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Hierarchically structured carbon-carbon nanocomposites: The preparation aspects
Composites Communications 7 (2018) 65–68
Contents lists available at ScienceDirect
Composites Communications journal homepage: www.elsevier.com/locate/coco
Hierarchically structured carbon-carbon nanocomposites: The preparation aspects
T
⁎
Irina V. Krasnikovaa,b, Ilya V. Mishakova,c, Aleksey A. Vedyagina,c, , Pavel V. Krivoshapkind, Denis V. Korneeve a
Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russian Federation Center for Electrochemical Energy Storage, Skolkovo Institute of Science and Technology, Moscow, Russian Federation c National Research Tomsk Polytechnic University, Tomsk, Russian Federation d Research and Educational Center of Chemical Engineering and Biotechnology, ITMO University, Saint-Petersburg, Russian Federation e State Research Center of Virology and Biotechnology, Novosibirsk, Russian Federation b
A R T I C L E I N F O
A B S T R A C T
Keywords: Carbon-carbon nanocomposite Hierarchical structure Catalytic chemical vapor deposition Nickel catalyst
The hierarchically structured carbon-carbon nanocomposites represent carbon microfibers covered with a layer of carbon nanomaterials. Having properties of both micro- and nano-level, such nanocomposites demonstrate perspectives in polymer reinforcement, membrane technologies and catalysis. The synthesis of the carboncarbon nanocomposites with controlled properties is a challenging task. This paper describes effect of catalyst deposition technique on the properties of hierarchically structured carbon-carbon nanocomposites. The synthesized samples were analyzed by XRD, SEM, TEM and BET. It was shown how the way of catalyst deposition affects both the yield and structure of the carbon nanofibers grown on the microfiber surface.
1. Introduction The hierarchically structured carbon-carbon nanocomposites represent a new class of materials consisting of carbon nanostructures deposited on the surface of carbon microfibers. The shape of the nanocomposites is determined by the microfiber (discrete fibers, thread or fabrics), while surface properties mainly depend on the nanoscale component of the composite (carbon nanotubes (CNT), nanofibers (CNF) or fullerenes). These materials considered to be promising in polymer reinforcement [1], membrane technologies [2] and catalysis [3]. As an example, addition of the carbon-carbon nanocomposites into polymers leads to 50% improvement of materials strength [4]. The nanocomposite CNF/’activated carbon fabric’ is known to be effective in adsorption of phenol and lead [2]. As we have recently reported, the metal particles anchored on the CNF/ACF composite provide superior catalytic performance due to the stabilization of the active component in a disperse state [5]. Usually, catalytic chemical vapor deposition (CCVD) is used for the synthesis of the carbon nanostructures. Various hydrocarbons can be decomposed on metals of iron subgroup (Ni, Fe, Co). Being versatile, CCVD remains rather complicated technique – the product of synthesis depends on a set of parameters such as nature and composition of the catalyst, type of the hydrocarbon, temperature and duration of the
⁎
process [6]. Synthesis of the carbon nanomaterials in the form of powders is well described in literature, while the design of hierarchically structured carbon-carbon nanocomposites with pre-determined properties is still required to be investigated. In this paper, we continue the step-by-step study on the impact of CCVD parameters on the properties of hierarchically structured carboncarbon nanocomposites. We have already shown that carbon source and catalyst composition influence both the carbon yield and the structure [7], while the nature of microfiber affects the carbon yield and the strength of CNF anchorage [8]. The scope of the present paper is elucidation of the impact of the catalyst deposition technique on the properties of the carbon-carbon nanocomposites. The methods based on an incipient wetness impregnation were used since they are considered as well controllable and easy-to-scale ones [8,9]. 2. Experimental Chopped carbon microfibers UKN-M 5000 (LLC “Argon”, Russia) of 5.6 μm in diameter were used as a framework (marked as CMF). A precursor of an active component (Ni) was deposited on the surface of microfibers via an incipient wetness impregnation according to three different routes followed by the thermal treatment procedure:
Corresponding author at: Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russian Federation. E-mail address: [email protected] (A.A. Vedyagin).
https://doi.org/10.1016/j.coco.2018.01.002 Received 20 December 2017; Received in revised form 16 January 2018; Accepted 17 January 2018 2452-2139/ © 2018 Elsevier Ltd. All rights reserved.
