Photocatalytic,phosphorus-doped,anatase oxide layers applicable to titanium implant alloys

Titanium alloys provide excellent corrosion resistance and favorable mechanical properties well suited for a variety of biomaterial applications. The native oxide surface on titanium alloys has been shown to be less than ideal and surface modification is often needed. Previously, an optimized anodization process was shown to form a porous phosphorus-enhanced anatase oxide layer on commercially pure Ti grade 4. The anodized layer was shown to improve osseointegration and to reduce bacteria attachment when photocatalytically activated with UVA preillumination. The primary objective of the present study was to create a similar phosphorus-enhanced anatase oxide layer on series of titanium alloys including commercially pure Ti grade 4, Ti-6Al-7Nb, Ti-6Al-4V ELI, alpha + beta Ti-15Mo, beta Ti-15Mo, and Ti-35Nb-7Zr-5Ta. Phosphorus-enhanced anatase oxide layers were formed on each titanium substrate. Anatase formation was shown to generally increase with oxide thickness, except on substrate alloys containing niobium. Phosphorus uptake was shown to be dependent on the titanium alloy chemistry or microstructure. Anodized layers formed on beta-structured titanium alloys revealed the lowest phosphorus uptake and the most nanosized surface porosity. A methylene blue degradation assay showed anodized layers on commercially pure Ti and both Ti-15Mo alloys to exhibit the highest levels of photocatalytic activity. Given the range of mechanical properties available with the commercially pure Ti and Ti-15Mo alloys, the results of this study indicate the benefits of phosphorus-enhanced anatase oxide coatings may be applicable to a wide variety of biomaterial applications.     

Effect of surface finishing on the formation of nanostructure and corrosion behavior of Ni–Ti alloy

In the present work, we have investigated the formation of nanostructured oxide layers by anodic oxidation on different surface finished (mirror finished, 600 and 400 grit polished) nickel–titanium alloy (Ni–Ti) in electrolyte solution containing ethylene glycol and NH₄F_. The anodized surface has been characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X‐ray photoelectron spectroscopy (XPS). The corrosion behaviors of the Ni–Ti substrate and anodized samples have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks' solution). The results show that the native oxide on the substrate is replaced by nanostructures through anodization process. XPS of Ni–Ti substrate shows the presence of Ni⁰, NiO, Ti⁰ and TiO₂ species, whereas Ni₂O₃ and Ni(OH)₂ and TiO₂ are observed in the samples after anodization. Corrosion resistance of the anodized sample is comparable with that of the untreated sample. Copyright © 2016 John Wiley & Sons, Ltd.     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface modification of titanium by anodic oxidation in phosphoric acid at low potentials. Part 2. In vitro and in vivo study

Electrochemical studies in SBF solution were performed, in order to determine the best corrosion resistance condition, comparing as‐received titanium, covered with its native surface oxide, and titanium anodized in phosphoric acid. The results indicate that the anodic films obtained at a constant potential of 30 V have higher barrier effect, and the protective layer remains effective against the aggressive anions present in SBF after 30 days of immersion. Due to the promising corrosion performance in simulated biological media coupled with the biocompatible surface characteristics, anodic films on titanium obtained at 30 V were implanted on Wistar Rats to compare the osseointegration results of this modified surface with that corresponding to as‐received titanium. It was found that, after 8 weeks of implantation, although the amount of bone surrounding the implant did not differ across the two different surface implants conditions, bone formation at the implant interface was found to be more homogeneous in anodized titanium. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation of RGO/TiO2 photocatalyst and the mechanism of its hydrothermal process

To improve the catalytic efficiency of nanotitanium dioxide, this research investigated the phase transformation, crystal growth, and hydrogen production efficiency of nanotitanium dioxide at different temperatures and pressures. The RGO/TiO₂ photocatalyst was prepared by a hydrothermal method using graphene oxide and butyl titanate as raw materials. Different types of photocatalyst samples were prepared by adjusting the reaction temperature and time in the hydrothermal process. X‐ray diffraction and transmission electron microscope techniques were employed to investigate the nucleation and growth processes of rutile and anatase in the hydrothermal process from the perspectives of thermodynamics and kinetics. The evolution of the titanium dioxide structure with hydrothermal temperature and hydrothermal time was analyzed. Finally, photocatalytic decomposition of water data shows that the photocatalyst with the best hydrogen production effect was obtained by 12 hr of hydrothermal treatment at a hydrothermal temperature of 180°C. The total hydrogen production of this sample was 0.037 mmol/g under a xenon lamp for 3 hr.     

