The role of oxygen functional groups attached to the GO in the electrical properties of GO is analyzed. The significant change in the electrical conductivity of the GO after annealing at 230 ˚C is observed in the IV characteristics.
Introduction
History of graphene oxide and its evolution
Thus, in one reaction, he succeeded in increasing the concentration of oxygen in graphite oxide to a carbon-oxygen ratio of 2:1. In 1958, Hummers synthesized graphite oxide using less harmful chemicals such as potassium permanganate (KMnO4), sodium nitrate (NaNO3) and highly concentrated sulfuric acid (H2SO4)15.
Structure of graphene oxide
He arranged the epoxy groups randomly, perpendicular to the basal plane of the graphitic structure. Correspondingly, the proposed oxygen functional groups are attached perpendicular to the basal plane of the graphitic system.
Mechanism of formation of graphene oxide
After adding water to the solution, the color of the solution changes to dark from dark brown, which is an exothermic reaction. This exothermic reaction is stopped by adding dilute H2O2 to the solution and the color of the solution changes to bright yellow from the dark.
Derivatives of graphene oxide
- Reduced graphene oxide
- Graphene quantum dots
The oxidized graphite flakes are identified from the optical microscope in both light modes; graphite oxides are observed in semi-transparent light brown in transmitted light mode and light yellow pearl in reflected light mode. However, the unoxidized graphite flakes with dark color in transmitted light mode and blue color in reflected light mode are obtained.
Properties of graphene oxide
- Electronic properties
- Transparent–conductor properties
- Mechanical properties
- Thermal conductivity properties
- Optical properties
However, the mechanical properties of GO can be tuned by controlling the degree of oxidation, its stacking orientation, intercalated water molecules/ions, and structural defects. The optical properties of GO can be tuned by controlling the degree of oxygen functional groups and structural defects44,45.
Surface modification using gas plasma treatment
GO is used in nonlinear optics because of the small cluster of sp2 hybridized carbons with sp3 hybridized carbon atoms. Due to its exceptional optical properties, GO can be a potential candidate for several applications such as in display due to its transparency, in biosensor due to its fluorescence, and in laser technology due to its nonlinear optical properties.
Synthesis of graphene oxide and its derivative materials
- Synthesis of graphene oxide
- Synthesis of reduced graphene oxide
- Synthesis of graphene quantum dots
RGO can be functionalized with oxygen-containing functional groups such as epoxy (C-O-C) and carboxyl (C-OH), using oxygen plasma treatment. The above techniques are used to remove the oxygen functional groups and restore the graphical structure of GO.
Applications of graphene oxide
- Surface-enhanced Raman scattering
- Photodetector
- CO 2 gas sensor
The quality of the GO-based photodetector can be improved by nanocomposite with other materials. A comparative overview of the CO2 sensors that use GO and the derived materials used is shown in table 1.5.
Organization of the Thesis
Exfoliation of graphite oxide in propylene carbonate and thermal reduction of the resulting graphene oxide platelets. Graphene oxide (GO) coated impedimetric gas sensor for selective detection of carbon dioxide (CO2) with temperature and humidity compensation.
Synthesis and characterization of large lateral-size graphene oxide and its
Introduction
The SERS effect of MO molecules on GO and RGO sheet is analyzed in the figure. The optical image of the GO sheet on the SiO2/Si substrate is shown in the figure. The attached oxygen functional groups can regulate the electrical properties of GO en route.
Synthesis of graphite oxide and its derivative materials
- Synthesis of graphite oxide
- Synthesis of reduced graphene oxide
- Synthesis of graphene quantum dots
Characterization techniques
The functional groups on the basal level and edge of GO and RGO were analyzed by Raman spectrometer (Horiba Jobin, LabRam HR). Fourier transform infrared (FTIR) spectroscopy (Perkin Elmer, Spectrum BX) was used to analyze the functional groups of GO and RGO.
Results and discussions
- Morphological and microstructural
- Structural analysis of graphene oxide and reduced graphene oxide
- Optimization of size particles of graphene quantum dots
- Structural analysis of graphene quantum dots
- XPS and FTIR analysis of graphene quantum dots
- UV absorption and PL analysis of graphene quantum dots
Further, the Raman spectra of the RGO synthesized from thermal and hydrazine are shown in Fig. The detailed investigation of the presence of oxygen functional groups and structural defects is demonstrated in the following chapters 3 and 4. The elemental composition of the GQDs is analyzed using XPS and FTIR spectra shown in Fig.
Conclusion
Origin of High Photoluminescence Yield and High SERS Sensitivity of Nitrogen-doped Graphene Quantum Dots. Graphene oxide-assisted liquid phase exfoliation of graphite in graphene for highly conductive film and electromechanical sensors. Impact of further thermal reduction on a low-reduced graphene oxide film and the n-p transition for gas sensing.
