Photocatalytic Decomposition of Acetaldehyde with Anatase Nanocrystals-Dispersed Silica Films Prepared by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals of 5 to 10 nm in diameter were formed in the silica-titania films by treatment with hot water. The formation of nanocrystals with hot water treatment was a unique phenomenon to the silica-titania system and the addition of organic polymers such as PEG was indispensable for the high dispersion of anatase nanocrystals in the films. The hydrolysis of Si—O—Ti bonds with hot water was considered to play an important role for the formation of anatase nanocrystals. The resultant films were transparent even after the formation of anatase nanocrystals. Acetaldehyde was photocatalytically decomposed into CO₂ on the films which were subjected to a hot water treatment. The amounts of generated CO₂ were twice of that of introduced acetaldehyde, indicating that the total acetaldehyde was completely decomposed to CO₂. Anatase nanocrystals-dispersed films can be formed on various kinds of substrates including those with poor heat resistance such as organic polymers and organisms by this process, so that the substrates coated with the films are expected to be widely used for photocatalytic applications.     

Formation of Anatase Nanocrystals in Sol-Gel Derived TiO2-SiO2 Thin Films with Hot Water Treatment

We have successfully prepared transparent and porous anatase nanocrystals-dispersed films by treating the sol-gel derived TiO₂-SiO₂ films containing poly(ethylene glycol), PEG, with hot water. This process was done at temperatures lower than 100°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The changes in structure and composition of the TiO₂-SiO₂ gel films with hot water treatment were related to the formation process of anatase nanocrystals in the TiO₂-SiO₂ gel films with hot water treatment. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si–O–Ti bonds and dissolution of SiO₂ component. In addition, porous film structure formed by leaching of PEG with hot water treatment led to homogenous dispersion of anatase nonocrystals in the films.     

Formation of Anatase Nanocrystals-Precipitated Silica Coatings on Plastic Substrates by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals-precipitated silica coatings were formed on plastic substrates such as poly(ethylene terephtalate) (PET), acrylic resin (AC) and polycarbonate (PC) from silica-titania gel coatings with and without addition of poly(ethylene glycol) (PEG) by hot water treatment. The maximum thickness of the coatings which can be formed without cracking or peeling-off was 100 to 200 nm for PET and PC substrates, whereas it was less than 50 nm for AC substrates. After a hot water treatment at 90°C for 120 min, the size of the anatase nanocrystals increased to be 30 and 50 nm for the coatings obtained with and without PEG, respectively. Anatase nanocrystals were formed throughout the whole of the coatings obtained with PEG and were formed only on the surface of the coatings obtained without PEG. Both coatings obtained with and without PEG were highly transparent. The plastic substrates with coatings obtained without PEG showed good weathering resistance owing to the protective effects of the residual silica under-layer. The coatings obtained with PEG showed higher photocatalytic activities than those obtained without PEG due to smaller size and higher dispersion of anatase nanocrystals in the coatings.     

Preparation and application of alumina- and titania- nanocrystals-dispersed thin films via sol-gel process with hot water treatment

A process to prepare nanocrystals-dispersed thin films at low temperatures using a hot water treatment of the gel films, and application of these nanocomposite thin films were demonstrated. When amorphous Al₂O₃ gel films were immersed in a hot water, we found that boehmite nanocrystals were formed on the surface of the films. In the hot water treatment of Al₂O₃-ZnO amorphous films, Zn-Al layered double hydroxide (LDH) was found to be formed on the films. When the SiO₂-TiO₂ gel films containing poly(ethylene glycol) were treated in a hot water, anatase nanocrystals were formed on the surface and inside of the films, and for the gel films without an organic polymer, the anatase nanocrystals were formed only on the surface of the films. In the hot water treatment of SiO₂-TiO₂ gel films under a vibration, titania nanosheets were found to be precipitated, instead of anatase nanocrysltals. Since formation of nanocrystals on the substrates using a hot water treatment is very mild conditions as the precipitation of crystals, we believe this process will open new application fields of nanocystals-dispersed thin films.     

