Preparation and photocatalytic activity of TiO2 powders from titanium citrate complex using two-step hydrothermal treatments

White, almost carbon-free TiO₂ powders were prepared from a titanium citrate complex ((NH₄)₄[Ti₂(C₆H₄O₇)₂(O₂)₂]·4H₂O) using a two-step hydrothermal treatment. The product yield, carbon contamination, and crystalline phase of TiO₂ depended on both the temperature and pH value for each treatment. Titanium was precipitated as a solid phase (H₂Ti₂O₅·H₂O) using the first hydrothermal treatment in the basic condition (pH = 12) at temperatures less than 150 °C. Then white rutile or anatase powder was crystallized using the second hydrothermal treatment at 200 °C. By changing the pH condition of the second hydrothermal treatment, rutile and anatase were synthesized selectively. The photocatalytic decomposition activity of obtained rutile powder for gaseous 2-propanol under visible light was increased by Cu-grafting.     

Preparation and characterization of Co-doped TiO2 materials for solar light induced current and photocatalytic applications

Different amounts of Co-doped TiO₂ powders and thin films were prepared by following a conventional co-precipitation and sol–gel dip coating technique, respectively. The synthesized powders and thin films were subjected to thermal treatments from 400 to 800 °C and were thoroughly investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive analysis with X-rays, FT-infrared, FT-Raman, diffuse reflectance spectroscopy, ultraviolet–visible spectroscopy, BET surface area, zeta potential, flat band potential measurements, band-gap energy, etc. The photocatalytic ability of the powders was evaluated by methylene blue (MB) degradation studies. The thin films were characterized by photocurrent and ultraviolet–visible (UV–Vis) spectroscopy techniques. The characterization results suggest that the Co-doped TiO₂ powders synthesized in this study consist mainly anatase phase, and possess reasonably high specific surface area, low band gap energy and flat band potentials amenable to water oxidation in photoelectrochemical (PEC) cells. The photocatalytic degradation of MB over Co-doped TiO₂ powders followed the Langmuir–Hinshelwood first order reaction rate relationship. The 0.1 wt.% Co-doped TiO₂ composition provided the higher photocurrent, n-type semi-conducting behavior and higher photocatalytic activity among various Co-doped TiO₂ compositions and pure TiO₂ investigated.     

Nanocrystalline anatase TiO2 prepared via a facile low temperature route

Nanocrystalline anatase TiO₂ was prepared by a facile sol-gel route at a temperature of 65 °C under mild conditions. Tetrabutyl titanate was used as a titanium precursor, glacial acetic acid was used as an inhibitor, and anhydrous ethanol was used as a solvent. XRD, TEM, FT-IR and XPS spectra were applied to characterize the crystal phase, microstructure, and other physicochemical properties of the nanoanatase TiO₂. The results showed that as prepared ellipse-shaped anatase TiO₂ with an average diameter of 7 nm, which is rich in surface hydroxyl groups, was found to exhibit high dispersibility.     

Solar photocatalytic degradation of isoproturon over TiO2/H-MOR composite systems

The photocatalytic degradation and mineralization of isoproturon herbicide was investigated in aqueous solution containing TiO₂ over H-mordenite (H-MOR) photocatalysts under solar light. The catalysts are characterized by X-ray diffraction (XRD), UV–Vis diffused reflectance spectra (UV–Vis DRS), Fourier transform-infra red spectra (FT-IR) and scanning electron microscopy (SEM) techniques. The effect of TiO₂, H-MOR support and different wt% of TiO₂ over the support on the photocatalytic degradation and influence of parameters such as TiO₂ loading, catalyst amount, pH and initial concentration of isoproturon on degradation are evaluated. 15 wt% TiO₂/H-MOR composite is found to be optimum. The degradation reaction follows pseudo-first order kinetics and is discussed in terms of Langmuir–Hinshelwood (L–H) kinetic model. The extent of isoproturon mineralization studied with chemical oxygen demand (COD) and total organic carbon (TOC) measurements and 80% mineralization occurred in 5 h. A plausible mechanism is proposed based on the intermediates identified by liquid chromatography–mass spectroscopy (LC–MS).     

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.     