水热处理锐钛矿TiO2纳米管阵列及其增强的光电催化活性

在含氟溶液中,通过电化学阳极氧化钛片成功制备了高度有序的TiO2纳米管阵列,先在450℃下煅烧使其晶化为锐钛矿相,再在不同温度下水热处理了这些锐钛矿阵列。用XRD、SEM和XPS表征了所制备的样品。通过在氙灯光照下光电催化降解对氯苯酚水溶液来检测样品的活性。以对苯二甲酸作为探测分子,用荧光光谱检测了在氙灯光光照下样品表面产生的羟基自由基(.OH)。通过线性伏安扫描的间隙光照实验,测定了样品的光电流响应。结果表明后水热处理对锐钛矿TiO2纳米管阵列的结晶度和形貌没有影响,但光电催化活性明显增强,而不同温度处理的样品的活性差别不大。水热处理后的TiO2纳米管阵列的光电催化活性增强的原因是,水热后TiO2纳米管阵列表面羟基含量明显增加,使得其在光电催化过程中生成的.OH增加。     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

Electrochemically induced anatase inhibits bacterial colonization on Titanium Grade 2 and Ti6Al4V alloy for dental and orthopedic devices

Bacterial contamination of implanted devices is a common cause of their failure. The aim of the present study was to assess the capability of electrochemical procedures to: (a) promote the formation of anatase on the surface of commercially pure Grade 2 Ti and Ti Grade 5 (Ti6Al4V) alloy; (b) inhibit in vitro biofilm formation of Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans and Porphyromonas gingivalis and oral plaque in vivo, (c) preserve favorable response of osteoblasts and fibroblasts to materials surfaces. Ti Grade 2 and Ti Grade 5 were respectively anodized at two different voltages: 90 and 130V for pure titanium; 100 and 120V for Ti6Al4V alloy. Surface characterization was performed by scanning electron microscopy (SEM) equipped with EDS probe, laser profilometry and X-ray diffractometry. Bacterial adhesion characterization was performed either in vitro and in vivo in patients. Osteoblast and fibroblast response was evaluated by metabolic activity assessment. The higher voltage applied in the anodization treatment of pure titanium (130V) and Ti6Al4V alloy (120V) surfaces, compared to the untreated pure titanium and Ti6Al4V and to lower voltage treatments, resulted in a greater decrease in bacterial attachment and biofilm formation in both in vitro and in vivo experiments. In contrast, the high voltage treatments were found to promote osteoblasts and fibroblasts proliferation. The observations indicated that the experimented high voltage anodization treatments may contribute to preserve the tissue integration and reduce bacteria colonization of titanium and titanium alloy for implantable applications.     

Surface modification of titanium by anodic oxidation in phosphoric acid at low potentials. Part 1. Structure,electronic properties and thickness of the anodic films

Titanium surface characteristics determine the degree of success of permanent implants. The topography, morphology of the surface in micro and nano scales, the impurities present and other characteristics are a main concern, and therefore a multi‐technique approach is required in order to evaluate modification process effects on the surface. Surface modification of titanium in the nanometrical range was performed by means of anodisation in phosphoric with the aim of improving both the biocompatibility and the corrosion resistance in the biological media. Biocompatible characteristics of the modified titanium surface, as the presence of anatase in the oxide film and the incorporation of phosphate to the surface, were determined. Moreover, the electronic properties of the surface oxide presented a carrier number adequate for biomedical applications. The increase in the film thickness from 3 to 42 nm was estimated from EIS results when anodising potentials from 0 to 30 V were applied, whereas a bi‐layer structure of the protective oxides formed was determined. Copyright © 2013 John Wiley & Sons, Ltd.     

