Doped Graphene Nanosheets Research Articles

Machine Learning-Assisted design of boron and nitrogen doped graphene nanosheets with tailored thermomechanical properties

Doping graphene with boron and/or nitrogen enhances its potential for various applications, such as electronics and energy devices. However, these modifications impact the material's properties, influencing its response to external forces, temperature, and heating. Investigating the connection between the structure of co-doped graphene nanosheets and their thermomechanical properties is crucial for accurate predictions and tailored nanosheet engineering. In the present study, molecular dynamics (MD) simulations were performed to compute the thermal and mechanical properties of 300 randomly generated boron/nitrogen co-doped graphene nanosheets with doping concentrations in the range of 0%-15%. Next, the obtained MD results were used to train, tune, and validate a wide spectrum of supervised machine learning models, including linear regression models, regression trees, support vector machines, Gaussian process regression models, kernel approximation models, ensembles of regression trees, and regression neural networks. Our aim is to find models that better estimate, without overfitting, the structure-properties relation of boron/nitrogen co-doped nanosheets. To this end, the models with the highest coefficient of determination (R2) and the lowest root mean square error (RMSE) were utilized. Finally, an appropriate implementation of guided random search algorithms, mainly Genetic Algorithms, was used to solve the inverse problem, i.e., find the nanosheet structure which exhibits the desired set of property values. To this end, thermal conductivity, Young’s modulus, failure stress, and failure strain were specified as target values. A detailed comparison between the employed models and their validation via MD simulations is also included. The achieved results provide sufficient evidence of the accuracy and viability of the applied procedure in both prediction of thermomechanical properties as well as identification of structures with desired properties. This study provides a roadmap that could help scientists and engineers develop nanosheets-based materials with tunable thermomechanical properties, ultimately leading to the creation of innovative and high-performance technologies.

Facile large–scale synthesis of 3D crumpled N, O co–doped graphene nanosheets and their electrochemical properties

Graphene, as a highly promising electrode material, has garnered significant attentions due to its remarkable properties. Nevertheless, challenges persist in its commercial application in the field of energy storage and conversion, including easy stacking, inert surface and limited yield. Rational regulation of the morphology, structure and composition of graphene is demonstrated as an effective way to conquer these challenges. Herein, we adopt a facile spray pyrolysis method to achieve large–scale synthesis of 3D crumpled N, O co–doped graphene nanosheets (NO–GNs). By comprehensive characterization and analysis, it is witnessed that our prepared NO–GNs possess unique 3D crumpled morphology as well as abundant structure defects, and achieve successful co–doping of N and O atoms. These optimized morphology, structure and composition effectively increase the specific surface area and substantially enhance the hydrophilicity and reactive activity of NO–GNs, thus leading to markedly improved electrochemical performance towards supercapacitor and oxygen reduction reaction. Evidently, the preparation of NO–GNs not only offers a promising material for advanced energy storage and conversion systems, but also presents a novel but versatile strategy for manufacturing high–performance carbon–based electrodes.

Tribocorrosion Framework of (Iron, Nickel, Zinc)-Doped Graphene Nanosheet: New Sights into Sulfur Dioxide and Hydrogen Sulfide Removal Using DFT/TD-DFT Methods

Tribocorrosion Framework of (Iron, Nickel, Zinc)-Doped Graphene Nanosheet: New Sights into Sulfur Dioxide and Hydrogen Sulfide Removal Using DFT/TD-DFT Methods

Metalloids (B, Si) and non-metal (N, P, S) doped graphene nanosheet as a supercapacitor electrode: A density functional theory study

Metalloids [Boron (B), Silicon (Si)] and Non -metals [Nitrogen (N), Phosphorus (P), Sulfur (S)] doped graphene nanosheets were considered for alternative lightweight electrode materials in energy storage device applications. The density functional theory studies were performed to investigate the structural stability, charge density distribution, excessive surface charge density, and quantum capacitance of doped graphene nanosheets. It is found that the structures are stable with negative formation energy, and the graphene nanosheet doped with P and S shows protrusion forming a pyramidal shape along the planar graphene nanosheet to maintain stability. Further, the doping of atoms into the graphene nanosheet introduced a minimal bandgap with a shift in the Fermi level, either into the conduction band or valence band, depending on the dopant type. This appearance of bandgap is attributed to the breaking of the symmetry in the graphene sublattice. Meanwhile, based on the type and concentration of dopant, localized and delocalized states are formed near the Fermi level. It is also found that the formation of a localized state near the Fermi level has profoundly improved the excessive surface charge density and quantum capacitance. The S – doped graphene nanosheet was observed to exhibit an excellent quantum capacitance of 38.88 μFcm−2 compared to all other structures and it can be used as a suitable light-weight electrode for asymmetric supercapacitors.

