水热法制备TiO2片晶及光催化性能

以稳定的金红石相TiO₂为原料,水热法制备出微米级TiO₂片晶。采用扫描电镜（SEM）、X射线粉末衍射（XRD）、N₂吸附-脱附等分析手段对样品进行了分析。将不同温度下煅烧后样品进行甲基橙降解实验。实验结果表明,反应48 h可获得长60～80μm、宽30～60μm、厚4～9 μm的介孔片晶。经450℃煅烧可得到锐钛矿相占83.6%的混晶,比表面和孔径分别为68 m²·g^-1、21.6 nm,对甲基橙降解率最高,在30 min内降解了92.4%,60 min几乎全部降解,其催化活性优于商用P25,且微米级的颗粒更容易回收再利用。     

Low Temperature Preparation and Characterization of N-doped and N-S-codoped TiO2 by Sol–gel Route

This paper reports a new method to prepare the N-doped and N-S-codoped anatase TiO₂ photocatalysts at 100 °C. The as-prepared photocatalysts were characterized by means of XRD, Raman spectra, TEM, BET, UV–Vis diffuse reflectance spectra (DRS) and XPS. The results showed that the N-doping and N-S-codoping extended the absorbance spectra of TiO₂ into visible region with different extent. The BET surface area of the N-S-codoped TiO₂ photocatalysts was high up to 245 m²g⁻¹. The results of degradation of methyl orange (MO) solution showed that the N-doped and N-S-codoped TiO₂ photocatalysts exhibited higher photocatalytic activity than that of Degussa P-25 and the as-prepared pure TiO₂ under visible irradiation. This property can be attributed to the results of synergetic effects of absorption in the visible light region, red shift in adsorption edge, good crystallization and large surface area of the as-prepared N-doped or N-S-codoped TiO₂.     

Preparation of titanium dioxide/tungsten disulfide composite photocatalysts with enhanced photocatalytic activity under visible light

Titanium dioxide/tungsten disulfide (TiO₂/WS₂) composite photocatalysts were fabricated via a one-step hydrothermal synthesis process, using TiCl₄ as titanium source and bulk WS₂ as sensitizer. The morphology, structure, specific surface area and optical absorption properties of the composite photocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), specific surface area analyzer and ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), respectively. The photocatalytic activity of as-prepared photocatalysts was evaluated by the degradation of methyl orange (MO) under illumination of 500W Xenon lamp. The results indicated that TiO₂/WS₂ composite photocatalysts possessed excellent photocatalytic activity, and ～95% of the degradation rate for MO was reached when molar ratio of WS₂ to TiO₂ was 0.004 and the irradiation time was 60 min. Moreover, the carrier trapping experiment and fluorescence spectra showed that ·O ₂ ^? was the key component in the photocatalytic degradation process and O₂ was reduced to be ·O ₂ ^? by the electrons from the conduction band of TiO₂ and WS₂ for the degradation of MO.     

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO₂) nanoparticles having enhanced surface area were synthesized under the interference of SiO₂. The mixed oxide, SiO₂-TiO₂ (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO₂ nanoparticles were added into the TiO₂ sols after hydrolysis. After condensation and calcination heat treatment, the SiO₂-TiO₂ nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO₂, the SiO₂ was removed subsequently by aqueous NaOH solution. The TiO₂ products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N₂ adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO₂ after calcination at 400^°C and the average pore diameter was about 7 nm. The porous TiO₂ products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ～43 nm remained constant upon calcinations from 500 to 700^°C. The specific surface area was increased up to 66% compared to regular TiO₂ samples that were prepared by the similar sol-gel procedure. The porous TiO₂ nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.     

One-step preparation of size-defined aggregates of TiO2 nanocrystals with tuning of their phase and composition

One-step route based on the thermal decomposition of the double salt (NH₄)₂TiO(SO₄)₂ (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO₂, nitrogen-doped TiO₂, TiN_xO_1−x, to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO₂ in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO₂, TiN_xO_1−x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH₃ gas by varying the temperatures. The network of anatase TiO₂ with a specific surface area up to 64 m² g⁻¹ contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO₂ and nitrogen-doped TiO₂ under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO₂ nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO₂ powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.     

