高质量多孔氧化铝模板的制备

在草酸电解液中研究了阳极氧化法制备多孔氧化铝模板(AAO模板)。采用场发射扫描电子显微镜对多孔模板的形貌进行表征,结果表明:模板孔的分布均匀有序,孔径在40~70 nm;电解液浓度、氧化电压、氧化温度和氧化时间都会影响模板的形态;不经过高温退火及抛光也可以制得规则排布的多孔AAO模板。X射线衍射分析表明:氧化铝膜的主要成分为非晶态Al2O3。     

Synthesis of ordered ZnO nanowire arrays from aqueous solution using AAO template

In this paper we report a simple method that enables the easy fabrication of ordered ZnO nanowire arrays using Anodic Aluminium Oxide (AAO) template. We have used a vacuum injection technique to fill solution into the pores of an AAO template. The AAO template has been fabricated by a two-step anodization process using 0.3 M oxalic acid (H₂C₂O₄) solution under a constant voltage of 40 V. The AAO template formed through this process has been detached from Al substrate via an anodic voltage pulse using perchloric acid (HClO₄) solution (70%). The nanowires of ZnO have been synthesized by injecting the saturated Zn(NO₃)₂ solution into the pores of the detached AAO template using a vacuum pump. The ZnO nanowires synthesized by this technique have been found dense & continuous with uniform diameter throughout the length of the wire. The structural characteristics of AAO template and ZnO nanowires have been studied by Field Emission Scanning Electron Microscope (FESEM), Atomic force microscope (AFM) and Transmission Electron Microscope (TEM).     

Synthesis of Y-junction carbon nanotubes within porous anodic aluminum oxide template

Y-junction carbon nanotubes with the average diameter about 200 nm were successfully synthesized within porous anodic aluminum oxide template, which was prepared by anodic anodizing aluminum sheet in 1.0 mol/l H₃PO₄ solution at a constant anodization voltage 90 V.     

Roughness evolution of highly ordered nanoporous anodic aluminum oxide films

In this paper, we report on the surface roughness evolution of highly ordered anodic aluminum oxide (AAO) films based on an atomic force microscopy (AFM) study. Root mean square of the surface roughness was measured on AFM images taken from highly ordered AAO films produced by two-step anodization under different conditions including electrolyte type, anodization voltage, and anodization time. Surface roughness of highly ordered AAO films increases step by step through the two-step anodizing process including electropolishing, first-step anodization, dissolution, and second-step anodization. However, increase of the surface roughness is proportional to the anodization voltage and time. The surface roughness of AAO films changes as a function of length scale until it finally approaches a maximum termed the saturation roughness. The variation of roughness of the growth of AAO could be scaled with an anomalous dynamic behavior as it saturates over a critical length scale while the saturation roughness is dependent on the anodizing time and voltage.     

Intense blue luminescence of anodic aluminum oxide

The luminescence spectra of aluminum oxide with an ordered system of through pores have been studied. The diameter and density of pores were ≈ 50 nm and 1.2 × 10¹⁰ cm^?2, respectively. Amorphous aluminum oxide formed by anodization of aluminum foil in an oxalic acid electrolyte shows intense luminescence in the blue spectral region. Processing of spectra with the use of an oxalic acid approximation by Gaussian curves gives three bands peaking at ～ 382 (3.2 eV), 461 (2.7 eV), and 500 nm (2.5 eV), which correspond to different types of defects. The bands at 382 and 461 nm can be assigned to optical transitions involving F⁺ and F centers (vacancies of oxygen with one or two electrons), respectively. The lower-energy band near 500 nm can be presumably assigned to luminescence from F⁺⁺ centers (vacancy of oxygen without an electron). Analysis of the luminescence excitation spectra has revealed an inhomogeneous character of the distribution of the corresponding luminescence centers in the Al₂O₃ matrix.     

Iron oxide nanoparticle synthesis in aqueous and membrane systems for oxidative degradation of trichloroethylene from water

The potential for using hydroxyl radical (OH^?) reactions catalyzed by iron oxide nanoparticles (NPs) to remediate toxic organic compounds was investigated. Iron oxide NPs were synthesized by controlled oxidation of iron NPs prior to their use for contaminant oxidation (by H₂O₂ addition) at near-neutral pH values. Cross-linked polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) microfiltration membranes were prepared by in situ polymerization of acrylic acid inside the membrane pores. Iron and iron oxide NPs (80–100 nm) were directly synthesized in the polymer matrix of PAA/PVDF membranes, which prevented the agglomeration of particles and controlled the particle size. The conversion of iron to iron oxide in aqueous solution with air oxidation was studied based on X-ray diffraction, Mössbauer spectroscopy and BET surface area test methods. Trichloroethylene (TCE) was selected as the model contaminant because of its environmental importance. Degradations of TCE and H₂O₂ by NP surface generated OH^? were investigated. Depending on the ratio of iron and H₂O₂, TCE conversions as high as 100 % (with about 91 % dechlorination) were obtained. TCE dechlorination was also achieved in real groundwater samples with the reactive membranes.     

