SnO2@TiO2核-壳纳米线的制备及其光催化性能研究

本文通过固-液-气(VLS)生长机制,利用化学气相沉积法(CVD)制备SnO₂纳米线。利用原子层沉积(ALD)以钛酸四异丙酯为前驱体在SnO₂纳米线表面沉积不同厚度的TiO₂壳层,形成SnO₂@TiO₂核-壳纳米线结构。通过中间Al₂O₃插层,分别制备出金红石和锐钛矿两种不同晶型的TiO₂,从而制备出两种不同复合结构的SnO₂@TiO₂核-壳纳米线。实验研究该复合结构中TiO₂的厚度与晶型对紫外光下光催化降解甲基橙溶液活性的影响。     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

TiO2/膨润土复合光催化材料的常温制备及性能研究

采用改进的溶胶-凝胶法,在以水为主要溶剂的反应体系中,控制钛酸四丁酯充分水解、缓慢聚合,在 常压、低温(70℃)的温和条件下制备出稳定的TiO₂纳米晶溶胶,并利用TiO₂纳米晶溶胶在膨润土表面负载,获得TiO₂/膨润土复合光催化材料。采用 X 射线衍射、扫描电镜、比表面积测定等研究手段对样品的结构形貌进行了表征,并考察了其光催化活性。结果表明：较高的水用量有利于TiO₂晶体形成,当去离子水:钛酸四丁酯摩尔比大于167:1时,在溶胶体系中出现了锐钛矿型TiO₂纳米晶体;TiO₂纳米晶主要负载于膨润土表面,并未嵌入到膨润土层间结构,但相对于单一膨润土,TiO₂负载显著提高了材料比表面积;当去离子水:钛酸四丁酯摩尔比=192:1时,在紫外光照射下,复合光催化材料表现出最高的光催化活性,对亚甲基蓝的降解率达到93.8%。     

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.     

Modification of Parylene film-coated glass with TiO2 nanoparticles and its photocatalytic properties

A titania film was deposited on Parylene-coated glass by a one-step, ultrasound-assisted procedure. The TiO₂ nanoparticles formed during the sonochemical hydrolysis of Ti(i-OPr)₄ were thrown to the surface and strongly attached to the Parylene substrate. By using different solvents (water, ethanol or their mixture) and reagent concentrations, the thickness, uniformity and crystallinity of the deposited layer were regulated. PVP was used to stabilize the highly homogeneous distribution of TiO₂ nanocrystals on the Parylene surface. The morphology and structure of the coated films were characterized by physical and chemical methods such as: X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and optical spectroscopy. The photocatalytic activity of the titania-modified Parylene film in the photo discoloration of methylene blue was demonstrated. The experimental results revealed a correlation between the uniformity of the nanostructured anatase titania film and its photocatalytic properties.     

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.     

Theoretical study on the electronic and optical properties of (N, Fe)-codoped anatase TiO2 photocatalyst

Electronic and optical properties of pure, N-doped, Fe-doped and (N, Fe)-codoped anatase TiO₂ were evaluated, respectively, by using the density functional theory. The results indicate that the elemental doping narrows the band gap of TiO₂ and realize its visible-light response activity; and incorporation of Fe into N-doped TiO₂ further increases the photocatalytic activity under visible-light irradiation compared with that of the N-doped TiO₂.     

Preparation and characterization of nano TiO2/micron Cr2O3 composite particles

Nano-TiO₂/micro-size Cr₂O₃ composite particles were first prepared by hydrolysis of Ti(OBu)₄ in an abundant acidic aqueous solution without calcinations at room temperature. XPS analysis shows that the element C, O, Ti and Sn existed on the surfaces of the composite particles. Observation by field emission scanning electronic microscope shows TiO₂ particles of 10-15 nm covers on Cr₂O₃ powder surfaces to form nanometer/micron composite particles. UV-vis spectra show a red shift of the absorption edge and a significant increase of absorption intensity in the visible region. These results confirm that TiO₂ of anatase type can be synthesized on the surface of Cr₂O₃.     

Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors

Spherical and rod like nanocrystalline Nd₂O₃ phosphors have been prepared by solution combustion and hydrothermal methods respectively. The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd₂O₃ has been obtained with calcination at 900 °C for 3 h and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of Nd₂O₃ phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method. TEM results also confirm the same. Raman studies show major peaks, which are assigned, to F_g and combination of A_g + E_g modes. The PL spectrum shows a series of emission bands at ∼326-373 nm (UV), 421-485 nm (blue), 529-542 nm (green) and 622 nm (red). The UV, blue, green and red emission in the PL spectrum indicates that Nd₂O₃ nanocrystals are promising for high performance materials and white light emitting diodes (LEDs).     

