Unusual functionalization of reduced graphene oxide for excellent chemical surface-enhanced Raman scattering by coupling with ZnO
Introduction
Graphene is a novel carbon nanomaterial of a two-dimensional conjugated structure, offering unique electronic properties, and has been intensively studied for many applications, such as electronic devices [1], solar cells [2], photocatalysts [3], and sensors [4]. There has been growing interest in graphene-based surface-enhanced Raman scattering (SERS) substrates for bio-chemical sensing due to the high surface area and great electrical conductivity of graphene. For example, Au nanoparticle (NP)–graphene oxide (GO) [5] and Ag–graphene [6] composites were recently synthesized for chemical sensing and cell imaging by taking advantage of the electromagnetic enhancement of plasmonic metal NPs. In addition, an ultraviolet/ozone treatment [7] has been used to oxidize graphene and demonstrated an efficient improvement in SERS compared with pristine graphene, due to charge transfer-induced chemical enhancement. However, these high-performance SERS substrates usually need expensive noble metals to enhance plasmonic resonance or toxic O3 gas to activate graphene. It thus remains a challenge to fabricate low-cost graphene-based SERS substrates with excellent enhancement performance.
In this work, an excellent SERS substrate comprised of annealed low-cost reduced GO (rGO)/ZnO composites is firstly demonstrated. The morphologies, structures, and functional groups of the rGO/ZnO composites after different heat treatments show significant variations, indicative of strong reactions between rGO and ZnO. The high SERS enhancement factor (EF) of about 104, even better than those reported for Ag/GO [8], Au/GO [5], Au/rGO [9], and Au/graphene [10] composites, is mainly attributed to the abundant oxygen-containing groups unusually generated on the surface of rGO by coupling with ZnO NPs at moderate temperature, as seen in the Fourier transform infrared spectroscopy (FTIR) spectra. This work demonstrates the preparation of low-cost SERS substrates with excellent performance by reactions of rGO with ZnO, which have good potential for bio-chemical sensing applications.
Section snippets
Preparation of rGO/ZnO composites
GO flakes were prepared following Hummers method [11]. The GO dispersion was prepared by dispersing 0.5 g GO flakes in 500 ml distilled water using centrifugal separation at a speed of 8000 rpm for 40 min. GO dispersion of 0.5 ml was then dropped onto a ZnO nanorod (NR)/Si substrate, synthesized by a hydrothermal route [12], and dried at 90 °C for 5 min. The dropping/drying processes were repeated for 10 cycles to obtain a pristine GO/ZnO composite. The prepared GO/ZnO composites were then annealed at
Morphologies, microstructures, and crystal structures of the rGO/ZnO composites
Based on the SEM results, the morphologies of the GO/ZnO composites show significant variations after annealing at different temperatures. Fig. 1(a) and (b) show the SEM images of the ZnO NRs and GO/ZnO composites before annealing, respectively. The GO flakes are uniformly attached to the surface of the NRs. After annealing at 150–200 °C for 1 h, the GO flakes were transformed into film-like structures, and small dots of lighter contrast were generated on the films, as shown in Fig. 1(c) and (d).
Conclusion
This work presents a novel and efficient SERS substrate based on low-cost rGO/ZnO composites. The high EF value, about 104 for R6G, is mainly attributed to the unusually abundant oxygen-containing groups generated on rGO by coupling with ZnO at a moderate temperature. The SEM, TEM, and XRD results show numerous ZnO NPs were generated on the surface of rGO, and the d-spacing of GO gradually decreased after the annealing treatments. Unusually, the functional groups of rGO/ZnO increased
Acknowledgement
This work was supported by the National Science Council of Taiwan under the Grant (NSC100-2221-E-390-009-MY3).
References (23)
- et al.
Graphene-based counter electrode for dye-sensitized solar cells
Carbon
(2011) - et al.
Fabrication of a graphene oxide–gold nanorod hybrid material by electrostatic self-assembly for surface-enhanced Raman scattering
Carbon
(2013) - et al.
Graphene modulated 2D assembly of plasmonic gold nanostructure on diamond-like carbon substrate for surface-enhanced Raman scattering
Electrochem Commun
(2012) - et al.