Lead(II) sulfide micro‐crystals doped graphene nanosheets dispersed thermoplastic and multifunctional poly(benzoxazines) cured epoxy resin nanocomposites for medium temperature proton exchange membrane fuel cell applications

AbstractThe amphiphilic polybenzoxazines‐co‐epoxy membrane (POPBOs/PTGP) was created by thermally cross‐linking the multi‐functional octylamine‐based benzoxazine monomer (OPBOs) with synthesized 1,3,5‐tris(oxiran‐2‐yl methoxy)benzene epoxy monomer (TGP). Fourier transform infrared spectroscopy, powder x‐ray diffraction, scanning electron microscopy, and high‐resolution transmission electron microscopy were used to investigate the functionality, crystallinity, and morphology of microcrystal lead(II) sulfide (PbS)/graphene nanosheets (mPbS/GNs). The bare POPBOs/PTGP and different amounts of mPbS/GNs dispersed polymer nanocomposites (PNCs) were obtained from the thermal curing process. Following that, these PNCs were used in medium‐temperature proton exchange membrane fuel cells. The water uptake, ion exchange capacity (IEC), swelling ratio, oxidative stability, and proton conductivity (PC) of bare and loaded mPbS/GNs hybrid nanostructures on POPBOs/PTGP composite membranes were determined. 3 wt% mPbS/GNs distributed with POPBOs/PTGP PNCs exhibit the highest IEC value of 3.61 mmol/g−1 at room temperature, and a PC value of around 6.33 × 10−2 S/cm−1 at 120°C was obtained for the POPBOs/PTGP PNCs. In addition, the single‐cell electrode analysis of the 3 wt% mPbS/GNs‐filled POPBOs/PTGP amphiphilic PNCs showed excellent peak power density and open circuit voltage values of 0.897 W cm−2 and 0.97 V at 120°C.

Doping of Graphene Nanostructure with Iron, Nickel and Zinc as Selective Detector for the Toxic Gas Removal: A Density Functional Theory Study

In this research, the ability of transition metals (TM)-doped graphene nanosheets to adsorb the toxic gas CO has been investigated. The Langmuir adsorption model was used, with a three-layered ONIOM, using the CAM-B3LYP functional accompanying the LANL2DZ and 6-31+G (d,p) basis sets, and using the Gaussian 16 revision C.01 program, on the complexes of CO adsorbed on (Fe, Ni, Zn)-doped graphene nanosheets. The order of the changes of charge density for the Langmuir adsorption of CO on Fe-doped, Ni-doped, and Zn-doped graphene nanosheets has been investigated. This shows the greatest change of charge density for the Ni-doped graphene nanosheet. However, based on NMR spectroscopy, sharp peaks around the Ni-doped area on the surface of the graphene nanosheet have been observed. In addition, the Ni-doped graphene nanosheet has a large effect on the bond orbitals of C-Ni in the adsorption of CO, having the maximum occupancy. The values of ΔGadso, calculated through IR, showed that ΔGads,CO→ Fe-doped GRo has the highest value, because of a charge density transfer from the oxygen atom in carbon monoxide to the Fe-doped graphene nanosheet. The frontier molecular orbitals, HOMO and LUMO, and the band energy gap accompanying some chemical reactivity parameters, have revealed the attributes of the molecular electrical transport of (Fe, Ni, Zn)-doped graphene nanosheets for the adsorption of CO. As a result, since a CO molecule interacts simultaneously with a Fe, Ni, or Zn atom and the C-C nanosheet, at first it might be separated, as in this state a CO atom constructs a physical bond with the Fe, Ni, or Zn atom, and then the other could be adsorbed chemically on the C-C nanosheet surface. Finally, our results have shown that a considerable amount of charge transfer occurs between CO molecules and TM-doped graphene nanosheets after adsorption, which suggests that TM-doped graphene is more sensitive and selective to the adsorption of CO than a pristine graphene surface.

