Article pubs.acs.org/Langmuir
Assembling Tin Dioxide Quantum Dots to Graphene Nanosheets by a Facile Ultrasonic Route Chen Chen,† Lijun Wang,† Yanyu Liu,† Zhiwen Chen,*,†,∥ Dengyu Pan,‡ Zhen Li,† Zheng Jiao,*,†,‡ Pengfei Hu,§ Chan-Hung Shek,∥ C. M. Lawrence Wu,∥ Joseph K. L. Lai,∥ and Minghong Wu*,†,‡ †
Shanghai Applied Radiation Institute, ‡Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, and §Laboratory for Microstructures, Shanghai University, Shanghai 200444, People’s Republic of China ∥ Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong ABSTRACT: Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp2 hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.
1. INTRODUCTION Nanocomposites have attracted widespread attention because of their potential to combine desirable properties of different nanoscale building blocks to achieve advantageous electronic, optical, magnetic, and mechanic properties.1−3 It has been demonstrated that the high-performance lightweight composites could be developed by dispersing strong and highly stiff fibers in a polymer matrix and tailored to individual applications.4 Graphene as the basic plane of graphite is a single atomic layer of sp2 hybridized carbon atoms arranged in a honeycomb lattice. Graphene materials have attracted special interest due to its excellent optical,5−7 mechanical,8−10 and electrochemical properties.11−15 After an extensive search in the published literature, we stand at a similar threshold in the realm of incorporation of well-dispersed graphene-based sheets, produced by mechanical exfoliation, solution exfoliation, and reduction of graphite oxide with metal oxides, to result in excellent applications. Many types of metal oxide/graphene nanocomposites have been effectively prepared and extensively discussed, including CoO/graphene, 16,17 Co 3 O 4 /graphene, 18−21 CuO/graphene, 22,23 Mn 3 O 4 /graphene, 24−26 Fe 3 O 4 /graphene, 27,28 NiO/graphene, 29 TiO 2 /graphene,30,31ZnO/graphene.32 These nanocomposites are achieved, not only by using the inherent properties of the nanofiller, but also more importantly by optimizing the dispersion, interface chemistry, and nanoscale morphologies to take advantage of the enormous surface area per unit volume of graphene. © 2013 American Chemical Society
On the other hand, the size and morphology of metal oxides on graphene greatly affect their properties as well as their applications. For instance, when the size of the particle decreased, the surface−volume ratio and the band gap will increase correspondingly. This effect will finally lead to enhancement of the sensitivity of gas sensors.33 Therefore, the quantum effects, particularly in size of quantum dots, have enhanced great interest in both basic and applied research.34,35 However, most metal oxide/graphene composites prepared so far have relatively larger sizes, over 10 nm up to hundreds of nanometers, with unsatisfactory dispersions. Furthermore, the main routes commonly used for the preparation of the metal oxide/graphene composites were carried out with complicated processes or often suffered from poor manipulation on metal oxide/graphene composites. Therefore, it is highly desirable to develop a facile and general approach for the synthesis of metal oxide/graphene composites with favored microstructures for high-performance electrochemical properties. In this article, we report a facile one-step ultrasonic way to synthesize SnO2 quantum dots (QDs) on graphene nanosheets (GNS) by using SnCl2·2H2O as a precursor at ambient temperature. The size distribution of SnO2 QDs was estimated to be a range from 4 to 6 nm and their average size was Received: November 30, 2012 Revised: March 3, 2013 Published: March 4, 2013 4111
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
calculated to be about 4.8 ± 0.2 nm. Although enhanced properties of these materials have been demonstrated by numerous researchers, the fundamental knowledge of SnO2 quantum dot effects is not fully developed. Understanding the nanoscale impact of nanofillers on nanocomposite is critical to the success of all of these applications. Up to now, a large number of research groups are focusing on understanding how the chemistry, microstructure, and morphology of these nanocomposites affect their electrochemical properties in order to develop a general framework for their fabrication. We reported our observations that the GNS was exfoliated and decorated with SnO2 QDs. The incorporation of well-dispersed graphene-based sheets with metal oxide is an effective way to achieve the SnO2 nucleation and SnO2 QD growth. It is reasonable to speculate that the increased ID/IG intensity ratio in SnO2 QDs/GNS composites is closely related to the SnO2 QDs on GNS surface. The specific surface area (250 m2/g) of the SnO2 QDs/GNS composite is higher than that of bare GNS (205 m2/g). The specific surface area of SnO2 QDs/GNS composites increased as the SnO2 nanoparticles on both sides of the GNS became smaller.
conducted on a STA 449C instrument (Netzsch Instrument Co., German) from 30 to 1000 °C at a speed of 10 °C/min under N2 atmosphere.
