纳米TiO_2的光催化性能改进及其在环境保护中的应用研究

基于纳米二氧化钛光催化性能的广泛应用及其在应用时效率偏低的问题,从抑制TiO2内载流子的复合、提高催化剂的比表面积和改变催化剂的结构与表面性质3个方面综述了修饰纳米二氧化钛以提高其光催化性能的各项措施,并从污水处理、空气净化、抗菌除臭等方面评述了纳米TiO2在环境保护领域中的应用。     

Photocatalytic degradation of selected dyes by titania thin films with various nanostructures

Titania thin films with various nanostructures of quasi-aligned nanorods, well-aligned nanotubes and nanoparticle aggregates were fabricated and utilized to assist photodegradation of three typical dye derivatives in water, i. e., rhodamine B (RB), methylene blue (MB) and methyl orange (MO). The thin films were characterized by X-ray diffraction, scanning electron microscope and UV-Vis diffuse reflectance spectra. It is found that the bandgap of most lab-fabricated thin films can be estimated more appropriately assuming a direct transition between the valance band and the conduction band of titania. The so-called natural ageing phenomenon was evidence for all the films to assist photodegradation of RB and MB in water; but not discernible for MO, which was much reluctant to photodegradation. MB decomposed much quickly than RB when assisted by titania with predominantly anatase; on the other hand, rutile favored the photodegradation of RB than that of MB. Titania thin films with top morphologies of quasi-aligned nanorods or nanotubes were found to possess advantageous turnover frequency and photonic efficiency over commercial P25 titania and sol-gel derived titania to assist photodegradation of RB and MB in water.     

Enhanced sorption and photodegradation of chlorophenol over fluoride-loaded TiO2

The presence of NaF in the aqueous suspension of TiO₂ can accelerate the photocatalytic degradation of organic pollutants. However, disposal of such a fluoride-containing wastewater is not allowed by environmental regulation. In the present work, we report on surface modification of TiO₂ with a hardly water soluble salt, fluorite and fluorapatite. The modified catalysts at low loading displayed a higher activity than bare TiO₂ for the sorption and photocatalytic degradation of phenol and 2,4-dichlorophenol in water. A kinetic study using butanol as hydroxyl radical scavenger revealed that the fluoride-modified catalysts produced more hydroxyl radicals than bare TiO₂. Five repeated experiments showed that the fluorapatite-modified TiO₂ was very stable, and could be re-used without significant loss in activity.     

Photocatalytic performance of Gd ion modified titania porous hollow spheres under visible light

In this work, Gd-doped titania hollow spheres were prepared using hydrothermally prepared carbon spheres as template. The prepared samples were characterized by XRD, TEM, SEM, DRS and XPS. The photocatalytic activity of as-prepared hollow titania spheres was determined by degradation of Reactive Brilliant Red dye X-3B (C.I. reactive red 2) under visible light irradiation. The effect of Gd content on the physical structure and photocatalytic properties of doped titania hollow sphere samples was investigated. Results showed that there was an optimal Gd-doped content (4%) for the photocatalytic activity of X-3B degradation.     

Low-temperature plasma-induced degradation of aqueous 2,4-dinitrophenol

The degradation behavior of 2,4-dinitrophenol (DNP) by low-temperature plasma was investigated and the effect of some factors that might affect the degradation process was further examined. The results indicated that DNP could be effectively removed from aqueous solution. The degradation value was 83.6% when the input power was 150 W and 60 s was selected as the discharge time. Increasing the input power increased the degradation efficiency. The degradation process fitted first-order dynamics and the reduction was mainly caused by the reaction of DNP with OH. The degradation efficiency decreased with the increase of initial concentration at the same discharge time. H2O2 at the concentration of 0.25% enhanced the degradation process, however, hindered the degradation at 1.00 and 2.00%. The presence of Fe2+ could benefit DNP degradation. However, the increment in degradation efficiency might be suppressed to some extent at a high concentration level. Cu2+ inhibited the degradation process within 30 s and enhanced the reduction after 30 s. Furthermore, the increment of Cu2+ concentration could enhance the effect. A little acid environment was conducive to DNP degradation and the pH value became lower with increasing discharge time by low-temperature plasma.     

