Promotional effects of carbon nanotubes on V2O5/TiO2 for NOX removal

A series of V₂O₅/TiO₂-carbon nanotube (CNT) catalysts were synthesized by sol-gel method, and their activities for NO_X removal were compared. A catalytic promotional effect was observed by adding CNTs to V₂O₅/TiO₂. The catalyst V₂O₅/TiO₂-CNTs (10 wt.%) showed an NO_X removal efficiency of 89% at 300 °C under a GHSV of 22,500 h⁻¹. Based on X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, NH₃-temperature-programmed desorption, temperature-programmed reduction, Brunauer-Emmett-Teller surface area measurements, differential scanning calorimetry, and thermogravimetric analysis, the increased acidity and reducibility, which could promote NH₃ adsorption and oxidation of NO to NO₂, respectively, contributed to this promotion.     

The fabrication of the antibacterial paste based on TiO2 nanotubes and Ag nanoparticles-loaded TiO2 nanotubes powders

ABSTRACT

We successfully synthesised TiO₂ nanotubes (TNTs) and silver nanoparticles (Ag NPs)-loaded TiO₂ nanotubes paste. These were coated on a glass substrate by spin coating method, and their antibacterial activities were surveyed. The morphology of materials was defined by transmission electron microscopy (TEM) image; the crystalline structure and the composition of the materials were determined by X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS). Vibrational properties of the molecules existing in the sample were investigated by Fourier transform infrared (FTIR) spectroscopy, and the transmittances of films were determined by UV–Vis transmittance spectroscopy. This research shows that the structure and morphology of TNTs did not change after they underwent the processes of paste preparing and film coating on a glass substrate. Furthermore, the transmittance of TNTs film (about 75%) is higher than Ag NPs-loaded TiO₂ nanotubes (Ag/TNTs) film (about 65%) in the visible region. Moreover, the antibacterial property of Ag/TNTs film shows its effectiveness against Escherichia coli bacteria, and the antibacterial efficiency is 99.06% for 24 h-incubation period in the dark condition.     

Nanostructural and chemical characterization of supported metal oxide catalysts by aberration corrected analytical electron microscopy

The performance of catalyst materials are usually governed by the precise atomic structure and composition of very specific catalytically active sites. Therefore, structural and chemical characterization at the atomic scale becomes a vital requirement in order to identify any structure-performance relationships existing in heterogeneous catalyst systems. Aberration-corrected scanning transmission electron microscopy (STEM) represents an ideal means to probe the atomic scale structural and chemical information via a combination of various imaging and spectroscopy techniques. In particular, high-angle annular dark-field (HAADF) imaging provides directly interpretable atomic number (Z) contrast information; while X-ray energy dispersive spectroscopy (XEDS) and electron energy-loss spectroscopy (EELS) spectrum imaging can be used to identify the chemical composition and oxidation state. Here we review some applications of aberration-corrected STEM to catalyst research, firstly in the context of supported metal catalysts, which serve as ideal material systems to illustrate the power of these techniques. Then we focus our attention on more recent progress relating to the characterization of supported metal oxide catalysts using aberration-corrected STEM. We demonstrate that it is now possible to directly image supported surface oxide species, study oxide wetting characteristics, identify the catalytic active sites and develop new insights into the structure-activity relationships for complex double supported oxide catalysts. Future possibilities for in situ and gentle low voltage electron microscopy studies of oxide-on-oxide materials are also discussed.     

Facile synthesis of copper oxide nanotubes decorated by TiO2 nanoparticles,optical and photocatalytic activity in water

Copper oxide nanotubes decorated by TiO₂ nanoparticles (CNTNs) were fabricated by simple three-step method. First, deposition of copper onto cellulose fibres, then thermal oxidation of copper and cellulose fibres and last simply mixing copper oxide nanotubes and TiO₂ nanoparticles (NPs). Scanning electron microscopy, transmission electron microscopy and X-ray diffraction showed that the synthesised nanotubes were monoclinic-structured polycrystalline CuO with diameter and wall thickness of approximately 50～100 nm and 20～25 nm, respectively. Moreover, the diameter of the TiO₂ NPs is about 20～30 nm. Optical properties of the solutions containing copper oxide nanotubes decorated by TiO₂ NPs were studied. Discrete dipole approximation was used for the calculation of absorption, scattering and extinction cross sections of the deposited CNTNs on a glass substrate. Our simulation results show that there are good agreements between the experimental date and the simulation results. Moreover, the photocatalytic tests were done by methyl orange under visible light (λ = 633 nm) irradiation for prepared samples.     

