Photocatalytic Decomposition of Acetaldehyde with Anatase Nanocrystals-Dispersed Silica Films Prepared by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals of 5 to 10 nm in diameter were formed in the silica-titania films by treatment with hot water. The formation of nanocrystals with hot water treatment was a unique phenomenon to the silica-titania system and the addition of organic polymers such as PEG was indispensable for the high dispersion of anatase nanocrystals in the films. The hydrolysis of Si—O—Ti bonds with hot water was considered to play an important role for the formation of anatase nanocrystals. The resultant films were transparent even after the formation of anatase nanocrystals. Acetaldehyde was photocatalytically decomposed into CO₂ on the films which were subjected to a hot water treatment. The amounts of generated CO₂ were twice of that of introduced acetaldehyde, indicating that the total acetaldehyde was completely decomposed to CO₂. Anatase nanocrystals-dispersed films can be formed on various kinds of substrates including those with poor heat resistance such as organic polymers and organisms by this process, so that the substrates coated with the films are expected to be widely used for photocatalytic applications.     

Formation of Anatase Nanocrystals-Precipitated Silica Coatings on Plastic Substrates by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals-precipitated silica coatings were formed on plastic substrates such as poly(ethylene terephtalate) (PET), acrylic resin (AC) and polycarbonate (PC) from silica-titania gel coatings with and without addition of poly(ethylene glycol) (PEG) by hot water treatment. The maximum thickness of the coatings which can be formed without cracking or peeling-off was 100 to 200 nm for PET and PC substrates, whereas it was less than 50 nm for AC substrates. After a hot water treatment at 90°C for 120 min, the size of the anatase nanocrystals increased to be 30 and 50 nm for the coatings obtained with and without PEG, respectively. Anatase nanocrystals were formed throughout the whole of the coatings obtained with PEG and were formed only on the surface of the coatings obtained without PEG. Both coatings obtained with and without PEG were highly transparent. The plastic substrates with coatings obtained without PEG showed good weathering resistance owing to the protective effects of the residual silica under-layer. The coatings obtained with PEG showed higher photocatalytic activities than those obtained without PEG due to smaller size and higher dispersion of anatase nanocrystals in the coatings.     

Formation of Anatase Nanocrystals in Sol-Gel Derived TiO2-SiO2 Thin Films with Hot Water Treatment

We have successfully prepared transparent and porous anatase nanocrystals-dispersed films by treating the sol-gel derived TiO₂-SiO₂ films containing poly(ethylene glycol), PEG, with hot water. This process was done at temperatures lower than 100°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The changes in structure and composition of the TiO₂-SiO₂ gel films with hot water treatment were related to the formation process of anatase nanocrystals in the TiO₂-SiO₂ gel films with hot water treatment. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si–O–Ti bonds and dissolution of SiO₂ component. In addition, porous film structure formed by leaching of PEG with hot water treatment led to homogenous dispersion of anatase nonocrystals in the films.     

液相沉积法制备光催化活性TiO2膜

锐钛矿型TiO2薄膜;液相沉积法制备光催化活性TiO2膜     

金红石/锐钛矿混晶结构的TiO2薄膜光催化活性

采用磁控溅射法制备出一组金红石/锐钛矿混晶结构的纳米TiO2薄膜催化剂,并通过光催化降解苯酚实验考察该薄膜的催化性能. 光催化实验证明, 随着催化剂中金红石含量减少, 催化剂的光催化活性逐渐提高. X射线衍射(XRD)、X射线光电子能谱(XPS)、表面光电压谱(SPS)和原子力显微镜(AFM)结果表明, 催化剂为金红石和锐钛矿混晶结构, 并随着金红石含量减少, 催化剂的表面羟基(OH)和桥氧(—O—)的含量逐渐增加, 而且费米能级逐渐提高. 表面羟基和桥氧是有利于光催化的“活性物种”; 费米能级的提高使TiO2/H2O 面处TiO2的表面带弯增大, 导致了价带光生空穴参加光催化反应的几率增大, 有效地促进了光生载流子的分离; 这些因素是催化剂光催化活性逐渐提高的主要原因.     

