Nitrogen-rich carbon nitride materials shock-synthesized from carbon tetrahalide and sodium dicyanoamide

Article abstract of DOI:10.1016/j.ssc.2006.07.021

Shock reactions between CX₄ (X=Br or I) and NaN(CN)₂ were investigated to prepare carbon nitrides. The post shock samples were characterized by the powder X-ray diffraction (XRD) technique. The XRD spectrum of the product showed a peak in the range of 0.324-0.336?nm in d-value corresponding to the (002) basal plane diffraction in graphitic structure. Elemental analysis (C, H, N, O) of the product showed that the atomic ratio of nitrogen to carbon (N/C) ranged from 0.38 to 1.3. Analysis of data revealed that the d-value increased and the nitrogen content decreased with the increase of the impact velocity.

Full text of DOI:10.1016/j.ssc.2006.07.021

Solid State Communications 139 (2006) 501–505
www.elsevier.com/locate/ssc
Nitrogen-rich carbon nitride materials shock-synthesized from carbon
tetrahalide and sodium dicyanoamide
Kazusato Shibata, Toshimori Sekine∗
Advanced Materials Laboratory, National Institute for Materials Science, Namiki, Tsukuba, Ibaraki 305-0044, Japan
Received 21 April 2005; received in revised form 20 July 2006; accepted 20 July 2006 by A. Pinczuk
Available online 4 August 2006
Abstract
Shock reactions between CX (X = Br or I) and NaN(CN) were investigated to prepare carbon nitrides. The post shock samples were
4
2
characterized by the powder X-ray diffraction (XRD) technique. The XRD spectrum of the product showed a peak in the range of 0.324–0.336 nm
in d-value corresponding to the (002) basal plane diffraction in graphitic structure. Elemental analysis (C, H, N, O) of the product showed that the
atomic ratio of nitrogen to carbon (N/C) ranged from 0.38 to 1.3. Analysis of data revealed that the d-value increased and the nitrogen content
decreased with the increase of the impact velocity.
c
ꢀ 2006 Elsevier Ltd. All rights reserved.
PACS: 62.50.+p; 81.05.Tp; 81.40.Vw
Keywords: A. Nanostructures; B. Shock compression; E. Strain, High pressure; E. X-ray and X-ray spectroscopies
Prediction of novel phases of C3N4 with high bulk
moduli [1,2] has produced vast number of studies [3–5] on
carbon nitride materials. From the conception analogous to the
high-pressure synthesis of diamond from graphite, graphitic
C3N4 (g-C3N4) is considered to be an appropriate precursor for
preparing the predicted phase. Proximity to the stoichiometry
of C3N4 in graphitic carbon nitride materials has been
attempted in several ways [6–11], including shock compression
techniques [12–15]. The starting materials generally employed
have clustered on 1,3,5-triazine-based compounds. The method
of preparation includes polycondensation of melamine [6–
9,15], condensation of melamine and cyanuric chloride [8],
pyrolysis of trichloromelamine [10], and reaction of cyanuric
chloride with sodium amide [11]. In this study we adopted
precursors such as carbon tetrahalide (CX4 (X = Br, I)) and
sodium dicyanoamide (NaN(CN)2) [13] which were exposed
to shock compression as described in Eq. (1). The starting
materials provide adequate composition of carbon and nitrogen
for synthesis of C3N4 materials. Shock compression generates
dynamic high-pressure and high-temperature to achieve denser
states. Chemical reaction induced by shock wave has a
characteristic feature of adiabatic compression attended with
increase of entropy. Pulsed pressure of short duration (typically
∼1 µs) where abrupt increase and release of pressure are
realized may provide an appropriate condition for approaching
the metastable phase. We now report a new synthetic route to
graphitic nitrogen-rich carbon nitride materials.
χCX4 + 4χNaN(CN)2 → [C3N4]3χ + 4χNaX.
(1)
All manipulations for the loading of starting materials into
sample containers were performed under dry N2 atmosphere.
In a typical experiment, CX4 (X = Br, I) and NaN(CN)2 were
mixed in an agate mortar with a molar ratio of 1:4 and ground
with an agate pestle for 5 min. The sample was then placed in
a sample container (Cu) and pressed at 300 kg/cm2 for 5 min.
The evaluated densities (g/cm3) for the samples (1.8–2.2 (X =
Br), 2.5 (X = I)) were consistent with the calculated ones
for the 1:4 mixture of CX4 and NaN(CN)2 (2.05 (X =
Br), 2.26 (X = I)). After the screw lid (Cu) was equipped,
R
the dip around the lid was covered with Aralditeꢀ to protect
the sample from air and moisture. The container was held
in the target assembly and used as the target of a propellant
gun for shock-recovery experiments [16]. Projectiles with
flyer plates (Cu) of 2 mm thickness were accelerated in a
∗
Corresponding author.
E-mail address: SEKINE.Toshimori@nims.go.jp (T. Sekine).
c
0038-1098/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2006.07.021

