Nitrogen-doped TiO2 nanotubes with enhanced photocatalytic activity synthesized by a facile wet chemistry method

Nitrogen-doped TiO₂ nanotubes with enhanced photocatalytic activity were synthesized using titanate nanotubes as raw material by a facile wet chemistry method. The resulting nanotubes were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and UV-vis absorption spectroscopy, etc. The photocatalytic activity of nitrogen-doped TiO₂ nanotubes was evaluated by the decomposition of methylene blue under artificial solar light. And it was found that nitrogen-doped TiO₂ nanotubes exhibited much higher photocatalytic activity than undoped titanate nanotubes.     

Synthesis of titanium dioxide nanotubes via one-step dynamic hydrothermal process

Titanium dioxide (TiO₂) nanotubes were synthesized via one-step dynamic hydrothermal process from commercial TiO₂ powder. The effects of NaOH concentration, reaction time, reaction temperature, stirring process and washing on the morphology, and the exchange ions of the nanotubes were investigated. The morphology of the nanotubes was characterized in detail with transmission electron microscopy and scanning electron microscope. In the dynamic hydrothermal process, stirring can reduce the reaction time of transformation from particles to nanotubes. The nanotubes were formed when the expected reaction temperature reached to 130 °C. Energy dispersive X-ray analysis was used to determine the exchange of sodium ions and protons in washing process. The Na⁺ ions attached in the nanotubes were removed completely by HCl aqueous solution and deionized water treatments. X-ray diffraction patterns showed the titanate phase of the as-synthesized sample and anatase phase of TiO₂ nanotubes after calcination process at 400 °C for 2 h.     

Efficiency of surface modified Ti coated with copper nanoparticles to control marine bacterial adhesion under laboratory simulated conditions

Titanium (Ti) used as condenser material in nuclear power plants encounter severe biofouling in marine environment which in turn affects the efficiency of the metal. To reduce the biofouling by marine microorganisms, surface modification of the Ti was carried out by anodization process to obtain nanotubes (TiO₂-NTs). The electrolyte solution containing 1% of ammonium fluoride resulted in uniform growth of TiO₂-NTs. TiO₂-NTs were further coated with chemically synthesized copper nanoparticles (NT-CuNP) using 3-amino propyl triethoxy silane as a coupling agent. NT-CuNP was characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy and X-ray diffraction. The stability of the coating was determined by the amount of Cu⁺ ions released into the surrounding using AAS. The microbial adhesion on the surface of Ti, TiO₂-NTs and NT-CuNP coupons were evaluated by sea water exposure studies using total viable count method and also characterized by FE-SEM for any morphological changes. The NT-CuNP coupons show a 60% reduction in microbial adhesion when compared to control Ti coupons.     

Influence of Na+ content on the structure and morphology of TiO2 nanoparticles prepared by hydrothermal transformation of alkaline titanate nanotubes

ABSTRACT

The objective of this study is to investigate the role of Na⁺ content in the morphology evolution of TiO₂ nanoparticles prepared by hydrothermal approach. Various TiO₂ morphology from 0-dimensional (0D) nanoparticles to 1-dimensional (1D) nanorods were synthesised by hydrothermally treating the alkali titanate nanotubes with different Na⁺ content. The XRD patterns show the phase transformation and crystallographic nature of alkali titanate nanotubes are strongly dependent on the Na⁺ content, the cation exchange of Na⁺ by H⁺ ion exchange affects the crystallinity of the tubes and causes disorder of the interlayers of nanotubes. The SEM and TEM images confirm that Na⁺ rich titanate nanotubes were thermally stable. Moreover, BET measurements revealed that the Na⁺ content plays an important role on the specific surface area of formed TiO₂ nanoparticles. The photocatalytic activity of the TiO₂ nanoparticles was characterised via the decomposition rate of an aqueous solution of methyl orange (MO) under UV light irradiation. The TiO₂ nanoparticles prepared by hydrothermally treating the alkali titanate nanotubes with no Na⁺ content has a surface area of 55.1 m²/g with nearly 100% photodecomposition of MO in 20 min.     