Composites Communications 7 (2018) 65–68
I.V. Krasnikova et al.
1. Impregnation with aqueous solution of nickel nitrate Ni (NO3)2·6H2O. The sample is labeled as Ni/CMF(imp). 2. Deposition of freshly prepared Ni(OH)2 (obtained by reaction of Ni (NO3)2 with NH4OH). CMF was impregnated with calculated amount of Ni(OH)2 dispersion. The sample is designated as Ni/CMF (dep). 3. Surface precipitation of Ni(OH)2. Firstly, CMF were impregnated with aqueous solution of nickel nitrate Ni(NO3)2·6H2O, then Ni (OH)2 was precipitated on the surface of the microfiber by adding NH4OH. The sample is labeled as Ni/CMF(prec).
Table 1 Coherent scattering regions for NiO and Ni particles, and average diameter of CNF obtained via CCVD of C2H4 at 600 °C. N
1 2 3
Amount of metal loading was calculated to be 2.5 wt% and then was controlled by weighing of ash residual after combustion of the sample in air. The synthesis of the hierarchically structured carbon-carbon nanocomposites (Ni/CNF/CMF) was carried out by CCVD of ethylene at 600 °C in a gravimetric flow setup equipped with McBain balance according the standard procedure with preliminary reduction [7]. The setup allows studying the kinetics of the carbon deposition in a real time regime. Х-ray diffraction (XRD) analysis of the samples was performed on a DRON-RM4 diffractometer using CuKα radiation with a wavelength of 1.54178 Å and a step of 0.05°. The phases were identified by comparison with JCPDS Powder Diffraction File data. The average crystallite size (coherent scattering region, CSR) was calculated using the Scherrer equation [10]. The microstructure of the prepared samples was examined by scanning electron microscopy (SEM) using a JSM 6460 instrument (Jeol, Japan) with magnifications from 8× to 300.000× and transmission electron microscopy (TEM) on a JEM 1400 microscope (Jeol, Japan) operated at 80 kV. Specific surface area (SSA) of the samples was determined by a lowtemperature nitrogen adsorption (BET method) using an ASAP 2400 instrument (Micromeritics, USA).
Catalyst
Ni/CMF(imp) Ni/CMF(dep) Ni/CMF (prec)
CSR, nm
Average CNF diameter, nm
Before reduction
After reduction
16 13 10
54 48 41
52 86 103
of corresponding oxides takes place under the used conditions. Appearance of the peaks assigned to an oxide phase after reduction in H2 is accounted for the contact of nickel with air during the sample passivation. The results of CSR calculation are shown in Table 1. As seen, the average crystallite size of NiO phase before reduction was 16, 13 and 10 nm for Ni/CMF(imp), Ni/CMF(dep) and Ni/CMF(prec), respectively. The reduction procedure leads to an enlargement of the crystallite sizes for Ni phase being formed due to the sintering process, which takes place in a hydrogen atmosphere. General trend is that CSR of Ni in metallic state is two times higher than that of NiO which is thought to be resulted from agglomeration of the catalyst particles occurring due to their high mobility on the carbon microfiber surface [11]. The sizes after the reduction were 54, 48 and 41 nm, correspondingly. Taking into account that the accuracy of calculations lies in a range of 10–20%, it can be concluded that the average crystallite size of NiO and Ni does not practically depend on the catalyst deposition technique. The kinetic studies revealed that the catalytic behavior of the samples is different (Fig. 2). Decomposition of ethylene on Ni/CMF (imp) resulted in the highest yield of CNF (193%). Ni/CMF(prec) and Ni/CMF(dep) samples show 92% and 73%, respectively (Fig. 2, curves 2 and 3). Note that all samples were completely deactivated after relatively short period of time (15–20 min). Since XRD data revealed no significant differences in a phase composition of the samples, their different catalytic behavior can be explained in terms of the CNF structure. Fig. 3 presents SEM images of the hierarchically structured carbon-carbon nanocomposites with comparable values of the carbon yield. As clearly seen from Fig. 3, the samples differ significantly in a diameter distribution. Thus, Ni/CMF(imp) gives relatively narrow distribution (d = 20 - 100 nm), which corresponds to the crystalline size of Ni particles after reduction (Table 1). Oppositely, both Ni/CMF(dep) and Ni/CMF(prec) produce nanocomposites with CNF diameters up to 600 nm. The average CNF diameters significantly exceed the CSR values for reduced Ni particles (Table 1), which might be explained by their
3. Results and discussion Prior to the synthesis of the hierarchically structured carbon-carbon nanocomposites, the catalyst precursors (Ni(NO3)2 or Ni(OH)2) were heated in air (350 °C for nitrates and 360 °C for hydroxides, 30 min) and then reduced in a hydrogen flow (600 °C, 15 min). At each step, XRD analysis was used to control the composition of the samples (Fig. 1). XRD patterns for the sample obtained by impregnation with aqueous solution of nickel nitrate Ni(NO3)2·6H2O are given in [8]. XRD data confirm that the total decomposition of the precursors with formation
Fig. 1. XRD patterns for the samples obtained via deposition of freshly prepared Ni(OH)2 (1, 2) and surface precipitation of Ni(OH)2 (3, 4): 1, 3 – after calcination; 2, 4 – after reduction in H2 and passivation in O2/Ar mixture.
