TiO2纳米管的研究进展

TiO2纳米管由于其新奇的光电、催化、气敏等性能而引起广泛的关注,在太阳能电池、光催化、环境净化、气体传感器等领域有潜在的应用价值.主要综述了TiO2纳米管的最新研究进展情况以及发展现状,介绍了其制备方法、形貌、晶体结构、形成机理及应用前景.     

Diameter controlled chemical vapor deposition synthesis of single-walled carbon nanotubes

In this study, we systematically investigated the influence of catalyst preparation procedures on the mean diameter of single-walled carbon nanotubes (SWNTs) synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) process. It was found that the SWNT diameter is dependent upon both reduction temperature and time, with lower reduction temperature and/or shorter reduction time resulting in smaller diameter SWNTs. The morphology of the SWNTs also changed from vertically aligned to randomly oriented when the reduction temperature was below 500 degrees C. We also found that introducing a small amount of water during the catalyst reduction stage significantly decreased the mean diameter of the SWNTs. Lastly, we report on the use of a new binary catalyst system in which rhodium was combined with cobalt. This new Co/Rh combination produced SWNTs of smaller diameter than the conventional Co/Mo catalyst.     

Vapor sensing performances of PVDF nanocomposites containing titanium dioxide nanotubes decorated multi-walled carbon nanotubes

Inorganic nanocarbon hybrid materials are good alternatives for superior electrochemical performance and specific capacitance to their traditional counterparts. Nanocarbons act as a good template for the growth of metal nanoparticles on it and their hybrid combinations enhance the charge transport and rate capability of electrochemical materials without sacrificing the specific capacity. In this study, titanium dioxide nanotubes (TNT) are synthesized hydrothermally in the presence of multi-walled carbon nanotubes (MWCNT) where the latter acts as base template material for the metal oxide nanotube growth. The MWCNT–TNT hybrid material possesses very high dielectric strength and this is used to enhance the dielectric property of the polymer polyvinyledene fluoride (PVDF). Solution mixing was used to prepare the PVDF/MWCNT–TNT nanocomposites by varying the filler concentrations from 0.5 to 2.5 wt%. Excellent vapor sensing was noticed for the PVDF nanocomposites with different rate of response towards commonly used laboratory solvents. The composites and the fillers were characterized for its morphology and structural properties using scanning and transmission electron microscopy, X-ray diffraction studies and infrared spectroscopy. Vapor sensing was measured as relative resistance variations against the solvent vapors, and the dielectric properties of the composites were measured at room temperature during the frequency 10²–10⁷ Hz. Experimental results revealed the influence of filler synergy on the properties of PVDF and the enhancement in the solvent vapor detectability and dielectric properties reflects the ability of these composite films in flexible vapor sensors and in energy storage.     

碳纳米管表面涂覆钛的新方法(英文)

采用TiCl4水解法对表面酸功能化的碳纳米管(CNTs)进行TiO2涂层,然后通过程序升温还原(TPR),使TiO2涂层转变为Ti涂层。利用SEM、TEM、XRD和EDAX对CNTs、CNT/TiO2纳米复合材料和Ti涂层CNTs进行表征。结果表明:超声波酸功能化CNTs后,可将TiO2成功地涂覆于CNTs表面;在850℃下、H2/Ar氛围中,通过TPR可将TiO2涂层还原为金属Ti涂层。该Ti涂层对CNTs和其他金属形成复合材料非常重要。     

Electrochemical deposition of iron nanoneedles on titanium oxide nanotubes

Iron as a catalyst has wide applications for hydrogen generation from ammonia, photodecomposition of organics, and carbon nanotube growth. Tuning the size and shape of iron is meaningful for improving the catalysis efficiency. It is the objective of this work to prepare nanostructured iron with high surface area via electrochemical deposition. Iron nanoneedles were successfully electrodeposited on Ti supported TiO₂ nanotube arrays in a chlorine-based electrolyte containing 0.15 M FeCl₂·4H₂O and 2.0 M HCl. Transmission electron microscopic analysis reveals that the average length of the nanoneedles is about 200 nm and the thickness is about 10 nm. It has been found that a high overpotential at the cathode made of Ti/TiO₂ nanotube arrays is necessary for the formation of the nanoneedles. Cyclic voltammetry test indicates that the electrodeposition of iron nanoneedles is a concentration-limited process.     

