Carbon nanotubes-nanoporous anodic alumina composite membranes: influence of template on structural, chemical, and transport properties

Abstract

This work presents the synthesis of carbon nanotubes−nanoporous anodic alumina composite membranes (CNTs−NAAMs) with controllable geometric features by a template-assisted catalyst-free chemical vapor deposition (CVD) approach using a mixture of toluene and ethanol as a carbon precursor. NAAMs templates were prepared by anodization of aluminum substrates in different electrolytes containing sulfuric, oxalic, and phosphoric acids with the aim of establishing the template effect on the CNTs growth. The deposition time during the CVD process was systematically modified to determine the formation mechanism of CNTs inside the pores of NAAMs without using metal catalysts. The structural features, chemical composition, and graphitic structures of the resulting CNTs−NAAMs composites were characterized by different techniques to provide a comprehensive understanding of the effect of the template on the formation of these carbon-based nanostructures. CNTs−NAAMs with inner pore diameters ranging from 15 to 180 nm were used. Our results reveal that the electrolyte type used to prepare NAAMs and the deposition time during the CVD process have a direct impact on the structural, chemical, and graphitic structural features of CNTs−NAAMs. The molecular transport properties of CNTs−NAAMs composite membranes featuring different geometries and chemical compositions were evaluated via the diffusion process of Rose Bengal, a dye model molecule. The obtained results show that the diffusional flux of the dye molecules can be controlled by tuning the inner pore diameter of CNTs deposited inside NAAMs, and the smaller the diameter of the nanotubes the faster the transport of dye molecules is. Our results provide novel insights into the fabrication of different CNTs composite membranes, establishing for the first time the influence of three common types of NAAMs templates on the properties of the resulting CNTs composite membranes. Our study enables the precise engineering of advanced CNTs composite membranes with controlled physical and chemical properties suitable for specific applications.