Co-doped Graphene Research Articles

S, N Co-Doped Graphene Quantum Dots for Novel Quantum Dots Solar Cell

Graphene quantum dots (GQDs) have been extensively studied in recent days due to their excellent optical photo-absorption, low-cost synthesis and nontoxic nature. Furthermore, the optical and electronic properties of GQDs can be modulated by adding various dopant (like N, S, B, F, K, Si etc.) and can be used as a potential candidate for green solar energy material. Here, we have synthesized GQDs, N and N, S co-doped GQDs using low-cost hydrothermal process. Quantum dot sensitized solar cells (QDSSCs) were fabricated by sensitizing doped and undoped GQDs with ZnO nanorods. Current-Voltage characteristics of GQD sensitized ZnO NRs, N-GQD sensitized ZnO NRs and S, N-GQD sensitized ZnO NRs have been studied. The superior photovoltaic performance was obtained using S, N co-doped GQDs sensitized ZnO NRs with conversion efficiency [Formula: see text]%, which was 1.75 times higher than undoped GQD sensitized QDSSC device.

High-performance flexible electrothermal Joule heaters from laser reduced F-N Co-doped graphene oxide with extended Sp2 networks

Phonons play an important role in heat generation and propagation across graphene lattice; however, this is hindered by graphene heteroatom doping which generates highly defected structures. Consequently, heteroatom doping has not been primarily explored in electrothermal materials despite presenting a cost-effective and metal-free method of improving electronic activity in flexible 2D materials. Herein, we present a facile and scalable technique for fabrication of fluorine-nitrogen co-doped laser reduced graphene oxide (FN-G) Joule heaters by ultrasonic wetchemical doping and maskless laser writing method. Films containing 6.14 at. % F and 3.22 at. % N, low sheet resistance of 24.49 O/sq. and uniquely high degree of atomic ordering indicated by an ID/IG of 0.16 were successfully fabricated. The heaters showed highly competitive transient electrothermal behaviour with a saturation temperature of 365 °C for only 9 V applied voltage, high heating rate of 385.33 °C/s, and average response time of 0.68 s. An excellent temperature distribution, low power requirement, and a net-zero degradation in the electrical and electrothermal properties even after 500 bending cycles was demonstrated. These high-performance features render the FN-G heater suitable for applications in wearable electronics powered by low voltage portable electrochemical cells.

Secondary-Heteroatom-Doping-Derived Synthesis of N, S Co-Doped Graphene Nanoribbons for Enhanced Oxygen Reduction Activity.

The rareness and weak durability of Pt-based electrocatalysts for oxygen reduction reactions (ORRs) have hindered the large-scale application of fuel cells. Here, we developed an efficient metal-free catalyst consisting of N, S co-doped graphene nanoribbons (N, S-GNR-2s) for ORRs. GNRs were firstly synthesized via the chemical unzipping of carbon nanotubes, and then N, S co-doping was conducted using urea as the primary and sulfourea as the secondary heteroatom sources. The successful incorporation of nitrogen and sulfur was confirmed by elemental mapping analysis as well as X-ray photoelectron spectroscopy. Electrochemical testing revealed that N, S-GNR-2s exhibited an Eonset of 0.89 V, E1/2 of 0.79 V and an average electron transfer number of 3.72, as well as good stability and methanol tolerance. As a result, N, S-GNR-2s displayed better ORR property than either N-GNRs or N, S-GNRs, the control samples prepared with only a primary heteroatom source, strongly clarifying the significance of secondary-heteroatom-doping on enhancing the catalytic activity of carbon-based nanomaterials.

Planar on-chip interdigital microelectrodes based on nitrogen and oxygen co-doped graphene quantum dots for microsupercapacitors

The electrochemical performances of microsupercapacitors depend on the electrode materials. And graphene quantum dots are a very ideal electrode materials. In particular, nitrogen or oxygen doping is beneficial to enhance the Faraday reaction kinetics and improve the interfacial wettability of the carbon electrode and electrolyte solution. In this paper, nitrogen and oxygen co-doped graphene quantum dots were used as electrode materials and the electrode film was prepared by a modified liquid-air interface self-assembly method. The microsupercapacitors had high electrochemical characteristics including the area capacitance which was 98 μF cm−2, the energy density which was 0.014 μWh cm−2, the power density which was 51.07 μW cm−2 and the excellent time constant which was 0.12 ms. Meanwhile, the capacitance retention rate was 97.3% after 10,000 cycles.

