Metal-doped Graphene Research Articles

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.

Enhanced non-linear optical response of alkali metal-doped nitrogenated holey graphene (C2N)

In the quest of better non-linear optical (NLO) materials, a DFT method is employed on alkali metals doped C2N to investigate the optoelectronic characteristics. To understand the optoelectronic properties the charge distribution is a key factor for which frontier molecular orbitals (FMOs), transition density matrix (TDM), density of states (DOS), electron density difference map (EDDM) and molecular electrostatic potential(MEP) analyses were carried out. Interaction energy (Eint) is computed to delve into thermodynamic stability. The projected results of all the complexes is lying in domain of effective NLO materials, like constricted EH-L, reduced Eopt, bathochromic shift in ʎmax and above all upgraded α0 and β0. When compared to C2N, doped complexes display extraordinary NLO response with 1st hyperpolarizability ranging from 2.4 × 104 (K@C2N) to 8.02 × 104 a.u. (Li@C2N). Furthermore, alkali metal doping also lessens the energy gap (EH-L)from 2.3 eV to 2.06 eV in Li@C2N. The nature of vibrations and interactions are probed via IR and NCI analysis. Doped molecules (Li@C2N-K@C2N) do possess greater dipole moment (2.48 D to 5.56 D) than C2N (2.04 D). All characteristics support the use of all doped complexes in integrated NLO devices, paving the way for new approach to computational designing of super-efficient NLO materials.

Metal-doped Magnetic Graphene Oxide Nanohybrid for Solid-phase Microextraction of Copper from Environmental Samples

Metal-doped Magnetic Graphene Oxide Nanohybrid for Solid-phase Microextraction of Copper from Environmental Samples

Green and cost-effective synthesis of 2D and 3D graphene-based nanomaterials from Drepanostachyum falcatum for bio-imaging and water purification applications

Herewith, we demonstrate a novel top-down approach for the cost-effective consecutive synthesis of 2D/3D graphene-based materials (GBM) from the extract and fibrous parts of the Drepanostachyum falcatum plant, using a two-stage thermal approach. At low temperature (150 °C), the extract of the D. falcatum showed the formation of a fluorescent 2D skeleton of the GBM i.e., metal-doped graphene oxide sheets (MDGOs) in presence of ethanol. On the other hand, the pyrolysis (∼300 °C) of the fibrous part showed the formation of a 3D skeleton of the graphene nanoribbons (GNR) in the N2 atmosphere. The presence of extensive π-π conjugated interactions with oxidative functional moieties in 2D-MDGOs is responsible for their blue fluorescent nature under UV irradiation at 365 nm. Meanwhile, 2D-MDGOs show excellent potential as a bio-imaging probe for non-tumorigenic prostate epithelial RWPE-1 cells. However, the very low cytotoxicity of 2D-MDGOs played a crucial role in upholding their bio-imaging potential. Simultaneously, the hydrophobic nature of 3D-GNR showed better adsorption towards the organic pollutants (dye) from the aqueous phase. The adsorption phenomenon of 3D-GNR was very fast and effective towards the removal of methylene blue (MB). Moreover, the Langmuir adsorption capacity for MB dye was found to be 31.94 mg/gm. This is the first time we are reporting the dual synthesis of 2D and 3D GBMs simultaneously, with different applicative potentials. Further, noticeable and in-depth observations were made for studying the reaction kinetics of the reaction to find a formal analytical connection between productivity, adsorptive, and applicability of 3D-GNR. Moreover, the market-based-cost analysis showed the huge industrial potential of these materials, which also make them inevitable and promising candidates for futuristic growth in their respective application in water purification.

Revealing intrinsic spin coupling in transition metal-doped graphene.

Graphene materials offer attractive possibilities in spintronics due to their unique atomic and electronic structures, which is in contrast to their limited applications in the design of sophisticated spintronic devices. This should be attributed to the lack of knowledge about the intrinsic characteristics of graphene materials, especially the diverse correlations between sites within the materials and their roles in spin-signal generation and propagation. This work comprehensively studies the spin couplings between transition metal atoms doped on graphene and reveals their potential application in spintronic device design through the realization of various logic gates. In addition, the effects of the distance between doped metal atoms and the number of carbon layers on the logic gate implementation further verify that the spin-coupling effect can exhibit a certain distance dependence and space propagation. The achievements in this work uncover the potential value of graphene materials and are expected to open up new avenues for exploring their application in the design of sophisticated spintronic devices.