Preparation,Microstructure and Photocatalytic Activity of the Porous TiO2 Anatase Coating by Sol-Gel Processing

In this study the porous TiO² anatase coatings are prepared from alkoxide solutions containing polyethylene glycol (PEG) by a dip-coating technique. The effects of PEG addition to the precursor solution on the photocatalytic activity and microstructure of the resultant coatings are studied. The larger amount and the larger molecular weight of PEG, the larger size and more pores produced in the resultant coatings on the decomposition of PEG during heat-treatment. The adsorbed hydroxyl content of such porous coatings is found to increase due to the larger size and more pores in the coatings. However, the transmittance of the coatings decreases due to the scattering by the larger size and more pores. Photocatalytic degradation experiments show that organophosphorous insecticide, dimethyl-2,2-dichlorovinyl phosphate (DDVP), was efficiently degraded in the presence of the porous TiO₂ coatings by exposing the DDVP solution to sunlight. Photocatalytic degradation rate was related to the adsorbed hydroxyl content, transmittance and morphology of the resultant coatings.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.     

TiCl4水解法制备TiO2薄膜的表征及光催化性能

TiCl4水解法制备TiO2薄膜的表征及光催化性能;TiCl4水解;TiO2薄膜;光催化;乙酸     

Defect-enhanced Photocatalytic Activity of ZnO Micro/nanostructures

ZnO micro/nanocrystals with controlled oxygen defects are successfully prepared through annealing precursors obtained via a simple solvothermal method. The size and surface defects of the as-synthesized ZnO mi- cro/nanocrystals increase with the solvent volume ratio of water/ethanol increasing; the BET surface areas of the corresponding samples decrease during these processes; photoluminescence reveals that the type and concentration of surface defects （oxygen vacancy and interstitial oxygen） are quite different for the samples prepared via different solvent volume ratio of water/ethanol. In addition, it is found that the photocatalytic activity of the synthesized ZnO nanocrystals is mainly dependent on the concentration of surface defects. The sample with more surface defects ex- hibits higher photocatalytic activity toward the degradation of methylene blue （MB）. The possible photocatalytic mechanism is discussed in detail.     

Interaction and Microstructure of Polyurethane/Silica Hybrid Films Prepared by Sol-Gel Process

The polyester/silica hybrid resins and their hybrid polyurethanes were prepared via in situ (IS) or blending (BL) method using different silica sols. The effects of preparation methods, silica type and content on the interaction and microstructure of polymer/silica hybrid materials were investigated by FTIR, viscosity measurement, TGA, DMA and SAXS, respectively. It was found that both IS and BL methods formed agglomerates of silica-rich phases and primary silica-rich phases in the hybrid films, but the former caused stronger interaction between silica and polymer than the latter, resulting in much bigger agglomerates and compacter structure. The ethoxy group at silica was favorable for enhancing the interaction between silica phase and polymer, even between silica phases as well. The interaction between silica phase and polymer caused increasing viscosity, modulus and Tg, while the interaction between silica phases themselves increased the extent of micro-phase separation, especially for the hybrid films prepared by IS method.     

醋酸处理对TiO_2纳米薄膜光催化性能的影响

用溶胶－凝胶方法在普通玻璃基体上制备了均匀透明的TiO_2纳米薄膜，并经 500℃煅烧2h，煅烧后的TiO_2薄膜在2 mol·L~(-1)的CH_3COOH水溶液中处理24h， 最后分别在100和500℃进行第二次热处理，醋酸处理前后的薄膜分别用UV－vis, SEM, XRD和XPS进行了表征，并用甲基橙水溶液的光催化降解评价TiO_2纳米薄膜 的光催化性能，结果发现：用醋酸处理后的TiO_2纳米薄膜的光催化活性高于处理 前薄膜的的光催化活性；而且，酸处理后经500℃热处理的TiO_2纳米薄膜的光催化 活性明显高于经100℃热处理的TiO_2纳米薄膜的光催化活性。     

Microporous Silica Particles Prepared by the Salt-Catalytic Sol-Gel Process with Extremely Low Content of Water

Microporous silica was synthesized by the salt catalytic sol-gel process with extremely low content of water to tetramethoxysilane. Silica particles were precipitated even when the extent of hydrolysis was very low, since ammonium carbonate as a salt catalyst made the polycondensation faster than an acid catalyst. Microporous silica with a high surface area (680 m² g^–1) was obtained by combustion of methoxy groups at 450°C. The methoxy groups can be removed by the post-hydrolysis before heating. A high specific surface area (>750 m²g^–1) of microporous silica was obtained with pore diameter between 1.2 and 2.0 nm.     