纳米多孔阳极氧化铁膜的形成及其形貌演变

阳极氧化法制备具有纳米多孔结构的阳极氧化铁膜因其潜在的应用价值而倍受关注。然而,在阳极氧化过程中多孔结构的形成机制至今尚不清楚。本文结合电流密度-电位响应（I-V曲线）及法拉第定律的推导,分析了形成纳米多孔阳极氧化铁膜的过程中阳极电流的组成。结果表明,离子电流（导致离子迁移形成氧化物）和电子电流（导致析出氧气）共同组成阳极电流,并且纳米多孔阳极氧化铁膜的形成与两种电流的占比相关。分段式氧化物之间的空腔以及在阳极氧化初期纳米孔道上覆盖的致密膜,表明氧气泡可能是从氧化膜内部析出。此时,阳离子和阴离子绕过作为模具的氧气泡实现传质,最终导致纳米多孔结构的形成。此外,在阳极氧化铁膜形貌演变过程中,氧气泡不断向外溢出会使表面氧化物被冲破,导致表面孔径不断增大。     

Interface stoichiometry and structure in anodic niobium pentoxide

High-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS) were performed on electrochemically anodized niobium and niobium oxide. Sintered anodes of Nb and NbO powders were anodized in 0.1 wt% H3PO4 at 10, 20, and 65 V to form surface Nb2O5 layers with an average anodization constant of 3.6 +/- 0.2 nm/V. The anode/dielectric interfaces were continuous and the dielectric layers were amorphous except for occurrences of plate-like, orthorhombic pentoxide crystallites in both anodes formed at 65 V. Using EELS stoichiometry quantification and relative chemical shifts of the Nb M4,5 ionization edge, a suboxide transition layer at the amorphous pentoxide interface on the order of 5 nm was detected in the Nb anodes, whereas no interfacial suboxide layers were detected in the NbO anodes.     

Effects of thermal treatment on hydrophilicity and corrosion resistance of Ti surface

Surface treatment of titanium (Ti) surface has been extensively studied to improve its properties for biomedical applications, including hydrophilicity, corrosion resistance, and tissue integration. In this present work, we present the effects of thermal oxidation as surface modification method on metallic titanium (Ti). The Ti foils were oxidized at 300°C, 400°C, 500°C, and 600°C under air atmosphere for 3 hours, which formed oxide layer on Ti surface. The physicochemical properties including surface chemistry, roughness, and thickness of the oxide layer were evaluated in order to investigate how these factors affected surface hydrophilicity, microhardness, and corrosion resistance properties of the Ti surface. The results revealed that surfaces of all oxidized samples were modified by formation of titanium dioxide layer, of which morphology, phase, and thickness were changed according to the oxidized temperatures. Increasing oxidation temperature led to the formation of thicker oxide layer and phase transformation of anatase to rutile. The presence of the oxide layer helped the improvement of corrosion resistance and microhardness. The most improvement in surface roughness was found in the specimens treated at 400°C, which significantly improved surface hydrophilicity. But both surface roughness and hydrophilicity reduced when oxidized at 500°C and 600°C, suggesting that hydrophilicity was dominated by the surface roughness. In addition, this surface treatment did not reduce the biocompatibility of the metallic Ti substrates against murine osteoblasts (MC3T3).     

Corrosion resistance and bioactivity of titanium after surface treatment by three different methods: ion implantation,alkaline treatment and anodic oxidation

The paper compares the effects of various surface modifications, ion implantation, alkaline treatment and anodic oxidation, upon the corrosion resistance and bioactivity of titanium. The chemical composition of the surface layers thus produced was determined by XPS, SIMS and EDS coupled with SEM. The structure of the layers was examined by TEM, and their phase composition by XRD. The corrosion resistance was determined by electrochemical methods after the samples were exposed to the test conditions for 13 h. The bioactivity of titanium was evaluated in a simulated body fluid at a temperature of 37°C after various exposure time.     