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO₂) nanoparticles having enhanced surface area were synthesized under the interference of SiO₂. The mixed oxide, SiO₂-TiO₂ (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO₂ nanoparticles were added into the TiO₂ sols after hydrolysis. After condensation and calcination heat treatment, the SiO₂-TiO₂ nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO₂, the SiO₂ was removed subsequently by aqueous NaOH solution. The TiO₂ products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N₂ adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO₂ after calcination at 400^∘C and the average pore diameter was about 7 nm. The porous TiO₂ products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ∼43 nm remained constant upon calcinations from 500 to 700^∘C. The specific surface area was increased up to 66% compared to regular TiO₂ samples that were prepared by the similar sol-gel procedure. The porous TiO₂ nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.     

Titanium(IV) oxide photocatalyst of ultra-high activity: a new preparation process allowing compatibility of high adsorptivity and low electron–hole recombination probability

Microcrystalline anatase titanium(IV) oxide (TiO₂) particles were synthesized by hydrothermal crystallization in organic media (HyCOM) followed by calcination, and used in a photocatalytic reaction system of silver metal deposition. Upon elevating the post-calcination temperature, the photocatalytic activity was enhanced in spite of the simultaneous decrease in amount of surface-adsorbed Ag⁺. Comparison with the effect of calcination temperature on the other reaction systems revealed that the annealing effect became more significant with increasing number of electrons (or holes) required to complete the photocatalytic reaction process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrodeposition of titanium(IV) oxide film from sacrificial titanium anode in I2-added acetone bath

A TiO₂ film was fabricated by a simple electrochemical method using a sacrificial titanium anode as a cationic source in an I₂-dissolved acetone bath, where the solvent contains iodide ions as a supporting electrolyte but no Ti salt as an electrolyte. At the initial stage of electrolysis, anodic oxidation of Ti anode occurred under the presence of water as an impurity to acetone. Subsequently, TiO²⁺ was produced as a result of the dissolution of oxide films under the influence of iodide ions, and was then electrodeposited on the cathode surface. The morphologies of as-deposited films were found to be dependent on the film thickness, which in turn is determined by the voltage applied during the electrolysis. Moreover, the obtained films show photocatalytic activity for decomposition of gaseous acetaldehyde without annealing. In this paper, the electrodeposition mechanism is discussed in detail.     

Direct Solvothermal Formation of Nanocrystalline TiO2 on Porous SiO2 Adsorbent and Photocatalytic Removal of Nitrogen Oxides in Air over TiO2–SiO2 Composites

Solvothermal decomposition of titanium(IV) tert-butoxide (TTB) in toluene at 573 K in the presence of silica gel (SiO₂) with continuous stirring yielded a titanium(IV) oxide (TiO₂)–SiO₂ composite in which agglomerates of nanocrystalline TiO₂ were deposited on the surfaces of SiO₂ particles. Various TiO₂–SiO₂ composites having different TiO₂ contents can be synthesized by changing the ratio of TTB and SiO₂, and the composites had large surface areas corresponding to porous properties of SiO₂. These TiO₂–SiO₂ composites were used for photocatalytic removal of nitrogen oxides in air and their photocatalytic performances were compared with those of other TiO₂–SiO₂ samples prepared by different methods. Solvothermally synthesized 74 wt.%TiO₂–SiO₂ composite exhibited excellent photocatalytic performance (almost stoichiometric removal of NO _x (98%) and very low NO₂ release (0.3%)) attributable to high photocatalytic activity of TiO₂ and high adsorption property of SiO₂. Lesser performance of 74 wt.%TiO₂–SiO₂ composites prepared by other methods suggested that pore-mouth plugging of SiO₂ by TiO₂ and lower level of mixing of TiO₂ and SiO₂ decreased photocatalytic performance of the composites.     

In situ photoacoustic FTIR studies on photocatalytic oxidation of 2-propanol over titanium(IV) oxide

Adsorption and photocatalytic reaction of 2-propanol over titanium(IV) oxide (TiO₂) were studied by Fourier transform infrared spectroscopy (FTIR) using a photoacoustic (PA) technique. At first, the validity of the FTIR system using a home-made PA cell was confirmed by comparison with conventional transmission FTIR. The spectrum of TiO₂ with 2-propanol showed different propoxy peaks from those of gaseous 2-propanol as a result of chemisorption on TiO₂. Finally, in situ FTIR observation of the photocatalytic oxidation of 2-propanol was carried out. Under ultraviolet irradiation, PA spectra changed due to complete oxidation of 2-propanol through acetone as an intermediate.     

