SERS study of Ag nanoparticles electrodeposited on patterned TiO2 nanotube films

In this work, Ag nanoparticles (NPs) were deposited on patterned TiO₂ nanotube films through pulse‐current (PC) electrodeposition, and as a result patterned Ag NPs films were achieved. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X‐ray diffraction (XRD) were used, respectively, to study the morphology, uniformity, and phase structure of the patterned Ag NP films. The size and density of the as‐deposited Ag NPs could be controlled by changing the deposition charge density, and it was found that the patterned Ag NP films produced under a charge density of 2.0 C cm⁻² gave intense UV–vis and Raman peaks. Two‐dimensional surface‐enhanced Raman scattering (SERS) mapping of rhodamine 6G (R6G) on the patterned Ag NP films demonstrated a high‐throughput, localized molecular adsorption and micropatterned SERS effect. Copyright © 2010 John Wiley & Sons, Ltd.     

Modification of TiO2 nanotube arrays by solution coating

Packed and sintered titania (TiO₂) nanoparticles are conventionally used as a photoanode for dye-sensitized solar cells. As a result, barriers are created for the electron transport and electron-hole recombination due to the large number of interfacial boundaries and voids in such a mesoporous photoanode. A high aspect ratio of length/diameter of titania nanotube arrays (TNAs) is required to meet the high surface area and the reduction of interfacial boundaries. TNAs prepared by the organic anodic oxidation method in this work possess a vertical nanotube structure that exhibits a high surface area, high degree of crystallinity, geometric pre-orientation and active electro-optical nanograins. Such a synthesized mesoporous structure is typically obtained by 60 V/2 h and 450 °C/30 min post-annealing and has a tube diameter of 110 nm, and a tube length of 15 mm. When the TNAs are modified by a TiO₂ nano-layer (TNL), the photocatalytic efficiency for methylene blue (MB) decomposition is further improved by up to 90%. Photosensitivity shows an obvious improvement when illuminating the UV light for the TNL modified TNAs and the visible light for the CuInS₂ layer modified TNAs.     

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.     

Facile fabrication, characterization, and enhanced photoelectrocatalytic degradation performance of highly oriented TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays were successfully fabricated using ethanol and water mixture electrolytes (40 vol% ethanol and 0.2 wt% hydrofluoric acid) by a facile electrochemical anodization method. The as-prepared nanotube arrays were grown perpendicular to the titanium substrate with about 90 nm in diameter, 20 nm in wall thickness, and around 500 nm in length. The formation mechanism of the samples is briefly discussed. A blue shift in the spectrum of UV–Vis absorption was observed with respect to a piece of the sol–gel derived TiO₂ film. Moreover, photocurrent response and photoelectrocatalytic degradation of methyl orange under ultraviolet light irradiation were adopted to evaluate the photoelectrocatalytic properties of the TiO₂ nanotube arrays. We demonstrate that the highly ordered TiO₂ nanotube arrays possess much better photoelectrocatalytic activity than the sol–gel derived TiO₂ film and good stability.     

Simultaneous synthesis of TiO2 microrods in situ decorated with Ag nanoparticles and their bactericidal efficiency

In this study, we report a simple and cost-effective method for in situ decoration of Ag NPs onto nanoporous TiO₂ microrods by one medium (ethylene glycol) that can produce two different morphologies. In order to investigate the morphology, phase composition, crystalline structure, and chemical state (valency) of samples before and after annealing in air at different temperatures, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed. The present results show that the size, morphology and crystallinity of both Ag NPs and TiO₂ microrod substrate depend on the post-annealing treatment temperatures. The annealed Ag–TiO₂ NP/microrod composites show large inhibition zones against E. coli bacteria. The obtained Ag–TiO₂ composites have the potential for use as a novel antibacterial material and in water treatment applications.     

Highly defined and ordered top‐openings in TiO2 nanotube arrays

We report a very simple and novel approach to produce anodic TiO₂ nanotube arrays with highly defined and ordered tube openings. It is based on carrying out anodization through a slowly soluble photoresist coating. This eliminates the formation of undesired initiation layers on the tube tops and protects them to a certain extent from etching by the electrolyte.

