Photoelectrochemical property and photocatalytic activity of N-doped TiO2 nanotube arrays

N-doped TiO₂ nanotube arrays (NTN) were prepared by anodization and dip-calcination method. Hydrazine hydrate was used as nitrogen source. The surface morphology of samples was characterized by SEM. It showed that the mean size of inner diameter was 65 nm and wall thickness was 15 nm for NTN. The ordered TiO₂ nanotube arrays on Ti substrate can sustain the impact of doping process and post-heat treatment. The atomic ratio of N/Ti was 8/25, which was calculated by EDX. Photoelectrochemical property of NTN was examined by anodic photocurrent response. Results indicated the photocurrent of NTN was nearly twice as that of non-doped TiO₂ nanotube arrays (TN). Photocatalytic activity of NTN was investigated by degrading dye X-3B under visible light. As a result, 99% of X-3B was decomposed by NTN in 105 min, while that of TN was 59%.     

Nanostructured carbon nanotube/TiO2 composite coatings using electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) has been used to combine multi-walled carbon nanotubes of diameter in the range 20–30 nm and commercially available TiO₂ nanoparticles (23 nm particle size) in composite films. Laminate coatings with up to four layers were produced by sequential EPD, while composite coatings were obtained by electrophoretic co-deposition of carbon nanotubes and TiO₂ nanoparticles, respectively. Scanning electron microscopy was used to characterize the resultant microstructures. The mechanism of EPD of carbon nanotube/TiO₂ nanoparticle composites is discussed.     

A non-aqueous electrolyte-based asymmetric supercapacitor with polymer and metal oxide/multiwalled carbon nanotube electrodes

A supercapacitor using non-aqueous electrolyte and multiwalled carbon nanotube (MWNTs) nanocomposite electrodes has been designed with polymer and metal oxide loaded carbon nanotubes as electrodes. These nanocomposites were coated on the carbon paper with Nafion solution to obtain the flexible electrodes. Carbon paper with the nanocomposite coating was pressed on either sides of the Nafion membrane, which acts both as a separator and as an electrolyte. The performance of asymmetric assembly of electrochemical double layer capacitor with polymer- and metal oxide-dispersed MWNTs composite materials with non-aqueous Nafion electrolyte is compared with symmetric assemblies, and the results are discussed.     

金属氧化物修饰对介孔纳米TiO2电极的染料敏化太阳能电池电化学性能的影响

将介孔TiO₂纳米粒子(m-TiO₂)多孔膜电极浸入相应的金属硝酸盐的500 oC热处理修饰金属氧化物(如Mg、ZnO、Al₂O₃或NiO).结果表明,金属氧化物修饰均可形成能垒对m-TiO₂膜电极的界面电荷传输过程产生影响,但外加偏压下其膜内电子传输和界面电荷复合均明显依赖于修饰氧化物的种类及其存在形态. 金属氧化物修饰的膜电极在电子传输和界面复合方面的变化与DSSCs的电流-电压特性曲线的变化规律具有明显的相关性,可不同程度地提高电池的光电压,而MgO、ZnO和NiO修饰的电池效率分别提高了23%、13%和6%. 上述结果表明调控电池的本征参数可以改善TiO₂-基DSSCs的性能.     

Synthesis and field emission of diamond-like carbon nanorods on TiO2/Ti nanotube arrays

Highly ordered TiO₂/Ti nanotube arrays were fabricated by anodic oxidation method in 0.5 wt% HF. Using prepared TiO₂/Ti nanotube arrays deposited Ni nanoparticles as substrate, high quality diamond-like carbon nanorods (DLCNRs) were synthesized by a conventional method of chemical vapor deposition at 750 °C in nitrogen atmosphere. DLCNRs were analyzed by filed emission scanning electron microscopy and Raman spectrometer. It is very interesting that DLCNRs possess pagoda shape with the length of 3–10 μm. Raman spectra show two strong peaks about 1332 cm⁻¹ and 1598 cm⁻¹, indicating the formation of diamond-like carbon. The field emission measurements suggest that DLCNRs/TiO₂/Ti has excellent field emission properties, a low turn-on field about 3.0 V/μm, no evident decay at 3.4 mA/cm² in 480 min.     