Preparation and characterization of titanate nanotubes/carbon composites

Titanate nanotubes/carbon composites(TNT/CCs) were synthesized by allowing carbon-coated TiO₂ (CCT) powder to react with a dense aqueous solution of NaOH at 120 °C for a proper period of time. As-prepared CCT and TNT/CCs were characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectrometry. The processes for formation of titanate nanotubes/carbon composites were discussed. It was found that the TiO₂ particles in TiO₂-carbon composite were enwrapped by a fine layer of carbon with a thickness of about 4 nm. This carbon layer functioned to inhibit the transformation from anatase TiO₂ to orthorhombic titanate. As a result, the anatase TiO₂ in CCT was incompletely transformed into orthorhombic titanate nanotubes upon 24 h of reaction in the dense and hot NaOH solution. When the carbon layers were gradually peeled off along with the formation of more orthorhombic titanate nanotubes at extended reaction durations (e.g., 72 h), anatase TiO₂ particles in CCT were completely transformed into orthorhombic titanate nanotubes, yielding TNT/CCs whose morphology was highly dependent on the reaction time and temperature.     

Photochemical synthesis and characterization of Ag/TiO2 nanotube composites

TiO₂ nanotubes were fabricated by a hydrothermal method. Silver nanoparticles with diameters around 3–5 nm were loaded onto the surface of TiO₂ nanotubes via a deposition approach followed by a photochemical reduction process under ultraviolet irradiation. Transmission electron microscopy (TEM), N₂ adsorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-vis), and fluorescence spectroscopy (FL) were applied to characterize the as-prepared Ag/TiO₂ nanotube composites. The photocatalytic activity of the as-prepared materials was investigated by photodegrading of methyl orange. The results showed that silver particles were in zero oxidation state and highly dispersed on the surface of TiO₂ nanotubes when the concentration of Ag⁺ was low. The presence of metallic silver can help the electron-hole separation by attracting photoelectrons. The Ag/TiO₂ nanotube composites with a suitable amount of silver showed a further improvement on the photocatalytic activity for degradation of methyl orange in water.     

Crystal structure and photocatalytic properties of titanate nanotubes prepared by chemical processing and subsequent annealing

Anatase TiO₂ nanoparticles were synthesized from sol–gel processing, and they were used as a precursor for titanate nanotubes (TNT) formation. TNT were synthesized under reflux heating of anatase TiO₂ in concentrated NaOH solution followed by repeated washing with distilled water and 0.1 M HCl. The nanotubular structure was preserved till 450 °C, above which nanorod formation started. The as-synthesized nanotubes were found to have mixed crystal structure of anatase and Na _x H_2?x Ti₃O₇·nH₂O (where 0 < x <  2), contrary to what has been reported before. The XRD peaks of titanate were slightly shifted to higher angles upon calcination along with prominent anatase peaks. Complete transformation to nanorods occurred at 600 °C and crystal structure was transformed to Na₂Ti₆O₁₃ and anatase. Sodium presence in TNT was confirmed by EDX, and Na–O and H–O–H along with Ti–OH vibrations were found by FTIR. Ti–OH/H–O–H vibrations were less prominent for samples calcined at 500 °C and above, which confirms structural water loss is associated with morphological change. The as-synthesized TNTs had a specific surface area of 157 m² g^?1, and it decreased by increasing calcination temperature. TNTs were applied to methylene blue aqueous solution to observe their decolorization capability under UV irradiation. The as-synthesized TNTs showed enhanced photocatalytic decolorization as compared to anatase titania nanoparticles due to presence of Ti–OH groups and higher specific surface area. The photocatalytic activity reduced when TNTs were annealed at high temperatures. The changes in the photocatalytic activity are related to the existence of hydroxyl groups in the structure, decrease in specific surface area of annealed nanotubes, change in morphology from nanotubes to nanorods, and bandgap shift to visible light when TNTs were calcined at higher temperatures.     

