- Email: [email protected]
Facile synthesis of graphitic mesoporous carbon materials from sucrose
Diamond & Related Materials 95 (2019) 1–4
Contents lists available at ScienceDirect
Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Facile synthesis of graphitic mesoporous carbon materials from sucrose a
Jianxiao Yang , Songlin Zuo
b,⁎
T
a College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University, Changsha 410082, China b College of Chemical Engineering, Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing 210037, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Sucrose Catalytic carbonization Porous carbon Mesopore Graphitization
A one-step catalytic carbonization approach has been developed to prepare graphitic mesoporous carbon, using iron (III) nitrate as the graphitization catalyst and the template for creating pores. The porosity, degree of graphitization, and morphology of the resultant carbon products have been investigated as a function of the carbonization temperature and the dosage of iron (III) nitrate. The results showed that graphitic mesoporous carbon with a Brunauer–Emmett–Teller surface area of 198 m2/g and a high degree of graphitization was prepared at a carbonization temperature of 700 °C with a molar ratio of iron (III) nitrate to sucrose of 1.0. Moreover, a small amount of carbon nanotubes could be observed in the graphitic mesoporous carbon. The origin of the mesopores and the formation of graphitic carbon are discussed in terms of the evolution of CO2, CO, H2, and CH4, produced during the carbonization process.
1. Introduction Porous carbon materials with a high degree of graphitization have attracted a great deal of attention for their potential application as electrocatalytic supports due to their good electrical conductivities and highly developed pore structures [1]. Recently, Fuertes and co-workers [2,3] synthesized graphitic mesoporous carbon materials by a hydrothermal synthetic method from sawdust, saccharides, and cellulose in the presence of various metal salts; a subsequent oxidation step with potassium permanganate served to remove disordered carbon from the carbonized samples. On the other hand, some more costly methods for preparing graphitic porous carbon materials, such as laser evaporation [4], arc discharge [5], and chemical vapor deposition [6], have also been explored. Although these methods can provide carbon materials with graphitic structures and low surface area, the synthetic methods are quite complicated. In fact, the preparation of graphitic porous carbon materials generally involves two synthetic steps: pore creation and graphitization. Pores in carbon materials can be created by impregnating carbonaceous precursors with metal salts [7]; a graphitic structure can subsequently be obtained under the heterogeneous catalysis of metal salts at relatively low temperatures [8–10]. Therefore, in this work, we have developed a simple one-step synthetic method for fabricating graphitic mesoporous carbon, using a high loading of metal salt as both the graphitization catalyst and a template for pore creation, based on this synthetic strategy [11–13]. In addition, the origin of the
⁎
mesopores and formation of the graphitic structure have been investigated by analyzing the gases evolved during the catalytic carbonization process. 2. Experimental 2.1. Preparation of materials To prepare graphitic porous carbon, sucrose (C12H22O11, analytical grade; 20.0 g) and iron (III) nitrate (Fe(NO3)3·9H2O, analytical grade) were mixed in deionized water (100 mL) in molar ratios ranging from 0.5 to 2. Each mixture was stirred at 80 °C in a water bath until it became a metal/sucrose composite paste. Subsequent carbonization of the composite was carried out in a tubular furnace under nitrogen atmosphere. The gases produced during the carbonization of sucrose were analyzed online using a Shimadzu GC 2014 gas chromatograph with a thermal conductivity detector. The carbonized samples thus obtained were washed with 6 mol/L aqueous HCl and copious deionized water to eliminate the metal particles that were formed during the carbonization. The final products, obtained in powder form, were then oven-dried at 120 °C for 24 h. The densities of the products, as measured in a 10 mL cylinder, were in the range 0.30–0.34 g/cm3. Samples were milled and sieved to obtain the final product particles of size < 74 μm. The samples obtained after removing the metal particles are denoted as C-X-Y; those prepared before removing the metal particles are denoted as C/Fe-X-Y,
Corresponding author. E-mail address: [email protected] (S. Zuo).
https://doi.org/10.1016/j.diamond.2019.03.018 Received 10 January 2019; Received in revised form 26 March 2019; Accepted 26 March 2019 Available online 27 March 2019 0925-9635/ © 2019 Elsevier B.V. All rights reserved.
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
where X is the carbonization temperature and Y is the molar ratio of iron (III) nitrate to sucrose.
