Effects of Cobalt Compounds on the Morphology and Structure of

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Effects of cobalt compounds on the morphology and structure of carbonaceous materials prepared by hydrothermal/solvothermal carbonization of furfural Xiujuan Chen, Xiaoli Li, Siping Liu, and Zhiguo Li Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b00230 • Publication Date (Web): 21 Apr 2015 Downloaded from http://pubs.acs.org on April 26, 2015

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Industrial & Engineering Chemistry Research

Effects of cobalt compounds on the morphology and structure of carbonaceous materials prepared by hydrothermal/solvothermal carbonization of furfural Xiujuan Chena, Xiaoli Lib, Siping Liua, Zhiguo Lia a College of Material Science and Engineering, Key Laboratory of Bio-Based Material Science and Technology, Northeast Forestry University, Harbin 150040, PR China b College of Science, Northeast Forestry University, Harbin 150040, PR China



Corresponding author: Tel: +86 13069881543 E-mail address: [email protected] (Z. Li) 1

ACS Paragon Plus Environment


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Abstract: The cobalt-assisted hydrothermal/solvothermal carbonization of furfural has been developed into a facile and versatile strategy to prepare structured carbonaceous materials. In this paper, the hierarchical flower-like, honeycomb-like and spherical particles can be readily obtained in the presence of different cobalt compounds. Also, it was demonstrated that the developing of hierarchical carbonaceous structures was strongly influenced by the formation of cobalt crystals in products during the reaction. We believe that the cobalt crystals could act as a kind of structure-directing agent to induce the fabrication of hierarchical carbonaceous structures. Organic cobalt compound was indicative of beneficial cobalt precursor for synthesis of hierarchical carbonaceous structures. The presence of ethanol facilitated the aggregation and assembly of primary nanoparticles to form hierarchical structures.

1. Introduction In the last decade, synthesis of carbonaceous materials from biomass has been a sustained hot topic, because of the highly efficient utilization and potential high-value conversion of abundant biomass resource as an important carbon precursor of carbonaceous materials.1,2 Among these synthetic methods for carbonaceous materials, hydrothermal/solvothermal process presents more sustainable, practical and low-cost characteristics, which has been considered as a promising route to synthesize carbonaceous materials with various structures and defined chemical functionality from 2


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biomass.3-8 In this process, controllable morphology and various structure of the products are problematic due to the multicomponent property of biomass and mild reaction conditions (≤200 °C). Many researches have been reported to overcome these obstacles through regulating the hydrothermal/solvothermal conditions, including the reaction time and temperature,9 solvents,10 templets or surfactants,11,12 and etc.13,14,15 However, effective adjustment of the regular and various structures of hydrothermal/solvothermal carbonaceous materials is still challenging. Thus much work still need to be done in improving or enhancing the regularity, variety and novelty of morphology and structure of hydrothermal/solvothermal carbonaceous materials. Recently，metal additive has been proved to have an important role on the formation of special carbonaceous structures. Many types of carbonaceous architectures, such as nanoporous,16 chain-like,17 dendritic-like18 and flower-like structures19 have been obtained by hydrothermal/solvothermal process in the presence of metal. The multifunctionality of carbon/metal hierarchical products was achieved.20-24 These three-dimensional carbon/metal architectures usually possess higher surface area and developed pore structure, which were advantageous to facilitate the diffusion and migration of electrolyte ions as electrode materials with excellent specific capacitance (supercapacitors, lithium batteries). Moreover, the unique intrinsic properties of hierarchical carbonaceous materials, including higher surface area, chemistry stability and environmentally sustainability, make them extremely attractive as supports for heterogeneous catalysts. Furthermore, based on particular metal or metal oxide, the 3



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hierarchical carbon/metal materials themselves could also be excellent catalysts for specific chemical interactions, or employ as magnetic materials for many fields. It clearly suggested that combining the effect of metal with hydrothermal/solvothermal technique could be an effective strategy to prepare novel hierarchical carbonaceous materials, meanwhile, the morphology and structure of carbonaceous materials could be easily regulated owing to the presence of different metals. 25,26 Interestingly, it was worth noting that the carbonaceous structures also could be dramatically affected by the metal additives with same metal species but different forms.27,22 Yu’s group reported that both hollow and massive carbon microspheres were obtained in the presence of Fe2+ ions, whereas the presence of Fe2O3 nanoparticles resulted in fine rope-like carbon nanostructures.28 Moreover, Li’s group prepared various carbonaceous structures via solid-state pyrolysis of cobalt compounds with different ligands, and the concept of precursor-controlled thermolysis to form novel carbon/metal materials was proposed.29,30 Based on these reports, it could be anticipated a novel precursor-controlled way to fabricate hierarchical carbonaceous structures by employing the metal compounds as metal precursors, especially the organic metal compounds. However, little research has been reported to focus on the effect of this kind of metal compounds on the morphology and structure of hydrothermal/solvothermal carbonaceous materials. Hence the relatively systemic research for this effect behavior of metal compounds on carbonaceous structures is especially essential for the formation of various and novel carbonaceous materials. In this paper, we planned to investigate the effects of cobalt compounds on the 4


