Letter pubs.acs.org/Langmuir
Green and Tunable Decoration of Graphene with Spherical Nanoparticles Based on Laser Ablation in Water: A Case of Ag Nanoparticle/Graphene Oxide Sheet Composites Hui He,*,† Haibo Wang,† Kai Li,† Jun Zhu,† Jianshuang Liu,† Xiangdong Meng,† Xiaoshuang Shen,† Xianghua Zeng,*,† and Weiping Cai‡ †
College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, P. R. China Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, P. R. China
‡
S Supporting Information *
ABSTRACT: A simple and green strategy is presented to decorate graphene with nanoparticles, based on laser ablation of targets in graphene auqeous solution. Ag and graphene oxide (GO) are chosen as model materials. The surface of GO sheets is strongly anchored with spherical Ag nanoparticles. The density and size of the Ag nanoparticles can be easily tuned by laser ablation conditions. Further, the GO sheets can be decorated with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. Additionally, the Ag nanoparticle/GO sheet colloids can be utilized as blocks to build three-dimensional structures, such as sandwich membranes by evaporation-induced self-assembly. These graphene-based composite materials could be very useful in catalysis, sensors, and nanodevices. Particularly, the Ag nanoparticle/GO sheet sandwich composite membranes exhibit excellent surfaceenhanced Raman scattering performance and possess the huge potential in trace-detecting persistent organic pollutants in the environment.
1. INTRODUCTION Graphene, a few layers of carbon atoms packed into a twodimensional (2D) honeycomb lattice,1 is identified as a valuable platform for the dispersion or immobilization of nanoparticles, owing to its large surface area, high chemical/thermal stability, and strong coupling effects between nanoparticles and graphene in photonic and electronic applications.2−4 For example, graphene decorated with noble metal nanoparticles, especially Ag nanoparticles, have exhibited excellent surfaceenhanced Raman scattering (SERS) performance due to their good structural stability and high density of hot spots along and between the sheets.5−7 Additionally, graphene itself has been used in SERS as an additional chemical enhancer,8 an antioxidative coating,9 a fluorescence quencher,10 a molecule enricher,11,12 and so forth. The key impediment for the decoration or deposition of nanoparticles on graphene is the lack of robust and facile fabrication strategies, which is challenging for current nanofabrication technology due to the small dimensions. The existing techniques fall into two main categories: chemical processes (chemical reduction,13−15 photochemical reaction,16 electroless plating,17 electrostatic selfassembly,18 chemical functionalization,19 etc.) and physical vapor deposition (pulsed laser deposition,20 thermal evaporation,21 etc.). However, these techniques are based on the bottom-up nanofabrication strategy and have many drawbacks © XXXX American Chemical Society
including the use of diverse additives or sophisticated equipment and the difficulty in tuning the size, density and component of coated nanoparticles. Furthermore, because of uneasiness of assembly, the large-sized nanoparticle/graphene composites prepared thus far are mostly in irregular organizations and macroscopically exhibit powder aggregates, which is unbeneficial for some practical applications, such as SERS. In this study, we propose a novel way to overcome these issues in decoration based on laser ablation in liquid. Laser ablation in liquid, which belongs to the top-down strategy, is a versatile and widely used technique to synthesize various nanoparticles.22,23 It has the advantages of simplicity, cleanness, and easy tunability of particle diameters from several to hundreds of nanometers. In addition to the targets and laser parameters, the used liquid media, which provides tight confinement of the ablated species, plays key roles in final products, such as using surfactants as capping agents to prevent the agglomeration of nanoparticles and inorganic salts as reactants to prepare various micro/nanostructures. If the liquid contains very small particles (e.g., graphene sheets), however, it Received: September 23, 2015 Revised: January 30, 2016
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DOI: 10.1021/acs.langmuir.5b03527 Langmuir XXXX, XXX, XXX−XXX
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duration of 10 ns) with a power of 110 mJ per pulse. The solution was stirred continuously during ablation. The Ag product in the solution was estimated to be approximately 35.6 ng per min according to the mass loss of the Ag target. 2.3. Characterization. The morphology and structure of the samples were characterized by using field-emission scanning electron microscope (FESEM, Sirion 200), transmission electron microscope (TEM, JEM-200CX) and X-ray diffraction (XRD, X′ Pert Pro MPD). Optical absorption was studied on a Cary 5E UV−vis−NIR spectrophotometer. X-ray photoelectron spectroscopic (XPS) analysis was performed on an ESCALAB MK2 photoelectron spectrometer with Mg Kα radiation. For SERS measurements, 10 μL R6G aqueous solutions of different concentrations were dispersed on the samples (5 mm × 5 mm) and dried in the air. For trace detection, PCB77 was dissolved in hexane. SERS spectra were recorded using a 514.5 nm laser in a confocal microprobe Raman system (JY, LABRAM-HR, France). The laser power was 1 mW and the laser spot focused on the sample surface was about 10 μm in diameter.
