Thick transparent rutile TiO2 films crystallized in solution

We report a novel process for the preparation of dense, transparent TiO2 films of 2.5 mum thickness on a F-doped SnO2-covered glass substrate. The starting solution contained peroxotitanate complex ions, which are relatively stable under the experimental conditions, permitting the deposition of highly textured rutile nanocrystalline films. The nanocrystals exhibit specific orientations along the (101) and (002) crystalline planes. Kinetic studies suggest that the precipitation started from the formation of amorphous solids, followed by crystallization through a dissolution-recrystallization process. Although a minor phase of anatase was detected only for powders collected from solutions after film preparation, not for films, the transformation from amorphous to anatase was believed to occur before further transformation of anatase to rutile. The present method enables film synthesis on a surface with a large area, and therefore could be integrated into the processing of electroluminescent devices.     

金红石/锐钛矿混晶结构的TiO2薄膜光催化活性

采用磁控溅射法制备出一组金红石/锐钛矿混晶结构的纳米TiO2薄膜催化剂,并通过光催化降解苯酚实验考察该薄膜的催化性能. 光催化实验证明, 随着催化剂中金红石含量减少, 催化剂的光催化活性逐渐提高. X射线衍射(XRD)、X射线光电子能谱(XPS)、表面光电压谱(SPS)和原子力显微镜(AFM)结果表明, 催化剂为金红石和锐钛矿混晶结构, 并随着金红石含量减少, 催化剂的表面羟基(OH)和桥氧(—O—)的含量逐渐增加, 而且费米能级逐渐提高. 表面羟基和桥氧是有利于光催化的“活性物种”; 费米能级的提高使TiO2/H2O 面处TiO2的表面带弯增大, 导致了价带光生空穴参加光催化反应的几率增大, 有效地促进了光生载流子的分离; 这些因素是催化剂光催化活性逐渐提高的主要原因.     

Relationship Between Photocatalytic Activity and Structure of TiO2 Thin Film

TiO2 thin films with different crystalline structures were prepared by the CVD method. The relationship between photocatalytic activity of a TiO2 thin film and its crystalline type was investigated. These films were characterized by XRD and AFM. Their photocatalytic properties were tested by the degradation of NO2-. The results showed that the crystalline structures of TiO2 thin films are primary anatase and/or rutile when the preparation temperatures were less than 573 K and higher than 773 K respectively. When the preparation temperature was around 623 K, the structures of TiO2 thin films were mixed crystalline structure, which showed the highest catalytic activity. When the ratio of rutile to anatase in TiO2 thin films fell between 0.5 and 0.7, the highest catalytic activity for the degradation of NO2- was found.     

Mobility enhanced photoactivity in sol-gel grown epitaxial anatase TiO2 films

Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.     

锐钛矿、金红石和板钛矿降解罗丹明B光催化活性的比较

详细考察并比较了采用低温制备的锐钛矿、金红石和板钛矿氧化钛降解罗丹明B的光催化活性.与传统高温焙烧制备的金红石相比,低温制备的金红石粒径小,比表面积大,表面羟基数目多,因此光催化效率明显增加.更重要的是,当锐钛矿和金红石具有相似粒径和比表面积时,金红石具有较高的光降解罗丹明B活性.对于板钛矿氧化钛而言,虽然其表观光催化...     

Gold nanoparticles located at the interface of anatase/rutile TiO2 particles as active plasmonic photocatalysts for aerobic oxidation

Visible-light irradiation (λ > 450 nm) of gold nanoparticles loaded on a mixture of anatase/rutile TiO(2) particles (Degussa, P25) promotes efficient aerobic oxidation at room temperature. The photocatalytic activity critically depends on the catalyst architecture: Au particles with <5 nm diameter located at the interface of anatase/rutile TiO(2) particles behave as the active sites for reaction. This photocatalysis is promoted via plasmon activation of the Au particles by visible light followed by consecutive electron transfer in the Au/rutile/anatase contact site. The activated Au particles transfer their conduction electrons to rutile and then to adjacent anatase TiO(2). This catalyzes the oxidation of substrates by the positively charged Au particles along with reduction of O(2) by the conduction band electrons on the surface of anatase TiO(2). This plasmonic photocatalysis is successfully promoted by sunlight exposure and enables efficient and selective aerobic oxidation of alcohols at ambient temperature.     

Photochemical reduction of oxygen adsorbed to nanocrystalline TiO(2) films: a transient absorption and oxygen scavenging study of different TiO(2) preparations

Transient absorption spectroscopy (TAS) has been used to study the interfacial electron-transfer reaction between photogenerated electrons in nanocrystalline titanium dioxide (TiO(2)) films and molecular oxygen. TiO(2) films from three different starting materials (TiO(2) anatase colloidal paste and commercial anatase/rutile powders Degussa TiO(2) P25 and VP TiO(2) P90) have been investigated in the presence of ethanol as a hole scavenger. Separate investigations on the photocatalytic oxygen consumption by the films have also been performed with an oxygen membrane polarographic detector. Results show that a correlation exists between the electron dynamics of oxygen consumption observed by TAS and the rate of oxygen consumption through the photocatalytic process. The highest activity and the fastest oxygen reduction dynamics were observed with films fabricated from anatase TiO(2) colloidal paste. The use of TAS as a tool for the prediction of the photocatalytic activities of the materials is discussed. TAS studies indicate that the rate of reduction of molecular oxygen is limited by interfacial electron-transfer kinetics rather than by the electron trapping/detrapping dynamics within the TiO(2) particles.     

