电镀法制备Pt/TiO2纳米管电极及其电催化析氢性能

采用阳极氧化法制备得到锐钛矿型二氧化钛(TiO₂)纳米管阵列,在其表面通过电镀法沉积Pt,得到了低铂的Pt/TiO₂纳米管电极(Pt/TiO₂?NTs)。通过扫描电子显微镜和透射电子显微镜对其进行形貌表征后发现,Pt较为均匀地分布于TiO₂纳米管阵列中。进一步的电催化析氢结果表明,Pb/TiO₂?NTs在10 mA·cm^-2时,过电位为0.079 V,塔菲尔斜率为42.7 mV·dec-1,较Pt/TiO₂致密膜电极(Pt/TiO₂?F)以及商业Pt/C催化剂显示了更为优异的催化活性。同时,在长循环稳定性测试(3000个周期)中,Pb/TiO₂?NTs相较于上述2种对比电极显示了更为优异的稳定性。     

Bi2WO6/TiO2纳米管异质结构复合材料的多模式下的光催化活性比较

以TiO₂纳米管为模板,采用多组分自组装结合水热法制备Bi₂WO₆/TiO₂纳米管异质结构复合材料。通过多种技术如X射线衍射（XRD）,X射线光电子能谱（XPS）,N₂吸附-脱附,扫描电镜（SEM）,高分辨透射电镜（HRTEM）和紫外可见漫反射吸收光谱（UV-Vis DRS）考察所制备样品的组成、结构、形貌、光吸收和电子性质。Bi₂WO₆纳米片或纳米粒子分布在TiO₂纳米管上,形成异质结构。随后,通过在紫外、可见和微波辅助光催化模式下降解染料罗丹明B（RhB）来评价复合催化剂的光催化活性。与TiO₂纳米管和Bi₂WO₆相比,Bi₂WO₆/TiO₂-35纳米管在多模式下表现出更优异的光催化活性。与紫外和可见降解模式相比,Bi₂WO₆/TiO₂-35纳米管在微波辅助光催化模式下对RhB的降解效率最高。这种增强的光催化活性源于适量Bi₂WO₆的引入、纳米管独特的形貌特征和降解模式所引起的增强的量子效率。降解过程中的活性物种被证明是h⁺,·OH和·O₂^-自由基。而且,在微波辅助光催化模式下,可产生更多的·OH和·O₂^-自由基。     

无模板电化学沉积法制备多孔WO3·2H2O薄膜及其电致变色性能

二水合氧化钨(WO₃·2H₂O)因其独特的层状结构且富含层间结构水,与无水WO₃相比显示出更加优异的电致变色性能。我们采用简单、无模板的阴极电化学沉积方法,成功在氧化铟锡(ITO)导电玻璃基底上制备了WO₃·2H₂O薄膜。通过改变电沉积液中过氧化氢(H₂O₂)的加入量优化沉积液的成分,获得了具有纳米多孔结构的薄膜。由此制备的WO₃·2H₂O薄膜显示出大的光学对比度(633 nm处的光学对比度大于90%)、快速的响应速度(着色、褪色时间均小于10 s),以及良好的循环稳定性(经10 000次循环后,光学对比度仍保持在90%左右)。     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

Synthesis and photocatalytic applications of Ag/TiO2-nanotubes

TiO₂- and Ag/TiO₂-nanotubes (NTs) were synthesized by hydrothermal methods and microwave-assisted preparation, respectively. Scanning electron microscopy, high resolution transmission electron microscopy, Brunauer-Emmett-Teller particle surface area measurement and X-ray diffraction were used to characterize the nanotubes. Rutile TiO₂-NTs with Na₂Ti₅O₁₁ crystallinity had a length range of 200-400 nm and diameters of 10-20 nm. TiO₂- and Ag/TiO₂-NTs with a 0.4% deposition of Ag had high surface areas of 270 and 169 m² g⁻¹, respectively. The evaluation of photocatalytic activity showed that Ag/TiO₂-NTs displayed higher photocatalytic activity than pure TiO₂-NTs and a 60.91% degradation of Rhodamine-B with 0.8% deposition of Ag species. Also 60% of Rhodamine-6G was physisorbed and 40% chemisorbed on the surface of TiO₂-NTs. In addition, the photocatalytic degradations of organochlorine pesticides taking α-hexachlorobenzene (BHC) and dicofol as typical examples, were compared using Ag/TiO₂-NTs, and found that their degradations rates were all higher than those obtained from commercial TiO₂.     

Blue TiO2 nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting

In the past years there has been a great interest in self-doped TiO₂ nanotubes (blue TiO₂ nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue TiO₂ nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue TiO₂ nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed TiO₂ nanotubes. The annealing temperature of undoped TiO₂ nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue TiO₂ nanotubes was achieved by adjusting the cathodic polarization parameters. Blue TiO₂ nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm^-2) compared to the undoped TiO₂ nanotube arrays (0.19 mA cm^-2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.     