Interfacial engineering for ultrafine Co3O4 confined in graphene macroscopic microspheres with boosting peroxymonosulfate activation

BackgroundAs an alternative to homogenous metal-catalyst for peroxymonosulfate activation, heterogeneous hybrid catalysts such as metal-doped graphene catalysts are highly desired due to their remarkable catalytic performance and ease of recovery. MethodIn this work, ultrafine Co3O4 confined in graphene macroscopic microspheres (Co3O4@rGO) were fabricated via coordination-driven interfacial self-assembly, followed by annealing in air. A series of characterizations and experiments verified that this kind of conductive and adsorptive graphitic structure facilitated the elimination of pollutants via a synergistic “adsorption-driven-catalysis’’ process. Significant findingsTherefore, almost 100% tetracycline (TC, 0.271 min−1) was eliminated after 30 min, which was far higher than those of reported catalysts. Besides, X-ray photoelectron spectroscopy (XPS) analysis, electron paramagnetic resonance (EPR), and quenching experiments demonstrated that confined cobalt species and oxygen vacancies as highly exposed active sites. The reactive oxygen species (ROS) follow a contribution order: SO4·− ˃ 1O2 ˃ O2·− ˃ ·OH More significantly, a fluidized-column catalytic unit enabled almost zero discharge of TC in continuous sewage treatment system. Overall, this work provided a generally applicable approach to fabricate removable and highly efficient heterogeneous catalysts for environmental remediation.

Formaldehyde gas sensing properties of transition metal-doped graphene: a first-principles study

The formaldehyde gas sensing properties of transition metal-doped graphene have been systematically investigated by first-principles calculations. The optimized geometries of transition metal-doped graphene with and without HCHO adsorption, adsorption energies, charge transfers and magnetic moments are obtained for various doped graphene systems. The calculated results show that Co-, Ni-, Cu-, Zn-, Pd- and Ag-doped systems have moderate adsorption energies, implying their potential applications as HCHO sensors. The two-probe sensor devices consisting of the central scattering region and pristine graphene electrodes with the armchair or zigzag transport directions are built, and the spin-polarized current–voltage curves are calculated by the non-equilibrium Green’s function method within the framework of density functional theory. For the Cu-, Zn- and Ag-doped systems, the average sensor response is over 80%, 40% and 290%, respectively. In particular, the Cu- and Ag-doped graphene devices have the highest value of response over 200% and 900% at low voltages, indicating a short response time and high sensitivity of these devices. The present study provides a theoretical basis for exploring practical applications of the transition metal-functionalized graphene as superior HCHO gas sensors.

Mechanistic insights into the CO oxidation reaction catalyzed by P-coordinated metal-doped graphene: The roles of phosphorus and metal atom

Encouraged by the great promise of metal–nitrogen–carbon materials in catalyzing CO oxidation and the successfully introduction of metal–P species into carbon matrices in experiments, it is proposed metal–P species might also possess high reactivity to CO oxidation. Our DFT calculations of CO oxidation on MP4-Gr (M = Fe, Co, Ni) suggest that multi-molecules adsorption can be easily achieved with one CO on metal and one O2 on each P atom, resulting in the step-by step LH processes and then leave the atomic O on P which can be furhter removal via ER mechanism. Moreover, reactivities of the catalysts are determined by the ER process and the reactivity differences are closely related to the doping metal. Electronic structure analysis inidcates that decreasing d-band center position of metal from FeP4-Gr to CoP4-Gr to NiP4-Gr will weaken the CO adsorption on metal site and upshift the p-band center position of P atom, finnally weaken the O binding strength with P. Thus, higher reactivity is for CoP4-Gr and NiP4-Gr when compared to FeP4-Gr. This work highlights the possibility to manipulate the performance of catalyst in CO oxidation with incoorperating metal which would be helpful for design and implementation of promissing catalysts.