A comparative study of surface‐enhanced Raman scattering from silver‐coated anodic aluminum oxide and porous silicon

Three types of Ag‐coated arrays from porous anodic aluminum oxide (AAO) were prepared and studied as substrates for surface‐enhanced Raman scattering (SERS). They were compared with Ag‐coated porous silicon (PSi) samples. AAO‐based substrates were prepared by the vapor deposition of silver directly onto the surface of porous AAO with different morphologies of the pores, whereas SERS‐active island films on the PSi were prepared by immersion plating. The resulting metallic nanostructures were characterized by UV‐vis absorption spectroscopy and scanning electron microscopy (SEM). Thermal evaporation leads to the formation of granular arrays of Ag nanoparticles on the surface of AAO. SERS activity of the substrates was tested using water‐soluble cationic Zn(II)‐tetrakis (4‐N‐methylpyridyl) porphyrin (ZnTMPyP4) as a probe molecule. The results indicate that all AAO‐based substrates studied here exhibit some degree of SERS activity. Noteworthy, for excitation at 532 nm, signals from AAO‐based substrates were comparable with those from the PSi‐based ones, whereas for 441.6 nm excitation they were about twice higher. The strongest SERS‐enhancement at 441.6 nm excitationwas provided by the AAO substrates with silver deposited on the monolith (originally nonporous) side of AAO. Preferential SERS‐enhancement of the bands ascribed to the vibrations of the N‐methylpyridinium group of ZnTMPyP4 when going to blue excitation was found. Copyright © 2010 John Wiley & Sons, Ltd.     

The synthesis of clusters of iron oxides in mesopores of monodisperse spherical silica particles

The method of obtaining nanoclusters α-Fe₂O₃ in the pores of monodisperse spherical particles of mesoporous silica (mSiO₂) by a single impregnation of the pores with a melt of crystalline hydrate of ferric nitrate and its subsequent thermal destruction has been proposed. Fe₃O₄ nanoclusters are synthesized from α-Fe₂O₃ in the pores by reducing in thermodynamically equilibrium conditions. Then particles containing Fe₃O₄ were annealed in oxygen for the conversion of Fe₃O₄ back to α-Fe₂O₃. In the result, the particles with the structure of the core-shell mSiO₂/Fe₃O₄@mSiO₂/α-Fe₂O₃ are obtained. The composition and structure of synthesized materials as well as the field dependence of the magnetic moment on the magnetic field strength have been investigated.

     

Optical properties of anodic aluminum oxide produced in a complex electrolyte

Features of the absorption, transmission, photoluminescence, and infrared (IR) spectra of anodic aluminum oxide (AAO) formed in a complex electrolyte and annealed at 800, 900, 1000, and 1300°C are investigated. The variations in the phase composition changes of the anodic aluminum oxide are reflected in the respective features of its optical properties. A decrease in the transmission coefficient in the visible range of the spectrum is shown for the phase series: amorphous AOA → γ-Al₂O₃, γ-, θ-, δ-Al₂O₃ mixture → α-Al₂O₃. It is established that the highest absorption coefficient is characteristic of α-Al₂O₃, and the amorphous samples are the most transparent in the visible range. An intensive luminescence band in the red region of the spectrum with maxima at 678 and 694 nm is found for α-Al₂O₃. The emergence of this band is explained by the presence of octahedrally coordinated Mn₊₄ and Cr₊₃ impurity ions in the structure. A luminescence band at 700–800 nm is observed for the mixture of low-temperature phases. Intense luminescence in the region 350–500 nm is found for amorphous AAO and γ-Al₂O₃.     

