Fabrication of carbon-modified TiO2 nanotube arrays and their photocatalytic activity

TiO₂ nanotube (TN) arrays were fabricated by an anodic oxidation process. Through a heat treatment of the as-fabricated TN arrays under a continuous Ar and acetylene flux, carbon-modified TN (C-TN) arrays were obtained. The as-fabricated catalysts were characterized by FE-SEM, HRTEM, XPS, Raman and UV-Vis spectra. Moreover, photocatalytic activity of the C-TN arrays was evaluated through the photodegradation of aqueous methyl blue. The experiments demonstrated that the C-TN arrays display an excellent photocatalytic activity. Under sunlight irradiation, the C-TN arrays are able to almost completely decompose the methylene blue pollutant of 1 × 10^− 5 M within 300 min.     

Enhanced photocatalytic activity of mesoporous TiO2 with MgO coating

To improve the photocatalytic activity of TiO₂ on decomposing anionic surfactants, MgO-coated mesoporous TiO₂ was fabricated by evaporation induced self-assembly (EISA) combined with impregnation method. MgO was uniformly dispersed on the surface of TiO₂, which played the role of stabilizing the ordered mesostructure of TiO₂ and improving the adsorption of anion surfactants, while inhibiting the crystallization of TiO₂. The powders coated with 5 wt.% MgO showed the highest photocatalytic activity for the decomposition of sodium dodecylbenzenesulfonate-6 (DBS).     

Enhanced photoelectrocatalytic activity in TiO2 nanotube arrays modified with TiO2 nanoparticles

The use of TiO₂ nanotube arrays fabricated by anode oxidation of titanium sheets as a photoelectrocatalyst is limited by low surface activity owing to passive crystallization post-treatment. We report here on a vacuum assisted filling route for modifying TiO₂ nanotube arrays using high-activity anatase TiO₂ nanoparticles as a filling. Photoelectrocatalytic degradation experiments show that a nearly 4-fold activity enhancement in photoelectrocatalysis is achieved and good photoelectrocatalytic stability is kept after the nanotube arrays are filled with the high-activity TiO₂ nanoparticles. The remarkable enhancement in photoelectrocatalysis is ascribed to the key modification of the TiO₂ nanotube arrays using the high-activity TiO₂ nanoparticles. Our findings provide an insight into designing excellent photoelectrocatalysts by filling TNAs with available high-activity TiO₂ nanoparticles.     

Fabrication of TiO2 nanostructured films by spray deposition with high photocatalytic activity of methylene blue

TiO₂ films were successfully deposited onto hot quartz substrates by airbrush spraying using an aqueous dispersion. The films consisting of cubic or cauliflower-shaped structures expressed higher photodegradation efficiencies of methylene blue than those with prism-, flower- or fan-blade-shaped morphology due to the difference in the optical band gap energy. The photodegradation obeyed the pseudo-first-order Langmuir-Hinshelwood kinetic model with apparent rate constants ranging from 3.95 × 10^− 3 to 19.38 × 10^− 3 min^− 1 based on the film surface morphology.     

Low-temperature hydrothermal synthesis of flower-like ZnO microstructure and nanorod array on nanoporous TiO2 film

A novel ZnO architecture, with flower-like microstructure on the top layer and nanorod arrays on the bottom layer, was hydrothermally synthesized on the Fluorine-doped SnO₂ (FTO) conducting glass pre-coated with nanoporous TiO₂ film. The as-prepared architecture was characterized with Field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometer (XRD). Dye-sensitized solar cell studies showed that the power conversion efficiency (η) was 1.26% for this novel ZnO architecture-covered TiO₂ electrode.     

Novel photocatalytic TiO2 coatings produced by HVOF thermal spraying process

Titanium dioxide coatings were deposited by high velocity oxy-fuel spraying (HVOF) using agglomerated nano-powders. Different spraying parameters were used to determine their influences on the crystallite structure and photocatalytic performance of the coatings. The as-sprayed TiO₂ coatings were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of ethanol. A high anatase content of 80% by volume was achieved for the coating deposited by a 120 ml/min fuel flow rate. The results show that the as-sprayed TiO₂ HVOF coatings were highly photocatalytically reactive for the degradation of ethanol.     

Fabrication of photocatalytic heat-mirror with TiO2/TiN/TiO2 stacked layers

The photocatalytic heat-mirror based on TiO₂/TiN/TiO₂ stacked layers is prepared by reactive magnetron sputtering on quartz substrates under substrate-heating condition. We find that the addition of a thin Ti interlayer between the TiN and the outer TiO₂ layers drastically improves the heat-insulating performance. This type of stacked layer also exhibits higher photocatalytic activity for decomposition of acetaldehyde gas, compared with a TiO₂ single layer. The optical property of the TiN in TiO₂/TiN/TiO₂ stacked layers is the key not only revealing excellent heat-insulating effect but also improving the photocatalytic performance of the outer TiO₂ layers in the stacked layers.     

