Preparation of Alumina Membrane Filters with Framework Structures by Al Anodization

Abstract

Alumina membrane filters consisting of a thin filter layer (200−700 nm in thickness) supported by a framework (30−100 μm in thickness) were fabricated on the basis of the anodization of an Al substrate. The solution permeability of alumina membrane filters with tubular pores of uniform size and shape varies with membrane thickness; therefore, membrane filters with a filter layer thickness of less than 1 μm showed high solution permeability. Although the filter layer is thin, it is reinforced by a thick framework, enabling the fabrication of large freestanding membrane filters (2.5 × 2 cm 2 in size). The pore size of the anodic porous alumina formed by the anodization of Al can be controlled in the range from 10 nm to ca. 2 μm by varying the preparation conditions. The alumina membrane obtained by this method is therefore useful as a membrane filter that can efficiently separate particles of various sizes, including microplastics, viruses, and bacteria. This method enables the fabrication of membrane filters with uniform pore size, high solution permeability, and sufficient mechanical strength for handling as freestanding membranes, which have been difficult to achieve with the reported preparation processes for membrane filters. The obtained membrane filters with frameworks can be applied to efficient microfiltration.

Highly Permeable Alumina Membrane with Mechanical Durability

“…We believe that further improvement of the pore size uniformity by improving the conditions of anodization and ALD will enable the reduction in error. In our previous study, alumina membranes with frameworks were found to have a higher permeability than commercial membrane filters with similar pore sizes . The permeation properties of the alumina membranes obtained by this process depend on the structure of the framework and the thickness of the thin filter layer; thus, further improvement of permeation properties is expected to be possible even when the pore size is reduced to a single nanometer by optimizing these structures.…”

“…It is necessary to resolve this incompatibility to expand the range of applications of alumina membranes. In our recent study, we developed a novel fabrication method for highly permeable and durable alumina membranes . Alumina membranes consisting of a thick framework layer that functions as a support film and a thin filter layer that functions as a filtration film were fabricated by the combination of the anodization and selective etching of the anodic oxide layer using a resist mask.…”