3. RESULTS AND DISCUSSION Figure 1 shows the typical X-ray diffraction (XRD) patterns of (a) bare pure GNS, (b) SQDs/GNS composites, and (c) SnO2
Figure 1. Typical XRD patterns of (a) bare pure GNS, (b) SQDs/ GNS composites, and (c) SnO2 nanoparticles.
2. EXPERIMENTAL SECTION The reaction procedure can be described as a two-step method: (i) in situ loading of SnO2 QDs (SQDs) onto graphene oxide (GO) and (ii) GO conversion to graphene. The detailed preparation procedure is as follows: GO solution was synthesized from natural graphite powders by a modified Hummer’s method.16 The GO was washed repeatedly with deionized water to completely remove metal and acid particles. SnO2 quantum dots and graphene nanosheets (SQDs/GNS) composites were prepared by the coprecipitation method of the GO and SnCl2·2H2O solution. In a typical synthesis, 100 mL GO solution was dispersed in 50 mL distilled water by ultrasonic treatment to form a colloidal suspension. Subsequently, the suspension was mixed with 10 mL aqueous solution of SnCl2·2H2O (0.45 g). The resulting mixture with the Sn/graphene ratio = 1:1 in weight was continually stirred for 30 min. The mixture was then placed in an ultrasonic bath for 60 min. The product was left for 24 h, washed completely with distilled water, and dried in vacuum at 60 °C. Finally, the product was annealed at 500 °C for 3 h in N2 atmosphere. For comparison, the pure graphene nanosheets were prepared by the reduction of dried GO in N2 atmosphere at 500 °C for 3 h. X-ray powder diffraction (XRD) patterns were obtained from a Japanese Regaku D/max-2500 machine using Cu Kα radiation in reflection geometry. An operating voltage of 40 kV and a current of 40 mA were used. XRD patterns were recorded at a scanning rate of 0.08 deg s−1 in the 2θ range 10−90°. Field emission-secondary electron microscopy (FE-SEM) imaging was carried out with a field emission scanning electron microanalyzer (JEOL-6700F, 15 kV). High-resolution transmission electron microscopy (HRTEM) observations were performed on a JEOL JEM-2010F electron microscope operating at 200 kV. Surface area determinations were performed by Brunauer−Emmett−Teller (BET) method using an ASAP-2000 Surface Area Analyzer (Micromeritics Instrument Corporation). Raman scattering measurements were obtained by backscattering geometry with a SPEX-1403 laser Raman spectrometer. The excitation source was an argonion laser operated at a wavelength of 514.5 nm in the backscattering configuration and a low incident power to avoid thermal effects. Thermogravimetric analysis (TGA) was
nanoparticles. The pure GNS only shows a strong (002) diffraction peak in the XRD pattern as shown in Figure 1a. This peak shows that the GNS is multilayer graphene stacked with an interlayer spacing of about 0.35 nm, indicating that the graphene is similar to natural graphene sheets (d002 = 0.34 nm).36 By comparing Figure 1a, b, and c, it can be seen that the major diffraction peaks of some lattice planes of the SQDs/ GNS composites as shown in Figure 1b are similar to the tetragonal unit cell structure of SnO2 with lattice constants a = 4.738 Å and c = 3.187 Å, consistent with the standard values for bulk SnO2 (International Center for Diffraction Data (ICDD), PDF File No. 77−0447). The observed (hkl) peaks are (110), (101), (200), (211), (220), (002), (112), and (202), indicating that the SnO2 particles in this composite are well-crystallized. The minor peak (particularly at ca. 15°) belonging to other tin oxide crystals or impurities were detected. The high intensity of these peaks suggests that this SQDs/GNS composite mainly consists of the crystalline phase, while the (002) diffraction peak of layered GNS has almost disappeared. Thus, we can speculate that the regular lamellar structure of the GNS sheets has been completely broken in the as-synthesized composites, forming exfoliated GNS nanosheets. Figure 2 shows the field emission scanning electron microscopy (FE-SEM) images of (a) GNS and (b) SQDs/ GNS composites on Si (100) substrates. Figure 2a shows a representative SEM image of the GNS from the top view. This image shows layered platelets composed of curled nanosheets, in accordance with the (002) diffraction peak in the XRD pattern of the GNS. Figure 2b shows the FE-SEM image of the SQDs/GNS composites prepared by the facile synthesis approach. It is found that the FE-SEM images of the GNS and SQDs/GNS composites have similar morphology, implying that a fine structural manipulation of the GNS was successfully achieved even after the reassembling process with SnO2 nanoparticles. Interestingly, it can be seen clearly that the SnO2 nanoparticles were uniformly distributed on the graphene nanosheets, by which graphene nanosheet restacking and SnO2 nanoparticle aggregation were prevented. The component of prepared composites was confirmed by energy-dispersive X-ray analysis (EDS) as shown in the inset of Figure 2b. It can be 4112
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
Figure 2. FE-SEM images of (a) GNS and (b) SQDs/GNS composites on Si (100) substrates.