Conversion of potassium titanate nanowires into titanium oxynitride nanotubes

Tunnel-structured potassium titanate with a K(3)Ti(8)O(17) phase was synthesized by direct oxidation of titanium powder mixed with KF(aq) in water vapor at 923 K. The reaction conditions were adjusted so that uniform single crystalline potassium titanate nanowires with [010] growth direction (length: 5-30 μm, diameter: 80-100 nm) were obtained. Nitridation of the nanowires by NH(3)(g) at 973-1073 K converted the titanate nanowires into rock-salt structured cubic phase single crystalline titanium oxynitride TiN(x)O(y) nanotubes (x = 0.88, y = 0.12, length = 1-10 μm, diameter = 150-250 nm, wall thickness = 30 - 50 nm) and nanorods (x = 0.5, y = 0.5, length = 1-5 μm, diameter = 100-200 nm) with rough surfaces and [200] growth direction. The overall conversion of the titanate nanowires into the nanotubes and the nanorods can be rationalized by Ostwald ripening mechanism. We fabricated an electrode by adhering TiN(x)O(y) nanotubes (0.2 mg) on a screen-printed carbon electrode (geometric area: 0.2 cm(2)). Electrochemical impedance spectroscopy demonstrated its charge transfer resistance to be 20Ω. The electrochemical surface area of the nanotubes on the electrode was characterized by cyclic voltammetry to be 0.32 cm(2). This property suggests that the TiN(x)O(y) nanostructures can be employed as potential electrode materials for electrochemical applications.     

Hydroxyapatite growth on multiwall carbon nanotubes grown on titanium fibers from a titanium sheet

Nano-hydroxyapatite (HA) was grown on functionalized multiwalled carbon nanotubes (MWCNTs) deposited on TiO₂ nanofibers (NFs) that were hydrothermally grown on Ti metal sheets. The HA was electrochemically grown on the MWCNTs/TiO₂ porous layer. It was found that the HA grows on the MWCNTs/TiO₂ NFs in the form of dense coating with nanorice grain-shaped. The incorporation of MWCNTs between HA and TiO₂ NFs has led to higher adhesion strength as measured by micro-scratching test indicating the benefit of MWCNTs on the improving the bonding strength of HA layer. The obtained coatings exhibit excellent corrosion resistance in simulated body fluid. It is expected that this simple route for preparing the new HA/MWCNTs/TiO₂/Ti-layered structure might be used not only in the biomedical field, but also in catalysis and biological sensing among others.     

Enhanced electron emission from titanium coated multiwalled carbon nanotubes

Enhanced field emission properties and improved crystallinity of titanium (Ti) coated multiwalled carbon nanotubes (MWCNTs), prepared by microwave plasma enhanced chemical vapour deposition have been observed. Ti films of extremely low thicknesses (0.5 nm, 1.0 nm and 1.5 nm) were coated over carbon nanotubes (CNTs) and their field emission behaviour was investigated. The turn on field of Ti coated CNTs was found to be low (~ 0.8 V/μm) as compared to pristine CNTs (~ 1.8 V/μm). The field enhancement factor for Ti coated CNTs was quite large (~ 1.14 × 10⁴) as compared to pristine CNTs (~ 6 × 10³). This enhancement in electron emission is attributed to the passivation of defects and improved crystallinity of CNTs. Surface morphological and microstructural studies were carried out to investigate the growth of pristine and Ti coated CNTs. It was observed that Ti nanoclusters adsorb on the edges of MWCNTs and increase their crystallinity. This increase is directly correlated with the thickness of Ti film deposited. Micro Raman spectroscopy confirmed the improved crystallanity of Ti coated CNTs.     

Synthesis and characterization of copper ions surface-doped titanium dioxide nanotubes

Copper ions surface-doped titanium dioxide nanotubes were prepared via an assembly process based on the reactions between Cu(NH₂CH₂CH₂NH₂)₂(OH)₂ and hydroxide radicals on the surface of TiO₂ nanotubes, followed by the heat treatment in air at 723 K. The as-prepared samples were characterized with infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and fluorescence spectroscopy (FL). The photocatalytic activity of the copper ions surface-doped titanium dioxide nanotubes was investigated by photodegradation of Rhodamine B. The results showed that copper ions were successfully introduced onto the surface of TiO₂ nanotubes. And two kinds of copper species of Cu(I) and Cu(II) were found on TiO₂ surface. Copper ions act as electron trappers facilitating the separation of electrons and holes on the surface of TiO₂ nanotubes, which allows more efficiency for the photodegradation of Rhodamine B.     

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.     

Fabrication of mesoporous titanium oxide nanotubes based on layer-by-layer assembly

Titanium oxide (TiO2)/polyacrylic acid (PAA) composite nanotubes were firstly fabricated through the sol-gel process of titanium alkoxide in the inner pores of alumina template followed layer-by-layer assembly with polyacrylic acid (PAA). Mesoporous TiO2 nanotubes could be obtained after the removal of PAA component by calcination and etching of the template with concentrated sodium hydroxide aqueous solution. The surface area of as-prepared porous TiO2 nanotubes was measured as twice larger than that of the conventional TiO2 nanotubes and the pore diameter in the wall of the tubes is several nanometers. Such assembled mesoporous nanotubes can serve as carriers for catalysis release and biomolecules.     

