- Email: [email protected]
Enhancement of graphitic order in carbon black using precursor additive
Journal Pre-proof Enhancement of graphitic order in carbon black using precursor additive
Surakanti Srinivas Reddy, A.K. Sinha, G. Amarendra, N.V. Chandra Shekar, G.M. Bhalerao PII:
S0925-9635(19)30474-1
DOI:
https://doi.org/10.1016/j.diamond.2019.107539
Reference:
DIAMAT 107539
To appear in:
Diamond & Related Materials
Received date:
16 July 2019
Revised date:
23 August 2019
Accepted date:
9 September 2019
Please cite this article as: S.S. Reddy, A.K. Sinha, G. Amarendra, et al., Enhancement of graphitic order in carbon black using precursor additive, Diamond & Related Materials (2019), https://doi.org/10.1016/j.diamond.2019.107539
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© 2019 Published by Elsevier.
Journal Pre-proof
Enhancement of graphitic order in carbon black using precursor additive Surakanti Srinivas Reddy1, 2, A.K.Sinha3, G. Amarendra4, N. V. Chandra Shekar1, 5 G.M.Bhalerao1* 1
UGC-DAE CSR Kalpakkam Node, Kokilamedu, T.N. - 603104, India
2
University of Madras, Chennai, Tamilnadu, 60005, India
3
HXAL, Synchrotron Utilization Section, Raja Ramanna Center for Advanced Technology, HBNI, Indore-
452001, M.P, India 4
Materials Science Group, IGCAR, HBNI, Kalpakkam, T.N. - 603102, India
5
India
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*Email: [email protected]
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Condensed Matter Physics Division, Materials Science Group, IGCAR, HBNI, Kalpakkam, T.N-603102,
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Abstract:
Our present work is aimed at increasing the degree of graphitization of carbon black during the
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synthesis stage itself. For this purpose, we used lamp black route to synthesize carbon black via catalytic graphitization using ferrocene as an organometallic additive into the precursor olive oil.
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Degree of graphitization was estimated using Raman spectroscopy and microstructure was determined using transmission electron microscopy (TEM). We found that the degree of
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graphitization as quantified by the Raman spectroscopy could be doubled by changing the concentration of ferrocene into the precursor oil. The TEM images show the presence of multi-
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layer graphenes, a few tens of nanometers large, which were completely absent when no additive
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was used. It is proposed that iron plays the role of graphitization enhancer as Raman, TEM and XRay diffraction (XRD) measurements show the presence of iron compounds in the product. Oxidation of iron catalyst mainly limits further growth of graphitic clusters. Keywords: Carbon Black, Raman Spectroscopy, Graphitization, Transmission electron microscopy. Introduction: Allotropes of graphitic carbon have a wide range of properties which can be usefully explored in a broad spectrum of applications. To give a few examples, graphene is found to be very useful as a catalyst support material in the field of single-atom catalysts [1], nanocatalysts [2], and heterogeneous catalysts [3,4], owing to its capabilities of high support area, preventing catalyst
Journal Pre-proof particle agglomeration, and support to oxygen reduction reactions, among others. Carbon foams are used in water purification, sensors, and energy storage devices [5]. Carbon coated iron oxide hybrids can be used as a lithium-ion anode in battery applications [6]. The difference in the properties of these materials originates from their structure, as well as the degree of graphitization in their structure. Carbon black (CB) also comes under this class as it consists of sp2 hybridized carbon particles and belongs to a class of turbostratic graphitic structure. The particle size of CB ranges from 10 to 1000 nm [7]. In crystalline graphite, the graphene layers are stacked in the perpendicular
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direction to c-axis in an AB-stacking arrangement. In turbostratic graphite there is no stacking
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order between adjacent layers and the interlayer space is larger than that for crystalline graphite [8]. Carbon black is widely used in rubbers and tyres as reinforcing fillers [9], and the daily life
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products such as inks, paints, plastics, adhesives, and ceramics contain the CB in them [10]. These
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are being used to reinforce the polymer to make electrically conductive composites which have potential application in Electromagnetic interference (EMI) shielding materials [11, 12]. They also
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find use in Li-ion batteries and in the fabrication of foldable and flexible devices on paper due to their electrical and mechanical properties [13, 14]. In EMI applications, CB containing polymeric
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materials shield the EMI by absorbing and dissipating the electromagnetic fields due to good electric conducting property of CB [12].
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Among many physical aspects of CBs, electrical conductivity is the key property which determines its usefulness in many of its applications. Electrical conductivity itself improves upon
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better graphitization. There are several methods in use to synthesize CB which includes Furnace black, Thermal black, Lamp black, Acetylene black and Channel black [10, 15]. CB produced from these methods differs in average particle size and structure/graphitization. However a suitable method can be chosen to produce CB with the desired structure, it is useful to further improve the graphitization. Thus, the quantity of CB in the composites could be minimized. Increase in the degree of graphitization of amorphous carbon has been reported in some previous studies by using activation process [16] and thermal annealing [17]. But at the same time, we do not witness much work towards controlling the graphitization during the synthesis itself. In the present work, our aim is to increase the graphitization of CB in a simple process called lamp black process by introducing organometallic additives into the precursor oil. We prepared CB
Journal Pre-proof nanoparticles by Lamp black process for its simplicity, low cost, and environment-friendly approach. The produced CB samples are then characterized by thermo gravimetric analysis (TGA), Raman spectroscopy, transmission electron microscopy (TEM) and X-Ray diffraction (XRD). Experimental: Commercially available olive oil was used as combustion precursor and varying amounts of ferrocene was added. Oleic acid is found to be very helpful in producing monodisperse nanoparticles and in controlling the particle size during the synthesis process [18]. Oleic acid
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which exhibits excellent surfactant property in organometallics-based syntheses, is an ingredient of olive oil and therefore it is also expected to blend well with the organometallic additives, which
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is the scheme of the present study. Ferrocene (Alfa Aesar – 99%) is an organometallic compound of iron and gives free iron upon thermal decomposition which acts as a catalyst for graphitic growth
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[19, 20], and is widely used for the synthesis of carbon nanotubes [19, 21]. The control sample
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was prepared by the combustion of olive oil without ferrocene. A series of samples were prepared using ferrocene as an additive with a concentration of 43, 86 and 172 mM/L respectively. CB was
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obtained by depositing combustion CB on to glass slides. These CB nanoparticles were then dispersed in propanol by ultra-sonication and deposited on to silicon wafers for Raman
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spectroscopy measurements. Raman spectroscopy is one of the most suitable and reliable technique for a quantitative assessment of graphitization in amorphous carbon, carbon
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nanostructures and other sp2 hybridized carbons [22]. Therefore, Raman spectroscopy was performed for quantitative characterization at room temperature using M/S Renishaw - InVia
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Raman spectrometer with 514 nm Ar laser as an excitation source. TEM measurements were carried out at 200 kV in order to analyze the microstructure using M/S Carl Zeiss - Libra 200HR machine. Thermal gravimetry analysis (TGA) was performed to investigate thermal oxidation behavior of the samples that are produced with and without ferrocene using M/S SETSYS-16/18 (setaram) device. C-constituent phases of CB were estimated from XRD analysis using 15.7535keV photons at Angle Dispersive X-ray Diffraction (ADXRD) beam line (BL-12) of the Indian synchrotron radiation source Indus-2 at RRCAT, Indore. XRD data were taken in transmission mode by sandwiching powder sample between Kapton foils. The scattering due to Kapton was subtracted from the XRD pattern of the samples for quantitative analysis.
