水热制备TiO2纳米管及其光催化性能

本文利用TiO₂粉体在高浓度NaOH溶液中水热反应制备TiO₂纳米管,采用X射线衍射(XRD)、扫描电镜(SEM),透射电镜(TEM),紫外可见分光光度计(UV-Vis)考察了NaOH浓度、水热反应温度、水热反应时间等因素对TiO₂纳米管结构和性能的影响。结果表明：当NaOH浓度为10mol/L,水热反应温度为160℃,水热反应时间20h时,所制备的TiO₂纳米管显示出较高的光催化活性,经紫外光照30min后,对甲基橙(MO)的降解率可达75.48%。     

Modification of TiO2 nanorods by Bi2MoO6 nanoparticles for high performance visible-light photocatalysis

In this work, TiO₂ nanorods were prepared by a hydrothermal process and then Bi₂MoO₆ nanoparticles were deposited onto the TiO₂ nanorods by a solvothermal process. The nanostructured Bi₂MoO₆/TiO₂ composites were extensively characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. The photocatalytic activity of the Bi₂MoO₆/TiO₂ composites was evaluated by degradation of methylene blue. The Bi₂MoO₆/TiO₂ composites exhibit higher catalytic activity than pure Bi₂MoO₆ and TiO₂ for degradation of methylene blue under visible light irradiation (λ > 420 nm). Further investigation revealed that the ratio of Bi₂MoO₆ to TiO₂ in the composites greatly influenced their photocatalytic activity. The experimental results indicated that the composite with Bi₂MoO₆:TiO₂ = 1:3 exhibited the highest photocatalytic activity. The enhancement mechanism of the composite catalysts was also discussed.     

Amphiphilic and photocatalytic behaviors of TiO2 nanotube arrays on Ti prepared via electrochemical oxidation

Amphiphilic TiO₂ nanotube arrays (TiO₂ NTs) were fabricated through electrochemical oxidation of Ti in solution containing H₃PO₄ and NaF. Scanning electron microscopic analysis shows that the as-prepared TiO₂ NTs have an average pore diameter of 100 nm and a wall thickness of 15 nm. The electrochemical oxidation of Ti can be divided into four stages. In the first stage, when the potential is very low, oxygen formation and Ti dissolution are the major reactions. The second stage corresponds to a slightly higher potential, but less than 2.5 V. In this stage, the formation of TiO₂ film occurs. When the potential is increased to the even higher range from 2.5 V to 6 V, the TiO₂ film dissolves and nanoporous surface structure is generated. This is the third stage. Further increase of the potential enters stage four. The high potentials cause the self-organization of the nanostructure and allow the formation of well-aligned TiO₂ NTs. We also found that the change in surface condition of Ti by annealing heat treatment affects the film dissolution kinetics. As compared with TiO₂ thin film, the TiO2 NTs show higher photocatalytic activity on decomposing Rhodamine B. The surface of the TiO₂ NTs can be wetted by both water and oil. Such an amphiphilic property comes from the capillary effect of the nanochannel structure of the TiO₂ NTs. Because of the amphiphilic property and the photocatalytic activity, we conclude that the TiO₂ NTs have the capability of self-cleaning.     

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

Improving the surface hardness and wear resistance of Ti3SiC2 by boronizing treatment

In order to modify surface properties of Ti₃SiC₂, boronizing was carried out through powder pack cementation in the 1100-1400 °C temperature range. After boronizing treatment, one mixture layer, composed of TiB₂ and β-SiC, forms on the surface of Ti₃SiC₂. The growth of the coating is processed by inward diffusion of boron and obeys a linear rule. The boronizing increases the hardness of Ti₃SiC₂ from 3.7 GPa to a maximal 9.3 GPa and also significantly improves its wear resistance.     

Nanoindentation study of the mechanical and damage behaviour of suspension plasma sprayed TiO2 coatings

TiO₂ coatings can be used as self-cleaning surfaces owing to their photocatalytic and hydrophilic properties. Suspension plasma spray (SPS) has proven to be a feasible and cheap technique for producing self-cleaning surfaces with acceptable photo-activity. This paper presents a nanoindentation study of the mechanical properties (hardness, Young's modulus and scratch resistance) of photoactive layers of suspension plasma sprayed TiO₂ coatings applied on to glass substrates. Microstructure observation showed that the rutile grains were surrounded by fine anatase crystals. Under the same spraying conditions, the resulting anatase/rutile concentrations varied depending on the cooling rate (the substrate being either cooled with water or in air). The results showed that higher concentrations of anatase, which is softer than rutile, reduced the scratch damage and increased the friction coefficient.     