found that only Sn, C, and O elements were detected and the atomic ratio of Sn and C atoms was 1:10, which was consistent with their weight ratio (1:1). This further proves that the SnO2 nanoparticles have been successfully assembled to the graphene nanosheets. The surface morphology, particle size, and microstructure of these SQDs/GNS composites were further investigated by HRTEM. Figure 3a shows a typical exfoliated nanostructure. The TEM image clearly illustrates that the nanoparticles on the surface of the GNS were composed of homogeneous ultrafine SnO2 nanoparticles. It is obvious that they can be called SnO2 QDs which were uniformly distributed on the surface of the GNS in as-prepared SQDs/GNS composites. During the calcination process, the GNS distributed between SnO2 QDs prevented the agglomeration of these SnO2 nanoparticles,37−39 which was of great benefit to the formation of SnO2 QDs. The SnO2 nanoparticles deposited on the GNS have also prevented the GNS from stacking into multilayers39−41 in accordance with the result that no obvious diffraction peak attributed to the GNS in the XRD pattern of the SQDs/GNS composites was observed. Figure 3b displays an HRTEM image of the SQDs/ GNS composites. This shows clearly that the SnO2 QDs can form in the SQDs/GNS composites. The size distribution of SnO2 QDs is estimated to be ranging from 4 to 6 nm and their average size is calculated to be about 4.8 ± 0.2 nm according to the XRD and HRTEM results. The clear lattice fringes
Figure 3. TEM images of SQDs/GNS composites: (a) Lowmagnification TEM image, (b) HRTEM image.
demonstrate that the SnO2 QDs were composed of ultrafine nanoparticles. In addition, the HRTEM image of a typical SnO2 quantum dot shown in the inset of Figure 3b proves that the clear crystal lattice with a spacing of 0.336 nm corresponds to the (110) face of the SnO2 rutile phase. Therefore, it is certain that the SnO2 QDs distributed uniformly on the surface of the GNS were well-crystallized and was pure SnO2. It is known that embedding SnO2 QDs in a graphene nanosheet matrix would be an ideal strategy to overcome the electrode material’s poor cycling performance in lithium-ion batteries, which is attributed to the large volume changes and serious aggregation of particles during repeated lithium insertion and extraction reactions.42 However, the synthesis of a single-layer graphene nanosheet 4113
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
matrix is very challenging due to its high surface energy.43 Here, the SQDs/GNS composites with very few layers of graphene nanosheets have been successfully synthesized via a facile ultrasonic method. In addition, the approach is environmentally friendly because there is no toxic gas release during the reaction. Results show that this method can effectively prevent graphene nanosheets from being restacked, probably due to in situ loading of nanoparticles, which can decrease the surface energy of the graphene nanosheets.42 In order to obtain further information on the microstructure evolution of chemical processing from GO to SQDs/GNS, Raman spectroscopy was employed owing to its fine sensitivity to the crystal surface. As seen in Figure 4, the Raman spectrum
the oxygen atom from the carboxy group of GO to form SnO2 nanoparticle during stirring and ultrasonic vibration. Therefore, the Raman results are consistent with the results of TEM and EDS, indicating the formation of SQDs/GNS composites. Thermoanalysis results of the pure GNS and SQDs/GNS composites are given in Figure 5a and b, respectively. As can be
Figure 5. TG curves of (a) GNS and (b) SQDs/GNS composites.
seen in Figure 5, thermogravimetric (TG) analysis of the pure GNS shows that the amount of weight loss (mass loss ≈ 16.65%) is smaller than that of the SQDs/GNS composites (mass loss ≈ 26.27%). The redundant portion may be attributed to loss of ammonia, physically absorbed water, and chemically bonded water in the SnO2 QDs. N2 adsorption/desorption isotherms were employed to investigate the pore structures of the GNS and SQDs/GNS composites as shown in Figure 6a and b, respectively. The Brunauer−Emmett−Teller (BET) surface areas of the GNS and SQDs/GNS composites are about 205 m2/g and 250 m2/g, respectively. Obviously, the BET specific surface area of the SQDs/GNS composites is bigger than that of the GNS. Because of the confinement effect of the GNS, the SnO2 QDs can be separated one by one. Thus, the SnO2 nanoparticles on both sides of the GNS are expected to become smaller and the specific surface area of the SQDs/GNS composites became larger. A hysteresis loop in the nitrogen adsorption/desorption isotherms of the pure GNS was observed as shown in Figure 6a, indicating that the graphene sheets are porous. This hysteresis loop resembles type-H3 IUPAC (International Union of Pure and Applied Chemistry) classification, and may result from slitshaped pores between parallel layers.51 However, a nitrogen sorption hysteresis loop in the SQDs/GNS composites was also clearly observed in Figure 6b. The differences are that the adsorption branch rises slowly to the higher relative pressure point and then reaches a constant value, whereas the desorption branch moves slowly to the middle P/P0 signal point and decreases sharply, showing a clear type-H2 of the SQDs/GNS composites.52 Furthermore, it should be pointed out that the nitrogen desorption of the SQDs/GNS composites occurs at much lower relative pressure than that of the GNS, indicating that desorption of N2 molecules from the larger cavity is retarded by the smaller necks. From the above evidence, the
Figure 4. Room-temperature Raman spectra of (a) GNS and (b) SQDs/GNS composites.