A detailed study of layer dependent properties of large lateral-size graphene
Introduction
Several top-down exfoliation techniques have been reported, highlighting the lateral size of graphene sheets, their functional property, scale-up practicality, and their feasible applications. Among them, the hydrothermal method has been shown to be a promising technique, showing its relative cost-effectiveness and giving an excellent yield with a controlled and large lateral size with outstanding electrical properties. Therefore, there is an additional requirement for a simpler and more cost-effective approach to exfoliate graphene-based sheets with very large lateral dimensions that exhibit high electrical and sensing properties.
Synthesis of graphene oxide and reduced graphene oxide
- Synthesis of graphene oxide
- Synthesis of reduced graphene oxide
Exfoliation from chemically synthesized graphene oxide is cost-effective and most functional properties can be tailored to the degree of oxidation-reduction processes. The rise of the initial exfoliated flake is observed in stage 4 driven by mild temperature.
Characterization techniques
Results and discussions
- Morphological and microstructural
- Electronic and electrochemical behaviors of large-area graphene oxide and reduced
- SERS-based sensing applications of large-area graphene oxide and reduced
A uniform distribution of the intensity of the Raman signals (D and G) was obtained, shown in the figure. The thickness of the GO sheet determined by FETEM and AFM imaging is shown in the figure. The intensity of the Raman signal for the RhB molecule can be enhanced on GO and RGO by the SERS technique.
Conclusion
Preparation of large-scale graphene from needle head and adsorption for malachite green with its graphene oxide. High-yield few-layer graphene oxide via efficient surfactant-assisted exfoliation of lightly oxidized graphite. Simplified production of graphene oxide assisted by high-shear layering of graphite with controlled oxidation.
Plasma treated graphene oxide surface for trace dye detection using surface
Introduction
Ling et al.1 reported the SERS effect for various dyes such as phthalocyanine (Pc), R6G, protoporphyrin (PPP), and crystal violet (CV) dyes on graphene. In most reports, the smallest lateral size of graphene-based substrates has been used for SERS analysis. The effect of large lateral size of graphene on SERS enhancement has not been reported yet.
Experimental Details
- Synthesis of graphene oxide and reduced graphene oxide
- Gas plasma treatment
- Synthesis of Au nanoparticles
The test samples are placed inside the quartz chamber of the plasma cleaner and the internal pressure is evacuated to mbar with the support of the rotary vacuum pump. The clean substrate was placed on the substrate holder of the sputtering system (Excel Instrument), and the chamber was evacuated to 1.5 × 10-5 mbar using a diffusion pump supported by a rotary vacuum pump. The Au thin film samples were placed inside the chamber of the RTA system (ULVAC-RIKO, MILA-3000), and then evacuated to 2.2×10-2 mbar inside the chamber using a rotary vacuum pump.
Characterization techniques
Based on the gases used, the samples of the GO and RGO are named Ar-GO for Ar plasma treated GO, N-GO for N2 plasma treated GO and O-GO for O2 plasma treated GO, H-GO for diluted H2 plasma treated GO. The Au NPs were synthesized using a two-step process: deposition of the Au thin film using RF sputtering and forming Au NPs from the Au thin film using RTA (rapid thermal annealing). High purity Ar gas was allowed to flow into the system and the chamber pressure was maintained at 1 mbar.
Results and discussions
- Morphological analysis
- Structural analysis
- PL analysis of RhB in graphene oxide and water solution
The C1s band of GO and RGO is equipped with four Gaussian peaks and three Gaussian peaks, respectively. Thus, the comparison between GO and RGO shows that RGO has a much lower (3.46 times) percentage of oxygen functional groups than GO. This is due to the strong interaction between GO and RhB at a higher concentration of the latter.
Gas plasma treatment on graphene oxide and reduced graphene oxide
- Optimization of plasma treated duration
- Raman analysis of gas plasma treated graphene oxide/ reduced graphene oxide
- XPS and FTIR analysis of gas plasma treated graphene oxide/ reduced graphene
- Analysis of Raman spectra on Ar plasma treated graphene quantum dots
Ar-GO and O-GO obtained more functional groups and defects from the D' position analysis. The FWHM of D' is determined by the degree of surface defect / presence of oxygen functional groups. Most of the analyzes are caused by the structural defects and functional groups of GO/RGO.
Analysis of SERS effect on various graphene oxide-based substrates
- Mechanism of SERS effect on graphene oxide/ reduced graphene oxide
- Mapping of Raman signals for RhB on graphene oxide
- Layer dependent study of the SERS effect on graphene oxide
- SERS for RhB on plasma treated graphene oxide/ reduced graphene oxide
- SERS effect on Au nanoparticles, nano-composite of Au and reduced graphene
However, the intensity of the Raman signals of the MO molecules on the GO and RGO sheets is significantly low. The effect of the thickness of the GO layers on the SERS signal of RhB is analyzed next, as shown in Fig. The SERS effect of the RhB is measured on the Au NPs, AuRGO and AuGO, as shown in Fig. 4.12(c-e) ), respectively.
Conclusion
The EF of RhB in Au NPs, AuRGO and AuGO are calculated using the previously mentioned formula. Thus, the EF of AuRGO and AuGO composite is higher than individual Au NPs or RGO/GO due to the combined effect of the former on EE and CE. Synthesis of graphene oxide (GO) by the modified Hummers method and its thermal reduction to obtain reduced graphene oxide (RGO)*.
