CC/PANI/TiO2复合材料的制备及其光催化性能研究

先采用原位聚合的方法在碳布上负载聚苯胺,然后利用溶剂热法在制备的碳布/聚苯胺(CC/PANI)复合材料上生长二氧化钛纳米片,得到了可便捷分离的CC/PANI/TiO₂复合光催化材料。通过SEM、XRD、UV、FTIR、XPS等手段对所制备的样品进行了形貌和结构表征,并比较了CC/PANI/TiO₂复合材料和纯TiO₂紫外-可见光条件下催化降解RhB的活性差异,结果表明CC/PANI/TiO₂复合材料具有比TiO₂更优异的光催化活性。光致发光光谱说明CC/PANI/TiO₂复合材料的发光强度比纯TiO₂的弱,有效抑制了光生载流子的复合;瞬态光电流响应和电化学阻抗谱(EIS)证明CC/PANI/TiO₂纳米复合材料更有效促进电子-空穴对分离和提高转移效率;活性物质捕捉实验证实?OH和?O_2^-是复合材料光催化降解RhB过程中的主要活性物质。CC/PANI/TiO₂复合材料循环利用6次后,仍然具有较高的催化活性,显示了其在污水处理领域中的良好应用前景。     

Properties of TiO2 support and the performance of Au/TiO2 Catalyst for CO oxidation reaction

Gold catalysts were prepared on TiO₂ supports of different phase structures (i.e., anatase, rutile and biphasic), TiO₂ crystal size (i.e., 9–23 nm), surface and textural properties (i.e., hydration and surface area). The CO oxidation on the gold catalysts was carried out in an operando-DRIFTS set-up equipped with DRIFTS reactor cell connected on-line to CO gas analyser and gas chromatograph enabling real time monitoring of surface reaction and simultaneous reaction rate measurements. Gold catalysts supported on pure anatase TiO₂ were more resistant to sintering compared to catalysts supported on rutile and bi-phasic TiO₂. Besides catalyst sintering, deposition of surface carbonates is an important cause of catalyst deactivation. The best gold catalyst was prepared on 13 nm anatase TiO₂. It displays both increased activity and stability for CO oxidation reaction at room temperature. Surface and textural properties of TiO₂ also play a role on the performance of the Au/TiO₂ catalyst.     

Preparation of a monolith-supported Au/TiO2 catalyst active for CO oxidation

The development of a method for making an adherent coating of Au/TiO₂ on a cordierite monolith is described. The optimum method entails first forming a wash-coat of TiO₂ by combining a colloidal dispersion of TiO₂ with Degussa P-25 TiO₂ that has been washed, dried and crushed. Subsequent deposition of gold from HAuCl₄ solution at pH 9 resulted in a catalyst that was less active for the oxidation of carbon monoxide than a similar preparation using only P-25, but reproducible values of T₅₀ of about 250 K were obtained.     

The activation of supported Au catalysts prepared by impregnation

In this study, Au/TiO₂, Au/γ-Al₂O₃, and Au/C catalysts were prepared by an incipient-wetness impregnation method. The CO oxidation activity after different pretreatment was analyzed. Two pretreatments are found possible to activate these catalysts for CO oxidation: (i) high-temperature hydrogen reduction and (ii) aqueous base treatment using NH3(aq). The high-temperature hydrogen reduction is effective for Au/TiO₂ and Au/C, but not Au/Al₂O₃. The base treatment is effective for Au/Al₂O₃ and Au/TiO₂, but not Au/C. Small Au particles of ca. 2 nm size were observed in activated Au catalysts from both pretreatments; however, the high-temperature H₂ reduction procedure also resulted in large Au particles of ca. 25 nm size which makes it a less efficient pretreatment than the base treatment. The activated Au/TiO₂ catalysts show comparable turnover frequency as the Au/TiO₂ catalyst prepared by a deposition precipitation method. The effective pretreatments were found to be accompanied by a reduced acidity, which is measured by the pH of aqueous catalyst suspension. Reasons for such activation are discussed.     