TiO2 nanofibre-assisted photodecomposition of Rhodamine B from aqueous solution

Using liquid phase deposition method on cellulose substrate, TiO₂ nanofibres were prepared with TiCl₄ as a precursor. TiO₂ nanofibres were obtained after heat treatment of the cellulose template. The remaining product was composed of micron-size TiO₂ fibres with a nanofiber microstructure. It is shown that nanofibres are formed through the aggregation of TiO₂ nanoparticles. X-ray diffraction analysis of the as-prepared solution indicates the formation of crystalline TiO₂ anatase phase. EDX analysis was employed to measure the adsorbed mass of TiO₂ on cellulose substrate. The effect of deposition time on the growth and morphology was investigated by scanning electron microscopy. Transmission electron microscopy studies demonstrate fine microstructures composed of 10–15?nm?nanoparticles. Surface area of the TiO₂ fibres, measured by Brunauer, Emmett and Teller analysis, was about 104?m²?g^?1. Photodegradation of Rhodamine B as a standard dye shows that the prepared samples have a high photocatalytic activity due to large surface area.     

Effect of TiO2-SiO2 sol-gel coating on the cpTi-porcelain bond strength

The effects of TiO₂-SiO₂ sol-gel coating with different firing temperatures (300 °C, 500 °C, and 750 °C) on the cpTi-porcelain bond strength were investigated in the present study. Prior to applying the low-fusing dental titanium porcelain, the phase, surface morphology, surface roughness and static water contact angle of the intermediate layer were evaluated. The cpTi-porcelain bond strength was measured using the three-point flexure test according to ISO 9693 standard. Statistical analyses were made using one-way ANOVA and Dunnett-t test. Significantly higher bond strength of TiO₂-SiO₂/750 °C (specimens coated with TiO₂-SiO₂ sol-gel coating and fired at 750 °C for 1 h) when compared to the control group was observed (p < 0.05). No rutile phase was found in all the tested specimens coated with TiO₂-SiO₂ sol-gel coating. The surface morphology of the intermediate layer was apparently different with different firing temperatures. It was found that the static water contact angle of TiO₂-SiO₂/750 °C significantly decreased (p < 0.05). However, no markedly different R_a of TiO₂-SiO₂/500 °C and TiO₂-SiO₂/750 °C in comparison to that of the control group was observed (p > 0.05). The results show that the TiO₂-SiO₂ sol-gel coating fired at 750 °C for 1 h can notably improve the cpTi-porcelain bond strength and may be suitable for clinical use.     

Deposition of TiO2 nano-particles on wood surfaces for UV and moisture protection

Deposition of TiO₂ nanoparticles on wood surface was realised to improve the wood stability against ultraviolet (UV) light and moisture degradation. Photocatalytic activity of TiO₂ nanoparticles was utilised for protection of the wood surface. TiO₂ nano-particles were achieved by a sol–gel deposition method using EtOH/TiCl4 solution. Dip-coating process and subsequent annealing were used to realise nano-particles on wood surface. This method of deposition was utilised for the conformal covering of the wood structure as demonstrated by morphological investigation of the prepared samples by field emission scanning electron microscopy. Colour change measurements and Fourier transform infrared spectroscopy were used to analyse the lignin and carbonyl degradation of uncoated and coated wood during the UV exposure. Moisture protection of the coated wood was investigated by measuring the contact angle of the distilled water and wood surface. The measurements showed the UV and moisture protection of the TiO₂ layer.     

Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

Modeling of the Phase Transformation Induced by Ball Milling in Anatase TiO2

A high-pressure and high-temperature phase of TiO₂ : TiO₂ II is formed transiently during room-temperature high-energy ball milling of anatase TiO₂ : TiO₂ anatase TiO₂ II TiO₂ rutile. Rutile is the only phase present after prolonged ball milling. The present paper focuses on the influences of physical and chemical processing conditions on the transformation kinetics. The effects of two milling parameters on the kinetics of phase transformation of anatase TiO₂ were investigated: the nature of milling tools and the powder-to-ball weight ratio R. Granulometric characterizations and TEM observations have demonstrated that the transformation of TiO₂ anatase into TiO₂ II occurs without fracturing of particles and that TiO₂ II nanograins form at the surface of anatase particles. The parameter R affects only the transformation rate. For a given R, the transformation rate is the largest with alumina grinding tools, intermediate with zirconia tools, and the smallest with steel tools. The parameters involved in current models of the mechanical alloying process do not suffice to explain the differences in transformation rates observed here. A parameter, which takes into account the influence of the mechanical properties of grinding materials, is considered.     