Table 1 Structural parameters of the graphitic mesoporous carbons. Sample
d002(nm)
g
DBJH(nm)
SBET(m2/g)
Vtot(cm3/g)
Vmes/ Vtot(%)
Graphite C-700-0 C/Fe-700-1 C-700-1 C-800-0.5 C-800-1 C-800-2
0.3354 – – 0.3370 0.3394 0.3370 0.3370
1 – – 0.81 0.53 0.81 0.81
– 10.1 11.6 10.2 10.8 10.4 15.1
– 310 102 198 217 145 68
– 0.18 0.27 0.44 0.57 0.33 0.24
– 15.6 95.4 94.3 98.4 97.3 97.9
2.2. Characterization X-ray diffraction (XRD) patterns were obtained on a Shimadzu XRD 6000 diffractometer operating at 40 kV and 30 mA using Cu-Kα1 radiation (λ = 0.154056 nm). Data were collected between 10° and 90° at a scanning speed of 0.05°/s. The interplanar distance (d002) was calculated by applying Bragg's equation to the (002) diffraction peak, and the parameter (g) expressing the degree of graphitization of the carbon material was obtained by applying the equation g = (0.344 – d002) / 0.0086 [14]. Transmission electron microscopy (TEM) was conducted with a JEM 2100 instrument operating at 200 kV. Nitrogen adsorption was performed at −196 °C with a Micromeritics ASAP 2020 apparatus. Brunauer–Emmett–Teller surface areas (SBET) were deduced from the nitrogen adsorption isotherm in the relative pressure range 0.03–0.30. The average pore size (DBJH) was determined from the nitrogen adsorption isotherm using the Barrett–Joyner–Halenda model. The total pore volume (Vtot) was obtained by converting the amount of nitrogen adsorbed at P/P0 = 0.99 to the volume of liquid nitrogen. The mesopore volume (Vmes) was obtained as the total pore volume (Vtot) minus the micropore volume (Vmic), which was obtained by the t-plot method.
The “–” denoted that the samples were without characterization and the data were not obtained.
(Table 1). This was because an increase in the iron (III) nitrate loading with respect to sucrose led to an increase in the size of the metal oxide particles produced by its decomposition during carbonization, and the pores that originated from the voids occupied by the metal oxide particles continuously widened [15]. Eventually, some of the pores became so wide that they no longer made any contribution to nitrogen adsorption, thereby resulting in decreases in the amount of nitrogen adsorbed (Fig. 1) and in the SBET and pore volume (Table 1) with increasing dosage of iron (III) nitrate. In order to discuss the origin of the mesopores, nitrogen adsorption–desorption isotherms of the samples C-700-0 prepared without adding iron (III) nitrate and C/Fe-700-1 obtained before removing metal particles in the carbonized sucrose are shown in Fig. 2. The nitrogen adsorption isotherm of sample C-700-0 conformed to type I, indicative of a prevalence of micropores in the resultant carbon (Fig. 2). Its Vmes/Vtot was only 15.6% (Table 1). However, the nitrogen adsorption isotherms of sample C-700-1 exhibited obvious hysteresis loops and a high adsorption uptake at P/P0 > 0.9. Its Vmes/Vtot reached 94.3%. This difference suggested that the catalytic carbonization of sucrose by iron (III) nitrate produced a large amount of mesopores at the expense of micropores, resulting in a decrease of SBET from 310 m2/g to 198 m2/g (Table 1). Furthermore, comparing samples C/ Fe-700-1 and C-700-1 obtained before and after the removal of metal particles in the carbonized sucrose, it can be seen that they both have a high value of Vmes/Vtot up to around 95% and exhibit similar hysteresis loops in their adsorption–desorption isotherms. However, the SBET and Vtot were significantly increased from 102 m2/g and 0.27 cm3/g to 198 m2/g and 0.44 cm3/g, respectively (Table 1), after removal of the metal particles in the carbonized sucrose. Specifically, their Vmes and Vmic were increased from 0.257 cm3/g and 0.013 cm3/g for C/Fe-700-1 to 0.404 cm3/g and 0.036 cm3/g for C-700-1, respectively. This implies
3. Results and discussion 3.1. Pore development Nitrogen adsorption–desorption isotherms of the samples are shown in Fig. 1. The pore parameters calculated from the adsorption isotherms are listed in Table 1. It can be seen that the nitrogen adsorption–desorption isotherms of the samples are of type IV and exhibit a hysteresis loop associated with capillary condensation. All of the samples adsorbed only a small amount of nitrogen at P/P0 < 0.01 (Fig. 1). Their average pore widths were > 10 nm, and their Vmes/Vtot values were in excess of 94% (Table 1). These results suggested that a mesopore structure with low microporosity was developed in the porous carbon materials due to the high molar ratio of iron(III) nitrate to sucrose used. This was confirmed by the fact that the nitrogen adsorption isotherms (Fig. 1) exhibited obvious hysteresis loops and a high adsorption uptake at P/P0 > 0.9. Fig. 1 and Table 1 show that the carbonization temperature and iron (III) nitrate loading had a significant influence on pore development. The SBET of the sample decreased from 217 to 68 m2/g and Vtot decreased from 0.57 to 0.24 cm3/g with increasing dosage of the metal
Fig. 1. Nitrogen adsorption isotherms of the prepared porous carbon materials.
