Raman Spectra Of Graphene Oxide Research Articles

Raman spectroscopy study on the vibration and structural changes of graphene oxide: effect of laser power and time

Graphene oxide and its nanocomposites play a crucial role in various applications. Laser irradiation is a low-cost technique to tune the graphene oxide material, and a detailed study of the vibrational modes and structural changes during the laser–graphene oxide interaction is required. The evolution of defect modes and reduction process in graphene oxide at varying laser power and different exposure time duration, respectively, via Raman spectroscopy, is of interest in the present study. Graphene oxide (GO) is synthesized via Improved Hummer's method and characterized by X-Ray Diffraction (XRD), Thermogravimetric analysis (TGA), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray analysis (EDX), UV-Vis-NIR and Raman spectroscopy. The first-order Raman spectrum of GO consists of broad D and G peaks around 1350 and 1584 cm-1, respectively, and the broad second-order band around 2700 cm-1 . Using the Lorentzian function, the first-order band is deconvoluted into five modes and the secondorder into four modes. The peak positions and FWHM of these modes undergo indicative changes. The variations in the intensity ratios of the defect modes and the (𝐷𝐷𝑖𝑖𝑖𝑖𝑖𝑖 ′ – 𝐺𝐺𝑎𝑎𝑎𝑎𝑎𝑎) with laser power at different exposure time durations indicates the predominance of edge defects and reduction of graphene oxide, respectively. These results broaden the understanding of the effect of laser power over different time durations on the graphene oxide features. Our study provides quantitative information on the laser-GO interaction.

High-efficiency recyclable reduced graphene oxide-tin oxide nanocomposite catalyst for esterification

Graphene oxide (GO) possesses 2D nanostructures and was synthesized indigenously via the enhanced Hummer method. It is well-accepted that the redox approach is a distinctive technique to fabricate GO on an expanded scale. Here, reduced graphene oxide-tin oxide (SnO2-rGO) nanocomposite material was produced for application as an efficient heterogeneous solid acid catalyst esterification reaction. Fourier transform infrared analysis was carried out to validate the incidence of oxygen functional groups in GO and SnO2-rGO nanocomposite. The Raman spectra of GO and SnO2-rGO nanocomposite have been simulated to get stable structure and functional groups. To get surface morphological and structural features, powder X-ray diffraction, scanning electron microscope-energy dispersive X-ray spectra, transmission electron microscope and high resolution-TEM analysis, and thermogravimetric analysis were delineated during this experimental study. It is seen that the catalyst has high efficiency for esterification reaction. The maximum efficiency (96% yield) was obtained when a 1:3 (acetic acid to benzyl alcohol) molar ratio, catalyst (25 mg), temperature (60 0C), and time (4 h) were maintained. The SnO2-rGO nanocomposite was recycled several times with a minimal loss of its efficiency.

Exploring the bioactivity of reduced graphene oxide and TiO2 nanocomposite for the regenerative medicinal applications

Millions of people globally suffer from issues related to chronic wounds due to infection, burn, obesity, and diabetes. Nanocomposite with antibacterial and anti-inflammatory properties is a promising material to promote wound healing. This investigation primarily aims to synthesize reduced graphene oxide and titanium dioxide (rGO@TiO2) nanocomposite for wound healing applications. The rGO@TiO2 nanocomposite was synthesized by the one-step hydrothermal technique, and the physicochemical characterization of synthesized nanocomposite was performed by X-ray diffraction, Fourier transforms infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, and dynamic light scattering. Further, the nanocomposite antibacterial, cytotoxicity, and wound-healing properties were analyzed by disc diffusion method, MTT assay, and in vitro scratch assay, respectively. Based on the TEM images, the average particle size of TiO2 nanoparticles was around 9.26 ± 1.83 nm. The characteristics peak of Ti–O–Ti bonds was observed between 500 and 850 cm−1 in the Fourier transforms infrared spectrum. The Raman spectrum of graphene oxide (GO) was obtained for bands D and G at 1354 cm−1 and at 1593 cm−1, respectively. This GO peak intensity was reduced in rGO, revealing the oxygen functional group reduction. Moreover, the rGO@TiO2 nanocomposite exhibited dose-dependent antibacterial properties against the positive and negative bacterium. The cytotoxicity for 5–100 µg/mL of rGO@TiO2 nanocomposite was above the half-maximal inhibitory concentration value. The in vitro scratch assay for rGO@TiO2 indicates that the nanocomposite promotes cell proliferation and migration. The nanocomposite recovered the wound within 48 h. The rGO@TiO2 nanocomposite shows potential materials for wound healing applications.