Synthesis and visible-light photocatalytic activity of Bi-doped TiO2 nanobelts

Bi-doped anatase TiO₂ nanobelts were synthesized from layer-structural titanate nanobelts using two-step hydrothermal treatment approach. X-ray diffraction (XRD) patterns and transmission electron microscopic (TEM) images show that the doping of Bi³⁺ cations does not change the crystal structure and morphology of TiO₂ nanobelts. The energy-dispersive X-ray (EDX) and inductively coupled plasma-mass spectrometry (ICP-MS) analytic results suggest that the doping cations mainly exist near the surface of the TiO₂ nanobelts. The ultraviolet-visible (UV-vis) absorption spectra show that the absorption edge for the samples with Bi³⁺ has red shift as compared with that of undoped TiO₂ nanobelts, and correspondingly, the photocatalytic degradation of methylene blue under visible-light illumination is enhanced with the increase of Bi-doping content.     

Study on photocatalysis of TiO 2 nanotubes prepared by methanol-thermal synthesis at low temperature

TiO₂ nanotubes were synthesized by the solvothermal process at low temperature in a highly alkaline water–methanol mixed solution. Their characteristics were identified by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), specific surface area (BET), Fourier transform infrared spectroscopy (FTIR) and UV–Vis absorption spectroscopy. The as-prepared samples were tested by the photodegradation reaction of methylene blue (MB) dye under visible-light irradiation. The ratios of methanol and water, as well as calcination temperature, affected the morphology, nanostructure and photocatalytic performance. The methanol solvent plays an important role in improving crystallization of the anatase phase, which affects the photocatalytic reaction. Titanate nanotubes were synthesized in methanol–water volume ratios of 10:90, 20:80 and 30:70 which still had high absorbability. Titania nanotubes formed at a calcination temperature of 300 °C using methanol–water volume ratio of 30:70 showed highest photocatalytic performance, much higher than that using water solvent and TiO₂–P25 powder.     

Direct imaging of titania nanotubes located in mouse neural stem cell nuclei

Titania nanotubes (TiO₂-NTs) are a potential drug vehicle for use in nanomedicine. To this end, a preliminary study of the interaction of a model cell with TiO₂-NTs has been carried out. TiO₂-NTs were first conjugated with a fluorescent label, fluorescein isothiocyanate (FITC). FITC-conjugated titania nanotubes (FITC-TiO₂-NTs) internalized in mouse neural stem cells (NSCs, line C17.2) can be directly imaged by confocal microscopy. The confocal imaging showed that FITC-TiO₂-NTs readily entered into the cells. After co-incubation with cells for 24 h, FITC-TiO₂-NTs localized around the cell nucleus without crossing the karyotheca. More interestingly, the nanotubes passed through the karyotheca entering the cell nucleus after co-incubation for 48 h. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were also employed in tracking the nanotubes in the cell. These results will be of benefit in future studies of TiO₂-NTs for use as a drug vehicle, particularly for DNA-targeting drugs. This article is published with open access at Springerlink.com     

Effect of lead on formation and dielectric tunability of (Pbx,Sr1? x )0.85Bi0.1TiO3 thin films

(Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb²⁺ and Sr²⁺. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing Pb²⁺ content because the radius of Pb²⁺ is larger than that of Sr²⁺. It appears at room temperature when the content of Pb²⁺/Sr²⁺ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb²⁺ ions increase due to its high polarization. The higher tunability of the (Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric phases. Pb²⁺ ions show a dominant factor to affect the Curie point of the system and then changing tunability. Translated from Journal of Inorganic Materials, 2006, 21(2): 466–472 [译自: 无机材料学报]     

Photocatalytic activities of Ion doped TiO2 thin films when prepared on different substrates

Pure and ion doped TiO₂ thin films were prepared by sol-gel dip coating process on metallic and non-metallic substrates. Test metal ion concentration ranged from 0.000002 to 0.4 at.%. The resulting films were annealed in air and characterized by optical spectroscopy and X-ray diffraction. The photodegradation of methyl orange under UV irradiation by pristine and ion-doped TiO₂ films was quantified in a photocatalytic reactor developed in this study. In general, both doped and undoped TiO₂ crystals appeared in anatase phase and the photocatalytic activities of the TiO₂ thin films varied with substrates, calcination temperature, doping ions and their concentrations. The best calcination temperature for different substrates ranged from 450 to 580 °C. Films prepared on the metallic substrates resulted in higher photocatalytic activities, while ion doping lowered their efficiencies. On the contrary, for non-metallic substrates except ceramic the photocatalytic efficiencies of undoped films were much lower (< 30%), while ion doping was shown to increase the photocatalytic efficiencies remarkably in some cases, e.g., Cr³⁺ with the tile substrate. Overall, ion doping affected the photocatalytic efficiency of TiO₂ films, and an optimal doping concentration of between 0.0002 and 0.002 at.%, close to an estimate by the Debye length equation, resulted in the highest efficiency for most substrates.     