Preparation and characterization of amine-functionalized SiO2/TiO2 films for formaldehyde degradation

This paper investigated the gaseous formaldehyde degradation by the amine-functionalized SiO₂/TiO₂ photocatalytic films for improving indoor air quality. The films were synthesized via the co-condensation reaction of methyltrimethoxysilane (MTMOS) and 3-aminopropyltrimethoxysilane (APTMS). The physicochemical properties of prepared photocatalysts were characterized with N₂ adsorption/desorption isotherms measurement, X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FT/IR). The effect of amine-functional groups and the ratio of MTMOS/APTMS precursors on the formaldehyde adsorption and photocatalytic degradation were investigated. The results showed that the formaldehyde adsorption and photocatalytic degradation of the APTMS-functionalized SiO₂/TiO₂ film was higher than that of SiO₂/TiO₂ film due to the surface adsorption on amine sites and the relatively high of the specific surface area of the APTMS-functionalized SiO₂/TiO₂ film (15 times higher than SiO₂/TiO₂). The enhancement of the formaldehyde degradation of the film can be attributed to the synergetic effect of adsorption and subsequent photocatalytic decomposition. The repeatability of photocatalytic film was also tested and the degradation efficiency was 91.0% of initial efficiency after seven cycles.     

Low resistance dye-sensitized solar cells based on all-titanium substrates using wires and sheets

Low resistance dye-sensitized solar cells (DSSCs) based on all-titanium substrates were proposed in this paper. To minimize the internal resistance of DSSCs, the titanium wires and titanium sheets were used as the substrates of the photoanode and the counter electrode, respectively. Compared with the FTO substrate, titanium wires could absorb much diffused light by back reflection since the reflectivity in the titanium sheet was highly increased up to 53.12%. Furthermore, the transmittance of the front cover was increased by 13.2% using the super white glass instead of FTO substrate. The thickness of TiO₂ thin film coated on titanium wire was optimized to achieve a high cell performance. The efficiency of 5.6% for the cell was obtained with a J_sc of 15.41 mA cm⁻², V_oc of 0.59 V, and FF of 0.62. The results showed that the titanium-based DSSCs had superiority for producing the large-scale DSSCs without metal grid line.     

FTIR, SEM and fractal dimension characterization of lipase B from Candida antarctica immobilized onto titania at selected conditions

Lipase B from Candida Antarctica (also known as Candida antarctica lipase B or CALB) was immobilized onto titanium dioxide (TiO₂) in a buffer-free, bidistilled aqueous medium. The adsorption isotherm was determined by UV-vis analysis of supernatant solution at 280 nm, revealing that in 7 h 98% of the theoretical lipase monolayer on the TiO₂ (with 45.7 m²/g BET area) was achieved.Samples withdrawn from the supernatant immobilization medium were analyzed by Fourier-transform infrared spectroscopy in the 1700-1600 cm⁻¹ range (where the Amide I Proteins band appears) in order to obtain quantitative information on the evolution of the secondary-structure elements of the protein. The analysis performed revealed that lipase conformation suffers only minor changes during its adsorption onto TiO₂. However, water associated to the lipase may interact of several ways with the surface of the hydrated oxide.Characterization of the immobilized biocatalyst (CALB/TiO₂) implied SEM, fractal dimension analysis and FTIR techniques. A proposal of lipase-hydrated oxide interaction is presented.     