Exploring the catalytic mechanisms of non-noble VIIIB metal dimer embedded in graphene toward CO oxidation by density functional theory analysis

Development of highly efficient, cost effective heteronuclear catalysts has been a huge interest in recent years due to its prime importance in environmental perpetuation. Among the developed catalysts, heteroatom-doped graphene catalysts for CO oxidation have attracted a global attention, due to its unique electronic properties suitable for CO oxidation. In this work, the oxidation mechanism of CO on various VIIIB dimeric metal-doped graphene with four atom vacancies systems (M1M2@C6) were investigated systematically by density functional theory (DFT) calculations. After a detailed analytic investigation through competition of adsorption performance and stability, FeFe@C6, FeCo@C6 and FeNi@C6 were found to be highly efficient and suitable as CO oxidation catalysts. Further, the heteronuclear dimeric catalysts (FeCo@C6 and FeNi@C6) were found to possess better catalytic activity over homonuclear dimeric catalyst (FeFe@C6) with much lower energy barrier for CO oxidation (0.79 eV, 0.49 eV, 0.42 eV for FeFe@C6, FeCo@C6, FeNi@C6). This investigation opens a new direction in designing the efficient and cost-effective graphene-based catalysts and also provides important hints for the understanding of catalytic reaction mechanisms for CO oxidation catalysis, which provides guidance and ideas for subsequent experimental synthesis of low-cost and efficient catalysts.

Computational Screening of Doped Graphene Electrodes for Alkaline CO2 Reduction

The electrocatalytic CO2 reduction reaction (CO2RR) is considered as one of the most promising approaches to synthesizing carbonaceous fuels and chemicals without utilizing fossil resources. However, current technologies are still in the early phase focusing primarily on identifying optimal electrode materials and reaction conditions. Doped graphene-based materials are among the best CO2RR electrocatalysts and in the present work we have performed a computational screening study to identify suitable graphene catalysts for CO2RR to CO under alkaline conditions. Several types of modified-graphene frameworks doped with metallic and non-metallic elements were considered. After establishing thermodynamically stable electrodes, the electrochemical CO2RR to CO is studied in the alkaline media. Both concerted proton-coupled electron transfer (PCET) and decoupled proton and electron transfer (ETPT) mechanisms were considered by developing and using a generalization of the computational hydrogen electrode approach. It is established that the CO2 electrosorption and associated charge transfer along the ETPT pathway are of utmost importance and significantly impact the electrochemical thermodynamics of CO2RR. Our study suggests an exceptional performance of metal-doped nitrogen-coordinated graphene electrodes, especially 3N-coordinated graphene electrodes.

Mass production of metal-doped graphene from the agriculture waste of Quercus ilex leaves for supercapacitors: inclusive DFT study.

This work reports a facile, eco-friendly, and cost-effective mass-scale synthesis of metal-doped graphene sheets (MDGs) using agriculture waste of Quercus ilex leaves for supercapacitor applications. A single step-degradation catalyst-based pyrolysis route was used for the manufacture of MDGs. Obtained MDGs were further evaluated via advanced spectroscopy and microscopic techniques including Raman spectroscopy, FT-IR, XRD, SEM/EDX, and TEM imaging. The Raman spectrum showed D and G bands at 1300 cm−1 and 1590 cm−1, respectively, followed by a 2D band at 2770 cm−1, which confirmed the synthesis of few-layered MDGs. The SEM/EDX data confirmed the presence of 6.15%, 3.17%, and 2.36% of potassium, calcium and magnesium in the obtained MDGs, respectively. Additionally, the FT-IR, XRD, TEM, and SEM data including the plot profile diagrams confirmed the synthesis of MDGs. Further, a computational study was performed for the structural validation of MDGs using Gaussian 09. The density functional theory (DFT) results showed a chemisorption/decoration pattern of doping for metal ions on the few-layered graphene nanosheets, rather than a substitutional pattern. Further, resulting MDGs were used as an active material for the fabrication of a supercapacitor electrode using the polymer gel of PVA–H3PO4 as the electrolyte. The fabricated device showed a decent specific capacitance of 18.2 F g−1 at a scan rate of 5 mV s−1 with a power density of 1000 W kg−1 at 5 A g−1.

Theoretical prediction of delivery and adsorption of various anticancer drugs into pristine and metal-doped graphene nanosheet

ABSTRACT The mechanism of this study is utilized the pristine GNS and metal-doped GNS as a carrier to the (5-FU, 6-MP, GB, and CP) anticancer drugs. We used the DFT method, which implemented in the Quantum espresso package, to calculate various electronic properties computed. These impurities altered the behavior of the GNS from metal to semiconductor. Metal-doped GNS and anticancer drugs/pristine GNS became more stable and lower reactivity due to the total energy of these structures increased compared to the pristine GNS. The electronic band gap of the anticancer drugs/pristine GNS rehabilitated and opened. Furthermore, the metal-doped GNS as a carrier to the anticancer drugs was an exothermic process. Then, anticancer drugs/metal-doped GNS thermodynamically stable due to these structures have negative adsorption energies. Besides, we detected that these complex structures were required higher energy to donating/accepting and electron to become cation/anion due to these structures have a lower value of the electron affinity and higher value of the chemical hardness. Moreover, there was a great interaction between pristine GNS and metal impurities; also between metal-doped GNS and anticancer drugs. Then, GNS and metal-doped GNS have been used as drug delivery systems.