may be completely different, and unique structures can be expected. Herein, Ag and graphene oxide (GO) are chosen as model materials to demonstrate the feasibility of the strategy. By using laser ablation of a Ag target in auqeous solution containing GO sheets, as schematically illustrated in Figure 1, we decorated Ag
3. RESULTS AND DISCUSSION 3.1. Morphologies and Structure. Figure 2a is a typical TEM image of the peeled-off GO sheets by a modified Hummers method. These sheets are well dispersed in colloidal solution, a few microns in lateral dimension, and several carbon atomic layers in thickness, as shown in Figure 2b. After laser ablation of a Ag metal plate for 40 min in the GO colloids, a new colloidal solution can be obtained. TEM observations suggest that individual GO sheets are densely coated with nanoparticles on both sides, exhibiting a hierarchical micro/ nanostructure (see Figure 2c). The selected area electronic diffraction pattern (SAED) reveals that these nanoparticles are crystallites with a face-centered cubic silver structure (inset in Figure 2c). The Ag nanoparticles are nearly spherical with a size range between 20 and 100 nm and a mean diameter of approximately 60 nm by statistics (Figure 2d). Overall, GO sheets act as a planar substrate to fix 0D Ag nanoparticles, while the nanoparticles separate the sheets as spacers. For such a structure, aggregation of both GO sheets and Ag nanoparticles are effectively avoided, which enables the active surface to be maintained and open channels left for mass transport. Optical absorption spectrum of the resultant colloidal solution, compared with that of the original GO colloids, presents a new peak at 390 nm apart from the GO absorption peaks (Figure 2e), which is ascribed to the dipole resonance absorption of Ag nanoparticles. The difference in optical absorption corresponds to the color change from deep yellow for GO colloids to medium gray for GO colloids with Ag nanoparticles (inset in Figure 2e). Further, the ID/IG ratio in the Raman spectra for the GO sheets after laser irradiation is almost unchanged, indicating an insignificant decreasement of property of the GO sheets upon laser irradiation and integration with Ag nanoparticles. To gain better insight into the surface composition and elements’ status of the GO and Ag, XPS analysis was carried out. In the high-resolution XPS spectrum about C 1s (Figure 2g), the peak located at about 284.6 eV is ascribed to nonoxygenated ring carbon atoms, and the other peaks positioned at 286.7, 287.8, and 289.1 eV are attributed to the oxygen containing groups (C−OH), (CO) and (OC− OH), respectively.26 Thus, the chemical properties of GO sheets are not dramatically changed during laser ablation, which
Figure 1. Schematic illustration for anchoring Ag nanoparticles to GO sheets.
nanoparticles on GO sheets at ambient temperature. The Ag nanoparticles are tightly bounded to each sheet’s surface, forming a hierarchical micro/nanostructure. The density and size of the Ag nanoparticles can be tuned by laser ablation parameters. The strategy is straightforward, economic, and easy to control. And it is an essentially clean process, thus ensuring a high surface activity of Ag nanoparticles. Such cleaning is impossible to reproduce even by green chemistry, since there are always some unreduced metal ions in the solution. Further, this strategy can be used to decorate GO sheets with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. In addition, because they are still in the colloidal state, the Ag nanoparticle/GO sheet composites can be used as blocks to construct three-dimensional structures, such as sandwich membranes by evaporation-induced selfassembly. The as-prepared Ag nanoparticle/GO sheet colloids and their sandwich membranes could be very useful such as in sensors, catalysis and nanodevices. It has been shown that the sandwich membranes exhibit strong SERS activity with good reproduction and stability and have the possibility of detecting the trace levels of persistent organic pollutants in the environment.