Fabrication and photoelectrochemical properties of porous ZnWO4 film

Porous ZnWO₄ films have been fabricated on Indium-tin oxide (ITO) glass and its photoelectrochemical properties and high photocatalytic activities towards degradation of rhodamine B (RhB) has been investigated. Using amorphous heteronuclear complex as precursor and with the addition of polyethylene glycol (PEG, molecular weight=400), the porous ZnWO₄ films have been achieved at the temperature of 500 °C via dip-coating method. It is composed of approximately 70 nm-sized particles and exhibits substantial porosity. The textures and porosity of ZnWO₄ films are dependent on preparation factors, such as the ratio of precursor/PEG and the annealing conditions. The formation mechanism of porous ZnWO₄ films was proposed. The porous ZnWO₄ films exhibited high photocatalytic activities towards degrading RhB. The top of valence band and the bottom of the conduction band was estimated to be −0.56 and 3.45 eV (vs. saturated calomel electrode (SCE)), respectively.     

Enhancing the Photocatalytic Activity of Anatase TiO2 by Improving the Specific Facet‐Induced Spontaneous Separation of Photogenerated Electrons and Holes

Recently, it has been proven that directional flow of photogenerated charge carriers occurs on specific facets of TiO₂ nanocrystals. Herein, we demonstrate that the photocatalytic activity of anatase TiO₂ nanocrystals in both photoreduction and photooxidation processes can be enhanced by selectively depositing Pt nanoparticles on the {101} facets, which strengthens spontaneously surface‐induced separation between photogenerated electrons and holes in the photocatalysis process. An optimal ratio of the oxidative {001} facets to the reductive {101} facets exists with regard to the photocatalysis of the faceted TiO₂ nanocrystals, and this is crucial for balancing the recombination and redox reaction rates of photogenerated electrons and holes. The present work might help us gain deeper insight into the relation between the specific surface of semiconductor photocatalysts and their photocatalytic activities and provides us with a new route to design photocatalysts with high photocatalytic activity.     

Low temperature deposition of nanocrystalline titanium dioxide from titanium tetraisopropoxide

Effect of ozone and water vapor on the chemical deposition of TiO₂ from the gas phase in the system of titanium tetraisopropylate-oxygen was examined. Introduction of ozone in the reaction medium was shown to result in the precipitation of smooth TiO₂ layers at 240°C, and the addition of water vapor leads to the formation with higher rate of unconsolidated layers. Adding ozone to the reaction medium with low moisture content (up to 0.65 Pa) allows obtaining at temperatures 250–350°C with high rate of growth the TiO₂ layers with the anatase nanocrystals of high photocatalytic activity.     

Antibacterial metal implant with a TiO2‐conferred photocatalytic bactericidal effect against Staphylococcus aureus

Photocatalysis with anatase Titanium dioxide (TiO₂) under ultraviolet A (UVA) has a well recognized bactericidal effect. There have been a few reports, however, on the effects of photocatalysis on bio‐implant‐related infections. The purpose of present study was to evaluate the photocatalytic bactericidal effects of anatase TiO₂ on Staphylococcus aureus (S. aureus) associated with surgical site infections. TiO₂ films were synthesized on commercially pure titanium substrates and SUS316 stainless steel using a plasma source ion implantation method followed by annealing. The chemical composition of the surface layers was determined using GXRD and XPS. The disks were seeded with cultured S. aureus and exposed to UVA illumination from black light. The bactericidal effect of the TiO₂ films was evaluated by counting the survived colonies statistically. A structural gradient anatase type TiO₂ layer formed on all substrates. The viability of the bacteria on the photocatalytic TiO₂ film coated on titanium was suppressed to 7.0% at 30 minutes and 5.5% at 45 minutes, whereas that on a similarly coated stainless steel was suppressed to 45.8% at 30 minute and 28.6% at 45 minutes (ANOVA: p < 0.05). Complete bacterial inactivation was achieved after 90 minutes on titanium and after 60 minutes on stainless steel. The photocatalytic bactericidal effect of TiO₂ is useful for sterilizing the contaminated surfaces of bioimplants. Copyright © 2008 John Wiley & Sons, Ltd.     