of the GNS as shown in Figure 4a contains both D band (∼1335 cm−1, k-point phonons of A1g symmetry)44 and G band (∼1593 cm−1, E2g phonons of sp2 atoms). Raman spectra with characteristic D and G bands are sensitive to detects, disorder, and carbon grain size, and have been extensively used to characterize carbon materials. The D band in the Raman spectra is an indication of disorder in the GNS originating from defects associated with vacancies, grain boundaries, and amorphous carbon species. The Raman spectrum of SQDs/ GNS composites as shown in Figure 4b contains the G band at 1600.97 cm−1 owing to the presence of isolated double bonds that resonates at higher frequencies than the G band (1593.88 cm−1) of the GNS. The ID/IG intensity ratio is a measure of the degree of disorder and average size of the sp2 domains.45−48 In Figure 4, the ID/IG of the GNS is 1.09, but the value of ID/IG is 1.20 for the SQDs/GNS composites. Thus, there is an increased ID/IG intensity ratio in SQDs/GNS. When pyrolyzing GO to form GNS in N2, the mass of GO sharply declined, accompanied by a large number of gas emissions, such as CO, CO2, and H2O. The graphene nanosheets are stripped by breaking the restraint of van der Waals force in this process.49 The emission of CO and CO2 results in a large loss of carbon atoms from the graphene layers. This generates a lot of carbon cavities, leading to disorder in pyrolyzed GNS. It is noticeable that an increased ID/IG ratio in SQDs/GNS (1.20) was observed in comparison with that of GNS (1.02) at the same annealing condition. This change suggests a decrease in the average size of the sp2 domains,50 and an increase in vacancies, grain boundaries, and amorphous carbon species. Because of the reduction effect of bivalent tin, the Sn2+ is integrated with 4114
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
Figure 6. Nitrogen adsorption/desorption isotherms of (a) GNS and (b) SQDs/GNS composites. Pore diameter distribution patterns of (c) GNS and (d) SQDs/GNS composites.
Figure 7. Schematic formation mechanism of SQDs/GNS composites: (a) GO, (b) electrostatic interaction between oxide functional groups of GO and Sn2+, (c) graphene decorated with SnO2 nanoparticles (filled circles) after the calcine treatment, and (d) TEM image of SQDs/GNS composites.
ink-bottle-like pore structure can be concluded for the SQDs/ GNS composites. For this structure, the desorption of N2 occurs from the narrow neck and this is replenished from the larger parts of the pore.53 Figure 6c shows that the main pore
size distribution of the GNS is about 3−5 nm, while Figure 6d shows that the SQDs/GNS pore size distribution is between 2 and 4 nm. Interestingly, the GNS possesses higher porosity than that of the SQDs/GNS composites. The total pore volume 4115
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
of the GNS (0.47 cm3 g−1) is larger than that of the SQDs/ GNS composites (0.22 cm3 g−1). It can be reasonably speculated that the decreased pore volume in the SQDs/ GNS composites could arise primarily from the SnO2 QDs, which filled the space of the close stacking of graphene nanosheets, consistent with the average size of 4.8 ± 0.2 nm for SnO2 QDs in HRTEM observations as shown in Figure 3b. Further development of the SQDs/GNS composites requires a clear understanding of their formation mechanism. On the basis of our experimental results, Figure 7 shows the formation processes of the SQDs/GNS composites, which could reasonably be described by a novel model, and be separated into three steps. A GO sheet solution is fabricated from pristine graphite. Many previous studies have confirmed that the GO sheets are heavily oxygenated with hydroxyl and epoxide functional groups decorated on their basal planes, in addition to carbonyl and carboxyl groups located at the sheets edges.51,54 First, the GO was well-dispersed in distilled water to form a uniform GO nanosheet suspension by the strong hydrophilic of these functional groups.39,55 Then, the GO solution was mixed with a certain concentration SnCl2 solution. Sn2+ ion is selectively bonded with carboxyl and carbonyl through electrostatic attraction.56 As a result of the strong stirring conditions, the mixture solution is homogeneously dispersed and Sn2+ ions are also