Enhanced thermal energy storage of sodium nitrate by graphene nanosheets: Experimental study and mechanisms

Molten salt is considered as one of the most promising candidate materials for solar energy storage due to its consistent performance and high energy storage density. The limited thermal conductivity of molten salt, on the other hand, has become a bottleneck for efficient energy storage and heat transfer. Here, we propose a composite phase change material (PCM) to realize ultrafast thermal energy storage based on sodium nitrate (NaNO3) doped graphene nanosheets (GNS). The thermal conductivity of the composite is improved by 245 % with GNS doping ratio of 3.0 wt%, which is due to better phonon vibration matching between GNS and NaNO3. The decrease of phase change enthalpy and melting point are explained from the perspective of mean square displacement. This paper provides a new idea for the selection criteria of the mass fraction of nano-enhancers for molten salt-based PCMs from the perspective of phonon vibration matching.

Nitrogen and nitrogen-sulfur doped graphene nanosheets for efficient hydrogen productions for HER studies

Carbon based electrocatalysts are promising candidates to achieve the production of hydrogen energy in a sustainable wayby simple water splitting technique. Thermally treated reduced graphene oxide (RGO) and N–S doped RGO employing urea and thiourea as electrocatalysts for hydrogen evolution reaction (HER). The performance of electrochemical HER has been thoroughly examined via linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. Furthermore, the Raman ID/IG ratio of RGO, N-RGO and NS-RGO were found to be 1.43, 1.10 and 1.11 respectively. From electrochemical HER analysis, we found that the NS-doped RGO exposed the low overpotential, low Tafel slope and low solution resistance value of 211 mV, 197 mV/dec and 0.34 Ω respectively. In addition, the chronoamperometry study revealed, the electrocatalyst NS-RGO showed an excellent stability (81.3% retention) with low 211 mV and remained unchanged for more than 16 h. Therefore, this work concludes that heteroatom dopant participate in improving electrocatalytic HER action.

Effect and mechanism of doped graphene nanosheets on phase transition properties of sodium nitrate

Molten salt is regarded as one of most promising candidates for solar energy storage due to possessing stable properties and large energy storage densities. However, the intrinsically low thermal conductivity of molten salt has become a bottleneck for rapid heat storage and transport. The addition of nanoparticles is generally considered to be a most effective way to improve the thermal conductivity of molten salt phase change materials (PCMs), while the phase change enthalpies of the nanocomposite phase change materials usually show two opposite trends of enhancement or decrement. Furthermore, the reason for the abnormal change of phase change enthalpy has not been clear in the literature so far, so the mechanism of change needs to be further explored. In this work, graphene nanosheets (GNS)@NaNO<sub>3</sub> (sodium nitrate) nanocomposite phase change materials are prepared by the hydration ultrasonic method. The materials are characterized by scanning electron microscope, and the phase change characteristics are measured using differential scanning calorimeter. Molecular dynamics simulation is carried out to explain the mechanism for the formation of the NaNO<sub>3</sub> dense layer and the non-collateral decrease of the enthalpy from the microscopic level. With the increase of GNS mass fraction, the melting point of the GNS@NaNO<sub>3</sub> composite phase change material decreases slightly while the phase change enthalpy decreases significantly with a non-colligative trend. A 13.81% decrease of the theoretical phase change enthalpy is observed with a GNS doping ratio of 1.5%. The NaNO<sub>3</sub> clusters observed on the surface of GNS are considered to have not melted, thereby resulting in a reduction in the phase change enthalpy. The mechanism is further investigated by molecular dynamics simulation, showing that the strong van der Waals attraction between GNS and NaNO<sub>3</sub> leads the 2–4 Å-thick NaNO<sub>3</sub> dense layer to form in the vicinity of GNS. With the increase of GNS mass fraction, the centroid equivalent distance between the dense layer and GNS gradually increases, which leads their mutual attraction to first increase and then weaken. When GNS mass fraction is 1.5%, the centroid equivalent distance reaches the position closest to the potential well, leading to a strongest mutual attraction. In other words, the phase change enthalpy decreases most obviously at this mass fraction. Thus, some conclusions can be drawn as follows. The type of interaction between molten salt and nano-enhancers and the position of the potential well are the fundamental reasons for the thickness of molten salt dense layer and the reduction of phase change enthalpy. The calculation of the interaction energy can be used to guide the selection of the mass fraction of the nano-enhancers, so as to avoid the loss of core material cluster and phase change enthalpy caused by the introduction of the nano-enhancers to a greatest extent. The preparation cost of the composite phase change material can also be reduced to a certain extent.

