Polymeric adsorption of methylene blue in TiO2 colloids-highly sensitive thermochromism and selective photocatalysis.

The polymeric adsorption of methylene blue (MB) on a TiO(2) surface is reported. The MB molecule on the TiO(2) surface mainly exists as the H-trimeric adsorption state, which results in the MB@TiO(2) polymeric sol. The trimeric adsorption leads to a remarkable "blueshift" of visible-light adsorption of MB. Electrostatic attraction is important for trimeric adsorption of MB on TiO(2) surfaces. The trimer-monomer equilibrium is highly sensitive on temperature changes, showing an interesting reversible thermochromism. The MB@TiO(2) polymeric sol can be photodegraded under UV illumination without destroying the equilibrium of trimer-monomer. Compared with anionic methyl orange, the TiO(2) colloid hydrosol shows highly selective photocatalysis of MB and other cationic dyes, including crystal violet, methylene green, and victoria blue B. The MB@TiO(2) polymeric sol is stable under visible-light illumination because interfacial transfer of electrons does not exist between MB and TiO(2).

Antireflection and self-cleaning properties of a moth-eye-like surface coated with TiO2 particles.

Poly(ethylene terephthalate) (PET) films with a moth-eye-like surface are coated with TiO(2) particles to form self-cleaning antireflective films. The use of a TiO(2) suspension of high concentration to coat the PET surface produces a thicker TiO(2) layer with smaller pores, whereas a low concentration of a TiO(2) suspension gives a thinner layer of TiO(2) with larger pores. The PET films coated with TiO(2) particles exhibit a high transmittance of 76-95% and almost no absorption in the range of 400-800 nm. The PET films coated with a TiO(2) suspension with a concentration of ≥2 vol % exhibit superhydrophilicity after irradiation with UV light. After irradiation, the superhydrophilic nature is retained for at least 18 days. The TiO(2)-coated PET films showed the ability to decompose methylene blue under UV irradiation.

Mesoporous TiO2 core-shell spheres composed of nanocrystals with exposed high-energy facets: facile synthesis and formation mechanism.

A facile new method that combines electrospray and hydrothermal treatment is used to prepare mesoporous core-shell TiO(2) spheres with high specific surface areas and high pore volumes. Interestingly, the resulting TiO(2) spheres are composed of anatase TiO(2) nanocrystals with exposed step-like {001} and smooth {010} facets. The percentage of exposed {001} facets can be adjusted by changing the experimental parameters used in the electrospray and hydrothermal treatment processes, such as the contents of poly(N-vinyl-2-pyrrolidone) and acetic acid. The combination of high specific surface area (>100 m(2) g(-1)), high pore volume (>0.30 cm(3) g(-1)), useful pore size (10-15 nm), spherical core-shell structure, and exposed high energy facets makes these TiO(2) spheres an important candidate for use in many photoelectrochemical applications. The formation mechanism of the mesoporous TiO(2) spheres is also studied. The great advantage of this method is that interesting and complicated mesoporous superstructures can be prepared using electrospray technology.

Facile fabrication and photocatalytic application of Ag nanoparticles-TiO2 nanofiber composites.

A novel chemical method has been developed for the fabrication of Ag nanoparticles-coated TiO2 nanofiber composites. The method involves dispersion of TiO2 nanofibers in silver salt solution under ultrasonication, followed by addition of sodium citrate as a reducing agent. The Ag-coated TiO2 composites were characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron microscopy (XPS). Furthermore, the photocatalytic performance was evaluated by the photocatalytic degradation of methyl orange under UV-light irradiation. It was found that the heterogeneous Ag-TiO2 composite showed a higher activity than the pure TiO2 nanofiber; the enhanced activity can be attributed to the excellent distribution and interaction of Ag nanoparticles with the TiO2 nanofiber support. A plausible mechanism for the formation of the Ag-coated TiO2 composite and reasons for the enhancement of photocatalytic activity are also discussed.

Electrochemical inactivation kinetics of boron-doped diamond electrode on waterborne pathogens.

