Influence of surface modified mixed metal oxide nanoparticles on the electrochemical and mechanical properties of polyurethane matrix

Newly synthesized functional nanoparticles, 3-amino-1,2,4-triazole (ATA)/SiO₂–TiO₂ were introduced to the polyurethane (PU) matrix. Electrochemical techniques were used to investigate the barrier properties of the synthesized PU–ATA/SiO₂–TiO₂ nanocomposite coated steel specimen. In natural seawater, electrochemical impedance spectroscopy experiments indicated outstanding protective behaviour for the PU–ATA/SiO₂–TiO₂ coated steel. The coating resistance (R_coat) of PU–ATA/SiO₂–TiO₂ was determined to be 2956.90 kΩ·cm^–2. The R_coat of the PU–ATA/SiO₂–TiO₂ nanocomposite coating was found to be over 50% higher than the PU coating. The current measured along the scratched surface of the PU–ATA/SiO₂–TiO₂ coating was found to be very low (1.65 nA). The enhanced ATA/SiO₂–TiO₂ nanoparticles inhibited the entry of electrolytes into the coating interface, as revealed by scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray diffraction analysis of the degradation products. Water contact angle testing validated the hydrophobic nature of the PU–ATA/SiO₂–TiO₂ coating (θ = 115.4°). When the concentration of ATA/SiO₂−TiO₂ nanoparticles was 2 wt %, dynamic mechanical analysis revealed better mechanical properties. Therefore, the newly synthesised PU–ATA/SiO₂–TiO₂ nanocomposite provided excellent barrier and mechanical properties due to the addition of ATA/SiO₂–TiO₂ nanoparticles to the polyurethane, which inhibited material degradation and aided in the prolongation of the coated steel’s life.     

Effects of hydrothermal temperature and time on the photocatalytic activity and microstructures of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with high photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate (TiO(C₄H₉)₄, TBOT) as precursor. The as-prepared TiO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption–desorption measurements. The photocatalytic activity of the as-prepared TiO₂ powders was evaluated by the photocatalytic degradation of acetone (CH₃COCH₃) under UV-light irradiation at room temperature in air. The effects of hydrothermal temperature and time on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. It was found that hydrothermal treatment enhanced the phase transformation of the TiO₂ powders from amorphous to anatase and crystallization of anatase. All TiO₂ powders after hydrothermal treatment showed bimodal pore-size distributions in the mesoporous region: one was intra-aggregated pores with maximum pore diameters of ca. 4–8 nm and the other with inter-aggregated pores with maximum pore diameters of ca. 45–50 nm. With increasing hydrothermal temperature and time, the average crystallite size and average pore size increased, in contrast, the Brunauer-Emmett-Teller (BET) specific surface areas, pore volumes and porosity steadily decreased. An optimal hydrothermal condition (180 °C for 10 h) was determined. The photocatalytic activity of the prepared TiO₂ powders under optimal hydrothermal conditions was more than three times higher than that of Degussa P25.     

SBA-15/Ni/TiO2/CNTs复合材料的制备及其光催化性能

通过溶胶凝胶法,经多次涂覆在SBA-15上负载掺杂镍的纳米TiO₂,得到SBA-15/NiO/TiO₂复合物;再以TiO₂中还原态金属镍为催化剂,通过化学气相沉积法（CVD）,在SBA-15/NiO/TiO₂表面原位生长碳纳米管,制得SBA-15/Ni/TiO₂/CNTs复合材料。通过XRD、SEM、TEM、UV-Vis和Raman等方法考察了SBA-15/Ni/TiO₂/CNTs复合材料的结构和性能,并通过降解亚甲基蓝溶液评价其光催化活性。结果表明,SBA-15/Ni/TiO₂/CNTs复合光催化剂的催化活性较SBA-15/NiO/TiO₂显著提高。 二次涂覆掺杂镍的二氧化钛制得的复合光催化剂的催化活性高于一次涂覆。     

Facile synthesis and enhanced visible-light photocatalytic activity of Ti3+-doped TiO2 sheets with tunable phase composition? ?

