The document describes a method for manufacturing a multilayer anodized aluminum oxide nano-porous membrane. The method involves three steps - electro-polishing the aluminum substrate, performing a combination of hard and mild anodization using different electrolytes, and removing the barrier layer. This results in a three-layer membrane with the first layer having concave surfaces 300 nm in diameter, the second layer having 5 nm pores, and the third layer having 15 nm pores. The membrane fabrication techniques are discussed and compared for producing membranes suitable for applications like dialysis.
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1. Multilayer Anodized Aluminium
Oxide Nano-Porous Membrane &
Method of Manufacturing*
Presented By
A s s a d U r R e h m a n
E S - 1 7 1 7
I n s t r u c t o r
Ta h s e e n A m i n K h a n Q a s u r i a
F a c u l t y o f E n g i n e e r i n g S c i e n c e s ,
G I K I n s t i t u t e o f E n g i n e e r i n g S c i e n c e s & Te c h n o l o g y ,
T o p i , P a k i s t a n
*Pub. N0.: US 2014/0202952 A1
2. Pub. N0.: US 2014/0202952 A1
1. Nitin Afzulpurka𝑟 𝑎
2. Ajab Khan Kas𝑖 𝑎
(a) ASIAN INSTITUTE OF TECHNOLOGY, Klong Luang (TH)
*Pub. N0.: US 2014/0202952 A1
4. Introduction
• Anodic Aluminum Oxide (AAO) is a self-organized
material with honeycomb structure. The diameter of
the nanopores can be from 5 to several hundred
nanometers, and length can be few hundred
micrometers.
• AAO is prepared in three layers. First layer is at the
surface in the form of concave pits which has 100 µm
to 300 nm diameter and 100 nm in depth, in second
layer pore diameter 5 to 10 nm with about 200 nm
depth, and third layer is hexagonal order of pores of
desired diameter ranging from 15 to 80 nm which
penetrate to remaining thickness of the membrane.
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5. Motivation
• Membranes are used for selective filtration of
solutes e.g. dialysis, gas separation, virus
separation and water filtration etc.
• Permeability of membrane is of prime interest for
filtration purpose and is a function of pore
diameter and membrane thickness.
• The conventional nano-porous multilayer
membrane comprises of two layers.
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6. Motivation
• US Pat. No. 7,396,382 discloses porous
membrane for separation of carbon dioxide from a
fluid stream at a temperature higher than about
200° C. This suffers from the drawback of
complex process, scalability and mass production
issues.
• The US Patent Application number 2003/0047505
discloses a nano-porous tubular filter having
membrane comprising branched pores formed by
anodizing a section of metal tubing.
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7. Motivation
• The first layer of AAO stops the larger
components of blood, and allows water and
smaller components to reach second layer, while
the third layer due to its larger pore size help to
speed up hemodialysis.
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8. Objectives
• The main object of the invention is to provide a
• Method to manufacture a multi-layer nano-porous
membrane. Further object of the invention is to
provide a multi layer nano-porous membrane.
• Plurality of pores and corresponding channels per
concave surface of the membrane.
• Membrane to obviate problems associated with
sticking/staying of the larger diameter solute
components on the surface of the membrane.
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9. Objectives
• Control pore sizes of the membrane in each of the
layer to desired diameters in accordance with the
end use of such membrane.
• Multilayered membrane of three layers and a
method to manufacture thereof.
• Method of manufacturing a multi-layer membrane
to be used in dialysis and the membrane thereof.
• Enhance mechanical strength of the membrane.
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10. Objectives
• Multi-layered membrane for dialysis application
to enable selective stopping of blood cells,
selective filtration of undesired toxic substances
such as urea and creatinine from blood and
enhance flow rate and reduce resistance for flow.
• Multi-layered membrane for gas separation, virus
separation, water filtration and dialysis
applications.
*Pub. N0.: US 2014/0202952 A1
11. Objectives
• Judicious combination of anodization and
respective electrolytes to manufacture the said
multi-layer membrane.
• Multilayer membrane to enhance hemofiltration
and hemodialysis processes.
*Pub. N0.: US 2014/0202952 A1
12. Objectives
• Because the larger component of blood cannot
approach the second layer of membrane. The
smaller pores in second layer ensures that just the
toxin substances such as urea and creatinine
which are small in size can filter out from the
blood while there is very less possibility of
albumin to filter out from the blood.
*Pub. N0.: US 2014/0202952 A1
13. Preparation
• This method of preparing multilayer nano-porous
membrane comprises of three steps
1. Electro-polishing of the substrate.
2. Combination of hard and mild anodization.
3. Barrier layer removal.
*Pub. N0.: US 2014/0202952 A1
14. 1. Electro-Polishing of the substrate
• Electro-polishing of the Aluminium substrate (Al)
comprises of steps
1. Placing the Al in the mixture of perchloric acid
and ethanol wherein the ratio of respective
chemicals is in the range of 1:3 to 1:5 by volume
wherein purity of ethanol is in the range of 99%-
99.9% and that of Perchloric acid is in the range
of 69-72%.
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15. 1. Electro-Polishing of the substrate
2. Applying potential at a temperature less than 10°
C wherein the potential is in the range of 10 to
20 V.
3. Applying potential for 3 to 10 min depending on
the surface roughness.