Cr-doped TiO2 thin films deposited by RF-sputtering

Cr-doped TiO₂ thin films with different band gaps were prepared. Higher Cr doping was beneficial to the formation of the rutile-TiO₂ phase over the anatase-TiO₂ phase. A 4.8% Cr-doped thin film indicated a band gap of 2.95 eV, which was lower than the band gap of the rutile-TiO₂. Cr doping was accompanied by the formation of not only the rutile-TiO₂ phase but also the Cr₂O₃ phase, lead to the degradation of the hydrophilicity. The TiO₂ thin films with the mixed phase were not desirable to improve the hydrophilicity.     

Superhydrophilic anatase TiO2 film with the micro- and nanometer-scale hierarchical surface structure

Nanosized anatase TiO₂ film on the ITO glass has been fabricated via spin coat process, with sodium dodecylbenzenesulfonate modified TiO₂ nanoparticles, which is synthesized by a sol-hydrothermal method, and also characterized mainly by means of field emission scanning electron microscopy (FESEM). The results show that the as-prepared anatase TiO₂ film exhibits superhydrophilic characteristic although it is not exposed to ultraviolet irradiation. The high roughness resulting from hierarchical surface structure is responsible for its superhydrophilicity. This work would provide a new route to fabricate newly nanostructured semiconductor films.     

Mn-doped TiO2 nanopowders with remarkable visible light photocatalytic activity

TiO₂ nanocrystalline powders with various Mn-doping levels were synthesized by the sol-gel process using tetrabutyl titanate and manganese nitrate as precursors. The crystal structure, morphology, doping concentration, optical absorption property, and elemental state of the obtained samples were analyzed. TEM results showed that the synthesized TiO₂ powders were anatase nanoparticles about 7 nm in size. EDX and XPS analyses proved the incorporation of Mn ions into the TiO₂ lattice. A remarkable red shift of the absorption edge was achievable by increased Mn content, leading to gigantically narrowed energy gap to permit absorption well into the infrared spectral region. The dramatic optical absorbance of the doped TiO₂ nanopowders in the visible spectral region led to strong photocatalytic activity under visible light illumination, which was observed by measuring the degradation of methylene blue. In contrast, little degradation was observed for the pure TiO₂ powder. The optimum Mn/Ti ratio was observed to be 0.2 at.% for photocatalytic applications.     

Microstructure and photocatalytic activity of mesoporous TiO2 film coated on an aluminum foam

A TiO₂ film was synthesized via a surfactant assisted sol-gel process and dip-coated on the surface of an open-celled aluminum foam. The film shows a typical mesoporous structure composed of anatase crystalline grains with the average size of 10 nm, and has the thickness of about 3.5 μm as well as the BET surface area of 78.1 m²/g. It exhibits high photocatalytic efficiency toward the decomposition of formaldehyde at continuous flow mode. The relatively small grain size of TiO₂ and relatively thick mesoporous structure, which is favorable for high photochemical activity and the mass transfer of the reactants, should be responsible for the properties.     

Preparation and photocatalytic activity of anatase TiO2 nanocrystallites with high thermal stability

Anatase TiO₂ nanocrystallites were prepared from TiCl₄ with addition of aqueous ammonia by changing Ti(OH)₄ hydrogel into its corresponding alcogel followed by supercritical drying in ethanol medium. The as-prepared TiO₂ was characterized by XRD, TG and BET. The results show that the prepared anatase TiO₂ has remarkable high thermal stability. The anatase structure of the prepared TiO₂ is maintained even after calcination up to temperatures as high as 800 °C. The photocatalytic activity of the prepared TiO₂ calcined at 800 °C in degradation of reactive brilliant red X-3B is comparable to commercially available nanosized P25 TiO₂.     

Mesoporous Au/TiO2 composites preparation,characterization, and photocatalytic properties

