Tubular arrays of TiO2 nanotubes (ranging in diameter from 40 to 110 nm) on a Ti substrate were used as a support for Ag, Au or Cu deposits obtained by the sputter deposition technique, where the amount of metal varied from 0.01 to 0.2 mg/cm2. Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples 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 metal-covered TiO2 nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag, Au and Cu substrates were also measured. The SERS activity of the composite samples was strongly dependent on the amount of metal deposit, e.g. at and above 0.06 mg Ag/cm2, the intensity of SERS signal was even higher than that for the Ag reference substrate. The high activity of these composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology of the substrate made it possible to monitor very small temporal changes in the Ag metal clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods. The SERS activity of Au or Cu clusters was distinctly lower than those of Ag. The spectral differences exhibited by the three kinds of composites as compared to the reference metal samples are discussed. 相似文献
SERS spectra of pyridine adsorbed on various kinds of vacuum evaporated (10?5 Torr) metals (Ag, Au, Ni, Pd, Pt, Ti and Co) and on single crystals of semiconductors (NiO and TiO2) were obtained at room temperature. The peak frequencies as shifted from those of free pyridine are assigned to the bands of N-bonded pyridine (chemisorbed pyridine). The λ0 dependence varied remarkably from metal to metal. The peak frequency and the λ0 dependence for the pyridine adsorbed on NiO or TiO2 are in good agreement with those on Ni or Ti, respectively, showing the chemical bonding between the N atom and the Ni or Ti atom. The effects of background and of polarization on the SERS spectra were examined in detail, thus revealing the orientation of the adsorbed molecules. Carbon monoxide chemisorbed on Ag was measured by infrared specular reflection as well as by SERS. The results indicate that chemisorbed species on the same substrate do not always give SERS. The SERS spectra obtained are well interpreted as being due to the mechanism of resonance Raman scattering via charge transfer excitation of the adsorbent-adsorbate interaction. 相似文献
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. 相似文献
We synthesized titanium dioxide (TiO2) and nitrogen-doped TiO2 nanoparticles (N-TiO2 NPs) via a sol-hydrothermal method using ammonium chloride (NH4Cl) as the nitrogen (N) source. Furthermore, an N-TiO2/4-mercaptobenzoic acid (4-MBA)/silver (Ag) nanocomplex served as an active substrate for surface-enhanced Raman scattering (SERS) and was prepared by self-assembly. During SERS, the Raman signals of 4-MBA of the N-TiO2/MBA/Ag nanocomplexes exhibited higher intensity and sensitivity than pure TiO2/MBA/Ag, with 1% N doping in N-TiO2, producing the strongest Raman signals. We characterized the N-TiO2 hybrid materials by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectra. N doping did not influence the phase of the TiO2 crystal. The doped N entered into the crystal lattice of the TiO2, replacing some oxygen (O) to form Ti-O-N or Ti-N-O linkage. The results indicated that an appropriate amount of N doping could enhance the SERS performance of the TiO2 SERS substrate via N substitution doping. These doping forms were beneficial to the molecular charge transfer (CT), and this resulted in improved SERS performance for N-doped TiO2 NPs. We attributed this improvement to the formation of N-doping energy levels that were beneficial to the process of TiO2 to MBA molecule CT. This work not only enriched the nonmetal-doped CT mechanism in SERS but also provided several reference values for practical applications.
Graphical abstract N-doped TiO2 nanoparticles were synthesized. Whereafter, N-TiO2/MBA/Ag nanocomplexes were prepared and served as a SERS-active substrate. An appropriate amount of N doping can enhance the SERS properties of TiO2 SERS-active substrate by nitrogen substitution doping. The nonmetal doping TiO2-to-molecule CT mechanism and the synergistic effect in N-TiO2/MBA/Ag charge transfer systems have been studied.
Oriented single crystalline titanium dioxide (TiO2) nano-pillar arrays were directly synthesized on the Ti plate in tetramethylammonium hydroxide (TMAOH) solution by one-pot hydrothermal method. The samples were characterized respectively by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Results showed that the TiO2 nano-pillar with a tetrahydral bipyramidal tip grew vertically on the titanium substrate. HRTEM and Raman results confirmed that the TiO2 nano-pillar arrays were single crystalline anatase. The controls of morphology, size, and orientation of the nano-pillar could be achieved by varying the solution concentration and hydrothermal temperature. Furthermore, the special morphology of the TiO2 nano-pillar arrays was caused by the selectively absorption of the tetramethylammonium (TMA) through hydrogen bonds on the lattice planes parallel to (0 0 1) of anatase TiO2. Less grain boundaries and direct electrical pathway for electron transferring were crucial for the superior photoelectrochemical properties of the single anatase TiO2 nano-pillar arrays. This approach provides a facile in situ method to synthesize TiO2 nano-pillar arrays with a special morphology on titanium substrate. 相似文献
Ag/TiO2 sol with narrow particle size distribution was synthesized using TiCl4 as the starting material. TiCl4 was converted to Ti(OH)4 gel. The Ag/TiO2 sol was prepared by a process where H2O2 was added and then heated at 90–97 °C. After condensation reaction and crystallization, a transparent sol with suspended Ag/TiO2 was formed. Ag/TiO2 was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, contact angle analysis, and X-ray photoelectron spectroscopy. The photocatalytic properties of Ag/TiO2 film were evaluated by degradation of methylene blue in aqueous solution under UV light irradiation. The suspended Ag/TiO2 particles were rhombus primary particles with the major axis ca. 40 nm and the minor axis ca. 10 nm. Ag nanoparticles were well dispersed on TiO2 and the particle size was only 1–2 nm. Ag could restrain the recombination of photo-generated electrons and holes effectively. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The thin film had strong hydrophilicity after being illuminated by UV light. Ag/TiO2 film showed a significant increase in photocatalytic activity compared to the TiO2 film. The high amount of surface hydroxyls on Ag/TiO2 film also played an important role in its photocatalytic activity. 相似文献
Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions. 相似文献
Highly ordered titanium oxide (TiO2) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO2 nanotubes on a Ti substrate and that of freestanding TiO2 membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO2 nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO2 membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO2 nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO2 nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C. 相似文献
Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl4 solution containing TiO2 colloid and accompanied by the TiO2 particles, were deposited on the substrate surface. The film consisting of Au/TiO2 particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO2 dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO2 film was also discussed. 相似文献