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16. 2. (A) Hard Anodization
• Selecting electrolyte from either of oxalic acid,
phosphoric acid, sulfuric acid and malunic acid
wherein the concentration of acid depends on the
pore size.
• Gradual application of voltage from 20 V up to
60-200 V wherein process time depends on the
membrane thickness, it can range from 5 minutes
to 20 minutes.
*Pub. N0.: US 2014/0202952 A1
17. 2. (A) Hard Anodization
• Chemical etching of the anodized aluminum
oxide comprises steps of
• Etching in chromic acid and phosphoric acid
wherein the temperature is in the range of 65-800
C wherein phosphoric acid is in the range of 6 wt
% to 7 wt % and chromic acid is in the range of 2
wt % to 3 wt % wherein purity of Chromic acid is
99% and purity of phosphoric acid is 85%
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18. 2. (A) Hard Anodization
• Upon etching AAO, hexagonal arrangement of
concave surfaces appear on Al surface.
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19. Fig. 1
(a) and (b) illustrates
schematic of the concave
surface of the membrane.
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20. 2. (B) Mild Anodization
• Selecting electrolyte from either of oxalic acid,
phosphoric acid, sulfuric acid and malunic acid
wherein the concentration of acid depends on the
pore size.
• Applying a constant voltage directly to the final
value without gradually increasing it from 20 V as
is the case of hard anodization that is lower than
that in the first step anodization wherein the said
final voltage is in the range of 20 to 195 V
depending on the electrolyte and pore size.
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21. 3. Barrier Layer Removal
• Barrier layer is removed using voltage pulse
method comprises steps of
1. Etching the substrate in perchloric acid and
ethanol with volume ratio in the range of 1:3 to
1:5 respectively.
2. Applying a voltage pulse from 45 to 50 V for 3
to 5 seconds that causes to detach AAO from Al
and remove BL.
*Pub. N0.: US 2014/0202952 A1
22. Fig. 2
(a) and (b) depicts the
surface and cross sectional
SEM image of the
multilayer membrane of the
present invention.
*Pub. N0.: US 2014/0202952 A1
23. Two Step Hard Anodization
• The nano-porous mutli-layer membrane is
prepared. Electro-polishing and barrier layer
removal processes were carried out as described
above. The two steps of hard anodization
comprised steps of:
*Pub. N0.: US 2014/0202952 A1
24. (1) First Step Hard Anodization
• First step anodization is performed at a voltage
selected in the range of 120 to 130V in oxalic acid
as electrolyte for 5 to 10 min wherein etching is
carried out in chromic acid and phosphoric acid
wherein the temperature is in the range of 65-80°
C. wherein preferably 6wt % phosphoric acid and
chromic acid is 2wt %. wherein purity of Chromic
acid is 99% and purity of phosphoric acid is 85%.
*Pub. N0.: US 2014/0202952 A1
25. (1) First Step Hard Anodization
• Upon etching hexagonal arrangement of concave
surfaces appeared on Al surface wherein the depth
of this layer is about 100 nm.
*Pub. N0.: US 2014/0202952 A1
26. (2) Second Step Hard Anodization
• Second step hard anodization is performed at 100
to 110 V using same electrolyte as used in the first
step anodization wherein average diameter of
pore is 25 nm;
*Pub. N0.: US 2014/0202952 A1
27. Fig. 3
Provides SEM image of such a
nano-porous multi-layer
membrane manufactured using
two steps of hard anodization as
mentioned above. FIG. 3(a)
depicts the surface SEM image of
this membrane in which first and
second layer are clearly observed.
The depth of first layer is about
100 nm as shown in FIG. 3(b). In
FIG. 3(c) all three layers are
visible; the diagonal cut in third
layer clearly shows the hexagonal
arrangement of pores in this layer.
*Pub. N0.: US 2014/0202952 A1
28. Two Step Mild Anodization
• Mild anodization is used in both the steps,
however the electrolytes used are different in both
the steps. The first step mild anodization is
performed at 40 V in oxalic acid and second step
at 20V in sulfuric acid. Three layered membrane
is formed with first layer concave surface
diameter 100 nm, second layer pore diameter
about 5 nm and third layer pores diameter about
15 nm.
*Pub. N0.: US 2014/0202952 A1
29. Fig. 4
Depicts the SEM image of
the surface and cross
section of the multilayer
membrane manufactured
using mild anodization in
two steps but different
electrolytes in both the
steps.
*Pub. N0.: US 2014/0202952 A1
30. Summary
• Three layers AAO membrane can be produced
using three step method i.e. electro-polishing of
substrate, hard and mild anodization and barrier
layer removal.
• A multilayer anodized aluminium oxide nano-
porous membrane Wherein a three layered
membrane comprises of the first layer concave
surface of diameter 300 nm, second layer pore
diameter 5 nm and third layer pores diameter
about 15 nm.
*Pub. N0.: US 2014/0202952 A1
31. Summary
• The present invention relates to a method of
producing multilayer anodized aluminium oxide
nano-porous membrane.
• Different techniques has been discussed for AAO
preparation and compared.
*Pub. N0.: US 2014/0202952 A1
32. Acknowledgement
• I am highly thankful to Prof. Dr. Ajab Khan Kasi,
Baluchistan University, Quetta for permission to
present his work.
*Pub. N0.: US 2014/0202952 A1