TiO2 Thin Film with Varied Porous Structure Applied on the Degradation of Methylene Blue

In this study, porous TiO₂ thin films were prepared by the sol‐gel method employing polyethylene glycol 1000 (PEG 1000) as an organic template. Pore sizes were adjusted by varying the concentration of PEG 1000. The optimal PEG concentration range required to form TiO₂ films with a regular porous structure was investigated and was found to be 0.01–0.015 M. As the PEG 1000 concentration increased, the surface of these films became rougher because of larger pores. Degradation of methylene blue (MB) under UV irradiation was used to determine the photocatalytic activity of the films. In addition, the effect of the pH value of the MB solution on the films was evaluated by controlling its pH value at 5, 7, and 9. The results showed that the photocatalytic activity was correlated to the pore size and pore density of the thin films. TiO2 thin films possessing pore sizes in the diameter range of 35–85 nm exhibited the best conversion of 98% after 8 h of UV irradiation when the pH value was 7.     

室温下制备以{211}晶面为主的Ti1-xVxO2薄膜及其可见光催化性能

以金属Ti和V作为靶材,采用直流反应共溅射技术在室温下制备了以{211}晶面为主的锐钛矿相Ti_1-xV_xO₂薄膜,研究了不同V靶功率对Ti_1-xV_xO₂薄膜的薄膜成分、晶相结构和可见光催化性能的影响。研究表明,Ti_1-xV_xO₂薄膜的晶相结构为锐钛矿相,择优取向为(211),而结晶度受V靶功率的影响。随着V靶功率的增加,薄膜中V元素含量逐渐增加,同时,晶粒和沉积速率也逐渐增加。另外,当V靶功率为150 W时,薄膜的表面粗糙度值有一个最大值。V的掺杂导致薄膜的能带间隙变窄,对光的吸收向可见光区偏移,从而有效地改善了薄膜的可见光催化能力。当V靶功率为150 W时,Ti_1-xV_xO₂薄膜的能带间隙值为 2.82 eV,其在2 h的可见光照射下分解了80%的RhB染料。这被归结于能带间隙窄,高能晶面{211}和结晶度高的共同作用。     

Preparation of highly active photocatalyst anatase TiO<Subscript>2</Subscript> by mixed template method

TiO₂ nanocrystals with diameters 8–10 nm have been prepared through sol–gel method using a mixed template of polyethylene glycol (PEG) and cetytrimethylammonium bromide (CTAB) at low temperature. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR) TEM and fourier transform infrared spectroscopy (FT-IR) etc. XRD analysis showed the TiO₂ photocatalysts prepared with mixed template are pure anatase. FTIR spectrum revealed that the cationic surfactant provides CTA⁺ molecules and bonds to Ti–O to prevent the condensation reaction. PEG plays a dispersant role in controlling the structure of nano-TiO₂ particles. CTAB and PEG incorporated with each other to restrain the growth of crystal nucleus and control the size of grain. The self-assembling process has been confirmed by HRTEM. PEG played different role in mixed template from the single template. The photocatalytic activity of samples was determined by using as a model reaction. The results showed that TiO₂ photocatalysts with mixed template have higher photocatalytic activity than P25.     

Structural,optical and photocatalytic applications of biosynthesized NiO nanocrystals

NiO is one of the most important candidates for semiconductors metal oxide nanocrystals by the arrangement of photocatalytic application. However, the photocatalytic performance of biosynthesized nanocrystals using Aspalathus linearis (Burm.f.) R. Dahlgren has not been investigated yet. In this contribution, we synthesize α-Ni(OH)₂ using an A. linearis. A heat treatment of the α-Ni(OH)₂ is carried out at 300–400°C for 2?h at normal air yields. Furthermore, we have characterized the structural, optical and photocatalytic activity of the samples. The optical results indicate that biosynthesized nanocrystals exhibit UV–visible light absorption and a narrow range distribution of intense green light (518.95?nm) emission, which decreases significantly as annealing temperature increases. The bandgap energies of the sample annealed at 300–400°C shift to lower photon energy, compared to bulk NiO (～ 4?eV). Moreover, the photocatalytic experimental results reveal that NiO nanocrystals enable color switching of methylene blue.     