Fig. 2. Kinetics of carbon growth on 1 – Ni/CMF(imp), 2 – Ni/CMF(prec) and 3 – Ni/CMF (dep) samples.
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I.V. Krasnikova et al.
Fig. 4. TEM data for the CNF obtained over: a – Ni/CMF(imp); b – Ni/CMF(prec).
Table 2 Effect of the catalyst deposition technique on the textural properties of the hierarchically structured carbon-carbon nanocomposites. Fig. 3. Effect of the catalyst deposition technique on the structure and size distribution of the carbon nanofibers (CNF yield ~ 20%): a – Ni/CMF(imp); b – Ni/CMF(dep); c – Ni/ CMF(prec).
weaker interaction with the surface of carbon microfibers that facilitates their migration and further agglomeration. It should be also noted that the CNF with larger diameters are characterized by more ‘fluffy’ structure, as it follows from TEM data shown in Fig. 4. Nanocomposite obtained over Ni/CMF(prec) contains large amount of segmented carbon fibers (Fig. 4b) with highly defective structure. In the case of Ni/ CMF(imp), the fibers of so-called ‘feathery’ morphology are well seen (Fig. 4a). Structural type of CNF influences the textural properties as well. Table 2 summarizes the corresponding data. Note that the pristine carbon microfiber has rather smooth surface (0.3 m2/g). In order to compare the samples with different morphology of CNF, the experiments on their synthesis were stopped while achieving the yield value
N
Catalyst
Y C, %
SSA, m2/g
Vp, cm3/g
Dp, Å
S*, m2/gC
1 2 3
Ni/CMF(imp) Ni/CMF(dep) Ni/CMF(prec)
24 24 21
25 21 84
0.05 0.05 0.18
155 96 87
130 110 485
YC – value of the carbon nanofibers yield, when the experiment was stopped; S* – surface area normalized to CNF yield.
of about 20%. In general case, deposition of CNF increases SSA up to two orders of magnitude. Despite the largest thickness within the prepared fibers, the carbon-carbon nanocomposite with segmented structure is characterized with the most developed surface area among the prepared samples. It indicates that the defining role for SSA value of CNF is played by a compactness of graphite layers inside the fiber. Considering that increase in SSA is caused by the carbon nanofibers only, one can recalculate the SSA values in relation to the weight fraction of CNF (the last column in Table 2). The obtained results are in
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I.V. Krasnikova et al.
good agreement with literature data for the CNF powders, where segmented fibers were shown to have SSA of about 400 m2/g [12,13].
University Competitiveness Enhancement Program (grant VIU-TOVPM316/2017).