2. EXPERIMENTAL SECTION 2.1. Preparation of GO. GO was produced by a modified Hummers method24,25 and purified by dialysis for a week to remove any impurities. In this work, natural graphite was used with an average particle size of 325 mesh. The concentration of GO in auqeous solution is approximately 0.2 mg mL−1. 2.2. Preparation of Ag Nanoparticle/GO Sheet Colloids. Ag nanoparticle/GO sheet colloidal solutions were prepared by laser ablation of a Ag metal target in the GO solution. Typically, a metal target was fastened 12 mm below the liquid surface on a bracket in a glass vessel filled with 20 mL of the GO solution. Then, the metal target was irradiated for 40 min by using the first harmonic of a Nd:YAG pulsed laser (wavelength of 1064 nm, frequency of 10 Hz, and pulse B
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The density of the Ag nanoparticles on the GO sheets depends strongly on the laser ablation time. Within a certain time range, longer ablation times correspond to higher densities, or vice versa. For instance, Figure 3a and Supporting
Figure 3. TEM images of Ag nanoparticle/GO sheet colloids in the colloidal solutions formed by laser ablation of Ag targets in the GO solution shown in Figure 2a (a) for 20 min and (b) with a power of 130 mJ per pulse, under the same other experimental conditions as those of the sample shown in Figure 2c. Insets: nanoparticle size distributions.
Figure 2. Morphologies, structure and optical properties of GO sheets before and after decoration with Ag nanoparticles. (a,b) Typical TEM image of one GO sheet and its corresponding local high resolution. (c) TEM image of GO sheets coated with Ag nanoparticles. Inset: the corresponding SAED pattern. (d) Nanoparticle size distribution. (e) Optical absorption spectra contrast. Inset: photo contrast. (f) Raman spectra contrast. (g,h) XPS data of GO sheets coated with Ag nanoparticles.
Information Figure S1 exhibit the morphologies of the composites with low and high densities of Ag nanoparticles (equal in mean size to those in Figure 2c), respectively corresponding to the colloidal solutions formed by laser ablation for 20 and 60 min. However, too long ablation time (e.g., > 1 h) should be avoided due to formation of some large particles by agglomeration of the small nanoparticles on the GO sheets and/or from laser ablation. In such a case, the extension of time alone will not increase the number of Ag nanoparticles on a single GO sheet significantly but broaden the size distribution. In addition, it should be mentioned that the GO sheets with too dense Ag nanoparticles are unbenificial to form the perfect Ag nanoparticle/GO sheet sandwich composite membranes by self-assembling resulting from the weak interaction involved between the GO sheets. Control of the density (or amount) of the Ag nanoparticles on the individual GO sheets can also be achieved by varying the number of GO sheets in solution. For a given period of laser ablation, the total Ag yield is constant. If the GO colloidal concentration and the ablation period are fixed, the number density of the Ag nanoparticles on the GO sheets, within a certain range, will increase with a decrease in the volume of solution because the total number of GO sheets decreases.
is consistent with the Raman spectrum characterization. Figure 2h displays the Ag 3d region. We can see that there are two main peaks centered at about 368.2 eV for 3d5/227 and 374.2 eV for 3d3/2,28 which are assigned to bulk silver. Obviously, the Ag production during laser ablation in water and the interfacial binding between Ag and GO did not significantly influence the metallic properties of the Ag nanoparticles. Therefore, in contrast to the chemical reduction method, such laser ablation offers the possibility of the controllable and contamination-free production of Ag nanoparticles on GO sheets, which is vitally important for surface activity. 3.2. Structural Tunability. Further experiments have revealed that the density and size of the Ag nanoparticles on the GO sheets are tunable by changing laser ablation conditions. The easy control of the structural polymorphism is important for actural applications. C