uniformly dispersed on the surface of GO sheets. Under ultrasonic vibration conditions, the interlayer spacing gradually increases, and Sn2+ ions could easily migrate into the enlarged layer. Then, Sn2+ ions, which are adsorbed firmly on both sides of the GO, prohibit the stacking of the GO by van der Waals forces. Sn2+ ions are not very stable due to electrostatic attraction. Finally, the precursor is heated at 500 °C in N2 for 3 h. The basic Sn2+ ions should be converted uniformly to small SnO2 QDs and the reduction of the GO. The GNS should occur simultaneously. We think that the rational selection of the SnCl2 precursor and the ultrasonic method may be critical for the successful preparation of uniformly dispersed SnO2 QDs on graphene substrates. First, the basic Sn2+ ions are firmly anchored on both sides of the GO through electrostatic attraction, and thus enhance the conjunction stability of the hybrids. This is an essential way to get the highly dispersed Sn 2+ ions on the GNS. Subsequently, the ultrasonic method provides a necessary driving force for complete uniform disposition. To sum up, we have reported a facile one-step ultrasonic way to synthesize SnO2 QDs on graphene nanosheets by using SnCl2·2H2O as a precursor at ambient temperature. We believe that the incorporation of well-dispersed graphene-based nanosheets with the metal oxides was an effective way to achieve the SnO2 nucleation and the SnO2 QDs growth. In this article, we provided some preliminary investigations in assembling SnO2 QDs to graphene nanosheets. Further detailed investigations on the influence of some specific synthetic conditions (such as Sn:GO ratio, calcination temperature, sonication time, and pH value of the solution) on the experimental results are in progress. The ultrasonic process indicated that the loading of SnO2 QDs was an effective way to prevent graphene nanosheets from being restacked during the reduction. The calcination process revealed that the graphene nanosheets distributed between SnO2 nanoparticles also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 QDs. The present results indicated that this research has brought about important developments to the SnO2/graphene nanocomposites.
4. CONCLUSIONS In conclusion, we have presented in detail a novel ultrasonic approach for the facile synthesis of the SQDs/GNS composites using GO as supporting materials and SnCl2 as a precursor. The microstructures of the SQDs/GNS composites were characterized by using XRD, EF-SEM, HRTEM, Raman, and TGA techniques. The results indicated that the GNS was exfoliated and decorated with SnO2 QDs, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 QDs was estimated to be a range from 4 to 6 nm, and their average size was calculated to be about 4.8 ± 0.2 nm. The clear lattice fringes of the SQDs indicated that the crystal planes of the SQDs were structurally perfect and uniform. The results revealed that the incorporation of well-dispersed graphenebased sheets with metal oxide is an effective way to achieve the SnO2 nucleation and the SnO2 QD growth. Investigations of the Raman spectra showed that the SQDs/GNS composites contain both D band and G band. It is reasonable to speculate that the increased ID/IG intensity ratio in the SQDs/GNS composites is closely related to the SQDs on the GNS. The BET surface area analysis indicated that the specific surface area (250 m2/g) of the SQDs/GNS is higher than that of the GNS (205 m2/g). The specific surface area of the SQDs/GNS composites increased as the SnO2 nanoparticles on both sides of the GNS became smaller.
■
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 21 66137503. Fax: +86 21 66137787. E-mail:
[email protected];
[email protected]; mhwu@staff.shu.edu. cn. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The work described in this article was financially supported by the National Natural Science Foundation of China (Project Numbers: 11074161, 11025526, and 41073073), Science and Technology Commission of Shanghai Municipality (Project Numbers: 10JC1405400, 09530501200), and Shanghai Leading Academic Discipline Project (Project Number: S30109). This work was also supported by strategic research grant (Project Number: 7008184) from the City University of Hong Kong.
