Controlled synthesis of TiO2 mesoporous microspheres via chemical vapor deposition

Anatase titanium dioxide (TiO₂) mesoporous microspheres with core-shell and hollow structure were successfully prepared on a large scale by a one-step template-free chemical vapor deposition method. The effects of various reaction conditions on the morphology, composition and structure of the products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) technique and photoluminescence (PL) method. The results indicate that the product near the source was composed of core-shell structure TiO₂ microspheres with diameters from 3 to 5 μm. With increasing the distance between the source materials and the substrate, the hollow TiO₂ spheres with 1-2 μm dominant the products. A localized Ostwald ripening can be use to explain the formation of core-shell and hollow structures, and the size of the initial TiO₂ solid nanoparticles plays an important role in determining the evacuation manner of the solid in the ripening-induced hollowing process. The surface area of TiO₂ hollow microspheres determined by the adsorption isotherms was measured to be 74.67 m²/g. X-ray photoelectron spectroscopy (XPS) analysis revealed that the O-H peaks of hollow structures have a chemical shift compared with the core-shell structures. The optical property of the products was also discussed.     

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.     

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.     

Low temperature growth of nanocrystalline TiO2 films with Ar/O2 low-field helicon plasma

TiO₂ thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO₂ was obtained for ion density on the substrate below 7 × 10¹⁶ m^− 3. Increasing the ion density over 7 × 10¹⁶ m^− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO₂. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO₂ thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.     

Novel thermal barrier coatings based on La2Ce2O7/8YSZ double-ceramic-layer systems deposited by electron beam physical vapor deposition

Novel thermal barrier coatings based on La₂Ce₂O₇/8YSZ double-ceramic-layer (DCL) systems, which were deposited by electron beam physical vapor deposition (EB-PVD), were found to have a longer lifetime compared to the single layer La₂Ce₂O₇ (LC) system, and even much longer than that of the single layer 8YSZ system under burner rig test. The DCL coating structure design can effectively alleviate the thermal expansion mismatch between LC coating and bond coat, as well as avoid the chemical reaction between LC and Al₂O₃ in thermally grown oxide (TGO), which occurs above 1000 °C as determined by differential scanning calorimetry (DSC) analysis. The failure mechanism of LC/8YSZ DCL coating is mainly due to the sintering of LC coating surface after long-term thermal cycling.     

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.     

Effect of Nd2O3 addition on the surface phase of TiO2 and photocatalytic activity studied by UV Raman spectroscopy

TiO₂ modified with Nd₂O₃ (Nd-TiO₂) nanoparticles were prepared by a co-precipitation method and utilized as the photocatalysts for the degradation of Rhodamine B (RhB). The influence of Nd₂O₃ on the bulk and surface phase, surface area, particle size, and optical response of TiO₂ was investigated by X-ray diffraction (XRD), UV Raman spectroscopy, transmission electron microscopy (TEM), BET, and UV-visible diffuse reflectance spectra. It is found that the crystalline phase and phase composition in the bulk and surface region of Nd-TiO₂ calcined at high temperatures can be tuned by changing the amount of Nd₂O₃. Based on the results from XPS, EDX, XRD, and UV Raman spectra, it is assumed that Nd³⁺ ions do not enter the TiO₂ lattice, but highly disperse onto the Nd-TiO₂ particle surface in the form of Nd₂O₃ crystallites. These crystallites inhibit the agglomeration, growth in crystal size, and anatase-to-rutile phase transformation of TiO₂. In the photocatalytic degradation of RhB reaction, Nd-TiO₂ nanoparticles with higher surface area and wider optical response are more reactive in case of the same surface anatase phase. When the mixed phases of anatase and rutile exist in the surface region of Nd-TiO₂, the synergetic effect over surface area and optical response is the important parameter which determines optimal photocatalytic activity.     

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.     

Effects of heat treatment scheme on the photocatalytic activity of TiO2 nanotube powders derived by a facile electrochemical process

TiO₂ nanotubes (NTs) in powder form were synthesized by a facile electrochemical process in a perchlorate-containing electrolyte. Transmission electron microscopy results indicate that the TiO₂ NT-powder is in an amorphous structure and has outer diameter of 20 nm and tube-wall thickness of 5 nm. X-ray diffraction analysis reveals that phase composition of the annealed TiO₂ NT-powders is related to the heat treatment scheme. Methyl orange was employed as a representative dye pollutant to evaluate the ultraviolet photocatalytic activity of the TiO₂ NT-powders. It was found that different post heat treatment schemes affect greatly the photocatalytic activities of the TiO₂ NT-powders, which should be ascribed to the changes in phase structural and morphological properties of the TiO₂ NT-powders. These results indicate that there should be a balance between crystal phase and nanotubular configuration for achieving the best photocatalytic activity of the TiO₂ nanotube powders.     

