and optimization.     

Photocatalytic performance of pure anatase nanocrystallite TiO2 synthesized under low temperature hydrothermal conditions

Photocatalytic performance of a hydrothermally synthesized pure anatase TiO₂ with 8 nm average crystallite size for decomposition of Reactive Red 141 was examined by investigating the effects of UV-light irradiation time, irradiation power, amount of TiO₂ and initial dye concentration. Change in the UV absorbance of the dye during irradiation was monitored. One wt.% TiO₂ in 30 mg/l Reactive Red 141 aqueous solution was found adequate for complete decolorization in 70 min at 770 W/m² irradiation power. It was realized that, compared to Degussa P-25, the synthesized nano-TiO₂ can be repeatedly used as a new catalyst. The results also proved that Reactive Red 141 is decomposed catalytically due to the pseudo first-order reaction kinetics.     

Preparation of YAG gel coated ZrB2–SiC composite prepared by gelcasting and pressureless sintering

In this paper, gelcasting and pressureless sintering of YAG gel coated ZrB₂–SiC (YZS) composite were conducted. YAG gel coated ZrB₂–SiC (YZS) suspension was firstly prepared through sol–gel route. Poly (acrylic acid) was used as dispersant. YZS suspension had the lowest viscosity when using 0.6 wt.% PAA as dispersant. Gelcasting was conducted based on AM–MBAM system. The gelcast YZS sample was then pressureless sintered to about 97% density. During sintering, YAG promoted the densification process from solid state sintering to liquid phase sintering. The average grain sizes of ZrB₂ and SiC in the YZS composite were 3.8 and 1.3 μm, respectively. The flexural strength, fracture toughness and microhardness were 375 ± 37 MPa, 4.13 ± 0.45 MPa m^1/2 and 14.1 ± 0.5 GPa, respectively.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Wear characteristics of mechanically milled TiO2 nanoparticles incorporated in electroless Ni–P coatings

Nanosized TiO₂ particles have been prepared by top down approach using mechanical milling with high energy planetary ball mill at 250 rpm for different extents of time (5, 10, 20, 30 and 40 h). Electroless (EL) Ni–P–TiO₂ nanocomposite coatings were developed using alkaline bath containing milled TiO₂ nanoparticles (4 g/l). The results show that, the morphology of TiO₂ particles milled for 40 h exhibit irregular shape with a particle diameter in the range of 33–45 nm. Wear studies of the coatings with 30 μm thickness were investigated using 1, 1.5 and 2 N loads with 0.1 and 0.2 m/s rotation speeds. The Ni–P–TiO₂ nanocomposite coatings exhibit the enhanced hardness and wear resistance as compared to that of Ni–P alloy coatings. Also the composite after heat treatment at 400 °C for 1 h in argon atmosphere showed improved hardness (1010 VHN) and wear resistance (1.5e-06 mm³/N m).     

Pt/TiO2 composite nanoparticles synthesized by electron beam irradiation for preferential CO oxidation

This paper describes a novel synthesis method of stabilizer-free Pt/TiO₂ composite nanoparticles using electron beam irradiation. The chemical compositions were analyzed by inductively coupled plasma-atomic emission spectroscopy. The microstructures of the samples were observed by using transmission electron microscope. Pt nanoparticles with the sizes of 2–4 nm were deposited on TiO₂ without any use of stabilizers. The concentrations of Pt ions and 2-propanol notably affected the size and shape of Pt nanoparticles. Their reactions of preferential CO oxidation were measured in temperature region from 60 to 140 °C. The Pt/TiO₂ catalyst with spherical Pt nanoparticles exhibited a 67% of CO conversion rate and 100% of selectivity at a low temperature of 60 °C.     

Effects of TiO2 nanoparticles addition on microstructure,microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO₂ nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO₂ (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag₃Sn grains, and estimate the spacing between the Ag₃Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag₃Sn grains and the spacing between the Ag₃Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO₂ nanoparticles. The microhardness is improved by 37% compared with TiO₂-free noncomposite solder as the weight percentage of TiO₂ nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO₂-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO₂-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10⁻³ s⁻¹ to 10⁻¹ s⁻¹ and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.     

Titanium dioxide based strategies to prevent algal fouling on cementitious materials

Algal growth is an important phenomenon largely affecting the aesthetical properties of building facades worldwide. Based on the photocatalytic degrading action together with the photo-induced hydrophilic nature of TiO₂, three TiO₂ containing white cements and one novel TiO₂ coating applied on autoclaved aerated concrete have been evaluated as strategies to avoid algal fouling on new and existing buildings, respectively. During 16 weeks (4 months), the evaluation was conducted using an accelerated algal growth test set-up running with Chlorella vulgaris as the algae specie. Monitoring of the fouling was based on visual inspections, algal coverage (%) and human perception of the color changes (ΔE) produced on the samples. A commercially available TiO₂ containing cement evidenced ‘not visible’ algal growth (ΔE ⩽ 0.2) and almost no significant algal coverage (0.1%). The new TiO₂ based coating evidenced 20% less algal coverage compared to uncoated reference samples after the test. However, ‘very large’ color changes (ΔE = 20) were observed on these samples.     

