Pore Size Of Nanotubes Research Articles

Cost-effective technique to fabricate a tubular through-hole anodic aluminum oxide membrane using one-step anodization

In order to reduce the time required to prepare a tubular through-hole anodic aluminum oxide (AAO) membrane, this study improved the manufacturing processes using one-step anodization. AAO membranes were first prepared by using 6063 commercial aluminum alloy tubes using an external anodizing method. The manufacturing processes for a tubular through-hole AAO membrane include: annealing, physically wet grinding, buff wheel polishing, ultrasonic cleaning, one-step anodizing, aluminum substrate removing, and barrier layer alumina (BLA) etching. The influence of chemical etching time on the nanostructure of AAO membranes was observed by a Field Emission Scanning Electron Microscope (FE-SEM). The results of the fabrication of a tubular through-hole AAO membrane showed that increasing the chemical etching time of the BLA etching process could result in an enhanced nanotube pore size and a reduced AAO membrane thickness, and excessive chemical etching time would collapse the nanotube structure. The tubular through-hole AAO membrane obtained was straight nanotubes with a thickness of 48 μm and an average bottom pore size of 109 nm.

Carbon nanotube-supported Cu-based catalysts for oxidative carbonylation of methanol to methyl carbonate: effect of nanotube pore size

The inner diameter of CNTs significantly affected the location, dispersion, autoreduction and stability of Cu species and thus the catalytic activity and stability for oxidative carbonylation of methanol to dimethyl carbonate.

TiO2 Nanofoam–Nanotube Array for Surface-Enhanced Raman Scattering

By tuning the anodic voltage and electrochemical reaction time, we have synthesized a series of TiO2 nanofoam–nanotube array structures via a two-step anodic oxidation process. The produced nanofoam–nanotube array demonstrated a remarkable Raman scattering enhancement. The maximum enhancement factors are 2.3 × 105 for methylene blue. Factors such as the nanotube pore size, nanofoam, and solute concentration have been investigated. The Raman scattering enhancement is attributed to the existence of the nanofoam structure, which enables multiple laser scatterings among the periodic voids and allows for the occurrence of Raman scattering. The proposed simple and inexpensive approach can promote the use of TiO2 materials for surface-enhanced Raman scattering applications in chemistry, biology, and nanoscience.

Negative effect of nanoconfinement on water transport across nanotube membranes.

Nanoconfinement environments are commonly considered advantageous for ultrafast water flow across nanotube membranes. This study illustrates that nanoconfinement has a negative effect on water transport across nanotube membranes based on molecular dynamics simulations. Although water viscosity and the friction coefficient evidently decrease because of nanoconfinement, water molecular flux and flow velocity across carbon nanotubes decrease sharply with the pore size of nanotubes. The enhancement of water flow across nanotubes induced by the decreased friction coefficient and water viscosity is markedly less prominent than the negative effect induced by the increased flow barrier as the nanotube size decreases. The decrease in water flow velocity with the pore size of nanotubes indicates that nanoconfinement is not essential for the ultrafast flow phenomenon. In addition, the relationship between flow velocity and water viscosity at different temperatures is investigated at different temperatures. The results indicate that flow velocity is inversely proportional to viscosity for nanotubes with a pore diameter above 1 nm, thereby indicating that viscosity is still an effective parameter for describing the effect of temperature on the fluid transport at the nanoscale.

Titania nanotube porosity controls dissolution rate of sputter deposited calcium phosphate (CaP) thin film coatings

Calcium phosphate (CaP) coatings are of continuing significant interest due to their ability to directly promote bone cell differentiation. Whereas sputter deposited CaP coatings have much to offer in this regard, in the as-deposited state they are inherently amorphous and readily undergo rapid dissolution. This behaviour severely limits their ability to support bone cell adhesion and the subsequent events of proliferation and/or differentiation without subsequent processing such as thermal annealing. Removal of the need for this additional processing step would significantly increase their utility. This paper reports a study of the use of nano-porous titania substrates to directly control the rate of dissolution of thin amorphous as-deposited CaP sputter coatings. Titania nanotubes with different pore sizes were prepared by electrochemical anodization of titanium foils and sputter coated with CaP. Dissolution studies were performed on the as-deposited CaP layers in cell culture media for periods of up to 21 days. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the potential of the nanotubes to prolong the rate of loss of CaP over the entire 21 day period as compared to coatings prepared on flat polished titanium surfaces, which dissolved completely in less than 48 h. The CaP coated titania nanotube surfaces showed high levels of osteoblast attachment and proliferation with no signs of cell death. Alkaline phosphatase (ALP) activity measurements at 21 days indicated that the highest levels of osteoblast differentiation occurred on CaP thin films deposited onto titania nanotubes with an average pore size of 30 ± 7.5 nm and tube length of 1.3 ± 0.2 μm. These results indicate that prolonged availability of the as-deposited sputtered CaP can be provided for by use of a substrate surface comprising titania nanotubes. Moreover, nanotube pore size and tube length affect the rate of CaP dissolution and attendant cell behaviour thereon.

Extreme Changes in the Electrical Resistance of Titania Nanotubes with Hydrogen Exposure

Extremely sensitive, drift‐free, and robust hydrogen sensors based on titania nanotube arrays (see Figure) are reported. Very large changes in the electrical conductivity of the nanotubes upon exposure to hydrogen gas have been measured, over one order of magnitude greater than the previous record. Dependence of the electrical conductivity on both temperature and nanotube pore size is found.

Structure and phase stability of novel ‘twisted’ crystal structures in carbon nanotubes

The stability of novel, low dimensional, crystal structures formed by a simple alkali halide (KI) in single-walled carbon nanotubes are investigated using a simple computer simulation model. ‘Twisted’ crystals, not clearly related to the bulk structure, and found to form dynamically in specific tube diameters, are investigated. A phase diagram for the confined structures as a function of the nanotube pore size is calculated. Specific ranges of nanotube diameters are shown to favour these unique structures over structures related directly to those adopted by the bulk alkali halide. The high resolution transmission electron microscopy pattern for an example stable twisted crystal is simulated.