■
REFERENCES
(1) Wang, D. H.; Kou, R.; Choi, D.; Yang, Z. G.; Nie, Z.; Li, J.; Saraf, L. V.; Hu, D. H.; Zhang, J. G.; Graff, G. L.; Liu, J.; Pope, M. A.; Aksay, I. A. Ternary self-assembly of ordered metal oxide-graphene nanocomposites for electrochemical energy storage. ACS Nano 2010, 4, 1587−1595. (2) Balazs, A. C.; Emrick, T.; Russell, T. P. Nanoparticle polymer composites: where two small worlds meet. Science 2006, 314, 1107− 1110. (3) Zeng, H.; Li, J.; Liu, J. P.; Wang, Z. L.; Sun, S. H. Exchangecoupled nanocomposite magnets by nanoparticle self-assembly. Nature 2002, 420, 395−398. (4) Ramanathan, T.; Abdala, A. A; Srankovich, S.; Dikin, D. A.; Herrera-Allonso, M. Functionalized graphene sheets for polymer nanocomposites. Nat. Nanotechnol. 2008, 3, 327−331. (5) Abergel, D. S. L.; Fal’ko, V. I. Optical and magneto-optical farinfrared properties of bilayer graphene. Phys. Rev. B 2007, 75, 155430− 1−155430−5. 4116
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
(6) Wang, F.; Zhang, Y. B.; Tian, C. S.; Girit, C.; Zettl, A.; Crommie, M.; Shen, Y. R. Gate-variable optical transitions in graphene. Science 2008, 320, 206−209. (7) Nair, R. R.; Blake, P.; Grigorenko, A. N.; Novoselov, K. S.; Booth, T. J.; Stauber, T.; Peres, N. M. R.; Geim, A. K. Fine structure constant defines visual transparency of graphene. Science 2008, 320, 1308− 1314. (8) Dresselhaus, M. S.; Dresselhaus, G. Intercalation compounds of graphite. Adv. Phys. 2002, 51, 1−186. (9) Hirata, M.; Gotou, T.; Horiuchi, S.; Fujiwara, M.; Ohba, M. Thinfilm particles of graphite oxide 1: high-yield synthesis and flexibility of the particles. Carbon 2004, 42, 2929−2937. (10) Yu, M. F.; Lourie, O.; Moloni, K.; Kelly, T. F.; Ruoff, R. S. Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load. Science 2000, 287, 637−640. (11) Berger, C.; Song, Z. M.; Li, T. B.; Li, X. B.; Ogbazghi, A. Y.; Feng, R.; Dai, Z. T.; Marchenkov, A. N.; Conrad, E. H.; First, P. N.; Heer, W. A. D. Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics. J. Phys. Chem. B 2004, 108, 19912−19916. (12) Zhang, Y.; Small, J. P.; Amori, M. E. S.; Kim, P. Electric field modulation of galvanomagnetic properties of mesoscopic graphite. Phys. Rev. Lett. 2005, 94, 176803−1−176803−4. (13) Zhang, Y.; Tan, Y. W.; Stormer, H. L.; Kim, P. Experimental observation of the quantum Hall effect and Berry’s phase in graphene. Nature 2005, 438, 201−204. (14) Novoselov, K. S.; Geim, A. K.; Morozov, S. K.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Twodimensional gas of massless Dirac fermions in graphene. Nature 2005, 438, 197−200. (15) Stankovich, S.; Dikin, D. A.; Dommett, G. H. B.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S. Graphene-based composite materials. Nature 2006, 442, 282−286. (16) Peng, C. P.; Chen, B. D.; Qin, Y.; Yang, S. H.; Li, C. Z.; Zuo, Y. H.; Liu, S. Y.; Yang, J. H. Facile ultrasonic synthesis of CoO quantum dot/graphene nanosheet composites with high lithium storage capacity. ACS Nano 2012, 6, 1074−1081. (17) Zhu, J. X.; Sharma, Y. K.; Zeng, Z. Y.; Zhang, X. J.; Srinivasan, M.; Mhaisalkar, S.; Zhang, H.; Hng, H. H.; Yan, Q. Y. Cobalt oxide nanowall arrays on reduced graphene oxide sheets with controlled phase, grain size, and porosity for Li-ion battery electrodes. J. Phys. Chem. C 2011, 115, 8400−8406. (18) Kim, H.; Seo, D. H.; Kim, S. W.; Kim, J.; Kang, K. Highly reversible Co3O4/graphene hybrid anode for lithium rechargeable batteries. Carbon 2011, 49, 326−332. (19) Li, B. J.; Cao, H. Q.; Shao, J.; Li, G. Q.; Qu, M. Z.; Yin, G. Co3O4@graphene composites as anode materials for high-performance lithium ion batteries. Inorg. Chem. 2011, 50, 1628−1632. (20) Chen, S. Q.; Wang, Y. Microwave-assisted synthesis of a Co3O4graphene sheet-on-sheet nanocomposite as a superior anode material for Li-ion batteries. J. Mater. Chem. 2010, 20, 9735−9739. (21) Wu, Z. S.; Ren, W. C.; Wen, L.; Gao, L. B.; Zhao, J. P.; Chen, Z. P.; Zhou, G. M.; Li, F.; Cheng, L. M. Graphene anchored with Co3O4 nanoparticles as anode of lithium ion batteries with enhanced reversible capacity and cyclic performance. ACS Nano 2010, 4, 3187−3194. (22) Wang, B.; Wu, X. L.; Shu, C. Y.; Guo, Y. G.; Wang, C. R. Synthesis of CuO/graphene nanocomposite as a high-performance anode material for lithium-ion batteries. J. Mater. Chem. 2010, 20, 10661−10664. (23) Xu, C.; Wang, X.; Yang, L. C.; Wu, Y. P. Fabrication of a graphene/cuprous oxide composite. J. Solid State Chem. 2009, 182, 2486−2490. (24) Wang, H. L.; Cui, L. F.; Yang, Y.; Casalongue, H. S.; Robinson, J. T.; Liang, Y. Y.; Cui, Y.; Dai, H. J. Mn3O4-graphene hybrid as a highcapacity anode material for lithium ion batteries. J. Am. Chem. Soc. 2010, 132, 13978−13980.