Effect of the internal stress relaxation during the post-annealing on the photo-induced properties of TiO2 coatings reactively sputtered

Photocatalyst TiO₂ coatings have been reactively sputtered at high pressure on cold glass substrates pre-coated by a SiN_x sodium diffusion barrier. The as-deposited coatings were amorphous and the TiO₂/SiN_x/glass samples were subsequently heated at different temperatures under air. The TiO₂ films crystallise in the anatase structure above temperatures of 250 °C with a [001] preferential orientation. The structural analyses have demonstrated that the crystallites are elongated following the c axis direction, perpendicularly to the surface. No modifications of grain size and texture have been observed over the complete temperature range studied (250-550 °C). However, the lattice parameters evolution shows a decrease of the tensile stress with a rise in annealing temperature. The microstructure is then completely relaxed around 400 °C and finally compressive stress is observed at higher temperature. The study of the photo-induced (photocatalytic and hydrophilic) properties shows an activity maximum at 400 °C. These results suggest that the photo-induced properties would be favoured by a relaxed microstructural state of titanium dioxide.     

N-doped TiO2/ZnO composite powder and its photocatalytic performance for degradation of methyl orange

The N-doped TiO₂/ZnO composite powder with a molar ratio of Ti to Zn of 3/1 was prepared via sol–gel process and then ammonia treated with NH₃ mass fractions of 0%, 7%, and 28% for 24 h at room temperature followed by thermal calcinations in air for 2 h at various temperatures of 500, 600, and 700 °C. The as-prepared composite powder was characterized in detail through thermo-gravimetric analyzer, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results showed that the phase transformation of anatase to rutile has been successfully retarded via the ammonia treating process, leading to the presence of anatase phase in the composite. The particle crystallization of the composite powder was significantly promoted with the increase of the calcining temperature. The photocatalysis evaluation through MO degradation revealed an enhanced photocatalytic activity for the composite powder that might be related to the good crystallization, the presence of anatase phase, and the particle size reduction of the powder.     

Microstructure characterization and photocatalytic activity of mesoporous TiO2 films with ultrafine anatase nanocrystallites

A series of mesoporous TiO₂ films on borosilicate glass with ultrafine anatase nanocrystallites were successfully synthesized using a non-acidic sol gel preparation route, which involves the use of nonionic surfactant Tween 20 as template through a self assembly pathway. The microstructure of these TiO₂ films was characterized by XRD, SEM, HR-TEM, UV-Vis spectroscopy, and N₂ adsorption-desorption isotherm analysis. Their photocatalytic activities were investigated by using creatinine as a model organic contaminate in water. It was found that all mesoporous TiO₂ films prepared with Tween 20 exhibited a partially ordered mesoporous structure. The photocatalytic activity of the TiO₂ films could be remarkably improved by increasing Tween 20 loading in the sol at the range of 50% (v/v), which yielded large amount of catalyst (anatase) on the glass support and enhanced specific surface area. The optimum Tween 20 loading was 50% (v/v) in the sol, above which good adhesion between TiO₂ films and borosilicate glass could not be maintained. The final TiO₂ film (Tween 20: final sol = 50%,v/v) exhibits high BET surface area (∼ 120 m²/g) and pore volume (0.1554 cm³/g), ultrafine anatase nanocrystallinity (7 nm), uniform and crack free surface morphology, and improved photocatalytic activity.     

Controlling the particle size of nanobrookite TiO2 thin films

In this study, pure nanobrookite TiO₂ thin films were successfully deposited on glass substrates with the spin-coating method using titanium butoxide and acetic acid. The particle size of TiO₂ films was controlled by the water:AcAc volume ratio. This study shows that it is possible to obtain single oriented pure brookite films. The structural and optical properties of the nanobrookite TiO₂ thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), spectrophotometer (NKD), and Fourier transform infrared spectrometer (FTIR).     