电化学法研究La-F两步共掺杂纳米TiO2的催化机理

以钛酸四丁酯、硝酸镧和氟化钠等为原料,采用原位掺杂的方式制备了La-F两步共掺杂TiO₂光催化剂。通过XRD、SEM、XPS和UV-Vis对样品进行了表征,并对样品进行了光催化性能及电化学交流阻抗的测试。结果表明所制样品均为锐钛矿型TiO₂,La-F共掺杂使TiO₂的晶格发生了较大畸变且晶粒得到了细化,两步共掺杂会加剧样品颗粒间的团聚,同时两步共掺杂也使TiO₂的吸收带边发生红移,禁带宽度降低。两步共掺杂样品中TiO₂与Lax-Fy-TiO₂之间形成的n-n异质结,由于二者费米能级不同而形成的内建电场,对半导体内部电子起到定向的迁移作用,从而有效降低光生电子-空穴的复合,提高载流子浓度。当La和F的掺杂比例分别为1.5%和10%时,两步共掺杂样品的载流子浓度为1.5×10₂₀/cm_-3,对亚甲基蓝表现出优异的可见光降解效果,120min降解率达到96%,为同等条件下纯TiO₂的2.6倍。     

Preparation of large scale photocatalytic TiO2 films by the sol-gel process

Nanocrystalline titanium dioxide films were formed on frosted and clear borosilicate glass with a large surface area (12 × 22 cm) using doctor blade and spray coating techniques. The films were subjected to a high temperature treatment at 550 °C. X-ray diffraction (XRD) analysis indicated that the TiO₂ films contain only the anatase phase. Optical microscopy was used to determine the morphology changes after the deposition of each layer. Scanning electron microscopy (SEM) was used to study the films surface morphology. The large scale TiO₂ films produced showed a high photocatalytic activity which was evaluated by the degradation of methyl orange (MO) in aqueous solution (10 mg L^− 1) under illumination of a UV light source with an overall irradiance of 0.9 mW cm^− 2. UV-visible spectrophotometry was used to monitor the degradation of MO through the decrease of the main absorbance peak at 464 nm. The results demonstrated that a complete decomposition of MO could be achieved after 2 h of UV irradiation.     

Surface pretreatment of austenitic stainless steel and copper by chemical, plasma electrolytic or CO2 cryoblasting techniques for sol-gel coating

The surface pretreatments of the austenitic stainless steel and copper surfaces for the sol-gel coating were carried out by chemical, plasma electrolytic or CO₂ cryoblasting techniques. With the austenitic stainless steel the smoothest surfaces were obtained with plasma electrolytic cleaning, after which the measured contact angles of water were clearly decreased revealing improved hydrophilicity. As well with the copper samples the smooth surface and improved hydrophilicity was obtained with the plasma electrolytic cleaning, but oxide layer formed to the copper surface immediately after the treatment. CO₂ cryoblasting provided rough surface with wetting properties close to the original surface both for austenitic stainless steel and copper surfaces. CO₂ cryoblasting provided best appearance for the copper surface because no oxidation happened with that treatment. XPS and SIMS studies showed that with the plasma electrolytic treatment the surface layer of the austenitic stainless steel enriched of chromium and the oxide layer formed on the surface was less than 10 nm thick. With the chemical cleaning and CO₂ cryoblasting, the chromium enrichment to the stainless steel surface was less. However XPS and SIMS studies showed that chemical treatment provided thinner oxide layer to copper surface than plasma electrolytic treatment.     

磁控溅射法制备TiN/TiO2周期薄膜

采用直流反应磁控溅射法在Si(111)衬底上制备了不同周期数的TiN/TiO2周期薄膜。采用X射线衍射分析仪分析了薄膜的物相结构、原子力显微镜表征了薄膜的表面微观形貌,采用光催化降解甲基橙溶液来评价薄膜光催化性能。结果表明:所制备的TiN/TiO2周期薄膜结晶良好,薄膜由TiO2和TiN两种物相组成,TiO2均属于锐钛矿型。薄膜表面均匀致密,随着周期数的增加,薄膜表面粗糙度增加,1周期薄膜表面粗糙度(Ra)为1.652nm,5周期则为4.339nm,1周期薄膜均方根粗糙度(Rms)为2.138nm,5周期达5.738nm。薄膜具有显著的光催化性能,随着周期数的增加,TiN/TiO2薄膜的光催化性能逐渐增强,5周期薄膜对甲基橙溶液的降解率达到74%。结晶良好、表面均匀致密的具有光催化性能的TiN/TiO2周期薄膜的制备,为高质量TiN/TiO2周期薄膜的制备提供了参考。     