Synthesis and photocatalytic property of SnO2/TiO2 nanotubes composites

SnO2/TiO2 nanotubes composite photocatalysts with different SnO2 contents were successfully synthesized by means of a simple solvothermal process. The synthesized products were characterized physically by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The composite photocatalysts can not only make the target pollutant, methylene blue (MB), adsorbed at a high concentration level around the surface of the composites but also decrease the recombination rate of electron-hole pairs so as to achieve good photocatalytic performance. The effect of SnO2 contents on the photocatalytic activities of the composites was also investigated. The results showed that the SnO2/TiO2 nanotubes composite photocatalyst with 5 wt.% SnO2 loading had the highest photocatalytic efficiency.     

Novel method for doping nano TiO2 photocatalysts by chemical vapour deposition

Highly active photocatalytic Fe-doped nano TiO₂ was successfully synthesised by chemical vapour deposition (CVD) method using FeCl₃ as Fe source. CVD was carried out by evaporating FeCl₃ at 350°C in nitrogen flow during 30–90?min. The amount of Fe incorporated into TiO₂ framework is adjusted by the amount of FeCl₃ used and the evaporation time. The obtained sample was characterised by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), energy dispersive X-ray spectroscopy (EDS), UV-Vis, Fourier transform-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of the samples were tested in photocatalytic decomposition of 2-propanol in liquid phase using visible light instead of UV light irradiation. Non-doped TiO₂ and high Fe loading TiO₂ samples showed very low photocatalytic activity, whereas the low Fe loading TiO₂ sample exhibited high photocatalytic activity under visible light. The high photocatalytic activity of this sample was rationalised by the existence of defects (Ti–OH groups) as the active sites.     

Photocatalytic reduction of Cr(VI) over different TiO2 photocatalysts and the effects of dissolved organic species

The toxic Cr(VI) in industrial wastewaters can be removed by a reduction from Cr(VI) to Cr(III) and a followed precipitation treatment. The reduction of Cr(VI) to Cr(III) is able to be achieved by a photocatalytic process. Thus, photocatalytic reduction of Cr(VI) over TiO2 catalysts was investigated in both the absence and presence of organic compounds. The TiO(2) catalyst was pre-calcined at different temperatures to tune the photocatalytic activity and surface area of the photocatalyst. Under the tested conditions, the photocatalytic reduction of Cr(VI) behaved as a pseudo-first-order reaction in kinetics. In the absence of any organic species, the rate constant (kCr) for the photocatalytic reduction of Cr(VI) was found to be increased initially, passing a maximum, and then decreased, as calcination temperature was increased. In the presence of organic compounds, however, kCr was decreased with the increase of calcination temperature. A marked synergistic effect between the photocatalytic reduction of Cr(VI) and organic compounds was observed over the photocatalyst with the largest specific surface area. These results demonstrated that the photocatalytic reduction of Cr(VI) alone was dependent on both of specific surface area and crystalline structure of the photocatalyst in the absence of any organic compounds, but was dominated by the specific surface area of the photocatalyst in the presence of organic compounds because of the synergistic effect between the photocatalytic reduction of Cr(IV) and the photocatalytic oxidation of organic compounds.     