A boron-doped diamond (BDD) electrode was constructed as a water disinfector for the inactivation of water borne pathogens. The bactericidal effect of the disinfector was evaluated on artificially contaminated waters containing, respectively, Escherichia coli, Pseudomonas aeruginosa and Legionella pneumophila at high density. By treating the bacterial suspensions with 4 V of constant voltage between the BDD and the counter-electrode for 50 min, the population of E. coli and P. aeruginosa decreased from (10E + 7-8 colony-forming unit mL(-1)) to below the detection limits of the colony-formation method. Meanwhile, L. pneumophila were reduced to virtually zero when analyzed by fluorescence-based staining. The influences of production parameters (voltage, NaCl concentration and flow rate) on the disinfection kinetics of the BDD disinfector were examined with respect to operational conditions. Voltage was the most significant factor for adjusting the extent of electrolysis, followed by NaCl concentration and flow rate, to influence the disinfection efficiency. The disinfection of natural river water samples containing numerous microbes was performed for a practicability investigation of the BDD electrode. Approximately 99.99% bactericidal efficiency was confirmed by viability detection for E. coli and common germs in treated water. The results showed that the BDD electrode is a promising tool for various wastewater disinfections to combat waterborne diseases.

Rewritable superhydrophilic-superhydrophobic patterns on a sintered titanium dioxide substrate.

This Letter describes a new fabrication process for superhydrophilic-superhydrophobic patterns on a TiO(2) surface using a combination of an inkjet technique and the site-selective decomposition of a self-assembled monolayer (SAM) by a photocatalytic reaction under UV irradiation. To induce high surface wettability, we carried out simple calcination of a Ti substrate. The substrate was thus oxidized to titanium oxide and had a vortex-like rough morphology, which was suitable for the formation of wettability patterns. Furthermore, the substrate can be regenerated after elimination of the superhydrophilic-superhydrophobic patterns by the photocatalytic decomposition of TiO(2) using UV irradiation, and the patterns are deposited again. The renewed surface that we created had a wettability pattern that was different from the preceding pattern. This process is based on a TiO(2) surface and should offer a renewable, resource-saving, and environmentally friendly methodology for the formation of wettability patterns.

Nanofibrous TiO2-core/conjugated polymer-sheath composites: synthesis, structural properties and photocatalytic activity.

Nanofibrous TiO2-core/conjugated polymer-sheath composite nanocables were synthesized by in-situ chemical oxidative polymerization of aniline with oxidant in the presence of TiO, nanofibers prepared through an electrospinning process. During the polymerization process, aniline molecules were adsorbed on the surface of TiO2. Upon the addition of oxidant, the polymerization of aniline takes place on the surface of the TiO2 nanofibers and polyaniline (PANI) is gradually deposited on their surface. The resulting TiO2-PANI nanocomposites have a coaxial nanocable structure. The morphological and structural properties of the composite nanocables were analyzed by using high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and UV-visible spectroscopy (UV-vis), respectively. The HRTEM images proved that PANI (20 nm thickness) covered the surface of the TiO2 nanofibers. Also, the photocatalytic activity for the degradation of organic dyes on fibrous photocatalysts under UV-light was studied. The photocatalytic experiments showed that dye could be degraded more efficiently on the TiO2-PANI composite nanocables than on pure TiO2, due to the charge transfer from PANI to TiO2. The method for the synthesis of these unique structured composite nanocables is simple, rapid and reproducible. This facile method may be developed to produce multifunctional nanocomposites of various polymers with metal oxide fibers on a large scale for various technological applications such as sensors, solar cells, and catalysts.

A transparent and photo-patternable superhydrophobic film.

A transparent superhydrophobic TiO2 film, prepared by spin-coating a TiO2 slurry on a glass substrate and modifying the resultant TiO2 film with fluoroalkylsilane molecules, was patterned by illumination with ultraviolet light through a photomask, producing a superhydrophobic/superhydrophilic surface micropattern with very small superhydrophilic areas, which we were able to selectively fill with alginate hydrogel.

Double-layered TiO2-SiO2 nanostructured films with self-cleaning and antireflective properties.