     

Raman investigations of TiO2 nanotube substrates covered with thin Ag or Cu deposits

A tubular array of TiO₂ nanotubes on Ti matrix was used as a support for Ag or Cu sputter‐deposited layers intended for surface‐enhanced Raman scattering (SERS) investigations. The composite samples of Ag/TiO₂–nanotube/Ti and Cu/TiO₂–nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) [and scanning Auger microscopy (SAM)] to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured after it had been adsorbed on the TiO₂–nanotube/Ti substrates covered with thin Ag or Cu deposit as well as on the bulk electrochemically roughened Ag or Cu reference substrates. It was found that the SERS spectra measured for pyridine adsorbed on the bulk silver substrate were significantly different than the spectra measured on the TiO₂–nanotube/Ti substrates covered the Ag layer. The spectra measured for pyridine adsorbed on the Ag/TiO₂–nanotube/Ti suggest that on the surface of such a composite substrate there are many Lewis acidic sites. Spectra typical for pyridine adsorbed on acidic sites were observed even after deposition of a relatively thick silver layer (e.g. an Ag layer with an average thickness of 80 nm) on the TiO₂–nanotube/Ti support. Our findings suggest that TiO₂–nanotube/Ti support is a promising substrate for the preparation of metallic nano‐clusters on a support containing acidic active sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of Cu2+ dopant in optical property of CdTe quantum dots and photoelectrochemical performance of CdTe:Cu2+/TiO2 nanotube arrays

A novel one-step synthesis process was used to prepare CdTe:Cu²⁺/TiO₂ nanotube arrays (TNTAs). X-ray powder diffraction and high-resolution transmission electron microscopy analyses confirmed that the obtained CdTe:Cu²⁺ quantum dots (QDs) possess cubic structures, which are approximately spherical, and a small particle size (2.95 nm). The photoluminescent and UV–visible absorption spectra of CdTe:Cu²⁺ QDs also display an obvious redshift, which was attributed to the replacement of Cd²⁺ with Cu²⁺. Compared with that of the TNTAs and CdTe/TNTAs, the photoelectric conversion efficiency of CdTe:5% Cu²⁺/TNTAs increased by 785.7% and 103.3%, respectively. The incident photo-to-current conversion efficiency of CdTe:5% Cu²⁺/TNTAs was 50.6%, which indicated the potential use of QDs in photochemical solar cells.     

有序Ti02纳米管阵列结构的可控生长及其物相研究

分别在HF水溶液、含NH4F和H2O的乙二醇有机溶液中对Ti箔进行阳极氧化,得到TiO2纳米管阵列结构.该结构高度有序、分布均匀、垂直取向,且通过阳极氧化工艺条件(如阳极氧化电压、电解液的选择与配比以及氧化时间等)可实现对其结构参数(如管径、管壁厚度、管密度、管长等)的有效控制.利用XRD研究了TiO2纳米管阵列的物相结构.结果表明:退火前的TiO2纳米管阵列为无定形结构;分别在真空和氧气氛中5I)0℃退火后,HF水溶液中制备的样品出现单一锐钛矿相,页在含NH4F和H2O的乙二醇有机溶液中氧化得到的样品则出现锐钛矿和金红石的混合相.前者在氧气氛中退火后锐钛矿晶化程度较高;后者在真空中退火后混合相的品化程度也较高.初步分析了TiO2纳米管阵列的形成机理.这些结果对基于TiO2,纳米管阵列的传感器及有机一无机异质结太阳电池的应用研究是非常有益的.     

Fabrication of Ag/TiO2 nanotube array with enhanced photo-catalytic degradation of aqueous organic pollutant

In this paper, the fabrication of Ag/TiO₂ nanotube arrays and their photo-catalytic activity have been studied. The SEM, TEM and XRD were performed to characterize the morphology and crystalline phase of the TiO₂ nanotube array and Ag/TiO₂ nanotube array. Ag nanoparticles with different loadings, which are aimed to suppress the electron–hole recombination so as to enhance the photo-catalytic oxidation efficiency, were systematically coated onto TiO₂ nanotubes. The photo-catalytic activity of these nano-materials was evaluated by the degradation of two different pollutants: methyl orange and glyphosate. The effects of various parameters, such as the amount of the photo-catalyst, the illumination time, and pH value on the photo-catalytic oxidation activity, were studied.     