Journal Pre-proof Results and discussion: Raman spectra of the samples are shown in Fig. 1. Spectra of all samples exhibit Gmode around 1600 cm-1 and the D-mode around 1350 cm-1, which is typical of the sp2 hybridized carbons [22]. The G-mode is attributed to the ‘in-plane’ vibrations, whereas disorder or defect in this lattice gives rise to the D-mode. The D-mode is silent in defect-free graphite and becomes active in defected graphite and also in small graphite crystallites where there could be a shortrange translational symmetry or due to the defects at the boundary of crystals [22]. The spectra were analyzed and the peak parameters for the D and G peaks were obtained, as shown in Table-
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of
I.
Table-I: Results of Raman spectroscopy analysis
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Peak position (cm-1 )
G-peak
1356 ± 0.6 1356 ± 0.8 1357 ± 0.7 1349 ± 0.8
1587 ± 0.3 1589 ± 0.3 1590 ± 0.3 1587 ± 0.4
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D-peak
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Ferrocene Concentration (mM/L) Nil 43 86 172
IG/ID
0.31 ± 0.004 0.33 ± 0.007 0.36 ± 0.006 0.49 ± 0.009
𝑳𝒂 (Å) 13 ± 0.2 14 ± 0.3 16 ± 0.3 21.7 ± 0.4
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G
D
Si
286 216
Fe2O3
240
360
480
Raman shift (cm-1)
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of
172mM/L
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86mM/L
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Intensity (a.u.)
86mM/L
389
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43mM/L
Without ferrocene
500
1000
1500
Raman shift (cm-1)
2000
Fig.1. Fitted Raman spectra of carbon black samples. Spectrum for highest ferrocene concentration (172 mM/L) shows prominent Fe2O3 modes, the signatures of iron oxide in 86mM/L sample are shown in the inset.
Journal Pre-proof The IG/ID ratio was used to determine the degree of graphitization. The corresponding graphitic crystallite size can be calculated using proportionate relationship between the lateral size of the graphitic cluster and the IG/ID ratio as per the following relation given by Tuinstra et al [23],
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𝐼𝐺 𝐿𝑎 = 𝐼𝐷 𝐶(𝜆)
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where IG and ID are intensities (area under the peak) of G and D peaks respectively, 𝐶(𝜆) ~ 44 Å for 𝜆= 515.5 nm [24-26] and the 𝐿𝑎 (Å) is the cluster size or the in-plane coherence length. The
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values of 𝐿𝑎 calculated from the above relation are tabulated in Table I.
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From the analysis of Raman spectra, we observe that the IG/ID ratio is increased from 0.31 (without additive) to 0.49 (with 172 mM/L ferrocene concentration). This corresponds to an
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increase in graphitic cluster size from ~13 to ~ 22 Å. This increase of about 80% in La is an important result of our experiments. In addition, we observed clear signatures of iron oxides in CB
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with the help of Raman spectroscopy, as marked in Fig.1 [27, 28]. The microstructures of the two CB samples are examined by transmission electron
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microscopy (TEM) and corresponding images are shown in Fig.2. We observed spherical
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particulate matter in both the samples in low-magnification images (Fig.2(a,b)), and highmagnification images (Fig.2(c,d)). In the image of the control sample (Fig.2(a)) the spherical carbon black particles stand arranged individually, but in the sample that was prepared with the highest ferrocene concentration, we observed the connecting chain of spherical CB nodes (Fig.2(b)). The individual CB particles seem to connect and form chain-like structure upon addition of the additive. In addition, the formation of graphitic clusters with straight graphitic planes can be observed after introducing ferrocene into the precursor oil. These multi-layered graphitic structures are shown in the micrograph of the Fig.2(e). In the sample with an additive concentration of 172 mM/L, multi-layer-graphene like structures are formed with a grain size of over tens of nanometers and are shown in Fig.2(f). The structure of these multiple graphene layers
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resembles
(b)
(a)
nodes
like of
multiwalled carbon nanotubes (MWCNTs) having
bamboo
structure, which
(d)
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(c)
common in CVD
of
200nm
30nm
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(f)
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(e)
70nm
d = 0.36 nm
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is
200nm
10nm
30nm
grown MWCNTs [29].
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Fig.2. Micrographs of Control sample (a), and sample with 172 mM/L ferrocene
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concentration (b) in low magnification. High magnification micrographs of these specimens are shown in (c) & (d) respectively. Presence of multi-layered graphenes (e) and bamboo
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structure of graphitic layers (f) in CB with ferrocene concentration 172 mM/L.
The presence of catalyst particles in the core of the catalytically grown CB particles is
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witnessed from chain-like structures as shown in Fig.2(d) also (marked with arrows). This
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observation is in agreement with Raman data, which shows prominent peaks corresponding to Fe2O3 in ferrocene aided samples. Whereas, at the core of non-catalytically grown CB, no iron
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oxide particles are observed, as seen in TEM image (Fig. 2(c)). Thus, it is the iron particles that
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clusters.
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appear to bring the individual carbon monomers together and help in the formation of graphitic
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@
@
@
@
@
172mM/L @
Intensity (a.u.)
@
of
86mM/L
without ferrocene
Kapton
5
10
15
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43mM/L
20
25
30
35
40
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2
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Fig.3. The XRD patterns of Kapton foil, CB without ferrocene and CBs with different amounts of ferrocene concentration. Reflections for #Kapton, *graphite (002), @Fe2O3 are
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marked.