Synthesis of CeO2/TiO2 nanoparticles by laser ablation of Ti target in cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) aqueous solution

A new synthesis process, laser ablation in an aqueous solution of target material, was applied to synthesize nanostructured CeO₂/TiO₂ catalyst particles. Reactivity within the laser plume (plasma) can be used to synthesize CeO₂ from an aqueous solution, 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution, and to fabricate TiO₂ from Ti target. CeO₂/TiO₂ nanoparticles were successfully synthesized by the laser ablation of Ti target in 2 M cerium (III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O) aqueous solution. Laser ablation of Ti in a liquid environment and chemical reactions of the solution within a plasma plume are discussed.     

Effect of Na diffusion from glass substrate on the microstructural and photocatalytic properties of post-annealed TiO2 films synthesised by reactive sputtering

Amorphous columnar TiO₂ films were synthesised by reactive sputtering on cold soda–lime glass substrates (TiO₂/glass films). The films were subsequently heated in order to crystallise the photoactive anatase phase. The surface chemical composition assessment demonstrates the occurrence of metallic Na, the amount of which increases with the annealing temperature. The evolution of the structural, microstructural and photocatalytic properties of the films with the annealing temperature was investigated and compared to that of TiO₂ films deposited in same conditions, but on glass pre-coated with a SiN_x diffusion barrier (TiO₂/SiN_x/glass films). Once crystallised, both series of TiO₂ films exhibit [001] preferential orientation corresponding to the columnar growth. Grain coalescence associated to a modification of the grain shape is only observed in TiO₂/glass films for annealing temperatures higher than 450 °C, whereas neither microstructural nor structural change is observed in TiO₂/SiN_x/glass films. The Na-contaminated TiO₂ films exhibit different photocatalytic behaviour with the annealing temperature compared to the Na-free TiO₂ films. A discussion is finally based on these differences.     

Structure differences between TiO2 and phosphorus implanted TiO2 films caused by thermal treatment

The titanium oxide film has been deposited on Si wafers (110) by unbalance reactive magnetron sputtering and modified by phosphorus ion implantation and succeeding vacuum annealing. The structural, states of surface chemistry and surface morphology of the films have been investigated by X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), atomic force microscope (AFM) and Scanning Electron Microscope (SEM), respectively. The results of XRD show rutile structure of as-deposited film, which is not changed by phosphorus implantation and vacuum annealing. However, a slightly shift of the peaks position to higher degree and the half width increases after ion implanted and vacuum annealing represent that the variety of the structure film caused by these treatments. The surface roughness is inclined to increase with the rising of annealing temperature for both undoped and P doped titanium oxide films. The surface chemistry presents significant difference between undoped and phosphorus doped films after a vacuum annealing, it may be attributed to the different evolvement of the surface defects existing in the film, which may be considered as an important influencing factor in the blood compatibility of the titanium oxide film.     

阳极氧化制备工艺对TiO_2纳米管阵列显微形貌的影响

为改善TiO_2纳米管阵列结构有序性和形貌完整性,以NH4F-丙三醇-水溶液为电解液,采用一次阳极氧化法和二次阳极氧化法在Ti片表面制备TiO_2纳米管阵列,借助扫描电子显微镜和原子力显微镜,研究一次阳极氧化电压、二次阳极氧化法制备过程中阳极氧化电压和一次阳极氧化时间以及退火温度对TiO_2纳米管阵列显微形貌的影响。结果表明,采用一次阳极氧化法在5~25 V电压下阳极氧化Ti片120 min后均可制得有序排列的TiO_2纳米管阵列,纳米管外侧面具有"竹节状"结构特征,纳米管平均管径和管间距随氧化电压升高而增大;一次阳极氧化法在20 V/120 min下制得的TiO_2纳米管阵列相对较优,其表面平整度高。在相同氧化电压下采用二次阳极氧化法制备TiO_2纳米管阵列不能有效改善阵列的有序程度和表面平整度。600℃退火会促进TiO_2纳米管层/钛金属界面处的热氧化物层生长。     

Microstructural characterization of plasma sprayed Al2O3-40 wt.% TiO2 coatings on high density graphite with different post-treatments

