Au-doped Graphene Research Articles

Pure and doped graphene as a suitable material for the detection of hazardous gases

The need for highly sensitive toxic gas sensors is significant, and achieving this sensitivity is possible. Researchers have utilized density functional theory (DFT) computations to examine adsorption of different gas molecules (COX2, where X is F, Cl, or Br) over Au-doped and pristine graphene. This investigation aims to determine possibility of employing Au-doped graphene as a basis for gas sensors. Multiple adsorption positions and orientations were examined for each gas molecule. The configuration that exhibited the highest stability was identified, and adsorption energy (Eads) values, considering van der Waals (vdW) interactions, have been computed using NCI analyses. In addition, the electronic properties, including LUMOHOMO orbital density and charge transfer, were analyzed to acquire a deeper understanding of process by which adsorption occurs. Findings indicated that gas molecules under investigation exhibited weak adsorption on pristine graphene, with low Eads values. In contrast, Eads values of every gas molecule on Au-doped graphene displayed varying degrees of increase. Notably, COX2 exhibited a high sensitivity to Au-doped graphene. Furthermore, in the effect of doping Au into graphene, the Eads absorption of COCl2 gas has increased from 0.155 to 1.028 eV. This indicates the strong tendency of Au-doped graphene to interact with gas COCl2 compared to two other COX2 gas species. This strong adsorption can be ascribed to significant substantial charge transfer (CT) between COCl2 and Au-doped graphene and orbital hybridization. The charge transfer amount of the doped states has increased by more than double compared to the pure state. The band gap of Au-doped graphene has decreased from 2.14 to 1.83 eV due to the absorption of gas COCl2, indicating the highest amount of reduction compared to other gases. Moreover, the enhanced electrical conductivity of Au-doped graphene renders it more valuable and sensitive in the context of sensing COX2 gases.

Adsorption performance of CNCl, NH3 and GB on modified graphene and the selectivity in O2 and N2 environment

Two-dimensional materials have shown desirable application prospects in the field of gas sensing. Through the modification of graphene gas-sensitive materials, more efficient and sensitive gas sensors can be further developed. The use of metal atoms or oxygen-containing groups to modify graphene can improve its detection performance for gases. Modified-graphene could be selected as an excellent gas sensor for poisonous gas detection. In this work, adsorption systems of CNCl, NH3 and GB on metal doped graphene (Au, Ag, Cu and Fe) and graphene oxide were established by the using of density functional theory (DFT). The adsorption energy, charge transfer, DOS, PDOS and energy band of these adsorption systems were investigated. The gas adsorption strength and gas selectivity factor were introduced to evaluate the selectivity of each substrate to these harmful gases in O2 and N2 environments. The calculation shown strong adsorption between the metal-doped graphene and the adsorbed gas, with Fe-doped graphene having better adsorption performance. By contrast, between graphene oxide and the adsorbed gas, the effect was slight. Moreover, the energy band change of metal- doped graphene was more obvious than that of graphene oxide. In addition, under O2 and N2 environment, Au-doped graphene may have good selectivity for CNCl and NH3 while Ag-doped graphene may have good selectivity for GB. This result will provide reference for the development of graphene based gas sensors for CNCl, NH3 and GB.

Hydrogen sulfide molecule adsorbed on doped graphene: a first-principles study.

First principles were used to investigate electronic properties of Au-doped graphene, Ag-doped graphene, and Cu-doped graphene and the effect of adsorption behavior of hydrogen sulfide (H2S) molecule on their electronic properties. Doped graphene exhibits interesting electronic properties. The gap value of Ag-doped graphene is 0.29eV, whereas Au-doped graphene is 0.48eV which is the largest one in three doped systems, a clear difference of structure and electronic properties among three doped systems absorbing H2S molecule. The doped atom and the H2S molecule are on the same side of the graphene for Au-doped graphene and Cu-doped graphene, which belong to a kind of bonding orbital hybridization of electron cloud showed from charge difference density plots. However, Ag-doped graphene adsorbed with H2S molecule exhibits a kind of antibonding orbital hybridization. With the analysis in this paper, it is beneficial to research H2S gas sensors.