4. Conclusions
References
The hierarchically structured carbon-carbon nanocomposites have been synthesized using different catalyst deposition techniques (impregnation with aqueous solution of nickel nitrate, deposition of freshly prepared hydroxide, and precipitation of hydroxide on the surface of CMF). Nanocomposites prepared after impregnation with nitrate showed relatively narrow diameter distribution of CNF (20 – 100 nm), while other samples were characterized by wide distribution (up to 600 nm). Additionally, the Ni/CMF(imp) sample allowed us to achieve the highest yield of CNF of 193%. The Ni/CMF(prec) and Ni/CMF(dep) samples gave 92% and 73% of carbon yield, respectively. The observed difference in catalytic behavior of the samples was shown to be independent from the phase composition of the catalytic particles. Most likely, the size of nickel particles is a key parameter defining the properties of the resulted carbon nanofibers. Finally, it can be concluded that use of the impregnation/precipitation techniques opens a new possibilities for the synthesis of the hierarchically structured carbon-carbon nanocomposites with developed surface area, which are of a great demand in modern catalytic and separation membrane technologies. The choice of the preparation route should be made in relation to desired morphological, textural and mechanical characteristics.
[1] E.S. Petukhova, M.E. Savvinova, I.V. Krasnikova, I.V. Mishakov, A.A. Okhlopkova, D.-Y. Jeong, J.-H. Cho, Reinforcement of polyethylene pipes with modified carbon microfibers, J. Korean Chem. Soc. 60 (2016) 177–180. [2] A. Chakraborty, D. Deva, A. Sharma, N. Verma, Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water, J. Colloid. Interface Sci. 359 (2011) 228–239. [3] S. Zarubova, S. Rane, J. Yang, Y. Yu, Y. Zhu, D. Chen, A. Holmen, Fischer–Tropsch synthesis on hierarchically structured cobalt nanoparticle/carbon nanofiber/carbon felt composites, ChemSusChem 4 (2011) 935–942. [4] H. Qian, E.S. Greenhalgh, M.S.P. Shaffer, A. Bismarck, Carbon nanotube-based hierarchical composites: a review, J. Mater. Chem. 20 (2010) 4751–4762. [5] E.A. Ponomareva, I.V. Krasnikova, E.V. Egorova, I.V. Mishakov, A.A. Vedyagin, Dehydrogenation of ethanol over carbon-supported Cu–Co catalysts modified by catalytic chemical vapor deposition, React. Kinet. Mech. Catal. 122 (2017) 399–408. [6] V. Jourdain, C. Bichara, Current understanding of the growth of carbon nanotubes in catalytic chemical vapour deposition, Carbon 58 (2013) 2–39. [7] I.V. Tokareva, I.V. Mishakov, D.V. Korneev, A.A. Vedyagin, K.S. Golokhvast, Nanostructuring of the carbon macrofiber surface, Nanotechnol. Russ. 10 (2015) 158–164. [8] I.V. Krasnikova, I.V. Mishakov, A.A. Vedyagin, Y.I. Bauman, D.V. Korneev, Surface modification of microfibrous materials with nanostructured carbon, Mater. Chem. Phys. 186 (2017) 220–227. [9] J.R.H. Ross, Heterogeneous Catalysis, Elsevier, Oxford, 2012. [10] B.D. Cullity, Elements of X-ray Diffraction, Second ed., Addison-Wesley, Reading, MA, 1978. [11] E. Kowalewski, I.I. Kamińska, G. Słowik, D. Lisovytskiy, A. Śrębowata, Effect of metal precursor and pretreatment conditions on the catalytic activity of Ni/C in the aqueous phase hydrodechlorination of 1,1,2-trichloroethene, React. Kinet. Mech. Catal. 121 (2017) 3–16. [12] I.V. Mishakov, R.A. Buyanov, V.I. Zaikovskii, I.A. Strel’tsov, A.A. Vedyagin, Catalytic synthesis of nanosized feathery carbon structures via the carbide cycle mechanism, Kinet. Catal. 49 (2008) 868–872. [13] J.H. Zhou, Z.J. Sui, P. Li, D. Chen, Y.-C. Dai, W.-K. Yuan, Structural characterization of carbon nanofibers formed from different carbon-containing gases, Carbon 44 (2006) 3255–3262.
