UV laser photodeposition of nanomagnetic soot from gaseous benzene and acetonitrile-benzene mixture

Article abstract of DOI:10.1016/j.jphotochem.2011.04.011

Megawatt KrF laser gas-phase photolysis of benzene and acetonitrile-benzene mixture was studied by using mass spectroscopy-gas-chromatography and Fourier transform infrared spectroscopy for analyses of volatile products, and by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, electron microscopy and magnetization measurements for analyses of solid products deposited from the gas-phase. The results are consistent with carbonization of benzene and decomposition of non-absorbing acetonitrile in carbonizing benzene through collisions with excited benzene and/or its fragments. The solid products from benzene and acetonitrile-benzene mixture have large surface area and are characterized as nanomagnetic amorphous carbonaceous soot containing unsaturated C centers prone to oxidation. The nanosoot from acetonitrile-benzene mixture incorporates CN groups, confirms reactions of benzene fragments with CN radical and has a potential for modification by reactions at the CN bonds.

Full text of DOI:10.1016/j.jphotochem.2011.04.011

Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
UV laser photodeposition of nanomagnetic soot from gaseous benzene and
acetonitrile–benzene mixture
a,∗
b,∗∗
c
c
d
d
e
ˇ
, M. Mary sˇ ko , V. Vorlí cˇ ek , Jan Subrt , S. Bakardjieva , Zden eˇ k Bastl
Josef Pola , Akihiko Ouchi
a
Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, 16502 Prague, Czech Republic
National Institute of Advanced Industrial Science and Technology, AIST Tsukuba, Ibaraki 305-8565, Japan
Institute of Physics, ASCR, 18223 Prague 8, Czech Republic
Institute of Inorganic Chemistry, ASCR, 25068 Re zˇ , Czech Republic
J. Heyrovsk y´ Institute of Physical Chemistry, ASCR, 18223 Prague, Czech Republic
b
c
d
e
ˇ
a r t i c l e i n f o
a b s t r a c t
Article history:
Megawatt KrF laser gas-phase photolysis of benzene and acetonitrile–benzene mixture was studied by
using mass spectroscopy–gas-chromatography and Fourier transform infrared spectroscopy for analyses
of volatile products, and by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy,
electron microscopy and magnetization measurements for analyses of solid products deposited from the
gas-phase. The results are consistent with carbonization of benzene and decomposition of non-absorbing
acetonitrile in carbonizing benzene through collisions with excited benzene and/or its fragments. The
solid products from benzene and acetonitrile–benzene mixture have large surface area and are char-
acterized as nanomagnetic amorphous carbonaceous soot containing unsaturated C centers prone to
oxidation. The nanosoot from acetonitrile–benzene mixture incorporates CN groups, confirms reactions
of benzene fragments with CN radical and has a potential for modification by reactions at the CN bonds.
© 2011 Elsevier B.V. All rights reserved.
Received 22 January 2011
Received in revised form 29 March 2011
Accepted 2 April 2011
Available online 12 April 2011
Keywords:
Benzene
Acetonitrile
Laser photodeposition
Nanomagnetic soot
CN-substituted soot
1
. Introduction
UV laser irradiation of gaseous benzene has been broadly stud-
Studies on UV laser gas-phase photolysis of benzene in colli-
sional conditions are limited for KrF laser-induced formation of
benzene clusters [13] and aerosol (biphenyl and phenylcyclohexa-
diene) photocondensation [14].
No UV laser photolytic deposition of carbon materials from
benzene have yet been reported, in spite of benzene use as a
precursor for carbon films and powders in plasma-assisted and
laser-pyrolytic degradations.
ied with the aim to identify the decomposition mechanism and
products. Early experiments revealed isomers (benzvalene, ful-
vene and 1,3-hexadiene-5-yne), fragmentation products (methane,
ethane, ethane, ethyne) and a carbonaceous solid deposited on the
cell walls (e.g. [1–3]).