Efficient surface enhanced Raman scattering from Cu2O porous nanowires transformed from CuO nanowires by plasma treatments
Mater Chem Phys
(2012) - et al.
Zinc oxide/reduced graphene oxide composites and electrochemical capacitance enhanced by homogeneous incorporation of reduced graphene oxide sheets in zinc oxide matrix
J Phys Chem C
(2011) - et al.
P25-graphene composite as a high performance photocatalyst
ACS Nano
(2010) - et al.
Nanostructured Pt decorated graphene and multi walled carbon nanotube based room temperature hydrogen gas sensor
Nanoscale
(2009) - et al.
Graphene-based high-efficiency surface-enhanced Raman scattering-active platform for sensitive and multiplex DNA detection
Anal Chem
(2012) - et al.
UV/ozone-oxidized large-scale graphene platform with large chemical enhancement in surface-enhanced Raman scattering
ACS Nano
(2011) - et al.
Competitive surface-enhanced Raman scattering effects in noble metal nanoparticle-decorated graphene sheets
Phys Chem Chem Phys
(2011)
Surface-enhanced Raman scattering study on graphene-coated metallic nanostructure substrates
J Phys Chem C
Cited by (25)
Design and fabrication of zinc oxide-graphene nanocomposite for gas sensing applications
2022, Applied Surface ScienceCitation Excerpt :Multiple-phonon scattering creates peaks located about 1145 cm−1 in ZnO samples [67], but the amplitude of this peak is decreased in graphene/ZnO nanocomposite. Because of the higher dispersion and interaction of graphene with ZnO, the Raman peaks corresponding to ZnO in graphene/ZnO nanocomposite are not observable [68]. The broad D band (1350 cm−1), sharp G band (1580 cm−1), and 2D band (2658 cm−1) are noticed in the Raman spectrum of the graphene and the graphene/ZnO nanocomposite powders.
Significant increase in dipole moments of functional groups using cation bonding for excellent SERS sensing as a universal approach
2021, Sensors and Actuators, B: ChemicalJustification of dipole mechanism over chemical charge transfer mechanism for dipole-based SERS platform with excellent chemical sensing performance
2020, Applied Surface ScienceCitation Excerpt :The reactions release hydroxyl radicals, which then attack OFGs, such as carbonyl and carboxyl, and proceed a series of chain reactions to produce more OFG radicals. Therefore, an increase in OFGs was found in the annealed samples [24]. However, the chain reactions eventually terminate, are accompanied by the generation of CO/CO2, and decrease the amount of OFGs upon over-annealing.
Ultrahigh sensitive metal-free SERS platforms by functional-groups
2018, Sensors and Actuators, B: ChemicalCitation Excerpt :In addition, mild O plasma treatment was reported to yield oxygen species on graphene, enhancing the Raman signals of dyes [25] by several folds. We recently found that oxygen-containing functional groups (OFGs) can be formed via unique reactions by coupling ZnO and GO at a low temperature of 200 °C,with an EF value approaching 104 reached [26] without using expensive plasma-generating equipment or toxic O3. However, the OFG formation mechanisms are not fully understood.
Field emission of graphene oxide decorated ZnO nanorods grown on Fe alloy substrates
2017, Journal of Alloys and CompoundsCitation Excerpt :It is theoretically expected to be observed in the XRD pattern. However, the GO peaks are not clearly seen in the XRD patterns due to the small amount of GO in the sample compared with ZnO, which is similar with the previous report [24]. Therefore, it can be seen that the diffraction peaks are mainly from the ZnO and Fe alloy substrate phase in the GO decorated ZnO NRs.
ZnO rods/reduced graphene oxide composites prepared via a solvothermal reaction for efficient sunlight-driven photocatalysis
2016, Applied Catalysis B: EnvironmentalCitation Excerpt :For ZnO rods, a strong absorption located at ca. 360 nm originating from the intrinsic band-edge absorption of ZnO particles can be observed. This peak is slightly shifted in the ZnO/rGO composite due to a coupling effect originating from the interaction between ZnO rods and rGO [64,65]. The absorption peak located at 264 nm is generally associated to the excitation of the π-plasmon of the graphitic structure, and can be observed in rGO and in the ZnO/rGO composite [35].