Ti³⁺-doped TiO₂ nanosheets with tunable phase composition (doped TiO₂ (A/R)) were synthesized via a hydrothermal method with high surface area anatase TiO₂ nanosheets TiO₂ (A) as a substrate, structure directing agent, and inhibitor; the activity was evaluated using a probe reaction-photocatalytic CO₂ conversion to methane under visible light irradiation with H₂ as an electron donor and hydrogen source. High-resolution transmission electron microscope (HRTEM), field emission scanning electron microscope, UV-Vis diffuse reflectance spectra, and X-ray diffraction (XRD) etc., were used to characterize the photocatalysts. XRD and HRTEM measurements confirmed the existence of anatase-rutile phase junction, while Ti³⁺ and single-electron-trapped oxygen vacancy in the doped TiO₂ (A/R) photocatalyst were revealed byelectron paramagnetic resonance (EPR) measurements. Effects of hydrothermal synthesis temperature and the amount of added anatase TiO₂ on the photocatalytic activity were elucidated. Significantly enhanced photocatalytic activity of doped TiO₂ (A/R) was observed; under the optimized synthesis conditions, CH₄ generation rate of doped TiO₂ (A/R) was 2.3 times that of Ti³⁺-doped rutile TiO₂.     

A chemical etching route to controllable fabrication of TiO2 hollow nanospheres for enhancing their photocatalytic activity

The TiO₂ hollow nanospheres with diameters of about 230 nm were prepared by a simple and controllable route based on hydrolysis of Ti(OBu)₄ on the surfaces of the Cu₂O solid nanospheres followed by inward etching of the Cu₂O nanospheres. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The further post-heat treatment led to the high crystallization of the TiO₂ hollow nanospheres. The photocatalytic performances of these samples were evaluated for the photodegradation of rhodamine B (RhB) under UV-light irradiation. The as-prepared TiO₂ hollow nanospheres showed higher photocatalytic activity than the CuO and the CuO/TiO₂ hollow nanospheres. Effects of temperature and time for post-heat treatment of TiO₂ as well as initial RhB concentrations on the RhB photodegradation have also been studied. The results show that the TiO₂ hollow nanospheres have the good reusability as photocatalysts and are promising in waste water treatment.     

TiO2基催化剂还原CO2研究进展

能源危机和环境污染是当今世界发展面临的两大挑战,如何有效缓解煤、石油等不可再生化石资源过度消耗所引发的能源危机,以及由此造成CO₂过量排放引起的温室效应问题,是当前人类发展亟待解决的重大科学问题之一。基于此,本文综述了近年来以TiO₂为光催化剂,以绿色、清洁的太阳光能催化还原CO₂成低价态含碳燃料(如CH₄、CH₃OH、HCHO、HCOOH、C₂H₅OH等)研究进展。在TiO₂光还原CO₂机理基础上,对元素掺杂、半导体复合与染料敏化、高活性晶面调控、低维纳米结构设计、助催化剂、Z型结构设计和单原子催化等方法来提高光还原CO₂反应效率和选择性进行分析,并指出目前研究存在的关键问题和未来CO₂光还原的发展方向。     

A high H2 evolution rate under visible light of a CdS/TiO2@NiS catalyst due to a directional electron transfer between the phases

The photocatalytic activity of CdS can be greatly improved by co-modification of NiS and TiO_2 materials; furthermore the order of connection affects much. A directional electron transfer route via CdS → TiO_2→ NiS is found crucial to the enhancement of ternary catalyst, where TiO_2 acts as an electron reservoir and Ni S works as an effective cocatalyst. Cd S/TiO_2@Ni S with Ni S loaded on TiO_2 has an activity of H_2 evolution 2.5 times higher than NiS@Cd S/TiO_2 with Ni S pre-loaded on Cd S. Faster e-/h+separation rates is obtained of Cd S/TiO_2@Ni S under visible light than under extra UV light irradiation, which in turn demonstrates the importance of directional electron transfer route.     

Gas-phase photo-oxidation of toluene using nanometer-size TiO2 catalysts

A modified sol–gel process was used to prepare nanostructured TiO₂ catalysts of controlled particle size (i.e. 6, 11, 16 and 20 nm). The influence of the TiO₂ particle size in the gas phase photocatalytic oxidation of toluene was investigated under both dry and humid conditions. The main products of reaction were carbon dioxide and water, although small amounts of benzaldehyde were also detected. The smaller particle size (i.e. 6 nm) lead to higher conversion and complete mineralization of toluene into CO₂ and H₂O. Both electronic and structural effects (i.e. size and ensemble effects) are responsible for the excellent performance of 6 nm TiO₂ catalyst for toluene photo-degradation. The structural differences between 6 nm TiO₂ and larger catalysts were analyzed using EPR spectroscopy.     