Comparative study of photocatalytic performance of titanium oxide spheres assembled by nanorods,nanoplates and nanosheets

TiO₂ spheres assembled by nanorods, nanoplates and nanosheets were fabricated by facile hydrothermal/solvothermal methods. The three samples were thoroughly characterised by scanning electron microscopy, X-ray diffraction, the Brunauer–Emmett–Teller method and UV spectroscopy. The surface area of spheres assembled by nanosheets was 83.9 m²g^–1, which is larger than that obtained for nanorods (10.8 m²g^–1) and nanoplates (6.31 m²g^–1). Their photocatalytic performance was evaluated in terms of the decomposition rate of methyl orange in these three samples under UV irradiation. The best photoactivity was observed in the samples constructed from nanosheets.     

Synthesis and enhanced photocatalytic activity of Mn/TiO2 mesoporous materials using the impregnation method through CVC process

TiO₂ particles were prepared by chemical vapor condensation and used to synthesize MnO_x/TiO₂ mesoporous materials by impregnation. The Mn-doped TiO₂ particles were smaller (8.5?nm vs. 10.5?nm) and had greater surface areas (203.7?m²?g^?1 vs. 134.4?m²?g^?1) than undoped particles. They were also smaller and had a greater surface area than similarly doped commercial P25, indicating highly dispersed Mn species on the surfaces of the crystalline TiO₂. The resulting materials?? photocatalytic activities towards methylene blue decomposition were compared: the synthesized TiO₂ particles with MnO₂ showed higher photocatalytic activity than the similarly doped commercial P25.     

Photocatalytic degradation of methylene blue with TiO2 nanoparticles prepared by a thermal decomposition process

The generation of TiO₂ nanoparticles by the thermal decomposition of titanium tetraisopropoxide (TTIP) was carried out experimentally using a tubular electric furnace at various synthesis temperatures (700-1300 °C) and TTIP heating temperatures (80-110 °C). The photocatalytic activity of the resulting TiO₂ nanoparticles was examined by measuring the rate of methylene blue decomposition. The TiO₂ nanoparticles were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) measurements and transmission electron microscopy (TEM). The crystallite size and crystallinity increased with increasing synthesis temperature and TTIP heating temperature. A TTIP heating temperature and synthesis temperature of 95 °C and 900 °C, respectively, were found to be the optimal synthesis conditions. The primary particle diameter obtained under optimum synthesis conditions was considerably smaller than the commercial photocatalyst (Degussa, P25). The specific surface areas were more than 134.4 m² g^− 1. Under the optimal conditions, the photocatalytic activity for methylene blue was higher than that of the commercial photocatalyst.     

Photocatalytic decomposition of acetaldehyde in air over titanium dioxide

The photocatalytic decomposition of acetaldehyde in air at initial concentrations ranging from 3 to 200 mg m⁻³ has been studied in a semitransparent closed box with an inlet volume of 0.056 m³. The photocatalytic reactors consisted of a glass tube, 250 mm long with inside diameters of 28, 35, or 45 mm, whose inner surface was coated with a thin film of titanium dioxide, and a 6‐W blacklight fluorescent lamp located at the axis of the glass tube. The decomposition of acetaldehyde was almost complete within 1–3 h and its main product was carbon dioxide. A kinetic study showed that the photocatalytic reaction obeys a Langmuir adsorption isotherm. Although the light intensity was certainly decreased with the distance from the light source, the degree of this decrease was much smaller than the degree of the decrease in the kinetic constants, which suggests that the light intensity is not simply proportional to the degree of the photo‐excitation of TiO₂ and the rate of the resulting photocatalytic decomposition of acetaldehyde. © 1999 Society of Chemical Industry     

Photocatalysis of methylene blue on titanium dioxide nanoparticles synthesized by modified sol-hydrothermal process of TiCl4

Titanium dioxide nanoparticles were synthesized by the hydrolysis and condensation of TiCl₄, an economic titanium precursor, in a mixed solvent of iso-propyl alcohol and water. As-prepared powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy filtering transmission electron microscopy (EF-TEM). To examine the photocatalytic activity of the as-prepared TiO₂, the photodegradation of MB which is a typical dye resistant to biodegradation has been investigated on TiO₂ powders in aqueous heterogeneous suspensions. The photocatalytic activity of TiO₂ powders prepared by the hydrolysis of TiCl₄ in the mixed solutions of iso-PrOH/H₂O exceeded that of commercial TiO₂ powders. The apparent first order rate constants (k _app) for the photodegradation of methylene blue (MB) showed a good correlation with the absorbance area obtained by UV-VIS DRS on wavelength in the limits of used lamp emission 300∼420 nm.     