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morphology and structure of hydrothermal/solvothermal carbonaceous products systematically. The biomass derivate-furfural was used as carbon precursor. Different cobalt compounds including Co(acac)2, Co(NO3)2 and CoCl2 were introduced as metal precursors. In addition, distilled water, ethanol and ethanol/water mixed solvents were employed as the reaction solvent. As a result, the hierarchical flower-like, honeycomb-like structures and spherical particles were easily obtained in the presence of different cobalt compounds with great control. The experimental and analysis results demonstrated that cobalt compound played a crucial role on the fabrication of hierarchical carbonaceous structures and solvent mainly affected the regularity and uniformity of the morphology and structure of hydrothermal/solvothermal products.

2. Materials and Methods 2.1. Chemicals and reagents Furfural (AR, ≥ 99.0%) and ethanol (AR, ≥ 99.7%) were purchased from Sinopharm Chemical Reagent Co. Ltd and Fuyu Chemical Reagents Company, respectively. Co(acac)2, Co(NO3)2·6H2O and CoCl2·6H2O were purchased from Adamas Reagent Co., Ltd., Guangfu Chemical and Hongyan Chemical, respectively. The ethanol/water mixed solvents were composed of ethanol and water with different volume ratio. All chemicals were used without further purification.

2.2. Synthesis of furfural-derived carbonaceous materials The typical synthesis of furfural-derived carbonaceous materials was carried out as follows: 0.2～0.9 g of different cobalt compounds, including Co(acac)2, Co(NO3)2·6H2O 5



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and CoCl2·6H2O, was dispersed in 40 mL of distilled water (ethanol, or water/ethanol mixture) by stirring. And then 1.0 g of furfural was added, stirring constantly until a homogeneous solution was obtained. The resulting solution was transferred into a stainless steel autoclave of 60 mL capacity, then sealed and heated at 180°C for 16 h. After above procedures, it was cooled to room temperature. The obtained dark precipitate was collected and separated by centrifugation. Then the washing and centrifugal separation were carried out alternately, distilled water and absolute alcohol were used in this process. Finally, the solid materials were dried in a vacuum at 60°C for 12 h. Table 1: The samples from different conditions. Samples

Cobalt precursor

Solvent

Temperature (°C)

Time (h)

C-Co(acac)2-H2O

Co(acac)2

water

180

16

C-Co(acac)2-ET

Co(acac)2

ethanol

180

16

C-Co(NO3)2-H2O

Co(NO3)2·6H2O

water

180

16

C-Co(NO3)2-ET

Co(NO3)2·6H2O

ethanol

180

16

C-CoCl2-H2O

CoCl2·6H2O

water

180

16

C-CoCl2-ET

CoCl2·6H2O

ethanol

180

16

A series of experiments were designed around above basic synthesis methodology. In each of experiment about according condition, all the other variables were kept constant. Sample labels of final products were based on the cobalt compound precursor, furfural and solvent, for example, C-Co(acac)2-H2O was the carbonaceous materials obtained from

the

Co(acac)2-assisted hydrothermal

process

of

furfural,

and

C-Co(NO3)2-ET was obtained from the Co(NO3)2-assisted solvothermal process of 6


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furfural in ethanol, etc. The detailed reaction conditions were listed in Table 1.

2.3. Characterization The scanning electron microscopy (SEM) was performed with a FEI QuanTa 200 microscopy. Samples for SEM was prepared by spreading a drop of dilute dispersion containing as-prepared products on aluminum foil, then sputter-coating with gold powder after drying at room temperature. The X-ray diffraction (XRD) pattern was recorded with a D/MAX 2200 diffractometer equipped with a rotating anode and a Cu-Kα source (λ = 0.15406 nm). Samples for XRD measurements were solid powder. The X-ray photoelectron spectroscopy (XPS) analysis was performed on K-Alpha X-ray photoelectron spectra (Thermo Fisher Scientific Co. Ltd, USA) with the vacuum chamber pressure of 5×10−7 Pa.

