Improved Photodegradation of Organic Contaminants Using Nano‐TiO2 and TiO2–SiO2 Deposited on Portland Cement Concrete Blocks

The photocatalytic activity of TiO₂ nanoparticles (nano‐TiO₂) and its hybrid with SiO₂ (nano‐TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was studied in this work. Nanohybrid photocatalysts were prepared using an inorganic sol–gel precursor and then characterized using XRD, SEM and UV–Vis. The grain sizes were estimated by Scherrer's equation to be around 10 nm. Then, a thin layer was applied to Portland cement concrete (PCC) blocks by dipping them into nano‐TiO₂ and nano‐TiO₂–SiO₂ solution. The efficiency of coated PCC blocks for the photocatalytic decomposition of two dyes, Malachite Green oxalate (MG) and Methylene Blue (MB), was examined under UV and visible irradiation and then monitored by the chemical oxygen demand tests. The results showed that more than 80% and 92% of MG and MB were decomposed under UV–Vis irradiation using blocks coated with nano‐TiO₂–SiO₂. TiO₂/PCC and TiO₂–SiO₂/PCC blocks showed a significant ability to oxidize dyes under visible and UV lights and TiO₂–SiO₂/PCC blocks require less time for dye degradation. Based on these results, coated blocks have increased photocatalytic activity which can make them commercially accessible photocatalysts.     

Ni控制掺杂TiO2薄膜的光电化学及光催化活性

采用溶胶-凝胶法通过分步控制工艺制备了镍离子不同掺杂方式的TiO₂薄膜。通过甲基橙的光催化降解动力学来表征其光催化活性。结果表明：镍离子非均匀掺杂在掺杂量0.5%时可以明显增强TiO₂的光催化活性，而均匀掺杂提高TiO₂的光催化活性较小。光电化学表征结果显示：镍离子非均匀掺杂TiO₂薄膜的瞬时光电流信号较强，说明其光生载流子易于生成且分离效果较好；循环伏安曲线表明，光照时Ni非均匀掺杂的TiO₂薄膜改变了体系的氧化还原电位，说明了薄膜内建电场的建立。基于半导体的P-N结原理探讨了镍离子非均匀掺杂TiO₂薄膜的光催化活性机理。     

Preparation and characterization of ZnTiO<Subscript>3</Subscript>–TiO<Subscript>2</Subscript>/pillared montmorillonite composite catalyst for enhanced photocatalytic activity

ZnTiO₃–TiO₂/organic pillared montmorillonite (pMt) composite catalyst was successfully prepared in this paper by immobilizing ZnTiO₃–TiO₂ onto pMt. The composition and texture of the prepared composite catalyst were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive spectrometry, ultraviolet–visible light (UV–Vis) diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested via photocatalytic degradation of methyl blue (MB) under both visible irradiation and UV light. The results indicated that the ZnTiO₃–TiO₂/pMt composite catalyst had an apparent absorption at the area of visible irradiation, and exhibited a higher efficiency of photocatalytic degredation of MB under visible irradiation. This was due to the heterostructure of ZnTiO₃–TiO₂, and the mesoporous structure and specific surface area of the ZnTiO₃–TiO₂/pMt composite. In addition, the results of the radical scavenging experiments showed that the holes and superoxide radicals are responsible for the degradation of MB under visible irradiation.     

Effect of HF treatment on the activity of TiO2 thin films for photocatalytic water splitting

The effects of HF treatment on the activity of TiO₂ thin films for the photocatalytic water splitting reaction have been investigated. TiO₂ thin films treated with HF solution (HF-TiO₂) were found to exhibit a remarkable enhancement of the photocatalytic activity for H₂ evolution from a methanol aqueous solution, as well as efficient photoelectrochemical performance under UV light irradiation as compared with the untreated TiO₂. Moreover, Pt-loaded HF-TiO₂ thin films were found to act as efficient and stable photocatalysts for the decomposition of water under UV light irradiation. The mechanistic insights obtained in the present study will be useful in the design of highly efficient photocatalysts for the decomposition of water.     

Preparation and Formation Mechanism of Porous TiO2 Films Using PEG and Alcohol Solvent as Double-Templates

Porous nanocrystalline TiO₂ anatase thin films have been synthesized on glass substrates via a sol-gel dip-coating method. The coating sol was obtained by suppressed hydrolysis of Ti(OC₄H₉)₄ through the addition of complexing molecules as stabilizers in an alcohol solution containing polyethylene glycol (PEG). Chemical changes taking place during the sol-gel process were discussed based on IR spectra analysis. A model concerning the pore formation was established to explain the role of PEG and solvent with core-shell configuration as double-templates. The structural characteristics of porous TiO₂ films were found to greatly depend on the concentration and molecular weight of PEG, the types of stabilizing agents and solvents. The pore size of the films was tunable in the range of 10–500 nm and their surface area varied from 51 to 72 m²·g^–1.     