MnO2 doped graphene nanosheets for carotid body tumor combination therapy.

Combination therapy is a cornerstone of tumor therapy, which can make up for the shortcomings of a single treatment and improve the cure rate of cancer. Near infrared induced therapy is widely applied owing to good accessibility, safety profile, and a wide range of effectiveness. Here, we use reduced nanographene oxide (rNGO) sheets with MnO2 nanoparticles as a photothermal agent to trigger further photodynamic therapy and chemotherapy. Doxorubicin (DOX, chemotherapeutic agent) and methyl blue (MB, photosensitizer) are loaded onto graphene oxide through a strong physical bond and rapidly released under high temperature. Besides, MnO2 nanoparticles can catalyze hydrogen peroxide inside of tumor and produce oxygen as a raw material for photodynamic therapy. In vitro experiments illustrated an effective ablation of PC-12 cells by rGO@MnO2/MB/Dox incubation combined with 808 nm near-infrared (NIR) laser radiation. For in vivo experiments in a model of carotid body tumor, rGO@MnO2/MB/Dox was locally injected, followed by 808 nm NIR laser irradiation. We found that the number of tumor cells was significantly reduced, the tumor volume was reduced, and there were no side effects. This may provide a new idea for the combination treatment of carotid body tumor.

Mesoporous Low Temperature Lithium Cobalt Oxide on Nitrogen and Sulphur Doped Graphene Nanosheets As an Efficient Bifunctional Oxygen Electrocatalyst

The quest for affordable and efficient electrocatalyst for Oxygen Evolution Reaction and Oxygen Reduction Reaction is vital for Metal-Air Batteries. In this work, we present Mesoporous Lithium Cobalt Oxide on Nitrogen and Sulfur doped Graphene annealed at 400oC (designated as LT-LiCoO2/N,S-GO). The spinel structured LT-LiCoO2 shows better electrocatalytic activity than Co3O4 and layered LiCoO2 (HT-LiCoO2) for Oxygen Evolution Reaction due to the direct coupling on adjacent Co3+/ Co4+ ions across a large number of cubanes which facilitates the formation of O–O bonds with ease.[1] Even though LT-LiCoO2 exhibits higher OER activities, it shows poor ORR activity than that of Co3O4. Electrocatalysts having mixed-valent Co3+ /Co4+ were expected to show better ORR activities, so as to enhance the ORR activity of the LT-LiCoO2, graphene a two-dimensional material was incorporated, however the zero-band gap of graphene decreases its catalytic activity.[2] The introduction of hetero atoms modifies the electron density and also creates more active sites for ORR. Further, the electrocatalytic activity can be improved by increasing the surface area which can be achieved by a simple and facile post templating method.[3] Herein, In this work we present Mesoporous LT-LiCoO2/N,S-Graphene a hybrid bifunctional electrocatalyst.

Nonlinear optical properties of nematic liquid crystal matrix doped with graphene nanosheets

ABSTRACT In this research, nonlinear optical (NLO) properties of the nematic liquid crystal doped with different concentrations of the graphene nanosheets are studied. The nematic liquid crystal molecules are aligned in parallel and perpendicular to the incident light polarization and accordingly order parameters of the aligned samples are studied using the dichroism method. We show how doped graphene nanosheets increase the nonlinear birefringence and nonlinear refractive index of the graphene guest-nematic liquid crystal host. Furthermore, we use LCR meter to obtain dielectric anisotropy of the mixture at the frequency of 1 kHz with varying temperatures. Obtained experimental results demonstrate doping 1% concentration of the graphene nanosheets increases significantly NLO properties and also the dielectric response of the nematic liquid crystal by the magnitude of two orders and shifts the phase transition point by about 15°.