Photocatalytic degradation of gaseous benzene over TiO2/Sr2CeO4: kinetic model and degradation mechanisms

Photocatalytic oxidation of benzene in air was carried out over TiO2/Sr2CeO4 catalysts. The prepared photocatalyst was characterized by SBET, UV-vis diffuse reflectance and XPS. TiO2/Sr2CeO4 absorbs much more visible light than TiO2 in the visible light region. The XPS spectrum shows that the binding energy value of Ti 2p3/2 transfers to a lower value. The main purpose was to investigate the kinetic model and degradation mechanisms. The kinetic data matched well with the Langmuir-Hinshelwood (L-H) kinetic model with the limiting rate constant and the adsorption constant in this case were 0.0064 mg l-1 min-1 and 9.2078 l mg-1, respectively. No gas-phase intermediates were detected by direct GC/FID analysis under the conditions despite the high benzene concentration. Ethyl acetate and (3-methyl-oxiran-2-yl)-methanol were two major identified intermediates which were accompanied by butylated hydroxytoluene, 2,6-bis(1,1-dimethylethyl)-4,4-dimethylycyclohe, 2,5-cyclohexadiene-1,4,dione,2,6-bis(1,1-dim). It is plausible that at least one of these less-reactive intermediates caused the deactivation of the photocatalyst. Finally, the photocatalytic oxidation mechanisms were speculated.     

An easier method of preparation of mesoporous anatase TiO2 nanoparticles via ultrasonic irradiation

Mesoporous anatase TiO₂ nanopowder was synthesised by the sol–gel method using ultrasonic irradiation. This method is simple and faster for the synthesis of phase pure mesoporous anatase TiO₂ nanopowder. The product is characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), thermo gravimetric analysis, Brunauer–Emmett–Teller (BET) surface area, UV–visible diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy. Analysis of XRD patterns, SEM and TEM image shows that the average particles size is of 19.9 nm and has an anatase structure. The mesoporous nature was determined by the BET method using the Barrett–Joyner–Halenda (BJH) model.     

Solar photocatalytic degradation of isoproturon over TiO2/H-MOR composite systems

The photocatalytic degradation and mineralization of isoproturon herbicide was investigated in aqueous solution containing TiO₂ over H-mordenite (H-MOR) photocatalysts under solar light. The catalysts are characterized by X-ray diffraction (XRD), UV–Vis diffused reflectance spectra (UV–Vis DRS), Fourier transform-infra red spectra (FT-IR) and scanning electron microscopy (SEM) techniques. The effect of TiO₂, H-MOR support and different wt% of TiO₂ over the support on the photocatalytic degradation and influence of parameters such as TiO₂ loading, catalyst amount, pH and initial concentration of isoproturon on degradation are evaluated. 15 wt% TiO₂/H-MOR composite is found to be optimum. The degradation reaction follows pseudo-first order kinetics and is discussed in terms of Langmuir–Hinshelwood (L–H) kinetic model. The extent of isoproturon mineralization studied with chemical oxygen demand (COD) and total organic carbon (TOC) measurements and 80% mineralization occurred in 5 h. A plausible mechanism is proposed based on the intermediates identified by liquid chromatography–mass spectroscopy (LC–MS).     

Photocatalytic degradation of aqueous propoxur solution using TiO2 and Hbeta zeolite-supported TiO2

Photocatalytic activity of TiO2 and zeolites supported TiO2 were investigated using propoxur as a model pollutant. Hbeta, HY and H-ZSM-5 zeolites were examined as supports for TiO2. Hbeta was chosen as the TiO2 support based on the adsorption capacity of propoxur on these zeolites (Hbeta>HY=H-ZSM-5). TiO2/Hbeta photocatalysts with different wt.% were prepared and characterized by XRD, FT-IR and BET surface area. The progress of photocatalytic degradation of aqueous propoxur solution using TiO2 (Degussa P-25) and TiO2 supported on Hbeta zeolite was monitored using TOC analyzer, HPLC and UV-vis spectrophotometer. The degradation of propoxur was systematically studied by varying the experimental parameters in order to achieve maximum degradation efficiency. The initial rate of degradation with TiO2/Hbeta was higher than with bare TiO2. TOC results revealed that TiO2 requires 600min for complete mineralization of propoxur whereas TiO2/Hbeta requires only 480min. TiO2/Hbeta showed enhanced photodegradation due to its high adsorption capacity on which the pollutant molecules are pooled closely and hence degraded effectively.     