Comparison of optical and structural properties of nanostructure TiO2 thin film doped by Sn and Nb

The thin films of TiO₂ doped by Sn or Nb were prepared by sol–gel method under process control. The effects of Sn and Nb doping on the structural, optical and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD) high resolution transmission electron microscopy and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy. XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO₂. Titania rutile phase formation in thin film was promoted by Sn⁴⁺ addition but was inhibited by Nb⁵⁺ doping. The activity of the photocatalyst was evaluated by photocatalytic degradation kinetics of aqueous methylene blue under UV and Visible radiation. The results show that the photocatalytic activity of the Sn-doped TiO₂ thin film have a larger degradation efficiency than Nb-doped TiO₂ under visible light, but under UV light photocatalytic activity of the Nb-doped TiO₂ thin film is better.     

Enhanced photocatalytic activities of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> nanohybrids immobilized on cement-based materials for dye degradation

Using cement-based material as a matrix for photocatalytic hybrids is an important development for the large-scale application of photocatalytic technologies. In this work, photocatalytic activity of nanosized hybrids of TiO₂/SiO₂ (nano-TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was highlighted. For this purpose, an optimal inorganic sol–gel precursor was firstly applied to prepare the composites of nano-TiO₂–SiO₂ which was characterized by XRD, SEM and UV–Vis. Then, a thin layer was successfully coated on white Portland cement (WPC) blocks using a dipping process in a nano-TiO₂–SiO₂ solution. The effect of nano-TiO₂–SiO₂-coated WPC blocks on photocatalytic decomposition of three dyes, including Malachite green oxalate (MG), Methylene blue (MB) and Methyl orange (MO) were studied under UV irradiation and monitored by chemical oxygen demand tests. The results showed an increase in photocatalytic effects which depends on the structure and pH of the applied cement.     

Enhanced photo-catalytic activity of TiO2 nanostructured thin films under solar light by Sn and Nb co-doping

In this study, preparation of Sn and Nb co-doped TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of co-doping content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), field emission SEM (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy (XPS). XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO₂. Titania Rutile phase formation in thin film was promoted by Sn⁴⁺ addition but was inhibited by Nb⁵⁺ doping. The prepared co-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue (MB) solution under solar irradiation. Comparison with undoped and Sn or Nb-doped TiO₂, codoped TiO₂ shows an obviously higher catalytic activity under solar irradiation.     

Novel Photodynamic Therapy Using Water-dispersed TiO2–Polyethylene Glycol Compound: Evaluation of Antitumor Effect on Glioma Cells and Spheroids In Vitro

Titanium dioxide (TiO₂) is thought to be a photocatalytic agent excited by UV light. Our aim was to investigate the photocatalytic antitumor effect of water-dispersed TiO₂ nanoparticles on C6 rat glioma cells and to evaluate the treatment responses by the spheroid models. Water-dispersed TiO₂ nanoparticles were constructed by the adsorption of chemical modified polyethylene glycol (PEG) on the TiO₂ surface (TiO₂/PEG). Each monolayer and spheroid of C6 cells was coincubated with various concentrations of TiO₂/PEG and subsequently irradiated with UV light. Damage of the cells and spheroids was evaluated sequentially by staining with the fluorescent dyes. The cytotoxic effect was correlated with the concentration of TiO₂/PEG and the energy dose of UV irradiation. More than 90% of cells were killed after 13.5 J cm⁻² of UV irradiation in the presence of 500 μg mL⁻¹ TiO₂/PEG. The irradiated spheroids in the presence of TiO₂/PEG showed growth suppression compared with control groups. In TiO₂/PEG-treated spheroids, the number of Annexin V-FITC-stained cells gradually increased during the first 6 h, and subsequently propidium iodide-stained cells appeared. The results of this study suggest that newly developed photoexcited TiO₂/PEG have antitumoral activity. Photodynamic therapy utilizing this material can be a clue to a novel therapeutic strategy for glioma.     

Atomic layer deposition of TiO2−xNx thin films for photocatalytic applications

Titanium dioxide (TiO₂) is recognized as the most efficient photocatalytic material, but due to its large band gap energy it can only be excited by UV irradiation. Doping TiO₂ with nitrogen is a promising modification method for the utilization of visible light in photocatalysis. In this work, nitrogen-doped TiO₂ films were grown by atomic layer deposition (ALD) using TiCl₄, NH₃ and water as precursors. All growth experiments were done at 500 °C. The films were characterized by XRD, XPS, SEM and UV–vis spectrometry. The influence of nitrogen doping on the photocatalytic activity of the films in the UV and visible light was evaluated by the degradation of a thin layer of stearic acid and by linear sweep voltammetry. Light-induced superhydrophilicity of the films was also studied. It was found that the films could be excited by visible light, but they also suffered from increased recombination.     

