Electronic Properties Of Graphene Oxide Research Articles

Theoretical and Experimental Analysis of Hydroxyl and Epoxy Group Effects on Graphene Oxide Properties.

In this study, we analyzed the impact of hydroxyl and epoxy groups on the properties of graphene oxide (GO) for the adsorption of methylene blue (MB) dye from water, addressing the urgent need for effective water purification methods due to industrial pollution. Employing a dual approach, we integrated experimental techniques with theoretical modeling via density functional theory (DFT) to examine the atomic structure of GO and its adsorption capabilities. The methodology encompasses a series of experiments to evaluate the performance of GO in MB dye adsorption under different conditions, including differences in pH, dye concentration, reaction temperature, and contact time, providing a comprehensive view of its effectiveness. Theoretical DFT calculations provide insights into how hydroxyl and epoxy modifications alter the electronic properties of GO, improving adsorption efficiency. The results demonstrate a significant improvement in the dye adsorption capacity of GO, attributed to the interaction between the functional groups and MB molecules. This study not only confirms the potential of GO as a superior adsorbent for water treatment, but also contributes to the optimization of GO-based materials for environmental remediation, highlighting the synergy between experimental observations and theoretical predictions in advances in materials science to improve sustainability.

Property Modulation of Graphene Oxide Incorporated with TiO2 for Dye-Sensitized Solar Cells.

Graphene oxide (GO) nano-powder is synthesized by the modified Hummer's method, and further thin films are deposited by using the water solution of GO through spin-coating. These films are thermally reduced along with the synthesized GO nano-powder at 50 to 200 °C in a high vacuum. Microstructural, electrical, and optical properties are expectedly controlled by thermal reduction. The electronic properties of GO are investigated by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. The reduction is confirmed by Raman spectroscopy. The work function and band gap of GO are tuned with the thermal reduction. The changes in properties of GO are not linear, and anomalous changes are observed for the reduction around 150 °C. Pristine and reduced GO nano-powder is incorporated into TiO2 paste to be the photoanode for dye-sensitized solar cells (DSSCs). It is observed that the performance of the fabricated cells is significantly enhanced for the GO reduced at 150 °C, and the cell exhibited a significant increment of ∼23% for the power conversion efficiency in comparison to DSSC based on an unmodified TiO2 photoanode.

Electronic properties of graphene oxide: nanoroads towards novel applications

In this work, we suggest an approach to manipulate the electronic properties of graphene oxide in a controllable manner. We study graphene nanoroads paved inside graphene oxide using density functional calculations. We show that this patterning allows transforming an insulator, graphene oxide, into a semiconductor or metal depending on the orientation of the nanoroads and their magnetic state. As a semiconductor, patterned graphene oxide is characterized by notably low effective masses of charge carriers. Additionally, we demonstrate the possibility to force the transition from a semiconducting to a half-metallic state in a controllable manner, by application of an external electric field. We believe that this remarkable opportunity to combine and control the electronic and magnetic properties of a material within a single sheet of graphene oxide paves the way towards new applications of graphene-oxide-based devices in 2D optoelectronics and spintronics.

Tuning optical and electronic properties of graphene oxide by surface adsorption of molecular halogens (X2 = I2, Br2, Cl2, and F2) for light harvesting

Surface adsorption of small molecules modulates both optical and electronic structure, which is beneficial for different applications. The molecular adsorption of halogens X2 (X2 = I2, Br2, Cl2, and F2) was investigated using density functional theory and the dispersion (Wb97xd) module. The electronic structure and optical properties of the pristine graphene oxide (GO) and its molecular complexes with halogens (GOI2, GOBr2, GOCl2, and GOF2) are explored. The adsorption of X2 (X2 = I2, Br2, and Cl2) molecules were stabilized by non-covalent lone pair-π bonding, (O)lp… π, interactions and π-π interactions. The F2 molecule were stabilized by lone pair-π bonding, (O)lp… π, as well as halogen bonding (XB). The GOX2 complexes were energetically stable and optically red shifted in polar solvents. The simulated optical absorption spectra at TD-DFT calculations of GOX2 complexes and TDOS uncover the presence of intermediate sates in the energy gap region, which is beneficial for harvest of visible light and photocatalysis.

