Heidy Visbal, Chanel Ishizaki and Kozo Ishizaki
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1833-122X) Volume 6 December 2010
IntroductionExperimentalResults and Discussion DRIFT Spectral Characteristics Modified Surface Reaction Mechanism and Activation EnergyConclusionsAcknowledgmentReferencesContact Details
Surface modification of diamond powder (5-12 µm) was achieved using a
CO2 disssolution. The effects of the reaction temperature were
studied. The diamond surface was characterized by diffuse reflectance infrared
Fourier transform (DRIFT) spectroscopy. Four chemical structures; epoxy (),
aliphatic ether (-C-O-C-) as well as methyl (-CH3) and methyne (-CH)
bands were identified in the diamond surface after the treatment. The total
intensity of the bands increases proportionally by augmenting the treatment
temperature. An activation energy of 51.2 kJ mol-1 was obtained, that
is in the range of a chemisorption reaction energy. From the results it is
concluded that methyl formate (HCOOCH3) was chemisorbed on the
diamond surface to a carbon with two unsaturated valences.
Diamond Powder, Surface Modification, Chemisorption, CO2
Dissolution, Diffuse Reflectance Infrared Fourier Transform (DRIFT)
Several studies have been focused on diamond powder surface modification.
They can be classified into two main groups: modifications in vapor phase [1-7]
and in liquid phase [8-14]. Modifications in the liquid phase of diamond surface
are more suitable for industrial applications, because the common technology of
chemical engineering can be used. Another advantage is that organic substances
with organic functional groups can be chemisorbed on a diamond surface and new
organic-inorganic functional materials can be developed. Silane coupling
reagents , carboxylic acids  have been reported as precursors for
modifying diamond surface. In the previous paper it was shown that formaldehyde
solution  could modify diamond surface. By this treatment, methyl formate is
chemisorbed to diamond surface. However, even these chemical methods require
solvents or expensive chemicals to activate the reaction. By far, the most
common acid maker is simple carbon dioxide (CO2). When this
dissolves, it makes carbonic acid (H2CO3). It is well
known that carbon dioxide is soluble in pure water and its value of solubility
is less than 0.039 mol l-1 at 40°C. Once it has dissolved, a small
proportion of the CO2 reacts with water to form carbonic acid.
“Disolved carbon dioxide” consists mostly of the hydrated oxide CO2
(aq) together with a small amount of carbonic acid. Carbon dioxide is an
extremely abundant and inexpensive resource because it is a waste product of
many industries, such as in the production of limestone and cement, fermentation
of carbohydrates, and on a vast scale in fossil-burning power plants. It may be
also produced by concentrated solar energy, by calcinations of limestone at
800-900°C. Therefore if carbon dioxide alone can be use to modify surfaces
instead of expensive reactives, it will be a promising source for industrial
applications. According to our knowledge nobody has reported about modifying the
diamond surface using a carbonate water solution and its mechanism. In this
paper, the feasibility of modifying the surface of diamond powder by dissolution
of CO2 in water is reported. The diamond surface after treatment was
characterized by diffuse reflectance infrared Fourier transform (DRIFT)
spectroscopy. The reaction between the species formed in the dissolution of
CO2 in water and the diamond powder is also discussed. The treatment
was studied at several reaction temperatures.