Later experiments under collisionless conditions using ArF and
KrF lasers have shown that primary photodissociation channels is
cleavage of the C–H bond and all possible fissions of benzene car-
bon ring (namely C H5 + H, C H + H , C5H + CH , and C H + C H
Here wereportonKrFlaser-induced photolysis ofbenzene inthe
absence and presence of non-absorbing acetonitrile for gas-phase
deposition of ultrafine carbonaceous powders (soot). We identify
volatile and solid products of both photolyses, reveal incorporation
of –CN substituents in soot produced from acetonitrile–benzene
mixture and establish magnetism in both types of soot.
6
6
4
2
3
3
4
3
2
3
[
4–6]). These steps were confirmed by ab initio RRKM study [7].
Other reactions were recognized in UV laser collisionless condi-
tions by using a CARS (coherent anti-Stokes Raman scattering) and
optical and mass spectral probe techniques. These are two-photon
ArF laser-induced formation of 1,3-hexadiene-5-yne and phenyl
2. Experimental
radical [8], multiphoton induced formation of C fragments [9] and
multiphoton ionization of benzene to a multitude of Cn/Hm ions
2
Laser irradiation experiments were carried out on gaseous
benzene (50 Torr) and a benzene (50–Torr)–acetonitrile (20 Torr)
mixture in helium (total pressure 760 Torr) admitted to a previ-
ously described reactor [15]. The reactor (140 ml in volume) had
two orthogonally positioned tubes: one furnished with UV-grade
synthetic silica and the other with KBr windows. It possessed two
side arms: one fitted with a rubber septum and the other connect-
ing to a standard vacuum manifold. The LPX 210i KrF laser used
[
10–12].
∗
Corresponding author. Tel.: +420 2 20390308; fax: +420 2 20920661.
Corresponding author. Tel.: +8129 861 4550; fax: +8129 861 4421.
E-mail addresses: pola@icpf.cas.cz (J. Pola), ouchi.akihiko@aist.go.jp (A. Ouchi).
∗
∗
1
010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.04.011

J. Pola et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
189
Fig. 1. Photolysis progress in benzene (a) and acetonitrile–benzene mixture (b).
for the irradiation was operated with a repetition frequency of
1
0 Hz at 248 nm. The pulses (580 mJ) were focused to an incident
2
area of ca. 0.20 cm and corresponded to ∼25 MW (megawatt) out-
put and 125 MW cm2 incident intensity. They represented critical
threshold, since the described sooting does not take place at lower
values.
The progress of benzene photolysis was monitored directly
in the reactor by Fourier Transform Infrared (FTIR) spectroscopy
(
a Shimadzu FTIR IR Prestige-21 spectrometer) using diagnostic
−1
absorption band at 3046 cm
. (Similar monitoring of ace-
tonitrile was hampered by a low infrared absorption of this
compound.) The irradiated reactor content was analyzed by gas-
chromatography–mass spectroscopy (a Shimadzu QP 5050 mass
spectrometer, 60 m capillary column Neutrabond-1, programmed
◦
temperature 30–200 C). The decomposition products were iden-
−
1
Fig. 2. GC/MS trace of volatile products in KrF laser photolysis of
benzene–acetonitrile mixture. (Peak designation: 1, CO; 2, ethyne; 3, propane;
tified through their FTIR diagnostic bands (ethyne, 730 cm
butadiyne, 628 cm ) and through mass spectra using the NIST
library.
The samples of the deposited ultrafine soot were analyzed by
X-ray photoelectron (XPS), FTIR and Raman spectroscopies and by
electron microscopy and were also diagnosed for physical absorp-
tion and examined for magnetic properties.
The C1s, N1s and O1s photoelectron and C KLL Auger elec-
tron spectra of the deposit were measured by using an ESCA 310
;
−1
4, cyanogen; 5, propene; 6, hydrogen cyanide; 7, C3H4 (propyne and allene); 8,
1,3-butadiene; 9, 1-buten-3-yne; 10, 1-butyne; 11, 1,3-butadiyne; 12, propi-
olonitrile; 13, acetonitrile; 14, C5H6; 15, 2-propenenitrile; 16, 3-penten-1-yne; 17,
propanenitrile; 18, C5H4; 19, 2-methylpropenenitrile; 20, 2-methylpropanenitrile;
21, 1-cyanoprop-1-yne or cyanoallene; 22, benzene; 23, hex-3-en-1,5-diyne; 24,
hexa-1,3,5-triyne; 25, pyridine; 26, toluene; 27, C4N2H2 (methylenepropanedinitrile
and/or 2-butanedinitrile); 28, ethynylbenzene; 29, benzonitrile. (CN-containing
products are given in italics).
