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Cite this: DOI: 10.1039/x0xx00000x
Data-centric optimization of vanadium dioxide
hydrothermal synthesis to control nanoparticle size
T. Moot a, J.F. Cahoon a, R. Lopezb and S. Mitranc ,
Received 00th January 2012,
Accepted 00th January 2012
Abstract text goes here. The abstract should be a single paragraph that summarises the
content of the article.
DOI: 10.1039/x0xx00000x
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Introduction
Vanadium dioxide (VO 2) is a thermochromic material that
exhibits a semiconductor to metal transition (SMT) from a
monoclinic, infrared transmitting VO2(M) phase to a rutile,
infrared reflecting VO2(R) phase at a critical temperature of
 c  68C . Additional metastable VO2(A/B) forms also coexist
at low temperatures. The thermochromic behavior has led to
interest in use of VO2 as a material to construct windows that
would modulate infrared (IR) transmission in accordance with
interior climate control needs 1,2. It has been shown that
tungsten doping3 can reduce the critical transition temperature
to typical interior ambient values of ~ 25C . The main
remaining impediments to practical application of VO 2 as
thermochromic window material 4 are low values for solar
energy modulation Tsol and luminous transmittance Tlum , i.e.,
ratios of transmitted to incoming range over the visible range
and total solar irradience spectrum, respectively. Single layers
of VO2 exhibit values5 of Tsol  10% and Tlum  50% , whereas
composites that combine nanoparticles6,7 of VO2 with a
dielectric polymer matrix improve thes values5 to Tsol  20%
and Tlum  60% . Such composite structures require synthesis of
nanoparticles of the thermochromic VO2(M) phase in a form
suitable for homogeneous mixing or patterned placement into
the polymer matrix.
Production of VO2(M) nanoparticles by hydrothermal
synthesis8,9, is a one-step, solution-based, low temperature
method that can be modulated by many parameters (Table 1) to
produce nanoparticles with various shapes and sizes, capable of
additional transmittance modulation through geometric effects
associated with plasmon resonances 10. Typical particles
produced by intrinsic nucleation exhibit columnar growth 8,9,
This journal is © The Royal Society of Chemistry 2013
while seeding the process with titanium dioxide nanoparticles
favors formation of quasi-spherical shells of VO 2 around the
seed, but still exhibiting large variations in grain morphology
(Fig.1). Experimental exploration of the parameter space in
order to control nanoparticle size and shape is not feasible due
to long reaction times and the complex observed dependence of
nanoparticle shape upon reaction parameters. It is therefore of
interest to guide an experimental program by mathematical
modeling of the synthesis process to establish regions of
interest in the parameter space.
Experiment 110
Experiment 111
Experiment 114
Experiment 116
Experiment 119
Experiment 131
Experiment 138
Experiment 171
Experiment 175
Fig. 1. Variety of VO2 nanoparticle shapes obtained by seeded
hydrothermal synthesis with various reaction parameters.
J. Name., 2013, 00, 1-3 | 1
ARTICLE
Experiments and methods
Materials
Vanadium Pentoxide (98+%), Oxalic Acid Dihydrate (99.5+%),
and Titanium Dioxide (aeroxide P25), and acetonitrile were
bought from Fisher Scientific and used without further
purification.
Synthesis
Varying amounts of vanadium pentoxide (0.0417 g – 0.1265 g),
oxalic acid dihydrate (0.0726 g – 1.9376 g), acetonitrile (0 g –
24.5532 g) and titanium dioxide (0 g – 0.0468 g) were added to
deionized water (14.108 g – 43.9753 g) totaling a solution
ranging from 37.9474 mL to 47.7108 mL and placed directly
into a 50 mL teflon-lined stainless steel sealed autoclave. The
autoclave was placed into a box furnace and heated to 210 C –
300 C for 3 to 84 hours then allowed to cool down to room
temperature before being opened. The precipitate was collected
by centrifuge and washed with nanopure water and ethanol and
typically dried at ~100 C for ~2 hours. The set of
hydrothermal synthesis parameters is listed in Table 1. Based
upon an empirical understanding of the influence of reaction
parameters upon nanoparticle size a series of 96 reactions were
carried out as specified in Table 2.