Acknowledgements This work was supported by Foundation of Innovation Assistance (project U.M.N.I.K. 2–16-5; agreement #12255GU2/2016, signed 16.08.2017). The experimental calculations were carried out at Tomsk Polytechnic University within the framework of Tomsk Polytechnic
68
Contents lists available at ScienceDirect
Composites Communications journal homepage: www.elsevier.com/locate/coco
Hierarchically structured carbon-carbon nanocomposites: The preparation aspects
T
⁎
Irina V. Krasnikovaa,b, Ilya V. Mishakova,c, Aleksey A. Vedyagina,c, , Pavel V. Krivoshapkind, Denis V. Korneeve a
Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russian Federation Center for Electrochemical Energy Storage, Skolkovo Institute of Science and Technology, Moscow, Russian Federation c National Research Tomsk Polytechnic University, Tomsk, Russian Federation d Research and Educational Center of Chemical Engineering and Biotechnology, ITMO University, Saint-Petersburg, Russian Federation e State Research Center of Virology and Biotechnology, Novosibirsk, Russian Federation b
A R T I C L E I N F O
A B S T R A C T
Keywords: Carbon-carbon nanocomposite Hierarchical structure Catalytic chemical vapor deposition Nickel catalyst
The hierarchically structured carbon-carbon nanocomposites represent carbon microfibers covered with a layer of carbon nanomaterials. Having properties of both micro- and nano-level, such nanocomposites demonstrate perspectives in polymer reinforcement, membrane technologies and catalysis. The synthesis of the carboncarbon nanocomposites with controlled properties is a challenging task. This paper describes effect of catalyst deposition technique on the properties of hierarchically structured carbon-carbon nanocomposites. The synthesized samples were analyzed by XRD, SEM, TEM and BET. It was shown how the way of catalyst deposition affects both the yield and structure of the carbon nanofibers grown on the microfiber surface.
1. Introduction The hierarchically structured carbon-carbon nanocomposites represent a new class of materials consisting of carbon nanostructures deposited on the surface of carbon microfibers. The shape of the nanocomposites is determined by the microfiber (discrete fibers, thread or fabrics), while surface properties mainly depend on the nanoscale component of the composite (carbon nanotubes (CNT), nanofibers (CNF) or fullerenes). These materials considered to be promising in polymer reinforcement [1], membrane technologies [2] and catalysis [3]. As an example, addition of the carbon-carbon nanocomposites into polymers leads to 50% improvement of materials strength [4]. The nanocomposite CNF/’activated carbon fabric’ is known to be effective in adsorption of phenol and lead [2]. As we have recently reported, the metal particles anchored on the CNF/ACF composite provide superior catalytic performance due to the stabilization of the active component in a disperse state [5]. Usually, catalytic chemical vapor deposition (CCVD) is used for the synthesis of the carbon nanostructures. Various hydrocarbons can be decomposed on metals of iron subgroup (Ni, Fe, Co). Being versatile, CCVD remains rather complicated technique – the product of synthesis depends on a set of parameters such as nature and composition of the catalyst, type of the hydrocarbon, temperature and duration of the
⁎
process [6]. Synthesis of the carbon nanomaterials in the form of powders is well described in literature, while the design of hierarchically structured carbon-carbon nanocomposites with pre-determined properties is still required to be investigated. In this paper, we continue the step-by-step study on the impact of CCVD parameters on the properties of hierarchically structured carboncarbon nanocomposites. We have already shown that carbon source and catalyst composition influence both the carbon yield and the structure [7], while the nature of microfiber affects the carbon yield and the strength of CNF anchorage [8]. The scope of the present paper is elucidation of the impact of the catalyst deposition technique on the properties of the carbon-carbon nanocomposites. The methods based on an incipient wetness impregnation were used since they are considered as well controllable and easy-to-scale ones [8,9]. 2. Experimental Chopped carbon microfibers UKN-M 5000 (LLC “Argon”, Russia) of 5.6 μm in diameter were used as a framework (marked as CMF). A precursor of an active component (Ni) was deposited on the surface of microfibers via an incipient wetness impregnation according to three different routes followed by the thermal treatment procedure:
Corresponding author at: Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russian Federation. E-mail address: [email protected] (A.A. Vedyagin).
https://doi.org/10.1016/j.coco.2018.01.002 Received 20 December 2017; Received in revised form 16 January 2018; Accepted 17 January 2018 2452-2139/ © 2018 Elsevier Ltd. All rights reserved.
