Transcript Document

NIRT: Active Nanoparticles in Nanostructured Materials Enabling
Advances in Renewable Energy and Environmental Remediation
David A. Dixon, James L. Gole, Andrei Federov, Clemens Burda, Greg Szulczewski
Department of Chemistry, The University of Alabama, Departments of Physics & Mechanical Engineering, Georgia Institute of
Technology, Department of Chemistry, Case Western University
Evidence for High Spin Transition Metal Ion
Induced Infrared Spectral Enhancement
Efficient Room Temperature Conversion of Anatase
to Rutile TiO2 Induced by High Spin Ion Doping
Development of Porous-Silicon-based Active Microfilters
Developed first single step etch-liftoff procedure (one step separation)
based on the formation and removal of macroporous silicon (PS) layers.
With silicon wafers with resistivities in the range from 14 to 22 ohm-cm,
films with pore diameters ranging from one to two microns and thickness
ranging from 3 to 70 micrometers have been prepared. These siliconbased films (filters), which carry a polarizing negative charge, represent
an alternative to porous alumina (films) filters (pore diameter not yet in
the one to two micron range) in terms of their size range and their
potential interaction-reaction at elevated temperature. Pt and Cu can be
introduced to these filters using electroless solutions to create an
effective reductive surface. Using these and alternate material
combinations, interactive-reactive filters in the one micron size range
which operate at temperatures well in excess of porous polymer films can
be realized.
440
8000
608
TiO2-xNx Co(Cl) 0.05
TiO2-xNx Co(Cl) 0.025
TiO2-xNx Co(Cl) 0.0125
7000
Raman Intensity
6000
5000
4000
240
3000
The surprising room temperature phase conversion of anatase
to rutile TiO2, a process that normally requires temperatures
well in excess of 700 C, is facilitated through the use of
transition metal ions with highly unpaired electron spin. Raman
spectroscopy is used to demonstrate this unexpected process,
facilitated through the use of high spin cobalt (CoII ) and nickel
(NiII) transition metal ion seeding into a TiO2 or TiO2-xNx
nanocolloid lattice. In distinct contrast, the effect is not
manifest upon seeding with low spin ions including CuII. The
Raman spectra also demonstrate the concomitant incorporation
of a spinel-like structure into the titania lattice.
6x10
Mechanical Lift-off of PS filter using the
ability to readily remove the silicon
oxyfluoride polymer that forms on the PS
surface.
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-1000
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430
10000
“Development of Porous-Silicon-based Active Microfilters,” J.Campbell, J.A.
Corno, Ni.Larsen, and J.L. Gole, J. Electrochem . Soc. Accepted, Oct. 2007
650
700
244
Raman Intensity
Raman Intensity
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1000
1200
-1
Wavenumber (cm )
Property
g-tensor
Experiment
pH = 3
pH = 7.8
pH = 11
Calculated pH =3
7
12
Calculated pH = 7.8
24
30
Calculated pH = 11
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2.28
gzz
gxx
gyy
coupling constant
(Gauss)
Azz
Axx
Ayy
2.40
2.21
2.27
2.09
2.08
2.03
2.08
2.09
2.11
±129 ±9
±187 ±3
±197 ±10
±20
±37
±40
2.40
2.38
2.15
2.12
2.16
2.15
−197 107
-200 95
91
89
2.20
2.20
2.06
2.05
2.07
2.06
−204 14
-203 11
-2
22
2.28
2.25
2.06
2.08
2.10
2.08
-171 36
-192 40
106
41
2.18
2.04
2.01
1.98
2.06
2.13
2.13
2.04
2.09
1.98
7
2.43
2.89
2.06
2.28
1.98
2.01
2.01
12
2.44
2.13
“Experimental and Theoretical Studies of the Photoreduction of Copper(II)Dendrimer Complexes,” H. Wan, S. Li, T. A. Konovalova, S. Shuler, D. A.
Dixon, and S. C. Street, J. Phys. Chem., accepted, Oct. 2007
400
“Efficient Room Temperature Conversion of Anatase to Rutile TiO2
Induced by High Spin Ion Doping,” J.L. Gole, S. M. Prokes, M. G. White,
J. Phys. Chem. B, submitted
N
H2 N
1000
Raman spectra for a TiO2 nanocolloid (<10 nm) prepared with various
concentrations of CoII using a) CoCl2 and b) Co(NO3)2. Note that the Raman
signal was obtained using a 1 μm spot size and a power of 25 mW or less.
2.04
O
TiO2-(NO3) 0.025
TiO2-(NO3) 0.05
TiO2-(NO3) 0.2
688
Wavenumber (cm )
N
H
HRTEM images of Cu/G0-NH2
nanoparticles formed upon UV
irradiation at pH = 3.0 (top), pH = 7.8
(middle), and pH = 11.0 (bottom).