Photocatalytic reduction of carbon dioxide into gaseous hydrocarbon using TiO2 pellets

It has been shown that CO₂ could be transformed into hydrocarbons when it is in contact with water vapour and catalysts under UV irradiation. This paper presents an experimental set-up to study the process employing a new approach of heterogeneous photocatalysis using pellet form of catalyst instead of immobilized catalysts on solid substrates. In the experiment, CO₂ mixed with water vapour in saturation state was discharged into a quartz reactor containing porous TiO₂ pellets and illuminated by various UV lamps of different wavelengths for 48 h continuously. The gaseous products extracted were identified using gas chromatography. The results confirmed that CO₂ could be reformed in the presence of water vapour and TiO₂ pellets into CH₄ under continuous UV irradiation at room conditions. It showed that when UVC (253.7 nm) light was used, total yield of methane was approximately 200 ppm which was a fairly good reduction yield as compared to those obtained from the processes using immobilized catalysts through thin-film technique and anchoring method. CO and H₂ were also detected. Switching from UVC to UVA (365 nm) resulted in significant decrease in the product yields. The pellet form of catalyst has been found to be attractive for use in further research on photocatalytic reduction of CO₂.     

Preparation of freestanding and crack-free titania–silica aerogels and their performance for gas phase, photocatalytic oxidation of VOCs

Freestanding and crack-free titania–silica aerogels with high titanium content (i.e., Ti/Si = 1) were successfully prepared by adjusting the hydrolysis of the two alkoxide precursors to a comparable rate during the sol–gel processing. Two titania–silica aerogels were prepared by ethanol and CO₂ supercritical drying methods. Well-dispersed, nanometer-sized anatase crystal domains (ca. 10 nm) were crystallized by high temperature, ethanol supercritical drying. The crystalline domains were solidly anchored to the aerogel network by Ti–O–Si bonds. Titania–silica aerogels prepared by CO₂ supercritical drying method were devoid of TiO₂ crystals. A molecular-level mixing was achieved and anatase TiO₂ was only crystallized with difficulty by high temperature calcination (1073 K). Both aerogels were mesoporous and displayed similar open pore structure that is readily accessible to reactant molecules. However, only the titania–silica aerogel with anatase TiO₂ prepared by ethanol supercritical drying was active for the gas phase, photocatalytic oxidation of volatile organic compounds (i.e., isopropanol and trichloroethylene). Catalysts prepared from Degussa P25 TiO₂ displayed lower activity under similar reaction conditions.     

Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

A new smooth potassium dititanate film was prepared by sol-gel method and characterized by thermogravimetry (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible diffuse reflectance and Raman spectroscopy. The gaseous photocatalytic activity of smooth K₂Ti₂O₅ films was studied using contact angle analysis from the photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayers (SAMs) formed on K₂Ti₂O₅ films. The photocurrent response of the film was determined by an electrochemical method. It was shown that the films were smooth, compact, and transparent when formed on glass. Compared with TiO₂ film, the K₂Ti₂O₅ film showed wide absorption in the ultraviolet and visible region. It was found that the monolayers on K₂Ti₂O₅ decomposed much faster than those on TiO₂ under UV irradiation of 254 nm in air. The film also exhibited a stronger photoresponse and a more stable anodic photocurrent. The K₂Ti₂O₅ film efficiently decomposes the alkylsiloxane monolayers under UV irradiation in air and it was found to be a good photocatalyst for gaseous organic pollutant treatment.     

染料敏化二氧化钛-石墨烯杂化材料光催化水分解制氢

以曙红、石墨氧化物与二氧化钛(P25)为原料,利用水热法制备曙红敏化的二氧化钛-石墨烯杂化材料。通过X射线光电子能谱(XPS)考察了石墨氧化物(GO)以及染料敏化二氧化钛石墨烯杂化材料(T-G-EY)的C1s信号的变化,水热过程使石墨烯含氧官能团含量大幅度减少,透射电镜照片清晰地显示二氧化钛纳米颗粒均匀分散在石墨烯片层上。紫外-可见漫反射光谱(DRS)分析发现复合材料的带隙变窄,从P25的3.25 eV降低到2.75 eV,吸光范围明显向可见光区拓展,并存在曙红的特征吸收峰。从荧光光谱上明显看出复合材料发生了荧光猝灭现象,确认是石墨烯与二氧化钛之间及曙红与石墨烯之间存在一定的相互作用。T-G-EY在500 W氙灯照射下光解水制氢气的效率比P25提高了10.2倍。     