Commercial available synthesized diamond powder of 5-12 µm grain size from
Matsumoto Yushi-seiyaku Co., Ltd. was used in this study. First, 27 ml of
distilled water was saturated with carbon dioxide (99.9% purity). Then, an
amount of 0.06 grams of diamond powder was put inside the flask containing the
saturated dissolution of CO2. To study the effects of the
temperature, the solution was heated in an oil bath with reflux at 60, 80 and
100°C for 3 h with continuous stirring. The temperature of the liquid inside the
flask was monitored each 20 min and was kept constant. After the treatment, the
solution was decanted and washed few times with distilled water and finally, the
powder was dried in an oven at 120°C for 20 h. The surface of the diamond was
characterized by DRIFT spectroscopy using a Shimadzu FT-IR 8300 spectrometer
equipped with a Spectra-Tech diffuse reflectance accessory, a triglycine sulfate
(TGS) detector and data processing software. Three samples were prepared for
each condition. DRIFT spectra of three different portions of the samples in the
range of 4000-400 cm-1 were obtained in dry air atmosphere with no
dilution. For each spectrum, 256 scans were accumulated at a resolution of 4
cm-1. Spectral processing such as baseline adjustment and smoothing
were performed using an OMNIC software package. The second derivative spectra
derived from the absorbance spectra were deconvoluted and the peaks quantified
using a Jandel peak separation and analysis software PeakFit™ 4.0 (AISN Software
Inc., USA) in log (1/R) units. Peak fitting was carried out until squared
correlation coefficients with r2 greater than 0.999 and best F
standard values were obtained.
Results and Discussion
DRIFT Spectral Characteristics
Diffuse reflectance DRIFT spectra of diamond modified by CO2 as a
function of reaction temperature is presented in fig. 1. This figure shows the
average spectra of raw diamond powder (RD), and the diamond after treatment. The
presented spectra are averaged spectra. In pure natural diamond, only two-phonon
(or second order) absorption process (the broad bands in the region 2300-2000
cm-1) are infrared-active, but the presence of impurities or defects
in the structure causes the forbidden single phonon modes to become infrared
active [15-16]. Therefore two bands in the region 2300-2000 cm-1 can
be observed in the spectrum of the diamond powder. Other small bands can be
observed in the region 1400 -1100 cm-1 due probably to impurities or
defects in the diamond . After the CO2 chemical treatment the
main differences observed in the spectra are the new bands that appear in the
ranges of 3000-2800 cm-1 and 1600-400 cm-1 (these are
superimposed to the defect bands observed in the raw diamond). The absorbance
intensity of these bands normalized by the intensity of the diamond band from
2250-2100 cm-1 for different reaction temperatures is shown in fig.
2. It can be observed that the total intensity of the bands increases by
augmenting the reaction temperature. Since the results show that the samples
prepared at 100°C shows the highest intensity, to study the effects of treatment
time, the reaction temperature was set at this temperature. Deconvolution of all
the spectra was performed and the identified peaks in both regions for a sample
treated at 100°C for 3 h are shown in fig.3. In fig. 3 (a), correspondent to the
C-H region, 4 peaks clearly defined around 2962, 2924, 2893 and 2855
cm-1 are observed. In the ?CH frequency region, the spectra are very
complex due to Fermi resonances between the ?CH fundamental and combinations or
overtones, and therefore these bands can be assigned to -CH stretching vibration
modes of methyl and or methyne [17-19]. Additionally, these bands have been
reported on adsorption of methyl formate on powders . In the region
1600-400cm-1 four main peaks can be observed as seen in fig. 3 (b).
The broad band from 1200 to 950 cm- 1 can be assigned to ether
stretching vibrations (? C-O-C) according to the literatures [3, 7, 10, 16-19].
Two other peaks located at 1260 and 810 cm-1 are observed. These two
bands can be assigned to asymmetric and symmetric vibration of epoxide ( )
[17-19, 21-25] respectively. Normally the strong band is due to asymmetrical
-C-O-C- stretching and the symmetrical stretching band is usually weak. However
the -C-O-C- group in a ring like epoxide and as the ring becomes smaller, the
asymmetrical -C-O-C- stretching vibration moves progressively to lower wave
numbers, whereas the symmetrical -C-O-C- stretching vibration moves to higher
wave numbers [21-22, 24]. Diamond has a very small lattice constant, so oxygen
bonded to it would also be highly strained and could exhibit this kind of
behavior . This can explain why the peak at 810 cm-1 has a higher
intensity than the band located at 1260 cm-1. An additional small
peak appears on the spectrum around 1400 cm-1. This peak can be
assigned to carbonate [26- 27].