Hierarchical flower-like titanium phosphate derived from H-titanate nanotubes for photocatalysis

Nanosheet-assembled hierarchical flower-like titanium phosphate (TiP) is synthesized via hydrothermal treatment of H-titanate nanotubes (Ti-NT) at the optimized conditions of 0.1 M of H₃PO₄ and hydrothermal temperature of 130 °C. A possible formation mechanism for the TiP flowers, involving the disintegration of Ti-NT and the growth and assembling of TiP nanosheets, is proposed. The main compositions of the uncalcined TiP flowers are titanium hydrogen phosphate hydrates (Ti(HPO₄)₂·xH₂O), which can be transformed to titanium phosphate (TiP₂O₇) after high temperature calcination. The photocatalytic activity of the prepared TiP flowers is increased with the increased calcination temperature, which may be attributed to the better photocatalytic activity of TiP₂O₇ than Ti(HPO₄)₂·xH₂O and the increased crystallization of TiP₂O₇.     

Biocompatibility of multi-walled carbon nanotubes grown on titanium and silicon surfaces

Cell adhesion and cell viability of aligned multi-walled carbon nanotube (MWCNT) films were verified using Fibroblast L929 mouse cells. The MWCNTs were produced by a microwave plasma chemical vapor deposition (2.45 GHz) on silicon (Si), with a nickel catalyst, and titanium (Ti), with an iron catalyst. MTT assay and cellular adhesion were used for biocompatibility tests (ISO 10993-5). The results show very high cell viability and many layers of cells adhered on the surface formed by the nanotube tips at films grown on silicon surfaces. The MWCNT grown on Ti surfaces presented lower cell viability and a reduced number of cells on the surface formed by the nanotube tips. The different behavior is most probably related to excess iron contamination present in the case of titanium substrate, while nickel catalyst is probably enclosed by the nanotubes.     

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.     

The multi-staged formation process of titanium oxide nanotubes and its thermal stability

The multi-staged formation process of titanium oxide nanotubes was investigated in detail under a hydrothermal treatment. During the synthesis procedure, an intermediate stage (tree-like structures) was observed before the formation of the titanium oxide layered structures. The layered structure of titanium oxide generally was considered to exfoliate directly from raw TiO₂ materials through the alkaline hydrothermal treatment. The rolling process of the layered structures of titanium oxide was confirmed by TEM observation after the alkaline hydrothermal treatment for the raw TiO₂ materials, followed by washing with 4 M HNO₃ aqueous solution. The thermal stability of the tube products was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that both the morphology and crystal phase of titanium oxide nanotubes could be retained even after calcination at 650 °C.     

TiO2纳米管晶型对钛生物活性的影响

利用阳极氧化法在HF电解液体系中制备了高有序TiO2纳米管。样品分别在400和600℃下热处理后,得到锐钛矿和金红石两种晶型的TiO2纳米管。对样品进行了表征,将样品浸泡于模拟体液中,观察表面HA沉积情况,并进行体外细胞毒性实验以探讨样品的生物相容性。结果发现,400和600℃退火处理的纳米管样品生物活性高于未退火处理样品,400℃退火处理纳米管活性高于600℃退火处理纳米管。由于不同后处理条件下制备的纳米管形貌相似,仅为晶型不同,故推断出锐钛矿型TiO2生物活性最好,金红石型TiO2次之,无定型TiO2生物活性相对最差。     

Diameter dependent growth mode of carbon nanotubes on nanoporous SiO2 substrates

Two different growth modes of carbon nanotubes (CNTs) are identified in ethylene chemical vapour deposition (CVD) using SiO₂ as support. With a series of electron microscopy observations, we have found that small-diameter nanotubes favor a root-growth mechanism on nanoporous SiO₂ support, while nanotubes with larger diameters prefer a tip-growth. The dependence of growth mode on tube diameter is explained in terms of the porosity of the support and the size distribution of the catalyst. Our results provide clues to control growth of CNTs and obtain well-organized nanotube structures.     

Powder metallurgy titanium metal matrix composites reinforced with carbon nanotubes and graphite

Carbon nanotubes (VGCF) and graphite (Gr) reinforced Ti metal matrix composites (TiMMCs) were prepared via powder metallurgy. 0–0.4 wt% VGCF/Gr and Ti mixture powders were prepared by rocking mill. The as-premixed powders were consolidated at 1073 K using spark plasma sintering (SPS). Hot extrusion was performed at 1273 K with an extrusion ratio of 37:1. Microstructures and mechanical properties of the as-extruded Ti composites were investigated to evaluate strengthening effects of VGCF/Gr on Ti matrix. Mechanical strength of Ti–VGCF/Gr composites was augmented when VGCF/Gr contents were increased from 0.1 to 0.4 wt%. Yield strength (YS) and ultimate tensile strength (UTS) of Ti-0.4 wt% VGCF composites were increased 40.4% and 11.4% as compared to pure Ti, while those values were 30.5% and 2.1% for Ti–0.4 wt% Gr. The strengthening mechanism including grain refinement, carbon solid solution strengthening and TiC/carbon dispersion strengthening was discussed in detail.