Fig. 2. Nitrogen adsorption isotherms of the prepared carbonized samples. 2
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
Fig. 3. XRD patterns of graphitic mesoporous carbon materials prepared at (A) different carbonization temperatures and (B) with different molar ratios of iron(III) nitrate to sucrose.
development due to their low content in the final products (Fig. 4). Similar nanostructures have previously been reported in carbon products prepared by carbonization of metal-impregnated polymeric gels [14], by arc discharge [17], and by thermal chemical vapor deposition of hydrocarbons over metal particles [18]. Comparison of the TEM images of the samples (Fig. 4) implied that the carbonization temperature and the metal loading influenced the carbon nanostructure morphologies.
that the pores that originated from voids occupied by iron particles were principally mesopores. Therefore, it can be concluded that the metal particles formed here during the carbonization of sucrose could function as a template for creating mesopores. 3.2. Graphitization The XRD patterns of the prepared samples are presented in Fig. 3. The carbon samples exhibited a well-resolved (002) diffraction peak at 2θ = 26°, which was significantly intensified on increasing the carbonization temperature (Fig. 3A) or increasing the dosage of iron (III) nitrate (Fig. 3B). The values of d002 spacing and the graphitization degree parameter (g) are also summarized in Table 1. The values of d002 spacing are seen to be in the range 0.3370–0.3394 nm, close to the value of 0.3354 nm for pure graphite and less than that of 0.344 nm for disordered carbon materials [16]. These observations suggest that the porous carbon materials have an ordered carbon framework. A comparison between the XRD pattern of sample C-800-0 (Fig. 3B) and the other samples reveals that the iron nanoparticles could significantly catalyze the graphitization of sucrose at a carbonization temperature as low as 700 °C with an equimolar dosage of iron (III) nitrate, and that the catalysis was promoted by an increased dosage of iron (III) nitrate. Therefore, a graphitic porous carbon (sample C-700-1) with a high surface area of 198 m2/g and a high degree of graphitization could be obtained using a molar ratio of iron (III) nitrate to sucrose of 1 as the catalyst and template.
3.4. Gas products Fig. 5 shows the evolution of gases, namely CO2, H2, CH4, and CO, during the preparation of samples C-700-1 and C-700-0 in order to provide some information on the catalytic carbonization of sucrose. It can be seen from Fig. 5 that the addition of iron (III) nitrate significantly lowered the temperature at which the release of CO2 and CO commenced, further confirming its catalytic effect on the carbonization of sucrose. Moreover, in the presence of iron (III) nitrate, the amount of CO2 was significantly increased, whereas the amounts of the reductive gases CO, H2, and CH4 were significantly decreased, accompanied by a decrease in the yield of the final product from 21.4% for sample C-7000 to 10.5% for C-700-1. These observations are indicative of reactions between iron oxides and the reductive substances produced during the carbonization of sucrose. These reductive substances included the gases CO, H2, and hydrocarbons such as CH4, as well as solid carbon. Therefore, the carbonized sucrose was etched due to reactions between carbon and metal oxides, leading to widening of the micropores and the formation of mesopores in the final products. This can explain the observations that the Vmes/Vtot of 95.4% for sample C/Fe-700-1 obtained before removing the metal particles is much higher than that of C-700-0 prepared in the absence of metal salt, whereas the SBET of 102 m2/g for C/Fe-700-1 is much less than that of 310 m2/g for C-700-0 (Table 1). Based on the above results, it could be inferred that the catalytic carbonization of sucrose may involve a continuous process of deposition of carbon on metal particles and etching by metal oxides. The deposition of carbon facilitates the formation of graphitic carbon around the iron particles or in their vicinity, whereas the carbon far away from the iron particles remains amorphous [19]. Consequently, when a high loading of iron (III) nitrate was employed, the carbon atoms that were deposited around metal particles were dominant, and hence a graphitic carbon product with a high degree of graphitization was obtained. In the process of catalytic carbonization, mesopores were developed due to the etching of carbon by metal oxides and the removal of metal particles present in the carbonized sucrose by washing.
3.3. Morphology TEM images of the graphitic porous carbon materials are shown in Fig. 4. It is evident that sample C-700-0 was composed of non-graphitized carbon with many micropores (Fig. 4a). In contrast, the graphitic mesoporous carbon materials were composed of characteristic carbon nanostructures (Fig. 4c–h). A TEM image of the sample C/Fe-700-1 showed that the size of the metal particles was < 100 nm (Fig. 4b). In the process of catalytic carbonization of sucrose, carbon atoms were deposited on the metal particles and were thereby catalytically graphitized. Consequently, the carbon atoms around the metal particles were transformed into graphitic carbon. After removing the metal particles, a large amount of nanocapsules could clearly be observed in the final products obtained under the catalysis of iron(III) nitrate [Fig. 4(c, e, f, g)], and the voids occupied by metal particles in the nanocapsules thus developed into mesopores. In addition, carbon nanotubes were also seen in the samples C-700-1 [Fig. 4(c, d)] and C-8000.5 [Fig. 4(g, h)], but these made little contribution to mesopore 3
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
Fig. 4. TEM images of samples (a) C-700-0, (b) C/Fe-700-1, (c, d) C-700-1, (e, f) C-800-1, and (g, h) C-800-0.5.