Further, we characterized the CB with XRD experiment to get the information about constituent phases that are present, mainly about amorphous and graphitic proportions and also to get an idea about how the graphitization is varying with the concentration of precursor additive. The XRD patterns are shown in Fig.3. All the XRD patterns show a distinctive hump at low angles extending up to 2Ɵ = 20◦, and a normal region beyond that. The hump at low angles is characteristic of amorphous scattering, with a few broad peaks of low intensity overriding it. The visible overall structure of this composite hump largely remains unaffected as the concentration of catalyst additive is changed. Generally, the XRD patterns of CB consists of three diffusive peaks, which
Journal Pre-proof are (0 0 ℓ) crystalline peak (002) and two dimensional (h k) reflections (10) and (11) [30]. The XRD pattern of control sample has only (002) and (10) peaks, whereas in sample with an additive concentration of 172 mM/L, these peaks were accompanied by reflections from iron oxides as well. The strong diffraction peaks in the sample with the highest additive concentration (172 mM/L) corresponds to reflections from Fe2O3 [28, 31]. Presence of these peaks confirms the presence of an iron catalyst in the form of iron oxide in our samples. We observe that the primary results from Raman, TEM, and XRD all corroborate with each other about the enhancement of the degree of graphitization upon addition of additive in the
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precursor. We further analyzed the XRD data in order to obtain quantitative information about
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how the degree of graphitization changes as a function of the concentration of the additive. It was observed that the graphitic (002) reflection falls on the trailing edge of the low angle hump, which
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itself comes from the Kapton foil on which the samples were placed to obtain the data. Accounting
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for the intensity of the Kapton reflection was given a careful attention because the scattering from amorphous part of our sample also contributes in the same region. In order to estimate the
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background, we recorded a XRD pattern of bare Kapton film and obtained a suitable profile with multiple peaks. Then this profile was used to evaluate the low angle background in our samples
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by normalizing with respect to the intensity of the most prominent background peak at 3◦. It is important to note that this 3◦ peak is the exclusive feature from Kapton scattering and is free from
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any other prospective feature from our sample. The fitted XRD data of Kapton, control sample and
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sample with ferrocene concentration of 172 mM/L are shown in Fig.4.
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#
*
Experimental
@
@
@
@
data
@
Experimental Cumulative Fit
Without ferrocene
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ro
data
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Cumulative Fit
Experimental
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Intensity (a.u.)
@
172mM/L
Cumulative Fit
Kapton
5
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data
10
15
2
20
25
30
35
Fig.4. Fitted XRD data of Kapton foil (bottom), control sample (middle) and sample with higher ferrocene concentration (top). Reflections for #Kapton, *graphite (002), @Fe2O3 are marked. The lines with different colors indicate different fitting peaks. The experimental data and the cumulative fits are marked for each spectrum. After such accounting for the true background, we rightly found that additional intensity was present in the low angle region which could be fit to broad amorphous like peaks. We attribute this additional amorphous like scattering to the amorphous part of our samples. A prominent
Journal Pre-proof sharper peak about 2θ = 12.94 (d = 0.349 nm) is attributed to (002) reflections from graphitic planes. The intensity of this peak increases with increasing the additive in precursor and is maximum for the highest ferrocene concentration. Intensity of this peak was used to estimate the fraction of true graphitic clusters in the sample. Other sharp peaks at higher angles are from Fe2O3, as marked in Fig.4. The area of the amorphous hump in the Kapton is 4.3, whereas its area was increased to 5.3 in the control sample and to 5 in the sample with the highest ferrocene concentration. We are attributing this increase in the area of hump to the amorphous carbon that is present in our samples.
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The area of (002) reflection was found to be 0.2 and 0.3 in the control sample and sample with
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highest ferrocene concentration, respectively. From these values, we have ascertained the graphitic carbon content in the control sample and additive assisted sample by taking the ratio of the area of
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(002) reflection and the intensity from amorphous carbon (i.e. the above samples as compared to
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the area of this hump in the Kapton). The interesting feature of this analysis is that this ratio was found to be 0.2 for the control sample and 0.4 for the sample with the highest ferrocene
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concentration. This indicates that the graphitic carbon content in the produced CB is almost doubled with an increase in ferrocene concentration and clearly emphasizes the increase in
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graphitization of CB with increased concentration of ferrocene. Thermal stability of produced CB samples was studied by TGA experiments. The
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experiments were carried out on the control sample and the sample with the highest additive concentration. The differential thermo gravimetry (DTG) figures were derived from the data and
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both the TGA and DTG curves are presented in Fig.5. Air was used as a purge gas with a flow rate of roughly 100 ml/min at a ramp rate of 2℃/min. For the control sample, significant weight loss starts at ~420℃ and then, when the temperature is increased beyond 540℃, only about 2% of CB has remained. This weight loss after 400℃ can be attributed to the combustion of carbon [32] into gaseous carbon oxides. Whereas, for sample showing highest graphitization, the temperature at which the major loss starts is observed to be around 360℃ which is about 60℃ less than the former one. The iron oxide particles catalyze the oxidation of carbon and reduce the temperature at which carbon oxidizes in the air [33, 34], which explains the fall in the oxidation temperature for catalytically grown CB as compared to non-catalytically grown CB, even if it has better graphitization. This also indicates an atomically intimate contact between iron oxide and carbon
Journal Pre-proof black particles in the catalytically grown samples. This close proximity also supports ironmediated graphitic growth in our sample.
20
(a)
without ferrocene (TGA) 1st derivative of TGA
0 -20
of
Wt%
-40
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-60
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-80 -100
(b)
-10
-40
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Wt%
-20 -30
172mM/L (TGA) 1st derivative of TGA
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0
100 200 300 400 500 600 700 800 900 Temperature(C)
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0
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-120
-50 -60 0 Fig.5.
100 200 300 400 500 600 700 800 900 Temperature(C)
TGA and DTG
curves of CB grown without ferrocene (a), and with 172 mM/L ferrocene (b) in olive oil precursor.
