Fabrication,characterization and biocompatibility of TiO2 nanotubes via anodization of Ti6Al7Nb

Ti6Al7Nb has been used as an implant material because of its good corrosion resistance and high mechanical properties. However, the presence of aluminium (Al), which may lead to ostemalacia, anaemia and nervous system disorders, limited its wide clinical use. In this study, a titanium oxide (TiO₂) nanoporous layer was fabricated on a Ti6Al7Nb alloy using an electrochemical anodic oxidation method. The structure of the TiO₂ nanoporous layer was examined by scanning electron microscopy. The chemical compositions of the samples were analysed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by culturing rat osteoblast cells. The result showed that TiO₂ nanoporous layers comprise a mixed oxide containing TiO₂ and a small amount of nobium oxides (Nb₂O₅) and almost no elemental aluminium. The outer layer of the TiO₂ nanoporous layer comprises highly ordered nanotubes and the inner layer forms disordered nanopores. The TiO₂ nanoporous layer could support the adhesion, proliferation, differentiation and gene expression of osteoblast cells. Therefore, a TiO₂ nanoporous layer could enhance the biocompatibility of Ti6Al7Nb alloy and is as a promising candidate for Ti6Al7Nb alloy implants.     

Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO2 nanotubes on Ti substrate and freestanding membrane

Highly ordered titanium oxide (TiO₂) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO₂ nanotubes on a Ti substrate and that of freestanding TiO₂ membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO₂ nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO₂ membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO₂ nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO₂ nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.     

Transparent titania nanotubes of micrometer length prepared by anodization of titanium thin film deposited on ITO

Transparent TiO₂ nanotube arrays of micrometer lengths were prepared by anodization of titanium thin film RF sputtered on indium tin oxide (ITO) which was coated on glass substrate. The sputtering process took place at elevated temperature of 500 °C. The structures of the films were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the optical properties of the films were investigated using UV-visible spectroscopy. Two types of electrolytes were used in this work: an aqueous mixture of acetic acid and HF solution and a mixture of NH₄F and water dissolved in ethylene glycol. The concentration of NH₄F, voltage and the thickness of the sputtered titanium film were varied to study their effect on the formation of TiO₂ nanotube arrays. It is demonstrated in this work that the nanoporous layer is formed on top of the ordered array of TiO₂ nanotubes. Furthermore, the optical transmittance of TiO₂ nanotubes annealed at 450 °C is much lower than the non annealed TiO₂ nanotubes in the visible wavelength region.     

Biomimetic Ca-P coating on pre-calcified Ti plates by electrodeposition method

A new electrodeposition method was presented for Ca-P coating on pre-calcified titanium (PTi) plates at room temperature. The biomimetic coating morphology was investigated by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) results indicated that the functional TiO_x layer with groups of -Ca and -OH was formed on PTi surface after pre-calcified chemical treatment. The TiO_x layer showed a lower water contact angle and lower surface energy than those of pure titanium surfaces, and the PTi surface natures are benefited by coupling biomimetic Ca-P layer with bioactivity in the electrodeposition process. Moreover, the crystallization of Ca-P precipitate and the bond strength of coating to PTi substrates were improved significantly by post-treatments. Our results suggest this new coating process and its subsequent application to biomedical implant devices.     

Influence of annealing on the structure of nanoporous oxide films on the surface of titanium‒aluminum powder alloy

Oxide films obtained during anodization of Ti?40% Al sintered powder samples in fluorine-containing electrolytes are investigated. With scanning electron microscopy and X-ray phase analysis, it is demonstrated that an X-ray amorphous nanoporous anodic oxide film is formed on the surface of the powder microparticles under optimal anodization conditions. After annealing at T = 1093 K in air and vacuum (10^?2 Pa), the oxide films are revealed to crystallize with its regular porous structure retained. The composition of the polycrystalline anodic-oxide films annealed in air is a mixture involving TiO₂ (anatase and rutile) and α- and γ-Al₂O₃ phases and Ti₂O₃ and Al₂TiO₅ traces. The vacuum annealing process makes it possible to identify TiO₂, in which anatase is the main phase, α- and γ-Al₂O₃, and Ti₂O₃ and TiO traces. However, rutile is not revealed. The presented results indicate that the application of the anodic nanostructuring of Ti?40% Al powders is promising for the obtainment of new photocatalytic active nanomaterials.     