Public Welfare Industry Research Project (Grant No. 201404611) and the National Natural Science Foundation of China Youth Project (51702094). References [1] S.H. Tang, G.Q. Sun, J. Qi, S.G. Sun, J.S. Guo, Q. Xin, Review of new carbon materials as catalyst supports in direct alcohol fuel cells, Chin. J. Catal. 31 (2010) 12. [2] M. Sevilla, C.S. Martínez-de Lecea, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Solidphase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports, Phys. Chem. Chem. Phys. 10 (2008) 1433. [3] M. Sevilla, C. Sanchís, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Direct synthesis of graphitic carbon nanostructures from saccharides and their use as electrocatalytic supports, Carbon 46 (2008) 931. [4] T. Guo, P. Nikolaev, A. Thess, D.T. Colbert, R.E. Smalley, Catalytic growth of singlewalled nanotubes by laser vaporization, Chem. Phys. Lett. 243 (1995) 49. [5] D. Ugarte, Onion-like graphitic particles, Carbon 33 (1995) 989. [6] C.K. Tan, K.P. Loh, J.T.L. Thong, C.H. Sow, H. Zhang, Plasma synthesis of wellaligned carbon nanocones, Diam. Relat. Mater. 14 (2005) 902. [7] W.M. Lu, D.D.L. Chung, Preparation of conductive carbons with high surface area, Carbon 39 (2001) 39. [8] J. Ozaki, M. Mitsui, Y. Nishiyama, Carbonization of ferrocene containing polymers and their electrochemical properties, Carbon 36 (1998) 131. [9] N. Kasahara, S. Shiraishi, A. Oya, Heterogeneous graphitization of thin carbon fiber derived from phenol-formaldehyde resin, Carbon 41 (2003) 1654. [10] I. Mochida, R. Ohtsubo, K. Takeshita, H. Marsh, Catalytic graphitization of nongraphitizable carbon by chromium and manganese oxides, Carbon 18 (1980) 117. [11] M. Sevilla, A.B. Fuertes, Catalytic graphitization of templated mesoporous carbons, Carbon 44 (2006) 468. [12] C.H. Kim, D.K. Lee, T.J. Pinnavaia, Graphitic mesostructured carbon prepared from aromatic precursors, Langmuir 20 (2004) 5157. [13] M. Inagaki, S. Kobayashi, F. Kojin, N. Tanaka, T. Morishita, B. Tryba, Pore structure of carbons coated on ceramic particles, Carbon 42 (2004) 3153. [14] F.J. Maldonado-Hódar, C. Moreno-Castilla, J. Rivera-Utrilla, Y. Hanzawa, Y. Yamada, Catalytic graphitization of carbon aerogels by transition metals, Langmuir 16 (2000) 4367. [15] T. Morishita, K. Ishihara, M. Kato, T. Tsumura, M. Inagaki, Mesoporous carbons prepared from mixtures of magnesium citrate with poly (vinyl alcohol), Tanso (226) (2007) 19. [16] M. Sevilla, C. Sanchis, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Synthesis of graphitic carbon nanostructures from sawdust and their application as electrocatalyst supports, J. Phys. Chem. 111 (2007) 9749. [17] Y. Satio, Nanoparticles and filled nanocapsules, Carbon 33 (1995) 979. [18] W.E. Alvarez, B. Kitiyanan, A. Borgna, D.E. Resasco, Synergism of Co and Mo in the catalytic production of single-wall carbon nanotubes by decomposition of CO, Carbon 39 (2001) 547. [19] M. Sevilla, A.B. Fuertes, Graphitic carbon nanostructures from cellulose, Carbon 490 (2010) 63.
Fig. 5. Evolution of gaseous products during the preparation of samples.