Diffusion of CO2/CH4 confined in narrow carbon nanotube bundles

ABSTRACT

The diffusion of a CO₂/CH₄ mixture in carbon nanotube (CNT) bundles was studied using molecular simulations. The effect of diameter and temperature on the diffusion of the mixture was investigated. Our results show that the single-file diffusion occurs when CO₂ and CH₄ are confined in CNTs of diameter less than 1.0 nm. In CNTs of diameter larger than 1.0 nm, both molecules diffuse in the Fickian style. The transition from single-file to Fickian diffusion was demonstrated for both CO₂ and CH₄ molecules. A dual diffusion mechanism was observed in the studied (20, 0) CNT bundle, single-file diffusion of CO₂ in the interstitial sites of (20, 0) CNT bundle and Fickian diffusion of CO₂ and CH₄ in the pores. For CO₂, the interaction energies (CO₂–CO₂ and CO₂–CNT) are larger than that of CH₄ in all cases. But only a very small difference in the diffusion coefficient was observed between CO₂ and CH₄. Temperature has a negligible effect on the difference between diffusion coefficients of CO₂ and CH₄ in the studied CNT bundles. The adsorption, diffusion and permeation selectivities are discussed and compared, and the adsorption is demonstrated to be the rate limiting step for the separation of CO₂/CH₄ in CNT bundle membranes.     

Fabrication and characterization of ZnO-coated TiO2 nanotube arrays

In this study, we prepared highly ordered TiO₂ nanotube arrays on Ti through an anodizing process. Then, utilizing its proven antibacterial properties, we coated our TiO₂ nanotubes (TiO₂-NTs) with ZnO using the sol–gel method. We characterized the morphology, structure, and composition of the ZnO-coated TiO₂ nanotubes (ZnO-TNTs) using field-emission scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, respectively. We investigated surface topography and roughness of the coatings by atomic force microscopy operated in the tapping mode. Our results revealed impurity-free, anatase-phase TiO₂ nanotubes that are uniformly coated with a ZnO layer. Finally, we tested the antibacterial activity of ZnO-TNTs against Staphylococcus aureus, and found ZnO-TNTs significantly improved the antibacterial properties of Ti implants. We conclude that ZnO-TNTs provide Ti with antibacterial activity, which highlights its potential in orthopedic and dental implants.     

Electromagnetic and mechanical properties of Fe3O4-coated amorphous carbon nanotube/polyvinyl chloride composites

Electromagnetic wave absorbing properties of absorbing composites depend on the dielectric and magnetic loss generally. In this paper, using Fe₃O₄-coated amorphous carbon nanotubes (ACNTs-Fe₃O₄) fabricated using a chemical synthesis–hydrothermal treatment method as an absorber and polyvinyl chloride (PVC) as a matrix, electromagnetic and mechanical properties of ACNT-Fe₃O₄/PVC composite were investigated. The results showed that the dielectric and magnetic losses of ACNT-Fe₃O₄/PVC composite were significantly enhanced in 8.2–12.4 GHz compared to ACNT/PVC composite, which improved absorbing properties, while slightly changing the mechanical properties.     

特定位点上CO2与(TiO2)n团簇相互作用的第一性原理研究

本文基于密度泛函理论系统地研究了(TiO₂)_n团簇上二氧化碳(CO₂)的吸附和活化性质. 计算结果表明,CO₂更倾向于吸附在(TiO₂)_n团簇的桥氧原子上,形成“化学吸附”碳酸盐络合物. 而CO更倾向于吸附到末端Ti-O的Ti原子上. 发现计算得到的碳酸盐振动频率值与实验获得的结果非常吻合,这表明配合物中CO₂的几何构型与其线性型相比,有微小的弯转. 通过对电子结构、电荷密度、电离势、HOMO-LUMO以及态密度的分析,证实了CO₂与团簇之间的电荷转移以及相互作用. 从预测的能量分布图来看,(TiO₂)_n团簇上的CO₂活化与结构密切有关,相比于块体的TiO₂,CO₂在团簇结构上更易于吸附和活化.     