氮自掺杂暴露（001）晶面TiO2微米片的可见光光催化CO2还原性能增强

化石能源的使用可产生大量CO2,带来严重的温室效应。光催化CO2还原生产太阳燃料技术既有望缓解温室效应,又可以将低能量密度的太阳能转化为高能量密度的化学能储存起来方便使用。高效光催化材料的开发是发展光催化技术的关键。迄今,在已开发的所有半导体光催化材料中, TiO2仍是广泛研究的明星材料。在实际使用中, TiO2的光催化效率仍受限于其极弱的可见光利用率和较高的电子-空穴复合几率。近年来,越来越多的研究表明TiO2的结构与形貌特征极大地影响其光催化效率。尤其, TiO2的外露晶面设计与晶面效应研究引起了广泛关注。由于具有较高表面能和较多表面不饱和键,起初大多数理论和实验研究认为锐钛矿TiO2(001)晶面是光催化活性晶面。后来,越来越多研究表明并非锐钛矿TiO2(001)晶面的暴露比例越高其光催化活性就越高。最近,我们发现锐钛矿TiO2(001)晶面与(101)晶面在调控光催化CO2还原性能上具有良好的协同效应。密度泛函理论计算表明,锐钛矿TiO2的(001)晶面与(101)晶面的能带结构有差异,(001)晶面的导带位置相对于(101)晶面而言较高,而(101)晶面的价带位置相对于(001)晶面而言较低。基于此我们提出,具有合适比例的锐钛矿TiO2的(001)晶面与(101)晶面的交界处可以形成最佳的表面异质结或晶面异质结。表面异质结的形成导致光生电子倾向于向(101)扩散,光生空穴倾向于向(001)扩散,从而促进光生电子-空穴分离,降低光生电子-空穴复合几率。在此工作基础上,我们直接以氮化钛为原料,氢氟酸为添加剂,通过简单的水热反应一步合成了氮自掺杂的TiO2微米片。利用X射线粉末衍射、扫描电镜、X射线光电子能谱、紫外-可见漫反射光谱、氮气吸附-脱附以及电化学阻抗谱等方法手段对所制备的光催化剂进行了基本结构与理化性质表征分析,并研究了其可见光光催化CO2还原性能。电镜照片结果表明,我们所制备的氮自掺杂锐钛矿TiO2微米片的(001)晶面与(101)晶面比例分别为65%和35%。基于我们前期研究结果, TiO2微米片的(001)晶面与(101)晶面可以形成表面异质结,具有良好的电荷分离效率,这也得到了电化学阻抗谱研究结果的证明。同时,由于N的原位掺杂,所制备的TiO2微米片具有优异的可见光捕获能力。由于可见光利用效率增强与光生电子-空穴分离效率提高这两方面的综合作用,所制备的氮自掺杂TiO2微米片具有非常好的可见光光催化CO2还原制甲醇性能,比商用P25及氮掺杂TiO2纳米粒子等参考样品的可见光光催化性能更优异。研究表明,通过原位自掺杂方法与晶面设计方法相结合,可以同时改善TiO2的可见光利用效率和光生电子-空穴分离效率,优化TiO2的可见光光催化性能,这也为后续开发新型高效光催化材料提供了新思路。     

TiO2纳米管阵列光电催化氧化处理氨氮废水

用电化学阳极氧化法制备了高度有序的钛基二氧化钛纳米管阵列薄膜。用场发射扫描电镜(FE-SEM)、X射线衍射(XRD)表征样品的形貌与晶型特征。以二氧化钛纳米管阵列为光阳极,石墨为对电极,测试了不同pH值和外加偏压条件下的光电流响应和光电催化氧化降解NH4Cl水溶液(以N计,100 mg·L-1)的效率。结果表明:所制备的TiO2纳米管阵列具有锐钛矿和金红石的混晶结构,且主要晶型为锐钛矿。光电流响应的强弱与光电催化氧化效率的高低相对应,降解氨氮废水的最佳条件为pH=11,偏压为1.0 V。     