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K. Shibata, T. Sekine / Solid State Communications 139 (2006) 501–505
Table 1
Shock-recovery experiments for preparation of carbon nitride materials
Shot# Reactants
Impact
Shock
Products
XRD
Elemental analysis (wt%)
Atomic
velocity
pressure
d (nm)
N/C
v
(km/s) P (GPa)
imp
C
–
H
–
N
–
O
–
Total
–
1173 NaN(CN) (518 mg), CBr (480 mg)
0.652
0.686
13
14
Dark grey powder
(13 mg )
Dark brown powder
0.324
0.324
–
2
4
a
1169 NaN(CN) (518 mg), CBr (480 mg)
34.1
1.89 49.2 11 96.19 1.24
2
4
(25 mg)
Brown powder (51 mg)
Dark brown powder
1177 NaN(CN) (264 mg), CBr (240 mg)
0.890
1.02
18
21
0.325
0.327
30.8 <0.01 45.3 11 87.1 1.26
2
4
1178 NaN(CN) (264 mg), CBr (240 mg)
35.8
2.09 46.1 9.4 93.39 1.10
2
4
(67 mg)
Brown powder (75 mg)
1174 NaN(CN) (246 mg), CBr (224 mg)
1.09
1.09
1.11
1.20
1.24
23
23
24
26
27
0.326
0.327
0.326
0.326
–
–
–
39.4
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
4
1166 NaN(CN) (518 mg), CBr (480 mg)
Black powder (24 mg)
Black powder (64 mg)
Black powder (64 mg)
Black powder (228
2
4
1179 NaN(CN) (264 mg), CBr (240 mg)
2
4
1180 NaN(CN) (264 mg), CBr (240 mg)
2.11 43.9 10 95.41 0.955
2
4
b
1164 NaN(CN) (532 mg), CBr (480 mg)
0.32–0.33
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
4
a
mg )
d
1165 NaN(CN) (532 mg), CBr (480 mg)
1.33
29
Black powder (259
0.329
–
–
2
4
c
mg )
e
1168 NaN(CN) (518 mg), CBr (480 mg)
1.43
1.46
1.50
1.64
1.51
<32
33
34
<38
34
–
–
2
4
1170 NaN(CN) (242 mg), CBr (220 mg)
Black powder (44 mg)
Black powder (44 mg)
0.327
0.336
–
48.4 <0.01 38.4 8.5 95.300 0.680
58.6 <0.01 29.2 8.2 96
–
2
4
1175 NaN(CN) (249 mg), CBr (226 mg)
0.427
–
2
4
e
1167 NaN(CN) (518 mg), CBr (480 mg)
–
–
–
–
–
2
4
1172 Cu powder (1.962 g), product of
#1164 (0.218 g)
1176 Cu powder (1.800 g), product of
Black powder (59 mg)
Black powder (64 mg)
Black powder (127 mg)
0.330
47.7 <0.01 33.5 13 94.2 0.602
1.90
1.01
45
21
0.335
0.328
55.9 <0.01 24.9 12 92.8 0.382
#1165 (0.200 g)
1196 NaN(CN) (264 mg), CI (376 mg)
–
–
–
–
–
–
2
4
a
b
c
d
e
The product was not treated with HNO aq.
3
Exact value was not acquired due to partial overlap of another peak.
The amount before treatment with HNO aq is described. 200 mg of the product was used in #1176.
3
59 mg of the product was treated with HNO aq to give a black solid (2 mg) which was subjected to the XRD measurement.
Products were not obtained due to breakage of sample containers.
3
Fig. 1. XRD patterns of sample obtained in shot 1169. As recovered (a), after washed by water (b), and after treatment with HNO (c), ꢀ = NaBr, × = NaC N ,
3
2 3
ꢀ = CuBr, 1 = Cu, ? = unknown.
launcher and impacted onto the target. The impact velocity was
measured with a magnetoflyer method [17]. Due to lack of
thermodynamic data are unavailable. After shock treatment
the recovered sample containers were opened to give solid
materials.
Hugoniot data for the starting mixture, impact velocity (vimp
)
has been used as a measure for harshness of shock condition.
The peak shock pressure (P) (described in Table 1) was
calculated with the shock impedance-matching method [18,
19] assuming that the pressure was equilibrated with container.
The shock temperature is not estimable because Hugoniot and
Powder X-ray diffraction (XRD) spectra of the products
were recorded on Rigaku RINT 2200V/PC with Cu Kα
radiation generated at 40 kV and 50 mA. In the XRD spectrum
(5–110◦) of the product (X = Br, #1169) as in part depicted
in Fig. 1(a), the strongest set of 14 peaks was attributed to