Cobalt-doped TiO2: a computational analysis of dopant placement and charge transfer direction on thin film anatase

ABSTRACT

Titanium dioxide (TiO₂) nanocrystals are promising materials for photo-electrochemical water splitting. This study focuses on how surface dopant placement can affect the electronic properties. TiO₂ anatase thin films are doped two ways: a cobalt ion replacing a surface titanium ion (surface ingrained) and a cobalt ion chemisorbed to two surface oxygen ions and two NH₃ ligands. Specifically, when studying the binding pattern, the cobalt ion dopant changes from an electron acceptor for the surface ingrained model to an electron donor for the chemisorbed model. The optical absorption peaks of the surface ingrained model are attributed to p→d transitions and are much stronger when compared to the d→d transitions for the chemisorbed model. It is the conclusion of this computational study that one can alter the cobalt dopant on the anatase thin film to focus a positive or negative charge at the surface by changing the surface dopant location.     

Fabrication and characterization of Fe-doped titania semiconductor electrodes with p-n homojunction devices

The nano-TiO₂ electrode with a p-n homojunction device was designed and fabricated by coating of the Fe³⁺-doped TiO₂ (p-type) film on top of the nano-TiO₂ (n-type) film. These films were prepared from synthesized sol-gel TiO₂ samples which were verified as anatase with nano-size particles. The semiconductor characteristics of the p-type and n-type films were demonstrated by current-voltage (I-V) measurements. Results show that the rectifying curves of undoped TiO₂ and Fe³⁺-doped TiO₂ sample films were observed from the I-V data illustration for both the n-type and p-type films. In addition, the shapes of the rectifying curves were influenced by the fabrication conditions of the sample films, such as the doping concentration of the metal ions, and thermal treatments. Moreover, the p-n homojunction films heating at different temperatures were produced and analyzed by the I-V measurements. From the I-V data analysis, the rectifying current of this p-n junction diode has a 10 mA order higher than the current of the n-type film. The p-n homojunction TiO₂ electrode demonstrated greater performance of electronic properties than the n-type TiO₂ electrode.     

N-doped TiO2 photo-catalyst for the degradation of 1,2-dichloroethane under fluorescent light

The photo-catalytic degradation of 1,2-dichloroethane (1, 2-DCE) using nitrogen-doped TiO₂ photo-catalysts under fluorescent light irradiation was investigated. Highly pure TiO₂ and nitrogen-doped TiO₂ were prepared by a sol-gel method and characterized by thermo-gravimetric/differential-thermal analysis (TG/DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results indicate that the photo-catalysts were mainly nano-size with an anatase-phase structure. The degradation reaction of 1,2-DCE was operated under visible-light irradiation, and the photo-catalytic oxidation was conducted in a batch photo-reactor with various nitrogen doping ratios (N/Ti = 0-25 mol%). The relative humidity (RH) was controlled at 0-20% and the oxygen concentration was controlled at 0-21%. The photo-degradation with nitrogen-doped TiO₂ showed superior photo-catalytic activity compared to that for pure TiO₂. TiO₂ doped with 15 mol% nitrogen exhibited the best photo-catalytic efficiency under the tested conditions. The products from the 1,2-DCE photo-catalytic oxidation were CO₂ and water; the by-products included dichloromethane, methyl chloride, ethyl chloride, carbon monoxide, and hydrogen chloride. The reaction pathway of 1,2-DCE indicates that oxygen molecules are the major factor that causes the degradation of 1,2-DCE in the gas phase.     

Annealing effects on microstructural and optical properties of Nanostructured-TiO2 thin films prepared by sol-gel technique