TiO2/SiOx core-shell nanowires generated by heating the multilayered substrates

By heating Au/TiN/Si substrates, we fabricated TiO₂/SiO_x core-shell nanowires. By changing the thickness of predeposited Au layers, we demonstrated that the thickness of the Au layer needs to be optimized to obtain nanowires. High-resolution transmission electron microscopy image, X-ray diffraction spectrum, and selected area electron diffraction pattern coincidentally revealed that the resultant core nanowires had a tetragonal rutile structure of TiO₂, and the shell was comprised of amorphous SiO_x. The dominant growth mechanism was a base-growth mode, in which Au played a catalytic role, resulting in morphological changes with variation of the Au layer thickness. The TiO₂/SiO_x core-shell nanowires exhibited a broad photoluminescence emission band, which comprised four peaks centered at 1.54, 2.34, 2.67, and 2.99 eV, respectively. We expected that the 1.54 eV- and 2.34 eV-centered peaks arised from the TiO₂ core, whereas the 2.67 eV- and 2.34 eV-peaks were ascribed to both the TiO₂ core and the SiO_x shell.     

CO oxidation: Deactivation of Au/TiO2 catalysts during storage

In a study of the phenomenon of catalyst deactivation during storage, Au/TiO₂ catalyst was stored under various conditions, viz. vacuum, nitrogen, air, refrigeration, dark, and light, and tested for CO oxidation activity at regular intervals. The data shows that the catalyst deactivates under all the storage conditions over 12 months and that storage in vacuum significantly enhances the rate and extent of deactivation. Storage in light accelerates the deactivation. The catalyst appears to deactivate through a combination of Au(III) reduction, Au nanoparticle agglomeration, loss of surface hydroxyl groups, loss of surface moisture, and accumulation of surface carbonates and formates. The rate and extent of catalyst deactivation can be limited by storing the catalyst in the dark at sub ambient temperature (refrigerator) and under inert atmosphere.     

Photo-catalytic effect enhanced by the chemisorption of phenylethyl-mercaptan-assembled monolayers on Au-clusters/TiO2-anatase thin film

A simple process is employed to increase the efficiency of TiO₂ photo-catalytic activity, for which the recombination probability of electron–hole pairs is relaxed. Au is selectively deposited on a high-transparency TiO₂-anatase thin film on a glass substrate, and then phenylethyl mercaptan (PEM) is chemisorbed onto the selectively covered Au-clusters/TiO₂-anatase thin film. The enhancement of the photo-catalytic activity on the PEM/Au-clusters/TiO₂-anatase thin film is evaluated via the induced degradation of methylene blue. The results demonstrate that the Au coverage ratio on TiO₂-anatase thin film and the photo-catalytic activity of the chemisorbed PEM/Au-clusters/TiO₂-anatase are related. The photo-catalytic contribution of PEM/Au-clusters/TiO₂-anatase differs from that of Au on a TiO₂-anatase thin film. An optimized photo-catalytic system, a composite of PEM/3.8% Au-clusters/TiO₂-anatase thin film, is proposed. The efficiency of the PEM/3.8% Au-clusters/TiO₂-anatase thin film is 52.1% higher than that of the as-deposited TiO₂-anatase thin film.     

Support effects in the selective gas phase hydrogenation ofp-chloronitrobenzene over gold