Pd-Rh/TiO2光催化CO2氧化乙烷脱氢研究

采用浸渍还原方法制备Pd-Rh/TiO₂催化剂用于常温光催化CO₂氧化乙烷脱氢制C₂H₄。研究不同Pd/Rh比催化剂的光反应性能,利用XRD、EDX-mapping、TEM、HRTEM、XPS技术表征催化剂表面和电子特性,通过UV-Vis、PL技术考察催化剂光响应性能,采用原位红外光谱技术分析Pd-Rh/TiO₂光催化CO₂氧化乙烷脱氢反应机理。研究表明,Pd-Rh双金属体系可有效提高光反应活性,光照下Pd和Rh金属之间存在内部电子转移的作用,降低了Pd表面的电子云密度,促进光生电子和空穴的分离,同时促进了C₂H₆和CO₂在材料表面的吸附。Ar替换CO₂的对比实验证明,反应中的CO₂消耗H₂,可消除催化剂表面积碳,促进C₂H₄生成。     

Surface nano-aggregation and photocatalytic activity of TiO2 on H-type activated carbons

The main objective of this work is to detect any associative or synergistic effects between TiO₂ and activated carbon in 4-chlorophenol photodegradation. Different activated carbons (AC) were prepared from Tabebuia pentaphyla wood by means of physical activation with CO₂ or by extensive carbonization under N₂ flow at temperatures from 450 °C up to 1000 °C during 1 h. Results indicate a clear correlation between photocatalytic activities of titania with texture and surface chemistry of AC. Kinetic results of 4-chlorophenol photodegradation indicate that for most of mixed TiO₂ and AC solids a synergistic effect between both solids is observed. Surface nano-aggregation of TiO₂ on AC was observed by scanning electronic microscopy and dispersion of TiO₂ nanoparticles was improved as a function of more basic surface pH of AC. In conclusion, an increase of electronic density in carbon support clearly introduces an enhancement in titania's photoactivity for 4CP photodegradation. This beneficial effect indicates that it is possible to obtain clean water in a much shorter period of time by employing some selected AC in conjunction with TiO₂.     

Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO2 from mesoporous precursors

Si-doped and rare earth-doped TiO₂ with large specific surface area were prepared by the hydrothermal method and sol–gel route, respectively, using C₁₈H₃₇NH₂ as template. The samples were characterized by XRD, FT-IR, low-temperature N₂ adsorption–desorption measurement, XPS and solid state UV–vis diffuse reflectance spectroscopy. The pore size for Si-doped TiO₂ exhibits both mesoporous and microporous distribution, and that for rare earth-doped TiO₂ exhibits a sharp and narrow distribution in microporous range. The photocatalytic activities were investigated with the degradation of phenol as probe reaction. Compared with pure TiO₂, the conversion of phenol and selectivity to CO₂ increases when adding rare earth elements, and the substitution of Si for Ti in an appropriate range also increases the conversion of phenol.     

Structure and photocatalytic performance of TiO2/clay nanocomposites for the degradation of dimethachlor

In the present study TiO₂/clay composites were synthesized by dispersion of TiO₂ on the surfaces of a natural montmorillonite and a synthetic hectorite in order to increase the sorption ability of TiO₂ and therefore its photocatalytic action. Six materials with different loading in TiO₂ (15, 30 and 55 wt%) were prepared and characterized by several analytical techniques including XRD, BET and SEM analysis. The synthetic procedure allows the development of delaminated layers for hectorite–TiO₂ samples, while in the case of montmorillonite–TiO₂ composites we have the formation of a more lamellar-like aggregation. It was found that, the greater the percentage of TiO₂, the greater the pore volume and the specific surface area of the montmorillonite–TiO₂ samples. On the contrary, in the case of hectorite–TiO₂ samples, as the content of TiO₂ increases, the surface area and pore volume decreases. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (dimethachlor) in water as model compound. The primary degradation of dimethachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. All supported catalysts exhibit good photodegradation efficiency and their overall removal efficiency per mass of TiO₂ was better than that of bare TiO₂ produced by the sol–gel method. In conclusion, together with their good sedimentation ability the composite materials could be considered as a promising alternative for the removal of organic water contaminants.     