(Nanocarbons Division Best Poster Award - 3rd Place) Reversible Quenching of Graphene Oxide Photoluminescence Under the External Electric Field

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in nanodevices such as bio and gas sensors, solid-state supercapacitors and solar cells. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to allow fine-tuning of its optical properties in the device geometry, new physical techniques are required that, unlike existing chemical approaches, yield substantial alteration of GO structure. Such a desired new technique is one that is electronically controlled and leads to reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modeling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/polyvinylpyrrolidone films with up to 6% reversible decrease under 1.6 V m−1 electric fields. On an individual flake level, a more substantial over 50% quenching is achieved for select GO flakes in a polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modeled on a single exciton level by utilizing Wentzel, Kremer, and Brillouin approximation for electron escape from the exciton potential well. In an aqueous suspension at low fields, GO flakes exhibit electrophoretic migration, indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.

Electric field quenching of graphene oxide photoluminescence

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in nanodevices such as bio and gas sensors, solid-state supercapacitors and solar cells. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to allow fine-tuning of its optical properties in the device geometry, new physical techniques are required that, unlike existing chemical approaches, yield substantial alteration of GO structure. Such a desired new technique is one that is electronically controlled and leads to reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modeling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/polyvinylpyrrolidone films with up to 6% reversible decrease under 1.6 V µm−1 electric fields. On an individual flake level, a more substantial over 50% quenching is achieved for select GO flakes in a polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modeled on a single exciton level by utilizing Wentzel, Kremer, and Brillouin approximation for electron escape from the exciton potential well. In an aqueous suspension at low fields, GO flakes exhibit electrophoretic migration, indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.

Study of the Electronic Properties of Graphene Oxide/(PANi/Teflon)

Graphene oxide (GO) has attracted enormous attention in the fabrication of electrochemical sensing systems as they have superior characteristics that enable them to be a perfect choice for the preparation of electrochemical devices. The usage of GO in preparation of polymer nanocomposites makes them a very promising material in electrical applications. Molecular modeling based on density functional theory (DFT) at B3LYP/6-31g(d, p) was utilized to study the interaction between the polyaniline (PANi) and Teflon composite with GO. The polymer blend model interacted with GO throughout the hydroxyl group (OH) located at the terminal and the oxygen atom in the middle of GO. Total dipole moment (TDM), HOMO-LUMO bandgap energy, and molecular electrostatic potential (MESP) are calculated for the studied structures. TDM found to be increased from 2.584 and 3.083 Debye for Go and PANi/ Teflon to 5.361, 4.208 and 5.839 for GO-Term (PANi/Teflon), GO- Mid (PANi/Teflon) and GO-Term (Teflon/PANi) respectively also band gap energy decreases to 0.347, 0.270 and 0.268 eV respectively. MESP shows that the reactivity is increased for the interaction of the polymer with GO through the oxygen atom in the middle. Obtained results confirmed that the proposed structure of GO/PANi/Teflon could be used in the fabrication of electrochemical devices.

Electric Field Quenching of Graphene Oxide Photoluminescence

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in biotechnology, electronics, photonics, materials and environmental science. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to enable fine-tuning of its optical properties in the device geometry, new physical techniques are required that unlike existing chemical approaches yielding substantial alteration of GO structure, enable electronically-controlled and, ideally, reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modelling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/PVP films with up to 6% reversible decrease under 1.6 V/µm electric fields. On an individual flake level a more substantial 50% quenching is achieved for select GO flakes in polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modelled on a single exciton level by utilizing WKB approximation for electron escape form the exciton potential well. In an aqueous suspension at low fields GO flakes exhibit electrophoretic migration indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.