Heteroatom engineered graphene-based electrochemical assay for the quantification of high-risk abused drug oxytocin in edibles and biological samples

The naive detection of scheduled H drug oxytocin is a vital requisite, owing to its deleterious impact on societal affluence prompted by unconstrained usage. Therefore, a reliable, cost-effective, and quick-to-respond analytic technique for this drug is in ample demand. In this work, we report electrochemical detection of oxytocin employing novel nitrogen, phosphorus co-doped coke-derived graphene (NPG) modified electrode. The electro-oxidation behavior of oxytocin was investigated on the NPG modified electrode by square wave stripping voltammetry (SWSV) in 0.1 M phosphate buffer of pH 7. The oxidation peak current was linear in two ranges, spanning from 0.1 nM to 10 nM and 15 nM to 95 nM. The limit of detection at the NPG electrode was calculated to be 40 pM. The practical application of developed sensor for the determination of oxytocin was examined in edible products and body fluids, hence signifying the possibility of having real-time surveillance over its misusage.

N, P co-doped graphene enriched phosphorus as a highly efficient oxygen reduction catalyst

• N -doped first to promote the introduction of P into Gr at secondary heat treatment. • While doping N, high content P doping with 2.61 at% is realized in P N Gr. • P N Gr shows high specific surface area and abundant micro- and mesopores. • P N Gr displays excellent ORR and alkaline zinc-air battery discharge performance. • P N Gr exhibits wonderful stability and methanol resistance. Heteroatoms doped metal-free carbon catalysts are considered as promising alternatives to commercial Pt/C for oxygen reduction reaction (ORR). Here, we report a phosphorus-enriched nitrogen and phosphorus co-doped graphene catalyst (P N Gr) via a facile and economical two-step pyrolysis approach. Thanks to its outstanding properties, such as unique honeycomb-like morphology, high Brunauer-Emmett-Teller (BET) surface area (935 m 2 /g), and abundant of phosphorus content (2.61 at%), the obtained P N Gr exhibits a high ORR activity with a half-wave potential of 0.82 V and a limiting current density of −5.98 mA cm −2 in alkaline electrolyte solution. Notably, the zinc-air battery assembled with P N Gr as cathode catalyst also shows an excellent discharge performance and stability.

Hierarchical Nanoflowers of MgFe2O4, Bentonite and B-,P- Co-Doped Graphene Oxide as Adsorbent and Photocatalyst: Optimization of Parameters by Box-Behnken Methodology.

In the present study, nanocomposites having hierarchical nanoflowers (HNFs) -like morphology were synthesized by ultra-sonication approach. HNFs were ternary composite of MgFe2O4 and bentonite with boron-, phosphorous- co-doped graphene oxide (BPGO). The HNFs were fully characterized using different analytical tools viz. X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectroscopy, transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry and Mössbauer analysis. Transmission electron micrographs showed that chiffon-like BPGO nanosheets were wrapped on the MgFe2O4-bentonite surface, resulting in a porous flower-like morphology. The red-shift in XPS binding energies of HNFs as compared to MgFe2O4-bentoniteand BPGO revealed the presence of strong interactions between the two materials. Box–Behnken statistical methodology was employed to optimize adsorptive and photocatalytic parameters using Pb(II) and malathion as model pollutants, respectively. HNFs exhibited excellent adsorption ability for Pb(II) ions, with the Langmuir adsorption capacity of 654 mg g−1 at optimized pH 6.0 and 96% photocatalytic degradation of malathion at pH 9.0 as compared to MgFe2O4-bentonite and BPGO. Results obtained in this study clearly indicate that HNFs are promising nanocomposite for the removal of inorganic and organic contaminants from the aqueous solutions.