Effects of post-deposition surface treatment on the optical, structural and hydrogen sensing properties of TiO2 thin films

TiO₂ thin films were prepared by DC reactive magnetron sputtering in a mixture of oxygen and argon on glass and oxidized silicon substrates. The effect of post-deposition annealing (300 °C, 500 °C and 700 °C for 8 h in air) on the structural and morphological properties of TiO₂ thin films is presented. In addition, the effect of Pt surface modification (1, 3 and 5 nm) on hydrogen sensing was studied. XRD patterns have shown that in the range of annealing temperatures from 300 °C to 500 °C crystallization starts and the thin film structure changes from amorphous to polycrystalline (anatase phase). In the case of samples on glass substrate, optical transmittance spectra were recorded. TiO₂ thin films were tested as sensors of hydrogen at concentrations 10,000-1000 ppm and operating temperatures within the 180-200 °C range. The samples with 1 nm and in particular with 3 nm of Pt on the surface responded to hydrogen fast and with high sensitivity.     

Fabrication of transparent TiO2 film with high adhesion by using self-assembly methods: Application to super-hydrophilic film

A transparent and super-hydrophilic TiO₂ film with high adhesion was prepared by simple self-assembly methods from aqueous solution at low temperature. The excellent adherence of TiO₂ films was accomplished by introducing a buffer layer with sulfonate-modified surfaces and nanoasperity. Moreover, the structure and morphology of the films were successfully controlled by deposition temperature and the pH of precursor solution. By optimizing the several parameters of solution as well as the surface functionality of the substrate, the nano-structured TiO₂ film with high adhesion showed a water contact angle of below 5° and the relative transmittance to slide glass of over 90%. The fabricated TiO₂ film deposited under the optimized condition is not removed from substrate after several Scotch tape (STT) tests and immersing into several kinds of solvent.     

Synthesis of Mixed-Phase TiO2 Powders in Salt Matrix and Their Photocatalytic Activity

Three mixed-phase TiO₂ powders, containing ～80 volume % anatase and ～20 volume % rutile, were prepared from amorphous titanium hydroxide and three different salt matrices—pure sodium chloride, pure Na₂CO₃, and pure disodium hydrogen phosphate (DSP). Amorphous titanium hydroxide and salt mixtures were heat treated at 875°C in a rapid thermal annealing system for different times, according to the time–temperature phase transformation graphs. Time-dependent UV degradation of aqueous solutions of methylene blue dye (15 ppm) in the presence of mixed-phase powders was used to monitor the activity of the catalysts. Microstructural study of the powders by scanning electron microscope and transmission electron microscope combined with phase analysis by XRD and optical absorbance by UV-absorption spectroscopy indicated that the higher photocatalytic activity of the powder obtained from pure DSP salt could be explained by its smaller rutile particle size and anatase–rutile interparticle bonding.     

Low temperature preparation of TiO2 nanodot film on substrates

Herein, we report a photoinduced transition of hydrophobicity to high hydrophilicity of TiO₂ nanodot films in applications of cell sheet engineering. A phase-separation-induced self-assembly process was adopted to prepare a TiO₂ nanodot gel film on a substrate. Subsequently, a hydrothermal treatment (with ethanol/water at 140 °C for 2 h) was used to convert the nanodot gel film to TiO₂ nanodot solid film. The resulting TiO₂ dots were amorphous with adjustable size and density. The amorphous TiO₂ nanodot film showed a conversion from a good hydrophobic surface, with a water contact angle (WCA) of 67.6 ± 2.0°, to a highly hydrophilic one, with a WCA of 5.3 ± 2.0° (i.e. almost superhydrophilic) after UV irradiation. A good reversibility was also observed.     