Synthesis and characterization of CuInSe2 nanoparticles via a solution method

Pure CuInSe₂ nanoparticles have been successfully synthesized via a solution method in the solvent of oleylamine. Anhydrous InCl₃, CuCl, and Se powder were used as the starting materials. The CuInSe₂ samples were characterized by XRD, TEM, and XPS techniques. It was found that tetragonal chalcopyrite structured CuInSe₂ nanoparticles were obtained with temperature above 230 °C. Sample prepared at 200 °C possesses triangular morphology and a minute amount of In₂Se₃ coexists as intermediate. CuInSe₂ nanoparticles with size of 20.2 ± 0.4 nm were prepared at 230 °C and the narrow size distribution was ascribed to the employment of hot injection, which was better for homogeneous nucleation. Stable “ink” can be formed when the as-synthesized CuInSe₂ nanoparticles were dispersed in organic solvents such as hexane and tolune, and such “ink” might have a practical application in CuInSe₂-based solar cells.     

Enhanced photocatalytic property of nanoporous TiO2/SiO2 micro-particles prepared by aerosol assisted co-assembly of nanoparticles

Nanoporous TiO₂/SiO₂ composite micro-particles were prepared by an aerosol assisted co-assembly (AACA) and their characteristics were investigated for photocatalytic application. The average diameter of resulting co-assembled TiO₂/SiO₂ particles was ranged 4–10 μm, and increased as the precursor concentration increased. The TiO₂/SiO₂ particles were spherical in shape and pores ranged 1–100 nm in diameter. Photocatalytic activity of the as-prepared nanoporous TiO₂/SiO₂ particles was evaluated by measuring the photodegradation of methylene blue (MB) and NO_x. Furthermore, the photocatalytic activity of nanoporous TiO₂/SiO₂ particles was compared with those of commercial TiO₂ nanoparticles and nanoporous TiO₂ particles. The nanoporous TiO₂/SiO₂ particles exhibited the highest photodegradation of MB and NO_x among three samples, which was 80% after 3 h and 55% at 10 min, respectively.     

Effect of processing methods on physicochemical properties of titania nanoparticles produced from natural rutile sand

Titania (TiO₂) nanoparticles were produced from natural rutile sand using different approaches such as sol–gel, sonication and spray pyrolysis. The inexpensive titanium sulphate precursor was extracted from rutile sand by employing simple chemical method and used for the production of TiO₂ nanoparticles. Particle size, crystalline structure, surface area, morphology and band gap of the produced nanoparticles are discussed and compared with the different production methods such as sol–gel, sonication and spray pyrolysis. Mean size distribution (d₅₀) of obtained particles is 76 ± 3, 68 ± 3 and 38 ± 3 nm, respectively, for sol–gel, sonication and spray pyrolysis techniques. The band gap (3.168 < 3.215 < 3.240 eV) and surface area (36 < 60 < 103 m² g^?1) of particles are increased with decreasing particle size (76 > 68 > 38 nm), when the process methodology is changed from sol–gel to sonication and sonication to the spray pyrolysis. Among the three methods, spray pyrolysis yields high-surface particles with active semiconductor bandgap energy. The effects of concentration of the precursor, pressure and working temperature are less significant for large-scale production of TiO₂ nanoparticles from natural minerals.     

Effect of SiO2 nanoparticles on the phase transformation of TiO2 in micron-sized porous TiO2–SiO2 mixed particles

Spherical and nanoporous TiO₂ and TiO₂–SiO₂ mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO₂/SiO₂) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO₂ and TiO₂–SiO₂ particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO₂–SiO₂ (50 wt.% SiO₂) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO₂ particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO₂ content in the TiO₂–SiO₂ mixed particles increased.     

High pressure behaviors of nanoporous anatase TiO2

High pressure behaviors of nanoporous anatase TiO₂ were studied using in situ Raman spectroscopy up to 37 GPa. The nanoporous anatase phase starts to transform into the baddeleyite phase with poor crystallinity at ～15.2 GPa, and the baddeleyite phase coexists with anatase phase up to 18.4 GPa. The baddeleyite form transforms into an amorphous phase above 20.5 GPa. Upon decompression, the amorphous phase recovers to the baddeleyite phase and then transforms to the α-PbO₂ phase. The phase transition from the baddeleyite phase to the amorphous form is reversible. The poor crystalline baddeleyite phase acts as an intermediate state in the amorphization process. The phase transitions of the nanoporous anatase TiO₂ are obviously different from the pressure-induced amorphization in the anatase TiO₂ nanoparticles. These results indicate that the porous microstructure plays important roles in the high pressure phase transitions of the nanoporous anatase TiO₂.     