Graphite is one of the candidate materials proposed for application in pyrochemical reprocessing plants involving aggressive molten chloride environment. Post treatments are promising techniques for the improvement of properties of thermal spray coatings for different industrial applications. In the present work, the effect of post treatments like vacuum annealing (VA) and laser melting (LM) on the microstructure and chemical modification of plasma sprayed Al₂O₃-40 wt.% TiO₂ coatings over high density (HD) graphite substrates has been investigated. When compared with sprayed coatings (SC), VA coatings showed cluster morphology and LM coatings exhibited homogenous microstructure. On laser melted surfaces networks of cracks were observed. XRD studies showed that the metastable γ-Al₂O₃ phase present in the SC is transformed to stable α-Al₂O₃ after post treatments. In LM coatings Al₂TiO₅ phase was more predominant in contrast to SC and VA coatings. The microhardness enhancement was observed in case of LM coating compared to the VA and SC. Due to elimination of coating defects in LM samples, there is a considerable reduction in the surface roughness.     

Microstructural and photocatalytic properties distribution of TiO2 coatings reactively sputtered as a function of the substrate position relatively to the Ti target

Amorphous and porous TiO₂ coatings were deposited by reactive magnetron sputtering at high pressure (3.4 Pa) on cold soda-lime glass placed at different positions relatively to the magnetron target, which corresponds to different impingement angles and target-to-substrate distances. The as-deposited coatings were heated at 450 °C under ambient air to crystallise into the photoactive anatase phase. The structural analyses combined with AFM experiments have shown a reduction of the crystallites and the lateral grain size with the removal of the substrate from the target axis inducing a specific area rise. Moreover, the stress state is all the less as compressive as the substrates are far away from the target. As a result, the photocatalytic properties are improved with the decrease of the incidence angle and with the target-to-substrate distance rise.     

First-principles study on the electronic and optical properties of F- and Nb-doped anatase TiO2

We present a comparative study on the electronic and optical properties of Nb- and F- doped anatase TiO₂ by first-principles calculations based on the density functional theory (DFT). Although both TiO₂:Nb and TiO₂:F have a similar band structure, the effective mass of TiO₂:F is larger than that of TiO₂:Nb, and the carriers density in the former is lower than that in the latter, indicating that TiO₂:Nb has better electronic conductivity than TiO₂:F. The interaction between photons and electrons in TiO₂:F is much stronger than that in TiO₂:Nb, resulting in increased photon absorption and reduced transmittance, especially in the visible and near-infrared regions. The results demonstrate that TiO₂:F is not suitable for transparent conductive oxide applications.     

In-situ TiB2 and Al2O3 formation by DC plasma spraying

In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB₂ and Al₂O₃ are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.     

Deposition of TiO2 thin films on steel using a microwave activated chemical bath

Microwave activated chemical bath deposition (MW-CBD) is a simple and novel technique in which the substrate is heated directly by microwaves and very well adhered layers are obtained. It has not been used previously for TiO₂ deposition on metals. We show that it is possible to coat stainless steel with TiO₂ using MW-CBD. Two different precursor solutions are used for TiO₂ deposition on steel grade 316. TiO₂ thin films on steel substrates were characterized using SEM and Raman spectroscopy. Raman analysis showed that amorphous TiO₂ is obtained using the precursor solution based on TiOSO₄; however, films show anatase crystal structure when using the precursor solution based on (NH₄)₂TiF₆. Thermal treatment of the films improved crystallinity and also allowed iron diffusion from the steel substrate into the film. Crystalline phases that appeared due to heat treatment were identified from Raman spectra. MW-CBD allows simple low temperature coating of a metal substrate with TiO₂ and this should be useful for a number of different applications.     

TiO2对水下湿法焊接熔渣形貌及微观组织的影响

文中采用自制的金红石型碳钢焊条进行水下湿法焊接,重点分析了药皮中TiO₂的加入量对熔渣形貌及微观组织结构的影响.由熔渣的成分及物相分析得出,熔渣的主要组成相为Fe₂MnTi₃O₁₀,还含有少量的Ca₂SiO₄和自由氧化物.对熔渣的宏观形貌及微观组织结构分析发现,当药皮中TiO₂加入量较大时,熔渣致密松脆,熔渣的微观组织中灰白色条状相粗大,有利于熔渣脱渣;当减小TiO₂的加入量,增大CaCO₃的加入量时,熔渣变得松散,出现粘渣现象,此时微观组织中的灰白色条状相变得细小,不利于熔渣脱渣.