In this work, mesoporous Au/TiO₂ composites have been synthesized and tested on photodegradation of methylene blue dye solution. Mesoporous TiO₂ prepared at 450 °C using triblock polymer F127 as structure-directing agent was applied as substrate, while various HAuCl₄ concentrations were used for Au loading through deposition-precipitation method using urea as precipitator and hydrogen reducing process. The influences of Au loading on the microstructures of mesoporous TiO₂ including degree of dispersion, particle size, surface area, light absorption, and band gap were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), diffuse reflection infrared Fourier transformed spectroscopy (DRIFT), N₂ adsorption–desorption isotherm analysis (BET), and UV–Vis diffuse reflectance spectra. With Au loading, the size of TiO₂ nanoparticles in Au/TiO₂ composites is similar as that of TiO₂ substrate. However, the degree of dispersion was greatly improved. Furthermore, an obvious surface plasmon resonance centered at 570 nm was found in UV–Vis diffuse reflectance spectra for Au/TiO₂ composites. Au loading also induced an obvious red shift of light absorption from UV region to visible region and strengthened both UV and visible light absorption in contrast to substrate. Photodegradation results verified that photocatalytic activity of mesoporous TiO₂ was improved by Au loading. 0.25%Au/TiO₂ composite showed the highest activity, which may be ascribed to its high surface hydroxyl content and the formed Schottky junction after Au loading. These results suggested that noble metal modification is a promising way to synthesize photocatalysts with both high activity and visible light sensitivity.     

Preparation and visible-light photocatalytic activity of In2S3/TiO2 composite

A novel In₂S₃/TiO₂ composite with visible-light photocatalytic activity was prepared by a chemical precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope and UV–vis diffuse reflectance spectroscopy. Under both UV- and visible-light irradiation, the In₂S₃/TiO₂ composite shows good photocatalytic activity to degrade methyl orange, ascribed to the absorption of visible light by In₂S₃ sensitizer and enhanced separation of photoinduced electron–hole pairs in the composite semiconductors.     

Investigation on solar photocatalytic activity of TiO2 loaded composite: TiO2/Eggshell, TiO2/Clamshell and TiO2/CaCO3

The TiO₂/Eggshell, TiO₂/Clamshell and TiO₂/CaCO₃ loaded composites were prepared by sol-gel method and characterized by XRD and SEM. Their photocatalytic activities were measured through the degradation of Acid Red B under solar light irradiation. The influences of TiO₂ loaded content, heat-treated temperature and time on the photocatalytic activities were reviewed. The effects of irradiation time and dye initial concentration on the photocatalytic degradation were also investigated. The results showed that the photocatalytic activity can be greatly enhanced by appropriate TiO₂ loaded content.     

TiO2-SnO2 system for gas sensing—Photodegradation of organic contaminants

Catalytic photodegradation of organic contaminants by means of UV light has been demonstrated for gas sensors based on composites of TiO₂-SnO₂. Thin film resistive-type gas sensors of TiO₂-SnO₂ have been deposited at 350 °C by RF sputtering from a Ti-SnO₂ target with varying surface ratio of SnO₂/Ti. Photodegradation experiments of bromothymol blue by UV light have been performed by means of the optical spectrophotometry over the wavelength range extending from 300 nm to 600 nm. The influence of the UV illumination on the sensor response to 100-20,000 ppm of H₂ has been investigated in situ on motor oil contaminated sensors. It has been found that sequential exposures to UV light lead to a partial recovery of the sensor signal to hydrogen.     

Fabrication of hollow VO2 microspheres by a facile template-free process

In the work, we report a facile template-free approach to prepare hollow VO₂ microspheres. Uniform hollow VO₂ assemblies composed of ordered microspheres with an average diameter of 3.0 µm and a hollow interior of 2.0 µm were prepared by calcining the precursor, which was synthesized via heat preservation process sealed in Teflon-lined stainless autoclave in the presence of urea. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scan electron microscopy (SEM) have been used to characterize VO₂ microspheres. The proposed mechanism for the formation of hollow VO₂ microspheres is discussed.     

Effects of internal stress on photocatalytic properties of TiO2 films

Effects of internal stress on photocatalytic properties have been investigated on titanium dioxide films deposited by reactive magnetron sputtering. Atomic peening effects by bombardments of high-energy particles in sputtering processes should generate not only compressive stress, but also oxygen defects in the films. Therefore, the films with higher compressive stress performed almost no photocatalytic activity. Furthermore, compressive or tensile stress was applied on the films deposited on curved micro sheet glasses by flattening the substrates after the deposition by external force. It was found that the photodecomposition activity of the films applied the slight compressive stress improved clearly, whereas the one of the films applied the tensile stress degraded.     

Dye sensitized solar cells using freestanding TiO2 nanotube arrays on FTO substrate as photoanode

The front-side illuminated dye-sensitized solar cells with TiO₂ nanotube arrays/FTO based photoanode were fabricated by a simple detachment and transfer method. The morphology and crystalline phase of the TiO₂ nanotubes were studied by scanning electron microscopy and X-ray diffraction. A photoconversion efficiency of 1.78% was obtained using TiO₂-nanotube/FTO glass as a photoanode. It was found that the average tubes diameter increased with anodizing voltage, and higher photoconversion efficiency was obtained for nanotubes synthesized at the higher voltage.