TiO2 activation using acid-treated vermiculite as a support: Characteristics and photoreactivity

Vermiculite was treated by sulfuric or nitric acid aqueous solutions with different concentration. These modified materials as the promising supports, were used to immobilize TiO₂. TiO₂ was prepared by the precursor, which was obtained by substituting partly isopropyl alcohol with Cl⁻ in titanium chloride {[Ti(IV)(OR)_nCl_m] (n = 2-3, m = 4 − n)}. The TiO₂/vermiculite composites were characterized by X-ray diffraction, scanning electron microscopy, and the nitrogen absorption. Their photocatalytic activity was evaluated by removal of methylene blue (MB). The pure anatase type crystalline phase was well deposited on the supports. The concentrations of acid for treatment had a significant influence on pore sizes and surface area of vermiculite. The treatment process changed microstructure of vermiculite, modified its characteristics, and farther improved the catalytic activity and absorption capacity of TiO₂/vermiculite composites. The treatment effect of nitric acid was superior to that of sulfuric acid.     

IR and XPS investigation of visible-light photocatalysis—Nitrogen-carbon-doped TiO2 film

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Nitrogen and carbon doping TiO_2−x−yN_xC_y films were obtained by heating the TiO₂ gel in an ionized N₂ gas and then were calcined at 500 °C. The TiO_2−x−yN_xC_y films have revealed an improvement over the TiO₂ films under visible light (wavelength, 500 nm) in optical absorption and photocatalytic activity such as photodegradation of methyl orange. X-ray photoemission spectroscopy, infrared spectrum and UV-visible (UV-vis) spectroscopy were used to find the difference of two kinds of films. Nitrogen and carbon doped into substitutional sites of TiO₂ has been proven to be indispensable for band-gap narrowing and photocatalytic activity.     

TiO2 thick films supported on reticulated macroporous Al2O3 foams and their photoactivity in phenol mineralization

TiO₂ thick films deposited on macroporous reticulated Al₂O₃ foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide^® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO₂ after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide^® P25 coated Al₂O₃ foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol-gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller.     

The synthesis and kinetic growth of anisotropic silver particles loaded on TiO2 surface by photoelectrochemical reduction method

Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO₂ films by photoelectrochemical reduction of Ag⁺ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO₂ film after UV irradiation in AgNO₃ solution is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO₂ film was obtained with the AgNO₃ concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO₂ films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO₂ films. The maximum growth rate of silver particles loaded on TiO₂ films can be up to 0.353 nm min⁻¹ among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO₂ is 1.751 × 10⁻³ min⁻¹.     

Preparation, characterization and photocatalytic performance of TiO2/CexZr1−xO2 toward the oxidation of gaseous benzene

Increasing environmental pollution caused by the volatile organic compounds due to their toxicity makes their removal imperative. So it is crucial to develop processes which can degrade these compounds effectively. The paper demonstrates that the photocatalytic activity of TiO₂ toward the decomposition of gaseous benzene in a batch reactor can be greatly enhanced by loading TiO₂ onto the surface of Ce_xZr_1−xO₂ (x ≥ 0.25) using sol-gel technology. This research investigated the relationship between x amount and the photocatalytic activity of TiO₂. The prepared photocatalysts were characterized by BET, XRD, UV-vis diffuse reflectance and XPS analyses. The specific surface area of photocatalyst decreases as x decreases. XRD results reveal the no peaks of titania were detected. Among the five catalysts prepared, only the binding energy values of Ti2p_3/2 of TiO₂/Ce_0.5Zr_0.5O₂ shift toward lower value. The order of photocatalytic activity is TiO₂/Ce_0.5Zr_0.5O₂ > TiO₂/Ce_0.75Zr_0.25O₂ > TiO₂/CeO₂ ≈ TiO₂/Ce_0.25Zr_0.75O₂ > TiO₂/ZrO₂ ≈ TiO₂. The mechanism role of Ceria-Zirconia mixed oxides in photocatalytic reaction was speculated.     

Preparation and characterization of Fe-doped TiO2 on fly ash cenospheres for photocatalytic application

Fe³⁺-doped TiO₂ film deposited on fly ash cenosphere (Fe-TiO₂/FAC) was successfully synthesized by the sol-gel method. These fresh photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA). The XRD results showed that Fe element can maintain metastable anatase phase of TiO₂, and effect of temperature showed rutile phase appears in 650 °C for 0.01% Fe-TiO₂/FAC. The SEM analysis revealed the Fe-TiO₂ films on the surface of a fly ash cenosphere with a thickness of 2 μm. The absorption threshold of Fe-TiO₂/FACs shifted to a longer wavelength compared to the photocatalyst without Fe³⁺-doping in the UV-vis absorption spectra. The photocatalytic activity and kinetics of Fe-TiO₂/FAC with varying the iron content and the calcination temperatures were investigated by measuring the photodegradation of methyl blue (MB) during visible light irradiation. Compared with TiO₂/FAC and Fe³⁺-doped TiO₂ powder (Fe-TiO₂), the degradation ratio using Fe-TiO₂/FAC increased by 33% and 30%, respectively, and the best calcined temperature was 450 °C and the optimum doping of Fe/Ti molar ratio was 0.01%. The Fe-TiO₂/FAC particles can float in water due to the low density of FAC in favor of phase separation to recover these photocatalyst after the reaction, and the recovery test shows that calcination contributes to regaining photocatalytic activity of Fe-TiO₂/FAC photocatalyst.     