Journal Pre-proof The presence of iron in additive assisted sample is evident from Raman spectroscopy, TEM as well as from XRD, corroborating each other. The Raman results show an increase in IG/ID ratio and increase in graphitic crystallite size with the increase in ferrocene concentration. The percolating carbonaceous structures and formation of multilayered graphene upon ferrocene addition are realized from TEM images. The sharpening of (002) peak with the increase in ferrocene concentration is observed from XRD patterns, which in turn says that the graphitization of produced CB is increasing upon an increase in additive concentration. During the synthesis, we did not change any parameter other than the introduction of iron-
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based additive in precursor oil. Hence, from the above results, it is clearly established that the iron
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due to ferrocene decomposition is playing a key role in the enhancement of graphitic order. Before we objectively look into the possible mechanism of enhanced graphitization, we
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need to revisit the mechanism of formation of CB from the lamp black process. In general, it is
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known that the yellow flame temperature in oil lamps is about 1000-1200C [35] at which the decomposition of the precursor takes place but the combustion of the resultant carbon is
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incomplete. Therefore, the free carbon species condense into the form of soot, more suitably known as CB in the present context. These carbon species may consist of mono-atomic or multi-
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atomic clusters but for the sake of convenience, we call them monomers. Interestingly, these free monomers condense in the form of CB during their transit within the flame and the deposition of
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CB on a surface is nothing more than the collection of these CB particles. The purpose of this discussion is to suggest that once the precursor is thermally decomposed, there are only carbon
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monomers and no memory of the original organic precursor/fuel is left. Hence, the quality of the CB is similar, provided the combustion is performed at similar flame conditions, not much affected by the choice of the precursor oil/fuel. However, when a catalyst is introduced, things do change. We can understand from the above discussion that the transit time of reactants within a flame is enough for the carbon monomers to nucleate an amorphous cluster which grows into a spherical amorphous CB particle having a diameter of about a few tens of nanometers. Given this, clearly in the similar flame conditions, the residence time should be enough for a catalytic agent to affect the mechanism of the reorganization of un-oxidized carbon monomers into a solid form which is energetically more stable. And it is no surprise that this stable form is that of graphite, which is the ground state configuration of elemental carbon.
Journal Pre-proof From our results, we observed clear signatures of iron oxides in CB with the help of Raman spectroscopy, as marked in Fig.1. Among all the specimens, we observed the most prominent vibrational features of Fe2O3 for the highest additive concentration (172 mM/L) sample. Successively weaker signatures of Fe2O3 are present in Raman spectra of other samples with an additive concentration of 86 and 43 mM/L (see inset of Fig. 1). Not only in Raman data but we also found the presence of iron oxides from electron diffraction from the samples derived using ferrocene (Fig. 6(b)), whereas these were absent in the control sample (Fig. 6(a)). The reflections from Fe2O3 are marked/indexed in circles (Fig. 6(b)) and match well with the literature [36]. These
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findings corroborate our findings from the Raman spectroscopy. These observations indicate
(b)
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(a)
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towards a certain role of iron in catalyzing the graphitization of CB.
1/ (0.04nm)
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1/ (0.04nm)
Fig.6. Electron diffraction patterns of carbon black derived without ferrocene (a) and with 172 mM/L ferrocene (b) in olive oil. The Fe2O3 reflections are encircled in (b). It is known that transition metals (Fe, No, Co) are widely used for the growth of carbon nanostructures [37]. This is because they aid in catalytic decomposition of organic precursors and provide a pathway for the formation of sp2 – hybridized layered network from carbon atoms via mechanisms like e.g. the vapor-liquid-solid route [37]. Iron is probably the most used among the transition metal catalysts in CNT growth. This can be associated to a higher affinity of iron to carbon as compared to other transition metals [38].
Journal Pre-proof In our case, the iron atoms form clusters within the flame and facilitate a catalyst for the formation of graphitic clusters using carbon monomers which are generated in their vicinity. Considering the catalytic association between iron and carbon atoms, we propose that the wellknown vapor-liquid-solid (VLS) mechanism for catalytic CVD growth of carbon nanotubes is also working in the present case when the iron nanoparticles and carbon monomers come in contact with each other, the carbon atoms dissolve and diffuse into iron particles. After reaching the solubility limit of carbon atoms in iron nanoparticles, they will precipitate out and form the graphitic clusters. This mechanism is similar to the growth mechanism of carbon nanotubes
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(CNTs) which are sp2 networks of carbon using iron particles as catalysts [39, 40]. In the case of
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preparation of CNTs, the reaction takes place inside the CVD chamber for around 20 minutes duration in vacuum. However, there could be two possible reasons for the synthesis of short, rather
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than long tubular graphitic structures in our samples. First, there is a very short travel time between the flame and the substrate. This may not be sufficient for the formation of longer structures that
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would look like CNTs. Second, since the experiment was held in the ambient atmosphere, the iron
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particles will get oxidized and their catalytic activity ceases quickly. Due to these reasons, small but well-graphitized clusters of CB are formed. The same reason could be responsible for the
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presence of amorphous carbon (a-C) shell around the iron oxide particles in TEM images (Fig.2b) making a core-shell structure. As soon as iron is formed from ferrocene decomposition in the flame, the iron particles could capture the carbon monomers in their vicinity and catalyze them
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into graphitic clusters only as long as the iron is not oxidized. However, if some of the iron particles
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are oxidized before they catalyze graphitic carbon, their catalytic activity no longer exists. As a result, these particles act only as nucleation centers for a-C deposition and a core/shell (Fe2O3/aC) CB particles are formed. The presence of iron oxide form strongly suggests that the oxidation of catalytic iron seems to be the main limiting factor in further growth of graphitic cluster in size. Thus, the present results indicate that the iron acts as a catalyst and promotes the formation of graphitic clusters in CB prepared by the lamp black process. As the concentration of ferrocene is raised, the graphitic order increases as a result of the increase in the number of available catalytic iron particles. As a result more number of carbon monomers catalytically convert into graphitic clusters. Conclusion:
Journal Pre-proof In the present work, for the first time, we synthesized carbon black with increased graphitization in a controlled way using ferrocene as organometallic additive via catalytic graphitization. The degree of graphitization was almost doubled and the corresponding graphitic cluster size (La) was increased from ~13 Å to ~22 Å. We found the presence of well-grown multilayered-graphitic clusters in the catalyst promoted samples, whereas these were absent in noncatalytically grown samples. The role of iron in promoting graphitization was confirmed using XRD as well, which confirms that the graphitic carbon content in the additive assisted sample is ~2 times greater than that in the non-catalyzed sample. Oxidation of iron catalyst is found to be
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the main limiting factor in size restriction of graphitic clusters.
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Conflicts of Interest:
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There are no conflicts to declare. Acknowledgments:
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measurements and help in the analysis.
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References: [1]
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Authors would like to thank Dr. P. K. Aji Kumar, IGCAR, Kalpakkam for the TGA
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Highlights:
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Ferrocene/olive oil based synthesis of carbon black (CB) via lampblack route. Graphitization of CB increased through ferrocene derived iron as catalyst. IG/ID ratio in Raman spectra of CB increases from 0.31 to 0.49. XRD shows Graphite/amorphous carbon ratio increases by 2 upon catalyst use. Multilayered graphene as well as graphitic bamboo-like structures were observed.
