Application of pulsed chemical vapor deposition on the SiO2-coated TiO2 production within a rotary reactor at room temperature

Pulsed chemical vapor deposition (P-CVD) is a promising technology for the surface modification of TiO₂ particles. For the scale-up application of P-CVD, a custom-designed rotary reactor and corresponding coating process at room temperature was developed in the present work. The obtained SiO₂-coated TiO₂ particles were characterized by various measures including high-resolution transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, etc. The results illustrated that the SiO₂ films with a thickness of (3.7 ±0.7) nm were successfully deposited onto the surface of TiO₂ particles. According to the dye degradation tests and acid solubility measurement, the deposited film can effectively inhibit the photocatalytic activity and enhance the weatherability of the TiO₂ particles. Zeta potential measurements showed that the SiO₂-coated TiO₂ is possible to be stably dispersed in the pH range of 6.9–11.6. The coating process made the whiteness of TiO₂ particles decreased slightly but still sufficient (97.3 ±0.1) for application. Furthermore, the properties of the TiO₂ particles coated by P-CVD were compared with the particles coated by traditional wet chemical deposition. It is shown that the P-CVD can produce thinner but denser films with better photoactivity suppression performance. The developed coating process within the rotary reactor was proved practically feasible and convenient for the scale-up production of SiO₂-coated TiO₂ via P-CVD.     

LIQUID-PHASE PHOTOCATALYTIC REACTION ON TiO22 THIN FILM

The photocatalytic decomposition process on TiO₂ thin films, was modeled by taking the decay of illumination intensity via Lambert-Beer law into account. For the sake of experimental verification of the proposed model, Ti02 thin films were prepared on a glass substrate by a dip-coating method combined with a sol-gel process and the photocatalyuc activity of the thin films was evaluated by the decomposition of 2-propanol (IPA) in an aqueous solution under illumination of UV light source. The film thickness up to 1.4 μm increased with the withdrawal speed raised to the power 0.6 and was proportional to the number of application (i.e., repetition of dip-coating process). The TiO₂ gel films prepared by a dip-coating technique, were subject to firing at 500°C. The photocatalytic decomposition rate could be expressed apparently as first-order with respect to IPA concentration. The observed relationship between apparent first-order rate constant of decomposition and the film thickness could satisfactorily be explained by the proposed model.     

Effect of TiO2 thin film thickness and specific surface area by low-pressure metal–organic chemical vapor deposition on photocatalytic activities

TiO₂ photocatalyst films having an anatase crystal structure with different thickness were prepared by the low-pressure metal–organic chemical vapor deposition (LPMOCVD) to examine the effect of growth conditions on photocatalytic activity. Film thickness was linearly proportional to the deposition time. Structure of the film was strongly dependent on the deposition time. In early stage of deposition, fine particles deposit on the substrate. As increasing the deposition time, crystal orientation is gradually selected following the Kolmogorov model and c-axis oriented columnar crystals become dominant. The photocatalytic activity strongly depends on the film deposition time (or film thickness) in nonlinear way. The optimum thickness of TiO₂ catalyst film grown by LPMOCVD may locate between 3 and 5 μm.     

Plasma-CVD-coated glass beads as photocatalyst for water decontamination

Amorphous TiO₂ films were deposited on glass microbeads using a specially designed circulating fluidized bed plasma-CVD reactor. The film thickness was varied between 7 and 120 nm. While only little carbon impurity was found, XPS analysis revealed the presence of silicon, sodium and alkaline earth elements in the titania coating. Reduced amounts of these substrate-originating impurities were observed in the thicker films. By ToF-SIMS imaging, cross-sectional TEM and time-resolved dissolution, the titania coatings were proven to be uniform, both per particle and in terms of the film thickness distribution.

