Facile approach to prepare multi-walled carbon nanotubes/graphene nanoplatelets hybrid materials
© Jia et al.; licensee Springer. 2013
Received: 17 April 2013
Accepted: 7 May 2013
Published: 16 May 2013
A facile approach was developed to prepare multi-walled carbon nanotubes/graphene nanoplatelets hybrid materials through covalent bond formation. First, poly(acryloyl chloride) was grafted onto oxidized multi-walled carbon nanotubes through the reaction between the acyl chloride groups of poly and the hydroxyl groups of oxidized multi-walled carbon nanotubes. Second, the remaining acyl chloride groups of poly were allowed to react with the hydroxyl groups of hydroxylated graphene nanoplatelets. Scanning electron microscopy and transmission electron microscopy data showed that the multi-walled carbon nanotubes and graphene nanoplatelets were effectively connected with each other. And Fourier transform infrared spectroscopy data indicated the formation of covalent bonds between carbon nanotubes and graphene nanoplatelets. Conformational changes were monitored by Raman spectroscopy. This novel kind of carbon hybrid materials may have the potential application in a wide field, especially in increasing the toughness and strength of the matrix resin.
KeywordsMulti-walled carbon nanotubes Graphene Hybrid materials Poly(acryloyl chloride) Microstructure
Recently, hybrid composites have attracted large attention and have received increasing interest in various fields [1–4]. Researchers with different mixtures have been tried out, such as multi-walled carbon nanotubes (MWCNTs) with carbon black , few layer graphene with single-walled carbon nanotubes , and MWCNTs with graphene nanoplatelets (GnPs) . Kumar et al.  brought together hybridized graphitic nanoplatelets and commercially functionalized MWCNTs in a polyetherimide composite. The results revealed a synergistic interaction between the GnPs and MWCNTs based on GnPs protection against fragmentation of the MWCNTs during high-power sonication. Chao Zhang et al.  revealed that the graphene oxide (GO) assisted the dispersion of pristine MWCNTs in aqueous media. Moreover, the solubility results indicated that the GO sheets leaned towards stabilizing MWCNTs with larger diameters, mainly depending on whether the MWCNTs are inclined to form bundles, twisted structures, or MWCNTs/GO complexes. S. Chatterjee et al.  studied the mechanical reinforcement in a widely used epoxy matrix with the addition of GnPs and various mixture ratios of MWCNTs with GnPs. It had been indicated that the size and synergy effects of nanofiller hybrids including GnPs and MWCNTs played an important role in the mechanical properties of epoxy composites. As mentioned above, these hybrid materials were obtained via the unstable π-stacking interaction, which could be damaged by mechanical stirring or long-time ultrasound. Young-Kwan Kim et al.  formed graphene oxide scrolls around MWCNT templates through covalent bond formation. Graphene oxide sheets were successfully made to adopt a scroll conformation around the surface of aminated MWCNT in solution by covalent bond formation. Like the stick wrapped with a film, the microstructure of this kind of hybrid material was still two-dimensional (2D) structure.
In this work, we chose carbon nanotubes and graphene nanoplatelets to prepare three-dimensional (3D)-structured hybrid materials. Due to their unique tubular structure, carbon nanotubes mainly reflect rigidity, while graphene nanoplatelets appear to have better toughness owing to its laminated structure [8–10]. A methodology of preparing multi-walled carbon nanotubes/graphene platelets (MWCNTs/GnPs) hybrid materials was proposed, using poly(acryloyl chloride) as bridges between carbon nanotubes and GnPs. Compared with the other hybrid methods [4–7], this approach is facile, efficient, and easy to control by regulating and controlling polymer chains of poly(acryloyl chloride) (PACl) which can provide numerous reactive groups. In addition, based on the theory of hybrid structure , this novel kind of MWCNTs/GnPs hybrid materials can combine the advantages of carbon nanotubes and graphenes, which would make this unique hybrid structures possess the potential application in a wide field, especially in increasing the toughness and strength of the matrix resins. The preparation process involved the following three steps: Firstly, hydroxyl groups on the surface of acid-oxidized multi-walled carbon nanotubes (MWCNTs-OH) reacted with linear PACl to generate highly reactive polymer grafting on the nanotube surface [12, 13]. Secondly, the generation of MWCNTs/GnPs hybrid materials could be obtained by the reaction of the acyl chloride groups of PACl on the surface of PACl-grafted MWCNTs (MWCNTs-PACl) and the hydroxyl groups on the surface of hydroxylated GnPs (GnPs-OH). Since PACl provided numerous reactive sites, a large quantity of MWCNTs could be assembled surrounding the GnPs.
MWCNTs-OH (95% pure, length of <5 μm, main range of outer diameter was 20 to 40 nm) were purchased from Shenzhen Nanotech Port Co Ltd. (Shenzhen, China). Graphene nanoplatelets (GnPs) (diameter of 1 to 20 μm, thickness of 5 to 15 nm) were purchased from Xiamen Knano Graphene Technology Co. Ltd. (Xiamen, China). Acryloyl chloride was supplied by J & K Scientific Ltd. (Shanghai, China). Nitric acid, sulfuric acid, tetrahydrofuran (THF), 1,4-dioxane and 2,2′-azosiobutyrontrile (AIBN) were provided by Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China).
Preparation of carbon nanotubes/graphene hybrid materials
The morphologies of the products were observed by scanning electron microscopy (SEM, Hitachi SU1510; Hitachi Ltd. (China), Beijing, China) and transmission electron microscopy (TEM, H-800-1), with the accelerating voltage of 20 to 30 kV, respectively. The microstructures of the samples were analyzed by Fourier transform infrared spectroscope (FTIR, Nexus 670; Thermo Fisher Scientific, Hudson, NH, USA) and Raman spectrometer. Thermal gravimetric analysis (TGA) was conducted on a TGA/SDTA851e instrument at a heating rate of 10°C/min in a nitrogen flow.
The morphology analysis
The structure analysis
In addition, it should be noted that the G band of MWCNTs was divided into two bands, and the new D′ band at 1,604 cm−1 could be related to the extent of the disorder [19, 20]. It was worth noting that the D′ band was hardly observed for other samples, which indicated that GnPs and hybrid materials have the smallest amount of impurities. Consequently, the hybrid materials possess higher mechanical properties and thermal conductivity with high crystalline structures [11, 21].
Thermal gravimetric analysis
In summary, MWCNTs/GnPs hybrid materials can be successfully obtained by a facile method using PACl as a bridge. MWCNTs were assembled onto the surface of GnPs through the reaction of the hydroxyl groups of GnPs and the acyl chloride groups of PACl. The results showed the unique microstructure and excellent thermal properties of MWCNTs/GnPs hybrid materials. It is a pleasure to see that MWCNTs/GnPs hybrid materials make their respective advantages complementary to each other as designed. Therefore, the presented approach will show a potential for preparing carbon hybrid materials through using polymer chains as bridges.
Fourier transform infrared spectroscope
hydroxylated graphene nanoplatelets
multi-walled carbon nanotubes
multi-walled carbon nanotubes/graphene nanoplatelets hybrid materials
oxidized multi-walled carbon nanotubes
scanning electron microscopy
Transmission electron microscopy
Thermal gravimetric analysis
This work was supported by the National Natural Science Foundation of China (no. 51203062), Cooperative Innovation Fund-Prospective Project of Jiangsu Province (no. BY2012064), and Science and Technology support Project of Jiangsu Province (no. BE2011014). KJ Yu thanks the Postdoctoral Fund Project of China (no. 2012M520995).
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