Dual function of self-cleaning and antireflection can be created in double-layered TiO2-SiO2 nanostructured films. The film were prepared by (1) layer-by-layer deposition of multilayered SiO2 nanoparticles with polydiallyldimethylammonium (PDDA) cations, (2) layer-by-layer deposition of multilayered titanate nanosheets with polications on PDDA/SiO2 multilayer films, and (3) burning out the polymer and converting titanate nanosheets into TiO2 by hearing at 500 degrees C. The as-prepared films, consisting of a porous SiO2 bottom layer and a dense TiO2 top layer, improved the transmittance of glass or quartz substrates, as demonstrated by transmission spectra collected at normal incidence. The photocatalytic properties of the films were studied by the change of the water contact angle together with the decay of the IR absorption of the hydrocarbon chain of octadecylphosphonic-acid-modified films under 2.6 mW cm-2 UV illumination. Both the antireflective and the photocatalytic properties of the films were dependent on the number of PDDA/nanosheet bilayers deposited. however, excellent surface wettability of the films for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the double-layered nanostructured film.

Fibrous TiO2-SiO2 nanocomposite photocatalyst.

The electrospinning method is employed to prepare a fibrous TiO2-SiO2 (Ti : Si = 1 : 2) nanocomposite photocatalyst, in which Degussa P25 T i O2 nanoparticles are embedded inthe body of SiO2 fibers and which shows good photocatalytic activity due to its 3-D open structure, as evidenced by photocatalytic reduction of silver ions and decomposition of acetaldehyde.

Photoelectrochemical behavior of Nb-doped TiO2 electrodes.

The photoelectrochemical behavior of degenerate Nb-doped TiO2 (Ti(1-x)Nb(x)O2: x = 0, 0.01, 0.03, 0.06, 0.1) electrodes prepared by pulsed laser deposition on LaAlO3 (LAO) and SrTiO3 (STO) was examined, revealing that an increase in Nb concentration causes a significant decay of titania photoactivity. One reason for such behavior may be a Burstein-Moss effect, which leads to a blue shift of the spectral limit of photoactivity. Another reason typical for metal-doped photocatalysts is the increase of the efficiency of charge carrier recombination.

Preparation and photocatalytic activity of robust titania monoliths for water remediation.

TiO(2) monoliths were prepared, characterized, and evaluated for photocatalytic performance. The TiO(2) monoliths were found to have an interconnected void lattice and a bimodal porous structure with macropores and mesopores after calcination at 500-700 °C. Monoliths calcined at 500 °C had high specific surface area (93.1 m(2)/g) and porosity (68%), which were maintained after calcination at 700-1100 °C (51-46%). The calcined monoliths had relatively high Vickers hardness (∼104) despite their porous structure. Monoliths calcined at 500 and 700 °C exhibited high performance for methylene blue decolorization because of their high specific surface area.

Photochromism-based detection of volatile organic compounds by W-doped TiO2 nanofibers.

W-doped TiO(2) nanofibers with various compositions (W/Ti: 2-8%) were fabricated by the electrospinning method from respective precursor solutions containing tungsten(V) pentaethoxide, titanium tetraisopropoxide (TTIP), and polyvinylpyrrolidone (PVP), followed with calcination at 550 °C. Morphological and structural characteristics of these nanofibers were studied with SEM, XRD and XPS. W-doping inhibited the crystal growth and anatase-to-rutile transformation of TiO(2) nanofibers. W-doped TiO(2) nanofiber mats showed good photocatalytic oxidation abilities for acetone. Obvious color change from white to blue of mats during the photocatalysis process can be detected by naked eyes, which provides a good way in detection of pollutants in indoor air, especially for the volatile organic compounds (VOCs).

UV/thermally driven rewritable wettability patterns on TiO2-PDMS composite films.

Composite films of TiO2 and polydimethylsiloxane (PDMS) are prepared by a sol-gel method, cured with UV irradiation, and then treated in hot water to crystallize the TiO2 in the film. The presence of anatase TiO2 contributes to the photoinduced superhydrophilicity of the film under UV irradiation. Contact angle studies reveal that the TiO2-PDMS composite film recovers its original hydrophobic state. Hydrophobic-superhydrophilic patterns are successfully formed on the films. The wettability patterns can be erased by UV irradiation and thermal treatment. New wettability patterns can be reconstructed, demonstrating that the film exhibits rewritable wettability without the need for organic chemicals.

Development of solar-driven electrochemical and photocatalytic water treatment system using a boron-doped diamond electrode and TiO2 photocatalyst.