3. Results and Discussions The effect of cobalt compound on the morphology and structure of resulting materials was explored by SEM. Figure 1 shows the SEM images of the samples obtained in water. It can be observed that the morphologies and structures of prepared products greatly varied with the presence of different cobalt compound. The absence of cobalt compound resulted in the synthesis of smooth and uniform carbon microspheres (Figure 1a), similar to the products from hydrothermal carbonization of saccharides, such as glucose, sucrose, and amylopectin.31,32 However, the hierarchical flower-like structures assembled by thin-sheets were obtained when there was Co(acac)2 in the reaction process with other conditions unchanged (Figure 1b). Moreover, more experimental results 7



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proved that the uniformity and integrity of the hierarchical structures could be controlled by regulating the mole ratio of furfural/Co(acac)2, but the basic flower-like framework of products could not been changed in the presence of Co(acac)2 (Figure S1). It suggested that the Co(acac)2 might act as a structure-directing agent for the fabrication of this flower-like structures, which induced the morphology evolution of hydrothermal products of furfural from microspheres to hierarchical carbonaceous structures. At the same time, furfural could be considered as the carbon supplementary for further growth of the hierarchical structures.16 Differ from flower-like structures of the C-Co(acac)2-H2O, only carbon spheres were obtained when Co(acac)2 was replaced by Co(NO3)2 or CoCl2 (Figure 1c, 1d). It indicated that the different cobalt compound could result in different morphology and structure of products.

Figure 1 SEM images of the samples obtained in water: (a) hydrothermal carbonization of furfural, (b) C-Co(acac)2-H2O, (c) C-Co(NO3)2-H2O, (d) C-CoCl2-H2O. 8


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In addition to cobalt compounds, it was reported that solutions also played an important role for the fabrication of hierarchical structures. Figure 2 shows the SEM images of the samples prepared in ethanol. It can be seen that both hierarchical honeycomb-like structures were obtained when the cobalt precursor was Co(acac)2 or Co(NO3)2, respectively (Figure 2a, 2b), whereas the presence of CoCl2 still resulted in the formation of microspheres with a wide size distribution (Figure 2c). Interestingly, it could be noted that the products were honeycomb-like structures when solvothermal treatment of Co(NO3)2 and furfural in ethanol, instead of the spherical particles obtained in water. In order to further study the effect of ethanol on the morphology and structure of the products, a series of blank experiments were performed by solvothermal treatment of different cobalt compounds (including Co(acac)2, Co(NO3)2 and CoCl2) in ethanol. As shown in Figure 2d, the flower-like structures were formed in the presence of Co(acac)2, similar to the products obtained from hydrothermal/solvothermal treatment of Co(acac)2 and furfural, further evidencing that the Co(acac)2 acted as the structure-directing agent in the fabrication of these hierarchical products. Structured microspheres assembled by numerous nanoparticles were obtained by the solvothermal treatment of Co(NO3)2 in ethanol (Figure 2e), it implied that the ethanol might facilitate the aggregation and assembly of nanoparticles. The products obtained from solvothermal treatment of CoCl2 in ethanol remained adhered nanoparticles (Figure 2f). All the above experimental results demonstrated that the morphology and structure of products resulted from the combined effect of cobalt precursors and solutions. From a technological point of view, it was 9



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conceivable to take advantage of this hierarchical structure characteristic of Co(acac)2 and Co(NO3)2 with different solution to fabricate novel structured materials.

Figure 2 SEM images of the samples obtained in ethanol: (a) C-Co(acac)2-ET, (b) C-Co(NO3)2-ET, (c) C-CoCl2-ET, (d) Co(acac)2-ET, (e) Co(NO3)2-ET, (f) CoCl2-ET.