CVD deposition and characterization of coloured Al2O3/ZrO2 multilayers

Coloured Al₂O₃/ZrO₂ multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO₂ process used in the multilayer, with ZrCl₄ as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO₂ phases. However by adding a relatively small amount of AlCl₃ during such a process results in ZrO₂ layers being composed of predominantly tetragonal ZrO₂ phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO₂ phase seem to be less perfect with existence of larger grains of ZrO₂ which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al₂O₃ layers.It is believed that, in the studied Al₂O₃/ZrO₂ multilayers, the observed tetragonal ZrO₂ phase is the result of a size effect, where small enough ZrO₂ crystallites energetically favor the tetragonal phase. However as the ZrO₂ crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO₂ phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO₂ based ceramics.     

Fe3O4/SiO2/Bi2WO6磁性复合光催化剂的制备及其光催化性能

钨酸铋(Bi₂WO₆),结构最简单的Aurivillius相化合物,是近期受到研究者关注的新型光催化材料。然而,光催化剂粉末在反应介质中难被回收,工业化应用成本较高。本文用三步方法合成了可回收的Fe₃O₄/SiO₂/Bi₂WO₆磁性复合光催化剂,通过溶剂热法合成具有磁性的Fe₃O₄,用溶胶凝胶法在Fe₃O₄表面覆盖SiO₂层,后将磁性颗粒与Bi₂WO₆纳米片相结合。光催化剂的形貌结构及性能通过XRD、SEM、PL、UV-vis进行表征测试。结果表明,直径约500 nm的Fe₃O₄微球附着在边长约500 nm的Bi₂WO₆纳米片的表面,SiO₂在两者之间起到了粘连作用。光催化剂Fe₃O₄/SiO₂/Bi₂WO₆对于罗丹明B的光降解活性较好,且有一定磁性,可以通过外加磁场将其从溶液中分离,有较大的应用潜力。     

Preparation of thermally stable anatase TiO2 photocatalyst from TiOF2 precursor and its photocatalytic activity

Preparation of anatase TiO₂ with high themal stability is of great importance for its environmental application. In this work, TiOF₂ was first synthesized by a simple microwave-assisted hydrothermal route using tetrabutyl titanate and hydrofluoric acid as precursors at 200 °C for 20 min. Then the resulted precipitates were calcined at different temperatures (300-1000 °C) for 2 h. The as-prepared samples were characterized by X-ray diffraction, Raman spectrum, scanning electron microscopy, N₂ adsorption-desorption isotherms and X-ray photoelectron spectroscopy. The photocatalytic activity was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic molecule under UV light irradiation. The results showed that the prepared TiOF₂ exhibited weak or no photocatalytic activity. The phase transformation of TiOF₂ to anatase TiO₂ occurred at about 300 °C. The prepared anatase TiO₂ from TiOF₂ showed very high thermal stability and the anatase-to-rutile phase transformation temperature was up to 1000 °C. Fluoride ions played an important role in the improvement of thermal stability of anatase TiO₂ by strongly adsorbing on the crystal planes of anatase to stabilize the anatase structure. The 700 °C-calcined sample showed the highest photocatalytic activity due to its relative good crystallization and high specific surface areas.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

TiO2-g-C3N4 composite materials for photocatalytic H2 evolution under visible light irradiation

In this investigation, we report the preparation of TiO₂-g-C₃N₄ composite materials with varying the wt.% of g-C₃N₄, the characterization of these materials by various techniques and photocatalytic hydrogen production under visible light irradiation in the presence of methanol. The X-ray powder diffraction (XRD) shows that the composite materials are consist of anatase TiO₂ and g-C₃N₄. Fourier transform infrared (FT-IR) spectra show that the absorbance band intensity of composite materials was stronger than that of C₃N₄. The UV-vis absorption spectra show that the absorption edge of the composite materials shifts to the lower energy region comparing to pure anatase and to longer wavelengths with increasing the amount of C₃N₄. The significant photoluminescence quenching was observed in TiO₂-C₃N₄ composite materials, indicating the charge transfer from C₃N₄ to TiO₂. The visible light induced H₂ evolution rate was remarkably enhanced by coupling TiO₂ with C₃N₄.     