A comparative experimental and density functional study of glucose adsorption and electrooxidation on the Au-graphene and Pt-graphene electrodes

At present, the graphene is covered on Cu foil with the 5 sccm hexane (C6H14) flow rate, 50 sccm hydrogen (H2) flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil is then covered onto few-layer ITO electrode. Furthermore, the Pt and Au metals are electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes are characterized by Raman spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-Ray analysis (SEM-EDX). The graphene structure is approved via Raman analysis. Au, Pt, and graphene network are openly visible from SEM results. In addition, glucose (C6H12O6) electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. As a result, Pt-graphene/ITO indicates the best C6H12O6 electrooxidation activity with 9.21 mA cm−2 specific activity (highly above the values reported in the literature). In all electrochemical measurements, Pt-graphene/ITO exhibits best electrocatalytic activity, stability, and resistance compared to the other electrodes. The adsorption of the C6H12O6 molecule is examined theoretically over metal atom (gold and platinum)-doped graphene surfaces using the density functional theory (DFT) method. The interaction between C6H12O6 molecule and OH adsorbed Pt-doped surface is stronger than that of OH adsorbed Au-doped graphene surface thermodynamically according to the reaction energy values.

Ferromagnetic topological crystalline insulating phase in the pi-stacked graphene nanobelts under a small pressure

This work presents a topological material based on the graphene nanobelts. It is intrinsically magnetic. The band inversion in this system is partial and anomalous, as it was recently found in the Au-doped graphene and 2D molecular crystal. The metallic edge states with the Chern number equal to 1 exist in the ferro- and antiferromagnetic phase. The edge states become gapless at a small pressure, around 0.87 GPa, applied along the stacking axis. Their dispersions are not symmetric for the spin up and down. The graphene nanobelts are pi-stacked with the AB-type, and the zigzag edges are terminated with the O and H atoms at the opposite sides, in the reversed order along the stacking axis. The propagation of the topological edge states is parallel to the OcdotsH-interaction direction, across the stacked belts.

Studying metal-doped graphene nanosheet as a drug carrier for anticancer drug β-lapachone using Density Functional Theory (DFT)

Graphene based materials have been widely used in biomedicine as drug delivery systems in recent years. In this work, the feasibility of utilizing pure and metal–doped (Pt, Au) graphene nanosheets was investigated as a carrier for β-lapachone (β-lap) anticancer drug using quantum mechanical methods based on Density Functional Theory (DFT). The intermolecular interactions between β-lap and graphene nanosheets were studied through analyzing adsorption behavior, adsorption energy and electronic density between the drug and the graphene nanosheets in the most stable structure of β-lap/graphene complex. As Pt and Au atoms replace with one of carbon atoms in the graphene nanosheet, the metallic dopant is moved out from the sheet. The adsorption mechanism of the drug for being loaded on the graphene nanosheets was studied with current models. It was found that β-lap prefers to attach via its –O atom to pure and metal-doped graphene nanosheets. Our results disclose that the interactions between β-lap molecule and pure graphene nanosheets are weak and can be classified as physisorption. Calculations showed that Pt-doped and Au-doped graphene nanosheets have much higher adsorption energies and shorter binding distances compared to pure graphene nanosheets. The adsorption energy of β-lap molecule on Pt–doped graphene nanosheet was significantly higher than Au-doped graphene nanosheet.

The adsorption of nitrogen oxides on noble metal-doped graphene: The first-principles study

The first-principles method based on density functional theory has been used to investigate the adsorption performance of NO/NO2 molecules on intrinsic, Ag-doped, Pt-doped and Au-doped graphene. Results show that graphene doped with Ag/Pt/Au has shorter final adsorption distance, larger adsorption energy and charge transfer amount with NO/NO2 molecules than intrinsic graphene, and the charge densities of doped graphene and NO/NO2 molecules overlap effectively. Therefore, doping graphene with noble metals can greatly enhance the adsorption between graphene and NO/NO2 molecules. Analysis also reveals that Au-doped graphene has the strongest adsorption effect on NO/NO2 molecules, followed by Ag-doped graphene, while Pt-doped graphene has the weakest role on the adsorption of NO/NO2 molecules. The work conducted in this research provides a theoretical guidance for the application of NO/NO2 gas sensors based on graphene.

First-principles study of Cu adsorption on vacancy-defected/Au-doped graphene

To enhance the interaction between Cu and graphene in graphene reinforced Cu matrix composites, the first principles calculation was carried out to study the adsorption of Cu atoms on graphene. P-type doping and n-type doping were formed, respectively, on vacancy-defected and Au-doped graphene based on band structure analysis, and this was verified by subsequent investigation on density of states. A computation on charge transfer confirmed that p-type doping could promote the electron transport between Cu and graphene, while n-type doping would prevent it. In addition, adsorption energy and Mulliken population analysis revealed that both vacancy defects and Au doping could improve the stability of the Cu–graphene system. The research conducted in this paper provides useful guidance for the preparation of Cu/graphene composites.

On the Elusive Link between Adsorbate's Binding Energy and Bond Strength: An Illustration from CO Adsorption on Metal-Doped Graphene

Adsorbates’ binding energy is often used as an indicator of the adsorbate-substrate bond strength. Although one can compute any binding energy, models to gauge bond-strength are developed to rationalize and anticipate it for the rational search for efficient catalysts. Unfortunately, bond-strength alone fails to predict trends in binding energy because, as hinted by models since the 1970s, the binding energy is the outcome of a complex response of the system to the created bond. Therefore further understanding the difference between binding energy and bond strength is essential to catalysts design. Indeed, the adsorbate-substrate bond formation perturbs, not only the geometry of the system, but also the substrate and adsorbate's electronic charge density. Both effects overall reduce the binding energy by an energy attached to such perturbations, the so-called perturbation energy. Here, with the example of carbon monoxide adsorption on metal-doped graphene, we show that such perturbation energy may exceed 1 eV and render an unusual situation: Namely, although the binding energy of CO to the Au-doped graphene indicates that binding does not happen, we find evidence of a strong bond between CO and such substrate. Thus, in this case, the large perturbation energy totally disrupts the equivalency between bond strength and binding energy. Here we propose a method to compute the perturbation energy that bypasses dealing with an excited electronic state of the system.

H2S nano-jetting through a p–n junction-like graphene/Au nano-injector: a molecular dynamics study

This paper uses fully atomistic molecular dynamics to outline the dynamics of H2S nano-jetting through a p–n junction-like graphene/Au nano-injector. We examined the effects of nano-injector diameter (d), system temperature (T), and the extrusion velocity (v) of a graphite piston plate on the formation of H2S nano-jets, system pressure, and the number of molecules (N m) in the outflow. The combined effects of high critical pressure and small orifice resulted in a larger jet angle, which increased the number of H2S molecules stuck to the graphene surface at the outlet. Moving the graphite piston plate toward the orifice of the nano-injector increased in the change in momentum and interactive forces between H2S molecules, resulting in three phases of pressure establishment in the nano-injector: incubation (phase I), steep pressure increase (phase II), and high pressure (phase III). When operated at T ≥ 300 K and v < 27.912 m/s, the proposed nano-jet device is able to produce a well-dispersed spray of H2S without H2S molecules sticking to the graphene surface at the outlet. The p–n junction-like Au-doped graphene surface provides an additional energy barrier preventing the transport of electrons from H2S molecule to the graphene. This inhibits the accumulation of H2S molecules and subsequent blockages at the exit of the nano-injector. Simulation results demonstrate the potential of using chemiresistive sensing to monitor H2S flow patterns during nano-jetting. The findings presented in this study could be transformative to the design of nano-injectors for other gases commonly used as biomarkers.

Au-IDA microelectrodes modified with Au-doped graphene oxide for the simultaneous determination of uric acid and ascorbic acid in urine samples

An electrochemical sensor based on graphene oxide decorated with gold nanoparticles has been prepared for the simultaneous quantification of uric acid (UA) and ascorbic acid (AA) in urine samples. The gold interdigitated microelectrodes array (Au-IDA) has been modified using graphene oxide doped with gold nanoparticles (AuNPs-GO/Au-IDA), which was characterized by TEM, FE-SEM, XPS and cyclic voltammetry. Excellent results were obtained for the separate quantification of UA and AA by chronoamperometry. The electrochemical sensor exhibits limits of detection (LODs) of 1.4μM and 0.62μM for AA and UA, respectively, limits of quantification (LOQs) of 4.6μM (AA) and 2.0μM (UA), and the working ranges obtained were between 4.6μM and 193μM for AA and between 2μM and 1.05mM for UA. The repeatability was studied at 20μM providing coefficients of variation of 16% for AA and 13% for UA. Moreover, UA does not interfere in the measurement of AA and viceversa (provided that the concentration of UA is equal to or higher than 450μM in the latter case). For lower concentrations of UA, an easy and fast strategy to quantify both analytes is presented. The good electrocatalytic activity achieved with this material makes it useful for the quantification of AA and UA in biological fluids. Other analytes like glucose, dopamine and epinephrine have been investigated. The results allow us to conclude that they do not interfere in the quantification of AA and UA in PBS (0.25M, pH 7.0). Human urine samples have been analyzed using the method proposed, contaning AA and UA concentration levels of (0.588±0.002) mM and (1.43±0.02) mM, respectively, which are in the concentration range of these analytes in urine samples for healthy people.

Gold-doped graphene: A highly stable and active electrocatalysts for the oxygen reduction reaction.

In addressing the growing need of renewable and sustainable energy resources, hydrogen-fuel-cells stand as one of the most promising routes to transform the current energy paradigm into one that integrally fulfills environmental sustainability. Nevertheless, accomplishing this technology at a large scale demands to surpass the efficiency and enhance the cost-effectiveness of platinum-based cathodes, which catalyze the oxygen reduction reaction (ORR). In this work, our first-principles calculations show that Au atoms incorporated into graphene di-vacancies form a highly stable and cost-effective electrocatalyst that is, at the same time, as or more (dependently of the dopant concentration) active toward ORR than the best-known Pt-based electrocatalysts. We reveal that partial passivation of defected-graphene by gold atoms reduces the reactivity of C dangling bonds and increases that of Au, thus optimizing them for catalyzing the ORR and yielding a system of high thermodynamic and electrochemical stabilities. We also demonstrate that the linear relation among the binding energies of the reaction intermediates assumed in computational high-throughput material screening does not hold, at least for this non-purely transition-metal material. We expect Au-doped graphene to finally overcome the cathode-related challenge hindering the realization of hydrogen-fuel cells as the leading means of powering transportation and portable devices.

Chemically doped three-dimensional porous graphene monoliths for high-performance flexible field emitters.

Despite the recent progress in the fabrication of field emitters based on graphene nanosheets, their morphological and electrical properties, which affect their degree of field enhancement as well as the electron tunnelling barrier height, should be controlled to allow for better field-emission properties. Here we report a method that allows the synthesis of graphene-based emitters with a high field-enhancement factor and a low work function. The method involves forming monolithic three-dimensional (3D) graphene structures by freeze-drying of a highly concentrated graphene paste and subsequent work-function engineering by chemical doping. Graphene structures with vertically aligned edges were successfully fabricated by the freeze-drying process. Furthermore, their number density could be controlled by varying the composition of the graphene paste. Al- and Au-doped 3D graphene emitters were fabricated by introducing the corresponding dopant solutions into the graphene sheets. The resulting field-emission characteristics of the resulting emitters are discussed. The synthesized 3D graphene emitters were highly flexible, maintaining their field-emission properties even when bent at large angles. This is attributed to the high crystallinity and emitter density and good chemical stability of the 3D graphene emitters, as well as to the strong interactions between the 3D graphene emitters and the substrate.

Electronic Properties of Au-Doped Narrow Armchair Graphene Nanoribbons: A First Principle Calculations

The centre Au-doped armchair graphene nanoribbons (AGNRs) are investigated using the local density approximation based on density function theory. The charge density, electronic energy band and project density of states of centre Au-doped AGNRs are calculated. Our results indicate the charge density is transferred between C and Au atoms and mainly located on the Au atoms. The centre Au-doped AGNRs are an indirect band gap semiconductor with an energy gap of 1.046 eV. The Fermi level is located on valence band so that the AGNRs of doping Au become into degenerate semiconductor. The project density of states is calculated to reveal localization and hybridization between C-2pand Au-6s, 5delectronic states. The localization and hybridization are much stronger in the valence band. The hybridization between C-2pand Au-6pelectronic states are strongly in the conduction band.

Formaldehyde molecule adsorbed on doped graphene: A first-principles study

Adsorption of formaldehyde (H2CO) on B-, N-, Si-, Al-, Cr-, Mn-, and Au-doped graphene was theoretically studied using first-principles approach based on density functional theory in order to exploit their potential applications as H2CO gas sensors. The electronic and magnetic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. H2CO molecule is adsorbed weakly on B- and N-doped graphene; in general, strong chemisorption is observed on Si-, Al-, Cr-, Mn-, and Au-doped graphene. The most stable adsorption geometries, adsorption energies, magnetic moments, charge transfers, and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of graphene-based chemical gas sensors for H2CO can be drastically improved by introducing appropriate dopant. Al and Mn are found to be the best choices among all the dopants.

Chlorine molecule adsorbed on graphene and doped graphene: A first-principle study

Adsorption of molecular chlorine (Cl2) on intrinsic and B-, Si-, Cr-, Cu-, Fe-, Mn-, Ni-, Ti- and Au-doped graphene was theoretically studied using first-principle approach based on density functional theory in order to develop their potential applications as Cl2 gas sensors. The structural, electronic and magnetic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. Cl2 molecule is adsorbed weakly on intrinsic and B-doped graphene; in general, strong chemisorption is observed on Si-, Cr-, Cu-, Fe-, Mn-, Ni-, Ti- and Au-doped graphene. The most stable adsorption geometries, energies, magnetic moments, charge transfers and density of states of these systems are thoroughly discussed. This work reveals that the sensitivity of graphene-based chemical gas sensors for Cl2 can be drastically improved by introducing appropriate dopant, and Ti as well as Au is the best choice among all the dopants.

Graphene electrodes transfer-printed with a surface energy-mediated wet PDMS stamp: impact of Au doped-graphene for high performance soluble oxide thin-film transistors

Unlike conventional dry stamp-based printing methodologies, the suggested wet PDMS stamping technique allows for the generation of well-patterned graphene source/drain electrode structures. It is clarified that the electrical characteristics of soluble In–Ga–Zn–O (IGZO) TFTs can be improved effectively by adjusting the work function of transfer-printed graphene electrodes with a simple, facile Au doping technique. By implementing the transfer-printed, Au-doped graphene layers as a source/drain electrode and the newly developed chemical structure-tailored IGZO semiconductors as a soluble channel layer, the high performance graphene/IGZO TFTs are demonstrated with a field-effect mobility of 3.2 cm2 V−1 s−1, which is far superior to the previously reported TFTs employing the printable electrode and a soluble oxide semiconductor.

Adsorption and Catalytic Activation of O2 Molecule on the Surface of Au-Doped Graphene under an External Electric Field

The interaction between oxygen molecule (O2) and metal-doped graphene has always been a heated discussed issue because O2 plays an important role in the graphene-based gas-storage materials, sensing platforms, and catalysts. In this article, the effect of an external electric field on the interaction between O2 and Au-doped graphene is studied using density-functional theory (DFT) calculations. The simulations show that O2 vertically moves away from Au-doped graphene substrate under a positive electric field, whereas under a negative electric field, accompanied by the vertical pushing out movement, O2 also moves toward the specific Au atom horizontally. Besides, the adsorption energy (Ead) of O2 is dramatically changed with electric field. A negative electric field strengthens the interaction between O2 and Au-doped graphene substrate, resulting in an enhanced Ead; the corresponding O–O distance (dO–O) is also elongated, while Ead is decreased and dO–O is shortened under a positive electric field. Because dO–O of the adsorbed O2 correlates with its catalytic activation, the findings can provide a new avenue to tune the O2 adsorption process onto Au-doped graphene substrate and may be useful in the future applications of graphene-based nanocatalyst.

First principle study of cysteine molecule on intrinsic and Au-doped graphene surface as a chemosensor device

To search for a high sensitivity sensor for cysteine, we investigated the adsorption of cysteine on intrinsic and Au-doped graphene sheets using density functional theory calculations. Binding energy is primarily determined by the type of atom which is closer to the adsorbed sheet. Compared with intrinsic graphene, Au-doped graphene system has higher binding energy value and shorter connecting distance, in which strong Au-S, Au-N and Au-O chemical bond interaction play the key role for stability. Furthermore, the density of states results show orbital hybridization between cysteine and Au-doped graphene sheet, but slight hybridization between the cysteine molecule and intrinsic graphene sheet. Large charge transfers exist in Au-doped graphene-cysteine system. The results of DOS and charge transfer calculations suppose that the electronic properties of graphene can be tuned by the adsorption site of cysteine. Therefore, graphene and Au-doped graphene system both possess sensing ability, except that Au-doped graphene is a better sensor for cysteine than intrinsic graphene.