The evolution of hydrogen induced defects and the restoration of [formula omitted]-plasmon as a monitor of the thermal reduction of graphene oxide

In this article, we study the modification of the optical, chemical and electronic properties of graphene oxide (GO) during thermal reduction in ultra-high-vacuum by combining the results of several electron spectroscopies. We find that the fraction of oxygen moieties on the surface, as deduced from the evolution of C 1s core level in photoemission, is progressively reduced upon increasing the annealing temperature from 150 to 650 °C. The intensity of the CH stretching mode, associated with CH defects on GO surface and measured in the low energy region of electron energy loss spectra (EELS), decreases as a function of the annealing temperature. The removal or the reduction of such hydrogen or oxygen defects induces a restoration of sp2 carbon hybridization. The presence of such hybridization is confirmed by the capability to excite π-plasmon as observed in the EELS spectra. In particular we find a critical annealing temperature (Tann = 300 °C) at which π-plasmon excitation via electron scattering is accessible suggesting the formation of graphene-like domains with size comparable with the plasmon wavelength (λp~5 nm). The linear dispersion of π-band close to Fermi level, as measured in UPS, confirms the formation of graphene-like domains.

Graphene Oxide and Derivatives: The Place in Graphene Family

Graphene oxide (GO) is useful and promising material for graphene based applications in electronic, optics, chemistry, energy storage and biology. At the beginning of graphene history GO was only a simple and cheap step for preparation of single and multilayer graphene films and bulk structures by reduction. The further studies revealed the substantial structure imperfection of graphene oxide derived materials due to the defects in initial graphite and incompletion of reducing process. However, the results of recent research demonstrated a great amount of unique chemical, optical and electronic properties of graphene oxide that allow regarding it as independent nanomaterial possessing a large area of applications. In general, it represents the ultra-large organic molecule containing 2D carbon mesh. Unlike conventional graphene it provides wide range of chemical methods for attachment of various functional groups to its surface for control optical transparency, electrical and thermal conductance. Recently developed methods for preparation of graphene oxide derivatives saturated by carboxyl groups open the new attractive application areas in green technologies including energy storage and utilizing nuclear wastes. The goal of the review is to summarize the results of recent studies of graphene oxide, derivatives and reveal the most promising directions to focus the efforts of researchers.

Electronic and Interface Properties in Graphene Oxide/Hydrogen‐Passivated Ge Heterostructure

Graphene oxide/H‐Ge (111) van der Waals (vdW) heterostructure is investigated by using first‐principle methods. An oxygen carbon ratio of 1:6 is applied to form a graphene oxide (GO) layer. A band inversion induced by built‐in electric field is observed, and a 7.4 meV indirect gap has been opened around the Dirac cone in GO layer. Being adsorbed on hydrogen‐passivated Ge surface, the band inversion occurs again around Fermi energy. Two‐dimensional electronic gas is confirmed with a 0.27 eV potential well appearing at the H layer. The charge transfer mechanism is revealed in order to illustrate band inversion and the electron accumulation on the Ge surface. Our calculation results provide insight into the electronic properties of GO and exhibit possible application of GO/H‐Ge (1111) heterostructure on the emerging electronic devices.

Electrochemical reduction of CO2 at metal-free N-functionalized graphene oxide electrodes

Exploring metal-free catalysts for electroreduction of CO2 into value-added fuels has been a crucial challenge in nowadays society. Herein we report some metal-free electrocatalysts for electrocatalytic reduction of CO2 to liquid products, such as ethanol and acetone. We develop functionalized graphene oxide (GO) surfaces with five pyridine derivatives: pyridoxine, 4-hydroxypyridine, 4-aminopyridine, 8-hydroxyquionline, and 5-amino-1,10-phenanthroline. Remarkably, pyridoxine modified on GO sheets with the pyridinic N content of 2.32% shows the optimum catalytic ability for electrochemical reduction of CO2, and the overall faradaic efficiency reaches up to 45.8%. Besides, other four pyridine derivatives functionalized GO exhibit various abilities for CO2 reduction to ethanol and acetone. The experimental results show that N-doping can alter the electronic properties of GO for enhancing the catalytic active for CO2 electroreduction, which is closely associated with the content of modified pyridinic N and the special structure of modified pyridine derivatives. Our work may provide inventive thought to design metal-free electrocatalysts for CO2 reduction to useful chemical fuels.

