Papers by Keyword: Nanoporous Materials

Abstract: Nanoporous materials find widespread application in material upgrading by separation (“molecular sieving”) and catalytic conversion. Mass transfer in these materials is a key phenomenon deciding about their technological performance. This chapter deals with the application of measurement techniques which are able to follow the diffusive fluxes of the guest molecules in such materials over “microscopic” distances, including the pulsed field gradient (PFG) technique of Nuclear Magnetic Resonance (NMR) and the techniques of microimaging by interference microscopy (IFM) and by IR microscopy (IRM). Microscopic measurement is a prerequisite for attaining unbiased information about the elementary steps of mass transfer and about their role within the overall process of technological exploitation. We dedicate this treatise to the memory of our dear and highly esteemed colleague Nicolaas Augustinus Stolwijk, notably in recognition of his manifold activities in the field of diffusion, distinguished by their impressively high standard in connecting the message of various techniques of measurement and in combining them to comprehensive views on quite intricate subjects.

Abstract: Anodic aluminium oxide (AAO) is a well-known material for nanofabrication. To obtain highly ordered nanoporous array, there is anodization process. AAO were fabricated by anodization method utilizing high purity aluminium foil as the substrate. The substrate was degreased with ultrasonic cleaner for 15 minutes. Then the substrate was anodized in an electrolyte of 0.3 M oxalic acid with various potentials: 10, 20, 30, and 40 V and various durations: 10, 30, 60, 120, and 180 minutes at room temperature. Field emission scanning electron microscope (FE-SEM) was used to investigate surface morphology of nanoporous aluminium oxide film. The wettability of nanoporous aluminium oxide surface was estimated by measuring water contact angle (WCA) of water droplets on the nanoporous aluminium oxide surface. The FE-SEM images showed that the pore size was in the range of 12 - 81 nm. This result can indicated that nanopore size of AAO film increased with the increasing of anodization potentials and anodization time. The water contact angle of AAO samples were approximately 90.55 - 44.33 degrees. The result of measurement proved that super hydrophilic surface obtained with the increasing of nanopore size and high porosity of AAO.

Abstract: Anodic aluminum oxide (AAO) is well known for its nanoscopic structures and its applications in microfluidics, sensors and nanoelectronics. The pore density, the pore diameter, and the interpore distance of an AAO substrate can be controlled by varying anodization process conditions. In this research, the self-organized two-step anodization is carried out with a low-grade (Al6061) aluminium substrate using a 40V voltage at the temperature of 2 to 5 °C. Three experiments are done with the anodization time of 24 hours, 48 hours and 72 hours. The structural features of AAO are characterized by a field emission electron microscope (FE-SEM). The data from FE-SEM show that the average pore diameter increases with the anodization time, and that the Al6061 aluminium substrate can be used to fabricate a nanoporous AAO film with an average pore diameter smaller than 17 nanometers.

Abstract: We report on magnetization reversal and geometry dependent magnetic anisotropy of Ni nanowire arrays electrodeposited in nanoporous alumina templates. Using micromagnetic simulation we have found that magnetization reversal mechanism in arrays with different nanowire diameters is curling. This magnetic behavior appears with propagation of the domain wall along a nanowire. The calculations have been proven by the analysis of hysteresis curves. To explain magnetic properties of closely-spaced nanowire arrays we have taken into consideration the magnetostatic interaction between adjacent nanowires and their structural defects, like as boundary grains. The investigated magnetic domain pattern of individual bended nanowires confirms rather complicated magnetization reversal mechanism than either coherent rotation of magnetization or its curling. Competition between the shape and magnetoelastic anisotropies can induce an unusual zigzag-like domain pattern in a single nanowire.

Abstract: Chinese drug-loaded nanoporous materials were prepared from electrospinning Poly (butylenes succinate) (PBS) solutions with an additive of Chinese drug and a mixed solvent of chloroform and iso-propylalcohol in a single processing step. Characterizations of the samples, such as morphology, wettability and permeability, were studied by means of scanning electron microscope, full automatic micro droplet wettability measurement instrument and fabric air permeability performance tester. The results showed these characterizations could be controlled by adjusting electrospinning parameters such as flow rate and drug concentration. And the electrospun nanoporous materials might offer the potential for direct fabrication of biologically based and high-surface-area porous materials.

Abstract: A charged jet can be accelerated by an electrostatic field for fabrication of continuous micro/nanofibers. A higher voltage results in smaller nanofibers. However, when the voltage surpasses a threshold value, discontinuous nanomaterials can be fabricated.

Abstract: Guest diffusion in nanoporous materials reveals a wide spectrum of phenomena associated with random mass transfer in condensed matter quite in general. Taking advantage of their potentials for monitoring mass transfer over microscopic dimensions, micro-imaging (by interference microscopy and IR spectroscopy) and pulsed field gradient (PFG) NMR are exploited for providing typical examples highlighting these options. Starting with the surprise provided by the application of these microscopic measuring techniques to nanoporous materials, namely discrepancies of up to five orders of magnitude in comparison with the so far well-established data, the review covers some of the most impressive further results, including the determination of sticking coefficients on the surfaces of these materials and the specification and detection of conditions where molecular mass transfer is accelerated rather than hampered by counter fluxes.