室温下制备以{211}晶面为主的Ti1-xVxO2薄膜及其可见光催化性能

以金属Ti和V作为靶材,采用直流反应共溅射技术在室温下制备了以{211}晶面为主的锐钛矿相Ti_1-xV_xO₂薄膜,研究了不同V靶功率对Ti_1-xV_xO₂薄膜的薄膜成分、晶相结构和可见光催化性能的影响。研究表明,Ti_1-xV_xO₂薄膜的晶相结构为锐钛矿相,择优取向为(211),而结晶度受V靶功率的影响。随着V靶功率的增加,薄膜中V元素含量逐渐增加,同时,晶粒和沉积速率也逐渐增加。另外,当V靶功率为150W时,薄膜的表面粗糙度值有一个最大值。V的掺杂导致薄膜的能带间隙变窄,对光的吸收向可见光区偏移,从而有效地改善了薄膜的可见光催化能力。当V靶功率为150W时,Ti_1-xV_xO₂薄膜的能带间隙值为2.82eV,其在2h的可见光照射下分解了80%的RhB染料。这被归结于能带间隙窄,高能晶面{211}和结晶度高的共同作用。     

Low Temperature Sol-Gel Preparation of Nanocrystalline TiO2 Thin Films

TiO₂ nanocrystalline thin films with varying degree of porosity have been prepared using a low temperature method. TiO₂ films of the anatase form have been obtained by using a polyethylene glycol (PEG) modified sol-gel method. Densification and crystallization of the films was found to result from the thermal treatment of the dip coated films in boiling water. The films have been characterized by Raman, XRD, FTIR, AFM and optical methods. Highly transparent films with transmission in excess of 85% and porosity as high as 58% are formed predominantly of anatase crystallites of dimensions of the order of 5 nm. Initial results on lithium intercalation into these films resulting in an efficient optical modulation in the visible and near infrared regions demonstrate a good potential of these films for electrochromic applications.     

Effects of anatase TiO2 morphology and surface fluorination on environmentally relevant photocatalytic reduction and oxidation reactions

Aiming at clarifying the interplay on TiO₂ photoactivity between particle morphology and surface fluorination, the photocatalytic performance of anatase nanocrystals, characterized by a pseudo-spherical shape or a nanosheet structure, is investigated in both a reduction and an oxidation reaction, either in the absence or in the presence of added fluoride anions. Cr(VI) photocatalytic reduction is strongly favored by a large exposure of anatase {001} facets; however, surface fluorination leads in this case to a morphology-independent photoactivity decrease, due to the decreased adsorption of the reaction substrate. More interestingly, a beneficial synergistic effect between the platelet-like anatase morphology and TiO₂ surface fluorination is clearly outlined in Rhodamine B photocatalytic degradation, possibly resulting from the intrinsic ability of fluorinated {001} anatase facets of boosting ^?OH radical mediated oxidation paths, due to their larger amount of surface –OH groups, as revealed using Fourier-transform infrared spectroscopy.     