Controlled preparation of macroporous TiO2 films by photo polymerization-induced phase separation method and their photocatalytic performance

TiO₂ films with controlled macroporous structures have been prepared from the precursor solution containing photo monomer pentaerythritol tetraacrylate by a photo polymerization-induced phase separation method (PIPS) in the absence of any surfactant and colloidal templates. The gel TiO₂ film deposited from the precursor solution by dip-coating was irradiated with ultraviolet light for some time. During the irradiation process, the polymerization of the photo monomer was induced, which resulted in the phase separation in the film system. After the reaction, two phases existed in the film, one was the emerging polymer rich phase, another was the residual monomer-TiO₂ oligomer rich phase. After heat-treatment at 600 °C, the entire polymer decomposed and a well-defined interconnected macroporous TiO₂ films could be obtained. X-ray diffraction, scanning electron microscopy, atomic force microscopy, thermogravimetric and differential thermal analysis were used to characterize the macroporous TiO₂ films. The results showed that the macroporous texture could be tuned by changing the composition of the precursor solution. The solvent evaporation was controlled by the addition of polyvinylpyrrolidone. Highly macroporous TiO₂ films prepared by the PIPS method exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than the dense TiO₂ film.     

Synthesis and electrophoretic deposition of hydrothermally synthesized multilayer TiO2 nanotubes on conductive filters

TiO₂ nanotubes were synthesized by the decomposition of titanium isopropoxide in water and the calcination at 450 °C for 2 h to form TiO₂ nanoparticles. The synthesized TiO₂ in anatase form nanoparticles were processed hydrothermally in 10 M NaOH solution at 130 °C for 24 h to obtain multilayer TiO₂ nanotubes. TEM analysis revealed that the diameters of the tubes were around 10 nm and they are in the length of 100 nm. Subsequently, colloidal suspensions containing 1% wt. Of TiO2 nanotubes were prepared with TEA and butanol and electrophoretic deposition (EPD) experiments were conducted in order to obtain coatings on Ni and carbon filters using a deposition time of 10 min. and an applied voltage of 65 V. It is also shown that multilayer TiO₂ nanotubes having outer diameter around 10 nm and inner diameters of 4.3 nm can be produced using the described technique. EPD is also shown to be an effective technique to coat three dimensional components, such as Ni and C filters for various applications including water and air purification systems.     

Photocatalytic properties of porous TiO2/Ag thin films

In this study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol-gel spin-coating technique. By introducing polystyrene (PS) spheres into the precursor solution, porous TiO₂/Ag thin films were prepared after calcination at a temperature of 500 °C for 4 h. Three different sizes (50, 200, and 400 nm) of PS spheres were used to prepare porous TiO₂ films. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry (XRD) and by scanning electron microscopy to reveal structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.When PS spheres of different sizes were introduced after calcination, the as-prepared TiO₂ films exhibited different porous structures. XRD results showed that all TiO₂/Ag films exhibited a major anatase phase. The photodegradation of porous TiO₂ thin films prepared with 200 nm PS spheres and doped with 1 mol% Ag exhibited the best photocatalytic efficiency where ∼ 100% methylene blue was decomposed within 8 h under UV exposure.     

A facile template-free method for preparing bi-phase TiO2 nanowire arrays with high photocatalytic activity

Ordered bi-phase TiO₂ nanowire arrays were simply obtained by heat treating TiO₂ nanotube arrays prepared by a two-step anodization method. The nanowire arrays are composed of anatase and rutile phases with uniform diameters around 50 nm. The photocatalysis activities of TiO₂ nanowire arrays were characterized by quantifying the degradation of methyl orange solution. And the results indicated that the bi-phase nanowire arrays, especially obtained at 700 °C, showed much higher activity than that of P25 film or anatase TiO₂ nanotube array.     

Nanoporous TiO2 thin film based conductometric H2 sensor

Nanoporous titanium dioxide (TiO₂) based conductometric sensors have been fabricated and their sensitivity to hydrogen (H₂) gas has been investigated. A filtered cathodic vacuum arc (FCVA) system was used to deposit ultra-smooth Ti thin films on a transducer having patterned inter-digital gold electrodes (IDTs). Nanoporous TiO₂ films were obtained by anodization of the titanium (Ti) thin films using a neutral 0.5% (wt) NH₄F in ethylene glycol solution at 5 V for 1 h. After anodization, the films were annealed at 600 °C for 8 h to convert the remaining Ti into TiO₂. The scanning electron microscopy (SEM) images revealed that the average diameters of the nanopores are in the range of 20 to 25 nm. The sensor was exposed to different concentrations of H₂ in synthetic air at operating temperatures between 100 °C and 300 °C. The sensor responded with a highest sensitivity of 1.24 to 1% of H₂ gas at 225 °C.