Significant enhancement of the photoelectrochemical activity of TiO2 nanotubes

In the present work, we report on a facile and effective approach to significantly enhance the photocatalytic activity of TiO₂ nanotubes. The TiO₂ nanotubes prepared by the electrochemical oxidation of titanium in dimethyl sulfoxide (DMSO) with 2% HF were treated in a methanol solution under UV light irradiation. In comparison with the untreated TiO₂ nanotubes, the treatment resulted in a dramatic increase in the donor density of the TiO₂ nanotubes by approximately 3 orders of magnitude. The treated TiO₂ nanotubes exhibited a 15-fold enhancement in photocurrent and a 6.8-fold increase in the photoelectrochemical degradation of 4-nitrophenol, significant for hydrogen generation and wastewater treatment.     

Preparation and photocatalytic behavior of TiO2-carbon nanotube hybrid catalyst for acridine dye decomposition

A new kind of hybrid catalyst, TiO₂-carbon nanotubes, was prepared via sol-gel method for the first time. Its photocatalytic activity in the photodegradation of acridine dye aqueous solution at low concentration was tested. There was no measurable effect on the formation of crystalline phase of TiO₂ catalyst with the addition of 10 wt.% carbon nanotubes to TiO₂ samples. AFM photograph of TiO₂-carbon nanotubes sintered at 300°C showed that the carbon nanotubes were enwrapped by TiO₂, which greatly increased the adsorbing ability of the catalyst and was in favor of photocatalytic reaction. Compared with naked TiO₂ powder the hybrid catalyst prepared in this way showed high efficiency in the photodecomposition of acridine dye.     

TiO2–carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

TiO₂–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO₂ layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO₂ layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO₂ layer proved to be best for efficient charge separation among the tested samples. The optimized TiO₂–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO₂ nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO₂–CNT heterojunctions and TiO₂ nanotubes were 0.75 h⁻¹ (R² = 0.983) and 0.39 h⁻¹ (R² = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO₂–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO₂ nanotubes. These results demonstrate the super capability of the TiO₂–CNT heterojunction arrays in photocatalysis with comparison to TiO₂-only nanomaterial.     

Preparation and characterization of Zr doped TiO2 nanotube arrays on the titanium sheet and their enhanced photocatalytic activity

This paper described a new method for the preparation of Zr doped TiO₂ nanotube arrays by electrochemical method. TiO₂ nanotube arrays were prepared by anodization with titanium anode and platinum cathode. Afterwards, the formed TiO₂ nanotube arrays and Pt were used as cathode and anode, respectively, for preparation of Zr/TiO₂ nanotube arrays in the electrolyte of 0.1 M Zr(NO₃)₄ with different voltage and post-calcination process. The nanotube arrays were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV-Vis diffusion reflection spectra (DRS). The photocatalytic activities of these nanotubes were investigated with Rhodamine B as the model pollutant and the results demonstrated that the photocatalytic efficiency of Zr doped TiO₂ nanotubes was much better than that of TiO₂ nanotubes under UV irradiation. Zr/TiO₂ nanotube arrays doped at 7 V and calcined at 600 °C (denoted as TiO₂-7 V-600) achieved the best photocatalytic efficiency and the most optimal doping ratio was 0.047 (Zr/Ti). TiO₂-7 V-600 could be reused for more than 20 times and maintained good photocatalytic activities.     

High activity of novel Pd/TiO2 nanotube catalysts for methanol electro-oxidation

Electro-oxidation of methanol in sulfuric acid solution was studied using palladium well-dispersed on titanium nanotubes, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell. Pd dispersed on titania nanotubes, which leads to high surface area substrates, showed excellent catalytic activities compared to those of pure Pd and Pd-TiO₂ nanoparticles. TEM results show a narrow distribution of TiO₂ nanoparticles whose particle size is about 10 nm, and uniform nano-sized TiO₂ nanotubes with 10 nm in diameters are seen from HRTEM . A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The composite electrode activities were measured by cyclic voltammetry (CV) and at 25 °C it was found that 3 wt% Pd in titania nanotubes had the best activity for methanol oxidation.     

Enhancement of ethanol electrooxidation on plasmonic Au/TiO2 nanotube arrays

Novel electrocatalysts Au/TiO₂ nanotube arrays (Au/TiO₂NTs) were prepared by loading low-content(1.9 at.%) of Au nanoparticles (AuNPs) onto highly ordered TiO₂ nanotube arrays (TiO₂NTs). Ethanol electrooxidation indicates that visible-light (λ > 400 nm) irradiation can significantly enhance the activity as well as resistpoisoning of Au/TiO₂NTs electrocatalysts that are activated by plasmon resonance. Au/TiO₂NTs catalysts calcinated at 300 °C display the highest performance due to the strong synergistic interactions between TiO₂ and Au NPs. The combination of visible-light irradiation with a controllable potential offers a new strategyfor enhancing the performance of anodes in direct ethanol fuel cell (DEFC).     