Reactive dyes remotion by porous TiO2-chitosan materials

In this work, the aim was to evaluate the remotion (adsorption plus degradation) of two reactive dyes, Methylene Blue (MB) and Benzopurpurin (BP), from aqueous solutions by the utilization of TiO2-chitosan microporous materials. Two different TiO2-chitosan hybrid materials were synthesized: TiO2-Chit A with 280 mg chitosan/gTiO2 and TiO2-Chit B with 46.76 mg chitosan/g TiO2. Adsorption data obtained at different solution temperatures (25, 35, and 45 degrees C) revealed an irreversible adsorption that decrease with the increment of T. Langmuir, Freundlich and Sips isotherm equation were applied to the experimental data. The obtained parameters and correlation coefficient showed that the adsorption of both dyes on TiO2-Chit A at the three work temperatures was best predicted by the Langmuir isotherm, while Sips equation adjusted better to adsorption data on TiO2-Chit B. The adsorption enthalpy was relatively high and varied with T, indicating that interaction between adsorbent and adsorbate molecules was not only physical but chemical. There is a change in the adsorption heat capacity, (Delta(ads)C(p)<0), related with intense hydrophobic interactions. The kinetic adsorption data were processed by the application of Lagergren and Avrami models. It was found that adsorption of both dyes on both adsorbents under the operating conditions was best predicted by Avrami model. The variation of kinetic order, n, and k(av) with T are related to a pore followed by intra particle diffusion control of the adsorption rate. MB photodegradation on both TiO2-chitosan hybrid materials was of 91 (in A) and 41% (in B) and augmented with the chitosan content. For BP can be seen that the process in darkness resulted in a high remotion capacity than in UV light presence.     

Study of the photocatalytic degradation of toluene over CdS-TiO2 nanoparticles supported on multi-walled carbon nanotubes by back propagation neural network

To optimize the photocatalytic conditions for the degradation of volatile organic compounds (VOCs), this study focused on the application of a back propagation (BP) neural network to determine the photocatalytic performance of CdS-TiO₂ nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) for toluene degradation. This was accomplished by first characterizing the photocatalyst using transmission electron microscopy (TEM), N₂ adsorption-desorption, X-ray diffraction (XRD) and UV-visible absorption spectrum (UV-vis). It was observed that TiO₂ and CdS particles were uniformly supported on the inner and outer walls of MWCNTs as a composite catalyst. Second, employing a test that included a training set and a prediction set, the results showed that the designed BP neural network exhibited a fast convergence speed and the system error was 0.0009702. Furthermore, the predictive values of the network were in good agreement with the experimental results, and the correlation coefficient was 0.9880. These results indicated that the network had an excellent training accuracy and generalization ability, which effectively reflected the performance of the system for the catalytic oxidation of toluene on a CdS-TiO₂/MWCNTs photocatalyst.     

Surface Modification of Sericite Using TiO2 Powders Prepared by Alkoxide Hydrolysis: Whiteness and SPF Indices of TiO2-Adsorbed Sericite

Titania (TiO₂) powders have been prepared from the 0.025-M titanium isopropoxide/ethanol solution and the 0.5-M distilled water/ethanol solution. The prepared TiO₂ powders showed an anatase phase and a rutile phase after heat treatment at 500°C for 2 h and 1000°C for 2 h, respectively. The heterocoagulation adsorption between TiO₂ powder and sericite surface in water was achieved in the range of pH 3.63.7 (where this pH range shows a maximum Zeta-potential difference for two powders). On the other hand, an anomalous transformation behavior appeared in the TiO₂-adsorbed sericite after heat treatment at 1000°C. The surface modification of sericite through the TiO₂-adsorption improved the whiteness as well as the SPF (Sun Protection Factor) indices.     