4. Conclusions Mesoporous carbon materials with a high degree of graphitization and a high SBET have been fabricated using sucrose as the carbonaceous precursor and iron (III) nitrate as both the graphitization catalyst and the template for pore creation. The porosity and degree of graphitization of these graphitic mesoporous carbon materials can be regulated by changing the dosage of metal salt and the carbonization temperature. The mesopores in the final products originated from the voids that were left after removing the metal particles that were present in the carbonized sucrose, and the etching that occurred due to the reaction between metal oxides and carbon during the carbonization of sucrose. Catalytic graphitization occurred during the deposition process of carbon atoms on the metal particles. A small amount of carbon nanotubes could also be observed in the final products. Thus, the obtained graphitic mesoporous carbon materials may find many interesting applications in electrodes for supercapacitors or as catalyst supports for electrocatalysis. Acknowledgement We are grateful for the financial support of the National Forestry
4
Contents lists available at ScienceDirect
Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond
Facile synthesis of graphitic mesoporous carbon materials from sucrose a
Jianxiao Yang , Songlin Zuo
b,⁎
T
a College of Materials Science and Engineering, Hunan Province Key Laboratory for Advanced Carbon Materials and Applied Technology, Hunan University, Changsha 410082, China b College of Chemical Engineering, Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing 210037, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Sucrose Catalytic carbonization Porous carbon Mesopore Graphitization
A one-step catalytic carbonization approach has been developed to prepare graphitic mesoporous carbon, using iron (III) nitrate as the graphitization catalyst and the template for creating pores. The porosity, degree of graphitization, and morphology of the resultant carbon products have been investigated as a function of the carbonization temperature and the dosage of iron (III) nitrate. The results showed that graphitic mesoporous carbon with a Brunauer–Emmett–Teller surface area of 198 m2/g and a high degree of graphitization was prepared at a carbonization temperature of 700 °C with a molar ratio of iron (III) nitrate to sucrose of 1.0. Moreover, a small amount of carbon nanotubes could be observed in the graphitic mesoporous carbon. The origin of the mesopores and the formation of graphitic carbon are discussed in terms of the evolution of CO2, CO, H2, and CH4, produced during the carbonization process.
1. Introduction Porous carbon materials with a high degree of graphitization have attracted a great deal of attention for their potential application as electrocatalytic supports due to their good electrical conductivities and highly developed pore structures [1]. Recently, Fuertes and co-workers [2,3] synthesized graphitic mesoporous carbon materials by a hydrothermal synthetic method from sawdust, saccharides, and cellulose in the presence of various metal salts; a subsequent oxidation step with potassium permanganate served to remove disordered carbon from the carbonized samples. On the other hand, some more costly methods for preparing graphitic porous carbon materials, such as laser evaporation [4], arc discharge [5], and chemical vapor deposition [6], have also been explored. Although these methods can provide carbon materials with graphitic structures and low surface area, the synthetic methods are quite complicated. In fact, the preparation of graphitic porous carbon materials generally involves two synthetic steps: pore creation and graphitization. Pores in carbon materials can be created by impregnating carbonaceous precursors with metal salts [7]; a graphitic structure can subsequently be obtained under the heterogeneous catalysis of metal salts at relatively low temperatures [8–10]. Therefore, in this work, we have developed a simple one-step synthetic method for fabricating graphitic mesoporous carbon, using a high loading of metal salt as both the graphitization catalyst and a template for pore creation, based on this synthetic strategy [11–13]. In addition, the origin of the
⁎
mesopores and formation of the graphitic structure have been investigated by analyzing the gases evolved during the catalytic carbonization process. 2. Experimental 2.1. Preparation of materials To prepare graphitic porous carbon, sucrose (C12H22O11, analytical grade; 20.0 g) and iron (III) nitrate (Fe(NO3)3·9H2O, analytical grade) were mixed in deionized water (100 mL) in molar ratios ranging from 0.5 to 2. Each mixture was stirred at 80 °C in a water bath until it became a metal/sucrose composite paste. Subsequent carbonization of the composite was carried out in a tubular furnace under nitrogen atmosphere. The gases produced during the carbonization of sucrose were analyzed online using a Shimadzu GC 2014 gas chromatograph with a thermal conductivity detector. The carbonized samples thus obtained were washed with 6 mol/L aqueous HCl and copious deionized water to eliminate the metal particles that were formed during the carbonization. The final products, obtained in powder form, were then oven-dried at 120 °C for 24 h. The densities of the products, as measured in a 10 mL cylinder, were in the range 0.30–0.34 g/cm3. Samples were milled and sieved to obtain the final product particles of size < 74 μm. The samples obtained after removing the metal particles are denoted as C-X-Y; those prepared before removing the metal particles are denoted as C/Fe-X-Y,
Corresponding author. E-mail address: [email protected] (S. Zuo).
https://doi.org/10.1016/j.diamond.2019.03.018 Received 10 January 2019; Received in revised form 26 March 2019; Accepted 26 March 2019 Available online 27 March 2019 0925-9635/ © 2019 Elsevier B.V. All rights reserved.
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
where X is the carbonization temperature and Y is the molar ratio of iron (III) nitrate to sucrose.