Hydrogen evolution by water splitting using novel composite zeolite-based photocatalyst

Novel zeolite-based material showing photocatalytic properties in the visible light have been synthesized by incorporating TiO₂, heteropolyacid (HPA) and transition metal, namely cobalt. This material shows high efficiency for water splitting under visible light irradiation. Hydrogen generation to the tune of 2171 μmol/h/g of TiO₂ has been achieved for the composite photocatalyst synthesized as compared to H₂ evolution rate to the tune of 131.6 μmol/h/g of TiO₂ for Degussa P25. This suggests that the TiO₂ which gets effectively dispersed and stabilized on the surface of zeolite works synergistically with cobalt and heteropolyacid to make the material active in visible light for evolution of hydrogen from water. TiO₂ is the photocatalyst, HPA functions as the dye sensitiser as well as redox system; zeolite functions as support matrix and as electron acceptor in synergy with cobalt. The probable mechanism for improved hydrogen evolution rate using such composite photocatalyst has been discussed.     

Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity

Ag–TiO₂ multiphase nanocomposite thin films were prepared on quartz substrates by the liquid phase deposition (LPD) method from a mixed aqueous solution of ammonium hexafluouotitanate, silver nitrate and boric acid under ambient temperature and atmosphere followed by calcination at 500 °C for 1 h. The grain growth of anatase was depressed upon Ag⁺ doping. However, silver ions not only promoted (or catalyzed) the formation of brookite phase but also reduced the phase transformation temperature of anatase to rutile. With increasing AgNO₃ concentration, the transmittance and band gap of the composite thin films decreased; however, the intensity of surface plasmon absorption (SPA) peaks increased and their peak position shifted to a longer wavelength range. When AgNO₃ concentration was higher than 0.03 M, the prepared samples consisted of anatase, brookite, rutile and metal silver nanocrystal particles, and their grain size ranges were 5–30 nm. The photocatalytic activity of the Ag–TiO₂ multiphase nanocrystal composite thin films prepared by this method exceeded that of pure TiO₂ thin films by a factor of more than 6.3 when AgNO₃ concentration was kept in the range of 0.03–0.05. This was attributed to the fact that there were many hetero-junctions, such as anatase/rutile, anatase/brookite, Ag/anatase, Ag/rutile and so on, existed in the Ag–TiO₂ multiphase nanocomposite films.     

Photoresponse and AC impedance characterization of TiO2–SiO2 mixed oxide for photocatalytic water decomposition

TiO₂–SiO₂ mixed oxides were prepared by sol–gel processes with one-stage (mix up fully hydrolyzed titania- and silica-sol), two-stage (with pre-hydrolysis) and modified two-stage synthesis routes. The photoresponse and AC impedance characterization of the derived catalysts are studied and correlated for the first time with the photocatalytic activities in water decomposition under UV illumination. Synergistic effects in terms of photocatalytic activity and electronic properties including band-gap energy, flat band potential and doping density were observed on atomically mixing TiO₂ and SiO₂ by the two-stage synthesis route. Meanwhile, the decline of photocurrent density were found on TiO₂–SiO₂ relative to bare TiO₂, which could be attributed to low quality crystalline structure of the former compared to that of the latter. The superior photocatalytic performance of TiO₂–SiO₂ is ascribed to the higher flat band potential, band-gap energy, and doping density than those of bare TiO₂.     

长程TiO2纳米管阵列表面的超声清洗及其光催化性能

通过阳极氧化法在NH4F/乙二醇/H₂O的电解液中制备了长程TiO₂纳米管阵列。借助超声手段分别采用蒸馏水、丙酮和异丙醇作为超声介质清除了TiO₂纳米管阵列表面的集束,探讨其对TiO₂纳米管阵列光催化活性的影响。采用SEM、TG和XRD等对TiO₂纳米管阵列进行表征。结果表明,超声处理明显清除了纳米管阵列表面集束,超声介质对清洗过程有重要影响,丙酮相对于蒸馏水和异丙醇更适合作为超声介质,且超声超过30 min,纳米管阵列的光催化活性得到明显提高。