In this paper we report on the effect of annealing on the microsctructural and optoelectronic properties of titanium dioxide (TiO₂) thin films prepared using sol-gel method onto silicon (Si) (100) and quartz substrates. The annealing temperatures range from 200 to 1000 °C. The Microstructural properties of annealed thin films were investigated by Thermal gravimetric analyses (TGA), X-ray diffraction (XRD) and Raman Spectroscopy. The surface morphology of the film was examined using Atomic Force Microscopy (AFM) method. The optical properties of TiO₂ thin films were characterized using UV-VIS and Spectroscopic ellipsometry. The results have shown that the TiO₂ thin films persist in the anatase phase even after annealing at 800 °C. The phase transformation from anatase to rutile occurred only when the films were annealed at 1000 °C. AFM studies revealed nanocrystalline structure where their shape and density depend strongly on the annealing temperatures. The elaborated nanostructured-TiO₂ thin films present a high transparency in the visible range. Spectroscopic ellipsometry (SE) study was used to determine the effect of annealing temperature on the thickness and on the optical constant of TiO₂ thin films. Spectroscopic ellipsometry and UV-VIS shows that the band gap of TiO₂ thin films was found to decrease when the annealing temperature increases. The Anatase phase was find to show higher photocatalytic activity than the rutile one.     

TiO2 Wedgy Nanotubes Array Flims for Photovoltaic Enhancement

In this study, TiO₂ wedgy nanotubes with rectangular cross-sections were fabricated on transparent conductive substrates by using TiO₂ nanorods as the precursor via the anisotropic etching route. TiO2 nanotubes with V-shaped hollow structure and the special crystal plane exposed on the tube wall possess nature of high surface area for more dye molecules absorption, and the strong light scattering effects and dual-channel for effective electron transport of the TiO₂ V-shaped nanotubes based dye-sensitized solar cell exhibit a remarkable photovoltaic enhancement compared with the TiO₂ nanorods. The photoanode based on our V-shaped TiO₂ nanotubes with a length of 1.5 μm show a 123% increase of the dye loading and a 182% improvement in the overall conversion efficiency when compared with 4 μm rutile TiO₂ nanorods photoanode.     

Preparation of TiO2–MWCNT core/shell heterostructures containing a single MWCNT and their electromagnetic properties

TiO₂–MWCNT core/shell heterostructures containing a single MWCNT have been successfully prepared via solvothermal method. TiO₂–MWCNT heterostructures with different morphologies and electromagnetic (EM) properties have obtained by adjusting the weight ratio of titanium dioxide (TiO₂₎ and multi-walled carbon nanotubes (MWCNT) (weight ratio: 1:1, 5:1 and 10:1). EDS spectrum and X-ray diffraction analysis reveal that the product is composed of Ti, O, and C elements, and the crystal structure of TiO₂ is tetragonal anatase phase. SEM and TEM images show that the MWCNTs are coated by a thin layer of TiO₂ crystals, and the average diameters of the needle-like TiO₂ nanocrystals are less than 100 nm. EM properties of the as-prepared TiO₂–MWCNT heterostructures are investigated in the 0.5–18.0 GHz range. The permittivity and permeability of the TiO₂–MWCNT heterostructures change obviously as the weight ratio of TiO₂ and MWCNT increases. Moreover, the typical resonance–antiresonance phenomenon can be observed in the permittivity and permeability curves.     

Hydrothermal treatment of gadolinium oxide in presence of silica

Abstract

Hydrothermal and solvothermal (isopropanol) treatments of gadolinium oxide and silica were investigated under different pressure and temperature conditions. Products were examined by infrared vibrational spectroscopy (IR), x-ray powder diffraction (XRD) and thermal analysis (DTA, TG). Hexagonal gadolinium hydroxide was obtained in hydrothermal conditions, even in presence of silica, while no change was observed from isopropanolic medium treatment. Hydrothermally treated samples are more reactive as precursors for solid state reactions in inorganic synthesis.     

STM/STS investigation of carbon nanotubes deposited on Bi2Te3 surface

This paper reports our scanning tunneling microscopy and spectroscopy (STM/STS) study of double-walled and multi-walled carbon nanotubes (CNTs) of different diameter deposited on Bi₂Te₃ (narrow gap semiconductor). The approximate diameter of the studied double-walled and multi-walled CNTs was 2 nm and 8 nm, respectively. Crystalline Bi2Te3 was used as a substrate to enhance the contrast between the CNTs and the substrate in the STS measurements performed to examine peculiarities of CNT morphology, such as junctions, ends or structural defects, in terms of their electronic structure.