The XRD pattern was employed to investigate the microstructure phase of the hydrothermal/solvothermal products prepared under different conditions. Figure 3a shows the XRD patterns of C-Co(acac)2-H2O, C-Co(NO3)2-H2O and C-CoCl2-H2O, respectively. The peak at 10～30° could be clearly observed in the XRD patterns of all three samples, which was attributed to the typical (002) plane of carbonaceous materials. The broadening of these peaks suggested the existence of amorphous carbon.33,34 In addition, it could be found that two weak peaks appeared at around 34° and 60° in the 10


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XRD pattern of C-Co(acac)2-H2O, which were assigned to the reflections of CoO phase, indicating the presence of CoO phase in C-Co(acac)2-H2O. However, no cobalt diffraction peaks were detected in the XRD patterns of C-Co(NO3)2-H2O and C-CoCl2-H2O, implying that the Co(NO3)2 and CoCl2 precursors could not be crystallized during the hydrothermal process.

Figure 3 XRD patterns of the samples obtained under different conditions: (a) in water, (b) in ethanol.

Figure 3b shows the XRD patterns of C-Co(acac)2-ET, C-Co(NO3)2-ET and C-CoCl2-ET, respectively. The cobalt peaks could be clearly observed from the XRD patterns of C-Co(acac)2-ET and C-Co(NO3)2-ET, which were well-assigned to the (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2) crystalline planes of cubic phase CoO structure, respectively.35,36 In addition, some weak peaks also occurred in the XRD pattern of C-Co(NO3)2-ET, which were considered the possible presence of Co3O4 phase in 11



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C-Co(NO3)2-ET.37,38 However, similar to the result of C-CoCl2-H2O (Figure 3a), only typical (002) peak resulted from amorphous carbon was observed in the XRD pattern of C-CoCl2-ET, no cobalt diffraction peaks could be detected. Different from the products obtained in water, all the above XRD results demonstrated that the CoO crystal could be formed in the products obtained in ethanol with the assistance of Co(acac)2 and Co(NO3)2. Important information about the chemical composition of the products can be further studied by XPS. Figure 4 shows the Co 2p XPS spectra of different products, and the corresponding data information for XPS was summarized in Table S1 and S2. It could be seen from Figure 4 that the Co 2p peaks clearly appeared in the XPS spectra of C-Co(acac)2-H2O, C-Co(acac)2-ET and C-Co(NO3)2-ET, rather than in that of C-Co(NO3)2-H2O, C-CoCl2-H2O and C-CoCl2-ET, which was mainly due to the low cobalt content (Table S1). It indicated that the cobalt content in the samples varied considerably as the presence of different cobalt compound and solvent, while keeping the original amount of furfural and cobalt compound constant. As shown in Co 2p XPS spectrum of C-Co(acac)2-ET (Figure 4d), the main peaks of Co 2p3/2 and Co 2p1/2 appeared at 780.35 and 796.39 eV, respectively, the satellite peaks of Co 2p3/2 and Co 2p1/2 were also found at 785.56 and 802.39 eV, respectively (Table S2), all these peaks could be attributed to the characteristic of CoO phase.35,39 Similarly, the CoO phase also could be confirmed by the Co 2p XPS analysis of C-Co(acac)2-H2O and C-Co(NO3)2-ET, which were well agreement with their corresponding XRD results, suggesting the 12


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presence of CoO crystal in C-Co(acac)2-H2O, C-Co(acac)2-ET and C-Co(NO3)2-ET. However, no corresponding Co 2p peaks of Co3O4 phase (779.84 eV for Co 2p3/2 and 794.80 eV for Co 2p1/2) were detected in the XPS spectrum of C-Co(NO3)2-ET (Table S2), further evidencing the absence of Co3O4 phase.34 Combined with the results of XPS and XRD experiments, it could be clearly concluded that the presence of Co(acac)2 resulted in the appearance of CoO crystal in C-Co(acac)2-H2O and C-Co(acac)2-ET, as Co(acac)2 was replaced by Co(NO3)2, the CoO crystal was only produced in C-Co(NO3)2-ET. However, no CoO phase could be obtained when CoCl2 was employed as cobalt precursor in the reaction process. Furthermore, it could be anticipated that the morphology and structure of as-prepared carbonaceous materials might be remarkably impacted by the formation of cobalt crystal. 6400

a

C-Co(acac)2-H2O

counts (s)

6000 5600 5200 4800

18000

4600

C-Co(NO3)2-H2O

b

780

790

800

3800

4200

3600

810

C-Co(acac)2-ET

d

4000

4400

4000 770

counts (s)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


780

790

800

810

C-Co(NO3)2-ET

e

770 6800

15000

20000

6600

12000

16000

6400

9000

12000

6200

6000

8000 770

780

790

800

810

Binding energy (eV)