The catalytic continuous gas phase hydrogenation of p-chloronitrobenzene (P=1 atm;T=423 K) has been investigated over a series of oxide (Al₂O₃, TiO₂, Fe₂O₃ and CeO₂) supported Au (1 mol %) catalysts. The application of two catalyst synthesis routes,i.e. impregnation (IMP) and deposition-precipitation (DP), has been considered where the DP route generated smaller mean Au particle sizes (1.5-2.8 nm) compared with the IMP preparation (3.5-9.0 nm). The catalysts have been characterised in terms H2 chemisorption and BET area measurements where the formation of metallic Au post-activation has been verified by diffuse reflectance UV-Vis, XRD and HRTEM analyses.p-Chloroaniline was generated as the sole reaction product over all the Au catalysts with no evidence of C-Cl and/or C-NO₂ bond scission and/or aromatic ring reduction. The specific hydrogenation rate increased with decreasing Au particle size (from 9 to 3 nm), regardless of the nature of the support. This response extends to a reference Au/TiO₂ catalyst provided by the World Gold Council. A decrease in specific rate is in evidence for smaller particles (< 2 nm) and can be attributed to a quantum size effect. The results presented establish the basis for the design and development of a versatile catalytic system for the clean continuous production of high value amino compounds under mild reaction conditions.     

Capacitance performance enhancement of TiO<Subscript>2</Subscript> doped with Ni and graphite

Nano-amorphous TiO₂ was prepared by a sol-gel method. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the composite electrode material (TiO₂-NiO-C) is made of powder with a grain size of 36.2 nm. Doping of nickel and graphite can increase the electrical conductivity and the specific surface area of nano-amorphous TiO₂. The electrochemical properties of TiO₂-NiO-C, such as self-discharge, leakage current, and cycle life, were studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge test. With a charge-discharge current density of 500 mA/g, the specific capacity of the TiO₂-NiO-C composite material reaches 12.88 mAh/g. Also, the expense of capacity is only 3.88% after 500 cycles. The electrochemical capacitor with the electrode material of TiO₂-NiO-C shows excellent capacity and cycling performance.     

Synthesis of TiO<Subscript>2</Subscript> Nanoparticles from Ilmenite Through the Mechanism of Vapor-Phase Reaction Process by Thermal Plasma Technology

Synthesis of nanoparticles of TiO₂ was carried out by non-transferred arc thermal plasma reactor using ilmenite as the precursor material. The powder ilmenite was vaporized at high temperature in plasma flame and converted to a gaseous state of ions in the metastable phase. On cooling, chamber condensation process takes place on recombination of ions for the formation of nanoparticles. The top-to-bottom approach induces the disintegration of complex ilmenite phases into simpler compounds of iron oxide and titanium dioxide phases. The vapor-phase reaction mechanism was carried out in thermal plasma zone for the synthesis of nanoparticles from ilmenite compound in a plasma reactor. The easy separation of iron particles from TiO₂ was taken place in the plasma chamber with deposition of light TiO₂ particles at the top of the cooling chamber and iron particles at the bottom. The dissociation and combination process of mechanism and synthesis are studied briefly in this article. The product TiO₂ nanoparticle shows the purity with a major phase of rutile content. TiO₂ nanoparticles produced in vapor-phase reaction process shows more photo-induced capacity.     

Synthesis and Characterization of Hydroxyapatite/TiO<Subscript>2</Subscript> Coatings on the β-Type Titanium Alloys with Different Sintering Parameters using Sol-Gel Method

In this study, hydroxyapatite (HA) based composite films were successfully syntheses on the β-type Ti29Nb13Ta4.6Zr (TNTZ). The solutionized TNTZ substrates coated with HA and HA/Titania (TiO₂) bioactive composite coatings by sol-gel method under various sintering parameters related to sintering temperatures and heating ramp rates. Microstructural observations of the coatings revealed that apatite was formed on the substrates. The hardness values of the coatings increase with increasing both the sintering temperature and the TiO₂ concentration in the coatings layer. However, it was found that the heating ramp rate of the sintering was not affecting the hardness values so much. Also, the hardness values of the HA/TiO₂ composite coatings at all sintering temperatures were higher than only HA coated TNTZ samples due to the existence TiO₂ phases in the HA matrix. Results indicating that the doping of HA with TiO₂, improve the physical consistency between the coating layer and the substrates and provide a better inter-particle bonding due to the existence TiO₂ phases in the HA.     