(25) Li, L.; Guo, Z. P.; Du, A. J.; Liu, H. K. Rapid microwave-assisted synthesis of Mn3O4−graphene nanocomposite and its lithium storage properties. J. Mater. Chem. 2012, 22, 3600−3605. (26) Lee, J. W.; Hall, A. S.; Kim, J. D.; Mallouk, T. E. A facile and template-free hydrothermal synthesis of Mn3O4 nanorods on graphene sheets for supercapacitor electrodes with long cycle stability. Chem. Mater. 2012, 24, 1158−1164. (27) Zhu, X. J.; Zhu, Y. J.; Murali, S.; Stoller, M. D.; Ruoff, R. S. Nanostructured reduced graphene oxide/Fe2O3 composite as a highperformance anode material for lithium ion batteries. ACA Nano 2011, 5, 3333−3338. (28) Li, B. J.; Cao, H. Q.; Shao, J.; Qu, M. Z.; Warner, H. H. Superparamagnetic Fe3O4 nanocrystals@graphene composites for energy storage devices. J. Mater. Chem. 2011, 21, 5069−5075. (29) Zou, Y. Q.; Wang, Y. NiO nanosheets grown on graphene nanosheets as superior anode materials for Li-ion batteries. Nanoscale 2011, 3, 2615−2620. (30) Qiu, Y. C.; Yan, K. Y.; Yang, S. H.; Jin, L. M.; Deng, H.; Li, W. S. Synthesis of size-tunable anatase TiO2 nanospindles and their assembly into anatase@titanium oxynitride/titanium nitride-graphene nanocomposites for rechargeable lithium ion batteries with high cycling performance. ACS Nano 2010, 4, 6515−6526. (31) Ding, S. J.; Chen, J. S.; Luan, D. Y.; Boey, F. Y. C.; Madhavi, S.; Lou, X. W. Graphene-supported anatase TiO2 nanosheets for fast lithium storage. Chem. Commun. 2011, 47, 5780−5782. (32) Zhang, S. L.; Zhang, Y. Z.; Huang, S. P.; Liu, H.; Wang, P.; Tian, H. P. First-principles study of field emission properties of grapheneZnO nanocomposite. J. Phys. Chem. C 2010, 114, 19284−19288. (33) Chen, Z. W.; Pan, D. Y.; Zhao, B.; Ding, G. J.; Jiao, Z.; Wu, M. H.; Shek, C. H.; Wu, L. C. M.; Lai, J. K. L. Insight on fractal assessment strategies for tin dioxide thin films. ACS Nano 2010, 4, 1202−1208. (34) Wang, J.; Du, J.; Chen, C.; Li, Z.; Jiao, Z.; Wu, M. H.; Shek, C. H.; Wu, C. M. L.; Lai, J. K. L.; Chen, Z. W. Electron-beam irradiation strategies for growth behavior of tin dioxide nanocrystals. J. Phys. Chem. C 2011, 115, 20523−20528. (35) Chen, Z. W.; Jiao, Z.; Wu, M. H.; Shek, C. H.; Wu, C. M. L.; Lai, J. K. L. Microstructural evolution of oxides and semiconductor thin films. Prog. Mater. Sci. 2011, 56, 901−1029. (36) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric field effect in atomically thin carbon films. Science 2004, 306, 666−669. (37) Liu, H. P.; Long, D. H.; Liu, X. J.; Qiao, W. M.; Zhan, L.; Ling, L. C. Facile synthesis and superior anodic performance of ultrafine SnO2 containing nanocomposites. Electrochim. Acta 2009, 542, 5782− 5788. (38) Wang, X. Y.; Zhou, X. F.; Yao, K.; Zhang, J. G.; Liu, Z. L. A SnO2/graphene composite as a high stability electrode for lithium ion batteries. Carbon 2011, 49, 133−139. (39) Lian, P. C.; Zhu, X. F.; Xiang, H. F.; Li, Z.; Yang, W. S.; Wang, H. H. Enhanced cycling performance of Fe3O4−graphene nanocomposite as an anode material for lithium-ion batteries. Electrochim. Acta 2010, 56, 834−840. (40) Zhang, L. S.; Jiang, L. Y.; Yan, H. J.; Wang, W. D.; Wang, W.; Song, W. G.; Guo, Y. G.; Wan, L. J. Mono dispersed SnO 2 nanoparticles on both sides of single layer graphene sheets as anode materials in