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(Supporting Information Figure S1). During ablation and/or subsequent laser irradiation, the big parent nanoparticles will be fragmented into smaller ones due to absorption of photon energy (Supporting Information Figure S2).32 Additionally, it should be pointed out that there could be few Ag nanoparticles that are free in solution. If the weight of GO sheets and the ablation period are fixed, Ag nanoparticles coated on GO sheets will decrease in number density with increasing volume of water because the collision frequency decreases between the Ag nanoparticles and GO sheets. 3.4. Universality of the Strategy. Due to the universality of laser ablation in water, the strategy can be used to coat GO sheets with other nanoparticles from simple metals or semiconductors to multicomponent hybrids provided that the targets for laser ablation are effectively chosen. To illustrate, Supporting Information Figure S4 gives the compositions and morphologies of the GO sheets coated with Au, ZnO, and Au1Ag2 nanoparticles, respectively based on laser ablation of Au, ZnO, and Au1Ag2 targets in the GO solution, under the same experimental conditions as those of the sample shown in Figure 2c. We can see the similar configuration to that shown in Figure 2c and the same structures of these nanoparticles as those of their corresponding targets. Moreover, various micro/ nanostructures could also be coated on GO sheets by chemical reaction of targets with liquid media during laser ablation. 3.5. Extension of the Strategy. It should be mentioned that the Ag nanoparticle/GO sheet colloids can be used as blocks to build three-dimensional structures by various processes. Particularly, evaporation is widely used to fabricate pure GO membranes. Generally, it is not easy for large-sized colloids like the Ag nanoparticle/GO sheet ones to assemble because of relatively lower surface activity.33,34 In our case, however, self-assembly possibly occurs because the GO sheets, although coated with the Ag nanoparticles by laser ablation, remain unaltered in chemical property, as confirmed by the spectral analysis above, and thus in interface assembling behavior. We have fabricated three-dimensional sandwich membranes by evaporation of the Ag nanoparticle/GO sheet colloidal solution shown in Figure 2c. Also, the membranes are tunable in architecture (or the density and diameter of nanoparticles; the size and thickness of membranes) by the preliminary laser ablation conditions and the subsequent selfassembly duration. Typically, Supporting Information Figure S5 displays the morphologies, structure, and optical properties of a sandwich membrane by a compact layer-by-layer stack of the Ag nanoparticle/GO sheet colloids. 3.6. SERS Performance. The Ag nanoparticle/GO sheet composite materials are of use in catalysis, sensors and nanodevices. Here, we take the membrane shown in Supporting Information Figure S5 as an example to demonstrate its application in SERS sensing. It has exhibited strong activity, good reproducibility, and high stability of SERS signals because of its unique structure. 3.6.1. Activity. The sandwich composite membrane shown in Supporting Information Figure S5 exhibits a strong SERS effect using R6G as a probe molecule under a normal Raman excitation wavelength of 514.5 nm (chosen according to its optical absorption spectrum shown in Supporting Information Figure S5e), as shown in Figure 4a. For comparison, the continuous 2D Ag film by ion beam sputtering deposition (SEM image is shown in Supporting Information Figure S6) and the self-assembled GO membrane without Ag nanoparticles (SEM image is shown in Supporting Information
The size of the Ag nanoparticles can be easily tuned by laser power and/or subsequent laser irradiation. The Ag nanopaticles increase in average size in a small range and slightly broaden in size distribution with increasing laser power. For example, in contrast with those shown in Figure 2c, the Ag nanoparticles shown in Figure 3b present a larger mean size of about 80 nm, which were prepared with a larger laser power of 130 mJ per pulse. Also, a higher production rate of nanoparticles is obtained at a larger laser power. Laser irradiation to the Ag nanoparticle/GO sheet colloidal solution without Ag targets can decrease the size of the Ag nanoparticles on the GO sheets and improve the uniformity of size distribution. As a demonstration, Supporting Information Figure S2 shows the sample from the colloidal solution by additional laser irradiation, for 30 min, of that shown in Figure 2c. It is obvious that the nanoparticles on the sheets are much smaller in mean size (about 12 nm) than those shown in Figure 2c. 3.3. Formation of Ag Nanoparticle/GO Sheet Colloids. 