Non-metal doped TiO2 nanotube arrays for high efficiency photocatalytic decomposition of organic species in water

Titanium dioxide is a well-known photoactive semiconductor with a variety of possible applications. The procedure of pollutant degradation is mainly performed using TiO₂ powder suspension. It can also be exploited an immobilized catalyst on a solid support. Morphology and chemical doping have a great influence on TiO₂ activity under illumination. Here we compare photoactivity of titania nanotube arrays doped with non-metal atoms: nitrogen, iodine and boron applied for photodegradation of organic dye - methylene blue and terephtalic acid. The doped samples act as a much better photocatalyst in the degradation process of methylene blue and lead to the formation of much higher amount of hydroxyl radicals (•OH) than undoped TiO₂ nanotube arrays. The use of a catalyst active under solar light illumination in the form of thin films on a stable substrate can be scaled up for an industrial application.     

Effect of Ag doping on the crystallization and phase transition of TiO2 nanoparticles

TiO₂ nanoparticles doped with different Ag contents were prepared by a modified sol–gel method, using titanium tetraisopropoxide and silver nitrate as precursors and 2-propanol as solvent. Silver was incorporated into the TiO₂ matrix via decomposition of AgNO₃ during thermal treatment in different atmospheres. Effects of Ag doping on the crystallization and phase transition of the TiO₂ nanoparticles were studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Raman spectroscopy techniques. While air annealing incorporates silver into TiO₂ matrix in silver oxide form, annealing in nitrogen incorporates metallic silver into TiO₂. Formation of silver oxide increases the thermal stability of the TiO₂ particles. Silver oxide affects the crystallization process of TiO₂ particles and the temperature of transition form anatase to rutile. On the other hand, presence of metallic silver in the samples annealed in nitrogen atmosphere decreases the temperature of phase transition of TiO₂ nanoparticles.     

Oriented ZnO nanotubes arrays decorated with TiO2 nanoparticles for dye-sensitized solar cell applications

Dye-sensitized solar cells (DSSCs) based on a novel composite photoanode of TiO₂ nanoparticles coating on electrodeposited ZnO nanotube arrays are fabricated and characterized. An efficiency of 3.94 % is achieved for the composite cell, increasing 86.7 % than 2.11 % of the ZnO nanotubes cell. The short-circuit current (J _sc) and open-circuit voltage (V _oc) are also enhancing 52.9 % and 25.3 %, respectively. The improvements are because of the high surface area of TiO₂ nanoparticles, as well as fast electron transport and light scattering effect of ZnO nanotubes.     

Experimental observation of two‐layer TiO2 nanotube arrays prepared by stepping‐voltage anodization

Two‐layer TiO₂ nanotube arrays were produced by stepping down the anodic voltage during which three nanotube interface structures between the top layer and the second layer were observed by SEM. We detected a polygonal ring structure on the top surface of the second layer and offer direct evidence of the growth of this second tube layer both at the cell boundary and right beneath the bottom of the first tube layer. For these processes, a possible growth mechanism is presented. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication of open‐ended TiO2 nanotube arrays by a simple two‐step anodization

We report a two‐step anodizing approach for the fabrication of large‐scale open‐ended TiO₂ nanotube arrays (TNAs) on a conductive Au layer. In this method, a deposited Ti/Au bilayer film is initially anodized under a high potential to form and shape the TNAs. A following low potential is then in situ applied at a suitable time to slowly eliminate the remaining barrier layer at the bottom of the TNAs without further treatment. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Site‐specific deposition of Ag nanoparticles on ZnO nanorod arrays via galvanic reduction and their SERS applications

A controllable heterostructure consisting of ZnO nanorod arrays with attached Ag nanoparticles at only one end has been synthesized via a facile and convenient galvanic reduction method. Scanning electron microscopic images of these nanostructures showed good selectivity of Ag deposition on the tip of ZnO nanorod arrays. The formation of these regular Ag ZnO heterogeneous nanorod arrays can be explained by a localization of the electrons at the ends of the ZnO nanorods after the electron transfer step. By tuning the reaction time and the concentration of silver nitrate, the density of Ag nanoparticles on the tip of ZnO nanorods can be well controlled. Owing to the introduction of Ag nanoparticles with different densities, the resulting Ag ZnO heterogeneous nanorod arrays have been proved to be a versatile substrate for surface‐enhanced Raman scattering not only for common organic molecules but also for label‐free protein detection. Copyright © 2009 John Wiley & Sons, Ltd.     