Photoluminescence of samarium-doped TiO2 nanotubes

Samarium (Sm)-modified TiO₂ nanotubes (TNTs) were synthesized by low-temperature soft chemical processing. X-ray powder diffraction analyses of the synthesized Sm-doped and non-doped TNTs show a broad peak near 2θ=10°, which is typical of TNTs. The binding energy of Sm ³d_5/2 for 10 mol% Sm-doped TNT (1088.3 eV) was chemically shifted from that of Sm₂O₃ (1087.5 eV), showing that Sm existed in the TiO₂ lattice. Sm-doped TNTs clearly exhibited red fluorescence, corresponding to the doped Sm³⁺ ion in the TNT lattice. The Sm-doped TNT excitation spectrum exhibited a broad curve, which was similar to the UV–vis optical absorption spectrum. Thus, it was considered that the photoluminescence emission of Sm³⁺-doped TNT with UV-light irradiation was caused by the energy transfer from the TNT matrix via the band-to-band excitation of TiO₂ to the Sm³⁺ ion.     

In-situ preparation and electrochromic properties of TiO2/PTPA-HTAN core-shell nanocomposite film

A new star-shaped structure conjugated microporous polymers, poly (2,8,14-tri[4-diphenyl-benzene]-hexaazatrinaphthylene) (PTPA-HATN), was designed and in-situ electrochemically polymerized on the surfaces of FTO electrodes with a directional alignment TiO₂ nanorod array to obtain TiO₂/PTPA-HATN core-shell nanocomposite films. Compared with the PTPA-HATN film, the TiO₂/PTPA-HATN composite film exhibits higher optical contrast and faster response time, with contrast of 57% at 783 nm, coloring time of 3.62 s and discoloring time of 2.55 s (43%, 4.63 s and 4.77 s for PTPA-HATN film, respectively). After 400 cycles, the contrast of nanocomposite film decreased by 28%, while the PTPA-HATN film basically lost its electrochromic properties. A simple three-layer EC prototype device based on TiO₂/PTPA-HATN nanocomposite film constructed with hydrogel electrolyte clearly shows color changes at different voltages. On the one hand, the formation of core-shell porous nanostructure of TiO₂/PTPA-HATN composite film provides a larger ion doping/de-doping interface, shortening the average diffusion length of ions. On the other hand, the large indented polymer-nanorods contact interface makes it difficult for the polymer to detach from the electrode, thus significantly improving the cyclic stability of the composite film.     

TiO2 nanotubes as recyclable catalyst for efficient photocatalytic degradation of indigo carmine dye

TiO₂ nanotubes have been synthesized in a hydrothermal system. The nanotubes were characterized by scanning electronic microscopy (SEM), FT-Raman spectroscopy and surface charge density by surface area analyzer. These nanocatalysts were applied to photocatalyse indigo carmine dye degradation. Photodegradation ability of TiO₂ nanotubes was compared to TiO₂ anatase photoactivity. Indigo carmine dye was completely degraded at 60 and 110 min of reaction catalysed by TiO₂ nanotubes and TiO₂ anatase, respectively. TiO₂ nanotubes presented high photodegradation activity at pH 2 and TiO₂ anatase at pH 4. TiO₂ nanotubes were easily recycled whereas the reuse of TiO₂ anatase was not effective. Nanotubes maintained 90% of activity after 10 catalytic cycles and TiO₂ anatase presented only 10% of its activity after 10 cycles.     

Nanosized CeO2–SiO2, CeO2–TiO2, and CeO2–ZrO2 Mixed Oxides: Influence of Supporting Oxide on Thermal Stability and Oxygen Storage Properties of Ceria