A high-performance, environmentally friendly water treatment system was developed. The system consists mainly of an electrochemical and a photocatalytic oxidation unit, with a boron-doped diamond (BDD) electrode and TiO(2) photocatalyst, respectively. All electric power for the mechanical systems and the electrolysis was able to be provided by photovoltaic cells. Thus, this system is totally driven by solar energy. The treatment ability of the electrolysis and photocatalysis units was investigated by phenol degradation kinetics. An observed rate constant of 5.1 x 10(-3)dm(3)cm(-2)h(-1) was calculated by pseudo-first-order kinetic analysis for the electrolysis, and a Langmuir-Hinshelwood rate constant of 5.6 microM(-1)min(-1) was calculated by kinetic analysis of the photocatalysis. According to previous reports, these values are sufficient for the mineralization of phenol. In a treatment test of river water samples, large amounts of chemical and biological contaminants were totally wet-incinerated by the system. This system could provide 12L/day of drinking water from the Tama River using only solar energy. Therefore, this system may be useful for supplying drinking water during a disaster.

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal with highly efficient photocatalytic capability.

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal (i-Ti-Si PC) with highly efficient photocatalytic activity has been synthesized by combining colloidal crystal template and amphiphilic triblock copolymer. It was found that the thermal stability of mesoporous structures in the composite matrix were improved due to the introduction of silica acting as glue and linking anatase nanoparticles together, and the photocatalytic activity of the i-Ti-Si PCs was affected by the calcination conditions. The influences of photonic and structural effect of the i-Ti-Si PCs on photocatalytic activity were investigated. Photodegradation efficiency of the i-Ti-Si PCs was 2.1 times higher than that of TiO(2) photonic crystals (i-TiO(2) PCs) in the photodegradation of Rhodamine B (RB) dye as a result of higher surface area. When the energy of slow photon (SP) was optimized to the abosorption region of TiO(2), a maximum enhanced factor of 15.6 was achieved in comparison to nanocrystalline TiO(2) films (nc-TiO(2)), which originated from the synergetic effect of SP enhancement and high surface area.

Fabrication and application of TiO2-based superhydrophilic-superhydrophobic patterns on titanium substrates for offset printing.

A fabrication process for superhydrophilic-superhydrophilic patterns on titanium substrates prepared through a combination of an ink-jet technique and site-selective decomposition of a self-assembled monolayer (SAM) by a TiO(2) photocatalyst under UV irradiation is described. We demonstrate that the prepared titanium substrate is applicable as an offset printing plate with high resolution (133 and 150 lines per inch). Furthermore, the superhydrophilic-superhydrophobic patterns on the substrate can be deposited repeatedly after elimination of the patterns by photocatalytic decomposition of TiO(2) under UV irradiation. A second printed image with the renewed substrate showed no significant difference in image quality compared with the initial image.

Assembly of self-assembled monolayer-coated Al2O3 on TiO2 thin films for the fabrication of renewable superhydrophobic-superhydrophilic structures.

A renewable superhydrophobic-superhydrophilic pattern with a minimum dimension of 50 microm is prepared from octadecyltrimethoxysilane self-assembled monolayer-covered superhydrophobic Al2O3 overlayers on a superhydrophilic TiO2 surface via self-assembly and calcination of boehmite (AlOOH.nH2O) particles. The resulting Al2O3 layer plays dual roles as a superhydrophobic layer and as a UV-blocking layer for the underlying TiO2.

Efficient photocatalytic degradation of gaseous acetaldehyde by highly ordered TiO2 nanotube arrays.

Highly ordered TiO2 nanotube array prepared by electrochemical anodization generates considerable interest as a practical air purifier, since a nanotube array can form a TiO2 film with a porous surface and straight gas diffusion channel, simultaneously reserving enough geometric thickness. Here, we reported on the application of highly ordered TiO2 nanotube arrays with different lengths for degradation of gaseous acetaldehyde pollutants in air. The results showed that increasing the lengths of nanotube arrays within a certain range could significantly improve the degradation rate of acetaldehyde molecules. The main product of acetaldehyde degradation was detected to be CO2, which indicated that the mineralization of acetaldehyde molecules was the major process in this photocatalytic reaction. When compared with a P25 TiO2 nanoparticulate film with similar thickness and geometric area, in the initial degradation of acetaldehyde, the nanotube array did not show obvious superiority. However, in the subsequent degradation, the nanotube array demonstrated an enhanced photocatalytic activity. It was suggested that this enhancement resulted from the special infrastructure of the nanotube array, which was favorable for the diffusion of intermediates and the reduced deactivation of photocatalyst in the photocatalytic reaction.