Introduction of nitrogen doped graphene nanosheets as efficient adsorbents for nitrate removal from aqueous samples.

Introducing and developing new kinds of adsorbents are always a significant challenge in water treatments. In this work, for the first time, graphene oxide (GO), nitrogen-doped graphene oxide (ND-GO), highly nitrogen-doped graphene oxide (HND-GO), and 3D high nitrogen-doped graphene oxide (3D-HND-GO) were synthesized and comparatively evaluated in the removal of nitrate content of tap and underground waters. The removal of the target analyte was performed through a batch adsorption approach, and the factors influencing its removal efficiency (i.e., initial pH of the sample, primary concentrations of nitrate, amount of adsorbent, and contact time) were evaluated through a central composite design (CCD) and response surface methodology (RSM). Based on the results, 3D-HND-GO showed the highest removal efficiency in comparison with the other mentioned nanoparticles. The nitrate removal using this adsorbent was modeled successfully so that R 2, adjusted R 2, and predicted R 2 values were 0.9717, 0.9508, and 0.9010, respectively. In addition, the optimal removal condition was achieved using the Nelder-Mead non-linear optimization algorithm as follow: the initial concentrations of nitrate (expressed as nitrogen): 15.0mg/mL, the amount of the adsorbent: 2.0mg/mL; pH of the sample: 3.0; and the contact time: 20.0min. Under this optimal condition, the actual removal result (92.5 ± 4.0%) was in good agreement with the expected value (94.8 ± 5.1%). Additional studies were also performed to comprehensibly evaluate the adsorption activity of the adsorbent (e.g., kinetic, isotherm, and desorption parameters). The adsorption isotherm complied with the Langmuir model illustrating the considerable mono-layer adsorption capacities for the target ions with qm of 8.7mg/g. The adsorption process was indicated to obey a pseudo 2nd order kinetic model, with the rate-limiting step for the adsorption phase. This study revealed which 3D-HND-G leads to improved yield in the nitrate ions elimination, particularly at acidic media, which was related to the enhanced dispersibility and larger surface area. The adsorbent was further successfully used for treating tap and underground water samples. At the present moment, research as grown to modify 3D-HND-G in orders to increase the potentiality for industrial applications. The online version contains supplementary material available at 10.1007/s40201-021-00741-7.

Cu decorated functionalized graphene for Arsenic sensing in water: A first principles analysis

The pristine graphene (G) and copper decorated boron/nitrogen doped graphene (Cu-B/NG) nanosheets have been computationally analyzed and demonstrated for their detection ability towards Arsenic, presence in the aqueous environment. The sheet’s detection ability has been analyzed in terms of it’s interaction stability and the observed variations in electronic and transport properties. The results reveal that the interaction stability of As has improved significantly for the Cu-BG/NG sheets in comparison to the pristine graphene. The computed electronic properties deduce the adsorption of As, transforms the semiconducting behavior of the Cu-BG/NG sheets into metallic, leading to the variation in its conductance. The observed variation in conductance found to be 25% and 55% for Cu-BG and Cu-NG sheets, respectively, which are relatively higher than the one computed for its pristine (19%) counterpart. Thus, the above results confirm that the functionalization of graphene sheet via doping and decoration with nitrogen and copper, respectively (Cu-NG), enhances the sheet's response by 189%, compared to the pristine sheet. Therefore, Cu-NG nanosheet can be implemented as a potential candidate as Arsenic detector in the aqueous environment.