Photocatalytic degradation of paraoxon-ethyl in aqueous solution using titania nanoparticulate film

Photocatalytic degradation of paraoxon-ethyl (o,o-diethyl o-(4-nitrophenyl) phosphate), a well known surrogate of chemical warfare agents, in aqueous solution was studied by using titania nanoparticulate film. Reaction followed pseudo first order behaviour. Photolytic degradation reaction of paraoxon-ethyl demonstrated relatively low rate with a value of rate constant of 2.5 × 10^− 3 min^− 1. Whereas, degradation reaction in the presence of titania nanoparticulate film and UV light displayed enhanced rate with a value of rate constant of 6.9 × 10^− 3 min^− 1 due to photocatalysis. Gas chromatography-mass spectrometry analysis showed the formation of p-nitrophenol, o,o-diethyl phosphonic acid, o-ethyl, diphosphonic acid, phosphoric acid, dimerized product of o,o-diethyl phosphonic acid, acetaldehyde, and carbon dioxide due to photocatalytic degradation of paraoxon-ethyl. It indicates that, photocatalytic degradation reaction begins with destruction of P-O-C bonds. Subsequently, P, C atoms were found to be oxidized gradually, and contributed to its photocatalytic degradation.     

Characterization and Photocatalytic Efficiency of TiO2 /Ti Beads Fabricated by Simple Heat-Treatment

The goal of the present study was to investigate the photocatalytic efficiency of titanium dioxide (TiO 2) formed on titanium (Ti) bead substrate (referred herein as TiO 2 /Ti beads) by heat treatment when exposing to ultraviolet (UV) light irradiation.Escherichia coli was used as the model test organism.The results show 4-log and 7-log decrease in bacterial concentration after a test time of 15 and 120 min,respectively,using TiO 2 /Ti beads irradiated with UV light in a tin-foil covered beaker.This article presents the potential of TiO 2 on Ti bead substrate formed by simple heat-treatment together with UV light for bacterial inactivation.     

Degradation of 2,4-dinitrophenol by combining sonolysis and different additives.

Based on the effects of various additives on ultrasonic degradation of 2,4-dinitrophenol (DNP) in aqueous solution, the degradation mechanisms and reaction kinetics of DNP in different processes were proposed. The results showed that some additives, such as CuO, CCl(4), O(3), NaCl and KI, were favorable for DNP sonochemical degradation. On the contrary, DNP degradation efficiency was restrained by Na(2)CO(3), indicating that OH radicals oxidation played an important role in DNP ultrasonic removal. The significant increases in DNP degradation in US/CuO/H(2)O(2), US/CCl(4) and US/O(3) systems were also related to the intermediates formed during the reactions, such as HO(2)/O(2)(-) radicals, chlorine-containing radicals and HClO. In addition, DNP ultrasonic removal was observed to behave as pseudo-first-order kinetics under different experimental conditions tested in the present work.     

Photocatalytic NOx degradation of concrete surface layers intermixed and spray-coated with nano-TiO2: Influence of experimental factors

TiO₂ incorporated Eco-blocks have been successfully developed and widely used worldwide. However, under real-life service, various environmental factors will significantly influence their photocatalytic performance. In this study, the photocatalytic NO_x conversion of two sets of concrete surface layers (intermixed and spray-coated with nano-TiO₂) was investigated and compared under different NO flow rates, initial NO concentrations, ultraviolet (UV) light intensities, light sources and relative humidity (RH) conditions. In addition, the abrasion resistance of all the samples was examined. The results showed that the TiO₂ spray-coated samples (SP) outperformed the 5% TiO₂-intermixed samples with respect to NO_x removal efficiency under all the investigated conditions. Both the NO flow rate and initial NO concentration had a positive impact on the NO_x removal rate but a negative influence on the NO_x removal ratio. An increase in photocatalytic NO_x removal rate and NO_x removal ratio was attained by an increase in UV light intensity. Whereas, the NO_x removal efficiency first increased, reached a peak, and then decreased with increasing RH. It was found that the most effective light source for photocatalytic NO_x removal was UV-A, but Solar light (SL) irradiation resulted in a comparable NO_x removal. Moreover, the SP samples harboured robust resistance to abrading. The findings from this study would provide the basis for effectively evaluating the NO_x removal performance of concrete surface layers under atmospheric conditions.     

Photocatalytic activities of Ion doped TiO2 thin films when prepared on different substrates

Pure and ion doped TiO₂ thin films were prepared by sol-gel dip coating process on metallic and non-metallic substrates. Test metal ion concentration ranged from 0.000002 to 0.4 at.%. The resulting films were annealed in air and characterized by optical spectroscopy and X-ray diffraction. The photodegradation of methyl orange under UV irradiation by pristine and ion-doped TiO₂ films was quantified in a photocatalytic reactor developed in this study. In general, both doped and undoped TiO₂ crystals appeared in anatase phase and the photocatalytic activities of the TiO₂ thin films varied with substrates, calcination temperature, doping ions and their concentrations. The best calcination temperature for different substrates ranged from 450 to 580 °C. Films prepared on the metallic substrates resulted in higher photocatalytic activities, while ion doping lowered their efficiencies. On the contrary, for non-metallic substrates except ceramic the photocatalytic efficiencies of undoped films were much lower (< 30%), while ion doping was shown to increase the photocatalytic efficiencies remarkably in some cases, e.g., Cr³⁺ with the tile substrate. Overall, ion doping affected the photocatalytic efficiency of TiO₂ films, and an optimal doping concentration of between 0.0002 and 0.002 at.%, close to an estimate by the Debye length equation, resulted in the highest efficiency for most substrates.     