(
1
Scienta) electron spectrometer with a base pressure better than
−
9
ethanol and applying a drop of very dilute suspension on Ni
grid.
0
Torr and Al K␣ radiation (1486.6 eV) for electron excitation.
The surface composition of the deposited film was determined
by correcting the spectral intensities for subshell photoionization
cross-sections.
The Raman spectra were recorded on a Renishaw (a Ramas-
cope model 1000) Raman microscope with a CCD detector using
the exciting beam of an Ar-ion laser (514.5 nm, 50 mW). The beam
was attenuated to obtain incident energy densities lower than
The magnetic measurements were performed in the temper-
ature region 5–300 K using a SQUID (Superconducting Quantum
Interference Device) magnetometer MPMS-5S. Deposited carbon
soot was treated with a mixture of sulfuric and nitric acid and
then elemental analyses for Fe, Co Mn and Ni were carried out by
atomic absorption spectroscopy (Avanta ꢀ, GBS) and showed these
impurities less than 20 ppm.
−
3
2
5
× 10 W/cm .
Benzene (Wako, purity 99.9%) and acetonitrile (Cica reagent,
purity 99.7%) were distilled prior to use.
The FTIR spectra of thin layers of the deposited soot accommo-
dated between KBr plates were obtained on a Nicolet Impact 400
spectrometer.
The SEM (Scanning Electron Microscopy) analyses were con-
ducted on a Philips XL 30 CP scanning electron microscope
equipped with energy dispersive analyzer (EDAX DX-4) of X-ray
radiation. A PV 9760/77 detector in low vacuum mode (0.5 Torr)
was used for quantitative determination of C, O and N elements.
The transmission electron micrographs (TEM) were obtained
using a JEOL JEM 3010 microscope (LaB6 cathode) operating
at 300 kV and equipped with EDS detector (INCA/Oxford) and
CCD Gatan (Digital Micrograph software). The samples were pre-
pared by grinding and subsequently dispersing the powder in
3. Results and discussion
3.1. Laser photolysis
KrF laser photolysis of gaseous benzene (50 Torr in He) car-
ried out for 5 min results in 80% decomposition of benzene
(Fig. 1), formation of a multitude of gaseous products (CO, ethyne,
propene, allene, propyne, 1-buten-3-yne, 1-butyne, 1,3-butadiene,
1,3-butadiyne, penten-1-yne, C5H , hex-3-en-1,5-diyne, 24, hexa-
1,3,5-triyne, toluene and phenylacetylene) and deposition of a dark
4

1
90
J. Pola et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
Fig. 3. SEM image of soot deposited from benzene (a) and benzene–acetonitrile mixture (b).
ultrafine carbon soot. The formation of CO proves the occurrence of
minor carbothermal reaction between carbon fragments and silica
KrF laser photolysis of benzene (50 Torr)–acetonitrile (20 Torr)
in He shows similar progress as the photolysis of benzene
(Fig. 1) and leads to hydrocarbons whose pattern is almost
the same as that observed in photolysis of benzene alone.
In this case, however, the hydrocarbons are accompanied not
reactor window [15]. The highly unsaturated C –C8 hydrocarbons
1
document a number of cleavage and combination reactions of C/H
fragments, which occur in collisional regime and finally lead to the
deposited carbonaceous solid. We estimate that the volatile hydro-
carbons are formed in amounts lower than 10% of the depleted
benzene, which is compatible with benzene mostly consumed for
deposition of the dark soot.