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Surakanti Srinivas Reddy, A.K. Sinha, G. Amarendra, N.V. Chandra Shekar, G.M. Bhalerao PII:
S0925-9635(19)30474-1
DOI:
https://doi.org/10.1016/j.diamond.2019.107539
Reference:
DIAMAT 107539
To appear in:
Diamond & Related Materials
Received date:
16 July 2019
Revised date:
23 August 2019
Accepted date:
9 September 2019
Please cite this article as: S.S. Reddy, A.K. Sinha, G. Amarendra, et al., Enhancement of graphitic order in carbon black using precursor additive, Diamond & Related Materials (2019), https://doi.org/10.1016/j.diamond.2019.107539
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© 2019 Published by Elsevier.
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Enhancement of graphitic order in carbon black using precursor additive Surakanti Srinivas Reddy1, 2, A.K.Sinha3, G. Amarendra4, N. V. Chandra Shekar1, 5 G.M.Bhalerao1* 1
UGC-DAE CSR Kalpakkam Node, Kokilamedu, T.N. - 603104, India
2
University of Madras, Chennai, Tamilnadu, 60005, India
3
HXAL, Synchrotron Utilization Section, Raja Ramanna Center for Advanced Technology, HBNI, Indore-
452001, M.P, India 4
Materials Science Group, IGCAR, HBNI, Kalpakkam, T.N. - 603102, India
5
India
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*Email: [email protected]
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Condensed Matter Physics Division, Materials Science Group, IGCAR, HBNI, Kalpakkam, T.N-603102,
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Abstract:
Our present work is aimed at increasing the degree of graphitization of carbon black during the
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synthesis stage itself. For this purpose, we used lamp black route to synthesize carbon black via catalytic graphitization using ferrocene as an organometallic additive into the precursor olive oil.
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Degree of graphitization was estimated using Raman spectroscopy and microstructure was determined using transmission electron microscopy (TEM). We found that the degree of
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graphitization as quantified by the Raman spectroscopy could be doubled by changing the concentration of ferrocene into the precursor oil. The TEM images show the presence of multi-
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layer graphenes, a few tens of nanometers large, which were completely absent when no additive
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was used. It is proposed that iron plays the role of graphitization enhancer as Raman, TEM and XRay diffraction (XRD) measurements show the presence of iron compounds in the product. Oxidation of iron catalyst mainly limits further growth of graphitic clusters. Keywords: Carbon Black, Raman Spectroscopy, Graphitization, Transmission electron microscopy. Introduction: Allotropes of graphitic carbon have a wide range of properties which can be usefully explored in a broad spectrum of applications. To give a few examples, graphene is found to be very useful as a catalyst support material in the field of single-atom catalysts [1], nanocatalysts [2], and heterogeneous catalysts [3,4], owing to its capabilities of high support area, preventing catalyst
Journal Pre-proof particle agglomeration, and support to oxygen reduction reactions, among others. Carbon foams are used in water purification, sensors, and energy storage devices [5]. Carbon coated iron oxide hybrids can be used as a lithium-ion anode in battery applications [6]. The difference in the properties of these materials originates from their structure, as well as the degree of graphitization in their structure. Carbon black (CB) also comes under this class as it consists of sp2 hybridized carbon particles and belongs to a class of turbostratic graphitic structure. The particle size of CB ranges from 10 to 1000 nm [7]. In crystalline graphite, the graphene layers are stacked in the perpendicular
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direction to c-axis in an AB-stacking arrangement. In turbostratic graphite there is no stacking
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order between adjacent layers and the interlayer space is larger than that for crystalline graphite [8]. Carbon black is widely used in rubbers and tyres as reinforcing fillers [9], and the daily life
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products such as inks, paints, plastics, adhesives, and ceramics contain the CB in them [10]. These
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are being used to reinforce the polymer to make electrically conductive composites which have potential application in Electromagnetic interference (EMI) shielding materials [11, 12]. They also
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find use in Li-ion batteries and in the fabrication of foldable and flexible devices on paper due to their electrical and mechanical properties [13, 14]. In EMI applications, CB containing polymeric
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materials shield the EMI by absorbing and dissipating the electromagnetic fields due to good electric conducting property of CB [12].
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Among many physical aspects of CBs, electrical conductivity is the key property which determines its usefulness in many of its applications. Electrical conductivity itself improves upon
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better graphitization. There are several methods in use to synthesize CB which includes Furnace black, Thermal black, Lamp black, Acetylene black and Channel black [10, 15]. CB produced from these methods differs in average particle size and structure/graphitization. However a suitable method can be chosen to produce CB with the desired structure, it is useful to further improve the graphitization. Thus, the quantity of CB in the composites could be minimized. Increase in the degree of graphitization of amorphous carbon has been reported in some previous studies by using activation process [16] and thermal annealing [17]. But at the same time, we do not witness much work towards controlling the graphitization during the synthesis itself. In the present work, our aim is to increase the graphitization of CB in a simple process called lamp black process by introducing organometallic additives into the precursor oil. We prepared CB
Journal Pre-proof nanoparticles by Lamp black process for its simplicity, low cost, and environment-friendly approach. The produced CB samples are then characterized by thermo gravimetric analysis (TGA), Raman spectroscopy, transmission electron microscopy (TEM) and X-Ray diffraction (XRD). Experimental: Commercially available olive oil was used as combustion precursor and varying amounts of ferrocene was added. Oleic acid is found to be very helpful in producing monodisperse nanoparticles and in controlling the particle size during the synthesis process [18]. Oleic acid
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which exhibits excellent surfactant property in organometallics-based syntheses, is an ingredient of olive oil and therefore it is also expected to blend well with the organometallic additives, which
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is the scheme of the present study. Ferrocene (Alfa Aesar – 99%) is an organometallic compound of iron and gives free iron upon thermal decomposition which acts as a catalyst for graphitic growth
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[19, 20], and is widely used for the synthesis of carbon nanotubes [19, 21]. The control sample
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was prepared by the combustion of olive oil without ferrocene. A series of samples were prepared using ferrocene as an additive with a concentration of 43, 86 and 172 mM/L respectively. CB was
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obtained by depositing combustion CB on to glass slides. These CB nanoparticles were then dispersed in propanol by ultra-sonication and deposited on to silicon wafers for Raman
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spectroscopy measurements. Raman spectroscopy is one of the most suitable and reliable technique for a quantitative assessment of graphitization in amorphous carbon, carbon
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nanostructures and other sp2 hybridized carbons [22]. Therefore, Raman spectroscopy was performed for quantitative characterization at room temperature using M/S Renishaw - InVia
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Raman spectrometer with 514 nm Ar laser as an excitation source. TEM measurements were carried out at 200 kV in order to analyze the microstructure using M/S Carl Zeiss - Libra 200HR machine. Thermal gravimetry analysis (TGA) was performed to investigate thermal oxidation behavior of the samples that are produced with and without ferrocene using M/S SETSYS-16/18 (setaram) device. C-constituent phases of CB were estimated from XRD analysis using 15.7535keV photons at Angle Dispersive X-ray Diffraction (ADXRD) beam line (BL-12) of the Indian synchrotron radiation source Indus-2 at RRCAT, Indore. XRD data were taken in transmission mode by sandwiching powder sample between Kapton foils. The scattering due to Kapton was subtracted from the XRD pattern of the samples for quantitative analysis.