Transition metal-doped graphene nanoflakes for CO and CO2 storage and sensing applications: a DFT study

The adsorptions of CO and CO2 on pristine and transition metal-doped graphene nanoflakes (GNFs) were theoretically investigated using the density functional theory. Doping of a series of 3d transition metals (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn) to pristine GNF can significantly enhance the adsorption abilities of GNF, leading to a stronger interaction between gas molecule and GNF. Among all transition metal-doped GNFs, Cr-doped GNF shows the highest adsorption strength toward both of CO and CO2 molecules. Calculated electronic properties for studied systems indicate that TM-doped GNFs present high sensitivity to CO and CO2 molecules. In addition, the adsorptions of the CO and CO2 molecules on TM-doped GNF are influenced on the electronic conductance of the TM-doped GNF. The results of this study may serve to enhance the application of effective CO and CO2 gas storage and sensor to preserve the environment based on GNF.

Density functional theory study of hydrogen sulfide adsorption onto transition metal-doped bilayer graphene using external electric fields

The adsorption of hydrogen sulfide molecules onto bilayer graphene (BG) doped with transition metals (TM), such as V, Cr, Mn, Fe, Co, and Ni, was studied using external electric fields and density functional theory calculations. The adsorption of H 2 S onto TM-doped BG was significantly improved compared with adsorption onto pristine BG. An external electric field can promote the adsorption of H 2 S onto BG, and the stability of this adsorption increases with the intensity of the electric field. Typically, this stability is independent of the direction of the electric field (upward or downward). However, H 2 S is sensitive to the direction of the electric field, and a downward (negative value) electric field is more favorable for H 2 S adsorption onto TM-doped BG. The desorption of H 2 S molecules from TM-doped BG was achieved using an upward (positive value) electric field, and the maximum desorption effect occurred at an electric field intensity of approximately 0.2 V/Å. The adsorption of gas molecules was also observed to modify the electronic structures of the TM/BG systems. All the TM/BG-H 2 S systems demonstrated semiconductive characteristics with different band gaps, except for the V/BG-H 2 S system. Overall, the results of this study showed that TM-doped BG has potential applications to methods for the adsorption, storage, and detection of H 2 S gas. • The TM/BG systems can significantly improve the adsorption stability of H 2 S compared with pristine bilayer graphene. • The external electric field promotes the adsorption of H 2 S onto bilayer graphene. • The adsorption of H 2 S is sensitive to the direction of the electric field. • The desorption of H 2 S gas molecules from TM-doped bilayer graphene can be achieved using an upward electric field. • The adsorption of gas molecules modifies the electronic structures of the TM/BG systems.

Enhancing of nitrogen reduction reaction to ammonia through CoB4-embedded graphene: Theoretical investigation

The development of affordable and green ammonia synthesis techniques is highly desirable. By employing first-principles calculations, we propose a nonnoble metal-doped graphene layer for N2-to-NH3 conversion. Our results show that the cooperation of Co and B in the form of CoB4 exhibits outstanding catalytic activity for N2 reduction reaction (NRR), and the reaction pathway preferably followed a distal or alternating mechanism with a small activation barrier of 0.36 eV, which is less than that of reported single-atom Ru (0.42) and Cr (0.59 eV) catalysts. The catalytic ability of the CoB4 catalyst arises from both the electronic effect of B dopants, which serve as charge contributors, and the complementary role of Co, which serves as a desorption site for NH3* formation or further NH3 release. This work provides a potential nonprecious-metal catalyst for N2 activation and conversion.