only with CO and
a dark soot, but also with many CN-
substituted volatile compounds (Fig. 2). The CN-containing
products are HCN (the main product), cyanogen (NC–CN), three-
carbon molecules (HC C–CN, H C CH–CN, C H5–CN), four-carbon
2
2
Ethyne (the main product) and other C –C6 unsaturated hydro-
molecules (H C C(CH )CH –CN, CH CH(CH )CH CN, CH C C–CN,
3
2 3 2 3 3 2 3
carbons (particularly 1,3-butadiyne and hexa-1,3,5-triyne) indicate
that carbonization takes place primarily through agglomerization
of small Cn (mostly C2n) species [7,15–17] and not through interme-
diary polyaromatic hydrocarbons [18]. The observed hydrocarbons
are in keeping with dehydrogenation steps, cleavage of C6 ring
to ethyne and ethynyl radical, isomerization of ethyne to ethyli-
dene [19], radical recombination and H-abstraction and attack onto
the ␲-electron density of the intermediates [20]. The presence of
ethynylbenzene suggests this molecule as a source of cyclic car-
bonaceous structures.
CH2 C CH–CN, (CN) C CH , CN–HC CH–CN) and benzonitrile.
2 2
In discussing formation of these CN-substituted products, we
note that acetonitrile is transparent above 190 nm and that the
248 nm irradiation of CH CN (20 Torr in He) for 5 min does not
3
lead to any decomposition. The CN-containing products therefore
indicate that CH CN molecules decompose thermally in the soot-
3
ing environment of photolyzed benzene through collisions with
hot C/H molecules and fragments. Such thermal decomposition
of CH CN may take place via H atom ejection and involvement
3
of open shell products which are, in the decreasing importance,
Fig. 4. TEM image and electron diffraction of soot deposited from benzene (a) and benzene–acetonitrile mixture (b).

J. Pola et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
191
component, since similar photoluminescence was also observed
27] in a-C:H carbon
[
3.2.3. XPS spectra
The XPS spectral analysis-derived stoichiometry of superficial
layers of both soot samples – C1.00Si0.07O0.15 (photolysis of ben-
zene) and C1.00Si0.04O0.19N0.05 (photolysis of benzene–acetonitrile
mixture) – shows the prevalence of carbon and low content of Si, O
and N elements. The presence of oxygen points out to easy oxi-
dation of topmost layers. Binding energies of C1s, N1s and O1s
electrons in both samples are in the given order 284.6, 399.6
and 532.5 eV. The C1s spectra are asymmetric in the region of
higher energies and resemble spectrum of glassy carbon. The N1s
and O1s spectra respectively correspond to N in nitriles and O in
3
2
C–OH bonds [28]. An estimation of the sp /sp hybridization ratios
29,30] was performed by using the energy difference between
Fig. 5. Raman spectrum of the soot deposited from benzene–acetonitrile mixture.
[
the most positive maximum and most negative minimum of the
C KLL derivative spectra. These values − 18.0 eV for soot from ben-
zene and 17.2 eV for soot from benzene–acetonitrile mixture –
were compared (Fig. 6) to those of diamond (13.1 eV) and graphite
(21.9 eV) and found as respectively consistent with 70 and 60% of
CH CN, CH , H, CH , CN and C H5 [21,22] and which give rise to
2
3
2
2
shock-tube formation of detected methane and hydrogen cyanide
main products), cyanogen and HnC –CN (n = 1, 3, 5) compounds.
(
2
Our observation of larger CN-substituted products (the four carbon
2
molecules and benzonitrile) is in line with combination of CH CN
sp state. We thus assume that both soot samples have very similar
2
carbon structure and that sp2 state population in the N-containing
soot is decreased due to small proportion of C N groups.
and CN radicals with Cn/Hm fragments of photolyzed benzene or
addition of HCN to C H . The presence of ethynylbenzene proves
2
2
the combination of CN and phenyl radicals and suggests, similarly
as that of ethynylbenzene in the benzene photolysis, that phenyl
radical is a source of cyclic carbonaceous structures.
3
.2.4. FTIR spectra
The FTIR spectra of the soot from benzene and
benzene–acetonitrile mixture (Fig. 7) have similar absorp-
tion pattern consisting of bands of C–H stretches centered
3
.2. Properties of soot
−
1
−1
ꢁ(C O) band at 1720–1730 cm ,
at 2920–2840 cm
,
a
a
−
1
The deposited black soot is difficult to handle, since it keeps
broad ꢁ(C C) band at 1550–1650 cm
and a ꢁ(C–O) band at
−
. Absorption bands at lower wavenumbers
1
electrostatic charge and flows in air. It has large surface area. The
determined Brunauer–Emmett–Teller (BET) surface area of the soot
deposited from benzene and benzene–acetonitrile mixtures is 176
1000–1300 cm
correspond to C–H deformation and C–C skeletal vibrations.