Introduction of Ag nanoparticles by picosecond LIFT to improve the photoelectric property of AZO films

The photoelectric properties of conductive films are improved by doping Ag on aluminum-doped zinc oxide(AZO) films by laser induced forward transfer(LIFT).Firstly,the picosecond laser induced transfer mechanism of Ag films was revealed by numerical simulation;then,different-thickness Ag films were deposited on the AZO films by picosecond LIFT.When the film thickness is 30 nm and,50 nm,we have successfully obtained some Ag-AZO films with better optoelectronic properties by adjusting the laser parameters.     

The C-V characteristics of TiO2/p-Si/Ag,GNR doped TiO2/p-Si/Ag and MWCNT doped TiO2/p-Si/Ag heterojunction devices

The TiO₂/p-Si/Ag, graphene (GNR) doped TiO₂/p-Si/Ag and multi-walled carbon nanotube (MWCNT) doped TiO₂/p-Si/Ag heterojunction devices were fabricated by electrospinning technique at same conditions. Their structural, morphological properties, thermal analyses (TGA), and capacitance voltage characteristics were studied and compared. The undoped, GNR and MWCNT doped TiO₂ structures obtained successfully according to XRD measurements. Morphological properties of the undoped, GNR and MWCNT doped TiO₂ composite structures have rod or ribbon like structures. The TGA result confirmed the GNR and MWCNT doped TiO₂ structures. The C-V and G-V measurements were employed for electrical characterization of the TiO₂/p-Si/Ag, GNR doped TiO₂/p-Si/Ag and MWCNT doped TiO₂/p-Si/Ag devices for various frequencies at room temperatures. The results imparted that the capacitance and conductance behaviors of all devices are strong functions of the frequency and voltage. The electrical parameters were calculated from C⁻²-V plots of the heterojunction devices and compared for three devices. The transient photocapacitance plots revealed that the devices can be employed for optical communication applications.     

Modernized H2S-treatment of TiO2 nanoparticles: Improving quantum-dot deposition for enhanced photocatalytic performance

One of the efficient strategies to enhance light harvesting capability of metal oxides nanoparticles (NPs) is to deposit low band gap metal sulfides on them via pseudo-successive ionic layer adsorption and reaction (p-SILAR). Resultant oxide-sulfide nanocomposites have a variety of applications, however there is still a need to increase the deposition of metal sulfide in the form of quantum-dots (QDs). In this work, we have successfully enhanced the deposition of QDs on TiO₂ NPs using a modernized H₂S-treatment strategy. A rotary reactor was employed for H₂S-treatment of TiO₂ NPs, ensuing higher deposition of PbS (in TiO₂–PbS) and CdS (in TiO₂–CdS) via p-SILAR. Resultantly, dye degradation of Rhodamine B increased from 63% to 75% and 72%–84%, respectively. X-ray photoelectron spectroscopy revealed the efficacy of modernized H₂S-treatment while intensive electrochemical characterization affirmed reduction in charge carrier transfer resistances due to superior deposition of PbS and CdS QDs on TiO₂ NPs.     

Enhancing the linear absorption and tuning the nonlinearity of TiO2 nanowires through the incorporation of Ag nanoparticles

We report on the enhanced linear absorption and modified nonlinear absorption of TiO2 nanowires coated with Ag nanoparticles. Experimental results indicated that the coated Ag nanoparticles significantly increased the linear absorption of the nanostructures in the wavelength range of visible light. Z-scan experiments showed that when the excitation energy increased, the nonlinear absorption of the TiO2 nanowires changed from reverse-saturable absorption to saturable absorption. When Ag nanoparticles were coated on the TiO2 nanowires, the reverse-saturable absorption was significantly inhibited. The as-prepared nanostructures may find potential applications in the field of solar cells and all-optical switching.