Photodegradation of dye pollutants on one-dimensional TiO2 nanoparticles under UV and visible irradiation

Titanium dioxides (TiO₂) nanoparticles with one-dimensional (1D) geometry, nanorods and nanostripes, were used as photocatalysts to photodegrade Rhodamine B (RhB) under ultraviolet (UV) and visible irradiation. The nanorods catalyst exhibited very interesting photocatalytic properties: under the UV irradiation its catalytic activity was slightly below that of the well-known TiO₂ catalyst P25, while under visible light it exhibited a better activity than P25.This fact indicates that the nanorods have a superior ability to utilize less energetic but more abundant visible light. Moreover, the 1D TiO₂ nanoparticles can be readily separated from aqueous suspensions by sedimentation after the reaction. With these advantages the 1D TiO₂ catalysts have a great potential for environmental applications. Various analytical techniques were employed to characterize TiO₂ catalysts and monitor the photocatalytic reaction. It was found that the catalytic performance of the catalysts is greatly dependent on their structures: The superior activity of P25 (consists of anatase and rutile nanocrystals) under UV light results probably from the interfacial interaction between anatase and rutile nanocrystals in this solid, which do not exist in the nanorods (only anatase). The titanate nanostripes (titanate) can absorb UV photons with shorter wavelength only.     

Influences of Solvent on Properties of TiO<Subscript>2</Subscript> Porous Films Prepared by a Sol-Gel Method from the System Containing PEG

Ethanol, n-butanol, mixed ethanol/terpineol and ethanol/1-decanol were used as the solvents to prepare porous TiO₂ films by the sol-gel method from the system containing tetrabutylorthotitanate as starting material and PEG as a template. The comparison of effects of the four solvents on the porous structure, film thickness, crystallization behavior from amorphous to anatase and optical properties of the resultant TiO₂ porous films are discussed. The maximum thickness of the film prepared by one-run dip-coating reaches over 1.17 μm when 1-decanol is used as the solvent. The mechanism for formation of the porous structure is interpreted based on the phase separation and self-assembly of PEG in the sol systems.     

Synthesis of Mesoporous TiO2/SiO2 Hybrid Films as an Efficient Photocatalyst by Polymeric Micelle Assembly

Thermally stable mesoporous TiO₂/SiO₂ hybrid films with pore size of 50 nm have been synthesized by adopting the polymeric micelle‐assembly method. A triblock copolymer, poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide), which serves as a template for the mesopores, was utilized to form polymeric micelles. The effective interaction of titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) with the polymeric micelles enabled us to fabricate stable mesoporous films. By changing the molar ratio of TEOS and TTIP, several mesoporous TiO₂/SiO₂ hybrid films with different compositions can be synthesized. The presence of amorphous SiO₂ phase effectively retards the growth of anatase TiO₂ crystal in the pore walls and retains the original mesoporous structure, even at higher temperature (650 °C). These TiO₂/SiO₂ hybrid films are of very high quality, without any cracks or voids. The addition of SiO₂ phase to mesoporous TiO₂ films not only adsorbs more organic dyes, but also significantly enhances the photocatalytic activity compared to mesoporous pure TiO₂ film without SiO₂ phase.     

The influence of titanium dioxide phase composition on dyes photocatalysis

A comparative study of TiO₂ powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes. The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification, for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples. It was found that the only TiO₂ anatase phase of the synthesized TiO₂ develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic properties. Different TiO₂ doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO₂ Aldrich with TiO₂ Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene blue using TiO₂ thin film were investigated.     

Properties of Peroxotitanium Acid Solution and Peroxo-Modified Anatase Sol Derived From Peroxotitanium Hydrate

In order to develop new preparation methods of peroxotitanium acid solution and peroxo-modified anatase sol which are useful for the low-temperature formation of photocatalytic thin films, peroxotitanium hydrate was used as a precursor of them. The formation of the transparent peroxotitanium acid solution was achieved by mixing concentrated H₂O₂ and peroxotitanium hydrate, which was precipitated by adding ammonia solution into a mixture of diluted TiCl₄ aqueous solution and H₂O₂ solution. The homogeneous and translucent peroxo-modified anatase sols were directly obtained by heating above 70°C the peroxotitanium hydrate suspended in water. The sizes of anatase crystals in the sols were close to that in other peroxo-modified anatase sol obtained by heating at 100°C peroxotitanium acid solution, but the anatase films prepared from the peroxo-modified anatase sol obtained by heating peroxotitanium hydrate showed higher photocatalytic oxidation rates of gaseous isopropanol to acetone.