3.3.1. Growth Mechanism. According to the generally accepted nanoparticle growth mechanism,29 a dense cloud of Ag atoms and clusters is generated over the laser spot of the target immediately after laser ablation. The ablated atoms and clusters prefer to aggregate into small embryonic nanoparticles rapidly. These nanoparticles continue to grow until all atoms in the close vicinity of embryonic nanoparticles are consumed completely. If the solution contains GO sheets, the Ag nanoparticles may directly sinter with GO sheets around them. This phenomenon is similar to what is called nanosoldering,30 which was used to explain the growth behavior of nanowebs consisting of platinum nanoparticles soldered by molten gold under laser irradiation onto a mixed solution of gold and platinum nanoparticles. Meanwhile, because of their small dimensions, those Ag nanoparticles without being anchored on the GO sheets undergo drastic Brownian motion. Collision inevitably occurs between the Ag nanoparticles free in solution and the GO sheets with micron-sized lateral dimensions, leading to their subsequent sintering by absorption of photon energy. Apart from sintering, adsorption possibly occurs between the Ag nanoparticles and GO sheets. To investigate the possibility of adsorption mechanism, we have done one experiment: mixing the GO colloids with the Ag colloidal solution formed by laser ablation of Ag targets in water under the same experimental conditions as those of the sample shown in Figure 2c. It has been found that the Ag nanoparticles exhibit aggregates on Si substrate, and a few are adsorbed on the surface of GO sheets during SEM characterization (see Supporting Information Figure S3 for SEM images). This result indicates that adsorption of the Ag nanoparticles on the GO sheets is difficult to occur in water and the adsorption forces are very weak. Therefore, sintering plays a dominant role in the formation of Ag nanoparticle/GO sheet composites. Owing to such sintering, the Ag nanoparticles have better interfacial connection and stronger binding with GO sheets. 3.3.2. Explanation of Influencing Factors. The density of ablated species in the gas phase is of great importance for the nanoparticle growth.31 A higher density means a higher probability of particle merging or growth. The density of the ablated species can be changed by adjusting the laser power. Ablation with a larger laser power can induce a bigger average size of nanoparticles (Figure 3b). Longer ablation represents more collision chances between the Ag nanoparticles and GO sheets, hence higher density of Ag nanoparticles on GO sheets D
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signal.40,41 Moreover, the sandwich membrane for SERS by the combined techniques of laser ablation in water and selfassembly has two advantages. First, the technique is green; thus, the Ag nanoparticles’ surfaces are fresh, which is advantageous for maintaining a high surface activity of Ag nanoparticles and capturing detected molecules. Second, the sandwich structure avoids aggregation of nanoparticles (a critical defect for nanoparticle films), making them stable. Additionally, it has multiple parameters for further optimization of the SERS activity. 3.6.2. Reproducibility, Uniformity, and Stability. The poor reproducibility of SERS signals is the main constraint in traditional analysis.42 For the sandwich membrane, the relative standard deviation values of the major SERS peaks from nine randomly selected positions across the whole substrate are less than 10%, as shown in Table 1, suggesting the good Table 1. Relative Standard Deviation (RSD) Values of the Major SERS Peaks for 10−9 M R6G from Nine Randomly Selected Sites on the Sandwich Membrane Shown in Supporting Information Figure S5a
Figure 4. Raman spectra of R6G molecules on different substrates (data integration time: 5 s). (a) For the substrates after immersion in 10−9 M R6G. Curve 1: sandwich membrane shown in Supporting Information Figure S5. Curve 2: smooth Ag film by ion beamsputtering deposition shown in Supporting Information Figure S6. Curve 3: self-assembled GO membrane without Ag nanoparticles shown in Supporting Information Figure S7. (b) For the sandwich membrane shown in Supporting Information Figure S5 after immersion in R6G solutions with different concentrations. Curves 1 and 2: 10−12 and 10−13 M R6G, respectively. (c) SERS spectra of 10−9 M R6G on three sandwich membranes prepared under the same experimental conditions as those of the sample shown in Supporting Information Figure S5. (d) SERS spectra of 10−9 M R6G on the sandwich membrane shown in Supporting Information Figure S5 after aging at room temperature for different times. Curves 1 to 4:1 to 4 months, respectively.
peak position (cm−1) RSD value a
611 6.03
771 8.12
1182 5.31
1361 4.57
1503 7.63
1647 5.41
The original curves can be seen in Supporting Information Figure S8.