Enhanced photocatalytic activity and stability of nano-scaled TiO2 co-doped with N and Fe

Titanium dioxide (TiO₂) nanoparticles co-doped with N and Fe were prepared via modified sol-gel process. The products were characterized by transmission electron microscopy (TEM), N₂ adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO₂ particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti-O-Si bond which fixed the TiO₂ on MCM-41 surface, thus restricted the agglomeration and growth of TiO₂ particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO₂ exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe³⁺ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO₂ catalysts.     

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO₂ sol-gels with various Ag/TiO₂ molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO₂ thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO₂ nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO₂ sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO₂ sol-gel, four types of the TiO₂ thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO₂), TA (bottom layer was pure TiO₂, surface layer was Ag modified), TT (pure TiO₂ thin film) and AA (TiO₂ thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I_ph). LSV confirmed the existence of Ag⁰ state in the TiO₂ thin film. SEM and XRD experiments indicated that the sizes of the TiO₂ nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO₂ thin film.     

Preparation and characterization of TiO2 photocatalysts co-doped with iron (III) and lanthanum for the degradation of organic pollutants

Titanium dioxide photocatalysts co-doped with iron (III) and lanthanum were prepared by a facile sol-gel method. The structure of catalysts was characterized by X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were evaluated by the degradation of methylene blue in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. Doping with Fe³⁺ results in a lower anatase to rutile (A-R) phase transformation temperature for TiO₂ particles, while doping with La³⁺ inhibits the A-R phase transformation, and co-doping samples indicate that Fe³⁺ partly counteracts the effect of La³⁺ on the A-R transformation property of TiO₂. Fe-TiO₂ has a long tail extending up the absorption edges to 600 nm, whereas La-TiO₂ results in a red shift of the absorption. However, Fe and La have synergistic effect in the absorption of TiO₂. Compared with Fe³⁺ and La³⁺ singly doped TiO₂, the co-doped simple exhibits excellent visible light and UV light activity and the synergistic effect of Fe³⁺ and La³⁺ is responsible for improving the photocatalytic activity.     

Sputter deposition of high transparent TiO2−xNx/TiO2/ZnO layers on glass for development of photocatalytic self-cleaning application

In this study, TiO_2−xN_x/TiO₂ double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO₂ film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO₂ film thickness, the optical transmittance of TiO_2−xN_x/TiO₂ film was compared with TiO₂ thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.     

Preparation, characterization and visible-light photocatalytic activity of AgI/AgCl/TiO2

In this paper, a novel composite photocatalyst AgI/AgCl/TiO₂ was prepared by ion exchange method and characterized by XRD, SEM and UV-Vis spectrometry. The as-prepared AgI/AgCl/TiO₂ composites show much higher photocatalytic activity than AgCl/TiO₂ and AgI/TiO₂ under visible-light irradiation (λ > 400 nm) in the process of methyl orange (MO) degradation. When the molar percentage of AgI to initial AgCl is 20% (sample SE-20%), the maximal degradation efficiency of MO has reached 85.8% after irradiation for 120 min. The enhancement of photocatalytic activity of the composite photocatalyst AgI/AgCl/TiO₂ will be attributed to its good absorption in the visible-light region, especially low recombination rate of the electron-hole pairs based on the photoluminescence (PL) spectra investigation of AgI/AgCl/TiO₂ and the matching band structures of AgI, AgCl and TiO₂. The detection of reactive species by radical scavengers displays that O₂⁻ and H₂O₂ are the main reactive species for the degradation of MO under visible-light irradiation. Moreover, PL analysis by using terephthalic acid (TA) as a probe molecule further reveals that OH can be negligible for the degradation of MO.     