X-ray diffraction area mapping of preferred orientation and phase change in TiO2 thin films deposited by chemical vapor deposition

This paper reports on an investigation into the formation of TiO(2) thin films, whereby X-ray diffraction is used to map systematic changes in preferred orientation and phase observed throughout the films. The key to this strategy is the recording of X-ray diffraction patterns of specific and isolated areas of a substrate, ensuring this specificity by the use of a small X-ray sample illumination area (approximately 3-5 mm(2)). A map of the variation in film composition can then be built up by recording such diffraction patterns at regular intervals over the whole substrate. Two titania films will be presented, grown using atmospheric pressure chemical vapor deposition, at 450 and 600 degrees C, from TiCl(4) and ethyl-acetate precursors. The film grown at 450 degrees C showed a systematic change in preferred orientation, while the film grown at 600 degrees C was composed of a mixture of the rutile and anatase phases of TiO(2) with the ratio of these phases altering with position on the substrate. The results of physical property measurements and electron microscopy carried out on the films are also reported, conducted at locations identified by the X-ray diffraction mapping procedure as having different compositions, and hence different physical responses. We found that the photocatalytic activity and hydrophobicity were dependent on the rutile:anatase ratio at any given location on the film.     

Atomic layer deposition in nanometer-level replication of cellulosic substances and preparation of photocatalytic TiO2/cellulose composites

TiO2 replicas of filter paper with nanometer-level accuracy were prepared by atomic layer deposition of thin conformal TiO2 coating, followed by a removal of the paper by air-anneal at 450 degrees C. Photocatalytic anatase TiO2/cellulose composites were also made by leaving the paper intact. The TiO2 films were deposited from Ti(OMe)4 and H2O at 150-250 degrees C. The photocatalytic activity of the TiO2/cellulose composite was verified by photocatalytic reduction of Ag(I) from an aqueous solution to Ag nanoparticles on the TiO2 surface. The TiO2/cellulose composites are mechanically more stable than the free-standing TiO2 replicas and are therefore potentially suitable as lightweight, high surface area photocatalysts.     

Charge separation at the rutile/anatase interface: a dominant factor of photocatalytic activity

Epitaxial and polycrystalline anatase films were grown by pulse-powered magnetron sputtering. The photoreduction of Ag ions showed the difference in the distribution of the photocatalytic active sites in these films. The polycrystalline anatase film was covered with an Ag layer. In contrast, discrete Ag particles were interspatially deposited on the epitaxial anatase film. Evaluation of the epitaxial film by micro-Raman spectrometry revealed that the rutile coexisted at only the site where the Ag particle was precipitated. These results suggest that the rutile/anatase interface is the active site for photocatalysis and is one of the dominant factors of the photocatalytic activity.     

不同制备条件对TiO2/beads光催化活性的影响

以空心玻璃微球为载体,采用浸涂法制备TiO₂/beads光催化剂;利用X射线衍射、扫描电镜、热分析对TiO₂/beads进行了表征。研究了不同制备条件对TiO₂/beads光催化活性的影响。结果表明,热处理600℃,5h,A/R为81/19时,TiO₂/beads光催化活性最高;样品由非晶向锐钛矿型转变的温度为429℃,当锐钛矿型TiO₂与金红石型TiO₂以一定的比例共存时,TiO₂/beads的光催化活性较好.     

玻璃和石英基体上沉积的TiO2薄膜的光催化性能

采用直流磁控反应溅射法,在玻璃和石英基体上制备了TiO2薄膜.在氧气流速超过阈值的条件下溅射,能够得到均匀透明的TiO2薄膜.在玻璃和石英基体上制备的薄膜都由均匀的锐钛矿型氧化钛晶粒组成,在晶粒中间分布着微小的孔隙.尽管在整个光谱区域内石英基体的透射率都比玻璃基体高,但在两种基体上制备的TiO2薄膜的光谱吸收边沿基本相同.薄膜中的Ti都以Ti4 形式存在.两种TiO2薄膜光催化降解甲基橙的能力相差不大.     

A new patterning method using photocatalytic lithography and selective atomic layer deposition

We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.     