K. Shibata, T. Sekine / Solid State Communications 139 (2006) 501–505
503
NaBr. This fact clearly shows that the reaction proceeded. The
second strongest set of 18 peaks belongs to α-NaN(CN)2 [20].
Identification of another peak was disturbed by these intense
peaks. CBr4, β-NaN(CN)2, and the trimer of NaN(CN)2
were significantly not recognizable. To remove the obstacles
disturbing identification of peaks with low intensity, the product
of #1169 was washed with water (rt) as a test. In the XRD
spectrum (5–110◦) of the resultant product (partly shown in
Fig. 1(b)), the strongest set of peaks was attributable to NaBr.
The second strongest set of 4 peaks belongs to γ -CuBr. This
fact implies formation of Br2 which subsequently reacted
with the container (Cu). The third strongest set of 5 peaks
results from Cu. The tiny peaks of γ -CuBr and Cu are now
recognizable also in Fig. 1(a). The product was further washed
with HNO3aq (13 N) to eliminate these coppery materials. The
XRD spectrum (5–110◦) of the final product (partly shown in
Fig. 1(c)) showed a broad peak.
Typically the product (X = Br) after opening the sample
container was suspended in HNO3aq (13 N, 50 mL). The
precipitates were washed with distilled water (rt and then
60 ◦C), dried at 120 ◦C with silica gel, and subjected to
XRD measurements and elemental analyses. The results are
summarized in Table 1 (the first 14 entries). In all cases except
#1168 and #1167, products were obtained as stable powder. The
typical XRD patterns of the products are shown in Fig. 2((a),
(b), and (c)). In the XRD spectra of the products, the strongest
peak at 26.5–27.5◦ (0.324–0.336 nm) corresponds to the (002)
basal plane diffraction in the graphitic structure. These data
are compatible with the calculated (d = 0.336 nm [3])
and experimental values of interlayer spacing for g-C3N4 and
related compounds (d = 0.327 [7], 0.322 nm [11] for proposed
g-C3N4, d = 0.325 nm for quasi graphitic carbon nitride [9],
Fig. 2. Comparison of XRD patterns of samples 1177 (a), 1178 (b), 1170 (c),
1172 (d), and 1176 (e). See Table 1 for the shock conditions, d-values and
elemental analyses.
d
= 0.324 nm for C3N4+x [10], d = 0.329 nm for
[(C3N3)2(NH)3]n [21], d = 0.322 nm for C6N9H+4 Cl− [22],
d = 0.327 nm for C6N7(NH2)3 [23], d = 0.323 nm for
[(C3N3)2(NH)3]n [24]).
As shown in Fig. 3, the d-value increases with the increase
of the impact velocity. To examine possible correlation of this
feature with nitrogen content, elemental analyses (C, H, and N)
for several products were carried out on SUMIGRAPH Model
NCH-21. The sample was subjected to oxygen circulating
combustion system at 850 ◦C. Carbon, hydrogen, and nitrogen
were detected as CO2, H2O, N2 respectively with thermal
conductivity detector. Acetanilide (Kishida Chemical, C,
71.072 wt% (R(range) = 0.050 wt%); H, 6.737 wt% (R =
0.044 wt%); N, 10.348 wt% (R = 0.021 wt%)) was used as
standard. The results disclosed that the atomic ratio of nitrogen
to carbon (N/C) decreased with the increase of the impact
velocity. Apparently, the more severe the shock condition, the
lower the nitrogen content of the product. Thus, the product
of the highest nitrogen content (N/C = 1.26) was obtained
when the reactants were shocked at the impact velocity of
0.890 km/s whereas the shock experiment at the highest impact
velocity (1.50 km/s) afforded the product of the lowest nitrogen
content (N/C = 0.427) with the largest d-value (0.336 nm).
The total weight percent for C, H, and N (76.1–87.8 wt%) is
indicative of existence of another atomic component. Elemental
Fig. 3. Plot of d-value versus impact velocity. The filled circles, squares, and
triangle represent the results for the 11 shots (× = Br), the 2 shots (1172,
1176), and the shot 1196 in Table 1, respectively.
analysis for oxygen was executed on LECO Nitrogen/Oxygen
Analyzer TC-436. Combustion of the sample was performed
with impulse furnace at 3000 ◦C. Oxygen was detected as
CO2 with infrared rays detector. Y2O3 (Shin–Etsu Chemical,
99.999%) was used as standard. As shown in Table 1 significant
amounts of oxygen contaminated the samples presumably as a
result of oxidation after opening the sample containers, because
doubly treated samples (#1172 and #1175) indicated highest
oxygen contents. There seems to be two groups with respect
to hydrogen content in products. Hydrogen-rich products were
obtained at relatively low impact velocities below 1.2 km/s, but
indicate no correlation with the oxygen content. The reasons for
the very low hydrogen contents are unclear at present.
According as the shock condition became harsher, nitrogen
would escape from the carbon nitride material, driving