Nitrogen and sulfur co-doped graphene quantum dot-modified electrode for monitoring of multivitamins in energy drinks

A glassy carbon electrode was modified with nitrogen and sulfur co-doped graphene quantum dots immobilized in chitosan for the monitoring of multivitamins. The graphene quantum dots were synthesized using a simple citric acid/l-cysteine pyrolysis procedure. The co-doping with nitrogen and sulfur in the graphene matrix was confirmed by spectroscopic techniques. Electron microscopy results showed that the synthesized quantum dots had a diameter of 3.4 ± 1.4 nm. Electrochemical techniques showed excellent current responses to vitamin oxidation provided by the modified electrode compared to the bare electrode. The parameters of square wave voltammetry were optimized in order to obtain the best current responses and to study the electrochemical oxidation of vitamins. The calibration plots for vitamins B2, B6 and B12 were constructed in 0.1 mol L−1 sodium acetate buffer (pH 5.0) with limits of detection of 0.30, 30.1 and 0.32 nmol L−1, respectively. Lastly, the modified electrode was effectively implemented in the quantification of vitamins in classic and fruit-based energy drink samples.

Photolithographic fabrication and electrochemical characterization of planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with superior capacitance retention rates

Compared with graphene, nitrogen and oxygen co-doped graphene quantum dots can make up for the limitation of graphene active sites. Here, we demonstrated the fabrication of planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots. The interdigital micro-electrodes were prepared on the surface of the electrode thin film by the photolithographic technique. Notably, the electrochemical performance of the micro-supercapacitors had significantly increased. The area capacitance was 18.74 μF cm−2. Furthermore, this work offered the areal energy density of 2.60 nWh cm−2 and the areal power density of 116.43 μW cm−2. After 10,000 cycles at 5000 Vs−1, the capacitance retention rate of 99.23% was obtained. Meantime, the corresponding time constant was 10.03 μs.

Multifunctional transitional metal-based phosphide nanoparticles towards improved polysulfide confinement and redox kinetics for highly stable lithium-sulfur batteries

The shuttle effect and the sluggish redox kinetics of lithium polysulfides (LiPSs) are the major issues impeding the practical applications of lithium-sulfur batteries (LSBs). Herein, a highly-efficient Ni2P electrocatalyst supported on N, P co-doped graphene (Ni2P@NPG) is developed via a simple “recrystallization-self-assembly” method to address the above issues. The ultrafine Ni2P nanoparticles ensure abundant adsorption-diffusion-conversion interfaces for accelerating LiPSs transformation and Li2S deposition, which extremely decreases the accumulation of LiPSs in the electrolyte and therefore prevents the migration of LiPSs. Their superior catalytic performance is demonstrated by reduced Gibbs free energy changes of rate-limiting step based on the systematic theoretical calculations and the reduced shuttle effect is tested by the three-dimensional reconstructions of Raman depth profiles. Benefiting from these synergistic effects, the LSBs with Ni2P@NPG modified separators present a superior cycling performance with an average capacity decay rate of 0.048 % per cycle at 1C around the 400 cycles and a high-rate capacity of 731 mAh/g at 2C. Even with a high-sulfur loading of 3.53 mg cm−2, the cell can still contain a reversible capacity of 809 mAh/g at 0.2C with a remarkable columbic efficiency of 98.4 %.

Ultrafast response planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with both ultrahigh power and energy densities

Great results had been achieved in the research of graphene-based planar on-chip micro-supercapacitors. The performances of fabricated micro-supercapacitors had been greatly improved. However, the energy characteristics of graphene-based planar on-chip micro-supercapacitors are generally low due to few active sites of graphene. Nitrogen and oxygen co-doped graphene quantum dots have the nanometer size, more active sites, and rich edge defects, are conducive to ion adsorption and desorption, and can solve the above-mentioned disadvantages of graphene. In this article, all-solid-state planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with both ultrahigh power and energy densities were fabricated by modified liquid–air interface self-assembly and photolithography for the first time. Planar on-chip electrodes were provided with a nanoscale thickness of 6 nm and an interdigital electrode width of 3 μm. Energy density of 11.49 mWh cm−3, power density of 41.42 W cm−3, and time constant of 3.16 μs were demonstrated. It should be emphasized that the above-mentioned energy density and power density are the highest for the planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots reported to date. The capacitance retention was 99% after 10000 cycles at 5000 V s−1.

