High-Flux Ceramic Membranes with a Nanomesh of Metal Oxide Nanofibers

Abstract

Traditional ceramic separation membranes, which are fabricated by applying colloidal suspensions of metal hydroxides to porous supports, tend to suffer from pinholes and cracks that seriously affect their quality. Other intrinsic problems for these membranes include dramatic losses of flux when the pore sizes are reduced to enhance selectivity and dead-end pores that make no contribution to filtration. In this work, we propose a new strategy for addressing these problems by constructing a hierarchically structured separation layer on a porous substrate using large titanate nanofibers and smaller boehmite nanofibers. The nanofibers are able to divide large voids into smaller ones without forming dead-end pores and with the minimum reduction of the total void volume. The separation layer of nanofibers has a porosity of over 70% of its volume, whereas the separation layer in conventional ceramic membranes has a porosity below 36% and inevitably includes dead-end pores that make no contribution to the flux. This radical change in membrane texture greatly enhances membrane performance. The resulting membranes were able to filter out 95.3% of 60-nm particles from a 0.01 wt % latex while maintaining a relatively high flux of between 800 and 1000 L/m2.h, under a low driving pressure (20 kPa). Such flow rates are orders of magnitude greater than those of conventional membranes with equal selectivity. Moreover, the flux was stable at approximately 800 L/m2.h with a selectivity of more than 95%, even after six repeated runs of filtration and calcination. Use of different supports, either porous glass or porous alumina, had no substantial effect on the performance of the membranes; thus, it is possible to construct the membranes from a variety of supports without compromising functionality. The Darcy equation satisfactorily describes the correlation between the filtration flux and the structural parameters of the new membranes. The assembly of nanofiber meshes to combine high flux with excellent selectivity is an exciting new direction in membrane fabrication.

High‐Performance Multifunctional TiO2 Nanowire Ultrafiltration Membrane with a Hierarchical Layer Structure for Water Treatment

“…The resulting membrane has a pore size of 60 nm and consists of a titanate fiber intermediate layer and alumina fiber separation layer. [2,19] Their study clearly showed that the fiber separation layer offers high flux with excellent selectivity. Among the materials used for the preparation of ceramic membranes, titanium dioxide (TiO 2 ) is unique due to its excellent performance under UV irradiation on mineralization of a variety of organic compounds.…”

Electrospinning of ceramic nanofibers: Fabrication, assembly and applications

“…Taking advantages of the highly porous fibrous nanostructures, ceramic nanofiber membrane can be used for filter and separator applications [128,[156][157][158][159]. separation layer on a porous substrate using large titanate nanofibers and smaller boehmite nanofibers [157].…”

“…separation layer on a porous substrate using large titanate nanofibers and smaller boehmite nanofibers [157]. Traditional ceramic separation membranes, which are fabricated by applying colloidal suspensions of metal hydroxides to porous supports, tend to suffer from pinholes and cracks that seriously affect their quality.…”

Direct growth of hierarchically structured titanate nanotube filtration membrane for removal of waterborne pathogens

“…Despite these varieties, all TiO 2 membranes share a common asymmetric structural feature-a TiO 2 dense layer (responsible for selectivity) forms on the top of a porous membrane substrate (i.e., porous stainless steel, alumina or silica, responsible for providing mechanical and other supports) [5,12,14,15,17]. In order to obtain defect-free, crack-free and uniform TiO 2 selective layer, most of reported fabrication methods adopted tedious and costly multiple-coating strategies [3,17,18]. A common problem associated with current fabrication methods is the blockage of the pores of the porous membrane substrate, which can lead to a dramatic reduction in flux [3,5].…”

“…To solve the problem, intermediate layers must be formed with larger size TiO 2 precursor particles before the desirable size TiO 2 particle can be coated [3,5]. Though these measures have significantly reduced the blockage problem, the flux of the resultant membranes is low, attributing to the inherent disadvantages of random particle packing and the multi-intermediate layer structures [17,18]. Introducing the intermediate layers unavoidably increases thickness, leading to a decrease in flux.…”