Hydrothermal synthesis of titanium dioxide using acidic peptizing agents and their photocatalytic activity

We have prepared TiO₂ nanoparticles by the hydrolysis of titanium tetraisopropoxide (TTIP) using HNO₃ as a peptizing agent in the hydrothermal method. The physical properties of nanosized TiO₂ have been investigated by TEM, XRD and FT-IR. The photocatalytic degradation of orange II has been studied by using a batch reactor in the presence of UV light. When the molar ratio of HNO₃/TTIP was 1.0, the rutile phase appeared on the titania and the photocatalytic activity decreased with an increase of HNO₃ concentration. The crystallite size of the anatase phase increased from 6.6 to 24.2 nm as the calcination temperature increased from 300 °C to 600 °C. The highest activity on the photocatalytic decomposition of orange II was obtained with titania particles dried at 105 °C without a calcination and the photocatalytic activity decreased with increasing the calcination temperature. In addition, the titania particles prepared at 180 °C showed the highest activity on the photocatalytic decomposition of orange II. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.     

Multifunctionality of poly(vinyl alcohol) nanofiber webs containing titanium dioxide

We prepared titanium dioxide/PVA nanocomposite fiber webs for application in multifunctional textiles by electrospinning. The morphological properties of the TiO₂/PVA nanocomposite fibers were characterized using scanning electron microscopy and transmission electron microscopy. Layered fabric systems with electrospun TiO₂ nanocomposite fiber webs were developed using various concentrations of TiO₂ and a range of web area densities, and then the UV‐protective properties, antibacterial functions, formaldehyde decomposition ability, and ammonia deodorization efficiency of the fabric systems were assessed. Layered fabric systems with TiO₂ nanocomposite fiber webs containing 2 wt% TiO₂ nanoparticles at 3.0 g m^?2 web area density exhibited an ultraviolet protection factor of greater than 50, indicating excellent UV protection. The same system showed a 99.3% reduction in Staphylococcus aureus. Layered fabric systems with TiO₂ nanocomposite fiber webs containing 3 wt % TiO₂ nanoparticles at 3.0 g m^?2 web area density exhibited a 85.3% reduction in Klebsiella pneumoniae. Titanium dioxide nanocomposite fiber webs containing 3 wt % TiO₂ nanoparticles at 3.0 g m^?2 web area density exhibited a formaldehyde decomposition efficiency of 40% after 2 h, 60% after 4 h, and 80% after 15 h under UV irradiation. The same system showed an ammonia deodorization efficiency of 32.2% under UV irradiation for 2 h. These results demonstrate that TiO₂ nanocomposite fibers can be used to produce advanced textile materials with multifunctional properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

Photocatalytic activity of titanium dioxide coatings: Influence of the firing temperature of the chemical gel

Heterogeneous photocatalysis can be exploited for the decomposition of micro-organisms which have developed on the surfaces of building materials. In this work, the efficiency of titanium dioxide coatings on fired clay products is examined. The sol–gel method is used to synthesize a fine TiO₂ powder with a specific surface area of 180 m² g^?1. Thermal treatment of the chemical gel at 340 °C leads to crystallisation in the anatase phase and with further temperature increase, crystallite growth. For thermal treatments in the range 580–800 °C, there is a progressive transition from anatase to rutile. However, despite a decrease in specific surface area of the powder attributed to aggregation/agglomeration, the coherent domain size deduced from X-ray diffraction measurements remains almost constant at 23 nm. Once the transition is completed, increase of thermal treatment temperature above 800 °C leads to further crystallite growth in the rutile phase. The thermally treated titania powders were then sprayed onto fired clay substrates and the photocatalytic activity was assessed by the aptitude of the coating to degrade methylene blue when exposed to ultraviolet light. These tests revealed that the crystallite size is the important controlling factor for photocatalytic activity rather than the powder specific surface area or the anatase/rutile polymorph ratio.     

Photocatalytic deoxygenation of sulfoxides to sulfides over titanium(IV) oxide at room temperature without use of metal co-catalysts

Deoxygenation of sulfoxides was examined in acetonitrile suspensions of metal-free titanium(IV) oxide (TiO₂) under irradiation of UV light at room temperature. Experimental results indicate that deoxygenation was induced by the TiO₂ photocatalyst and that organic acids such as formic acid and oxalic acid are appropriate as hole scavengers in the photocatalytic reaction. Diphenyl sulfoxide was successfully deoxygenated to diphenyl sulfide with high yields, and the TiO₂ photocatalyst could be repeatedly used for deoxygenation without loss of activity. The present photocatalytic method could be applied for deoxygenation of various sulfoxides to corresponding sulfides, and phenyl vinyl sulfoxide was chemoselectively reduced to phenyl vinyl sulfide without hydrogenation of a CC double bond.