Synthesis and Characterization of Lead Sulfide Nanoparticles in Zirconia-Silica-Urethane Thin Films Prepared by the Sol-Gel Process

PbS nanocrystals (NCs) ranging between 4–8 nm were incorporated into Zirconium-Silica-Urethane (ZSUR) matrix obtained by the sol-gel method. The sizes of the particles were controlled by temperature treatment and by concentration of PbS in ZSUR matrix. The sizes of PbS NCs were determined by TEM measurements. The quantum size effect could also be extracted from optical absorption and photoluminescence spectra. The new matrix allows incorporation of up to 40% PbS forming a characteristic structure of dendrite by reacting lead acetate with ammonium thiocyanate in sol-gel matrix. The sol precursors of the matrix for Zirconium-Silica-Urethane contained zirconium oxide (ZrO₂) matrix solution, tetramethoxysilane (TMOS), 3-glycid oxypropyl trimethoxysilane (GLYMO) and polyethylene urethane silane (PEUS) synthesized separately. The ZrO₂ matrix solution was obtained from zirconium n-tetrapropoxide in propanol and acetic acid was used as a chelating agent to stabilize the zirconium oxide precursor.     

Formation of Superhydrophobic Alumina Coating Films with High Transparency on Polymer Substrates by the Sol-Gel Method

Transparent, superhydrophobic coating films have been prepared on polymer substrates at low temperatures through the sol-gel method. Al₂O₃ gel films were prepared on poly(ethylene terephthalate) substrates from Al(O-sec-C₄H₉)₃ chemically modified with ethyl acetoacetate. A small roughness of about 20–50 nm was found to form on the surface of the Al₂O₃ gel films dried at room temperature and then immersed in hot water at 60°C. The electron diffraction measurements have shown that this roughened surface consists of pseudoboehmite nanocrystals. The coating of hydrolyzed fluoroalkyltrimethoxysilane on the Al₂O₃ gel films with the small roughness produced transparent, superhydrophobic films with contact angle for water larger than 150°.     

后处理对TiO_2纳米薄膜的表面结构和光催化活性的影响

半导体TiO2光催化材料对环境中各种污染物的明显去除效果已引起人们的广泛关注犤1～6犦。在普通钠钙玻璃表面涂制高光催化活性的TiO2纳米薄膜,制成环保建筑材料,不仅可以自洁玻璃表面,而且可以用于净化空气、处理废水等。但由于在热处理过程中玻璃基体内的Na+离子扩散到薄膜表面,形成光生电子和空穴的复合中心,使TiO2纳米薄膜的光催化活性大大降低犤7～10犦。为了减少玻璃中Na+离子对TiO2薄膜光催化活性的有害影响,Paz等犤8犦研究了将钠钙玻璃浸入酸溶液中,使玻璃表面的钠离子被酸中的氢离子置换出来;在玻璃表面形成SiO2凝胶层,以便阻…     

Evaluation of Photocatalytic Activity by Dye Decomposition

A novel rapid evaluation method for the photocatalytic activity of TiO₂ thin films was developed. An organic dye with a polyvinyl alcohol (PVA) binder was spin coated on the TiO₂ thin film, and the decrease in the absorbance of the dye's absorption peak during UV light irradiation was measured. Acid Blue 9 (Brilliant Blue FCF; CI-42090) could be used as the probe, while Methylene Blue (CI-52015) was not applicable to this method because of the reversible color change after the UV irradiation was stopped. PVA has virtually no interaction with oxidizing radicals, therefore, it is regarded as a simple binder holding dye molecules in the coated dye-PVA film. It was found that the ambient humidity during the UV irradiation strongly accelerates the discoloration rate of the dye, probably due to the increase in the photogenerated oxidizing radicals on the TiO₂ surface. This dye discoloration could be explainedby the one-dimensional diffusion model with a first order reaction.     