Journal Pre-proof Results and discussion: Raman spectra of the samples are shown in Fig. 1. Spectra of all samples exhibit Gmode around 1600 cm-1 and the D-mode around 1350 cm-1, which is typical of the sp2 hybridized carbons [22]. The G-mode is attributed to the ‘in-plane’ vibrations, whereas disorder or defect in this lattice gives rise to the D-mode. The D-mode is silent in defect-free graphite and becomes active in defected graphite and also in small graphite crystallites where there could be a shortrange translational symmetry or due to the defects at the boundary of crystals [22]. The spectra were analyzed and the peak parameters for the D and G peaks were obtained, as shown in Table-
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of
I.
Table-I: Results of Raman spectroscopy analysis
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Peak position (cm-1 )
G-peak
1356 ± 0.6 1356 ± 0.8 1357 ± 0.7 1349 ± 0.8
1587 ± 0.3 1589 ± 0.3 1590 ± 0.3 1587 ± 0.4
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D-peak
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Ferrocene Concentration (mM/L) Nil 43 86 172
IG/ID
0.31 ± 0.004 0.33 ± 0.007 0.36 ± 0.006 0.49 ± 0.009
𝑳𝒂 (Å) 13 ± 0.2 14 ± 0.3 16 ± 0.3 21.7 ± 0.4
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G
D
Si
286 216
Fe2O3
240
360
480
Raman shift (cm-1)
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172mM/L
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86mM/L
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Intensity (a.u.)
86mM/L
389
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43mM/L
Without ferrocene
500
1000
1500
Raman shift (cm-1)
2000
Fig.1. Fitted Raman spectra of carbon black samples. Spectrum for highest ferrocene concentration (172 mM/L) shows prominent Fe2O3 modes, the signatures of iron oxide in 86mM/L sample are shown in the inset.
Journal Pre-proof The IG/ID ratio was used to determine the degree of graphitization. The corresponding graphitic crystallite size can be calculated using proportionate relationship between the lateral size of the graphitic cluster and the IG/ID ratio as per the following relation given by Tuinstra et al [23],
of
𝐼𝐺 𝐿𝑎 = 𝐼𝐷 𝐶(𝜆)
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where IG and ID are intensities (area under the peak) of G and D peaks respectively, 𝐶(𝜆) ~ 44 Å for 𝜆= 515.5 nm [24-26] and the 𝐿𝑎 (Å) is the cluster size or the in-plane coherence length. The
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values of 𝐿𝑎 calculated from the above relation are tabulated in Table I.
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From the analysis of Raman spectra, we observe that the IG/ID ratio is increased from 0.31 (without additive) to 0.49 (with 172 mM/L ferrocene concentration). This corresponds to an
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increase in graphitic cluster size from ~13 to ~ 22 Å. This increase of about 80% in La is an important result of our experiments. In addition, we observed clear signatures of iron oxides in CB
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with the help of Raman spectroscopy, as marked in Fig.1 [27, 28]. The microstructures of the two CB samples are examined by transmission electron
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microscopy (TEM) and corresponding images are shown in Fig.2. We observed spherical
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particulate matter in both the samples in low-magnification images (Fig.2(a,b)), and highmagnification images (Fig.2(c,d)). In the image of the control sample (Fig.2(a)) the spherical carbon black particles stand arranged individually, but in the sample that was prepared with the highest ferrocene concentration, we observed the connecting chain of spherical CB nodes (Fig.2(b)). The individual CB particles seem to connect and form chain-like structure upon addition of the additive. In addition, the formation of graphitic clusters with straight graphitic planes can be observed after introducing ferrocene into the precursor oil. These multi-layered graphitic structures are shown in the micrograph of the Fig.2(e). In the sample with an additive concentration of 172 mM/L, multi-layer-graphene like structures are formed with a grain size of over tens of nanometers and are shown in Fig.2(f). The structure of these multiple graphene layers
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resembles
(b)
(a)
nodes
like of
multiwalled carbon nanotubes (MWCNTs) having
bamboo
structure, which
(d)
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(c)
common in CVD
of
200nm
30nm
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(f)
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(e)
70nm
d = 0.36 nm
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is
200nm
10nm
30nm
grown MWCNTs [29].
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Fig.2. Micrographs of Control sample (a), and sample with 172 mM/L ferrocene
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concentration (b) in low magnification. High magnification micrographs of these specimens are shown in (c) & (d) respectively. Presence of multi-layered graphenes (e) and bamboo
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structure of graphitic layers (f) in CB with ferrocene concentration 172 mM/L.
The presence of catalyst particles in the core of the catalytically grown CB particles is
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witnessed from chain-like structures as shown in Fig.2(d) also (marked with arrows). This
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observation is in agreement with Raman data, which shows prominent peaks corresponding to Fe2O3 in ferrocene aided samples. Whereas, at the core of non-catalytically grown CB, no iron
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oxide particles are observed, as seen in TEM image (Fig. 2(c)). Thus, it is the iron particles that
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clusters.
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appear to bring the individual carbon monomers together and help in the formation of graphitic
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@
@
@
@
@
172mM/L @
Intensity (a.u.)
@
of
86mM/L
without ferrocene
Kapton
5
10
15
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43mM/L
20
25
30
35
40
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2
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Fig.3. The XRD patterns of Kapton foil, CB without ferrocene and CBs with different amounts of ferrocene concentration. Reflections for #Kapton, *graphite (002), @Fe2O3 are
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marked.
