Great efforts are currently devoted to the studies on one-dimensional (1D) nanostructures due to a wealth of unique physical and chemical properties associated with the 1D structural confinement in nanoscale [1]. Due to their high thermal stability and chemical inertness, inorganic nanofibers including nanowires and nanotubes can be assembled into a free standing membrane (FSM) for important applications at high temperatures and in harsh environments [2]. To make the FSM robust, the inorganic nanofibers should be ultra-long and “woven” properly. Such inorganic FSMs could then possess unique porosity, permeability, thermal stability, chemical inertness, robustness, and catalytic properties, all of which would largely differentiate the nanofiber FSMs from the monodispersed nanofibers and the bulk phases of the same/similar chemical formula.
The fabrication of inorganic nanostructured FSM was demonstrated in 1996 on the growth of an oriented mesoporous silica film at the mica-water interface under the help of surfactant molecules [3]. Later, a different solution route to making a mesoporous FSM of anatase nanocrystallites has been developed [4]. Thereafter, fabrications of functional FSMs using 1D inorganic nanostructures have been discussed more often in literature. Recently, nanofibers of microporous manganese oxides have been cast into a paper-like FSM with a precisely controlled layer-by-layer alignment for the nanofibers [5]. Sheets of entangled V2O5 nanofibers were made to have the high Young's modulus, large actuator-generated stress, and significant actuator stroke at low applied voltage [6]. In addition, carbon nanotubes (CNT) have been used for fabricating functional FSMs. The buckypaper containing coaxial carbon nanotubes with improved mechanical property, thermal conductivity, and structural stability has been first reported [7]. Lately, strong, transparent, and multifunctional sheets of orthogonally organized CNTs were made with the gravimetric strength better than that of sheets of high-strength steel [8].
However, the abovementioned inorganic nanofiber FSMs may not be stable during a prolonged heating in air above 550° C. [5]. CNTs, on the other hand, may be fast oxidized in such a harsh calcination. Thus, the development of a thermal stable and chemically inert TiO2-based nanofiber FSM would be of great interest for advancing the existing technologies in high temperature catalysis, sensing, sorption and separation. Furthermore, large scale fabrication of robust, thermal-stable, and multifunctional macroscopic three-dimensional (3D) structures directly from the ID nanomaterials has remained as a challenge.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.