铈、锂盐对铝阳极氧化膜的协同封闭作用

研究了铈、锂盐在铝阳极氧化膜封闭处理中的协同作用.场发射扫描电镜和X射线衍射谱对铈、锂盐协同封闭前后铝阳极氧化膜形貌和结构的研究结果表明，封闭后膜表面的孔洞消失，封闭产物分布均匀，封闭后膜仍然以非晶态形式存在.根据X射线光电子能谱的结果，封闭后的膜主要由含结晶水的Al2O3及铈、锂的混合氢氧化物组成，同时膜中还含有及封闭溶液组分中的一些阴离子.电化学阻抗谱的研究结果表明铈、锂盐协同封闭能够显著提高膜的耐蚀性能.在实验结果基础上，初步认为铈、锂盐封闭是通过生成结构紧密的封闭产物填充、覆盖膜孔，从而显著提高铝阳极氧化膜的耐蚀性能.     

Low-voltage anodized TiO<Subscript>2</Subscript> nanostructures studied by alternate current electrochemical microscopy and photoelectrochemical measurements

This paper presents the characterization of TiO₂ nanostructures obtained by low-voltage anodization using alternate current electrochemical microscopy (AC-SECM) and photoelectrochemical (PEC) measurements. TiO₂ nanostructures were obtained from the exposure of titanium foils to several aqueous acidic solutions of hydrofluoric acid + phosphoric acid at potentials of 1 to 3 V. Scanning electron microscopy, X ray diffraction, and atomic force microscopy studies evidence the formation of a thin porous amorphous layer (<600 nm) with pore size in the range of 200–1,000 nm. By AC-SECM studies at different bias, we were able to confirm the unambiguous semiconducting properties of as-obtained porous titania films, as well as differences in surface roughness and conductivity in specimens obtained at both potentials. The difference in conductivity persists in air annealed samples, as demonstrated by electrochemical impedance spectroscopy and PEC measurements. Specimens obtained at 3 V show lower photocurrent and dark current than those obtained at 1 V, regardless of their larger conductivity, and we proposed it is due to differences on the oxide layer formed at the pore bottom.     

Formation Mechanistism Study of TiO2 Film Comprising Nanotubes and Nanoparticles

A novel titanium dioxide (TiO₂) film comprising both nanotubes and nanopaticles was fab-ricated by an anodization process of the modified titanium. The local electric field at the anodized surface was simulated and its influence on the morphology of the TiO₂ film was discussed. The results show that the electric field strength is enhanced by the covering. The growth rate of TiO₂ increases with the assist of the local electric field. However, TiO₂ dis-solution is hindered since the local electric field prevents [TiF₆]^6- from diffusing. It means that the balance condition for the formation of nanotubes is broken, and TiO₂ nanoparticles are formed. Moreover, the crystal structure of the TiO₂ film was confirmed using X-ray diffraction and Raman analysis. The anatase is a main phase for the proposed film.     

Modification of titanium phosphate precipitated from titanylsulfate

The titanium phosphate-synthesized sol–gel method was subjected to the mechanochemical treatment in a planetary ball mill Pulverisette 6 in air or water environment or the hydrothermal treatment at 873 K or 1073 K. The properties of such modified/treated samples were examined using the XRF, XRD, TGA, static light scattering, FTIR Raman and adsorption/desorption of N₂ methods. The mechanochemical treatment of xerogel samples leads to a small decrease in water contents in the sample, but the structure remains amorphous. Additionally, during milling of the sample aggregation of titanium phosphate particles and a decrease in specific surface area were observed. The hydrothermal treatment of the xerogel sample leads to a crystal product composed of titanium oxide phosphate hydrate, titanium oxide phosphate and titanium dioxide. The TGA analysis confirms the presence of titanium oxide phosphate hydrate. The hydrothermally treated titanium phosphate samples are monodispersed and have a larger specific surface area than the initial sample.