Further, we characterized the CB with XRD experiment to get the information about constituent phases that are present, mainly about amorphous and graphitic proportions and also to get an idea about how the graphitization is varying with the concentration of precursor additive. The XRD patterns are shown in Fig.3. All the XRD patterns show a distinctive hump at low angles extending up to 2Ɵ = 20◦, and a normal region beyond that. The hump at low angles is characteristic of amorphous scattering, with a few broad peaks of low intensity overriding it. The visible overall structure of this composite hump largely remains unaffected as the concentration of catalyst additive is changed. Generally, the XRD patterns of CB consists of three diffusive peaks, which
Journal Pre-proof are (0 0 ℓ) crystalline peak (002) and two dimensional (h k) reflections (10) and (11) [30]. The XRD pattern of control sample has only (002) and (10) peaks, whereas in sample with an additive concentration of 172 mM/L, these peaks were accompanied by reflections from iron oxides as well. The strong diffraction peaks in the sample with the highest additive concentration (172 mM/L) corresponds to reflections from Fe2O3 [28, 31]. Presence of these peaks confirms the presence of an iron catalyst in the form of iron oxide in our samples. We observe that the primary results from Raman, TEM, and XRD all corroborate with each other about the enhancement of the degree of graphitization upon addition of additive in the
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precursor. We further analyzed the XRD data in order to obtain quantitative information about
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how the degree of graphitization changes as a function of the concentration of the additive. It was observed that the graphitic (002) reflection falls on the trailing edge of the low angle hump, which
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itself comes from the Kapton foil on which the samples were placed to obtain the data. Accounting
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for the intensity of the Kapton reflection was given a careful attention because the scattering from amorphous part of our sample also contributes in the same region. In order to estimate the
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background, we recorded a XRD pattern of bare Kapton film and obtained a suitable profile with multiple peaks. Then this profile was used to evaluate the low angle background in our samples
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by normalizing with respect to the intensity of the most prominent background peak at 3◦. It is important to note that this 3◦ peak is the exclusive feature from Kapton scattering and is free from
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any other prospective feature from our sample. The fitted XRD data of Kapton, control sample and
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sample with ferrocene concentration of 172 mM/L are shown in Fig.4.
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#
*
Experimental
@
@
@
@
data
@
Experimental Cumulative Fit
Without ferrocene
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data
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Cumulative Fit
Experimental
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Intensity (a.u.)
@
172mM/L
Cumulative Fit
Kapton
5
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data
10
15
2
20
25
30
35
Fig.4. Fitted XRD data of Kapton foil (bottom), control sample (middle) and sample with higher ferrocene concentration (top). Reflections for #Kapton, *graphite (002), @Fe2O3 are marked. The lines with different colors indicate different fitting peaks. The experimental data and the cumulative fits are marked for each spectrum. After such accounting for the true background, we rightly found that additional intensity was present in the low angle region which could be fit to broad amorphous like peaks. We attribute this additional amorphous like scattering to the amorphous part of our samples. A prominent
Journal Pre-proof sharper peak about 2θ = 12.94 (d = 0.349 nm) is attributed to (002) reflections from graphitic planes. The intensity of this peak increases with increasing the additive in precursor and is maximum for the highest ferrocene concentration. Intensity of this peak was used to estimate the fraction of true graphitic clusters in the sample. Other sharp peaks at higher angles are from Fe2O3, as marked in Fig.4. The area of the amorphous hump in the Kapton is 4.3, whereas its area was increased to 5.3 in the control sample and to 5 in the sample with the highest ferrocene concentration. We are attributing this increase in the area of hump to the amorphous carbon that is present in our samples.
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The area of (002) reflection was found to be 0.2 and 0.3 in the control sample and sample with
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highest ferrocene concentration, respectively. From these values, we have ascertained the graphitic carbon content in the control sample and additive assisted sample by taking the ratio of the area of
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(002) reflection and the intensity from amorphous carbon (i.e. the above samples as compared to
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the area of this hump in the Kapton). The interesting feature of this analysis is that this ratio was found to be 0.2 for the control sample and 0.4 for the sample with the highest ferrocene
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concentration. This indicates that the graphitic carbon content in the produced CB is almost doubled with an increase in ferrocene concentration and clearly emphasizes the increase in
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graphitization of CB with increased concentration of ferrocene. Thermal stability of produced CB samples was studied by TGA experiments. The
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experiments were carried out on the control sample and the sample with the highest additive concentration. The differential thermo gravimetry (DTG) figures were derived from the data and
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both the TGA and DTG curves are presented in Fig.5. Air was used as a purge gas with a flow rate of roughly 100 ml/min at a ramp rate of 2℃/min. For the control sample, significant weight loss starts at ~420℃ and then, when the temperature is increased beyond 540℃, only about 2% of CB has remained. This weight loss after 400℃ can be attributed to the combustion of carbon [32] into gaseous carbon oxides. Whereas, for sample showing highest graphitization, the temperature at which the major loss starts is observed to be around 360℃ which is about 60℃ less than the former one. The iron oxide particles catalyze the oxidation of carbon and reduce the temperature at which carbon oxidizes in the air [33, 34], which explains the fall in the oxidation temperature for catalytically grown CB as compared to non-catalytically grown CB, even if it has better graphitization. This also indicates an atomically intimate contact between iron oxide and carbon
Journal Pre-proof black particles in the catalytically grown samples. This close proximity also supports ironmediated graphitic growth in our sample.
20
(a)
without ferrocene (TGA) 1st derivative of TGA
0 -20
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Wt%
-40
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(b)
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Wt%
-20 -30
172mM/L (TGA) 1st derivative of TGA
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0
100 200 300 400 500 600 700 800 900 Temperature(C)
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0
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-120
-50 -60 0 Fig.5.
100 200 300 400 500 600 700 800 900 Temperature(C)
TGA and DTG
curves of CB grown without ferrocene (a), and with 172 mM/L ferrocene (b) in olive oil precursor.