Nitrogen doped Graphene Nano sheets (N−Gns) as Electrocatalyst for Electro‐Fenton Process for the Degradation of Highly Toxic Chlorophenoxy acid Herbicides from Water

AbstractFor the development of a highly active and energy‐effective electro‐Fenton process, highly efficient 2e−pathway oxygen reduction reaction electrocatalytic materials forin situelectrochemical synthesis of H2O2are extremely important. A novel nitrogen‐doped graphene nanosheets (N‐Gns) is prepared, characterized, investigated for the oxygen reduction reaction, and employed for highly toxic chlorophenoxy acid herbicides degradation in water. Herein, we report novel nitrogen‐doped graphene nano sheets (N‐Gns), which exhibit superior electrocatalytic activity and stability for oxygen reduction reaction (ORR) in acidic medium, which is utilized for Electro Fenton's reaction. The effects of operating parameters such as applied current, pH of the solution, inter‐electrode distance, ferrous ion concentration, oxygen flow rate and initial concentration of herbicides were investigated. The herbicides such as 2,4‐dichlorophenoxyacetic acid (2,4‐D), 2‐(2,4‐ dichlorophenoxy) propanoic acid (2,4‐DP), 4‐chloro‐2‐methylphenoxyacetic acid (MCPA), 2,4,5‐Trichlorophenoxyacetic acid (2,4,5‐T), 2‐(2‐methyl‐4‐chlorophenoxy) propionic acid (MCPP) were degraded by electro‐Fenton process. All the herbicides exhibited the total organic carbon removal efficiency greater than 95 % within 240 minutes. The four various places of Madurai district, Tamil Nadu, India, real water samples were collected and spiked with standard 2,4‐D solution and its degradation was studied by as‐prepared electrodes. The degradation efficiency was greater than 95 % with 300 min. It is comparatively less high than synthetic waste water (herbicides). It is due to the presence of natural organic matter in the real water samples. Hence the herbicides 2,4‐D, 2,4‐DP, 2,4,5‐T, MCPA and MCPP were successfully removed by the as‐synthesizedN doped graphene nano sheets (N‐Gns). The as‐prepared (N‐Gns) exhibits high activity and desirable stabilityand represents a potential candidate material as electro‐Fenton cathode for energy‐effective water treatment.

Ab Initio Modeling of the Electronic and Energy Structure and Opening the Band Gap of a 4p-Element-Doped Graphene Monolayer

In this paper, we study the electronic and band structure of 4p-elements (M = Ge, Si)-doped graphene nanosheets with vacancies by the density functional theory method. The adsorption energy of the doping atoms and the relative stability of doped graphene monolayers are estimated. An antiferromagnetic ordering is discovered in these graphene-based systems. Based on the analysis of the electronic populations of atomic orbitals according to Mulliken, the states’ densities in graphene systems are calculated. The equilibrium parameters of the electronic structure of graphene nanosheets are obtained. The regularities of changes in the electronic structure of the valence band and the induction of an energy gap in M-doped graphene monolayers containing vacancies are studied. The features of the electronic structure near the Fermi level, as well as the role of the structural effect in opening the energy gap in graphene–M systems, are discussed. Doping with 4p elements opens the energy gap in graphene–Ge(Si) systems. The local magnetic moments for antiferromagnetic ordering are estimated on carbon atoms of graphene nanosheets including Ge(Si). The calculated values ​​of the local magnetic moments on carbon atoms in graphene–M (Ge, Si) systems are comparable with each other.

Nitrogen doping effect of graphene nanosheets towards metacomposites with tunable negative permittivity

Metacomposites obtained from nitrogen doped graphene nanosheets (NGR) with tunable negative permittivity were firstly reported. Compositions of the NGR were analyzed by Raman spectroscopy and X-ray photoelectron spectroscopy. Dielectric properties of the metacomposites were investigated in detail. It was found that the different nitrogen bonding type including pyridinic nitrogen, pyrrolic nitrogen and graphitic nitrogen played different roles on the negative permittivity of the NGR/phenolic resin metacomposites, which was easily tuned by nitrogen bonding types and doping amount. The tunable negative permittivity was ascribed to the different nitrogen doping effects. The pyrrolic N and graphitic N contributed to appearance of the negative permittivity behavior, while the pyridinic N acted as a barrier for realization of the negative permittivity.

