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Published on the web March 31, 2010
Heterogeneous Inorganic Acid/Organic Acid-salt Reaction
inside Anodic Aluminum Oxide Templates
Rabih O. Al-Kaysi
Department of Basic Sciences, College of Medicine (3124),
King Saud Bin Abdulaziz University for Health Sciences, Riyadh 11423, Saudi Arabia
(
Received February 23, 2010; CL-100175; E-mail: kaysir@ksau-hs.edu.sa)
Reaction of gaseous HCl with Eosin-Y disodium salt
Eosin-Y¢2Na) nanorods nested inside anodic aluminum oxide
(
templates (AAO), produced perforated Eosin-Y free acid (Eosin-
Y-FA) nanorods with surface nanoholes on the order of 50 nm in
diameter. Diffusion of different acids yielded different surface
patterns with retention of the overall nanorod structure. Also,
different pattern formation was observed for different templated
organic acid salts/inorganic acid interactions.
Figure 2. Normalized spectra of Eosin-Y¢2Na (solid line) and
Eosin-Y-FA (dotted line) in methanol.
We have shown that it is possible for one reactant 1,2,4,5-
tetracyanobenzene (TCNB) to diffuse inside AAO-templated 9-
methylanthracene (9-MA) nanorods to produce highly crystal-
line 1:1 cocrystals (TCNB/9-MA) with retention of nanorod
under an SEM to reveal the presence of solid EosinY¢2Na
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morphology. But, can we move beyond the solid nanorod
clogging the AAO nanopores (Figure S1a). Gravimetric analy-
morphology and design nanorods with nanopatterns on the
surface via heterogeneous diffusion? Formation of hole patterns
sis of the loaded AAO template suggested full packing of the
nanopores.
2
on 200-nm diameter polymer nanotubes was previously ob-
When templated Eosin-Y¢2Na nanorods were suspended in
an atmosphere of dry HCl gas, the acid slowly diffused inside
the 55-¯m thick template, from either end, converting the Eosin-
Y¢2Na to Eosin-Y-FA and NaCl. UVvis absorption spectra
of the material inside the template, in an appropriate solvent,
confirmed the complete conversion of the Eosin-Y¢2Na to
Eosin-Y-FA as shown in Figure 2.
served when PMMA nanotubes embedded inside AAO tem-
3
plates were heated above their T . A similar pseudo hole pattern
g
formation was observed on inorganic silica nanotubes prepared
4
by passing tetraethoxysilane sol through an AAO template. This
hole pattern formation contributed to Rayleigh instability inside
the alumina nanopores. Hole patterns were also individually
5
drilled on a single pentacene nanotube using FIB lithography.
FTIR spectra of the before and after are shown in
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0
An interesting hole pattern formation was observed when
AAO-templated nanorods of the organic salt compound Eosin-
Y¢2Na were allowed to react with HCl gas via a heterogeneous
reaction (gas/solid reaction).6 Strong acids such as HCl react
with the Eosin-Y¢2Na to protonate the oxide anion and yield
Eosin-Y free acid (Eosin-Y-FA) and an inorganic ionic salt
NaCl. The type of ionic salt produced depends on the inorganic
acid/organic-salt reaction (Figure 1).
Figure S1b. The conversion was monitored gravimetrically
showing the absorption of two equivalents of HCl («4%) per
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0
one equivalent of EosinY¢2Na (Supporting Information 1).
,7
The polished surface of the Eosin-Y¢2Na-loaded template was
observed under an SEM to reveal the formation of nanometer
sized crystals of NaCl. Formation of NaCl crystals was similar
to those formed on the surface of microcrystals of Eosin-Y¢2Na
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0
after a brief exposure to HCl gas (Figure S2). Washing the
surface of the HCl-exposed Eosin-Y¢2Na microcrystals with
water resulted in a pitted surface with nanoholes replacing the
Eosin-Y¢2Na nanorods were grown inside AAO templates
8
with 200-nm pore diameter using solvent annealing. It was
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0
previously shown that solvent-annealing organic compounds
inside AAO templates yields crystalline molecular crystal
dissolved NaCl crystals (Figure S3). When the HCl-treated
AAO template was dissolved with 50% H3PO4, Eosin-Y-FA
nanorods were liberated. Upon closer inspection, the surface of
these nanords was perforated with random sized elliptical holes
on the order of 5070 nm in diameter, as shown in Figure 3b
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nanorods. After solvent annealing, cubic crystals of EosinY¢
2Na formed on the surface of the template. The surface crystals
were polished off using fine sand paper (Supporting Information
1
0
10
1
). A sample of the polished template was crushed and viewed
(Figures S4aS4e). These holes were not deep or wide enough
to cause the nanorod to fragment. Because the tips of the
liberated nanorods were semitubular (Figure 3c), it was thought
that the perforated nanorods were hollow along the whole
nanorod length (bamboo flute). Porosity of the Eosin-Y-FA
nanorods was tested by placing the water-washed template
containing Eosin-Y-FA nanorods on a glass frit funnel. Suction
was applied and water was added to the surface of the template.
Not a single drop of water passed through, thus proving that the
Eosin-Y-FA-perforated nanorods were not continuously hollow
Br
Br
Br
Br
X+
-O
O
O
HO
Br
O
OH
Br
2
HCl
+
2 XCl
Br
Br
COO- X+
O
O
+
+
+
X = Na , K , NH4
Figure 1. Chemical structure and general reaction of Eosin-Y¢2Na.
Chem. Lett. 2010, 39, 470471
© 2010 The Chemical Society of Japan