Detection of 2,4-dinitrotoluene by graphene oxide: first principles study

The surface of graphene oxide (GO) with different oxidation level is widely used in gas sensing applications. Otherwise, detection of 2,4-dinitrotoluene (DNT) have been extensively attend as a high explosive and environmental sources by various methods. Atomic level modelling are widely employed to explain the sensing mechanism at a microscopic level. The present work is an attempt to apply density functional theory (DFT) to investigate the structural and electronic properties of GO and adsorption of oxygen atom and hydroxyl on graphene surface. The focus is on the adsorption mechanisms of DNT molecule on the GO monolayer surface to detect DNT molecule. The calculated adsorption energy of DNT molecule on the GO surface indicates physisorption mechanism with −0.7 eV adsorption energy. Moreover, basis-set superposition errors correction based on off site orbitals consideration leads to −0.4 eV adsorption energy which it is more in the physisorption regime. Consequently, the results could shed more light to design and fabrication an efficient DNT sensor based on GO layers.

Unravelling Some of the Structure-Property Relationships in Graphene Oxide at Low Degree of Oxidation.

Graphene oxide (GO) is a versatile 2D material whose properties can be tuned by changing the type and concentration of oxygen-containing functional groups attached to its surface. However, a detailed knowledge of the dependence of the chemo/physical features of this material on its chemical composition is largely unknown. We combine classical molecular dynamics and density functional theory simulations to predict the structural and electronic properties of GO at low degree of oxidation and suggest a revision of the Lerf-Klinowski model. We find that layer deformation is larger for samples containing high concentrations of epoxy groups and that correspondingly the band gap increases. Targeted chemical modification of the GO surface appears to be an effective route to tailor the electronic properties of the monolayer for given applications. Our simulations also show that the chemical shift of the C-1s XPS peak allows one tounambiguously characterize GO composition, resolving the peak attribution uncertainty often encountered in experiments.

Exploring the effect of substitutional doping on the electronic properties of graphene oxide

Through molecular and solid-state approaches, structural and electronic properties of graphene oxide (GO) using substitutional doping were studied. Nitrogen, boron, phosphorus, silicon, aluminum, arsenic, and germanium atoms were integrated to GO at various sites to search for a suitable candidate that can reduce the energy gap of GO. As per our molecular investigations, Si- and Ge-doped GO reduces nearly 10% of the gap compared to the undoped molecule, while P, As, and N doping enhance the gap more than 50%. B and mainly Al (more energetically favorable structures) were found to be a suitable choice to be doped in GO, as it causes up to a 60% reduction in the energy gap compared to that of pristine GO. Moreover, the periodic calculations revealed that the introduction of Al can turn the GO structure into a metallic one. In addition, our studies disclosed that not only the dopant type but also the dopant sites are crucial in order to alter the electronic properties of GO.

Chemically Tunable Properties of Graphene Covered Simultaneously with Hydroxyl and Epoxy Groups

We investigate the chemically tunable properties of understoichiometric graphene oxide as a function of the growth temperature and the amount of hydroxyl and epoxy groups adsorbed on graphene. The structural disorder is modeled within a statistical approach based on a cluster expansion. A set of 308 cluster symmetry classes is investigated with ab initio calculations based on density functional theory. A complete scenario of energetics and phase stability is developed, yielding insight into the structure and electronic properties of graphene oxide. Our results show that the tendency to agglomeration of oxygen-containing groups is independent of their relative proportion and indicate the favorable formation of a unique oxygen-rich phase with both groups. Structural and electronic properties are predicted for the whole range of chemical compositions. The optical properties of oxygen-rich phases are also discussed in detail for different growth conditions.