The three distinct bands of the soot from benzene at 2720,
2
−1
and 170 m /g, respectively. These values indicate similarity of both
1455 and 1380 cm
(as well as similar absorption for the soot
samples to carbon nanocomposites prepared by MW laser photol-
ysis of toluene and pyridine [15,23].
from benzene–acetonitrile mixture) correspond to stretches and
deformation vibrations of –(O–)C–H moieties found [31] e.g. in
aromatic methylene dioxy compounds. The spectrum of the soot
from benzene–acetonitrile mixture has, in addition, a band at
3.2.1. Electron microscopy
The SEM images of both powders show fluffy morphology
(
(
Fig. 3). The SEM-EDX-derived stoichiometries – C1.00O0.08Si0.03
photolysis of benzene) and C1.00O0.12Si0.04N0.05 (photolysis of
benzene–acetonitrile mixture) – indicate a small incorporation of
a silica (silica spallation [15]) and a low content of N element. The
incorporation of N confirms reactivity of CN-substituted interme-
diates produced from benzene–acetonitrile and their inclusion into
carbonizing soot.
The TEM images and electron diffraction reveal that both soot
samples are amorphous and consist of ca. 10 nm-sized bodies that
merge into spongy network (Fig. 4).
3.2.2. Raman spectra
The visible Raman spectra of both soot samples show broad
−
1
−1
(D-band) and 1575–1600 cm
bands at 1350–1365 cm
(
G-band) of unsaturated sp2 carbon with intensity ratio
ID/IG = 0.50–0.60. Typical spectrum of the sample obtained from
benzene–acetonitrile mixture is illustrated on Fig. 5. The G-band
reflects stretches of all pairs of sp2 atoms in rings and chains, the
D-band relates to breathing modes of rings [24,25]. The shoulder
of the G-band becomes more apparent upon deconvolution of
the G-band and corresponds to a contribution of amorphous
−
1
carbon (A-band) [26] which is peaked at 1510–1530 cm . The
identified D, G and A bands and the ID/IG values are consistent with
a disordered graphitic carbon. The observed high photolumines-
cence background is suggestive of a contribution of a polymeric
Fig. 6. C KLL X-ray excited derivative Auger spectra of natural diamond (a), grahite
(b), and soot obtained with benzene (c) and benzene–acetonitrile mixture (d).

1
92
J. Pola et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
7
6
1
5
,0x10
,0x10
-
6
1
,0x10
,0x10
-7
5
0
10
20
30
T(K)
0,0
0
100
200
300
T(K)
Fig. 9. Temperature dependence of mPM/H for soot obtained from benzene (×) and
acetonitrile–benzene mixture (ꢀ). In the inset the value H/mPM corresponding to
the inverse susceptibility 1/ꢂ and the straight lines extrapolated to H/M → 0.
Fig. 7. FTIR spectra of the soot from benzene (a) and benzene–acetonitrile mixture
b).
mFM represents an apparent saturation magnetization related to
the total weight of the sample.) The ferromagnetic moment is with
highest probability given only by a part of the total volume, where
the intrinsic saturation magnetization Ms is much larger (see [32]).
Towards lower temperatures mFM(sat) increases and at T = 10 K
achieves for both samples the value roughly equal 1.5 mFM(sat)
(
T= 300 K
0
0
,004
,000
(300 K).