A study on photo-generated charges property in highly ordered TiO2 nanotube arrays

In this study TiO₂ nanotube arrays were fabricated by potentiostatic anodization of titanium sheet. The X-ray diffraction (XRD) pattern and field emission scanning electron microscopy (FE-SEM) image indicated the TiO₂ nanotube arrays were of pure anatase form and highly ordered. The properties of the photo-generated charges in the nanotube arrays were investigated by transient photovoltage (TPV) technique and surface photovoltage (SPV) technique based on lock-in amplifier with dc bias, in comparison with the commercial powder derived film. The separation processes of the photo-induced charges in the system of TiO₂ nanotubes on Ti have been demonstrated to be correlated with the incident light intensity, surface trapping states, and the interfacial electric field between Ti and TiO₂. The results also show that the highly ordered nanotube film could generate much stronger SPV responses under external electric field than the commercial powder derived film.     

The effect of pre-pattern on the morphology and growth speed of TiO2 nanotube

In this work, we presented a new method which directly acts on the surface of the Ti sheet by mechanical micro-etching using a grating ruling engine. The effect of the pre-pattern on the morphology and growth speed of TiO₂ nanostructure formed on the Ti sheet with the traditional anodization method was investigated. A novel wall structure was observed and the growth speed of TiO₂ nanotube (NT) was greatly affected by the pre-pattern. The wall structure increases the surface-to-volume ratio of the nanotube arrays. The new method provided the possibility of further optimization of fast growth of TiO₂ nanostructure and improving the efficiency of dye-sensitized solar cell (DSSC) and photocatalysis.     

Effect of crystallographic orientation on the anodic formation of nanoscale pores/tubes in TiO2 films

Self-organized nanopores and nanotubes have been produced in thin films of titanium (Ti) prepared using filtered cathodic vacuum arc (FCVA), DC- and RF-sputter deposition systems. The anodization process was performed using a neutral electrolyte containing fluoride ions with an applied potential between 2 and 20 V (for clarity the results are only presented for 5 V). Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques were used to characterise the films. It was found that the crystallographic orientation of the Ti films played a significant role in determining whether pores or tubes were formed during the anodic etching process.     

Photoemission investigations on nanostructured TiO2 grown by cluster assembling

Nanostructured titanium dioxide (ns-TiO₂) films were grown by supersonic cluster beam deposition method. Transmission electron microscopy demonstrated that films are mainly composed by TiO₂ nanocrystals embedded in an amorphous TiO₂ phase while their electronic structure was studied by photoemission spectroscopy. The cluster assembled ns-TiO₂ films are expected to exhibit several structural and chemical defects owing to the large surface to volume ratio of the deposited clusters. Ultraviolet photoemission spectra (hv = 50 eV) from the valence band unveil the presence of a restrained amount of surface Ti 3d defect states in the band gap, whereas Ti 2p core level X-ray photoelectron (hv = 630 eV) spectra do not manifestly disclose these defects.     

A microstructural study of the structure of plasma electrolytically oxidized titanium foils

The structure and distribution of TiO₂ rutile and anatase phases of anodized titanium foil, subjected to a special high-voltage electrochemical preparation technique, are reported. We applied X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy on samples that were oxidized for various times. Combining data from the different techniques led to a model in which the initially formed porous, micrometer-thick TiO₂ layer, consisting in a large part of anatase, is transformed into rutile. The result is a porous rutile layer on top of anatase, which is in direct contact with the Ti metal. The first structural model is derived from the evaluated data and the phenomena that occurred during preparation are clarified.     