Effect of Silver Nanoparticles on the Optoelectronic Properties of Graphene Oxide Films

The effect of Ag nanoparticles (NPs) on the optical and optoelectronic properties of films based on graphene oxide has been studied. In the presence of Ag NPs, the morphology, as well as the thickness of graphene oxide films, were not changed. When Ag NPs were added, a change in the shape and position of the absorption bands and Raman spectra of graphene oxide was observed. It is shown that with the addition of Ag NPs, the G band of graphene oxide shifts to low frequencies, which may be the result of the absence of separate double bonds, while the ID/IG ratio was not changed, as did the number of Gr layers. In the absorption spectrum of the films, along with the absorption band of graphene oxide, a shoulder was registered, which can be associated with the absorption of Ag NPs. The optical density of Gr films with plasmonic NPs is higher than without them. Measurements of the optoelectronic characteristics showed that, in the presence of Ag NPs, an increase in the values of the photocurrent of graphene oxide is observed. The sensitivity of graphene oxide films was increased by almost 20 times when plasmonic NPs were added to them, and the detection ability increased by 25 times.The results obtained can be used in the development of new photosensitive devices for optoelectronic and applications.

Highly Sensitive, Cost‐Effective, and Flexible SERS Substrate Based on Green Synthesized GO/rGO for Pesticide Detection**

AbstractIn this work, a novel approach is adopted to synthesize graphene oxide (GO) and reduced graphene oxide (rGO) from a natural precursor Desmostachya bipinnata (halfa grass). GO is synthesized by treating ash of halfa grass with aqueous and molten KOH. Further, reduced with lemon extract to synthesize rGO. Then GO and rGO active SERS substrates are fabricated with flexible adhesive tape. Structural and morphological features of SERS substrates are analyzed. Raman spectrum of GO and rGO consists of characteristic D and G peaks around 1331 and 1600 cm−1 and a 2D peak around 2700 cm−1. The variation in ID/IG ratio, decreasing inter‐planar spacing, and the redshift of UV – Vis absorption peak from 225 to 280 nm confirm the reduction of GO on lemon extract treatment. SERS activity of fabricated substrates is analyzed with agro pesticide thiabendazole (TBZ). The detection range of TBZ by SERS substrate lies between 1 mM to 1 nM with a minimum detection limit of 1 nM. This study emphasizes the use of GO synthesized from aqueous KOH treatment and reduced with lemon extract (rGO) for the development of highly sensitive, low cost and flexible SERS substrates to detect TBZ in various agricultural products.

Towards Understanding the Raman Spectrum of Graphene Oxide: The Effect of the Chemical Composition

Raman spectroscopy is a technique widely used to detect defects in semiconductors because it provides information of structural or chemical defects produced in its structure. In the case of graphene monolayer, the Raman spectrum presents two bands centered at 1582 cm−1 (G band) and 2700 cm−1 (2D band). However, when the periodic lattice of graphene is broken by different types of defects, new bands appear. This is the situation for the Raman spectrum of graphene oxide. It is well established that the existence of these bands, the position and the intensity or width of peaks can provide information about the origin of defects. However, in the case of the graphene oxide spectrum, we can find in the literature several discrepant results, probably due to differences in chemical composition and the type of defects of the graphene oxide used in these studies. Besides, theoretical calculations proved that the shape of bands, intensity and width, and the position of graphene oxide Raman spectrum depend on the atomic configuration. In the current work, we will summarize our current understanding of the effect of the chemical composition on the Raman spectrum of graphene oxide. Finally, we apply all this information to analyze the evolution of the structure of graphene oxide during the thermal annealing of the heterostructures formed by graphene oxide sandwiches in a hexagonal boron nitride.