Adsorption factor and photocatalytic degradation of dye-constituent aromatics on the surface of TiO2 in the presence of phosphate anions

The photocatalytic degradation for some kinds of dye-constituent aromatics with TiO₂ in the presence of phosphate anions in aqueous dispersion was investigated under both visible light (λ>480 nm) and UV irradiation. The influences of phosphate anion upon the degradation of organics under these different conditions was revealed by the measurement of point of zero ξ-potential (P _ZC) of TiO₂, UV-VIS spectra, HPLC and LC-MS. The adsorption and photodegradation of some organics, which adsorb on the surface of TiO₂ by a dominating group bearing a positive charge, was enhanced, while that of others, which adsorb on the surface of TiO₂ by a dominating group bearing negative charge, was depressed by the presence of phosphate anions under UV irradiation at the experimental conditions (pH 4.3). It was confirmed that better adsorption of organics on the surface of TiO₂ had an advantage in their photocatalytic degradation under UV irradiation. On the other hand, although the adsorption of rhodamine B (RhB) and methylene Blue (MB) markedly increased, their degradation under visible light irradiation was depressed in the presence of phosphate anions. It is suggested that phosphate anion greatly blocked the electron transfer from excited RhB and MB molecules as RhB and MB molecules predominantly adsorbed on the surface of TiO₂ through the electrostatic interaction with surface adsorbed phosphate anions.     

Photocatalytic Oxidation of Aniline in the Gas Phase Using Porous TiO2 Thin Films

The gas-phase photocatalytic oxidation of aniline on a new kind of porous nano-TiO₂ composite films is investigated. The composite film was prepared on glass fiber with the water glass as binders and dilute H₂SO₄ solution as solidifying reagent. The surface characters were observed by scanning electron microscope. The photocatalytic degradation of aniline on the composite films was carried out in a TiO₂/UV system. Some important factors affecting the photodegradation, such as the concentration of TiO₂, the initial concentration of aniline, and the existing water vapor, are also studied. The product of photocatalytic oxidation was detected by Fourier transform-Infrared. The partial intermediate products were absorbed on TiO₂ surface, which resulted in catalyst deactivation. But when it was irradiated under UV illumination or solar irradiation for some time, the catalyst could be reused without loss of catalytic activity. Translated from the Journal of Wuhan University (Natural Science Edition), 2005, 51(2) (in Chinese)     

Fabrication of Ordered TiO2 Porous Thin Films by Sol-Dipping PS Template Method

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS and porous TiO₂ thin films were prepared by using sol-dipping template method to fill TiO₂ sol into the interstices among the close-packed PS templates and then annealing to remove the PS templates. The effects of TiO₂ precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed pore size of the ordered TiO₂ porous thin film depended mainly on PS size and partly on TiO₂ sol concentration. The shrinkage of pore diameter was about 10% for 0.2 M and 20% for 0.4 M TiO₂ sol concentrations. X-ray diffraction (XRD) spectra indicated the porous thin film was anatase structure. The transmittance spectrum showed that optical transmittance of the porous thin film kept above 70% beyond the wavelength of 430 nm. Optical band-gap of the porous TiO₂ thin film (fired at 550^∘;C) was 3.12 eV.     

Enhanced photocatalytic activity of Ni doped TiO2 nanowire–nanoparticle hetero–structured films prepared by hydrothermal and sol–gel methods

TiO₂ nanowire-nanoparticle hetero-structured films were prepared via a sol–gel method and coated on glass substrates by dipping method for photocatalytic activity. In this study 0, 1, 3, and 5 mol% of Ni doped were studied. One-dimensional TiO₂ nanowires (NWs) were prepared by hydrothermal treatment with TiO₂ nanoparticles (NPs) which are commercially available. XRD, FESEM, DRS, and XPS were used to characterize the prepared nanowire-nanoparticle hetero-structures films. 3%Ni doped TiO₂ hetero-structured film (TNi3) had the highest photocatalytic activity on the degradation of methylene blue (MB). TNi3 films provided about 4.3 times of degradation rate compared to undoped TiO₂ (T). It revealed that TNi3 film resulted in shifting the absorption wavelength towards narrowing the energy band gap and small crystallite size. Therefore, the TNi3 film exhibited a photocatalytic activity on the degradation of MB under visible light irradiation greater than undoped film.     