Composites Communications 7 (2018) 65–68
I.V. Krasnikova et al.
1. Impregnation with aqueous solution of nickel nitrate Ni (NO3)2·6H2O. The sample is labeled as Ni/CMF(imp). 2. Deposition of freshly prepared Ni(OH)2 (obtained by reaction of Ni (NO3)2 with NH4OH). CMF was impregnated with calculated amount of Ni(OH)2 dispersion. The sample is designated as Ni/CMF (dep). 3. Surface precipitation of Ni(OH)2. Firstly, CMF were impregnated with aqueous solution of nickel nitrate Ni(NO3)2·6H2O, then Ni (OH)2 was precipitated on the surface of the microfiber by adding NH4OH. The sample is labeled as Ni/CMF(prec).
Table 1 Coherent scattering regions for NiO and Ni particles, and average diameter of CNF obtained via CCVD of C2H4 at 600 °C. N
1 2 3
Amount of metal loading was calculated to be 2.5 wt% and then was controlled by weighing of ash residual after combustion of the sample in air. The synthesis of the hierarchically structured carbon-carbon nanocomposites (Ni/CNF/CMF) was carried out by CCVD of ethylene at 600 °C in a gravimetric flow setup equipped with McBain balance according the standard procedure with preliminary reduction [7]. The setup allows studying the kinetics of the carbon deposition in a real time regime. Х-ray diffraction (XRD) analysis of the samples was performed on a DRON-RM4 diffractometer using CuKα radiation with a wavelength of 1.54178 Å and a step of 0.05°. The phases were identified by comparison with JCPDS Powder Diffraction File data. The average crystallite size (coherent scattering region, CSR) was calculated using the Scherrer equation [10]. The microstructure of the prepared samples was examined by scanning electron microscopy (SEM) using a JSM 6460 instrument (Jeol, Japan) with magnifications from 8× to 300.000× and transmission electron microscopy (TEM) on a JEM 1400 microscope (Jeol, Japan) operated at 80 kV. Specific surface area (SSA) of the samples was determined by a lowtemperature nitrogen adsorption (BET method) using an ASAP 2400 instrument (Micromeritics, USA).
Catalyst
Ni/CMF(imp) Ni/CMF(dep) Ni/CMF (prec)
CSR, nm
Average CNF diameter, nm
Before reduction
After reduction
16 13 10
54 48 41
52 86 103
of corresponding oxides takes place under the used conditions. Appearance of the peaks assigned to an oxide phase after reduction in H2 is accounted for the contact of nickel with air during the sample passivation. The results of CSR calculation are shown in Table 1. As seen, the average crystallite size of NiO phase before reduction was 16, 13 and 10 nm for Ni/CMF(imp), Ni/CMF(dep) and Ni/CMF(prec), respectively. The reduction procedure leads to an enlargement of the crystallite sizes for Ni phase being formed due to the sintering process, which takes place in a hydrogen atmosphere. General trend is that CSR of Ni in metallic state is two times higher than that of NiO which is thought to be resulted from agglomeration of the catalyst particles occurring due to their high mobility on the carbon microfiber surface [11]. The sizes after the reduction were 54, 48 and 41 nm, correspondingly. Taking into account that the accuracy of calculations lies in a range of 10–20%, it can be concluded that the average crystallite size of NiO and Ni does not practically depend on the catalyst deposition technique. The kinetic studies revealed that the catalytic behavior of the samples is different (Fig. 2). Decomposition of ethylene on Ni/CMF (imp) resulted in the highest yield of CNF (193%). Ni/CMF(prec) and Ni/CMF(dep) samples show 92% and 73%, respectively (Fig. 2, curves 2 and 3). Note that all samples were completely deactivated after relatively short period of time (15–20 min). Since XRD data revealed no significant differences in a phase composition of the samples, their different catalytic behavior can be explained in terms of the CNF structure. Fig. 3 presents SEM images of the hierarchically structured carbon-carbon nanocomposites with comparable values of the carbon yield. As clearly seen from Fig. 3, the samples differ significantly in a diameter distribution. Thus, Ni/CMF(imp) gives relatively narrow distribution (d = 20 - 100 nm), which corresponds to the crystalline size of Ni particles after reduction (Table 1). Oppositely, both Ni/CMF(dep) and Ni/CMF(prec) produce nanocomposites with CNF diameters up to 600 nm. The average CNF diameters significantly exceed the CSR values for reduced Ni particles (Table 1), which might be explained by their
3. Results and discussion Prior to the synthesis of the hierarchically structured carbon-carbon nanocomposites, the catalyst precursors (Ni(NO3)2 or Ni(OH)2) were heated in air (350 °C for nitrates and 360 °C for hydroxides, 30 min) and then reduced in a hydrogen flow (600 °C, 15 min). At each step, XRD analysis was used to control the composition of the samples (Fig. 1). XRD patterns for the sample obtained by impregnation with aqueous solution of nickel nitrate Ni(NO3)2·6H2O are given in [8]. XRD data confirm that the total decomposition of the precursors with formation
Fig. 1. XRD patterns for the samples obtained via deposition of freshly prepared Ni(OH)2 (1, 2) and surface precipitation of Ni(OH)2 (3, 4): 1, 3 – after calcination; 2, 4 – after reduction in H2 and passivation in O2/Ar mixture.