The photocatalytic performance of the composite particles was evaluated in a fully irradiated fluidized-bed photoreactor. The thinnest films had some photocatalytic activity in the as-deposited state, possibly induced by the high specific power of the microwave plasma or silicon doping. The thicker films needed a post-deposition calcination at 723 K to achieve catalytic activity. Both the degree of anatase crystallization and the activity were improved by applying thicker films and after UV irradiation-plus-calcining. All films showed good adhesion and abrasion resistance during the photocatalytic tests. The best plasma-CVD films were about 70% as efficient (per unit reactor volume) as the reference material, P-25 immobilized on quartz sand.     

TiO2 optical coating layers for self-cleaning applications

TiO₂ films deposited by various coating techniques were investigated for self-cleaning applications. The optical coating layers of TiO₂ films prepared from a sol–gel precursor were deposited on glass substrates using spin coating, dip coating and screen printing techniques. Effects of film deposition techniques on crystal structure, microstructure, thickness, photocatalytic activity, hydrophilicity and optical properties of the films were investigated using XRD, AFM, SEM, surface profilometer, UV–vis spectrophotometer and contact angle measurement. Dip coating the TiO₂ optical film two and three times resulted in superhydrophilic surfaces. Increasing number of dipping times was found to increase the photocatalytic activity.     

The dependence on temperature of gas-phase photocatalytic oxidation of methyl tert-butyl ether and tert-butyl alcohol

The influence of temperature on the mechanism and kinetics of gas-phase photocatalytic oxidation (PCO) and thermal oxidation (TO) of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA) over TiO₂ was studied in a continuous flow annular reactor. The reaction products of PCO of both substances included acetone, water, carbon dioxide and carbon monoxide. Volatile TO products of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Thermal oxidation of MTBE became noticeable at 388 K, TBA started to decompose thermally at 393 K. Both PCO and TO fit well to the Langmuir–Hinshelwood (L–H) model for monomolecular reactions. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation. The TiO₂ catalyst showed no deactivation at temperatures above 373 K but gradually lost its activity below 373 K.     

The photocatalytic activity and stability of a nanosized TiO2 film prepared by carbon black modified method

Regard to the poor adsorbability of the fixing film photocatalyst, we prepared a new nanosized TiO₂ thin film modified by carbon black acting as the pore-forming agent and baked by a kind of new method. The film was characterized by XRD, TEM, SEM, DRS and FT-IR techniques. The results showed that the prepared TiO₂ films were mainly anatase structure, containing a little rutile. Their mean sizes of crystal grains are about 20–30 nm. Comparing to the ordinary TiO₂ film, we found that both carbon black modification and new baking method could make the characteristics of films change, such as more pores, looser structure, smaller crystal grains and longer excitation wavelength. It should be owed to these advantaged characteristics that the photocatalytic activity of the new film was largely improved during the degradation of benzamide. Furthermore, it also had wonderful stability, keeping its activity for 4 months applied to degrade reactive brilliant red X-3B in the continuous flow reactor.     

AUGMENTATION OF PHOTOCATALYTIC ACTIVITY OF TiO2 THIN FILMS PREPARED BY A SOL-GEL TECHNIQUE

In order to increase the photocatalytic activity on TiO₂ thin film per its external surface area, the structure of flat thin film was modified by adding a small amount of polyethylene glycol (PEG) to TiO₂ sol solution. By firing PEG contained in a TiO₂ gel film, a porous structure was developed. The photocatalytic activities of the thin films prepared thus were evaluated by the degradation of 2-propanol in the aqueous solutions under black light illumination. The photocatalytic activity of TiO₂ thin film prepared with added PEG 400 by 2.6 wt% or PEG 2000 by 9.5 wt% was increased by about 30% as compared to that prepared without added PEG.     