Table 1 Structural parameters of the graphitic mesoporous carbons. Sample
d002(nm)
g
DBJH(nm)
SBET(m2/g)
Vtot(cm3/g)
Vmes/ Vtot(%)
Graphite C-700-0 C/Fe-700-1 C-700-1 C-800-0.5 C-800-1 C-800-2
0.3354 – – 0.3370 0.3394 0.3370 0.3370
1 – – 0.81 0.53 0.81 0.81
– 10.1 11.6 10.2 10.8 10.4 15.1
– 310 102 198 217 145 68
– 0.18 0.27 0.44 0.57 0.33 0.24
– 15.6 95.4 94.3 98.4 97.3 97.9
2.2. Characterization X-ray diffraction (XRD) patterns were obtained on a Shimadzu XRD 6000 diffractometer operating at 40 kV and 30 mA using Cu-Kα1 radiation (λ = 0.154056 nm). Data were collected between 10° and 90° at a scanning speed of 0.05°/s. The interplanar distance (d002) was calculated by applying Bragg's equation to the (002) diffraction peak, and the parameter (g) expressing the degree of graphitization of the carbon material was obtained by applying the equation g = (0.344 – d002) / 0.0086 [14]. Transmission electron microscopy (TEM) was conducted with a JEM 2100 instrument operating at 200 kV. Nitrogen adsorption was performed at −196 °C with a Micromeritics ASAP 2020 apparatus. Brunauer–Emmett–Teller surface areas (SBET) were deduced from the nitrogen adsorption isotherm in the relative pressure range 0.03–0.30. The average pore size (DBJH) was determined from the nitrogen adsorption isotherm using the Barrett–Joyner–Halenda model. The total pore volume (Vtot) was obtained by converting the amount of nitrogen adsorbed at P/P0 = 0.99 to the volume of liquid nitrogen. The mesopore volume (Vmes) was obtained as the total pore volume (Vtot) minus the micropore volume (Vmic), which was obtained by the t-plot method.
The “–” denoted that the samples were without characterization and the data were not obtained.
(Table 1). This was because an increase in the iron (III) nitrate loading with respect to sucrose led to an increase in the size of the metal oxide particles produced by its decomposition during carbonization, and the pores that originated from the voids occupied by the metal oxide particles continuously widened [15]. Eventually, some of the pores became so wide that they no longer made any contribution to nitrogen adsorption, thereby resulting in decreases in the amount of nitrogen adsorbed (Fig. 1) and in the SBET and pore volume (Table 1) with increasing dosage of iron (III) nitrate. In order to discuss the origin of the mesopores, nitrogen adsorption–desorption isotherms of the samples C-700-0 prepared without adding iron (III) nitrate and C/Fe-700-1 obtained before removing metal particles in the carbonized sucrose are shown in Fig. 2. The nitrogen adsorption isotherm of sample C-700-0 conformed to type I, indicative of a prevalence of micropores in the resultant carbon (Fig. 2). Its Vmes/Vtot was only 15.6% (Table 1). However, the nitrogen adsorption isotherms of sample C-700-1 exhibited obvious hysteresis loops and a high adsorption uptake at P/P0 > 0.9. Its Vmes/Vtot reached 94.3%. This difference suggested that the catalytic carbonization of sucrose by iron (III) nitrate produced a large amount of mesopores at the expense of micropores, resulting in a decrease of SBET from 310 m2/g to 198 m2/g (Table 1). Furthermore, comparing samples C/ Fe-700-1 and C-700-1 obtained before and after the removal of metal particles in the carbonized sucrose, it can be seen that they both have a high value of Vmes/Vtot up to around 95% and exhibit similar hysteresis loops in their adsorption–desorption isotherms. However, the SBET and Vtot were significantly increased from 102 m2/g and 0.27 cm3/g to 198 m2/g and 0.44 cm3/g, respectively (Table 1), after removal of the metal particles in the carbonized sucrose. Specifically, their Vmes and Vmic were increased from 0.257 cm3/g and 0.013 cm3/g for C/Fe-700-1 to 0.404 cm3/g and 0.036 cm3/g for C-700-1, respectively. This implies
3. Results and discussion 3.1. Pore development Nitrogen adsorption–desorption isotherms of the samples are shown in Fig. 1. The pore parameters calculated from the adsorption isotherms are listed in Table 1. It can be seen that the nitrogen adsorption–desorption isotherms of the samples are of type IV and exhibit a hysteresis loop associated with capillary condensation. All of the samples adsorbed only a small amount of nitrogen at P/P0 < 0.01 (Fig. 1). Their average pore widths were > 10 nm, and their Vmes/Vtot values were in excess of 94% (Table 1). These results suggested that a mesopore structure with low microporosity was developed in the porous carbon materials due to the high molar ratio of iron(III) nitrate to sucrose used. This was confirmed by the fact that the nitrogen adsorption isotherms (Fig. 1) exhibited obvious hysteresis loops and a high adsorption uptake at P/P0 > 0.9. Fig. 1 and Table 1 show that the carbonization temperature and iron (III) nitrate loading had a significant influence on pore development. The SBET of the sample decreased from 217 to 68 m2/g and Vtot decreased from 0.57 to 0.24 cm3/g with increasing dosage of the metal
Fig. 1. Nitrogen adsorption isotherms of the prepared porous carbon materials.