微波原位制备作为锂离子电池电极材料的石墨烯/TiO2 纳米复合物

通过改造的家用微波炉,实现了原位高效制备石墨烯/TiO₂纳米复合物。结果表明：微波辅助法能够在商用锐钛矿型TiO₂纳米颗粒表面均匀制备石墨烯纳米片,通过SiO₂/Si的剧烈电晕放电,其制备时间仅需数分钟（最短3 min）。石墨烯纳米片的尺寸大约为50 nm且缺陷很少。TiO₂晶体结构仍为锐钛矿型,主要归功于极短的制备周期和较低的反应温度（600~700 ℃）。石墨烯具有优异的电导率,可以提升锂离子扩散速率、提高电子传输速率并降低接触电阻。在1 C（170 mA·g^-1）条件下石墨烯/TiO₂纳米复合物的电池放电比容量提高了2倍。与商业化锐钛矿型TiO₂纳米颗粒相比,在1 C到5 C的不同充放电倍率下,石墨烯/TiO₂纳米复合物的比容量差距显著扩大。     

Laser-induced enhancement of the surface hardness of nanoparticulate TiO2 self-cleaning layer

We here report that the abrasion resistance of nanoparticulate TiO₂ self-cleaning layers can be highly enhanced without a considerable loss of photocatalytic capability. TiO₂ coating layers solution-deposited onto the glass substrate were irradiated by a pulsed ultraviolet (UV) laser at 355 nm, which modified the surface morphologies via laser-induced local melting of TiO₂ nanoparticles. The surface hardness, measured by pencil scratch test, improved with increasing laser power (P). While an unmodified TiO₂ layer revealed a hardness of 6B, it increased to 2H after the surface was irradiated at P = 0.3 W. Almost all of the stearic acid deposited on an unmodified sample disappeared after UV exposure for 12 h. The photocatalytic decomposition was slowed down on laser-irradiated TiO₂ surfaces and this is attributed to the reduction of specific surface areas as a result of the morphological modifications. However, a TiO₂ layer hardened to 2H still exhibited fairly good photocatalytic activity, decomposing more than 75% of the stearic acid after exposure for the same duration.     

Dominant microstructural feature over photocatalytic activity of high velocity oxy-fuel sprayed TiO2 coating

TiO₂ photocatalytic coatings were deposited through high velocity oxy-fuel spray using anatase powder and rutile powder as feedstock. The as-sprayed TiO₂ coating was composed of anatase phase and rutile phase. The anatase content in the coating was significantly influenced by fuel gas flow and melting condition of spray powder. A high anatase content of 35% was achieved for the coating deposited using rutile powder. The anatase content in the coating deposited using anatase powder reached 55-65%. The as-sprayed TiO₂ coating was photocatalytically reactive for degradation of acetaldehyde in air. The photocatalytic activity was influenced by spray conditions. The surface morphology and phase structure of coatings deposited at different spray conditions were investigated to clarify the relationship between the coating microstructure and activity. It is found that the photocatalytic activity is significantly influenced by anatase content and surface area.     

Micro-arc oxidation of TC4 substrates to fabricate TiO2/YAG:Ce compound films with enhanced photocatalytic activity

This paper introduces a process for “in situ” preparing TiO₂ photocatalytic film compounded with YAG:Ce³⁺ semiconductor upon titanium alloy by using micro-arc oxidation (MAO). The surface morphology, chemical compositions, phase structures and photocatalytic properties of the films were characterized and measured by field emission gun scanning electron microscope (FEG-SEM), energy-dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electro-chemical workstation and UV-vis spectrophotometer. The results show that the YAG:Ce³⁺ semiconductor particles which were added in the electrolyte had been homogenously compounded within the TiO₂ film during MAO. Compared with the pure TiO₂ film, the compounded film exhibited much larger specific surface area, stronger absorption in the visible light and higher photo-generated current density, which improves the photocatalytic property markedly. It is expected that MAO will provide a simple, economic and promising approach for preparing a superior photocatalytic TiO₂ film.     

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.     

Characteristics of N-doped TiO2 nanotube arrays by N2-plasma for visible light-driven photocatalysis

N-doped TiO₂ nanotube arrays were prepared by electrochemical anode oxidation of Ti foil followed by treatment with N₂-plasma and subsequent annealed under Ar atmosphere. The morphologies, composition and optical properties of N-doped TiO₂ nanotube arrays were characterized using field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectrometer (XRD), Photoluminescence (PL) and UV-vis diffusion reflection spectroscopy (UV-vis DRS). Methylene blue (MB) solution was utilized as the degradation model to evaluate the photocatalytic activity of the samples under visible light irradiation. The results suggested N₂-plasma treatment created doping of nitrogen onto the surface of photoelectrodes successfully and the N-doped TiO₂ nanotube arrays display a significantly enhancement of the photocatalytic activity comparing with the pure TiO₂ nanotube arrays under the visible light irradiation.