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K. Shibata, T. Sekine / Solid State Communications 139 (2006) 501–505
(N/C = 0.602 (vimp = 1.51 km/s) and even 0.382 (vimp
=
=
1.90 km/s)) than that in #1180(N/C = 0.955 (vimp
1.20 km/s)).
Finally, the shock-recovery experiment for the mixture of
CI4 and NaN(CN)2 was examined (#1196 in Table 1). In the
XRD spectrum (10–110◦) of the product before treatment with
acid and water, the strongest set of 14 peaks is attributable
to CuI. The second strongest set of 30 peaks corresponds to
NaI2H2O. Formation of CuI is suggestive of generation of
I2 in the reaction process. CI4, NaN(CN)2, and the trimer
of NaN(CN)2 were significantly not recognizable. After the
product was suspended in HNO3aq (13 N, 50 mL), the
precipitates were washed with distilled water (rt and then 60 ◦C)
◦
and dried at 120 C with silica gel. The shape and position of
the peak in the XRD spectrum of the product were essentially
unaltered although the yield was doubled compared with that in
the experiments for CBr4 and NaN(CN)2.
In conclusion, nitrogen-rich carbon nitride materials with
N/C up to 1.26 have been successfully prepared from
Fig. 4. High-resolution TEM image of amorphous carbon nitride produced in
shot 1175.
its composition and structure closer to graphite (d002
=
CX4 (X
=
Br, I) and NaN(CN)2 by shock synthesis.
0.335 nm). To confirm the nitrogen escape, the products
obtained in #1164 and #1165 were exposed to the shock
condition. After the sample was mixed with 90 wt% Cu powder
in an agate mortar, the mixture was ground with an agate pestle
for 5 min. and put into the sample container (Cu). Preparation
of the sample container was according to the same method as
described above. The densities (g/cm3) of the samples were
evaluated as 5.7 (#1172) and 6.6 (#1176). A large excess of
copper powder enhances the shock condition due to greater
shock impedance relative to the sample without copper. After
shock treatment the product was collected from the recovered
sample container and suspended to HNO3aq (13 N, 50 mL).
The precipitates were washed with distilled water (rt), dried at
120 ◦C with silica gel, and subjected to XRD measurement and
elemental analysis. The results were described at #1172 and
#1176 in Table 1.
Obviously, exposure of the materials at elevated temperatures
should be avoided for further transformation to a predicted
metastable phase without release of nitrogen. Investigation
along this line is currently in progress.
Acknowledgements
This work was supported in part by a Grand-in Aid for
Exploratory Research. K.S. acknowledges support by NIMS
for his stay. K.S. is grateful to Professor A. Sawaoka for
encouragement. Elemental analyses of C, H, and N were
performed by Sumika Chemical Analysis Service. The authors
thank Mr. Y. Yajima and K. Kurashima in Ceramics Analysis
Group, NIMS for elemental analysis of oxygen and analytical
TEM, respectively.
Samples #1175 and #1179 were investigated by transmission
electron microscopy (TEM) coupled with EDX analysis. Both
samples indicated significant amounts of bromine and copper,
heterogeneously distributed, and no sodium. Fig. 4 shows a
typical TEM image of sample #1175. It consists of disordered
lattice images mostly and very limited areas such as the
left-bottom portion in Fig. 4 display partial ordering similar
to layered structures. These results explain that samples are
contaminated by CuBr probably covered with amorphous C–N
material.
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