Photocatalytic degradation of two volatile fatty acids in monocomponent and multicomponent systems: Comparison between batch and annular photoreactors

This study investigates the influence of the inlet concentrations on the degradation rates of a binary mixture of volatile fatty acids (propionic and butyric acids). TiO₂-coated non-woven fibre textile was used as the photocatalyst in a batch reactor and in an annular reactor at laminar flow regime. The humidity level, temperature, UV intensity and flow rate were kept constant. First, the adsorption isotherms were determined and these showed that the propionic acid is less adsorbed than the butyric acid onto the catalyst. Conversely to the adsorption, the photodegradation of pure propionic acid is better than the degradation of pure butyric acid. Photodegradation is greatly inhibited when the two acids are mixed in comparison to the pure compounds. The propionic acid is more affected. This inhibition is attributed to the competitive adsorption of the two species on the active sites of the catalyst. A model which takes into account the competitive adsorption is proposed in order to determine the outlet concentrations of the compounds knowing the inlet concentrations in the annular reactor.     

Photocatalytic decomposition of methyl tert-butyl ether in aqueous slurry of titanium dioxide

The photocatalytic degradation of methyl tert-butyl ether (MTBE) was investigated in the aqueous slurry of titanium dioxide (TiO₂) particles irradiated with xenon lamp in a batch reactor. The reaction was found to follow a pseudo-first-order kinetics and the reaction rate increased by raising the TiO₂ loading and the UV light intensity. The reaction rate constant was proportional to the square root of the UV intensity. An upper plateau level was observed for the reaction rate constant, corresponding to a steady photoproduction of hydroxyl radicals at high catalyst concentrations. The experimental data was analyzed using a modified Turchi–Ollis model to account for changes in the catalyst loading. It was found that this model predicted the observed trend in the pseudo-first-order rate constant if the reaction pathway involves the interaction between adsorbed hydroxyl radicals and solvated molecules.     

SBA-15/Ni/TiO2/CNTs复合材料的制备及其光催化性能

通过溶胶凝胶法,经多次涂覆在SBA-15上负载掺杂镍的纳米TiO₂,得到SBA-15/NiO/TiO₂复合物;再以TiO₂中还原态金属镍为催化剂,通过化学气相沉积法（CVD）,在SBA-15/NiO/TiO₂表面原位生长碳纳米管,制得SBA-15/Ni/TiO₂/CNTs复合材料。通过XRD、SEM、TEM、UV-Vis和Raman等方法考察了SBA-15/Ni/TiO₂/CNTs复合材料的结构和性能,并通过降解亚甲基蓝溶液评价其光催化活性。结果表明,SBA-15/Ni/TiO₂/CNTs复合光催化剂的催化活性较SBA-15/NiO/TiO₂显著提高。 二次涂覆掺杂镍的二氧化钛制得的复合光催化剂的催化活性高于一次涂覆。     

LED可见光下Au/TiO2光催化氧化甲醛表观动力学

甲醛是室内空气中典型的挥发性有机化合物（VOCs）之一。等离子激元型光催化剂可吸收可见光,可在室温常压下利用太阳光驱动光催化氧化脱除室内空气中甲醛的反应,其表观反应动力学研究对设计等离子激元型光催化剂及应用于脱除VOCs等污染物具有重要意义。研究了LED可见光下等离子激元型Au/TiO₂光催化脱除气相中甲醛的表观反应动力学,考察不同波长的可见光源、光强及反应气相对湿度对表观反应动力学的影响,根据对实验数据的分析求得LED可见光催化氧化甲醛表观反应速率常数k（I,H）。结果表明,在13%相对湿度、蓝光光强为38.5 mW·cm^-2的条件下,光反应的甲醛转化率达77%,是暗反应的近5倍。在LED红、绿、蓝、白光照射下,随着光强增加,甲醛转化率快速增加后缓慢增至基本不变。相同光强（低于42 mW·cm^-2）和湿度条件下,红、绿、蓝光源的甲醛转化率相近,白光略低于其他光源。干气氛下,光反应和暗反应的甲醛转化率几乎为0。湿气氛下,光反应和暗反应均有甲醛转化率,光反应的甲醛转化率更高。不同光源条件下甲醛转化率随相对湿度变化规律相似。相对湿度为21.9%时甲醛转化率最高,而后保持不变,基本在80%左右。通过对红、绿、蓝、白光的数据拟合计算,得到表观动力学参数k（I）_H、k（H）_I、k（I,H）以及速率方程。     

