Controllable nanonet assembly utilizing a pressure-difference method based on anodic aluminum oxide templates.

  • Zhixun Luo, Yuanyuan Liu, +5 authors Boon Hian Loo
  • Published 2008 in Angewandte Chemie

Abstract

Self-assembly of organic molecules from solution is one of the simplest methods to generate ordered nanostructures with potentially new properties. In particular, nanostructured architectures on the macroscopic scale have possible applications in the fields of electronics, catalysis, and medicine. However, controllable fabrication of nanostructured materials is still limited by the available processing methods. Template synthesis has been widely used as a controllable approach to achieve desirable nanostructured materials. Of the many different types of templates, anodic aluminum oxide (AAO) offers clear advantages in the making of onedimensional nanostructured materials and arrays; the AAO templates provide hexagonally packed, uniform pore arrays with a pore diameter that can be varied up to 200 nm. Amongst other applications, AAO has been used as a template for the syntheses of nanotubes for biomedicine and biotechnology, Bi1 xSbx nanowires as thermoelectric wires, SBA-15 nanorod arrays for protein separation and catalysis, and lipid nanotube arrays as a model of cellular membranes. Despite such progress, there have been few reports on the application of AAO as a substrate for the control of surface morphology on the macroscopic scale. Herein, we report for the first time the synthesis of the largearea (ca. 12 cm) nanonet architecture of 5,10,15,20-tetrakis(p-chlorophenyl)porphyrin (TClPP; C44H26Cl4N4) using the AAO template as a substrate. Figure 1 shows the 3D structure of the TClPP molecule and its stacking. Alkylated polycyclic discotic molecules, such as porphyrins, are frequently employed as building blocks because of their ability to stack and form architectures and liquidcrystalline phases. We were able to use the stacking property of TClPP to successfully cultivate nanonet network architectures on the AAO templates. The TClPP nanonets were fabricated as follows. A 2-cm-diameter AAO disk about 15 mm in thickness was laid on a Buchner funnel fitted with a fritted disk. The funnel was then placed on a filter flask connected to a vacuum pump, which was used to maintain a pressure differential across the AAO disk. A solution of TClPP (1 mL, 0.13m) in CH2Cl2 was added dropwise to the AAO template. TClPP nanonets of different meshes in accordance with the AAO pore sizes were thus grown on the rear of the AAO template, that is, the side opposite to that of TClPP deposition. This process was repeated several times to obtain nanoparticles of larger size. Experimental parameters, such as the pressure differential, concentration of the TClPP solution, and the number of times of solution deposition, affected the type and the quality of the nanostructures formed, which will be discussed below. The morphology and size of the nanostructures were examined by field-emission scanning electron microscopy (SEM; Hitachi S-4300). Figures 2a and b show the SEM images of the TClPP nanonet structures formed on the AAO templates. It is evident that the nanonet structures were created as a result of uniform self-assembly of interlocking TClPP nanoparticles. The SEM images also suggest that the knots of the nanonets were formed by a single larger nanoparticle or by several assembled nanoparticles. In Figure 2a, the inner pores of the AAO substrate can be seen behind the floating nanonet. An advantage of this synthesis method was that the fabricated nanonet structure could be easily removed from the AAO substrate. Figure 2b shows the SEM image of a nanonet after it was removed from the substrate. The weblike nanonets showed ordered network structures with meshes mimicking the pore sizes of the AAO templates. Apparently the orderly pores of the AAO template aided the formation of the periodic pattern of the nanonets on the back surface of the template. Three different pore sizes (50, 100, and 200 nm) of the AAO templates were tried in the making of nanonets. A small Figure 1. 3D structure of the TClPP molecule (left) and its stacking (right).

DOI: 10.1002/anie.200802788

Cite this paper

@article{Luo2008ControllableNA, title={Controllable nanonet assembly utilizing a pressure-difference method based on anodic aluminum oxide templates.}, author={Zhixun Luo and Yuanyuan Liu and Longtian Kang and Yaobing Wang and Hongbing Fu and Ying Ma and Jiannian Yao and Boon Hian Loo}, journal={Angewandte Chemie}, year={2008}, volume={47 46}, pages={8905-8} }