380
-1
2.02
NH2
606
100
200
2743 cm-1
1837
H
N
442
1000
H 2N
O
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Wavenumber(cm )
TiO2- .0125 Co
TiO2- .025 Co
TiO2- .05 Co
TiO2- 0.1 Co
with Co(Cl)2
606
240
O
H
N
500
Raman spectra of (a) untreated anatase TiO2 powder (Degussa P25) and (
b) anatase nitridized TiO2 nanocolloid powder. The dashed lines represent
the fit to the experimental data and the solid line corresponds to the data.
(Raman spectrometer extends to 200 cm-1)
NH 2
N
400
-1
Zero valent Cu polyamidoamine (PAMAM) dendrimer nanocomposites
were synthesized using UV irradiation starting from the aqueous
Cu(II)/dendrimer system. The size of the nanoparticles is strongly
dependent on the generation of the dendrimers and the pH of the solution.
Larger nanoparticles are obtained with higher generation dendrimers, as
well as in more basic solution. EPR spectra show that the sites bonded to
the Cu(II) ion are significantly different at different pH. Density functional
theory (DFT) calculations have been used to predict the structures and
EPR spectra of the Cu(II)-dendrimer complexes. At pH = 3, the hydrated
ion complexes Cu(H2O)62+ or Cu(H2O)52+ are present, as expected and
previously reported. At pH = 7.8, a chelating complex with two tertiary
amine sites with or without two amide oxygen sites is present. At pH = 11,
the Cu(II) ion binds to either the primary amine and amide oxygen sites on
a single branch, or to two tertiary amines and four amide oxygen sites on
all four branches. Our results show the importance of the amide sites in
Cu(II)-dendrimer complexes in neutral and basic solutions.
SEM micrographs of a porous silicon filter. In the top images, the tips
of the pores can be seen before (left) and after (right) they begin to
spread out in their face directions. The bottom images show the front
(left) and back (right) of a filter. Note that pore spreading is significant
in the filter back.
4
Wavenumber (cm )
Photoreduction of Copper(II)-Dendrimer Complexes
N
H
anatase
-1
“Evidence for High Spin Transition
Metal Ion Induced Infrared Spectral
Enhancement,” J. L. Gole, S. M.
Prokes, M. G. White, T.-H. Wang, R.
Craciun, and D. A. Dixon, J. Phys.
Chem., 2007, WEB ASAP, Oct
O
4
300
Raman spectra of TiO2-xNx nanocolloid for
various CoII concentrations, using CoCl2.
Laser power is less than 10 mW.
2595 cm-1
2115
4x10
3x10
Wavenumber
2317 cm-1
2769
4
TiOxN1-x
0
ν(N-H)
I (km/mol)
anatase
anatase
380
690
0
Direct Lift-off of PS-based filmfilter (~ 20 microns) from the
surface of an etched PS film.
Pore diameter is approximately
one micron.
TiOxN1-x
5x10
1000
Note enhancement between 2000 and 3000 cm-1.
4
nano TiO2
Fit to data
Raman Intensity
The seeding of the high spin transition metal ions Co (II) and Ni (II) into porous
nanoscale nitrogen doped titanium oxynitride, TiO2-xNx structures leads to a
significant enhancement of the infrared spectrum due to adventitious water and
minor contaminants associated with the oxynitride synthesis from a porous TiO2
nanocolloid sample. There are a number of contributions to the infrared
enhancement (1) the formation of protonated amines near the oxynitride
surface; (2) modification of the anatase ionic crystal dipole moment due to the
displacement of charged ions by the electric field associated with the high spin
Co (II) and Ni (II) ions; and (3) the incorporation of a spinel-like structure into the
TiO2 lattice as demonstrated by Raman spectra. The presence of partial proton
transfer from the amines to the surface can lead to enhanced intensities. The
higher the proton affinity of the amine, the less proton transfer occurs leading to
a higher N-H stretch frequency with less enhancement. A goal is to form
improved visible light absorbing oxynitride photocatalysts at the nanoscale.
Raman Intensity (Arb. Units)
Focus is the modification of interfaces with enhanced catalytic and sensing
capabilities. A key property of decorated and decorating nanostructures is that
they must undergo changes in their states in order to catalyze a chemical
reaction. Doped nanoparticles of TiO2 such as the oxynitride (TiO2xNx) can be
used to create improved photocatalytic absorbers in the visible part of the
spectrum. These nanoparticles can be doped with metal ions to change how
they interact with ligands including water molecules for potential photochemical
splitting of water. A combination of materials synthesis, advanced
characterization techniques, and computational chemistry are being used to
study active nanostructures.
NIRT: CTS-0608896
2.94
1.99
2.28
2.34
24
2.07
87.3
2.05 2.18
2.05
2.10
2.03
25
2.03
2.25
30
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