Fig. 2. Kinetics of carbon growth on 1 – Ni/CMF(imp), 2 – Ni/CMF(prec) and 3 – Ni/CMF (dep) samples.
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Fig. 4. TEM data for the CNF obtained over: a – Ni/CMF(imp); b – Ni/CMF(prec).
Table 2 Effect of the catalyst deposition technique on the textural properties of the hierarchically structured carbon-carbon nanocomposites. Fig. 3. Effect of the catalyst deposition technique on the structure and size distribution of the carbon nanofibers (CNF yield ~ 20%): a – Ni/CMF(imp); b – Ni/CMF(dep); c – Ni/ CMF(prec).
weaker interaction with the surface of carbon microfibers that facilitates their migration and further agglomeration. It should be also noted that the CNF with larger diameters are characterized by more ‘fluffy’ structure, as it follows from TEM data shown in Fig. 4. Nanocomposite obtained over Ni/CMF(prec) contains large amount of segmented carbon fibers (Fig. 4b) with highly defective structure. In the case of Ni/ CMF(imp), the fibers of so-called ‘feathery’ morphology are well seen (Fig. 4a). Structural type of CNF influences the textural properties as well. Table 2 summarizes the corresponding data. Note that the pristine carbon microfiber has rather smooth surface (0.3 m2/g). In order to compare the samples with different morphology of CNF, the experiments on their synthesis were stopped while achieving the yield value
N
Catalyst
Y C, %
SSA, m2/g
Vp, cm3/g
Dp, Å
S*, m2/gC
1 2 3
Ni/CMF(imp) Ni/CMF(dep) Ni/CMF(prec)
24 24 21
25 21 84
0.05 0.05 0.18
155 96 87
130 110 485
YC – value of the carbon nanofibers yield, when the experiment was stopped; S* – surface area normalized to CNF yield.
of about 20%. In general case, deposition of CNF increases SSA up to two orders of magnitude. Despite the largest thickness within the prepared fibers, the carbon-carbon nanocomposite with segmented structure is characterized with the most developed surface area among the prepared samples. It indicates that the defining role for SSA value of CNF is played by a compactness of graphite layers inside the fiber. Considering that increase in SSA is caused by the carbon nanofibers only, one can recalculate the SSA values in relation to the weight fraction of CNF (the last column in Table 2). The obtained results are in
67
Composites Communications 7 (2018) 65–68
I.V. Krasnikova et al.
good agreement with literature data for the CNF powders, where segmented fibers were shown to have SSA of about 400 m2/g [12,13].
University Competitiveness Enhancement Program (grant VIU-TOVPM316/2017).