Li-ion batteries. J. Mater. Chem. 2010, 20, 5462−5467. (41) Du, Z. F.; Yin, X. M.; Zhang, M.; Hao, Q. Y.; Wang, Y. G.; Wang, T. H. In situ synthesis of SnO2/graphene nanocomposite and their application as anode material for lithium ion battery. Mater. Lett. 2010, 64, 2076−2079. (42) Zhong, A.; Wang, J. Z.; Chen, Z. X.; Liu, H. K. SnO2-graphene composite synthesized via an ultrafast and environmentally friendly microwave autoclave method and its use as a superior anode for lithium-ion batteries. J. Phys. Chem. C 2011, 115, 25115−25120. (43) Xu, Y. X.; Bai, H.; Lu, G. W.; Li, C.; Shi, G. Q. Flexible graphene films via the filtration of water-soluble noncovalent functionalized graphene sheets. J. Am. Chem. Soc. 2008, 130, 5856−5857. 4117
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
Langmuir
Article
(44) Liang, J. F.; Wei, W.; Zhong, D.; Yang, Q. L.; Li, L. D.; Guo, L. One-step in situ synthesis of SnO2/graphene nanocomposites and its application as an anode material for Li-ion batteries. Appl. Mater. Interfaces 2012, 4, 454−459. (45) He, H.; Klinowski, J.; Forster, M.; Lerf, A. A new structural model for graphite oxide. Chem. Phys. Lett. 1998, 287, 53−56. (46) Lerf, A.; He, H.; Forster, M.; Klinowski, J. Structure of graphite oxide revisited. J. Phys. Chem. B 1998, 102, 4477−4482. (47) Hirata, M.; Gotou, T.; Ohba, M. Thin-film particles of graphite oxide 2: preliminary studies for internal micro fabrication of single particle and carbonaceous electronic circuits. Carbon 2005, 43, 503− 510. (48) Szabo, T.; Szeri, A.; Dekany, I. Composite graphitic nanolayers prepared by self-assembly between finely dispersed graphite oxide and a cationic polymer. Carbon 2005, 43, 87−94. (49) Zhong, L. S.; Hu, J. S.; Cui, Z. M.; Wan, L. J.; Song, W. G. Insitu loading of noble metal nanoparticles on hydroxyl-group-rich titania precursor and their catalytic application. Chem. Mater. 2007, 19, 4557−4562. (50) Tuinstra, F.; Koenig, J. L. Raman spectrum of graphite. J. Chem. Phys. 1970, 53, 1126−1130. (51) Paek, S. M.; Yoo, E. J.; Honma, I. Enhanced cyclic performance and lithium storage capacity of SnO2/graphene nanoporous electrodes with three-dimensionally delaminated flexible structure. Nano Lett. 2009, 9, 72−75. (52) Salmas, C. E.; Androutsopoulos, G. P. Rigid sphere molecular model enables an assessment of the pore curvature effect upon realistic evaluations of surface areas of mesoporous and microporous materials. Langmuir 2005, 21, 11146−11160. (53) Zhao, D. Y.; Feng, J. L.; Huo, Q. S.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science 1998, 279, 548−552. (54) Noerochim, L.; Wang, J. Z.; Chou, S. L.; Li, H. J.; Liu, H. K. SnO2-coated multiwall carbon nanotube composite anode materials for rechargeable lithium-ion batteries. Electrochim. Acta 2010, 56, 314− 320. (55) Wang, Y.; Zeng, H. C.; Lee, J. Y. Highly reversible lithium storage in porous SnO2 nanotubes with coaxially grown carbon nanotube overlayers. Adv. Mater. 2006, 18, 645−649. (56) Lian, P. C.; Zhu, X. F.; Liang, S. Z.; Li, Z.; Yang, W. S.; Wang, H. H. High reversible capacity of SnO2/graphene nanocomposite as an anode material for lithium-ion batteries. Electrochim. Acta 2011, 56, 4532−4539.
4118
dx.doi.org/10.1021/la304753x | Langmuir 2013, 29, 4111−4118