Yttrium doped graphene oxide as a new adsorbent for H2O, CO, and ethylene molecules: Dispersion-corrected DFT calculations

A Grimme dispersion-corrected density functional theory (DFT-D) calculations are performed to explore the electronic structures and adsorption behaviors of graphene oxide (GO) and Yttrium doped graphene oxide (Y doped GO) toward the adsorption of H2O, CO, and C2H4 molecules. The HOMO and LUMO spatial distributions, the electrostatic potential charges, and the field that corresponds to the electrostatic potential are evaluated to understand the effect of the Yttrium doping on the electronic properties of the pristine graphene oxide. Calculated molecular and thermodynamic parameters indicate that the electronic structure of GO is obviously affected by the presence of yttrium atom. It can be seen that the adsorption energies of H2O, CO, and C2H4 molecules adsorption increase from 69.5, 17.4 and 34.7 kJ/mol over the pristine GO to 133.1, 182.4 and 214.2 kJ/mol for the Yttrium doped GO. We believe that the obtained results will provide beneficial insights for experimental research about the potential application of metal-doped graphene oxides as nanoscale adsorbents for water, carbon monoxide, and ethylene molecules.

(Invited) Biocompatible Doped Graphene Quantum Dots Enabling Visible/Near-Infrared Imaging, Drug Delivery and Cancer Detection

Despite significant advances of nanomedicine, the issues of biocompatibility, accumulation-derived toxicity and the lack of sensing and in vivo imaging capabilities hamper the translation of many nanocarriers into clinic. To address these needs we develop and test the feasibility of new nitrogen, sulfur or metal-doped graphene quantum dots (GQDs) as fully biocompatible multifunctional platforms enabling theranostic image-guided approaches both in vitro and in vivo. These GQDs scalably produced in one-step synthesis from a single biocompatible carbon-rich precursor form 3-5 nm few-layer structures functionalized with oxygen-containing groups, however, showing high crystallinity and lattice spacing indicative of a graphitic platform. They are water-soluble, show no cytotoxicity at high concentrations of 1 mg/mL, and demonstrate substantial degradation at 36h in biological environments as verified by TEM imaging. Due to their small sizes, GQDs exhibit efficient internalization maximized at 12 h followed by further degradation/excretion and enable active agent delivery. Their intrinsic fluorescence in blue/green with up to 62% quantum yield and near-infrared allows for multicolor in vitro imaging on its own or in combination with other fluorophores and offers the potential capabilities for in vivo near-IR fluorescence tracking. Additionally, several GQD types exhibit pH-dependent fluorescence response that is successfully utilized as a sensing mechanism for acidic extracellular environments of cancer cells. It allows for deterministic, ratiometric discrimination between cancerous (HeLa and MCF-7 cell) and healthy (HEK-293 cell) environments with substantial spectral peak intensity ratios of 1.6 to 8 in healthy versus cancer cells. Such spectral technique, less prone to quenching discrepancies, provides a useful tool for pH-sensing of microenvironments. These results suggest fully biocompatible doped GQDs as multifunctional candidates for in vitro delivery of active agents, multicolor visible/near-IR fluorescence imaging, and pH-sensing of cancerous environments.

Density functional theory analysis of selective adsorption of AsH3 on transition metal-doped graphene.

The removal of AsH3 from synthesis gas is crucial to prevent methanol synthesis catalyst from poisoning. In this work, Ti-, Mn-, Fe-, Co-, Ni-, Cu-, and Ag-doped graphene were proposed and their adsorption capabilities for AsH3 and CO were investigated by DFT method. The optimized structures, adsorption energies, electron transfers, electron density difference, and density of states were thoroughly discussed. It was found that pristine graphene had a slight interaction with AsH3 or CO, while doping Ti, Mn, Fe, Co, Ni, and Ag could greatly facilitate the AsH3 or CO adsorption with the adsorption energies of -0.95 to -1.45eV (AsH3) and - 1.00 to 2.02eV (CO). The partial density of states (PDOS) results showed that hybridizations between AsH3 orbitals, CO orbitals, and transition metals orbitals indicate that there were chemical interactions between them. The charge transfer and density of states (DOS) plots showed that AsH3 and CO have the same adsorption modes on transition metals-doped graphene. Among seven transition metals-doped graphene, Ni-doped graphene had the best selectivity for AsH3 but not for CO due to its larger adsorption energy discrepancy between AsH3 and CO than that of other transition metals-doped graphene, suggesting that Ni-doped graphene is a good candidate adsorbent for AsH3 removal in CO gas stream. Graphical abstract Seven transition metal (Ti, Mn, Fe, Co, Ni, Cu, Ag)-doped graphenes were investigated for AsH3 and CO adsorption by DFT method. Their most stable structure, adsorption energy, and electronic characters were thoroughly studied. The results showed that Ni-doped graphene was a good candidate for selective AsH3 adsorption.

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.