The PM magnetization was examined by measuring the tem-
perature dependence of m under an applied field H = 10 kOe and
field dependence m(H) at T = 2 K. The mPM contributions obtained
after subtracting mDM + mFM are shown in Figs. 9 and 10. In this
procedure the temperature dependence of mFM was assumed to be
in the form used e.g. in [15] and field dependence was described
by the exponential relation m = m0 (1 − exp(−˛H)). The tempera-
ture dependence mPM(T) was approximated by the Curie–Weiss
law mPM = C/(T − ꢃ), where C is the Curie constant (Table 1) and ꢃ
a temperature connected with an exchange interaction between
the PM centers. The quality of this approximation in the low tem-
perature region is demonstrated by a straight line character of the
1/ꢂ vs. T plot (inset of Fig. 9). The temperatures ꢃ determined as
intercepts on the T axis are −1 and −2.2 K for the B and AB sam-
ple respectively, with the accuracy better than 10%. Let us remark
that in the whole temperature region, i.e. up to 300 K the qual-
ity of the C–W approximation is not so good mainly with respect
to an uncertainty in the substracted mFM component. From the
-
0,004
-
10
-5
0
5
10
H(kOe)
Fig. 8. The hysteresis loops at room temperature for soot obtained from benzene
(×) and acetonitrile–benzene mixture (ꢀ).
−1
−1
(assignable to C N stretch) and at 1200–1300 cm
2
180 cm
(
tentatively assignable to –C N–O structure).
3.2.5. Magnetic measurements
The magnetic measurements revealed that soot from ben-
zene (B) and acetonitrile–benzene (AB) exhibit, in addition to a
small diamagnetic (DM) background, a paramagnetic (PM) and a
minor ferromagnetic (FM) contributions. The measured magneti-
zation m can be thus expressed as a sum of 3 terms in the form
m = mDM + mPM + mFM. The FM magnetization can be evaluated at
room temperature (RT), where the PM and DM contribution is
proportional to the applied magnetic field H. In Fig. 8, the hys-
teresis loops mFM(H) measured at room temperature are shown.
For both samples the loop exhibits a small coercivity and a finite
remanent magnetization. The saturation magnetizations at room
temperature mFM(sat) are listed in Table 1. (Let us remark that
S= 5/2, θ = -1 K
S= 5/2, θ = 0
T= 2 K
1,0
0
0
,5
,0
S= 1, θ = -1 K
S= 1.9, θ = -2.2 K
Table 1
Magnetic parameters of soot.
0
1
2
3
4
5
6
7
8
Sample from
mFM(sat)
C (emu K/(g Oe))
mPM(sat)
(emu/g)
H(kOe)
(
(
RT)
emu/g)
Fig. 10. The reduced PM magnetization vs. magnetic field for soot obtained from
benzene (×) and acetonitrile–benzene mixture (ꢀ). By the full line the theoreti-
cal calculation for g = 2, S = 1, ꢃ = −1 K and almost identical curve for g = 2, S = 1.9,
ꢃ = −2.2 K, by the dashed lines the calculations for S = 5/2 with ꢃ = 0 and −1 K.
3.6 × 10−
7.2 × 10−
6
0.0357
0.0637
Benzene
Acetonitrile–benzene
0.00235
0.0043
6

J. Pola et al. / Journal of Photochemistry and Photobiology A: Chemistry 220 (2011) 188–194
193
field dependence mPM(H) at T = 2 K we determined the saturated
PM magnetization mPM(sat) by extrapolating mPM (1/H) to the
value 1/H = 0 (Table 1). In Fig. 10 the reduced PM magnetization
mPM/mPM(sat) is displayed as a function of H. For a given spin S, g-
factor g = 2 and temperature ꢃ the reduced magnetization should
follow a Brillouin-like function, which can be obtained by solv-
ing a transcendental equation with the Brillouin function on the
right side. Starting from the values of ꢃ determined above, the
best fit for the B and AB soots yields S = 1 and S = 1.9 respectively.
In Fig. 10 we show reduced magnetization fit for the B and AB
samples and also for comparison the S = 5/2 and S = 1 curves for
ꢃ = 0.
This phenomenon of carbon magnetism is of continuing inter-
est (e.g. [32,33,34,44,45]), but it is still not well understood. Our
data are in qualitative agreement with the occurrence of ferromag-
netic and paramagnetic spins located on C (and also possibly on N
[37]) atoms. A contribution from dangling Si-bonds of the minor
diamagnetic SiO2 constituent can be ruled out.
