Optical properties of silver nanowires grown electrochemically in nanoporous alumina

We report fabrication and optical properties of electrochemically deposited silver nanowires into nanoporous alumina template. A finite element method is used to study plasmonic coupling of dipole emitters with the silver nanowires.

Fabrication of macro–mesoporous titania/alumina core–shell materials in oil/water interface

A series of macro–mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesized. The materials were calcined at 723 K and were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy (UV–visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100 °C), which makes it possible to synthesize such materials on industrial scale. The performance–morphology relationship of as-synthesized TiO2/Al2O3 nanocomposites was investigated by the photocatalytic degradation of a model organic pollutant under UV irradiation. The samples with 1D (fibrous) morphology exhibited superior catalytic performance than the samples without, such as titania microspheres.

Settling behaviours of low alumina/caustic ratios during seawater neutralisation of Bayer liquor

Factors that affect the settleability of seawater neutralised bauxite refinery residues are poorly understood, in particular, the settleability of precipitates in the absence of red mud and those formed with different alumina/caustic (AC) ratios. The influence of temperature, AC ratio, caustic concentration and the volumetric ratio of seawater on the settleability of seawater neutralisation precipitates and their respective compositions and stabilities have been determined. An array of techniques have been used to determine the composition and stability of precipitates and include pH, conductivity, inductively coupled plasma optical emission spectroscopy, infrared spectroscopy and X-ray diffraction. Temperature has been shown to have a significant influence on the settleability and calcium carbonate phase distributions in precipitates, as well as the overall stability of the precipitates. More complex phase compositions have also been found for Bayer liquors with lower AC ratios. The caustic concentration and temperature of the reaction have the greatest influence on the settling efficiency of the precipitates. Assessments on the chemical stability of the precipitates, precipitate settleability and discharge water quality have been made. In addition, productivity and environmental impacts caused by changes in precipitate settleability have also been considered.

Free-standing alumina nanobottles and nanotubes pre-integrated into nanoporous alumina membranes

A novel interfacial structure consisting of long (up to 5 μm), thin (about 300 nm), highly-ordered, free-standing, highly-reproducible aluminum oxide nanobottles and long tubular nanocapsules attached to a rigid, thin (less than 1 μm) nanoporous anodic alumina membrane is fabricated by simple, fast, catalyst-free, environmentally friendly voltage-pulse anodization. A growth mechanism is proposed based on the formation of straight channels in alumina membrane by anodization, followed by neck formation due to a sophisticated voltage control during the process. This process can be used for the fabrication of alumina nanocontainers with highly controllable geometrical size and volume, vitally important for various applications such as material and energy storage, targeted drug and diagnostic agent delivery, controlled drug and active agent release, gene and biomolecule reservoirs, micro-biologically protected platforms, nano-bioreactors, tissue engineering and hydrogen storage.

Carbon nanotubes on nanoporous alumina: From surface mats to conformal pore filling

Control over nucleation and growth of multi-walled carbon nanotubes in the nanochannels of porous alumina membranes by several combinations of posttreatments, namely exposing the membrane top surface to atmospheric plasma jet and application of standard S1813 photoresist as an additional carbon precursor, is demonstrated. The nanotubes grown after plasma treatment nucleated inside the channels and did not form fibrous mats on the surface. Thus, the nanotube growth mode can be controlled by surface treatment and application of additional precursor, and complex nanotube-based structures can be produced for various applications. A plausible mechanism of nanotube nucleation and growth in the channels is proposed, based on the estimated depth of ion flux penetration into the channels.

Multipurpose nanoporous alumina-carbon nanowall bi-dimensional nano-hybrid platform via catalyzed and catalyst-free plasma CVD

Simple, rapid, plasma-assisted synthesis of large-area arrays of vertically-aligned carbon nanowalls on highly-porous, transparent bare and gold-coated alumina membranes with the two pore sizes is reported. It is demonstrated that the complex patterns of vertically aligned nanowalls can nucleate and form different morphologies in the low-temperature plasmas. The process is stable, and the twofold change in the gas flow (10 and 20 sccm) does not noticeably influence the morphology of the nanowall pattern. Application of a thin (5 nm) gold layer to nanoporous membrane prior to the nanowall growth allows controlling the network morphology.

High temperature deformation and densification in alumina-yttria composites

Pinning by second phase particles offers a potent means for limiting grain growth and enhancing superplasticity in alumina-based ceramics. In the present study, a colloidal technique was used to produce green bodies of alumina-yttria composites; at elevated temperatures, the yttria particles react with alumina to produce YAG particles. The densification and high temperature deformation characteristics of alumina-YAG composites were studied using conventional free sintering and sinter-forging, which involves the application of a compressive stress without any lateral constraints. It is shown that the YAG particles retard both densification and grain growth. The experiments indicate also that the presence of YAG particles does not significantly alter the stress exponent for creep deformation.

An EXAFS study of the cobalt-molybdenum/.gamma.-alumina hydrodesulfurization catalyst

While Mo in the Co-Mo/y-A1203 hydrodesulfurization catalyst is present as a sulfidic species similar to MoS2, Co shows two types of coordination, one with six sulfurs (but not a bulk sulfide) and the other with four oxygens. The significance of such species is discussed. In addition to an additive relation of the EXAFS function and the residual spectra, the ratio of amplitude terms of the catalyst and the model system has been employed in the analysis.