Preparation of fine,uniform nitrogen- and sulfur-modified TiO2 nanoparticles from titania nanotubes

Abstract

TiO₂ nanoparticles modified with nitrogen and sulfur were prepared from titania nanotubes by a facile wet chemistry method. The samples synthesized with different thiourea/TiO₂ ratios showed a uniform nanoparticle size distribution centred at approximately 10 nm with a developed specific surface area of 246 m² g^-1. These modified nanosized photocatalysts exhibited higher photocatalytic activity for the degradation of gaseous isopropanol than unmodified titania nanotubes under visible illumination. This could be attributed to the synergistic effects of a large specific surface area, strong absorption in the visible region, a redshift in the adsorption edge, and surface adsorption modification induced by nitrogen and sulfur compounds.     

Preparation of fine,uniform nitrogen- and sulfur-modified TiO2 nanoparticles from titania nanotubes

TiO₂ nanoparticles modified with nitrogen and sulfur were prepared from titania nanotubes by a facile wet chemistry method. The samples synthesized with different thiourea/TiO₂ ratios showed a uniform nanoparticle size distribution centred at approximately 10 nm with a developed specific surface area of 246 m² g^-1. These modified nanosized photocatalysts exhibited higher photocatalytic activity for the degradation of gaseous isopropanol than unmodified titania nanotubes under visible illumination. This could be attributed to the synergistic effects of a large specific surface area, strong absorption in the visible region, a redshift in the adsorption edge, and surface adsorption modification induced by nitrogen and sulfur compounds.     

Ti靶及TiO2靶溅射TiO2薄膜微观形貌、结构及光学性质研究

利用射频磁控溅射技术通过Ti靶及TiO2靶在氩氧气氛中同时溅射制备TiO2薄膜,并对所得的样品进行不同温度的退火处理。采用X射线衍射、扫描电子显微镜、拉曼光谱和吸收谱研究了不同的靶材及退火温度对TiO2薄膜晶体结构、微观形貌及光学性质的影响。结果表明:由于靶材的不同,Ti靶溅射时氧分压较低,造成薄膜中存在大量的氧缺陷,晶相发育不完善,颗粒相比TiO2靶溅射时较小,从XRD和拉曼光谱来看,Ti靶溅射得到的TiO2薄膜更有利于金红石相的形成。薄膜的透过率随退火温度的升高而降低,TiO2靶材溅射的薄膜的光学带隙随温度升高而明显降低,而Ti靶得到的薄膜的光学带隙对退火温度的依赖关系不明显。     

Different methods in TiO2 photodegradation mechanism studies: gaseous and TiO2-adsorbed phases

The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution. It is proved that the photo-oxidizing properties of photocatalyst (TiO(2)) activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by TiO(2). This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant's adsorption on the photocatalyst and radical degradation reactions. The main objective of the study is the understanding of the TiO(2)-photocatalysis phenomenon including gaseous and adsorbed phase mechanisms. Results obtained with three different apparatus are compared; gaseous phases are analysed and mechanisms at the gaseous phase/photocatalyst interface are identified. This study leads to improve understanding of various mechanisms during pollutant photodegradation: adsorption of pollutants on TiO(2) first takes place, then desorption and/or photodegradation, and finally, desorption of degradation products on TiO(2). The association of analytical methods and different processes makes the determination of all parameters that affect the photocatalytic process possible. Mastering these parameters is fundamental for the design and construction of industrial size reactors that aim to purify the atmosphere.     

The multi-staged formation process of titanium oxide nanotubes and its thermal stability

The multi-staged formation process of titanium oxide nanotubes was investigated in detail under a hydrothermal treatment. During the synthesis procedure, an intermediate stage (tree-like structures) was observed before the formation of the titanium oxide layered structures. The layered structure of titanium oxide generally was considered to exfoliate directly from raw TiO₂ materials through the alkaline hydrothermal treatment. The rolling process of the layered structures of titanium oxide was confirmed by TEM observation after the alkaline hydrothermal treatment for the raw TiO₂ materials, followed by washing with 4 M HNO₃ aqueous solution. The thermal stability of the tube products was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that both the morphology and crystal phase of titanium oxide nanotubes could be retained even after calcination at 650 °C.