The impact of adsorption on the localization of spins in graphene oxide and reduced graphene oxide, observed with electron paramagnetic resonance

We report the observations of electronic properties of graphene oxide and reduced graphene oxide, performed with electron paramagnetic resonance technique in a broad temperature range. Both materials were examined in pure form and saturated with air, helium, and heavy water molecules. We show that spin localization strongly depends on the type and amount of molecules adsorbed at the graphene layer edges (and possible in-plane defects). Physical and chemical states of edges play crucial role in electrical transport within graphene-based materials, with hopping as the leading mechanism of charge carrier transport. Presented results are a good basis to understand the electronic properties of other carbon structures made of graphene-like building blocks. Most active carbons show some degree of functionalization and are known of having good adsorptive properties; thus, controlling both phenomena is important for many applications. Sample treatment with temperature, vacuum, and various adsorbents allowed for the observation of a possible metal-insulator transition and sorption pumping effects. The influence of adsorption on the localization phenomena in graphene would be very important if to consider the graphene-based material as possible candidates for the future spintronics that works in ambient conditions.

Electronic and magnetic properties of nitrogen functionalized graphene-oxide

Graphene oxide potentially used as an intermediary in the production of single layer or few-layer graphene sheets. To achieve this, an oxidization and reduction process is used to developed single/few-layers and separate them without changing their structure. Graphene oxide has potential applications in many areas, e.g., electronics, magnetic, catalysis, and energy storage, because of its high charge-carrier mobility and high specific surface area. This study investigates the electronic and magnetic properties of graphene oxide (GO), and nitrogen functionalised graphene oxide (GO-Nx). GO is prepared using chemical process and hence functionalized with nitrogen precursors. GO and GO-Nx are characterised using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and Raman spectroscopy. Nitrogen functionalized GO become more graphitic in structure as observed from Raman spectroscopy and N 1s XPS spectrum that turn into higher magnetization observed from M-H hysteresis loops. The electronic density of states of GO-Nx is significantly higher than as compared to the GO as a result the magnetic properties also enhanced on GO-Nx. Our experimental results thus provide new evidences to control the magnetic and electronic properties of GO and GO-Nx for different electronic and magnetic device applications.

Role of substrate on interaction of water molecules with graphene oxide and reduced graphene oxide

We study local electronic properties of graphene oxide (GO) and reduced graphene oxide (RGO) on metallic (Pt) and insulating (Si3N4) substrates in controlled humidity environment. We demonstrate that the supporting substrate plays a crucial role in interaction of these materials with water, with Pt making both GO and RGO insensitive to humidity variations and change in environment. On the other hand, in the case of Si3N4 substrate a significant difference between GO and RGO with respect to humidity variations is demonstrated, indicating complete water coverage at ∼60% R.H for RGO and ∼30% R.H. for GO. Irrespective of the substrate, both GO and RGO demonstrate relative independence of their electronic properties on the material thickness, with similar trends observed for 1 and 2 layers when subject to humidity variations. This indicates a relatively minor role of material thickness in GO-based humidity sensors.

Investigation of the surface plasmon polariton and electrochemical properties of covalent and non-covalent functionalized reduced graphene oxide.

The surface electronic properties of graphene oxide (GO) were modified through reduction and functionalization. Non-covalent functionalization was found to be superior compared to covalent functionalization due to the formation of few-layer graphene with a low defect content and average crystalline length. Because of the restoration of sp2 hybridization, non-covalently functionalized reduced graphene oxide (rGO) showed a better plasmonic response compared to GO, rGO and covalently functionalized rGO. Due to the available π electrons from the sp2 network of graphene as well as surface functionality, non-covalent functionalized rGO exhibited elevated donor density. Furthermore, due to the synergistic effect of surface electronic properties as well as adsorption and recombination at the barrier, superior charge transfer was achieved at the electrode-electrolyte interface for non-covalent functionalized rGO.