双层分等级TiO_2纳米线制备及其光伏性能研究

采用两步溶剂热反应制备了底层为分等级锐钛矿的TiO_2纳米线阵列,上层为分等级锐钛矿的TiO_2纳米线薄膜的双层结构电极.通过XRD和SEM对其组成和形貌进行了表征,并考察了纳米线薄膜对染料敏化太阳电池(DSSC)光伏性能的影响.实验结果表明,分等级锐钛矿的TiO_2纳米线作为DSSC的光阳极,光电转换效率为4.39%,其效率高于光滑的TiO_2纳米线光阳极电池效率(2.07%).     

微乳法合成纳米SiO2/TiO2及其光催化性能

采用聚乙二醇辛基苯基醚(Triton X-100)/正己醇/环己烷/氨水微乳体系合成了纳米TiO2和SiO2/TiO2复合物,用X射线衍射、红外光谱和透射电镜对其结构进行了表征,并以甲基橙降解评价了其光催化性能,讨论了SiO2/TiO2摩尔比、晶相组成及粒径与光催化活性的关系.结果表明,SiO2/TiO2催化剂中形成了新的Ti-O-Si键和无定形SiO2;在纳米TiO2中复合SiO2能有效抑制锐钛矿向金红石的转变,增加锐钛矿的稳定性,并阻止TiO2晶粒的聚集生长.催化剂的光催化活性随金红石含量的增加而降低,加入适量SiO2能明显提高TiO2的光催化活性,其中摩尔比为1/7的SiO2/TiO2光催化活性最高.     

Photocatalytic properties of titania nanostructured films fabricated from Titania nanosheets

We examined the photochemical properties of well-ordered multilayer films of titania nanosheets prepared on quartz-glass substrate using the layer-by-layer deposition method. The photocatalytic decomposition of gaseous 2-propanol and bleaching of Methylene Blue dye under UV light illumination were measured to evaluate the photocatalytic oxidation ability. Photoinduced hydrophilicity was also studied by measuring the contact angle of water droplets on the film. The results indicated that titania nanosheets had good photoinduced hydrophilicity. The monolayer film of titania nanosheets showed almost identical activity compared with well investigated sol-gel derived anatase TiO(2) film, while its photocatalytic oxidation activity was low by more than an order of magnitude. This fact suggests that photoinduced hydrophilicity could not be explained simply in terms of the photocatalytic removal of hydrophobic organic species adsorbed on the surface. The photocatalytic oxidation activity and the photoinduced hydrophilic conversion rate decreased with increasing number of nanosheet layers, suggesting that photogenerated carriers produced in the internal part of the multilayer films can hardly diffuse to the surface layer. Photochemical properties of ultrathin anatase films obtained simply by heating the titania nanosheet films were evaluated as well, and also revealed high photoinduced hydrophilicity.     

Rutile TiO2 nanowires on anatase TiO2 nanofibers: a branched heterostructured photocatalysts via interface-assisted fabrication approach

A water-dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO(2) nanowires (NWs) on electrospun anatase TiO(2) nanofibers (NFs), using highly reactive TiCl(4) as precursor. The water-dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water-dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO(2) heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase-rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures.     

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.     

Anatase TiO2 nanoparticles on rutile TiO2 nanorods: a heterogeneous nanostructure via layer-by-layer assembly

We report here the use of a layer-by-layer assembly technique to prepare novel TiO2 heterogeneous nanostructures in which anatase nanoparticles are assembled on rutile nanorods. The preparation includes assembling anatase nanoparticle multilayers on rutile nanorods via electrostatic deposition using poly(sodium 4-styrene sulfonate) as a bridging or adhesion layer, followed by burning off the polymeric material via calcination. The composition of the heterogeneous nanostructures (i.e., the anatase-to-rutile ratio) can be tuned conveniently by controlling the experimental conditions of the layer-by-layer assembly. It was found that, with the optimum preparation conditions, the heterogeneous nanostructures showed better photocatalytic activity for decomposing gaseous acetaldehyde than either the original anatase nanoparticles or the rutile nanorods. This is discussed on the basis of the synergistic effect of the existence of both rutile and anatase in the heterogeneous nanostructure.     

Site selective micro-patterned rutile TiO2 film through a seed layer deposition

Micro-patterned films obtained from micro-contact printing (microCP) method are often challenged by site selectivity limitation. For applications site-selectivity requires improvements. In this paper a site-selective deposition of the rutile TiO2 thin films on patterned SnO2 film, which was formed on the patterned octadecyltrichlorosilane (OTS) SAMs through microCP is described. The depositions proceeded in an environmentally friendly aqueous solution (SnCl4 and peroxotitanium acidic solution) at a lower temperature (80 degrees C). It is shown that the OTS SAMs has a good selectivity deposition for SnO2 particles, which was mainly dominated by the heterogeneous nucleation mechanism. The SnO2 layer had a structure-directing effect for growth of the rutile TiO2, which was usually formed above 600 degrees C. The patterned films were characterized by a variety of techniques, including ellipsometry, optical microscopy, SEM, AFM, XPS, and DLS to determine the thicknesses, topologies, microstructures, chemical compositions of the films, particle sizes and zeta potentials of the titanium particles.