Fig. 2. Nitrogen adsorption isotherms of the prepared carbonized samples. 2
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
Fig. 3. XRD patterns of graphitic mesoporous carbon materials prepared at (A) different carbonization temperatures and (B) with different molar ratios of iron(III) nitrate to sucrose.
development due to their low content in the final products (Fig. 4). Similar nanostructures have previously been reported in carbon products prepared by carbonization of metal-impregnated polymeric gels [14], by arc discharge [17], and by thermal chemical vapor deposition of hydrocarbons over metal particles [18]. Comparison of the TEM images of the samples (Fig. 4) implied that the carbonization temperature and the metal loading influenced the carbon nanostructure morphologies.
that the pores that originated from voids occupied by iron particles were principally mesopores. Therefore, it can be concluded that the metal particles formed here during the carbonization of sucrose could function as a template for creating mesopores. 3.2. Graphitization The XRD patterns of the prepared samples are presented in Fig. 3. The carbon samples exhibited a well-resolved (002) diffraction peak at 2θ = 26°, which was significantly intensified on increasing the carbonization temperature (Fig. 3A) or increasing the dosage of iron (III) nitrate (Fig. 3B). The values of d002 spacing and the graphitization degree parameter (g) are also summarized in Table 1. The values of d002 spacing are seen to be in the range 0.3370–0.3394 nm, close to the value of 0.3354 nm for pure graphite and less than that of 0.344 nm for disordered carbon materials [16]. These observations suggest that the porous carbon materials have an ordered carbon framework. A comparison between the XRD pattern of sample C-800-0 (Fig. 3B) and the other samples reveals that the iron nanoparticles could significantly catalyze the graphitization of sucrose at a carbonization temperature as low as 700 °C with an equimolar dosage of iron (III) nitrate, and that the catalysis was promoted by an increased dosage of iron (III) nitrate. Therefore, a graphitic porous carbon (sample C-700-1) with a high surface area of 198 m2/g and a high degree of graphitization could be obtained using a molar ratio of iron (III) nitrate to sucrose of 1 as the catalyst and template.
3.4. Gas products Fig. 5 shows the evolution of gases, namely CO2, H2, CH4, and CO, during the preparation of samples C-700-1 and C-700-0 in order to provide some information on the catalytic carbonization of sucrose. It can be seen from Fig. 5 that the addition of iron (III) nitrate significantly lowered the temperature at which the release of CO2 and CO commenced, further confirming its catalytic effect on the carbonization of sucrose. Moreover, in the presence of iron (III) nitrate, the amount of CO2 was significantly increased, whereas the amounts of the reductive gases CO, H2, and CH4 were significantly decreased, accompanied by a decrease in the yield of the final product from 21.4% for sample C-7000 to 10.5% for C-700-1. These observations are indicative of reactions between iron oxides and the reductive substances produced during the carbonization of sucrose. These reductive substances included the gases CO, H2, and hydrocarbons such as CH4, as well as solid carbon. Therefore, the carbonized sucrose was etched due to reactions between carbon and metal oxides, leading to widening of the micropores and the formation of mesopores in the final products. This can explain the observations that the Vmes/Vtot of 95.4% for sample C/Fe-700-1 obtained before removing the metal particles is much higher than that of C-700-0 prepared in the absence of metal salt, whereas the SBET of 102 m2/g for C/Fe-700-1 is much less than that of 310 m2/g for C-700-0 (Table 1). Based on the above results, it could be inferred that the catalytic carbonization of sucrose may involve a continuous process of deposition of carbon on metal particles and etching by metal oxides. The deposition of carbon facilitates the formation of graphitic carbon around the iron particles or in their vicinity, whereas the carbon far away from the iron particles remains amorphous [19]. Consequently, when a high loading of iron (III) nitrate was employed, the carbon atoms that were deposited around metal particles were dominant, and hence a graphitic carbon product with a high degree of graphitization was obtained. In the process of catalytic carbonization, mesopores were developed due to the etching of carbon by metal oxides and the removal of metal particles present in the carbonized sucrose by washing.
3.3. Morphology TEM images of the graphitic porous carbon materials are shown in Fig. 4. It is evident that sample C-700-0 was composed of non-graphitized carbon with many micropores (Fig. 4a). In contrast, the graphitic mesoporous carbon materials were composed of characteristic carbon nanostructures (Fig. 4c–h). A TEM image of the sample C/Fe-700-1 showed that the size of the metal particles was < 100 nm (Fig. 4b). In the process of catalytic carbonization of sucrose, carbon atoms were deposited on the metal particles and were thereby catalytically graphitized. Consequently, the carbon atoms around the metal particles were transformed into graphitic carbon. After removing the metal particles, a large amount of nanocapsules could clearly be observed in the final products obtained under the catalysis of iron(III) nitrate [Fig. 4(c, e, f, g)], and the voids occupied by metal particles in the nanocapsules thus developed into mesopores. In addition, carbon nanotubes were also seen in the samples C-700-1 [Fig. 4(c, d)] and C-8000.5 [Fig. 4(g, h)], but these made little contribution to mesopore 3
Diamond & Related Materials 95 (2019) 1–4
J. Yang and S. Zuo
Fig. 4. TEM images of samples (a) C-700-0, (b) C/Fe-700-1, (c, d) C-700-1, (e, f) C-800-1, and (g, h) C-800-0.5.