Surface properties and photocatalytic activity of nanocrystalline titania films

In this work the efficiency and physicochemical details of a thin film produced by help of a microwave assisted sol gel technique is compared to different commercial powders (Degussa P25 and Hombikat UV100) deposited on glass substrates. Furthermore, a supercritical produced TiO₂ powder (SC 134) was included in the comparison.The prepared TiO₂ films were characterized using XRD, XPS, AFM, DSC and DLS. The photocatalytic activity was determined using stearic acid as a model compound. Investigation of the prepared films showed that the Degussa P25 film and the sol–gel film were the most photocatalytic active films. The activity of the films was found to be related to the crystallinity of the TiO₂ film and the amount of surface area and surface hydroxyl groups. Based on the XPS investigation of the films before and after UV irradiation it was suggested that the photocatalytic destruction of organic matter on TiO₂ films proceeds partly through formation of hydroxyl radicals which are formed from surface hydroxyl groups created by interactions between adsorbed water and vacancies on the TiO₂ surface. Furthermore a correlation between the amount of OH groups on the surface of the different TiO₂ films and the photocatalytic activity was found.     

Effect of dopant concentration on photocatalytic activity of TiO2 film doped by Mn non-uniformly

The thin films of TiO₂ doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO₂ films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO₂ films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO₂ thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO₂ films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO₂ films in terms of effective separation of the photon-generated carriers in the semiconductor.     

Preparation of nanocrystalline porous titania films on titanium substrates by a sol–gel method with polyethylene glycol as a template

Porous nanocrystalline TiO₂ films have been prepared on cp-Ti substrates for biomedical usage by a sol–gel process from the solutions containing polyethylene glycol (PEG) as a template. Variations of the crystal structure with heat-treatment temperature determined by XRD are different for TiO₂ films and powders, due to the effect of titanium substrate. The surface texture of porous TiO₂ films is analyzed by means of SEM and found to greatly depend on the concentration and molecular weight of PEG. The pore formation mechanism is discussed in relation to the self-assembly of PEG and phase separation between PEG adsorbed on TiO₂ oligomers and ethanol.     

Effect of Pt loading on the photocatalytic reactivity of titanium oxide thin films prepared by ion engineering techniques

Platinum-loaded titanium oxide thin-film photocatalysts were prepared by using an ionized cluster beam (ICB) deposition method and a RF magnetron sputtering (RF-MS) deposition method as dry processes. From the results of the photocatalytic oxidation of acetaldehyde with O₂ under UV light irradiation, small amounts of Pt loading (less than 10 nm film thickness) were found to dramatically enhance the photocatalytic reactivity. However, when TiO₂ thin films were loaded with relatively larger amounts of Pt (more than 30 nm as the film thickness), the photocatalytic reactivity became lower than for the pure TiO₂ thin films. Moreover, investigations of the ratio of Pt loaded onto the surface of the thin film catalysts by XPS measurements revealed that the small amounts of Pt loaded exist as very small clusters working to efficiently enhance the charge separation, whereas, large amounts of Pt covers the entire surface of the TiO₂ thin films, resulting in a decrease of the photocatalytic reactivity.     

Synthesis and photocatalytic properties of core–shell TiO~2@ZnIn_2S_4 photocatalyst

A novel core–shell TiO2@ZnIn2S4composite has been synthesized successfully by a simple and flexible hydrothermal route using TiO2as precursors.The as-synthesized samples were characterized by X-ray diffraction,UV–vis diffuse reflectance spectra and transmission electron microscopy.The photocatalytic properties of samples were tested by degradation of aqueous methylene blue（MB）under visible light irradiation.It was found that the as-synthesized TiO2@ZnIn2S4photocatalyst was more effcient than TiO2and ZnIn2S4in the photocatalytic degradation of MB.Moreover,TEM images confrmed the TiO2@ZnIn2S4nanoparticles possessed a well-proportioned core–shell morphology.     

Photocatalytic Degradation of Glyphosate in Water by N‐Doped SnO2/TiO2 Thin‐Film‐Coated Glass Fibers

Photocatalytic degradation of glyphosate contaminated in water was investigated. The N‐doped SnO₂/TiO₂ films were prepared via sol–gel method, and coated on glass fibers by dipping method. The effects of nitrogen doping on coating morphology, physical properties and glyphosate degradation rates were experimentally determined. Main variable was the concentration of nitrogen doping in range 0–40 mol%. Nitrogen doping results in shifting the absorption wavelengths and narrowing the band gap energy those lead to enhancement of photocatalytic performance. The near optimal 20N/SnO₂/TiO₂ composite thin film exhibited about two‐ and four‐folds of glyphosate degradation rates compared to the undoped SnO₂/TiO₂ and TiO₂ films when photocatalytic treatment were performed under UV and solar irradiations, respectively, due to its narrowest band gap energy (optical absorption wavelength shifting to visible light region) and smallest crystallite size influenced by N‐doping.