不同晶相结构和形貌TiO2负载Ru催化剂的CO选择甲烷化

用水热法得到的钛酸纳米纤维前体,通过不同后处理方法合成了多种纳米结构的TiO₂．采用N₂等温吸附和BET比表面、X射线衍射、透射电镜和能量分散X射线分析表征了TiO₂及负载Ru催化剂的微结构,包括比表面、晶相结构和形貌以及Ru纳米颗粒尺寸分布等．对负载Ru催化剂在富氢条件下CO选择甲烷化反应活性测试表明：金红石相TiO₂和TiO₂-B为载体负载的Ru催化剂比锐钛矿相TiO₂负载的Ru催化剂表现出更高的反应性能．其活性区别说明了不同晶相结构和形貌TiO₂载体与Ru纳米颗粒的相互作用存在差异．     

Investigation of the growth and local stoichiometric point group symmetry of titania nanotubes during potentiostatic anodization of titanium in phosphate electrolytes

Potentiostatic anodization of commercially pure, 50 µm-thick titanium (Ti) foil was performed in aqueous, phosphate electrolytes at increasing experimental timeframes at a fixed applied potential for the synthesis of titania nanotube arrays (TNAs). High resolution scanning electron microscopy images, combined with energy dispersive spectroscopy and x-ray diffraction spectra reveal that anodization of the Ti foil in a 1 M NaF+0.5 M H₃PO₄ electrolyte for 4 h yields a titanate surface with pore diameters ranging between 100 and 500 nm. The presence of rods on the Ti foil surface with lengths exceeding 20 µm and containing high concentrations of phosphor on the exterior was also detected at these conditions, along with micro-sized coral reef-like titanate balls. We propose that the formation of these structures play a major role during the anodization process and impedes nanotube growth during the anodization process. High spatially resolved scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) performed along the length of a single anodized TiO₂ nanotube reveals a gradual evolution of the nanotube crystallinity, from a rutile-rich bottom to a predominantly anatase TiO₂ structure along its length.     

Effect of iron doping on the hydrophobicity of titanium dioxide film: experiment and simulation

In this study, we carried out experiments and molecular dynamics simulations to identify the effect of Fe doping on the hydrophobicity of a titanium dioxide film. TiO₂ and Fe-doped TiO₂ films were fabricated in situ by atomic layer deposition without annealing. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterise the crystal structure and elemental composition. Iron doping resulted in the TiO₂ becoming more hydrophobic at a macroscopic level, as estimated by atomic force microscopy observations and static contact angle measurements. Furthermore, the effect of iron doping on the structure and kinetics of water molecules on the exterior of TiO₂ were studied by molecular dynamics simulations. On the basis of the XPS results, the Fe-TiO₂ surface matrix has a Ti:Fe ratio of 36:5. In addition, the density distribution of oxygen and hydrogen atoms indicate that interfacial water molecules enter the Fe-TiO₂ film more easily and hydrogen atoms in the water molecules are oriented upward at the interface. The self-diffusion coefficients indicate that iron doping makes the TiO₂ more hydrophobic, which is consistent with the macroscopic test results.     

Comparison of surface films formed on titanium by pulsed Nd:YAG laser irradiation at different powers and wavelengths in nitrogen atmosphere

The nitridation of titanium (Ti) caused by a Q-switched Nd:YAG laser under nitrogen gas atmosphere was investigated in situ using X-ray photoelectron spectroscopy (XPS). A laser having a wavelength of 1064 nm and 532 nm (SHG mode) was irradiated on a titanium substrate in an atmosphere-controlled chamber, and the substrate was then transported to an XPS analysis chamber without exposing it to air. The characteristics of the surface layer strongly depend on the laser power. When the power is relatively low, a titanium dioxide layer containing a small amount of nitrogen is formed on the substrate. Laser irradiation beyond a certain laser power is required to obtain a stoichiometric titanium nitride (TiN) layer. A TiN layer and an oxynitride layer with a TiO_xN_y-like structure are formed as the topmost and the lower surface layer, respectively, when the laser power exceeds this threshold value. The threshold laser power strongly depends on the wavelength of the laser, and this threshold value for the 532-nm laser is quite lower than that for the 1064-nm laser.     

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Low temperature deposition and characterization of TiO2 photocatalytic film through cold spray

Cold spray was employed as a novel low temperature approach to deposit titanium dioxide (TiO₂) photocatalytic film. The film microstructure was characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic performance was examined through acetaldehyde degradation under ultraviolet illumination. Results showed that TiO₂ film was successfully deposited on substrate surface through cold spray. The film thickness reached up to 15 μm. The film presented a rough surface and porous structure. Owing to the low temperature of spray powder, no phase and particle size changes occurred to TiO₂ during deposition. It was found that the cold-sprayed TiO₂ film was active for photodegradation of acetaldehyde.     