Low temperature methane oxidation on differently supported 2 nm Au nanoparticles

Low temperature CH₄ oxidation was studied on 2 nm gold nanoparticles supported on various metaloxides. The differences in reaction rates for the different systems suggest that the support material has an effect on the activity. From TEM analysis, we found that the gold particles were stable in size during the reaction. In addition to full oxidation to CO₂, traces of C₂H₆ were detected when Au/TiO₂ was used, indicating limited partial CH4 oxidation. TiO₂ was found to be the best support for gold nanoparticles both in terms of activity and gold particle stability.     

Aqueous phase epoxidation of 1-butene catalyzed by suspension of Au/TiO2 +TS-1

A combination of two catalysts, Au/TiO₂ and TS-1 were used to catalyze the demanding reaction of butene epoxidation in an aqueous solution using molecular oxygen under very mild reaction conditions. Peroxy initiator was not necessary but carbon monoxide as a sacrificial reductant was needed. Carbon monoxide conversions increase with time on stream suggesting the generation of a highly active aqueous phase CO oxidation catalyst.     

Investigation of the active site and the mode of Au/TiO2 catalyst deactivation using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

CO is a useful probe in the characterization of surface properties of both metal and metal oxide via adsorption. Adsorption of CO was used to monitor the possible active site of an Au/TiO₂ catalyst for the CO oxidation reaction. CO adsorption on the reduced catalyst results in the band at 2104 cm⁻¹ indicative of Au⁰. During the reaction (in the presence of both CO and O₂ present) the band is shifted to higher wave numbers indicating non-competitive adsorption on the surface of Au species. This study also reveals the relationship between the presence of CO (in the absence of oxygen) and the build-up of surface species such as bicarbonates, formates and carbonate species which decreases the activity of the catalyst. The presence of both the reduced and the cationic species of Au seem to be requirement for the activity of the catalyst.     

Au负载N掺杂TiO2纳米管阵列的制备及其性能

TiO₂ 纳米管阵列较大的禁带宽度是导致其光催化效率较低的重要原因,采用磁控溅射、阳极氧化以及气氛退火相结合的方法对 TNAs 改性后制备了 Au 负载 N 掺杂 TiO₂ 纳米管阵列(Au@ N-TNAs),然后以甲基橙为目标污染物, 进一步分析了 Au@ N-TNAs 在不同 Au 负载量时光降解效率的变化情况。 采用 SEM、XRD、TEM 和 X 射线光电子能谱 (XPS)等对 Au 和 N 在 Au@ N-TNAs 中的存在形式进行表征和分析,发现 Au 主要是负载在 TiO₂ 纳米管阵列上,而 N 元素则是以掺杂的方式进入 TiO₂ 纳米管阵列的晶格中。 此外,在光降解试验中发现通过 Au 负载与 N 掺杂相结合的方法对 TiO₂ 纳米管阵列进行复合改性后,TiO₂ 纳米管阵列的光催化效率得到显著提升,其中 20s-Au@ N-TNAs 具有最佳的光降解效率。 但 Ti-N 薄膜中间的 Au 层太厚时会影响阳极氧化过程中 TiO₂ 纳米管阵列的生长,而且过量的 Au 在退火处理时很难及时地扩散均匀,进而使得改性后的 TiO₂ 纳米管阵列(40s-Au@ N-TNAs)的光催化效率明显降低。     

Grain growth and thermal stability of nanocrystalline Ni–TiO2 composites

The grain growth and thermal stability of nanocrystalline Ni–TiO₂ composites were systematically investigated. The nanocrystalline Ni–TiO₂ composites with different contents of TiO₂ were prepared via electroplating method with the variation of TiO₂ nano-particles concentration. The effect of TiO₂ content on the grain size, phase structure and microhardness was investigated in detail. The corresponding grain growth and diffusion mechanisms during the heating process were also discussed. The optimal microhardness of HV₅₀ 270 was achieved for the composite with addition of 20 g/L TiO₂ nano-particles after annealing at 400 °C for 90 min. The calculation of the activation energy indicated that lattice diffusion dominated at high temperatures for the nanocrystalline Ni–TiO₂ composites. It was indicated that the increase of TiO₂ nano-particles content took effect on restricting the grain growth at high temperatures by increasing the grain growth activation energy.     