Public Welfare Industry Research Project (Grant No. 201404611) and the National Natural Science Foundation of China Youth Project (51702094). References [1] S.H. Tang, G.Q. Sun, J. Qi, S.G. Sun, J.S. Guo, Q. Xin, Review of new carbon materials as catalyst supports in direct alcohol fuel cells, Chin. J. Catal. 31 (2010) 12. [2] M. Sevilla, C.S. Martínez-de Lecea, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Solidphase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports, Phys. Chem. Chem. Phys. 10 (2008) 1433. [3] M. Sevilla, C. Sanchís, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Direct synthesis of graphitic carbon nanostructures from saccharides and their use as electrocatalytic supports, Carbon 46 (2008) 931. [4] T. Guo, P. Nikolaev, A. Thess, D.T. Colbert, R.E. Smalley, Catalytic growth of singlewalled nanotubes by laser vaporization, Chem. Phys. Lett. 243 (1995) 49. [5] D. Ugarte, Onion-like graphitic particles, Carbon 33 (1995) 989. [6] C.K. Tan, K.P. Loh, J.T.L. Thong, C.H. Sow, H. Zhang, Plasma synthesis of wellaligned carbon nanocones, Diam. Relat. Mater. 14 (2005) 902. [7] W.M. Lu, D.D.L. Chung, Preparation of conductive carbons with high surface area, Carbon 39 (2001) 39. [8] J. Ozaki, M. Mitsui, Y. Nishiyama, Carbonization of ferrocene containing polymers and their electrochemical properties, Carbon 36 (1998) 131. [9] N. Kasahara, S. Shiraishi, A. Oya, Heterogeneous graphitization of thin carbon fiber derived from phenol-formaldehyde resin, Carbon 41 (2003) 1654. [10] I. Mochida, R. Ohtsubo, K. Takeshita, H. Marsh, Catalytic graphitization of nongraphitizable carbon by chromium and manganese oxides, Carbon 18 (1980) 117. [11] M. Sevilla, A.B. Fuertes, Catalytic graphitization of templated mesoporous carbons, Carbon 44 (2006) 468. [12] C.H. Kim, D.K. Lee, T.J. Pinnavaia, Graphitic mesostructured carbon prepared from aromatic precursors, Langmuir 20 (2004) 5157. [13] M. Inagaki, S. Kobayashi, F. Kojin, N. Tanaka, T. Morishita, B. Tryba, Pore structure of carbons coated on ceramic particles, Carbon 42 (2004) 3153. [14] F.J. Maldonado-Hódar, C. Moreno-Castilla, J. Rivera-Utrilla, Y. Hanzawa, Y. Yamada, Catalytic graphitization of carbon aerogels by transition metals, Langmuir 16 (2000) 4367. [15] T. Morishita, K. Ishihara, M. Kato, T. Tsumura, M. Inagaki, Mesoporous carbons prepared from mixtures of magnesium citrate with poly (vinyl alcohol), Tanso (226) (2007) 19. [16] M. Sevilla, C. Sanchis, T. Valdés-Solís, E. Morallón, A.B. Fuertes, Synthesis of graphitic carbon nanostructures from sawdust and their application as electrocatalyst supports, J. Phys. Chem. 111 (2007) 9749. [17] Y. Satio, Nanoparticles and filled nanocapsules, Carbon 33 (1995) 979. [18] W.E. Alvarez, B. Kitiyanan, A. Borgna, D.E. Resasco, Synergism of Co and Mo in the catalytic production of single-wall carbon nanotubes by decomposition of CO, Carbon 39 (2001) 547. [19] M. Sevilla, A.B. Fuertes, Graphitic carbon nanostructures from cellulose, Carbon 490 (2010) 63.
Fig. 5. Evolution of gaseous products during the preparation of samples.
4. Conclusions Mesoporous carbon materials with a high degree of graphitization and a high SBET have been fabricated using sucrose as the carbonaceous precursor and iron (III) nitrate as both the graphitization catalyst and the template for pore creation. The porosity and degree of graphitization of these graphitic mesoporous carbon materials can be regulated by changing the dosage of metal salt and the carbonization temperature. The mesopores in the final products originated from the voids that were left after removing the metal particles that were present in the carbonized sucrose, and the etching that occurred due to the reaction between metal oxides and carbon during the carbonization of sucrose. Catalytic graphitization occurred during the deposition process of carbon atoms on the metal particles. A small amount of carbon nanotubes could also be observed in the final products. Thus, the obtained graphitic mesoporous carbon materials may find many interesting applications in electrodes for supercapacitors or as catalyst supports for electrocatalysis. Acknowledgement We are grateful for the financial support of the National Forestry
4