3.2.6. Possible chemical modification
We note that the incorporation of –CN group into the carbona-
ceous network keeps a promise for synthesis of other nanobodies,
because the –CN group can be changed for other substituents
through nucleophilic addition, reduction or hydrolysis. Such chem-
ical modification of nanosoot has been previously described for
Cl-substituted nanosoot [46] that was found reactive with nucle-
ophilic ammonia.
In the discussion, we first consider the possibility that the
observed moment arises from transition metal (typically Fe) impu-
rities for which the content was determined to be less than 20 ppm.
In the case of the PM magnetic moment it is necessary to com-
pare the measured saturated PM moment (Table 1) with the
estimated saturated PM magnetizations mPMimp(sat) 0.008, 0.008,
4. Conclusions
3
+
2+
0
.006, 0.004 emu/g corresponding to 20 ppm of the ions Fe , Mn ,
KrF laser photolysis of benzene yields low amounts of unsat-
2+
2+
2+
2+
Co , Ni respectively. We see that for Co and Ni the measured
urated hydrocarbons and allows chemical vapor deposition of
amorphous ultrafine soot. These products are compatible with car-
bonization of benzene.
The photolysis of benzene in the presence of non-absorbing ace-
tonitrile yields the same unsaturated hydrocarbons together with
HCN, cyanogens and a number of volatile CN-substituted hydrocar-
bons and allows deposition of amorphous ultrafine CN-substituted
soot. These products are compatible with decomposition of
acetonitrile in sooting benzene and with incorporation of CN-
substituents in the forming carbonaceous phase.
value is by an order of magnitude larger than m
(sat), which
PMimp
2+
2+
practically excludes a larger influence of Ni and Co impurities.
3
+
2+
For Fe and Mn ions this ratio is about 8 (AB) and 4 (B), but in
this case an additional argument can be given suggesting the intrin-
sic nature of the PM contribution. This is the field dependence of
the reduced magnetization (Fig. 10) which seems to correspond to
the values of the spins S = 1 and S = 1.9 in contrast to the course
S = 5/2 expected for Fe3 and Mn impurities. For the FM moment
an impurity FM contribution at room temperature can be produced
by Fe, Co or Ni atoms. In the same way as for the PM impurities an
estimate of mFMimp(sat) leads to 0.004, 0.0033, and 0.001 emu/g
for Fe, Co and Ni respectively. The measured value mFM for the AB
sample exceeds mFMimp(sat)(Fe) and in the case of the B sample
mFM is less than mFMimp(sat)(Fe). Taking into account these facts
we may assume that the measured PM and FM magnetizations are
unlikely to be caused by impurities, but are predominantly of the
intrinsic nature. The PM magnetization mPM(sat) for the B and AB
+
2+
The respective solid materials have large surface area and
were identified as ca.10 nm-sized bodies agglomerated into spongy
agglomerates. They contain C–H bonds, have a structure of disor-
3
2
dered graphite and their sp /sp hybridization ratios consistent
with 70 and 60% of sp2 state. Both soot samples are reactive to
atmosphere and develop C O bonds. They belong among carbon
magnets and show both paramagnetic and ferromagnetic contri-
butions.
−5
−4
samples are equivalent to 9 × 10 and 1.8 × 10 ꢄB per carbon
atom respectively (1 ꢄB corresponds to S = 1/2). In the same way,
We suggest that CN-containing soot may be chemically modified
through reactions on the CN bonds and similarly as Cl-substituted
nanosoot [46] could find use as a precursor for construction of novel
nanobodies.
−
6
for the FM apparent saturation magnetization we obtain 5.9 × 10
−5
and 1.2 × 10 ꢄB per carbon atom. The ratio between the PM and
FM magnetizations is for both soot samples nearly the same (≈15),
which suggests that the FM moment is caused only by a small part
Acknowledgement
(
≈1/15) of the centers which are ferromagnetically exchange cou-
pled. A ferromagnetically active relative volume (or weight) can be
very roughly estimated from the ratio mFM/Ms, where the real sat-
uration magnetization Ms ≈ 10 emu/g [32]. This yields 0.0036 and
This work was supported by GA ASCR (Grant 400720619).
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electrons, S = 1) and in the AB case there exist probably paramag-
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