Investigation of the active site and the mode of Au/TiO2 catalyst deactivation using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)

CO is a useful probe in the characterization of surface properties of both metal and metal oxide via adsorption. Adsorption of CO was used to monitor the possible active site of an Au/TiO₂ catalyst for the CO oxidation reaction. CO adsorption on the reduced catalyst results in the band at 2104 cm⁻¹ indicative of Au⁰. During the reaction (in the presence of both CO and O2 present) the band is shifted to higher wave numbers indicating non-competitive adsorption on the surface of Au species. This study also reveals the relationship between the presence of CO (in the absence of oxygen) and the build-up of surface species such as bicarbonates, formates and carbonate species which decreases the activity of the catalyst. The presence of both the reduced and the cationic species of Au seem to be requirement for the activity of the catalyst.     

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)_ad species over the surface of Au/Fe₂O₃ catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst.     

Electrochemical synthesis,studies and modification of TiO<Subscript>2</Subscript> nanotubes

TiO₂ nanotubes (TiO₂ NTs) were synthesized using the electrochemical method in a 1 M H₂SO₄ + 0.15% HF electrolyte. The initial nanotubes have a diameter of 100 ± 10 nm (with the length of up to 150–200 nm) and a wall thickness of 20 ± 5 nm. Nanotube treatment at 400°C results in negligible changes in their structure compared to the initial samples. At 600°C, a change occurs in the nanotube structure and morphology, i.e., the amount decreases drastically; the diameter changes; and, as a consequence, the surface area value decreases. Changes in the structure lead to changes in the electrochemical properties, which is apparently related to a transition from the amorphous structure to anatase and rutile. It is shown that a reversible two-electron reaction, including hydrogen intercalation and Ti⁴⁺/Ti³⁺ oxidation/reduction in the potential range of (−0.6−0.4 V), occurs as a result of moderate thermal treatment. The possibility of the use and promising character of TiO₂ NTs as support for a nonplatinum catalyst based on cobalt tetra(p-methoxyphenyl)porphyrin are brought to light. The electrocatalytic activity of the synthesized catalyst per nominal CoTMPP mass in the reaction of O₂ reduction at E = 0.7 V is ≈25 A/g_CoTMPP, which is comparable to nonplatinum systems on a carbon support.     

Catalytic performance of gold catalysts in the total oxidation of VOCs

Catalysts for the oxidation of volatile organic compounds (VOCs) were prepared by supporting 1% gold on cerium and zirconium oxides (CeO2, Ce_0.5Zr_0.5O₂, ZrO₂) using a simple impregnation method followed by reduction of gold in the presence or absence of ammonia (N). The catalysts were tested in model reactions, namely the total oxidation of benzene, hexane and chlorobenzene, using a micro flow reactor at atmospheric pressure in the temperature range 100–500°C and their activity was compared to that of Au/TiO₂ and Au/Fe₂O₃ reference catalysts supplied by the World Gold Council (WGC). Benefits on the light-off temperatures were observed by adding gold to cerium-containing oxides: 100% conversion of hexane was obtained with Au/Ce_0.5Zr_0.5O₂ at the lowest temperature (300°C). Full conversion of benzene was reached at only 250°C with Au/CeO₂ (N), at 290°C with Au/Fe₂O₃ (WGC) and at 300°C with Au/Ce_0.5Zr_0.5O₂. In the case of chlorobenzene oxidation, the addition of gold was of even greater relevance because of a drop in the light-off temperature of over 100°C for Au/Ce_0.5Zr_0.5O₂ and Au/CeO₂, with respect to the gold-free oxide supports; but in this case rapid deactivation took place.