measurement reproducibility. This result is ascribed to the homogeneity of such a membrane at the micrometer scale (equivalent to the laser spot size during Raman measurement) from a viewpoint of statistics. The uniformity of SERS signals between different substrates prepared under the same experimental conditions is vitally important for quantitative analysis. The poor signal uniformity leads to large errors in traditional SERS analysis, especially SERS-based trace detection. In this case, under normal Raman test conditions, almost equal signal intensities can be acquired between three different substrates prepared under the same experimental conditions, as shown in Figure 4c, revealing a good signal uniformity. This result should be attributed to the simplicity and controllability of the technique. To investigate the protection effect of GO sheets from oxidation of Ag nanoparticles, the sandwich membrane was exposed to ambient condition for different designated durations. It can remain stable for up to 3 months, much longer than pure noble metal substrates (one month in general), as no significant changes in the Raman intensity are observed, as shown in Figure 4d. This long-term stability is of great importance in practical applications. 3.7. Applications. More importantly, the strong interaction between graphene basal plane and aromatic groups gives the sandwich membrane a greater capture capacity toward aromatic compounds than pure noble metal SERS substrates. 3,3,4,4tetrachlorobiphenyl (PCB77) is selected as a trial analyte of polychlorinated biphenyl (PCB) congeners. Figure 5a shows the SERS spectra of PCB77 at different concentrations. At a low concentration of 10−10 M, several main bands of PCB77 are still distinguishable. The positions of the characteristic peaks are in agreement with those of the standard Raman spectrum of solid PCB-77 (see Figure 5b), including 677 cm−1 (C−Cl stretching), 1031 cm−1 (ring breathing), 1245 cm−1 (C−H wagging), 1300 cm−1 (biphenyl C−C bridge stretching), and 1599 cm−1 (ring stretching).43 And two other broad peaks at 1350 and 1580 cm−1 appear, which correspond to the D and G
Figure S7) were also measured under identical test conditions, including the same laser power and integration time. Clearly, the SERS signal from the sandwich composite membrane (curve 1) is several times higher than that from the Ag film (curve 2). Correspondingly, no signal was detected on the pure GO membrane for 10−9 M R6G (curve 3). For the sandwich membrane, the minimum detectable concentration of R6G is found to be as low as 10−13 M (data integration time is 5 s), as shown in Figure 4b, implying the possibility of molecule-level detection. The enhancement factor (EF) is estimated to be as high as 6 × 105. (The EF can be roughly calculated as I1361,SERS/ I1361,NR × CNR/CSERS, where I1361,SERS and I1361,NR represent the intensities of the SERS peak at 1361 cm−1 on the sandwich membrane and clean sapphire, respectively, and CSERS and CNR denote the corresponding R6G concentrations of the two different substrates.)35 Theoretically, large SERS occurs on a substrate with nanoscale particle gaps.36−38 Relative to the 2D Ag film, the great SERS activity for the sandwich membrane should be derived from its unique structure. On one hand, the 3D sandwich structure carries more Ag nanoparticles, enables their efficient coupling along and between the GO sheets with good transmittance. Such structure results in greater enhancement than 2D planar films which have fewer nanoparticles and nanogaps. Upon optical excitation, the local hot spots lead to strong electromagnetic fields and significant Raman signals of the adsorbed molecules.39 On the other hand, the ability of GO sheets to absorb and enhance detected molecules chemically may contribute to the further improvement of the SERS E
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is financially supported by the Natural Science Foundation of China (Grant 51301152) and the Natural Science Foundation of Education Bureau of Jiangsu Province, China (Grant 14KJB150028).
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Figure 5. Raman spectrum of bulk PCB-77 (lower part), and SERS spectra of the PCB-77 with different concentrations adsorbed on the sandwich membrane shown in Supporting Information Figure S5. In all cases, the integration time was 20 s.
modes of graphene, respectively. This result indicates that the sandwich membrane could be used for the trace detection of persistent organic pollutants in the environment.
4. CONCLUSION We anchored Ag nanoparticles on GO sheets based on laser ablation of Ag targets in GO auqeous solution. The density and size of the Ag nanoparticles on the GO sheets can be easily tuned by laser ablation conditions. The Ag nanoparticle/GO sheet colloids can act as blocks to build three-dimensional structures. The built sandwich composite membranes by selfassembly exhibit excellent SERS performance and are promising platforms for trace-detecting persistent organic pollutants in the environment. Green and inexpensive in process and controllable in structure, the strategy presented in this study provides a new opportunity for decorating graphene with nanoparticles for a variety of applications.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b03527. TEM images and size distribution of Ag nanoparticle/ GO sheet colloids formed under different experimental conditions. SEM images of the sample prepared by mixing the GO colloids with the Ag colloidal solution formed by laser ablation of Ag targets in water. TEM images and EDX spectra of the GO sheets coated with Au, ZnO, and Au1Ag2 nanoparticles for demonstrating universality of the strategy. Morphologies, structure, and optical properties of assembled Ag nanoparticle/GO sheet composite membranes. Experimental section, sample description, and mechanism explanation of the assembled membranes. SEM images and Raman spectra of some samples for SERS analysis. (PDF)
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DOI: 10.1021/acs.langmuir.5b03527 Langmuir XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.langmuir.5b03527 Langmuir XXXX, XXX, XXX−XXX