Fe2O3-CaO-TiO2 体系下铁酸钙的合成过程及TiO2 和CaTiO3 的影响

为了确定高钛型钒钛磁铁矿烧结过程中铁酸钙的生成是受TiO₂还是TiO₂和CaO形成的CaTiO₃影响,首先利用Fe₂O₃和CaO的纯试剂合成了铁酸钙,并研究了TiO₂和CaTiO₃对钛铁酸钙 （FCT） 形成的影响。在Factsage 7.0软件进行热力学计算的基础上,通过在空气气氛下进行烧结,获得了在1023~1423 K温度范围内、不同烧结时间的不同样品。通过X射线衍射和扫描电镜-能谱分析等表征手段,对烧结样品的物相转变和微观结构变化进行了表征。发现FCT的形成过程主要分为2个阶段：前一阶段为1023~1223 K温度范围内Fe₂O₃与CaO之间的反应,合成产物为Ca₂Fe₂O₅,反应方程式为“Fe₂O₃(s)+ 2CaO(s)= Ca₂Fe₂O₅(s)”;后一阶段为1223~1423 K温度范围内Ca₂Fe₂O₅和Fe₂O₃的反应,主要产物为CaFe₂O₄,反应为“Ca₂Fe₂O₅(s)+ Fe₂O₃(s)= 2CaFe₂O₄(s)”,该阶段尤其是温度为1423 K时,反应速率显著加快,随温度的升高CaTiO₃显著增加。然而,Ti元素在铁酸钙中的固溶很难实现,TiO₂与铁酸钙之间的反应不是形成FCT的有效途径。随着保温时间的延长,CaTiO₃和FCT相界中Fe元素含量增加。FCT主要是通过Fe组分在CaTiO₃中固溶形成的,主要反应是“Fe₂O₃+CaTiO₃(s)=FCT(s)”。     

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%。     

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.     

Structural, optical and charge transport study of rutile TiO2 nanocrystals at two calcination temperatures

In this study the influence of two different calcination temperatures 80 °C and 450 °C on the structural, optical and charge transport properties of rutile TiO₂ nanocrystals has been investigated. TiO₂ nanocrystals have been prepared at low temperature by a simple hydrolysis method using titanium tetrachloride as starting precursor. The results of X-ray diffraction (XRD) showed that the prepared nanocrystals have a rutile tetragonal crystalline structure. Specific surface area of 80 °C and 450 °C calcinated rutile TiO₂ nanocrystals are 25.38 × 10⁵ cm²/g and 7.61 × 10⁵ cm²/g respectively, which has been calculated by X-ray diffraction data. Williamson-Hall plot results indicate the presence of compressive strain at 80 °C and tensile strain at 450 °C. Ultraviolet-visible (UV-vis) absorption spectroscopy is used to calculate the band gap of the material and the shift in absorption edge and it has been observed that the absorption spectra are strongly modified by the calcination temperature. The red-shift in photoluminescence (PL) is attributed to the change in strain from compressive to tensile. Photoconductivity (PC) measurements showed that capture cross-section of 80 °C (R1) and 450 °C (R2) calcinated rutile nanocrystals are 55.10 × 10⁻¹⁰ and 39.50 × 10⁻¹⁰ cm² respectively. High value of electron life-time, low value of radiative recombination and a four order increase in photogenerated charge carriers have been reported for the rutile TiO₂ nanocrystals calcinated at 450 °C.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

Charge transport and recombination in dye-sensitized solar cells based on hybrid films of TiO2 particles/TiO2 nanotubes

In this paper, anodic TiO₂ nanotubes are blended into the TiO₂ mesoporous films based on P25 nanoparticles to assemble a list of dye-sensitized solar cells (DSSCs) with different nanotube concentrations. The electron properties of transport and recombination in the fabricated DSSCs are studied by using electrochemical impedance spectroscopy and the open-circuit voltage decay technique under AM 1.5 illumination. Results indicate that the electron lifetime increases with increasing the concentration of the anodic TiO₂ nanotubes, the electron transport time at a blending level of 10 wt% TiO₂ nanotubes is short as compared to that at 0 wt%, and above 10 wt%, the electron transport time has a trend of becoming large. Due to the combining effects of the electron transport and recombination, the electron collecting efficiency and the electron diffusion length obtain maxima at a blending level of 10 wt% nanotubes, which results in a highest short circuit current and a maximum energy conversion efficiency at this point in the DSSCs. This study gives a clear explanation for the performance enhancement of TiO₂ particle-based DSSCs at a blending level of 10 wt% anodic TiO₂ nanotubes and for the performance decrease at a blending level over 10 wt% anodic TiO₂ nanotubes from the angle of the electron transport and recombination. This study also supplies a feasible and easy way to improve the performance of particle-based DSSCs by restraining electron recombination and accelerating electron transportation.     

纳米颗粒增强TiO_2涂层的制备及其防污性能

为提高二氧化钛涂层的防污性能,采用KH-550硅烷改性锐钛矿型TiO_2颗粒,并充分分散于二氧化钛凝胶涂层中。通过降解亚甲基蓝溶液、细菌贴附试验、藻类贴附试验,分别评价了涂层的光催化性能、抗菌性能及抗藻类附着性能,并利用激光共聚焦显微镜及扫描电子显微镜对藻类在涂层表面的附着情况进行分析。结果表明,添加TiO_2纳米颗粒涂层的防污性能较未添加TiO_2纳米颗粒涂层有较大程度的提高。添加粒径为5~10 nm TiO_2颗粒的二氧化钛涂层对小球藻、三角褐指藻及小新月菱形藻的附着降低率分别达到了92.1%、71.5%和62.1%,相较于纯二氧化钛涂层对3种藻类的附着降低率分别提高了29.7%、68.4%和43.5%。TiO_2颗粒的加入可以有效地提高涂层的光催化性能,光催化使得涂层具有亲水、抗菌及自清洁的性能进而有利于提高涂层的防污性能。