Anodic aluminum oxide (AAO) membranes use chromic acid, sulfuric acid, oxalic acid & phosphoric acid for their formation. Porous and non-porous membranes are used for hydrogen separation and purification.
Anodic alumina membranes have 2 major categories:
Porous alumina anodic membrane (PAA)
Non-Porous alumina anodic membrane
Porous alumina anodic (PAA) membrane is ordered in parallel columnar way with hexagonal cells and its structure similar to novel pore structure and its various small pores embedded in each big shallow pore on the top layer of membrane and one pore in one cell at their bottom.
Membrane cells are arranged in periodic arrangement from both sides. To create novel pore structure PAA membranes uses different current densities (30200 mA cm−2) and it is obtained by maintaining constant voltage (40V. PAA membranes can be controlled with the adjustment of anodization voltage and current density simultaneously.
Anodized alumina membrane types:
1- AAO on Aluminum
2- Single Pass and double pass AAO
3- AAO Filter
4- Isotropic AAO
Their Advantages are as follows:
Growth and micro colony imaging of microorganisms on AAO
Physical detection technologies
Replacement of e-beam lithography
PAA Membrane has uniform nanostructure, due to its nanostructure it uses in nanotechnology, now a days porous anodized alumina membranes became widely recognized and it is very popular platform for researchers for designing and synthesis of high density arrays of nanostructures and functional nanocomposites.
PAA membranes have a broad range of applications, from nanoelectronics to photonics and energy conversion to nanoporous substrates and in bioanalysis. Researchers basically focused on use of AAO in nanotechnology, and its continuously growing rapidly and researchers are continuously working on fabrication costs and now days its reduced around 500 times. AAO templates are majorly used for fabrication of Ag, Au, and Sn nanowire arrays.
Membrane properties are dependent on:
Uniform distribution of PAA chains in the network,
Rate of immobilization of PAA,
Morphology of the membrane.
PAA membranes are good for ultra filtration of different heavy metal solutions and dye molecules. PAA membrane is a hydrophilic polymer that can be able to develop strong interactions with water.
Despite of all advantages it has some drawbacks also; chemical and physical instability and slight toxicity of these porous anodized alumina membranes have limited applications in biomedical devices.
Some of the main applications of these membranes are:
Templates for fabrication
Removal of bacteria from medical preparations
Solutions is used to test samples for liquid chromatography
Counting and cell identification
Biosorting and filtering biomolecules
Finding targeted molecules, such as DNAs, proteins or even cancer cells.
Researchers are continuously working on these areas for advancements like more sensible devices & accurate measurements and many more.