Highly porous TiO2 films from anodically deposited titanate hybrids and their photoelectrochemical and photocatalytic activity

Hybrid films of TiO₂ and benzoquinone, its derivative 2-methyl-benzoquinone or the dye 2,9,16,23-tetrasulfophthalocyaninatonickel(II) were prepared by anodic electrodeposition from titanium alkoxide solutions. Calcination of the films at 450 °C led to removal of the organics and the formation of crystalline and highly porous TiO₂ films as seen in XRD and Kr adsorption measurements, respectively. In dye-sensitized solar cells the films achieved an overall light-to-electricity conversion efficiency of 0.8% despite a low film thickness of 0.55 μm. In the photocatalytic decomposition of methylene blue the films showed photonic efficiencies of up to 0.09% for film thicknesses around 0.5 μm, which is much higher than those of comparable TiO₂ films prepared by sol–gel method.     

The effect of Pt on the photocatalytic degradation pathway of methylene blue over TiO2 under ambient conditions

The high performance photocatalytic TiO₂ films were successfully obtained by a galvanostatic anodization of metallic titanium using the optimum anodization condition, subsequent to pre-nitridation treatment. The optimized anodization parameters on the formation of high photocatalytic TiO₂ film were investigated. The pre-nitridation treatment was performed by annealing metallic Ti under a nitrogen atmosphere of 0.1 MPa. The anodized TiO₂ film showed the high photocatalytic activities to decompose not only gaseous acetaldehyde but also tetrachloroethylene, which revealed that the anodized TiO₂ film is a possible candidate of the photocatalyst for environmental purifications comparable to the best photocatalyst of fine crystalline powder.     

Photocatalytic oxidation of multicomponent systems of herbicides: Scale-up of laboratory kinetics rate data to plant scale

The reaction kinetics of the photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO₂ (Degussa P25) suspensions were studied in multicomponent systems in a laboratory-scale annular photoreactor operated in recirculation batch mode. The multicomponent kinetic model established was then extended to take into account the direct effect of radiation absorbed by the TiO₂ photocatalyst in order to obtain intrinsic kinetic parameters independent of the radiation field in the photoreactor. An analysis of the radiation field in the photoreaction space was accomplished using a recently published Six-Flux Radiation Absorption-Scattering model (SFM) to decouple the values of the apparent reaction kinetic constants from the local volumetric rate of photon absorption (LVRPA) in the rate law of PCO of herbicide. The resulting rate laws with explicit dependence on the LVRPA were then used to predict, through accurate reactor modeling, the degradation of the herbicides in an optimal configuration of a flow-through, pilot-scale, falling film photoreactor. In a plant treatment scenario the total operating costs of the PCO of herbicides were calculated to be 3.75 Euro m⁻³.     

铋及钴掺杂TiO2陶瓷负载膜的制备及光催化性能

以钛酸四丁酯为钛源,Bi(NO₃)₃·5H₂O为铋源,Co(NO₃)₂·6H₂O为钴源,采用溶胶-凝胶法在陶瓷基片上分别制备了应用于固定式光催化反应器的Bi-TiO₂复合膜及Co-TiO₂复合膜。研究了涂膜方式及煅烧升温速率对膜表面形态的影响,并以甲基橙溶液为目标降解物,对比了旋涂法及浸渍提拉法制备的薄膜在不同升温速率下的光催化活性。通过热分析仪(TG-DSC)、X射线衍射仪(XRD)和扫描电镜(SEM)等测试手段分析了掺杂薄膜的结构。结果表明,采用旋涂法制备的薄膜与陶瓷基体结合较为紧密,而浸渍提拉法制备的薄膜催化活性较高。当煅烧温度为500 ℃,升温速率为10 ℃/min时,其对甲基橙的降解率较高。当摩尔比为0.010时Bi-TiO₂复合膜的催化活性较佳,100 min光降解甲基橙比率达到8.10%。钴或铋掺杂TiO₂均可提高TiO₂催化剂的光催化活性,Bi-TiO₂膜的催化活性优于Co-TiO₂膜。     