Photocatalytic degradation mechanisms of dimethyl phthalate esters by MWCNTs-anatase TiO2 nanocomposites using the UHPLC/Orbitrap/MS technique

Dimethyl phthalate esters (DMPEs) have been identified as endocrine disrupting plastisizers and emerging contaminants which can be released readily upon exposure to the environment. In this study, MWCNTs/TiO₂ nanocomposites, which possess the potential application for the photocatalytic degradation of DMPEs under UV irradiation, were prepared via simple one-pot sol-gel reaction using titanium isopropoxide (TTIP) as titania precursor and multiwalled carbon nanotubes (MWCNTs). The MWCNTs/TiO₂ nanocomposites was calcined in air for 2 h at the temperatures ranging from 350 to 750 °C. As a result, the MWCNTs/TiO₂ nanocomposites synthesized at calcination temperature of 450 °C demonstrated the highest photodegradation efficiency of 97% after 180 min UV irradiation and its degraded products were evaluated using the ultra high performance liquid chromatography (UHPLC) coupled with a high resolution (HR) Orbitrap mass spectrometry (MS). A primary degradation mechanism was proposed and it was noteworthy that some new intermediates were discovered and reported. This work has developed a simple method for qualitative determination of DMPEs based on HPLC with UV detection.     

Facile synthesis of nano-TiO2/stellerite composite with efficient photocatalytic degradation of phenol

In this paper, we report a kind of nano-TiO₂/stellerite composite with enhanced photoactivity, which was synthesized by a typical homogeneous precipitation method followed by a calcination crystallization process using natural stellerite as support. The as-prepared composites were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption-desorption, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results showed that TiO₂ loading amounts and calcination temperatures had significant influence on the adsorption and photocatalytic degradation properties of phenol. Moreover, it was indicated that the TiO₂ nanoparticles (NPs) with smaller grain size (around 12.0?nm) and narrower size distributions were uniformly deposited on the surface of stellerite as a layer of film. Compared with commercial P25, the received composite exhibited more superior photocatalytic degradation performance towards phenol. The enhanced photocatalytic degradation performance should result from the better dispersibility of TiO₂ NPs and higher separation efficiency of photogenerated electron-hole pairs. This work may set foundation for the practical application of this new composite photocatalyst in the field of wastewater treatment.     

Photocatalytic activity of vanadium-doped titania-activated carbon composite film under visible light

A V-doped titania-activated carbon composite film was prepared by a modified sol-gel method under mild condition. X-ray diffraction analysis revealed that the titania was a pure anatase phase. From scanning electron microscopy and N₂ adsorption-desorption measurements, we found that the composite film was porous since it formed a micro-nano structure. The photocatalytic activity of such film was evaluated through degradation of azo-dye Reactive Brilliant Red under visible light, and was compared to commercially available TiO₂, pure titania and vanadium-doped titania films. Results showed that the photocatalytic activity was enhanced a lot. It was due to expansion of the absorption edge by vanadium doping, and the synergistic effect of activated carbon with titania. Furthermore, the hydrophilic property of the as-prepared composite film was superior to other samples.     

Study on degradation of methyl orange using pelagite as photocatalyst

Pelagite of East Pacific Ocean as a low-price, very high reserve photocatalyst, has been successfully used for the first time to realize total degradation and decoloration of methyl orange within 120 min through photocatalysis. The photocatalysis and degradation performance of pelagite for methyl orange under the effect of various factors has been studied. Results show that pelagite has satisfactory photocatalysis effect in degradation of organic compounds.     

Reaction paths and efficiency of photocatalysis on TiO2 and of H2O2 photolysis in the degradation of 2-chlorophenol

The kinetics of 2-chlorophenol (2-CP) degradation and mineralization in the aqueous phase was investigated under irradiation at 254 nm, employing either photocatalysis in the presence of titanium dioxide, or hydrogen peroxide photolysis, to compare the efficiency of these photoinduced advanced oxidation techniques. Photocatalysis under 315-400 nm wavelength irradiation was also investigated. The concentration versus time profiles of the degradation intermediates catechol, chloro- and hydroxy-hydroquinone allowed the identification of the reaction paths prevailing under the different experimental conditions. Efficient CCl bond cleavage occurred as a consequence of direct light absorption by 2-CP, while hydroxyl radicals, photogenerated at the water-photocatalyst interface or during H(2)O(2) photolysis, were the main oxidation agents, able to attack both 2-CP and its degradation intermediates. Highest degradation and mineralization efficiencies were achieved under H(2)O(2) photolysis at 254 nm.     