Journal Pre-proof The presence of iron in additive assisted sample is evident from Raman spectroscopy, TEM as well as from XRD, corroborating each other. The Raman results show an increase in IG/ID ratio and increase in graphitic crystallite size with the increase in ferrocene concentration. The percolating carbonaceous structures and formation of multilayered graphene upon ferrocene addition are realized from TEM images. The sharpening of (002) peak with the increase in ferrocene concentration is observed from XRD patterns, which in turn says that the graphitization of produced CB is increasing upon an increase in additive concentration. During the synthesis, we did not change any parameter other than the introduction of iron-
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based additive in precursor oil. Hence, from the above results, it is clearly established that the iron
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due to ferrocene decomposition is playing a key role in the enhancement of graphitic order. Before we objectively look into the possible mechanism of enhanced graphitization, we
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need to revisit the mechanism of formation of CB from the lamp black process. In general, it is
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known that the yellow flame temperature in oil lamps is about 1000-1200C [35] at which the decomposition of the precursor takes place but the combustion of the resultant carbon is
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incomplete. Therefore, the free carbon species condense into the form of soot, more suitably known as CB in the present context. These carbon species may consist of mono-atomic or multi-
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atomic clusters but for the sake of convenience, we call them monomers. Interestingly, these free monomers condense in the form of CB during their transit within the flame and the deposition of
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CB on a surface is nothing more than the collection of these CB particles. The purpose of this discussion is to suggest that once the precursor is thermally decomposed, there are only carbon
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monomers and no memory of the original organic precursor/fuel is left. Hence, the quality of the CB is similar, provided the combustion is performed at similar flame conditions, not much affected by the choice of the precursor oil/fuel. However, when a catalyst is introduced, things do change. We can understand from the above discussion that the transit time of reactants within a flame is enough for the carbon monomers to nucleate an amorphous cluster which grows into a spherical amorphous CB particle having a diameter of about a few tens of nanometers. Given this, clearly in the similar flame conditions, the residence time should be enough for a catalytic agent to affect the mechanism of the reorganization of un-oxidized carbon monomers into a solid form which is energetically more stable. And it is no surprise that this stable form is that of graphite, which is the ground state configuration of elemental carbon.
Journal Pre-proof From our results, we observed clear signatures of iron oxides in CB with the help of Raman spectroscopy, as marked in Fig.1. Among all the specimens, we observed the most prominent vibrational features of Fe2O3 for the highest additive concentration (172 mM/L) sample. Successively weaker signatures of Fe2O3 are present in Raman spectra of other samples with an additive concentration of 86 and 43 mM/L (see inset of Fig. 1). Not only in Raman data but we also found the presence of iron oxides from electron diffraction from the samples derived using ferrocene (Fig. 6(b)), whereas these were absent in the control sample (Fig. 6(a)). The reflections from Fe2O3 are marked/indexed in circles (Fig. 6(b)) and match well with the literature [36]. These
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findings corroborate our findings from the Raman spectroscopy. These observations indicate
(b)
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(a)
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towards a certain role of iron in catalyzing the graphitization of CB.
1/ (0.04nm)
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1/ (0.04nm)
Fig.6. Electron diffraction patterns of carbon black derived without ferrocene (a) and with 172 mM/L ferrocene (b) in olive oil. The Fe2O3 reflections are encircled in (b). It is known that transition metals (Fe, No, Co) are widely used for the growth of carbon nanostructures [37]. This is because they aid in catalytic decomposition of organic precursors and provide a pathway for the formation of sp2 – hybridized layered network from carbon atoms via mechanisms like e.g. the vapor-liquid-solid route [37]. Iron is probably the most used among the transition metal catalysts in CNT growth. This can be associated to a higher affinity of iron to carbon as compared to other transition metals [38].
Journal Pre-proof In our case, the iron atoms form clusters within the flame and facilitate a catalyst for the formation of graphitic clusters using carbon monomers which are generated in their vicinity. Considering the catalytic association between iron and carbon atoms, we propose that the wellknown vapor-liquid-solid (VLS) mechanism for catalytic CVD growth of carbon nanotubes is also working in the present case when the iron nanoparticles and carbon monomers come in contact with each other, the carbon atoms dissolve and diffuse into iron particles. After reaching the solubility limit of carbon atoms in iron nanoparticles, they will precipitate out and form the graphitic clusters. This mechanism is similar to the growth mechanism of carbon nanotubes
of
(CNTs) which are sp2 networks of carbon using iron particles as catalysts [39, 40]. In the case of
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preparation of CNTs, the reaction takes place inside the CVD chamber for around 20 minutes duration in vacuum. However, there could be two possible reasons for the synthesis of short, rather
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than long tubular graphitic structures in our samples. First, there is a very short travel time between the flame and the substrate. This may not be sufficient for the formation of longer structures that
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would look like CNTs. Second, since the experiment was held in the ambient atmosphere, the iron
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particles will get oxidized and their catalytic activity ceases quickly. Due to these reasons, small but well-graphitized clusters of CB are formed. The same reason could be responsible for the
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presence of amorphous carbon (a-C) shell around the iron oxide particles in TEM images (Fig.2b) making a core-shell structure. As soon as iron is formed from ferrocene decomposition in the flame, the iron particles could capture the carbon monomers in their vicinity and catalyze them
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into graphitic clusters only as long as the iron is not oxidized. However, if some of the iron particles
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are oxidized before they catalyze graphitic carbon, their catalytic activity no longer exists. As a result, these particles act only as nucleation centers for a-C deposition and a core/shell (Fe2O3/aC) CB particles are formed. The presence of iron oxide form strongly suggests that the oxidation of catalytic iron seems to be the main limiting factor in further growth of graphitic cluster in size. Thus, the present results indicate that the iron acts as a catalyst and promotes the formation of graphitic clusters in CB prepared by the lamp black process. As the concentration of ferrocene is raised, the graphitic order increases as a result of the increase in the number of available catalytic iron particles. As a result more number of carbon monomers catalytically convert into graphitic clusters. Conclusion:
Journal Pre-proof In the present work, for the first time, we synthesized carbon black with increased graphitization in a controlled way using ferrocene as organometallic additive via catalytic graphitization. The degree of graphitization was almost doubled and the corresponding graphitic cluster size (La) was increased from ~13 Å to ~22 Å. We found the presence of well-grown multilayered-graphitic clusters in the catalyst promoted samples, whereas these were absent in noncatalytically grown samples. The role of iron in promoting graphitization was confirmed using XRD as well, which confirms that the graphitic carbon content in the additive assisted sample is ~2 times greater than that in the non-catalyzed sample. Oxidation of iron catalyst is found to be
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the main limiting factor in size restriction of graphitic clusters.
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Conflicts of Interest:
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There are no conflicts to declare. Acknowledgments:
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measurements and help in the analysis.
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Authors would like to thank Dr. P. K. Aji Kumar, IGCAR, Kalpakkam for the TGA
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Highlights:
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Ferrocene/olive oil based synthesis of carbon black (CB) via lampblack route. Graphitization of CB increased through ferrocene derived iron as catalyst. IG/ID ratio in Raman spectra of CB increases from 0.31 to 0.49. XRD shows Graphite/amorphous carbon ratio increases by 2 upon catalyst use. Multilayered graphene as well as graphitic bamboo-like structures were observed.
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