Hydrothermal synthesis of lead doped barium titanate

Lead doped barium titanate was synthesized hydrothermally at 363 K for 140 h. A molar formula of Ba_(1–x)Pb _x TiO₃ was used, where x ranged between 0.025 and 0.75. The crystal structure, phase purity, and particle morphology was investigated by x-ray diffraction, Raman spectroscopy and electron microscopy. Under the synthesis conditions used, lead (Pb²⁺) was shown to incorporate into the perovskite structure when the dopant was kept below 20%. Above 20% Pb, other phases appeared and at 75% Pb no reaction to the perovskite structure took place. Unexpectedly, barium titanate containing from 2.5% Pb to 10% Pb appeared to be of orthorhombic symmetry. This was concluded by total pattern fitting of x-ray diffraction profiles and from splitting of the 222 reflection. The factors controlling the tendency for these materials to adopt orthorhombic symmetry as opposed to the more commonly observed tetragonal or cubic symmetries are briefly discussed.     

Sonication–hydrothermal combination technique for the synthesis of titanate nanotubes from commercially available precursors

Titanate nanotubes with inner diameters of 2–6 nm, outer diameters of 5–10 nm and lengths up to 600 nm were fabricated by directly using commercial TiO₂ powders as the precursors via sonication–hydrothermal combination approach. The formation processes during sonication treatment under different sonication powers and times and hydrothermal treatment were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization. The chemical composition of the titanate nanotubes was determined in terms of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analysis. The influence of the particle size of the precursors on the formation processes was also examined. The tubular structure of the titanate nanotubes can be remained at the calcination temperature ≤450 °C, but was completely destroyed at high calcination temperature 600 °C.     

Synthesis and characterization of TiO2/WO3 composite nanotubes for photocatalytic applications

TiO₂/WO₃ composite nanotubes were synthesized in an anodic aluminum oxide (AAO) template by a sol–gel method. The prepared nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, and Brunauer–Emmett–Teller surface area. Using the nanotubes embedded in the AAO templates as catalysts, photocatalytic degradation of methyl orange aqueous solution was carried out under UV light irradiation. The results showed that the TiO₂/WO₃ composite nanotubes with the thickness about 50 nm could be successfully synthesized by this method. TiO₂ showed anatase phase and WO₃ displayed monoclinic phase. The composite nanotubes (TiO₂/WO₃) exhibited higher photocatalytic activity than the pure nanotubes (WO₃ or TiO₂). The possible reason for improving the photocatalytic activity was also discussed.     

Formation of titanium oxide nanotubes using chemical treatments and their characteristic properties

Needle-shaped titanium oxide crystals with a diameter of 8 nm were obtained when titania nanopowders were treated chemically with NaOH aqueous solution and subsequently with HCl aqueous solution under various conditions (e.g., at 110 °C for 20 h). Transmission electron microscopy showed that the needle-shaped products have a tube structure with an inner diameter of approximately 5 nm and an outer diameter of approximately 8 nm. TiO₂ nanotubes with a large specific surface area of ≈ 400 m²/g are expected to have great potentials for use as high-performance photocatalysts or adsorbents. The amount of residual Na⁺ ions in the nanotubes can be controlled by HCl treatment, resulting in the formation of Na-Ti-O titanate nanotubes. The titania and titanate nanotubes can also be modified during the treatment. When calcium acetate solution was used for the treatment, a new type of bioactive nanotube was prepared. An apatite layer was formed on a compact composed of the nanotubes within 1 day of soaking in simulated body fluid. An animal test using rats showed that new-bone-tissue formation around the nanotube compact started 3 days after implantation. When oxoacid solutions, such as perchloric acid, phosphoric acid or sulfuric acid, were used in the treatment, new types of nanotube showing proton conduction were prepared; one of the nanotube compacts showed a high electrical conductivity of 8 × 10^− 2 S/cm at 150 °C. These nanotubes are expected to have applications in the fields of medicine and energy generation, as well as photocatalytic applications.     