Fabrication and analysis of photodetector devices based on surface modified
- Introduction
- Experimental Details
- Synthesis of graphene oxide, reduced graphene oxide, and graphene quantum dots
- Fabrication of Inter digitated electrode
- Synthesis of nano hybrid of SnO 2 on graphene oxide
- Characterization Techniques
- Photodetector set-up
- Results and discussions
- Morphological and structural analysis
- UV absorption and PL studies of graphene oxide
- Analysis of interdigitated electrode pattern
- Electrical characterizations
- I-V characteristics of graphene oxide and different temperature annealed graphene
FTIR spectra of the GO and thermally annealed GO are studied in the presence of oxygen functional groups and graphitic structure (sp3 and sp2 carbon bonds), which are shown in Fig. FESEM image of the GO sheets deposited on the IDE pattern is studied and viewed in Fig. The stability of the photodetector device is better in GO-85 due to the removal of unstable oxygen functional groups from the GO.
NPs on GO-85
- Photocurrent of GO-85, Ar plasma treated GO, and nano hybrid of SnO 2 NPs on
- Time response of GO-85, Ar plasma treated GO, and nano hybrid of SnO 2 NPs on
- Voltage-dependent study of GO-85, Ar plasma treated GO, and nano hybrid of SnO 2
- Excitation power study of GO-85, Ar plasma treated GO, and nano hybrid of SnO 2
- Responsivity (R) and Detectivity (D)
- Conclusion
The origin of the continued growth of the baseline/dark current is not very clear. The dark current of Ar-GO increases after plasma treatment on GO-85. The drop in response current down to 280 nA after applying a bias voltage of 2.5V is unusual.
Fabrication of CO 2 sensors based on graphene oxide based 2D materials and
Introduction
The presence of oxygen functional groups on the graphene sheets reduces the electron mobility that typically becomes an insulator and so removing these functional groups to restore conductivity is a challenging task. In addition, oxygen is known to have better charge transfer to planar defect graphite due to the presence of defects, resulting in stronger semiconducting properties for GO6. GO with numerous oxygen functional groups was too electrically insulated to be used in a resistance-based sensor.
Experimental details
- Synthesis of reduced graphene oxide and graphene quantum dots
- Fabrication of SnO 2 NPs, nano hybrids of reduced graphene oxide, and graphene
- Characterization techniques
- Gas sensing set-up
Then 10 µl of the solution is poured dropwise onto the IDE cartridge and dried for 60 minutes at 85 ˚C. SO-RGO sensor is fabricated by deposition of SnO2 NPs on the RGO, which is placed on the IDE pattern. The morphology of the RGO, GQDs, SnO2 NPs and their nanohybrids on the SiO2/Si was observed using a field emission scanning electron microscope (FESEM) (JEOL, JSM- 7610F).
Results and discussions
- Morphological analysis
- Structural analysis
- UV absorption and PL analysis
The XRD pattern of nano hybrids of SnO2 NPs (SO) and GO (SO-GO) and nano hybrids of SnO2 NPs and RGO (SO-RGO) are shown in Fig. The XRD pattern of SO-GO reflected the composition of SnO2 and GO, shown in Fig. Similarly, the SO-RGO peak was analyzed based on the integral area of the fitted peaks.
Electrical characterizations
- Analysis of CO 2 sensor of SO and SO-RGO
- Mechanism of resistive-based CO 2 sensor
- Response and recovery time for CO 2 sensors
- CO 2 sensing in GQDs-SO
- Response and recovery time of GQDS-SO device
- Sensitivity of CO 2 sensors
While S: CO2 sensitivity; Rs: maximum resistance value during CO2 exposure. GQDs-SO improved the sensitivity of 5000 ppm CO2 by 3 times over SO and 2 times over SO-RGO. Furthermore, the GQDs-SO nanohybrids improved the sensitivity by >300% compared to SnO2 NPs.
Conclusion
A novel sensing mechanism for resistive gas sensors based on layered reduced graphene oxide thin films at room temperature. Influence of reduced graphene oxide on structural, optical, thermal and dielectric properties of SnO2 nanoparticles. Role of oxygen vacancies in vanadium oxide and oxygen functional groups in graphene oxide for.
Summary and outlook
- Highlights of the thesis
- Synthesis and characterization of large lateral-size graphene oxide and its derivative
- A detailed study of layer dependent properties of large lateral-size graphene oxide and
- Plasma treated graphene oxide surface for trace dye detection using surface
- Fabrication and analysis of photodetector devices based on surface modified graphene
- Fabrication of CO 2 sensors based on graphene oxide based 2D materials and its nano
- Scope for future work
The properties of SnO2 and SnO2-RGO are measured in CO2 and air environments. The restoration of the graphitic structure after annealing at 230 ˚C has been confirmed by XRD and Raman spectrum analysis. IV properties of SO and SnO2-RGO (SO-RGO) measured in CO2 and air environments.
