ABSTRACT
Harvesting osmotic energy through nanofluidic devices with diverse materials has received considerable attention in recent years. Often, a small testing area on a membrane was chosen to assess its power performance by calculating power density as output power per effective area. Since the choice of this testing area is arbitrary, and it is usually quite small, the result obtained can be too optimistic. There is a need to come up with a common standard so that the performance of a device/membrane can be assessed reasonably. In this study, we systematically investigate the power density as a function of testing area in nanoporous anodic-aluminum-oxide membranes. Through changing the aperture size of substrates, we clearly show that the obtained power density decreases drastically with increasing testing area. For instance, the power density acquired from the testing area of µm2-scale can be five orders of magnitude larger than that from the pristine membrane of cm2-scale. We also advance simulations by building a 3D model to simulate osmotic-driven ion transport in the multichannel system. The result of modeling agrees with our experimental observation that the power density decreases with increasing number of channels, and the ionic concentration profile reveals that the concentration polarization becomes serious as the number of channels increases. Our result highlights the importance of effective area on testing the power performance in nanofluidic devices.
ABSTRACT
Lead (Pb) nanowire arrays were fabricated with anodic aluminum oxide (AAO) templates of 30, 100 and 300 nm in pore diameters. Through vacuum injection molding process, Pb/AAO composite was obtained, and lead sulfide (PbS) could further be synthesized after exposing to sulfur gas. AAO templates with different pore sizes were fabricated by using pure aluminum in a two-step anodization. Three types of solutions, which are 10 vol% sulfuric acid, 3 wt% oxalic acid and 1 vol% phosphoric acid, were adopted to achieve AAO of various pore sizes. Different sulfurization temperatures and time spans were applied for studying on the formation mechanism of PbS. Finally, the morphology, composition, structure and elements distribution of the as-prepared Pb and PbS nanowires were confirmed through the use of scanning electron microscopy, energy dispersive x-ray spectroscopy, element-mapping, x-ray diffraction and transmission electron microscopy analysis. The results indicated that Pb nanowires were successfully obtained after applying vacuum injection molding process with 50 kgf cm-2hydraulic pressure, and PbS nano arrays can be formed by sulfurization at 500 °C for 5 h. Furthermore, an optical property, ultraviolet-visible (UV-Vis) absorption, was also measured. The measurement of the PbS nanowires showed that a significant quantum confinement effect made the energy gap produce a blue shift from 0.41 eV to 1.65 eV or 1.72 eV.