C-CoCl2-H2O

3400 770

24000

c

780

790

800

810

C-CoCl2-ET

f

6000 770

780

790

800

810

Binding energy (eV)

770

780

790

800

810

Binding energy (eV)

Figure 4 XPS spectra of the samples obtained under different conditions: (a) C-Co(acac)2-H2O, (b) C-Co(NO3)2-H2O, (c) C-CoCl2-H2O, (d) C-Co(acac)2-ET, (e) C-Co(NO3)2-ET, (f) C-CoCl2-ET. 13



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In review of the above XRD, XPS and SEM results, the XRD and XPS peaks of CoO phase were detected in C-Co(acac)2-H2O, C-Co(acac)2-ET and C-Co(NO3)2-ET. Correspondingly, the SEM results showed that hierarchical carbonaceous structures were only obtained in C-Co(acac)2-H2O, C-Co(acac)2-ET and C-Co(NO3)2-ET, which was well correlated with the CoO phase approved by the XRD and XPS results. It was further revealed that the fabrication of hierarchical carbonaceous structures was depended on the formation of cobalt crystal in the reaction process. Figure 5 shows the possible schematic illustration of the formation of as-prepared products. It was reasonable to assume that the hierarchical Co crystal nuclei could be formed before the carbonization of furfural at the early hydrothermal/solvothermal process. Then the carbonaceous molecule clusters aggregated toward the surface of hierarchical Co crystal nuclei as the proceeding of hydrothermal/solvothermal treatment. The carbonization and further growth was going on subsequently, finally the three-dimensional hierarchical structures were formed. The cobalt crystal was considered acted as a structure-directing agent in the fabrication of hierarchical carbonaceous structures. It could be explained that the difference of morphology and microstructure of the products obtained in presence of different cobalt compounds was mainly due to the different composition of these cobalt compounds. Compared with Co(NO3)2 and CoCl2, Co(acac)2 was an organic cobalt compound, which was favor of the formation of cobalt crystal structure under hydrothermal/solvothermal carbonization. During the hydrothermal treatment of Co(acac)2 and furfural, Co(acac)2 could be crystallized preferentially and growth into cobalt crystal framework, inducing 14


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the aggregation and further growth of the carbonaceous precursor as a structure-directing agent, and thus the hierarchical cobalt/carbon architectures were produced.29,40 In contrast with Co(acac)2, Co(NO3)2 and CoCl2 were composed of cobalt ions and inorganic ligands, which were unfavorable to be crystallized into cobalt crystal under hydrothermal treatment, hence no hierarchical structures were formed in the presence of Co(NO3)2 and CoCl2 during the hydrothermal process.16 It was known that the morphology and structure of materials depended strongly on the reaction surroundings as well as the precursors. In our work, it was worth mentioning that the ethanol also played a significant role in the formation process of hierarchical carbonaceous materials. In the absence of furfural, flower-like structures were formed by the solvothermal treatment of Co(acac)2 in ethanol, whereas no products were obtained in water. It implied that ethanol provided a beneficial solution surrounding for the formation of flower-like structures. Under the ethanol-assisted solvothermal treatment, ethanol could facilitate the aggregation and assembly of furfural clusters towards the surface of hierarchical Co crystal nuclei, or assist the gather of cobalt nanoparticles themselves into hierarchical framework. After continuous carbonization and further growth, the hierarchical products were formed. Consequently, it was the mainly reason why hierarchical carbonaceous materials with different morphologies were obtained in water (flower-like) and ethanol (honeycomb-like) system keeping other conditions constant.

15



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Figure 5 Schematic illustration of formation of C/Co materials.

In order to further investigate the assisted effect of ethanol on fabrication and growth of hierarchical carbonaceous materials, the ethanol/water mixed solvent was employed in following experiments. Figure 6 shows the SEM images of the products obtained from solvothermal treatment of Co(acac)2 and furfural in different volume ratio of ethanol/water system. The products were honeycomb-like structures in ethanol (Figure 6a). However, when volume ratio of ethanol/water solution was 2:1, the products contained a large number of thin-flakes and a few hierarchical nanoparticles which seemed to adhere with each other (Figure 6b). After increasing the ethanol/water volume ratio to 1:1, the products were similar to that in 2:1, expect the thin-flakes became bigger (Figure 6c). As the ethanol/water volume ratio was further increased to 1:2, expect a few 16


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flake structures, numerous irregular flower-like structures were obtained (Figure 6d). When the ethanol was fully replaced by water, the products were converted into regular flower-like structures (Figure 6e). These results further confirmed that the morphology and structure of final products were significantly influenced by the solvent composition. Especially, the ethanol mainly affected the regularity and uniformity of product morphologies.