Polyaniline/Silica Hybrid Composite Gels Prepared by the Sol-Gel Process

The preparation of polyaniline/silica hybrid gel was studied by chemical polymerization of aniline with sodium dodecyl sulfate (SDS) during the sol-gel processing. As a typical procedure, aqueous solutions of SDS, aniline, HCl, and tetramethoxysilane (TMOS) were mixed. Then ammonium peroxodisulfate (APS) in an acidic aqueous solution was added as initiator oxidant into the sol-gel systems at different sol-gel stages: (A) just after mixing (sol), (B) after gelation (wet gel), and (C) after 7 d (dried gel). As for the condition (A), several green areas and several tens of dark green spots with absorption peaks at 343, 422, and 802 nm were seen in the xerogel, indicating that emeraldine salt type polyaniline is aggregated in the silica xerogel. Polymerization of aniline little occurred in the dried gel (C), possibly because APS could not soak the silica pores and/or aniline could not polymerize in the gel. The xerogel from (B) showed a homogeneously green color with peaks at 339, 425, and 769 nm, showing that emeraldine salt type polyaniline can be uniformly dispersed in sol-gel silica.     

Preparation of Anatase Hollow TiO2 Spheres and Their Photocatalytic Activity in the Photodegradation of Chlorpyrifos

Hollow anatase titania (TiO₂) spheres were synthesized using fructose and tetrabutyl titanate (Ti(OC₄H₉)₄, TBT) as the precursors via the conventional hard template method. The morphological, structural and thermal properties of the products were characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG‐DTA), Brunauer? Emmett? Teller (BET) surface area analysis and diffuse reflectance ultraviolet visible (DR UV? Vis) spectroscopy. XRD revealed that the hollow TiO₂ prepared was in the anatase phase and the BET surface area measured was about 22 m² g^?1. The photocatalytic activity of the synthesized hollow anatase TiO₂ in the photodecomposition of chlorpyrifos was 18.67 % higher than that obtained using commercial TiO₂.     

Molecular‐Level Understanding of the Photocatalytic Activity Difference between Anatase and Rutile Nanoparticles

The generation of oxidants on illuminated photocatalysts and their participation in subsequent reactions are the main basis of the widely investigated photocatalytic processes for environmental remediation and selective oxidation. Here, the generation and the subsequent diffusion of ^.OH from the illuminated TiO₂ surface to the solution bulk were directly observed using a single‐molecule detection method and this molecular phenomenon could explain the different macroscopic behavior of anatase and rutile in photocatalysis. The mobile ^.OH is generated on anatase but not on rutile. Therefore, the photocatalytic oxidation on rutile is limited to adsorbed substrates whereas that on anatase is more facile and versatile owing to the presence of mobile ^.OH. The ability of anatase to generate mobile ^.OH is proposed as a previously unrecognized key factor that explains the common observations that anatase has higher activity than rutile for many photooxidative reactions.     

Synthesis and Photocatalytic Activity of TiO2/CdS Nanocomposites with Co-Exposed Anatase Highly Reactive Facets

In this work, TiO₂/CdS nanocomposites with co-exposed {101}/[111]-facets (NH4F-TiO2/CdS), {101}/{010} facets (FMA-TiO2/CdS), and {101}/{010}/[111]-facets (HF-TiO2/CdS and Urea-TiO2/CdS) were successfully synthesized through a one-pot solvothermal method by using [Ti₄O₉]²⁻ colloidal solution containing CdS crystals as the precursor. The crystal structure, morphology, specific surface area, pore size distribution, separation, and recombination of photogenerated electrons/holes of the TiO₂/CdS nanocomposites were characterized. The photocatalytic activity and cycling performance of the TiO₂/CdS nanocomposites were also investigated. The results showed that as-prepared FMA-TiO₂/CdS with co-exposed {101}/{010} facets exhibited the highest photocatalytic activity in the process of photocatalytic degradation of methyl orange (MO), and its degradation efficiency was 88.4%. The rate constants of FMA-TiO₂/CdS was 0.0167 min⁻¹, which was 55.7, 4.0, 3.7, 3.5, 3.3, and 1.9 times of No catalyst, CdS, HF-TiO₂/CdS, NH₄F-TiO₂/CdS, CM-TiO₂, Urea-TiO₂/CdS, respectively. The highest photocatalytic activity of FMA-TiO₂/CdS could be attributed to the synergistic effects of the largest surface energy, co-exposed {101}/{010} facets, the lowest photoluminescence intensity, lower charge-transfer resistance, and a higher charge-transfer efficiency.