Synthesis and photochemical properties of Cu2+ doped layered hydrogen titanate

Cu²⁺ doped layered hydrogen titanate was prepared by the calcination of K₂CO₃, TiO₂ and CuO mixtures with the K₂CO₃:TiO₂:CuO molar ratio of 1:2.5(1−x):2.5x at 1200°C for 5 h followed by an ion-exchange reaction in 1 M HCl solution. The crystalline phase changed from monoclinic hydrogen tetratitanate to an orthorhombic lepidocrocite-type hydrogen titanate by increasing the amount of Cu²⁺ doped. Both compounds could be excited by visible light irradiation (λ>400 nm) and were capable of hydrogen gas evolution from an aqueous methanol solution, where the photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was slightly greater than that of Cu²⁺ doped lepidocrocite-type hydrogen titanate. The photocatalytic activity of Cu²⁺ doped hydrogen tetratitanate was enhanced by constructing Pt and TiO₂ pillars in the interlayer, and the incorporation of Pt in Cu²⁺ doped hydrogen tetratitanate enabled the cleavage of water into hydrogen and oxygen by irradiating visible light (λ>400 nm) without a sacrificial hole acceptor.     

Effect of the crystallinity of BaTiO<Subscript>3</Subscript> powders prepared using the merker method on the properties of PTCR ceramics

Barium titanate powders differing in particle size (110–740 nm) were prepared by calcining barium titanyl oxalate precipitated by the Merker method. The powders were sintered to produce PTCR ceramics with the composition 100(Ba_0.89Ca_0.08Pb_0.03)TiO₃ + ^0.8TiO₂ + ^0.7Y + ^0.1Mn + ^2.5SiO₂ and electrical properties of the ceramics were studied. The results demonstrate that improving the crystallinity of the barium titanate powder suppresses recrystallization of the ceramics and has a significant effect on their resistance ratio and electric strength. We found the optimal range of calcination temperatures (950–1000°C) for barium titanyl oxalate which ensures the highest electric strength of thermistors with a resistance of 31 Ω. The average crystallite size of the parent barium titanate powder is ∼250–320 nm.     

Facile tailoring of titanate nanostructures at low alkaline concentration by a solvothermal route

Nanostructured titanates with different morphologies such as nanoflakes, nanotubes, and nanofibers have been selectively synthesized by a simple solvothermal treatment of commercial anatase TiO₂ using the mixed water–ethanol cosolvent at low alkaline concentration. The effects of solvothermal temperature, volume ratio of H₂O to C₂H₅OH, amount of NaOH and solvents on the formation of titanate nanostructures have been systematically studied through X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At low concentration of NaOH solution (the actual concentration of OH⁻ in the solution is only 0.58 M), different titanate nanostructures are achieved by simply changing the volume ratio of H₂O to C₂H₅OH at 180 °C and titanate nanotubes can be synthesized between 100 and 180 °C. A probable formation mechanism is proposed based on XRD, SEM and TEM analysis. The influence of cosolvent on the transformation from anatase TiO₂ to titanate is also investigated.     

Characterization of LiF-doped TiO2 and its photocatalytic activity for decomposition of trichloromethane

LiF-doped TiO₂ was prepared by hydrolysis of tetrabutyl titanate in a mixed LiF-H₂O-alcohol solution. The prepared LiF-doped TiO₂ powders were characterized by X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectroscopy and photoluminescence spectra (PL). The photocatalytic activity was evaluated by the decomposition of trichloromethane (CHCl₃). The results showed that LiF-doping increased the amount of O_OH and oxygen vacancy (OV) on the surface of TiO₂, which were beneficial to photocatalytic activity. LiF-doping inducted the new isolated energy band located above the valence band of TiO₂, which extended the absorption region of TiO₂ to visible light. The results of photocatalytic reaction showed that the photocatalytic activity of LiF-doped TiO₂ was 2.5 times higher than that of pure TiO₂.