Preparation and visible light photocatalytic activity of mesoporous N, S-codoped TiO2(B) nanobelts

The mesoporous N, S-codoped TiO₂(B) nanobelts are synthesized via hydrothermal synthesis and post-treatment, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption-desorption measurements (BET), X-ray photoelectron spectra (XPS), and UV-vis diffuse reflectance spectra (DRS). The results show that the prepared samples are mesoporous structured and exhibit stronger absorption in the visible light region with red shift in the absorption edge. The photocatalytic activity of N, S-codoped mesoporous TiO₂(B) nanobelts is evaluated by the photocatalytic photodegradation of potassium ethyl xanthate (KEX) under visible light irradiation. It is found that the photocatalytic activity of the prepared samples increases with increasing the molar ratio of thiourea to Ti (R). At R = 3, the photocatalytic activity of the N, S-codoped TiO₂(B) sample TBLTS-3 reaches a maximum value. With further increasing R, the photocatalytic activity of the sample decreases. The high photocatalytic activity of N, S-codoped TiO₂(B) nanobelts can be attributed to the balance between strong absorption in visible light region and low recombination rate of electron/hole pairs.     

Effect of TiO2/Al2O3 film coated diamond abrasive particles by sol-gel technique

The diamond abrasive particles were coated with the TiO₂/Al₂O₃ film by the sol-gel technique. Compared with the uncoated diamonds, the TiO₂/Al₂O₃ film was excellent material for the protection of the diamonds. The results showed that the incipient oxidation temperature of the TiO₂/Al₂O₃ film coated diamonds in air atmosphere was 775 °C, which was higher 175 °C than that of the uncoated diamonds. And the coated diamonds also had better the diamond's single particle compressive strength and the impact toughness than that of uncoated diamonds after sintering at 750 °C. For the vitrified bond grinding wheels, replacing the uncoated diamonds with the TiO₂/Al₂O₃ film coated diamonds, the volume expansion of the grinding wheels decreased from 6.2% to 3.4%, the porosity decreased from 35.7% to 25.7%, the hardness increased from 61.2H_RC to 66.5H_RC and the grinding ratio of the vitrified bond grinding wheels to carbide alloy (YG8) increased from 11.5 to 19.1.     

Visible-light-activated Ce-Si co-doped TiO2 photocatalyst

To enhance the visible photocatalytic activity and thermal stability of TiO₂, Ce-Si co-doped TiO₂ materials were synthesized through a nonaqueous method of which the purpose was to reduce the aggregation between TiO₂ particles. The obtained materials maintained anatase phase and large surface area of 103.3 m² g⁻¹ even after calcined at 800 °C. The XPS results also indicated that Si was weaved into the lattice of TiO₂, and Ce mainly existed as oxides on the surface of TiO₂ particles. The doped Si might enhance surface area and suppress transformation from anatase to rutile, while the doped Ce might cause visible absorption and inhibit crystallite growth during heat treatment. Evaluated by decomposing dye Rhodamine B, visible photocatalytic activity of Ce-Si co-doped TiO₂ was obviously higher than that of pure TiO₂ and reached the maximum at Ce and Si contents of 0.5 mol% and 10 mol%.     

Low temperature synthesis of iodine-doped TiO2 nanocrystallites with enhanced visible-induced photocatalytic activity

Iodine-doped TiO₂ nanocrystallites (denoted as I-TNCs) were prepared via a newly developed triblock copolymer-mediated sol-gel method at a temperature of 393 K. I-doping, crystallization and the formation of porous structure have been simultaneously achieved. The obtained particles were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-vis spectrophotometer. The results indicated that the as-prepared I-TNCs possessed a diameter of ca. 5 nm with anatase crystalline structure and a specific surface area of over 200 m² g⁻¹. The presence of iodine expanded the photoresponse in visible light range, and led to enrich in surface hydroxyl group on the TiO₂ surface. Compared with the commercial photocatalyst P25, the I-TNCs significantly enhanced the photocatalytic efficiency in the degradation of rhodamine B and 2,4-dichlorophenol, and the I-TNCs with 2.5 mol% doping ratio exhibited the best photocatalytic activity.     

Preparation and characterization of visible light responsive Fe2O3-TiO2 composites

In this study we present the effects of iron oxide (Fe₂O₃) on titanium dioxide (TiO₂) in synthesising visible-light reactive photocatalysts. A Fe₂O₃-TiO₂ composite photocatalyst was synthesized from Fe₂(SO₄)₃ and Ti(SO₄)₂ by a ethanol-assisted hydrothermal method. The preparation conditions were optimized through the investigation of the effects of hydrothermal temperature and time as well as molar ratio of Ti to Fe on the photocatalytic activity. The visual, physical and chemical properties of the Fe₂O₃-TiO₂ composites were investigated. The results showed that α-Fe₂O₃ and anatase TiO₂ were present in the composites. The Fe₂O₃-TiO₂ synthesized under optimum condition consisted of mesoporous structure with an average pore size of 4 nm and a surface area of 43 m²/g. Under visible and solar light irradiation, the photocatalytic activity of optimized sample was significantly higher than that of pure TiO₂. This sample led to a photodegradation efficiency of 90% and 40% of auramine under visible light and solar light, respectively.     