Magnetic properties of SiO2-coated iron oxide nanoparticles studied by polarized small angle neutron scattering

The structural and magnetic properties of non-coated and SiO₂-coated iron oxide (Fe₃O₄) nanoparticles (NPs) were investigated by a polarized small-angle neutron scattering (P-SANS) method. Measurement of the P-SANS allowed us to obtain nuclear and magnetic scattering cross sections of the NPs under applied magnetic field. The analysis of the scattering intensity provided the structural parameters and the spatial magnetization distribution of the non-coated and the SiO₂ coated core–shell NPs. The measured radius of both NPs and the shell thickness of the core–shell NPs were in consistent with those measured by the transmission electron microscopy. In comparison, the magnetic core radii of both NPs were 0.12–0.6 nm smaller than the nuclear radii, indicating the magnetization reduction in the surface region of core Fe₃O₄ in both NPs. However, the reduced magnetization region, which is the surface spin canting region, of the SiO₂-coated NPs was relatively narrower than that of the non-coated NPs. We suggest that the SiO₂ coating on the Fe₃O₄ NPs may stabilize the spin order of atoms and prohibit the oxidation or defect formation at the surface region of the Fe₃O₄ NPs, and enhance the corresponding magnetization of the Fe₃O₄ NPs by the reduction of the spin canting layer thickness.     

Growth mechanism of ZnO nanorod/Fe3O4 nanoparticle composites and their photocatalytic properties

ZnO nanorods/Fe₃O₄ nanocomposites as the recyclable photocatalyst were synthesized by a co-precipitation method, with microwave assistant by dropping alkaline solution with Fe₃O₄ nanoparticles into the aqueous of zinc salt. These Fe₃O₄ nanoparticles were the nucleated centers for the ZnO nanorods growth so that these nanorods ended with aggregated Fe₃O₄ nanoparticles. The growth processes and mechanism are explained as those insoluble zinc hydroxides prefer to nucleate on the surface of Fe₃O₄ nanoparticles (heterogeneous nucleation) rather than nucleated as isolated ZnO nanostructures (homogeneous nucleation). These nanocomposites have strong photocatalytic ability to reduce RhB and moderate magnetization, which make them being good recyclable photocatalysts.     

Synthesis of ultrasmall magnetic iron oxide nanoparticles and study of their colloid and surface chemistry

Colloidal nanoparticles of Fe₃O₄ (4 nm) were synthesized by high-temperature hydrolysis of chelated iron (II) and (III) diethylene glycol alkoxide complexes in a solution of the parent alcohol (H₂DEG) without using capping ligands or surfactants: [Fe(DEG)Cl₂]²⁻+2[Fe(DEG)Cl₃]²⁻+2H₂O+2OH⁻→Fe₃O₄+3H₂DEG+8Cl⁻ The obtained particles were reacted with different small-molecule polydentate ligands, and the resulting adducts were tested for aqueous colloid formation. Both the carboxyl and α-hydroxyl groups of the hydroxyacids are involved in coordination to the nanoparticles’ surface. This coordination provides the major contribution to the stability of the ligand-coated nanoparticles against hydrolysis.     

Analysis of XPS spectra of Fe and Fe ions in oxide materials

Samples of the iron oxides Fe_0.94O, Fe₃O₄, Fe₂O₃, and Fe₂SiO₄ were prepared by high temperature equilibration in controlled gas atmospheres. The samples were fractured in vacuum and high resolution XPS spectra of the fractured surfaces were measured. The peak positions and peak shape parameters of Fe 3p for Fe²⁺ and Fe³⁺ were derived from the Fe 3p XPS spectra of the standard samples of 2FeO·SiO₂ and Fe₂O₃, respectively. Using these parameters, the Fe 3p peaks of Fe₃O₄ and Fe_1−yO are analysed. The results indicate that high resolution XPS techniques can be used to determine the Fe²⁺/Fe³⁺ ratios in metal oxides. The technique has the potential for application to other transition metal oxide systems.     

Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Dependence of pH and surfactant effect in the synthesis of magnetite (Fe3O4) nanoparticles and its properties

Nanoparticles of Fe₃O₄ were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe₃O₄. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe₃O₄ nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were ε-Fe₂O₃ or Fe₃O₄ phase. To further prove the composition of the product, as-prepared Fe₃O₄ were examined by X-ray photoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces ε-Fe₂O₃. Whereas a pH value of 11 produces magnetite (Fe₃O₄) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe₃O₄) nanoparticles.     

Electrochemical sensing of H2O2 using cobalt oxide modified TiO2 nanotubes

Cobalt oxide (Co₃O₄) modified anatase titanium dioxide nanotubes (ATNTs) have been investigated for the electrochemical sensing of hydrogen peroxide (H₂O₂). ATNTs have been synthesized by a two-step anodization process. ATNTs were then modified with Co₃O₄ employing chemical bath deposition method. The structure and morphology of ATNTs and their modification with Co₃O₄ has been confirmed by X-ray diffraction by scanning electron microscopy. H₂O₂ sensing has been studied in 0.1 M PBS solution, by cyclic voltammetry and amperometry. Variation in the peak positions and current densities was observed with addition of H₂O₂ for Co₃O₄ modified ATNTs. Sensitivity and limit of detection improved with modification of ATNTs with Co₃O₄ with precursor concentration up to 0.8 M. However, at higher precursor concentrations sensitivity and limit of detection toward H₂O₂ deteriorated. Co₃O₄ Modified ATNTS using 0.8 M precursor concentration are comparatively more suitable for H₂O₂ sensing applications due to the optimum formation of Co₃O₄/ATNTs heterojunctions.     