Figure 1. Common scale DRIFT spectra of raw and
chemically modified diamond powder with CO2 dissolution for 3 h at
Figure 2. Normalized absorbance intensity of bands as a
function of reaction temperature by region, a) 3000-2800 cm-1, b)
1300-750 cm-1. The total intensity of the bands increases by
augmenting the reaction temperature.
Figure 3. Deconvolution of the spectrum obtained for a
diamond sample treated at 100°C for 3 h by region, a) 3000-2800 cm-1
b) 1300-750 cm-1
Based on the four chemical units obtained from the spectral results; epoxy
aliphatic ether (-C-O-C-), methyl (-CH3) and methyne (-CH), we
proposed that methyl formate: is
attached to one surface carbon with two unsaturated valences as follows:
where Cs represents diamond surface carbons.
Reaction Mechanism and Activation Energy
When carbon dioxide gas (CO2) dissolves in water (H2O),
its molecules often cling to water molecules in such a way that they form
carbonic acid molecules (H2CO3). Carbonic acid is a weak
acid, an acid in which most molecules are completely intact at any given moment.
But some of those molecules are dissociated and exist as two dissolved
fragments: a negatively charged HCO3- ion and a positively charged
H+ ion. The H+ ions are responsible for acidity—the higher
their concentration in a solution, the more acidic that solution is. For the
water dissociation reaction, it had been shown that the value of the free-energy
change, hence the electrochemical potential, decreases as the temperatures is
raised. The following reaction has been reported in photo catalysis of
CO2(g)+2 H2O →
HCOOH + ½ O2
CO2(g)+ H2O →
HCHO + O2
CO2(g)+ 2H2O →
CH3OH + 3/2O2
CO2(g)+ 2H2O →
CH4 + 2 O2
The electrochemical potentials of these reactions of CO2 are
affected by changes in temperature. The formation of methanol (CH3OH)
and formaldehyde (HCHO) is enhanced by temperature. If formaldehyde and methanol
are formed in the system, formaldehyde can be produced to methyl formate as
explain in previous paper . Therefore methyl formate could chemisorb to the
diamond surface as follows
This mechanism is in agreement with the spectral data. Figure 4 shows the ln
of the absorbance intensity of the 810 cm-1 epoxy band normalized by
the diamond peak area versus 1/T. The extent of the reaction is temperature
dependent. From Arrhenius equation we can calculate the activation energy, as
shown in Equation 1.
ln C = ln A - E/RT
where A is the pre exponential factor, E the activation energy, T the
absolute temperature, C the concentration of the reaction product and R the gas
constant. The activation energy of this process was calculated from the slope of
the graph shown in the fig. 4 in accordance with equation (1). The calculated
activation energy is 51.2 kJ mol-1. This value is in the range of
activation energy reported in the literature for chemisorption mechanisms
Figure 4. Ln normalized intensity of the 810
cm-1 epoxy band vs. 1/T. The activation energy is calculated from the
slope of this graph.
The experimental results show that it is possible to modify the surface of
diamond powder using a CO2 dissolution. Four chemical structures that
increase proportionally with reaction temperature and time could be identified
as follows; epoxy (),
aliphatic ether (-C-O-C-), methyne (-CH) and methyl (-CH3). From the
spectral results and the obtained value of activation energy for the reaction
(51.2 kJ mol-1), it is concluded that methyl formate
(HCOOCH3) chemisorbed to a diamond surface carbon with two
The authors are indebt to the Japanese government for financial support to
Heidy Visbal through the Monbukagakusho scholarship as well as the partial
support to the research through the 21st century Centers of
Excellence (COE) program of the Ministry of Education, Culture, Sports, Science
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KRI, Inc., Kyoto Research Park
134 Chudoji Minami
Machi, Shimogyo-ku, Kyoto, 600-8813, Japan
Nano-TEM Co., Ltd.
Shimogejo 1-485, Nagaoka,
Niigata, 940-0012, Japan
Nagaoka University of Technology
E-mail: [email protected]
This paper was also published in print form in "Advances in
Technology of Materials and Materials Processing", 11 (2009)