The influence of SiO₂, TiO₂, and ZrO₂ on the structural and redox properties of CeO₂ were systematically investigated by various techniques namely, X-ray diffraction (XRD), Raman spectroscopy (RS), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HREM), BET surface area, and thermogravimetry methods. The effect of supporting oxides on the crystal modification of ceria was also mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahigh dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO₂–SiO₂ sample primarily consists of nanocrystalline CeO₂ on the amorphous SiO₂ surface. Both crystalline CeO₂ and TiO₂-anatase phases were noted in the case of CeO₂–TiO₂ sample. Formation of cubic Ce_0.75Zr_0.25O₂ and Ce_0.6Zr_0.4O₂ (at 1073 K) were observed in the case of CeO₂–ZrO₂ sample. The cell ‘a’ parameter estimations revealed an expansion of the ceria lattice in the case of CeO₂–TiO₂, while a contraction is noted in the case of CeO₂–ZrO₂. The DRS studies suggest that the supporting oxides significantly influence the band gap energy of CeO₂. Raman measurements disclose the presence of oxygen vacancies, lattice defects, and displacement of oxide ions from their normal lattice positions in the case of CeO₂–TiO₂ and CeO₂–ZrO₂ samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation states, Si(IV), Ti(IV), and Zr(IV) at the surface of the materials. Cerium is present in both Ce⁴⁺ and Ce³⁺ oxidation states. The HREM results reveal well-dispersed CeO₂ nanocrystals over the amorphous SiO₂ matrix in the case of CeO₂–SiO₂, isolated CeO₂ and TiO₂ (A) nanocrystals and some overlapping regions in the case of CeO₂–TiO₂, and nanosized CeO₂ and Ce–Zr oxides in the case of CeO₂–ZrO₂ sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO₂ is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of mixed oxides is more than that of pure CeO₂ and the CeO₂–ZrO₂ exhibits highest OSC.     

Synthesis of Various Metal/TiO2 Core/shell Nanorod Arrays

We present a general approach to fabricate metal/TiO₂ core/shell nanorod structures by two-step electrodeposition. Firstly, TiO₂ nanotubes with uniform wall thickness are prepared in anodic aluminum oxide (AAO) membranes by electrodeposition. The wall thickness of thenanotubes could be easily controlled by modulating the deposition time, and their outer diameter and length are only limited by the channel diameter and the thickness of the AAO membranes, respectively. The nanotubes' tops prepared by this method are open, while the bottoms are connected directly with the Au film at the back of the AAO membranes. Secondly, Pd, Cu, and Fe elements are filled into the TiO₂ nanotubes to form core/shell structures. The core/shell nanorods prepared by this two-step process are high density and free-standing, and their length is dependent on the deposition time.     

Fabrication and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst ZnTe/TiO2 nanotube arrays

A new ZnTe modified TiO₂ nanotube (NT) array catalyst was prepared by pulse potential electrodeposition of ZnTe nanoparticles (NPs) onto TiO₂ NT arrays, and its application for photocatalytic degradation of anthracene-9-carboxylic acid (9-AnCOOH) was investigated. The even distribution of ZnTe NPs was well-proportionately grown on the top surface of the TiO₂ NT while without clogging the tube entrances. Compared with the unmodified TiO₂ NT, the ZnTe modified TiO₂ NT (ZnTe/TiO₂ NT) showed significantly enhanced photocatalytic activity towards 9-AnCOOH under simulated solar light. After 70 min of irradiation, 9-AnCOOH was degraded with the removal ratio of 45% on the bare TiO₂ NT, much lower than 80%, 90%, and 100% on the ZnTe/TiO₂ NT with the ZnTe NPs prepared under the pulsed “on” potentials of −0.8, −1.0, and −2.0 V, respectively. The increased photodegradation efficiency mainly results from the improved photocurrent density as results of enhanced visible-light absorption and decreased hole-electron recombination due to the presence of narrow-band-gap p-type semiconductor ZnTe.     

Raman investigations of SERS activity of Ag nanoclusters on a TiO2-nanotubes/Ti substrate

Tubular arrays of TiO₂ nanotubes (ranging in diameter from 40 to 110 nm) on a Ti substrate were used as a support for Ag deposits obtained by the sputter deposition technique where the amount of Ag varied from 0.01 to 0.2 mg Ag/cm². Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples of Ag/TiO₂ nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the Ag-covered TiO₂ nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag substrate were also measured.The SERS activity of the composite samples was strongly dependent on the amount of Ag deposit. At and above 0.06 mg Ag/cm², the SERS signal was even higher than that for the Ag reference substrate. The high activity of the composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology made it possible to monitor very small temporal changes in the Ag clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods.     

Preparation, characterization, and infrared emissivity property of optically active polyurethane/TiO2/SiO2 multilayered microspheres

Optically active polyurethane/titania/silica (LPU/TiO₂/SiO₂) multilayered core–shell composite microspheres were prepared by the combination of titania deposition on the surface of silica spheres and subsequent polymer grafting. LPU/TiO₂/SiO₂ was characterized by FT-IR, UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), SEM and TEM, and the infrared emissivity value (8–14 μm) was investigated in addition. The results indicated that titania and polyurethane had been successfully coated onto the surfaces of silica microspheres. LPU/TiO₂/SiO₂ exhibited clearly multilayered core–shell construction. The infrared emissivity values reduced along with the increase of covering layers thus proved that the interfacial interactions had direct influence on the infrared emissivity. Besides, LPU/TiO₂/SiO₂ multilayered microspheres based on the optically active polyurethane took advantages of the orderly secondary structure and strengthened interfacial synergistic actions. Consequently, it possessed the lowest infrared emissivity value.