Effects of ZrO2 addition on phase stability and photocatalytic activity of ZrO2/TiO2 nanoparticles

ZrO₂/TiO₂ nanoparticles with various Zr/Ti ratios (0–0.9) were prepared by a polymer complex solution method (PCSM). The prepared samples were characterized using transmission electron microscopy (TEM), the Brunauer, Emmett & Teller (BET) method, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The ZrO₂/TiO₂ photocatalyst showed a high specific area and small crystal size. The XRD pattern for the Zr/Ti = 0.1 sample indicated that the addition of ZrO₂ stabilized the anatase phase of TiO₂ up to 800 °C. The photocatalytic activity of Zr/Ti = 0.1 sample was higher than that of the TiO₂ sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the visible light region, higher specific area, smaller crystal size and increased surface OH groups.     

Facile preparation and photoelectrochemical properties of CdSe/TiO2 NTAs

In the present work we report the design and synthesis of CdSe/TiO₂ nanotube arrays (NTAs) and their implementation as a photoanode for photoelectrochemical (PEC) application. CdSe nanoparticles with well dispersion were decorated on the inner and outer surfaces of 2.5 μm-long TiO₂ nanotubes via electrodeposition. These CdSe/TiO₂ NTAs exhibit a significant photocurrent responds under visible light illumination (λ ≥ 420 nm). The results presented in this study display a promising method that the photoelectrochemical performance could be improved via composition, size and crystalline control of CdSe/TiO₂ NTAs. And the tubular morphology is also able to facilitate charge transport in nanostructure-based PEC cells. This research demonstrates a new approach, which have great potential applications in fabricating novel heterostructure-photoelectrochemical devices.     

Fluidization behavior of binary mixtures of nanoparticles in vibro-fluidized bed

The fluidization behavior of different mixed SiO₂, TiO₂ and/or ZnO nanoparticles under the application of vibrated fields of constant vibrated frequencies (40 Hz) and amplitude (3.0 mm) is studied. The single nanoparticles experiments show that SiO₂ nanoparticles have a better fluidization quality than TiO₂ and ZnO nanoparticles. For binary mixtures of the nanoparticles, the amount of SiO₂ nanoparticles generally has a beneficial effect on the fluidization quality of the binary mixtures. Using the linear regression, the Richardson–Zaki exponents of three kinds single and their binary mixture of nanoparticles are calculated. The Richardson–Zaki analyses indicate that the particulate fluidization degree of mixed nanoparticles can be greatly improved in agglomerate particulate fluidization (APF) behavior.     

Synergistic effects of hollow structure and surface fluorination on the photocatalytic activity of titania

To study the synergistic effects of hollow structure and surface fluorination on the photoactivity of TiO₂, TiO₂ hollow microspheres were synthesized by a hydrolysis–precipitate method using sulfonated polystyrene (PS) as templates and tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 500 °C for 2 h. The calcined samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ sorption. Photocatalytic activity was evaluated using reactive brilliant red X3B, an anionic organic dye, as a model pollutant in water. The results show that the photocatalytic activity of TiO₂ hollow microspheres is significantly higher than that of TiO₂ nanoparticles prepared in the same experimental conditions. At pH 7 and 3, the apparent rate constants of the former exceed that of the latter by a factor of 3.38 and 3.15, respectively. After surface fluorination at pH 3, the photoactivity of hollow microspheres and nanoparticles further increases for another 1.61 and 2.19 times, respectively. The synergistic effect of surface fluorination and hollow structure can also be used to prepare other highly efficient photocatalyst.     

Band gap tuning and nonlinear optical characterization of TiO2–SiO2 nanocomposites with respect to composition and phase

We report on the linear and nonlinear optical studies on TiO₂–SiO₂ nanocomposites with varying percentage ratio. It is found that optical band gap of the material varies with respect to the amount of the SiO₂ in the composite. Nonlinear optical characterization of these samples was studied by using open as well as closed aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). The nanocomposites showed enhanced nonlinear optical properties than pure TiO₂ and this can be attributed to the surface states and weak dielectric confinement of TiO₂ nanoparticles by SiO₂ matrix. The nanocomposites were thermally treated and similar studies were performed. The anatase form of TiO₂ in the nanocomposites showed superior properties relative to the amorphous and rutile phase of the composite. The involved mechanism is explained by taking into account the dominant role played by the excitons in the TiO₂ nanoparticles.