Efficient destruction of pathogenic bacteria with AgBr/TiO2 under visible light irradiation

The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with AgBr/TiO₂ under visible light (λ > 420 nm) irradiation. The catalyst was found to be highly effective for the killing of Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive bacterium. The decomposition of the cell wall and cell membrane was directly observed by TEM and further confirmed by K⁺ leakage from the inactivated bacteria. A possible cell damage mechanism by visible light-driven AgBr/TiO₂ is proposed. In addition, the effects of pH, inorganic ions on bacterial photocatalytic inactivation were investigated. The electrostatic force interaction of the bacteria–catalyst is crucial for the efficiency of disinfection. Moreover, AgBr/TiO₂ supported on porous nickel showed much higher bactericidal activity than fixed P25 TiO₂ under visible or near UV light irradiation.     

镍、碳共掺杂纳米二氧化钛薄膜的制备与光催化性能研究

为了增强纳米二氧化钛薄膜在紫外光下光催化降解罗丹明B溶液的能力,分别采用磁控直流溅射与射频溅射的方法,使用二氧化钛靶材、镍靶材、碳靶材,分别制备了碳非金属掺杂、镍金属掺杂以及镍、碳共掺杂的纳米二氧化钛薄膜,并利用扫描电子显微镜（SEM）、X射线衍射仪（XRD）和紫外可见分光光度计（UV-Vis）进行表征。SEM结果表明,与纯二氧化钛薄膜相比镍、碳共掺杂纳米二氧化钛薄膜晶粒细化,比表面积增大,薄膜表面聚集体为不规则的多边形颗粒状,有利于增大与污染物的接触面积;XRD结果表明该薄膜的晶粒减小,加快了光生电子空穴对的分离;薄膜的吸收极限红移,禁带宽度减小。在紫外光照射下,镍、碳共掺杂纳米二氧化钛薄膜的光催化性能最优,1 h降解了29.54%的罗丹明B溶液。     

Photocatalytic degradation of imidazolinone fungicide in TiO2-coated optical fiber reactor

The photocatalytic degradation of the fungicide fenamidone is studied in a TiO₂-coated optical fiber photoreactor. Fenamidone is slowly transformed with a kinetic order of 1 and a degradation rate of 0.02 h⁻¹. Intermediate products were isolated and identified by means of solid phase extraction (SPE) coupled to liquid chromatography-mass spectrometry techniques (LC-MS). A proposed degradation pathway of fenamidone is presented, involving mainly hydroxylation and oxidation reactions. Carboxylic acids and sulfate ions resulting from the same reaction in a powder reactor were also identified.     

NEW FUNCTIONS FOR MICROFLUIDIC COMPONENTS BY USING MICRO METAL INJECTION MOLDING (μ-MIM)

Microfluidics and microreaction technology constitute an upcoming field in a variety of industrial branches. As this technique is implemented in the daily business of industrial companies the cost-effectiveness of the production process starts to become an issue. The micro metal injection molding (μ-MIM) process provides freedom of design for a broad spectrum of materials (metals, metal alloys, and polymers). Catalytic as well as bio-compatible materials have already been structured using this technology. Furthermore, μ-MIM shows the potential of a cost-effective production technique that can be adapted to produce microstructured parts for various applications. As a case example a microfluidic structure was applied for water purification. The reactor surface was coated with an active photocatalytic (TiO₂) modified nano-layer using dip coating. Subsequently, it was covered with a glass plate adhered with a two-component adhesive. For determination of hydrodynamics, measurements by means of μPTV have been performed. For investigations of water purification and sanitization the reactor was first fed with a water stream contaminated by a special dye to optimize the hydrodynamic parameters and afterwards with a water stream contaminated by Escherichia coli to investigate the degradation of germs. This was done by illuminating the TiO₂-coated reactor with UV light. The results indicate that this new type of reactor has an exceptional high potential to eliminate germs in drinking water.