Figure 6 SEM images of the samples obtained from solvothermal treatment of Co(acac)2 and furfural in ethanol/water system with different volume ratio: (a) 1:0, (b) 2:1, (c)1:1, (d)1:2, (e) 0:1. 17



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As previous reported, the solution such as polyethylene glycol and its intermediate produced in heating process might play as a template or carbon precursor during the formation of hierarchical structures at higher temperature (about 500 ～600oC). In addition, the alcohol could induce the self-assembly of colloidal carbon spheres or generated oligomers into spheroids in solvothermal process at lower temperature (about 160～200oC). Furthermore, it also indicated that the surface tension of alcohol might lead to the formation of low-symmetric carbon spheroids with different aspect ratio.10,19 In this case, it was credible that the morphology and structure of the prepared materials could be significantly influenced by ethanol. The experimental results of solvothermal treatment of furfural in ethanol/water system also demonstrated that ethanol was advantageous for the aggregation of carbon nanoparticles (Figure S2). It could be reasonably concluded that ethanol effectively facilitated the aggregation and assembly of primary products to form hierarchical structures during the solvothermal process. In brief, this metal precursor-controlled strategy and solvent assisted route are very essential to develop for the specifically fabrication of novel hierarchical carbonaceous architectures which could be potentially applied in many fields such as supercapacitors, heterogeneous catalysis and catalysis supports. According to the hierarchical 3D nanostructures with porous characteristic of the resulting carbon/cobalt products, it can be anticipated that these materials have potential application as electrode materials for electrochemical capacitors. The previous research reported that the capacitance of capacitive materials predominantly depends on the surface area and pore-size distribution 18


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accessible to the electrolyte ions. In our work, the preliminary results showed that the C-Co(acac)2-H2O activated at 700 oC possessed a high BET surface area (307 m2/g) by N2 adsorption-desorption test, which is favorable to excellent specific capacitance. Additionally, the coexistence of carbon and cobalt could also benefit to higher rate capability and specific capacitance with good electric double-layer capacitance. Moreover, these hierarchical carbon/cobalt products could be considered as promising catalysis and supports for heterogeneous catalysis, according to the higher surface area and porous structure, which are advantages to facilitate the well-dispersed of metal catalysis nanoparticles on the surface of supports. Further work is under way.

4. Conclusions In our research, we have reported a facile and versatile methodology for the synthesis of carbonaceous materials with novel morphology and structure by cobalt-assisted hydrothermal/solvothermal treatment of furfural. It was worth noting that cobalt compounds have significant effect on the morphology and structure of the resultant carbonaceous structures. Hierarchical flower-like structures were obtained by hydrothermal process of furfural in the presence of Co(acac)2, while spherical particles were produced as Co(acac)2 was replaced by Co(NO3)2 or CoCl2 keeping other conditions constant. With ethanol as solvent, the presence of Co(acac)2 and Co(NO3)2 all led to the formation of hierarchical honeycomb-like structures by solvothermal process of furfural, respectively, while the presence of CoCl2 resulted in spherical particles. Especially, the further experimental results demonstrated that the formation of hierarchical carbonaceous 19



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structures was strongly depended on the presence of cobalt crystal. These results were explained that organic cobalt compound could be easily crystallized into cobalt crystal under hydrothermal/solvothermal treatment, which induced the formation of hierarchical carbonaceous structures. In addition, the morphology evolution of carbonaceous materials resulted from ethanol was mainly due to its assisted aggregation and assembly of primary products to form hierarchical structures during the solvothermal process.

Acknowledgements The authors thank the financial support of the Fundamental Research Funds for the Central Universities (2572014DB03), The Science and Technology Research Foundation of Heilongjiang Province Department of Education (12513005), Youths Science Foundation of Heilongjiang Province of China (QC2011C010).

Supporting Information Available SEM images of the C-Co(acac)2-H2O samples prepared with different molar ratio of furfural/ Co(acac)2, and the solvothermal production of Co(acac)2. SEM images of the samples obtained from furfural in ethanol/water system. Elemental analysis date from XPS. Co 2p XPS BE values data of samples. This information is available free of charge via the Internet at http://pubs.acs.org/.

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Effects of Cobalt Compounds on the Morphology and Structure of

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