Precious Metal Free Materials As Efficient Catalysts for Water Splitting

Precious Metal Free Materials as Efficient Catalysts for Water Splitting Pei Kang Shen*, Zhi Qun Tian Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University100 Daxue Road, Nanning 530004, Guangxi, China*E-mail address: pkshen@gxu.edu.cn Water electrolysis is a promising approach for large-scale and sustainable hydrogen production. However, its kinetics is slow and requires precious metal catalysts to efficiently operate. Therefore, great efforts are being undertaken to design and prepare low-cost and highly efficient catalysts to boost the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Currently, we developed different noble metal free materials as efficient catalysts for HER, OER, and full water splitting. For HER, the catalysts with novel nanostructures were prepared, such as carbon-encapsulated WOx (WOx@C), N-doped porous MoN nanobelts, nitrogen and fluorine dual-doped porous graphene-nanosheets, K0.4TaO2.4F0.6 nanocubes, Ni3S2 nanowires, TiN nanowires, nanoflower-like MoO2, et al. For OER catalysts, the Mo- and Fe-modified Ni(OH)2/NiOOH nanosheets, nitrogen-decorated iron-nickel sulfide nanosheets, Mo-doped NiOOH nanosheets, tantalum dioxyfluoride, pristine carbon nanotubes, graphene supported MnO2 nanowires were studied. For full water splitting, the porous WO2 hexahedral networks, heteroatoms dual doped porous graphene nanosheets, three-dimensional porous MoNi4 networks, porous MoO2 nanosheets, dye functionalized carbon nanotubes were studied. The synthesized materials displayed excellent catalytic activity for hydrogen evolution, oxygen evolution, and full water splitting, and can be applied as low cost and highly active multifunctional catalysts with excellent ORR and OER performance. The improved activity and active origin of aforementioned catalysts are clarified through experimental analysis and DFT calculation. These studies pave the way for the design and development of cheaper, highly efficiently and more durable catalysts for wider applications.

Silicon on a graphene nanosheet with triangle- and dot-shape: Electronic structure, specific heat, and thermal conductivity from first-principle calculations

The electronic structure, specific heat, and thermal conductivity of silicon embedded in a monolayer graphene nanosheet are studied using Density Functional Theory. Two different shapes of the substitutional Si doping in the graphene are studied, a triangular and a dot shape. The silicon doping of a graphene nanosheet, with the silicon atoms arranged in a triangular configuration in ortho- and para-positions, opens up a band gap transforming the sheet to a semiconducting material. The opening of the band gap is caused by the presence of the repulsion force between the silicon and carbon atoms decreasing the density of states around the Fermi energy. Consequently, the specific heat and the thermal conductivity of the system are suppressed. For graphene nanosheet doped with a dot-like configuration of silicon atoms, at the ortho-, meta-, and para-positions, the valence band crosses the Fermi level. This doping configuration increases the density of state at the Fermi level, but mobile charge are delocalized and diminished around the silicon atoms. As a result, the specific heat and the thermal conductivity are enhanced. Silicon substitutionally doped graphene nanosheets may be beneficial for photovoltaics and can further improve solar cell devices by controlling the geometrical configuration of the underlying atomic systems.

Adsorption of Anionic Dye on Graphene Nanosheets Doped with Ag Nanoparticles: Kinetics and Thermodynamic Study

AgNPs doped graphene nanosheets (Ag@GNs) nanocomposites were prepared using an environment-friendly one-pot hydrothermal method. The performance in the removal of anionic dye methyl orange (MO) onto graphene-based materials, such as graphene oxide (GO), graphene nanosheets (GNs) and Ag@GNs were investigated extensively. Ag@GNs displays a relative high adsorption capacity of 75.87 mg g–1 at 318 K, and can be easily recycled from liquid-phase owing to the hydrophobicity of GNs. On the base of XRD, FTIR and UV–Vis analysis, the excellent ability of Ag@GNs to MO is mainly due to the high dispersion of AgNPs, which can result in strong π–π interactions, electrostatic interactions between the dye molecules and GNs. Furthermore, SEM results show that the doped AgNPs effectively avid the aggregation of GNs, which is necessary for the adsorption of MO molecules. Finally, the kinetics, isotherm and thermodynamics results demonstrate that the adsorption of MO on Ag@GNs are mainly controlled by chemisorption and endothermic in nature, which matches well with Langmuir isotherm model and kinetic data reveal a good correlation to a pseudo-second-order equation.