The Study of Aggregation Processes in Colloidal Solutions of Magnetite–Silica Nanoparticles by NMR Relaxometry,AFM, and UV–Vis-Spectroscopy

Colloidal solutions of magnetic nanoparticles were studied as a promising magnetic resonance imaging (MRI) contrast agent. The problem of aggregative stability of solutions is considered. Sol-gel synthesis of magnetite colloidal solutions stabilized by silica is described. Transmittance spectra were measured to analyze sedimentation of nanoparticles in magnetite–silica solutions of different compositions and concentrations. It is shown that the synthesized nanoparticles can be used as MRI contrast agents. The surface morphology and particle size of Fe₃O₄/SiO₂ layers were estimated by atomic force mictroscopy (AFM) technique. The mechanism of magnetic-field-induced aggregation of Fe₃O₄/SiO₂ nanoparticles into chain-like and fractal structures is described.     

AFM study of gold nanowire array electrodeposited within anodic aluminum oxide template

Uniform gold nanowires were synthesized by electrodepositing the gold under a very low ac frequency in the pores of an anodic aluminum oxide (AAO) template. The surface of the Au/AAO composite is very even and appeared purplish red. Atomic force microscopy observation indicates that the template membranes we obtained have hexagonally close-packed nanochannels. The gold nanowire array is very orderly arranged after partially dissolving the aluminum oxide membrane. Gold nanowires were also characterized by transmission electron microscopy and the phase structure of the Au/AAO composite was proved by X-ray diffraction. Received: 19 April 2001 / Accepted: 28 April 2001 / Published online: 27 June 2001     

Control synthesis of magnetic Fe3O4–chitosan nanoparticles under UV irradiation in aqueous system

Novel magnetic Fe₃O₄–chitosan nanoparticles were synthesized via photochemical method in an emulsifier-free aqueous system at room temperature for the first time. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the Fe₃O₄–chitosan nanoparticles were in regular shape with a mean diameter of 41 nm, whereas the average size in aqueous solution measured by photocorrelation spectroscopy (PCS) was 64 nm, which indicated that the nanoparticles had water-swelling properties. X-ray diffraction (XRD) patterns indicated that the Fe₃O₄ nanoparticles were pure Fe₃O₄ with a spinel structure, and the irradiation under UV light did not result in a phase change. The Fe₃O₄–chitosan nanoparticles were also characterized by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Magnetic measurement revealed that the saturated magnetization (Ms) of the Fe₃O₄–chitosan nanoparticles reached 48.6 emu/g and the nanoparticles showed the characteristics of superparamagnetism. The stability test showed these novel nanoparticles had high magnetic stability. The PCS and TGA results indicated that the size and chitosan content of Fe₃O₄–chitosan nanoparticles formed was pH- and chitosan/Fe₃O₄ ratio-dependent, which could be used to synthesize magnetic Fe₃O₄–chitosan nanoparticles with different size to meet the requirements of different applications.     

Dual effects of ultrasound on fabrication of anodic aluminum oxide

Ultrasound has been proven to enhance the mass transfer process and impact the fabrication of anodic aluminum oxide (AAO). However, the different effects of ultrasound propagating in different media make the specific target and process of ultrasound in AAO remain unclear, and the effects of ultrasound on AAO reported in previous studies are contradictory. These uncertainties have greatly limited the application of ultrasonic-assisted anodization (UAA) in practice. In this study, the bubble desorption and mass transfer enhancement effects were decoupled based on an anodizing system with focused ultrasound, such that the dual effects of ultrasound on different targets were distinguished. The results showed that ultrasound has the dual effects on AAO fabrication. Specifically, ultrasound focused on the anode has a nanopore-expansion effect on AAO, leading to a 12.24 % improvement in fabrication efficiency. This was attributed to the promotion of interfacial ion migration through ultrasonic-induced high-frequency vibrational bubble desorption. However, AAO nanopores were observed to shrink when ultrasound was focused on the electrolyte, accompanied by a 25.85 % reduction in fabrication efficiency. The effects of ultrasound on mass transfer through jet cavitation appeared to be the reason for this phenomenon. This study resolved the paradoxical phenomena of UAA in previous studies and is expected to guide AAO application in electrochemistry and surface treatments.