The assembly of a composite based on nano-sheet graphene oxide and montmorillonite

Graphene oxide (GO) nano-sheets were synthesized using a modified Hummers’ method from graphite powder. The Raman spectrum of GO displayed a D-band at 1359 cm−1 and a G-band at 1594 cm−1. The ID/IG value of GO was calculated to be 0.97, suggesting the formation of new sp2 clusters upon reduction. A method was designed to investigate the assembly of the GO/montmorillonite (MMT) composite. After the addition of GO, the typical peaks of montmorillonite in FT-IR spectra shifted, indicating the assembly between GO and MMT. The D-band and G-band reduced sharply in the GO/MMT composite. More importantly, the D-band (1344 cm−1) and G-band (1574 cm−1) shifted significantly and the ID/IG value of the GO/MMT composite was calculated to be 1.13, showing a change in the GO structure. In the addition of 0.04 wt% GO to MMT, the value of interlayer space (d) was up to 13.0 Å measured by XRD due to the insertion of GO into MMT. The evident increases in contents of carbon atoms (26.59%) and nitrogen atoms (3.44%) indicate that GO was successfully combined with MMT. The nano-pores and clay sheets were not observed in the SEM image of GO/clay, but obvious wrinkles, while flexible sheets were observed in the typical scanning electron microscopy images of GO. This further proves that GO was combining with clay. The TEM image shows that the GO nano-sheets were tiled on the surface of MMT sheets. This observation suggests that a stable assembly structure was formed between GO sheets and MMT sheets. The change in particle size of MMT with the addition of GO shows that interaction occurred between GO sheets and MMT sheets, which was further confirmed by the results of zeta potential. Adsorption and insertion were the main mechanisms to assemble GO and MMT.

Nanomaterial resistant microorganism mediated reduction of graphene oxide

In this study, soil bacteria were isolated from nanomaterials (NMs) contaminated pond soil and enriched in the presence of graphene oxide (GO) in mineral medium to obtain NMs resistant bacteria. The isolated resistant bacteria were biochemically and genetically identified as Fontibacillus aquaticus. The resistant bacteria were allowed to interact with engineered GO in order to study the biotransformation in GO structure. Raman spectra of GO extracted from culture medium revealed decreased intensity ratio of ID/IG with subsequent reduction of CO which was consistent with Fourier transform infrared (FTIR) results. The structural changes and exfoliatied GO nanosheets were also evident from transmission electron microscopy (TEM) images. Ultraviolet⿿visible spectroscopy, high resolution X-ray diffraction (XRD) and current-voltage measurements confirmed the reduction of GO after the interaction with resistant bacteria. X-ray photoelectron spectroscopy (XPS) analysis of biotransformed GO revealed reduction of oxygen-containing species on the surface of nanosheets. Our results demonstrated that the presented method is an environment friendly, cost effective, simple and based on green approaches for the reduction of GO using NMs resistant bacteria.

Structural and vibrational study of graphene oxide via coronene based models: theoretical and experimental results

We use the Coronene (C24H12), a simple and finite molecule, to make a model to study the spectroscopic and structural alterations generated by oxygenated groups in graphene oxide (GO). Based on the Lerf–Klinowski model, we chose the hydroxyl [OH−], the carboxyl [COOH−] and the epoxy [the ring C2O inside the molecule] as our radicals of interest and study their collective and isolated effects. We perform geometry optimization, vibrational IR (via AM1 and DFT-B3LYP) and Raman spectra (via DFT-B3LYP) of a series of functionalized coronene molecules. As results, we obtain some useful data for the analysis of IR and Raman spectra of GO, which facilitate the understanding and identification of the peaks found in the experiment. Finally, we suggest a new model to study GO, producing an accurate signature when compared to our experimental data. Such molecule shows in more details of the structural effects caused by functionalization when compared to experimental data.

Charge transport mechanism of hydrazine hydrate reduced graphene oxide

Chemically assisted graphene oxide (GO) is synthesised by improved Hummers’ method. It has been further reduced by hydrazine hydrate by hydrothermal method to form reduced GO (rGO). Raman spectra of GO and rGO suggest the formation of D-band and G-band at 1360 and 1590 cm−1, respectively. Along with D and G modes, 2D and D′ + G′ modes have been observed at 2710 and 2950 cm−1, respectively. Tuinstra and Koenig relation is used to calculate the relative size of the sp2-carbon domain. Scanning electron micrographs reveal the separation of flakes during reduction. The dc conductivity measurement covers the peculiar study of conduction mechanism of rGO. On reduction, a remarkable increase in the room temperature conductivity (from 4.25 × 10−10 to1.9 × 10−2 S/cm) of GO has been observed. The accomplish study of dc conductivity measurement of rGO in the temperature range of 77–400 K is reported. It is explained on the basis of 3D variable range hopping model. The slope of a plot between activation energy and temperature on logarithmic scale is found to be 0.75 which suits well with the theoretical result.