Role of Cl ions in photooxidation of propylene on TiO2 surface

The effect of Cl⁻ ions on photooxidation of propylene on TiO₂ semiconductor was investigated. Cl⁻/TiO₂ catalysts were prepared by annealing Degussa P25 TiO₂ in the gas flow of N₂ and Cl₂ under 100-400 °C. The photocatalytic oxidation of propylene was carried out in a continuous flow system, with the chromatograph to analyze the products on line. The experimental results showed that the activity of Cl⁻/TiO₂ catalysts increased as heat-treated temperature decreased. The activity of the sample heat-treated at 100 °C was about two times higher than that of pure TiO₂. Moreover, as to TiO₂, the main product of the propylene photocatalytic oxidation was CO₂, but with Cl⁻/TiO₂ catalysts, not only CO₂ but also trace CO was determined. The adsorbed species on TiO₂ surface before and after reaction were analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric/differential thermal analyses (TG-DTA) coupled to a mass spectrometer (MS). XPS analysis showed that there was Cl⁻ absorbed on the Cl⁻/TiO₂ surface, and the absorption amount of Cl⁻ decreased after the photooxidation reaction of propylene. TG-DTA-MS analysis confirmed chlorine absorbed on the surface of TiO₂ in the form of Cl⁻ ion. These results illuminated that absorbed Cl⁻ on the surface of TiO₂ formed a weak physical absorption on TiO₂ at low temperature, and subsequently participated in the photooxidation of propylene, finally removed from TiO₂ surface.     

Synthesis and photocatalytic properties of porous TiO2 films prepared by ODA/sol-gel method

Porous TiO₂ films were deposited on SiO₂ pre-coated glass-slides by sol-gel method using octadecylamine (ODA) as template. The amount of ODA in the sol played an important role on the physicochemical properties and photocatalytic performance of the TiO₂ films. The films prepared at different conditions were all composed of anatase titanium dioxide crystals, and TiO₂ crystalline size got larger with increasing ODA amount. The maximum specific surface area of 41.5 m²/g was obtained for TiO₂ powders prepared from titanium sol containing 2.0 g ODA. Methyl orange degradation rate was enhanced along with increasing ODA amount and reached the maximal value at 2.0 g addition of ODA. After 40 min of UV-light irradiation, methyl orange degradation rate reached 30.5% on the porous film, which was about 10% higher than that on the smooth film. Porous TiO₂ film showed almost constant activity with slight decrease from 30.5% to 28.5% after 4 times of recycles.     

New high-resolution analysis of the {ν1 + ν3} band of the NO2 isotopomer of nitrogen dioxide: Line positions and intensities

The high-resolution Fourier transform absorption spectrum of an isotopic sample of nitrogen dioxide, ¹⁵N¹⁶O₂, was recorded in the 3.4 μm region. Starting from the results of a previous study [Y. Hamada, J. Mol. Struct. 242 (1991) 367-377] a new analysis of the ν₁ + ν₃ band located at 2858.7077 cm⁻¹ has been performed. This new assignment concerns (1 0 1) energy levels involving rotational quantum numbers up to K_a = 10 and N = 54. Using a theoretical model which accounts for both the electron spin-rotation resonances within each vibrational state and the Coriolis interactions between the (1 2 0) and (1 0 1) vibrational states, the spin-rotation energy levels of the (1 0 1) vibrational state could be reproduced within their experimental uncertainty. In this way, the precise vibrational energy, rotational, spin-rotation, and coupling constants were achieved for the {(1 2 0), (1 0 1)} interacting states of ¹⁵N¹⁶O₂. Using these parameters and the transition moment operator which was obtained for the main isotopic species, ¹⁴N¹⁶O₂, a comprehensive list of the line positions and intensities was generated for the ν₁ + ν₃ band of ¹⁵N¹⁶O₂.     

A novel approach towards high-performance composite photocatalyst of TiO2 deposited on activated carbon

TiO₂ photocatalysts deposited on activated carbon (TiO₂/AC) were prepared by dip-hydrothermal method at 180 °C using peroxotitanate as a precursor, then calcinated at 300-800 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and the nitrogen absorption. Their photocatalytic activity was evaluated by degradation of methyl orange (MO). The results showed that TiO₂ particles of anatase type were well deposited on the activated carbon surface. TiO₂/AC calcinated at 600 °C exhibited the best photocatalytic performance. For the comparison, the same photocatalysis experiment was carried out for two mixtures of commercial TiO₂ (Degussa P25) with AC and synthetic TiO₂ with AC. It was found that the composite catalyst TiO₂/AC was better than the two mixtures. Besides, different from fine powdered TiO₂, the granular TiO₂/AC photocatalysts could be easily separated from the bulk solution and reused; indeed, its photocatalytic ability was hardly decreased after a five-cycle for MO degradation. The kinetics of the MO degradation fitted well the Langmuir-Hinshelwood model.