A novel combustion process for the synthesis of fine particle α-alumina and related oxide materials

Synthesis of fine particle α-alumina and related oxide materials such as MgAl2O4, CaAl2O4, Y3Al5O12 (YAG), Image , β′-alumina, LaAlO3 and ruby powder (Image ) has been achieved at low temperatures (500°C) by the combustion of corresponding metal nitrate-urea mixtures. Solid combustion products have been identified by their characteristic X-ray diffraction patterns. The fine particle nature of α-alumina and related oxide materials has been investigated using SEM, TEM, particle size analysis and surface area measurements.

An Electron-Microscopic Investigation Of Oxides Related To Beta-Alumina

High resolution electron microscopic (HREM) investigation of potassiumbeta-alumina and the related gallate and ferrite has revealed that whereas the aluminate and gallate are highly disordered, consisting of random sequence ofbeta andbetaPrime units, the ferrite is more ordered. The aluminate and gallate are sensitive to electron beam irradiation exhibiting beam-induced damage similar to sodiumbetaPrime-alumina. Significantly, the ferrite is beamstable, the difference in behaviour amongst these related oxides arising from the different mechanisms by which alkali metal nonstoichiometry is accommodated. Barium hexaaluminate and hexaferrite are both highly ordered; specimens prepared by the barium borate flux method exhibit a new radic3a×radic3a superstructure of the hexagonal magnetoplumbite cell.

Effect of the method of preparation and pretreatment on the texture of alumina and related catalysts

The effect of the method of preparation and pretreatment on catalyst texture was investigated in the case of alumina, silica-alumina, 10 × molecular sieve and thoria catalysts. All the catalysts were characterised with respect to their specific surface area, surface acidity, pore size distribution and pore volume. The above properties were found to reflect the textural changes that might have been undergone by the catalyst surface as a result of the method of preparation and pretreatment. The method of preparation was found to influence markedly the acidity of the surface and to a lesser extent the surface area and pore size distribution. Acid-treatment was found to increase selectively the acidity of the catalyst while heat-treatment was found to decrease proportionally the acidity as well as surface area of the catalyst.

Influence of surface chemistry of mesoporous alumina with wide pore distribution on controlled drug release

The crucial role of the drug carrier surface chemical moeities on the uptake and in vitro release of drug is discussed here in a systematic manner. Mesoporous alumina with a wide pore size distribution (2-7 nm) functionalized with various hydrophilic and hydrophobic surface chemical groups was employed as the carrier for delivery of the model drug ibuprofen. Surface functionalization with hydrophobic groups resulted in low degree of drug loading (approximately 20%) and fast rate of release (85% over a period of 5 h) whereas hydrophilic groups resulted in a significantly higher drug payloads (21%-45%) and slower rate of release (12%-40% over a period of 5 h). Depending on the chemical moiety, the diffusion controlled (proportional to time(-0.5)) drug release was additionally observed to be dependent on the mode of arrangement of the functional groups on the alumina surface as well as on the pore characteristics of the matrix. For all mesoporous alumina systems the drug dosages were far lower than the maximum recommended therapeutic dosages (MRTD) for oral delivery. We envisage that the present study would aid in the design of delivery systems capable of sustained release of multiple drugs.

Abatement of fluoride from water using manganese dioxide-coated activated alumina

Batch adsorption of fluoride onto manganese dioxide-coated activated alumina (MCAA) has been studied. Adsorption experiments were carried out at various pH (3–9), time interval (0–6 h), adsorbent dose (1–16 g/l), initial fluoride concentration (1–25 mg/l) and in the presence of different anions. Adsorption isotherms have been modeled using Freundlich, Langmuir and Dubinin–Raduskevich isotherms and adsorption followed Langmuir isotherm model. Kinetic studies revealed that the adsorption followed second-order rate kinetics. MCAA could remove fluoride effectively (up to 0.2 mg/l) at pH 7 in 3 h with 8 g/l adsorbent dose when 10 mg/l of fluoride was present in 50 ml of water. In the presence of other anions, the adsorption of fluoride was retared. The mechanism of fluoride uptake by MCAA is due to physical adsorption as well as through intraparticle diffusion which was confirmed by kinetics, Dubinin–Raduskevich isotherm, zeta-potential measurements and mapping studies of energy-dispersive analysis of X-ray.

Enhanced adsorption capacity of activated alumina by impregnation with alum for removal of As(V) from water

Alum-impregnated activated alumina (AIAA) was investigated in the present work as an adsorbent for the removal of As(V) from water by batch mode. Adsorption study at different pH values shows that the efficiency of AIAA is much higher than as such activated alumina and is suitable for treatment of drinking water. The adsorption isotherm experiments indicated that the uptake of As(V) increased with increasing As(V) concentration from 1 to 25 mg/l and followed Langmuir-type adsorption isotherm. Speciation diagram shows that in the pH range of 2.8–11.5, arsenate predominantly exists as H2AsO4− and HAsO42− species and hence it is presumed that these are the major species being adsorbed on the surface of AIAA. Intraparticle diffusion and kinetic studies revealed that adsorption of As(V) was due to physical adsorption as well as through intraparticle diffusion. Effect of interfering ions revealed that As(V) sorption is strongly influenced by the presence of phosphate ion. The presence of arsenic on AIAA is depicted from zeta potential measurement, scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) mapping study. Alum-impregnated activated alumina successfully removed As(V) to below 40 ppb (within the permissible limit set by WHO) from water, when the initial concentration of As(V) is 10 mg/l.