4. Conclusions
References
The hierarchically structured carbon-carbon nanocomposites have been synthesized using different catalyst deposition techniques (impregnation with aqueous solution of nickel nitrate, deposition of freshly prepared hydroxide, and precipitation of hydroxide on the surface of CMF). Nanocomposites prepared after impregnation with nitrate showed relatively narrow diameter distribution of CNF (20 – 100 nm), while other samples were characterized by wide distribution (up to 600 nm). Additionally, the Ni/CMF(imp) sample allowed us to achieve the highest yield of CNF of 193%. The Ni/CMF(prec) and Ni/CMF(dep) samples gave 92% and 73% of carbon yield, respectively. The observed difference in catalytic behavior of the samples was shown to be independent from the phase composition of the catalytic particles. Most likely, the size of nickel particles is a key parameter defining the properties of the resulted carbon nanofibers. Finally, it can be concluded that use of the impregnation/precipitation techniques opens a new possibilities for the synthesis of the hierarchically structured carbon-carbon nanocomposites with developed surface area, which are of a great demand in modern catalytic and separation membrane technologies. The choice of the preparation route should be made in relation to desired morphological, textural and mechanical characteristics.
[1] E.S. Petukhova, M.E. Savvinova, I.V. Krasnikova, I.V. Mishakov, A.A. Okhlopkova, D.-Y. Jeong, J.-H. Cho, Reinforcement of polyethylene pipes with modified carbon microfibers, J. Korean Chem. Soc. 60 (2016) 177–180. [2] A. Chakraborty, D. Deva, A. Sharma, N. Verma, Adsorbents based on carbon microfibers and carbon nanofibers for the removal of phenol and lead from water, J. Colloid. Interface Sci. 359 (2011) 228–239. [3] S. Zarubova, S. Rane, J. Yang, Y. Yu, Y. Zhu, D. Chen, A. Holmen, Fischer–Tropsch synthesis on hierarchically structured cobalt nanoparticle/carbon nanofiber/carbon felt composites, ChemSusChem 4 (2011) 935–942. [4] H. Qian, E.S. Greenhalgh, M.S.P. Shaffer, A. Bismarck, Carbon nanotube-based hierarchical composites: a review, J. Mater. Chem. 20 (2010) 4751–4762. [5] E.A. Ponomareva, I.V. Krasnikova, E.V. Egorova, I.V. Mishakov, A.A. Vedyagin, Dehydrogenation of ethanol over carbon-supported Cu–Co catalysts modified by catalytic chemical vapor deposition, React. Kinet. Mech. Catal. 122 (2017) 399–408. [6] V. Jourdain, C. Bichara, Current understanding of the growth of carbon nanotubes in catalytic chemical vapour deposition, Carbon 58 (2013) 2–39. [7] I.V. Tokareva, I.V. Mishakov, D.V. Korneev, A.A. Vedyagin, K.S. Golokhvast, Nanostructuring of the carbon macrofiber surface, Nanotechnol. Russ. 10 (2015) 158–164. [8] I.V. Krasnikova, I.V. Mishakov, A.A. Vedyagin, Y.I. Bauman, D.V. Korneev, Surface modification of microfibrous materials with nanostructured carbon, Mater. Chem. Phys. 186 (2017) 220–227. [9] J.R.H. Ross, Heterogeneous Catalysis, Elsevier, Oxford, 2012. [10] B.D. Cullity, Elements of X-ray Diffraction, Second ed., Addison-Wesley, Reading, MA, 1978. [11] E. Kowalewski, I.I. Kamińska, G. Słowik, D. Lisovytskiy, A. Śrębowata, Effect of metal precursor and pretreatment conditions on the catalytic activity of Ni/C in the aqueous phase hydrodechlorination of 1,1,2-trichloroethene, React. Kinet. Mech. Catal. 121 (2017) 3–16. [12] I.V. Mishakov, R.A. Buyanov, V.I. Zaikovskii, I.A. Strel’tsov, A.A. Vedyagin, Catalytic synthesis of nanosized feathery carbon structures via the carbide cycle mechanism, Kinet. Catal. 49 (2008) 868–872. [13] J.H. Zhou, Z.J. Sui, P. Li, D. Chen, Y.-C. Dai, W.-K. Yuan, Structural characterization of carbon nanofibers formed from different carbon-containing gases, Carbon 44 (2006) 3255–3262.
Acknowledgements This work was supported by Foundation of Innovation Assistance (project U.M.N.I.K. 2–16-5; agreement #12255GU2/2016, signed 16.08.2017). The experimental calculations were carried out at Tomsk Polytechnic University within the framework of Tomsk Polytechnic
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