Surface modification of pure titanium by hydroxyapatite-containing composite coatings

Micro-arc oxidation (MAO) is commonly applied to modify the surface of titanium (Ti)-based medical implants with a bioactive and porous Ti oxide (TiO₂) coating. The study reports a new method of incorporating hydroxyapatite (HA) within the TiO₂ coating by MAO and alkali heat treatment (AHT) in the solution containing Ca ion and P ion. The morphology, composition and phase composition of the coatings were analyzed with scanning electron microscopy with energy-dispersive X-ray spectrometer and X-ray diffraction. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in the tapping mode. The results showed that TiO₂-based coatings were obtained on pure Ti by MAO with an electrolyte containing Ca ion and P ion; the prepared MAO coatings were mainly composed of Ca, P, O and Ti. AHT transformed Ca and P to HA crystals. In conclusion, the TiO₂/HA composite coatings can be obtained on the surface of pure Ti by MAO and AHT, and the addition of Ca ion and P ion to the AHT solution contributed to the formation of HA.     

Preparation and electrochemical performances of nanoporous/cracked cobalt oxide layer for supercapacitors

Nanoporous/cracked structures of cobalt oxide (Co₃O₄) electrodes were successfully fabricated by electroplating of zinc–cobalt onto previously formed TiO₂ nanotubes by anodizing of titanium, leaching of zinc in a concentrated alkaline solution and followed by drying and annealing at 400 °C. The structure and morphology of the obtained Co₃O₄ electrodes were characterized by X-ray diffraction, EDX analysis and scanning electron microscopy. The results showed that the obtained Co₃O₄ electrodes were composed of the nanoporous/cracked structures with an average pore size of about 100 nm. The electrochemical capacitive behaviors of the nanoporous Co₃O₄ electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in 1 M NaOH solution. The electrochemical data demonstrated that the electrodes display good capacitive behavior with a specific capacitance of 430 F g^?1 at a current density of 1.0 A g^?1 and specific capacitance retention of ca. 80 % after 10 days of being used in electrochemical experiments, indicating to be promising electroactive materials for supercapacitors. Furthermore, in comparison with electrodes prepared by simple cathodic deposition of cobalt onto TiO₂ nanotubes(without dealloying procedure), the impedance studies showed improved performances likely due to nanoporous/cracked structures of electrodes fabricated by dealloying of zinc, which provide fast ion and electron transfer routes and large reaction surface area with the ensued fast reaction kinetics.     

Surface phenomena in the process of titanium hydride formation

Surface phenomena which occur in the course of titanium hydride TiH_x formation during the H₂ interaction with thin Ti films deposited in situ under UHV conditions were studied by means of surface potential and pressure measurements. The elementary steps of this process were distinguished and described.     

Surface characteristics of Zinc–TiO2 coatings prepared via micro-arc oxidation

Titanium (Ti) and its alloys are widely used as metallic biomaterials for fabrication of dental and orthopedic implants due to their favorable biocompatibility and corrosion resistance in a body environment. However, the thin oxide layer (TiO₂) on Ti substrate formed naturally in air or in many aqueous environments is bioinert and surrounded by fibrous tissues without producing any chemical or biological bond to bone when implanted. In the present work, Zinc-incorporated porous TiO₂ coatings (Zn–TiO₂) were prepared on Ti substrate by micro-arc oxidation (MAO) technique in the zinc gluconate-containing electrolyte. The surface morphology, cross-sectional morphology, composition, and phase of the coatings were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, respectively. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in tapping mode. The results showed that Zn was successfully incorporated into the porous TiO₂ coatings, which did not alter apparently its surface topography and phase composition. In conclusion, the formation of porous Zn–TiO₂ coatings endow Ti with potential bioactivity and antibacterial activity, and we believe that the porous Zn–TiO₂ coatings on Ti by MAO technique might be promising candidates for orthopedic and dental implants