The Importance of Interbands on the Interpretation of the Raman Spectrum of Graphene Oxide

Raman spectra of graphene oxide and thermally reduced graphene oxide were analyzed in order to relate spectral parameters with the structural properties. The chemical composition of different graphene oxides was determined by organic elemental analysis, and the microstructure of nanocrystals was analyzed by X-ray diffraction. We find five reported bands (D, D′, G, D″, and D*) in the region between 1000 and 1800 cm–1 in all spectra. The band parameters such as position, intensity ratio, and width have been related with structural properties such as oxygen content, crystallinity, and disorder degree of GO and rGO platelets. An assessment of the validity of the Tuinstra–Koenig and Cuesta models was carried out by using the results obtained from the fit of the first-order spectra of graphene oxide derivatives at five functions: two Gaussian and three pseudo-Voigt peaks.

Effects of graphene reduction degree on capacitive performances of graphene/PANI composites

Reduced graphene oxide (RGO) was compounded with polyaniline (PANI) to prepare supercapacitor electrode materials. For the preparation, graphene oxide (GO) was reduced with glucose and ammonia, and then PANI was in situ deposited onto the RGO nano-sheets by polymerizing aniline with ammonium persulfate (APS) as oxidizing agent. The obtained composites were characterized with scanning electron microscope, Fourier transform infrared spectroscopy, Raman spectroscopy, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy (EIS). It was found that with increasing reduction time, the oxygen content on the surface of GO was decreased, leading to increased ID/IG ratio in the Raman spectra of GO and increased conductivity of GO. Consequently, the capacitance properties of RGO/PANI composites could be significantly improved by the reduction of GO. It was also observed that the initial concentrations of aniline being used for the polymerization could influence the rate performance of the composite. Under the optimal preparation conditions (the reduction time of graphene 60min, the initial concentration of aniline 0.025molL−1, and the molar ratio of aniline to APS 1:1), the obtained composites exhibited a specific capacitance as high as 1045Fg−1, along with a retention of 97% after 1000 cycles.

In Situ Raman Studies of Electrically Reduced Graphene Oxide and Its Field-Emission Properties

Electric-field-dependent in situ Raman studies have been carried out on chemically prepared graphene oxide. The Raman spectra show significant changes with increase in the applied electric field; in particular, the intensity of the G peak decreases with electric field. This behavior is typical for chemically or thermally reduced graphene oxide. To understand the nature of reduction, we compared the temperature-dependent and electric-field-dependent Raman spectra of graphene oxide and found that the evolutions of Raman spectra are not in agreement with each other, except the intensity of the G peak that decreases in both cases. The D peak broadens significantly with increase in temperature, whereas it sharpens in the case of applied electric field. The electron-field-emission properties of the electrically reduced graphene oxide were also carried out, and the turn-on field was found to be 9.1 V/μm.

Raman spectroscopy for the study of reduction mechanisms and optimization of conductivity in graphene oxide thin films

Highly reduced few-layer graphene oxide films with conductivities of up to 500 S cm−1 are obtained. The thin films with an optimized compromise between sheet resistance (3.1 kΩ sq−1) and transparency (around 80% to 90%) are suitable for touch screens and transparent electrodes in OLEDs. We discuss the effects of low temperature annealing and chemical reduction on the properties of the films and present an optimized reduction process that allows the original 2D/G Raman intensity ratio of few-layer graphene to be recovered. The Raman spectrum of graphene oxide is found to be only related to oxygen-free graphene-like regions with Raman bands at 1130 and 3155 cm−1 that probably involve C–H vibrations of rings and edges, while a band at 1700 cm−1 is assigned to irregular rings such as Stone Wales defects. All the bands involve resonant Raman processes and disappear in highly reduced samples. Clear correlations of the D band width with the sp2 content in thin films and resistivity have been observed, indicating that this is a good Raman parameter for evaluating the quality of the samples. The structural defects produced by the release of embedded water and some of the oxygen functional groups during annealing are detrimental for intra-grain conductivity but greatly enhance inter-grain connectivity.

Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir–Blodgett technique

Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air–water interface and transferred to silicon substrates by Langmuir–Blodgett technique as closely spaced monolayers of 20–40μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp2 bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8–12cm−1 and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3±0.3 to 0.8±0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction.