Doped Graphene Sheets Research Articles

The promising 2D monolayers supported single f-electrons atom (Ce, Th, and U) catalysts in the ammonia synthesis via electrochemical nitrogen reduction reaction

The production of environmentally friendly through electrocatalytic nitrogen reduction under ambient conditions holds great promise for green energy. Efficient catalysts play a crucial role in this process. In this study, we employed density functional theory calculations to examine the catalytic performance of three types of monolayers, namely four surrounding N atom doped graphene sheet (GN4), graphdiyne, and Ti2CO2, supported by three different single atoms (Ce, Th, and U) with f-electrons. Our results identified that U@GN4 exhibits excellent catalytic activity through the distal pathway, with a ΔG of only 0.64 eV for the potential determining step. Furthermore, theoretical analysis reveals that the synergistic action of U d and f electrons plays a crucial role in the N2 reduction catalyzed by the U@GN4. The catalytic performance for hydrogen evolution was also examined for these nine single-atom catalysts. Th@GN4 and Th@Ti2CO2 demonstrate promising performance in hydrogen evolution, with ΔGH* of 0.03 and 0.10 eV, respectively. This study holds significant value for the design and utilization of single-atom catalysts with f-electrons for efficient N2 reduction reaction and hydrogen evolution reaction electrocatalysts.

Tunable gas absorption capability for graphene doped silica aerogel by wrinkle structure: Effects of gas absorption, mechanical properties and thermal insulation

Gas absorption capability of material proposes a dominant role in the energy storage, selective gas absorption/capture. Aerogels with ultra-high porosity, ultra-low thermal conductivity have been widely used in gas absorption. However, a persistent limitation of these materials is their static and unalterable gas absorption capacity. In this work, a wrinkled graphene structure is proposed to adjust the gas capability. A series of molecular dynamics (MD) simulations are carried out to propose an atomic-level understanding of the effects of wrinkled structure, including effects of pressure, surface wettability, number of gas molecules, thermal insulation, and mechanical properties. It is found that the gas capability can be reduced by 20% with wrinkle structure. Notably, the linear response between pressure and gas absorption capability is observed. Moreover, wrinkle structure functions as a thermal resistance to restrict solid heat transfer. The mechanical property of the aerogel composite is improved by a doped graphene sheet with a high wrinkle degree. This work will pave the way for the development of aerogel with high and selective gas absorption capability.

Probing the influence of defects and Si-doping in graphene sheet as an efficacious carrier for drug delivery system in gas and aqua phases - Combined DFT and classical MD simulation

In this study, for the bioavailability and distribution of the drug on the tumor cells we have chosen targeted drug delivery system and for the delivery system, pristine, defected, and doped graphene sheets are chosen with the anticancer drugs as lapachol and β – lapachone which are studied using density functional theory (DFT) for efficacious drug delivery. The defect formation and doping are shown to alter the properties of pristine sheets, which results in the enhanced adsorption of anticancer drugs. The cohesive energy found for all the sheets are in the 7 eV range which shows their high stability. This study revealed that the adsorption of lapachol and β – lapachone in pristine graphene sheet is poor with low adsorption energy of about −1.49 (−1.39) eV and −1.52 (−1.43) eV in gas (water) medium respectively and the adsorption energy is enhanced about 30–70% by introducing defects and about 55% by doping of silicon in the pristine graphene sheet. The highest adsorption energy for both lapachol and β – lapachone are found to be about −2.69 (−2.59) eV and −2.55 (−2.41) eV in mono vacant graphene sheet in gas (water) medium respectively. The major interaction within the complexes is studied using quantum theory of atoms in molecule (QTAIM) analysis and it is further studied via non-covalent interaction (NCI) analysis with the help of reduced density gradient (RDG) map. The ρ values at bond critical points (BCP) lie between 0.007 and 0.01 a. u. With ∇2ρ and H(r) > 0, −G/V > 1 for all the complexes showing that non-covalent interaction plays a major role in the adsorption of active drugs. Furthermore, NCI analysis shows that the van der Waals interaction and hydrogen bonding play a major influence on the interaction between the anticancer drug and the carrier sheets. The molecular dynamic (MD) study shows that all the drug-loaded complexes are stable with minimal variation in the van der Waals energy during the production run. Thus, the results obtained from DFT and MD shows that the defected and Si-doped graphene sheets are much more suitable as a carrier for drug delivery than the pristine sheet. This study paves the way for the future research on the defected and doped graphene sheets as a suitable drug carrier for numerous drugs in the targeted drug delivery system.

He adsorption and sensing properties of graphene nanoflakes doped with Mo and Nb

DFT calculations have been performed to study the He adsorption on the surface of Mo-doped graphene and Nb-doped graphene nanoflakes in order to evaluate the capability of studied doped graphene sheets as effective gas sensor materials. The ωB97XD (including dispersion)/6-311++G(d,p) (LanL2DZ for Mo and Nb) level of theory were utilized in this investigation. The HOMO-LUMO gap (Eg) of the Mo-doped and Nb-doped graphene structures decreased upon He adsorption on both sheets (−37.77% and −8.33%, respectively). Therefore, the electrical conductivity of both surfaces have increased. However, alteration of the Eg value in Mo-doped graphene is very higher than that of Nb-doped graphene. So, the Mo-doped graphene is more sensitive to He molecule in comparison with Nb-doped graphene and it could be used as a gas sensor material to detect He gas. Variety analyses such as natural bond orbital (NBO), density of states (DOS), electron density distribution (ED), electron localization function (ELF) and non-covalent interaction-reduced density gradient (NCI-RDG) have been carried-out in order to better evaluate the He adsorption nature on the investigated surfaces.

Al/Si dopants effect on the electronic and optical behaviors of graphene mono-layers useful for infrared detector devices

Two-dimensional (2D) graphene with different forms is a prosperous class of materials beneficial in nano-electronics, and infrared-detector devices. Herein, we analyze the electronic and optical behaviours of electron acceptor (Al)- and isovalent (Si) inserted into graphene sheets, which are computed by utilizing ab-initio simulations. We find that the individual doping impurities of Al or Si atoms onto monolayer graphene result in p-type and semiconducting behaviours, respectively, attributed to the contribution of the valence electrons number of these atoms to the host 2D honeycomb lattice of graphene. Even though the Al atom contributing one less electron to the host lattice, both individual impurities of the Al- or Si-doped materials are found to cause a splitting in the valence states and conduction states at the K-point, leading to the opening of the Dirac cone. In monolayer graphene, doping two Al atoms into the nearest neighbour sites creates a trivial metallic system, while doping two Si atoms into the nearest neighbour sites causes the Dirac cone to re-emerge. Owing to the stark difference in the electronic structure results of mono- and double-atom substitution of Al/Si in graphene single-layers, we find different optical behaviours in these doped systems. Additionally, X-ray absorption spectroscopy simulations are employed to inspect the core-level spectra of pure and substitutional doped graphene single layers. Accordingly, the optical spectral features of graphene single-layers substituted with foreign impurities, such as Al/Si have revealed the tailoring of optical absorption from the infrared to the visible windows. Due to the outstanding characteristics of this 2D dimensional gapless graphene, our simulated results could provide a guidance for future experimental investigations into the fabrication of doped graphene sheets suitable for infrared detectors, photonics, and modern optoelectronic devices integrated into advanced technologies.

Mesoporous hydroxyl vanadium oxide/nitrogen-doped graphene enabled fast polysulfide conversion kinetics for high-performance lithium-sulfur batteries

Transition metal vanadium (V)-based oxides with various morphologies have been used in lithium-sulfur (Li-S) batteries to restrain the polysulfide shuttling because of their strong chemical interaction with polysulfides and the high catalytic activity toward the polysulfide transformation. Herein, hollow vanadium oxide spheres (VOOH) with several integrated merits are prepared and used to construct an interlayer between separator and cathode. The mesopore-abundant thin shells of VOOH are beneficial for the fast ion transport. Combined with nitrogen (N)-doped graphene sheets (NG), the as-obtained VOOH/NG interlayer allows fast electron/ion transport, finally enhancing polysulfide transformation kinetics. The Li-S batteries with the VOOH/NG exhibit a high initial discharge capacity (1441.1 mAh g−1 at 0.1C), low capacity decay rate (0.075% per cycle at 1C after 600 cycles), good rate capability, and high areal discharge capacity exceeding that of commerical lithium ion batteries. In addition, the real application of such VOOH-based interlayer is further demonstrated by the successful assembly and good performance of the corresponding pouch cells.

A DFT studies on absorbing and sensing possibilities of glucose on graphene surface doped with Ag, Au, Cu, Ni & Pt atoms

The adsorption of glucose is theoretically examined using the Density Functional Theory method (DFT) over pure graphene and graphene surface doped with transition metal atoms (silver, gold, copper, nickel, and platinum). The graphene sheets are altered by substitutional doping of silver, gold, copper, nickel, and platinum atoms remarks in altering the electronic properties and actively reassuring glucose absorption. The outcomes revealed that metal atoms doped with graphene sheets improve the reactivity. Our study found that the interaction of glucose with pure graphene is weak when compared to metal-doped graphene flakes. Our studies concluded that due to strong adsorption energies, high bandgap variation, and excellent work function values of metal-doped graphene sheets make them beneficial for glucose sensing devices. The sensitivity and conductivity variations are high for the metal doped graphene sheets except nickel, however the recovery time value is high, suggesting that these sheets can be used as a disposable sensor.

The Effect of Nitrogen on the Structural and Electronic Properties of Graphene Sheet using Density Functional Theory

Abstract The present research focuses on a theoretical study of structural and electronic properties of pure graphene sheet and then adding different number of N2 atoms. The calculations are carried out using the density functional theory (DFT) with hybrid functional B3LYP/6-31G level to investigate the proposed structures. Gauss View 5.0.8 program is used to design the structures of pure and doped graphene sheets. These structures are relaxed by employing the PM6 semi-empirical method with the hybrid functional B3LYPDFT at Gaussian 09 package. The results of the structural properties of the studied graphene sheets showed that good relaxation of the structures, the constant bonds values in the pure graphene sheets in the same ranges of the carbon rings structures. We calculate the total energy, High Occupied Molecular Orbital (HOMO) and Low Unoccupied Molecular Orbital (LUMO) energies and forbidden energy gap. The result of the total energy of that doping graphene sheets is result of the binding energy of each structure and indicates that these structures have relaxation, and the effect of adding N2 atoms in pure graphene sheet on the total energy of the molecule is effective. All doping graphene sheets have small forbidden energy gap, but it vibrates depending on the length and number of each sheet and the position of N2 atoms in the sheets.

Sensing properties of propylene oxide on Pt and Pd doped graphene sheets: A DFT Investigation

The adsorption and detection of propylene oxide (PO), which is a volatile organic compound produced on a large scale industrially and used in polymerization reactions, is an important issue. In this study, the adsorption of propylene oxide on the metal-doped graphene sheets were investigated by periodical Density Functional Theory calculations. The HSEH1PBE (HSE06) hybrid method was used for theoretical calculations. It has been determined that Pt-doped and Pd-doped graphene structures give adsorption energy values of − 78.6 and − 75.4 kJ/mol, respectively. The sensors have been evaluated in terms of work function (Φ) showing that each can be described as an Φ-type gas sensor. In addition, it has been revealed that periodical theoretical calculations utilized in this study give more accurate results than calculations made with the GGA-PBE method. As a result, it has been determined that Pt-doped and Pd-doped graphene sheets are effective for PO adsorption, Pt-doped graphene layer can be used as an electronic sensor for PO, whereas Pd-graphene layer cannot be used.

Sensitive electrochemical detection of bisphenol A at screen-printed graphite electrode modified with nitrogen-doped graphene sheets

A novel voltammetric sensor was developed by modifying screen-printed graphite electrode (SPGE) with nitrogen doped graphene sheets (N-GSs) to detect bisphenol A. The electrochemical results exhibited that N-GSs / modified SPGE has high sensing performance towards the oxidation of bisphenol A. Excellent results were obtained for bisphenol A detection in the linear range from 0.08 to 300.0 µM with a sensitivity of 0.1626 µA µM-1 and limit of detection of 0.02 µM. Also, the fabricated N‑GSs/SPGE sensor showed good stability. The as-prepared sensor was tested towards the detection of bisphenol A in real samples. The measured results established the great sensing ability of N-GSs/SPGE for bisphenol A with high selectivity and good stability in real samples.

Casimir pressure in peptide films on metallic substrates: Change of sign via graphene coating

We find that the Casimir pressure in peptide films deposited on metallic substrates is always repulsive which makes these films less stable. It is shown that by adding a graphene sheet on top of peptide film one can change the sign of the Casimir pressure by making it attractive. For this purpose, the formalism of the Lifshitz theory is extended to the case when the film and substrate materials are described by the frequency-dependent dielectric permittivities, whereas the response of graphene to the electromagnetic field is governed by the polarization tensor in (2+1)-dimensional space-time found in the framework of the Dirac model. Both pristine and gapped and doped graphene sheets are considered possessing some nonzero energy gap and chemical potential. According to our results, in all cases the presence of graphene sheet makes the Casimir pressure in peptide film deposited on a metallic substrate attractive starting from some minimum film thickness. The value of this minimum thickness becomes smaller with increasing chemical potential and larger with increasing energy gap and the fraction of water in peptide film. The physical explanation for these results is provided, and their possible applications in organic electronics are discussed.

High-performance porphyrin-like graphene quantum dots for immuno-sensing of Salmonella typhi

The extraordinary optical properties of porphyrins have inspired their applications in various fields. Herein, we introduce iron porphyrin bio-mimicked graphene quantum dots (Fe–N-GQDs) as a novel paramagnetic and fluorescent label. The Fe–N-GQD was prepared by the mechanochemical mixing of Fe, N, and C sources followed by pyrolysis at high-temperature and next, the solvothermal treatment was performed. The Fe–N sites in graphene matrix, the structural alterations during the solvothermal treatment, the optical properties, and paramagnetic behaviour were studied using FTIR, Raman and X-ray spectroscopies, and Vibrating sample magnetometer. The structural studies revealed that under solvothermal condition, Fe–N doped graphene sheets cut into ultra-small Fe–N-GQDs containing well-dispersed particles with an average diameter of about 2.5 nm. As a result of Fe–N doping, the photoluminescence quantum yield was enhanced to 86% and strong paramagnetic behaviour was observed. Due to the rich oxygen-containing groups at Fe–N-GQDs surface, it has proper sites for bio-conjugation. The bioconjugated Fe–N-GQDs serve as donors in a prominent fluorescence resonance energy transfer system, while graphene oxide acts as an acceptor. The proposed immunosensor was successfully applied for the detection of Salmonella Typhi Vi antigen in real human serum in the concentration range from 1 pg/mL to 1 μg/mL with the detection limit of 1 pg/mL.

Fracture Analysis of Vacancy Defected Nitrogen Doped Graphene Sheets Via MD Simulations

The novel hexagonal monolayer sheet of carbon atoms, graphene, has attracted great attention due to their exceptional electrical and mechanical properties. Their phenomenally high strength and elastic strain, nevertheless, can be altered by structural defects due to stress concentration. In this paper, the fracture behaviour of graphene sheets and nitrogen doped graphene sheets with vacancies were investigated using molecular dynamics (MD) simulations at the different temperatures of 300K, 500K, and 900K. The results reveal a significant strength loss caused by both the defects and vacancies and doped nitrogen in graphene. The deformation process of graphene at various strain rate levels, with regard to the failure behaviour, is discussed. The validity of the proposed MD simulations is verified by comparing the simulation results with the available predictions from the quantized fracture mechanics.

Enhanced dispersive properties of graphene plasmons on substrates of composite materials

Graphene plasmons (GPs) have opened new perspectives for nanophotonic applications due to their intense fields and low losses at certain frequencies. In this work, we investigate transverse magnetic or p-polarized plasmonic modes supported by a doped graphene sheet cladded between a dielectric and a nanocomposite material in tera Hertz regimes. We show that if there is a certain mechanism to excite and couple localized surface plasmons (LSPs) on the surfaces of the metal-nanoparticles to GPs, this coupling leads to higher wave vectors for the GPs, which gives significant wave localization and intense fields near the surface. Along with dispersion relation, we discuss different properties of GPs supported by the waveguide geometry and its interaction with LSPs. Moreover, we compare the results with GPs supported by dielectric/graphene/dielectric geometry and discuss their tunability with different controlling parameters. We adopt realistic parameters to describe the geometry, therefore the study can be realized experimentally.

DFT analysis of nitrogen and Boron doped Graphene sheet as lead detector

In the last few decades, the heavy metal contamination in water has affected the human health in a big way and hence an area of great scientific concern. Among these heavy metals, lead (Pb) is highly toxic and leads to the adverse effect on human body, causing severe health problems like anemia, hypertension, renal impairment, immunotoxicity, toxicity to the reproductive organs, cancer etc. here, the Boron and Nitrogen functionalized graphene sheets (B-Graphene and N-Graphene), have been analysed for its suitability to detect the lead, by computing the band structure, density of state, charge transfer and Current-Voltage characteristics, using the Density Functional Theory based ab-initio approach. The computed results demonstrate that the N-doped Graphene is relatively better sensor for lead in aqueous environment, with a sensitivity of ~ 67% at lower bias voltage, high detection range and short recovery time. However, the Pb sensitivity of the N-Graphene sheet at low bias is very high 329% in absence of water environment.

Computational evaluation of B(OH)-doped graphene efficiency for detecting of Methyl isocyanate (MIC)

Within the exploring for a sensitive sensor of Methyl isocyanate (MIC) gas molecule, the adsorption of MIC molecule on pristine and doped graphene sheets was investigated by DFT calculations. The adsorption of MIC gas molecule was monitored on the Si, Ge and B-OH doped graphene and the results showed that B(OH)- doped graphene was better than intrinsic, Si-doped and Ge-doped graphene for the MIC gas sensing with acceptable adsorption energy (−18.15 kcal·mol−1), work function changes (−43.75%) and appropriate recovery time (0.16 s). Thus, B-OH doped graphene can be considered as a hopeful candidate for designing of efficient MIC gas sensor.

First-principles investigation of carbon dioxide adsorption on MN4 doped graphene

We predict the CO2 gas molecule absorption and sensing performance of transitional MN4 (M = Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn) doped graphene by a systematic first-principles investigation based on density functional theory. Our results demonstrate that graphene doped with different transition metals, MN4, produce similar adsorption behaviors and electronic structures of carbon dioxide. We discovered that the TiN4 doped 4 × 4 graphene sheet (CO2/TiN4 G) is the most suitable candidate for carbon dioxide gas sensors. CO2/TiN4 G shows the strongest adsorption capability and the highest charge transfer between the TiN4 doped graphene sheet and carbon dioxide molecules for all the calculated systems. We conclude that TiN4 G can be designed for efficient CO2 gas sensors.

In vitro Cytotoxicity Analysis of Hybrid Graphene Oxide (hGO) Nano Structures in Caprine Wharton’s Jelly Derived Mesenchymal Stem Cells (WJ-MSCs)

Background: Nanotechnology is used in stem cell culture as well as in vivo delivery and tracking of stem cells. Graphene oxide (GO) is a carbon based nanomaterial and it has large surface area as well as good biocompatibility and heteroatoms doped GO exploit its properties. Hybrid GO (hGO) nano structures biocompatibility is depends on its size, dose and exposure time as well as in vitro cell models and hence, need thorough cytotoxicity studies in different species in vitro cell models. Methods: Caprine Wharton’s jelly derived mesenchymal stem cells (WJ-MSCs) were isolated, characterized and dose dependent (100, 50, 25, 10 and 0µg /ml) in vitro cytotoxicity of three different hGO nano structures (phosphorus doped graphene oxide titanium oxide tubes, rods and sheets) were analysed in caprine WJ-MSCs by studying cell cytotoxicity assays. Result: All three hGO nano structures were damaged cell morphology at 100 and 50 µg /ml doses, however, morphologically more good cells were observed in hGO tubes treated group than hGO rods and hGO sheets at 25 and 10 µg/ml doses as compared to control. Cell viability percentage was significantly (P less than 0.01) decreased at dose 100 µg/ml and it was significantly (P less than 0.01) increased at 25 µg/ml dose as compared to 50, 10 and 0 µg/ml doses. But, hGO tubes significantly (P less than 0.01) increased cell viability % as compared to hGO rods and hGO sheets. Cell population doubling time (PDT) was not altered significantly by all hGO nano structures, but 100 and 50 µg/ml doses significantly (P less than 0.01)increased cell PDT as compared to 25, 10 and 0 µg/ml doses. All hGO nano structures were non significantly altered growth curve, however, all hGO nano structures at 25 µg /ml dose altered (inclined) shape of growth curve, while 100 and 50 µg /ml doses significantly declined growth curve shape as compared to 10 and 0 µg /ml doses. Cell proliferation % was significantly (P less than 0.01) increased at 25 and 10 µg/ml doses, while, it was significantly (P less than 0.01) decreased at 100 µg /ml dose as compared to 50 and 0 µg /ml. However, there was no significance difference was observed in cell proliferation % in groups treated by different hGO nanostructures. In last, it was concluded as, hGO nano structures cytotoxicity was dose dependent and hGO nano tubes were least cytotoxic in caprine WJ-MSCs.

Density functional theory study on the adsorption of CO on X= (Mn and Tc)-doped graphene sheets in the presence and absence of static electric fields

The adsorption of CO molecule on pristine and X= (Mn and Tc) doped graphene sheets (G) in the presence and absence of applied static electric fields (SEF, 0.010-z, 0.011-z, 0.012-z, 0.013-z, 0.014-z and 0.015-z) has been investigated using density functional theory (DFT). The changes in geometric and electronic structures of all adsorption configurations were analysed to characterise the sensitivity of G towards CO molecules. Our calculated results showed that with doping Mn and Tc atoms and in the presence of SEF field, the adsorption of CO on the surface on G increased and adsorption process was chemisorptions type. The partial electronic density of states (PDOS) indicated that the doping Mn and Tc atoms and SEF combination effect increased the interaction and hybridisation between 2p orbitals of CO molecule with 2p orbitals carbon atoms of the G. According to the obtained results, due to applying X-doped and SEF, the primary symmetry of G changes significantly from the original state and thereby the chemical activity of G towards CO molecules enhanced. The results showed that Mn and Tc-doped with SEF field might be a good strategy for enhancing the CO adsorption capability on the surface of G and improving their sensor applicability.

New capability of graphene as hydrogen storage by Si and/or Ge doping: Density functional theory

We studied the adsorption of water molecules via the density functional theory on the pure and silicon and/or germanium doped graphene. We investigated the electrostatic surface potential of the structures to predict the possible interactions. Also, we examined the interaction between every possible side of the water molecule and possible sites of the pure and doped graphene. There was no interaction between the water molecule and the graphene. The only interaction was between the oxygen atom of the water molecule and the doped atoms. We also studied the decomposition of the water molecule on these doped graphene sheets and the possible intermediates and transition states and reaction pathway for the decomposition process. We calculated the interaction energies for the adsorption steps and the thermodynamic parameters for all steps of reaction pathway. The results showed that the adsorption of the water molecule on silicon and/or germanium doped graphene. Also, the decomposition of one of the hydrogen atoms of water molecule was thermodynamically favored at room temperature.