Journal Name
𝐹𝐴𝑑𝐻𝑜𝑐,𝑚𝑎𝑥 = 0.064. Log-normal distributions were used to
describe grain size, and parameter sensitivity was obtained by
correlation analysis (Table 1). Quadratic optimization of the
extracted PDFs furnished parameter values (amount of TiO 2
precursor ~0.03g, reaction time at high temperature of ~9h),
and predicted an estimated maximum value of 𝐹𝑚𝑎𝑥,𝑒𝑠𝑡 = 0.12.
We recently carried out the experiments with parameters
suggested by the mathematical model, and obtained an even
better performance figure of 𝐹𝑚𝑎𝑥,𝑒𝑠𝑡 = 0.27, a 422% increase
over 𝐹𝐴𝑑𝐻𝑜𝑐,𝑚𝑎𝑥 ..
Results and Discussion
B Headings should always be subordinate to A headings e.g.
Synthetic procedures, Materials and methods, Crystallography.
C headings should always be subordinate to B headings e.g.
General procedure for synthesis of compound X. The main
paragraph text follows directly on here.
The main text of the article should go here with headings as
appropriate.
Inserting Graphics
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(unless they are equations, which appear in the flow of the
text). They can be single column or double column as
appropriate.
Characterization
Powder X-ray diffraction (XRD) experiments were performed
on a Rigaku Multiflex from 20 to 60 2 at a scan rate of 2
2/min. Ratios of VO 2 (M): VO2 (B) were taken from the
relative peak heights at 27.8 2 and 25.5 2, respectively.
Scanning electron microscopy (SEM) images were obtained
using a Hitachi S-4700 Cold Cathode Field Emission Scanning
Electron Microscope with powder samples deposited on carbon
tape.
Energy dispersion spectroscopy (EDS) was taken with an
INCA PentaFET -x3 (Oxford instruments) attached to the SEM
and multiple values over a 5+ micron area were averaged.
Differential scanning calorimetry (DSC) was done on a TA
Instruments DSC Q200 with a liquid N2 cooling unit from 0C
to 100C at a scanning rate of 10C/min .
Table 3 lists the
Synthesis parameter optimization
Our goal was to maximize the objective function 𝐹(𝑝) =
𝑃𝑉𝑂2 (𝑀) (1 − 𝑟)3 , where 𝑃𝑉𝑂2 (𝑀) is the percentage of VO 2(M)
phase determined by XRD, 𝑝 is a vector of experimental
processing parameters, and 𝑟 = 𝑅𝑇𝑖𝑂2 /𝑅𝑔𝑟𝑎𝑖𝑛 is the ratio of the
TiO2 precursor grain size to that of the synthesized grain,
assuming a spherical shell model. The objective function
expresses the desire to obtain small grain sizes with high
VO2(M) content, and the highest value obtained in the ad hoc
experimental investigation of the parameter space was
2 | J. Name., 2012, 00, 1-3
Conclusions
The conclusions section should come at the end of article,
before the acknowledgements.
Acknowledgements
The acknowledgements come at the end of an article after the
conclusions and before the notes and references.
Notes and references
a
Department of Chemistry, University of North Carolina, Chapel Hill,
NC 27599-3290.
b
Department of Physics and Astronomy, University of North Carolina,
Chapel Hill, NC 27599-3255.
c
Department of Chemistry, University of North Carolina, Chapel Hill,
NC 27599-3250, Email: mitran@unc.edu.
† Footnotes should appear here. These might include comments
relevant to but not central to the matter under discussion, limited
experimental and spectral data, and crystallographic data.
This journal is © The Royal Society of Chemistry 2012
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Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
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