Photocatalytic behavior of different titanium dioxide layers

Many recently developed applications are related to the photocatalytic behavior of semiconductive oxides. Among the different oxides, titanium dioxide (TiO₂) is one of the most interesting due to its high photocatalytic efficiency towards a great number of reactions and to its hydrophilic properties. Aim of this work is the evaluation and comparison of the photocatalytic properties of different crystalline titanium dioxide films, directly grown on titanium substrates by surface anodization (eventually followed by thermal annealing) and by Pulsed Laser Deposition (PLD) on titanium and silicon substrates, followed by thermal annealing. The structure and morphology of the layers were characterized by Scanning Electron Microscopy and X-Ray Diffraction and photocatalytic tests on stearic acid mineralization were performed. Results showed that the PLD layers possess a higher photocatalytic efficiency than anodized titanium. This can be attributed to the microstructured/microporous morphology of the related surfaces. Instead, PLD TiO₂ layers with a relatively high content of the rutile phase have a reduced photocatalytic efficiency with respect to mainly anatase containing layers.     

Photocatalytic and electrochemical combined treatment of textile wash water

Various chemical and physical processes for treatment of textile effluent are not destructive but they only transfer the contaminants from one form to another. The presence of high concentration of organic dye and total dissolved solids (TDS) in the effluent that are not removed by biological treatment must be eliminated by an alternative method to the conventional ones is the advanced oxidation process (AOP). A procion blue dye effluent was treated by photo and electrochemical oxidation process as well as by combining photocatalytic degradation using TiO2 suspensions. Chemical oxygen demand (COD) and colour removal can be used to follow the degradation of the organic pollutant. The effects of pH, current density, flow rate of effluent that passes into the reactor and supporting electrolyte were studied. Comparative studies were carried out on photocatalytic and electrochemical process to degrade the procion blue. The maximum COD reduction and colour removal were 96 and 100%, respectively. Photodegradation efficiency of dye was high when photolysis was carried out in the presence of 40 mg/l of TiO2.     

Photocatalytic degradation of organic dyes by mesoporous nanocrystalline anatase

Mesoporous nanocrystalline anatase was prepared via EISA employing P123 and CTAB as structure directing agents. The resultant mesoporous crystalline phases exhibited specific surface areas as high as ∼150 m² g⁻¹, average unimodal pore sizes of ∼3 nm and ∼6 nm, and average crystallite size of ∼10 nm; and were used as photocatalysts for the UV degradation of methylene blue, methyl orange, methyl red and rhodamine 6G. The mesoporous anatase phases photodegraded MB, MO and MR ∼2–3 times faster than conventional nanocrystalline anatase and showed limited photocatalytic activity for rhodamine 6G.     

Photocatalytic degradation of methyl tert-butyl ether in the gas-phase: a kinetic study

Methyl tert-butyl ether (MTBE) is the basic oxygenated motor fuel additive in Europe and is included in volatile organic compounds (VOCs), which can produce photochemical oxidants. In the present study the gas-phase photocatalytic oxidation (PCO) of MTBE over illuminated titanium dioxide was carried out at ambient temperature in a plug flow reactor. The intermediates detected are mainly tert-butyl formate and acetone, while the final products are CO(2) and water. The system was sensitive to the oxygen concentration, for concentrations up to 15% (v/v). Moisture had a positive effect on the reaction, obtaining an optimum value near 45% relative humidity for 200ppmv MTBE initial concentration. A reaction scheme has been proposed for the interpretation of the experimental results and a kinetic study was conducted, using the Langmuir-Hinshelwood kinetics equation. The MTBE rate constant was 1.545 x 10(-6)Ms(-1)g(cat)(-1) for the reaction without moisture and 2.46 x 10(-6)Ms(-1)g(cat)(-1) for the reaction in the presence of moisture and the adsorption constant was 2.187 x 10(5)M(-1) independent of humidity.     

锐钛矿型TiO2胶体制备抗菌陶瓷的特性研究

利用锐钛矿晶型的纳米TiO2 胶体溶液 ,将硅胶作为粘结剂按不同配比加入TiO2 胶体 ,用提拉法在陶瓷表面形成均匀薄膜并在高温下烘烤成膜。研究TiO2 和硅胶在不同比例情况下的薄膜特性 ,讨论了退火温度对亲水性及光催化活性的影响 ,利用分光光度计测量了TiO2 薄膜对亚甲基蓝的分解活性 ,测定了薄膜对洗涤剂、消毒剂、3 %NaOH和沸水的抗腐蚀能力。结果表明 ,利用这种方法制备的薄膜具有较好的光致亲水性和光催化性 ,并具有良好的抗腐蚀能力。