All-solid-state planar on-chip micro-supercapacitors with excellent areal power performance at ultrahigh scan rates by photolithography

All-solid-state planar on-chip micro-supercapacitors (MSCs), as a new type of energy storage device, can be well integrated with micro-nano devices and exhibit good practical performance. Nitrogen and oxygen co-doped graphene quantum dots (GQDs), as one of the electrode materials for fabricating supercapacitors, exhibiting novel chemical/physical properties including nanometer-size, abundant edge defects, good conductivity and better surface grafting. In this article, the GQDs film was prepared by modified liquid–air interface self-assembly method and fabricated interdigital electrodes with electrode width and interdigital gap of 6 μm by simple photolithography technology. Electrochemical measurements revealed that the obtained GQDs electrodes for all-solid-state MSCs exhibited the areal power density of up to 0.107 mW cm−2 at the scan rate of 10,000 V s−1 and 95.6% capacitance after charging and discharging for 10,000 cycles. Specially, there was still the ultra-fast charging-discharging time (4.17 μs). The favorable performances make the GQDs film interdigital electrodes prepared by photolithography have good application prospects.

Design of effective graphenes co-doped by transition metal and nonmetal atoms for nitrate electroreduction: A first-principles study

Developing high-efficient electrocatalysts driven by renewable electricity to eliminate hazardous nitrate (NO3−) in daily life is of great scientific value. Thereby, a valid heterogeneous catalyst is proposed based on single titanium atom supported on sulfur co-doped graphene (TiS-G) for nitrate reduction reaction (NO3RR) using density functional theory (DFT). Under an external potential of 0.53 V, the overall reduction progress is thermodynamic spontaneous at ambient temperature and the maximum kinetic determining step is the formation of ammonia with a barrier of 0.63 V, comparable with experimental benchmark Cu(111). Intriguingly, this increased activity originates from reasonable accumulation of d orbital electrons around Fermi level, which contributes to a linear relationship between the atomic charge and classic d band center of the transition metal. Furthermore, metal clustering aggression, oxide poisoning, and dynamic stability are thorough examined in order to ensure the robustness of TiS-G structure under actual environment. This work not only opens up a novel avenue for the potential application of carbon-based electrodes in NO3RR, but also offers an atomic insight into catalytic reaction mechanism.

First-principle calculation of electronic structure and optical properties of (P, Ga, P–Ga) doped graphene

Abstract First-principle calculations are used to study the electronic structures, electronic and optical properties of pure, phosphorus-doped, aluminum-doped, and phosphorus and aluminum co-doped graphene. The gap between the conduction band and valence band of intrinsic graphene is zero. However, when graphene is doped with P, Ga, and P–Ga, the gap in energy will be opened and to a different extent. In the three different doping results, the gap values between the conduction and valence bands of P, Ga, and P–Ga graphene are 0.11, 0.35, and 0.39 eV, respectively. When graphene is doped with P–Ga, more electrons (1.40 e) will be gained by carbon atoms compared to P-doped graphene (0.61 e), while fewer electrons (1.49 e) will be transferred to carbon atoms compared to Ga-doped graphene (1.75 e). After doping with P, Ga, and P–Ga, the overall intensity of the graphene absorption peak is weakened and more pronounced relative to the low-frequency peaks. This result can fully demonstrate that the band gap of the doped graphene system can be better tuned by adding phosphorus and gallium atoms.

Mn, B, N co-doped graphene quantum dots for fluorescence sensing and biological imaging

The fluorescent and quantum yield (QY) of graphene quantum dots has been improved in recent years by doped atoms, which have good application prospects in fluorescence sensors and biological imaging. Here, a one-step hydrothermal synthesis method was used to synthesize manganese ions bonded with boron and nitrogen-doped graphene quantum dots (Mn-BN-GQDs). Compared with the boron and nitrogen co-doping graphene quantum dots (BN-GQDs), the fluorescence properties and quantum yield of Mn-BN-GQDs are significantly improved. Meanwhile, Mn-BN-GQDs exhibit low toxicity and good fluorescence imaging in living cells and has high selectivity to Fe3+ ions. Therefore, this experiment design Mn-BN-GQDs as a fluorescence sensor to detect Fe3+ ions, providing strong evidence for the advanced high sensitivity, selectivity and wide detection range of the Mn-BN-GQDs as a fluorescence sensor. These results indicate a dual linear relationship with good linear relationships in the 10–100 μM and 100–800 μM ranges, and limit of detection are 0.78 μM and 9.08 μM, respectively. Cellular imaging results demonstrate that Mn-BN-GQDs can be used as fluorescence sensors in biological imaging. Mn-BN-GQDs can be used for fluorescence sensing in biological imaging in combination with low toxicity, QY and quantum dot lifetime.

Sub-Second Joule-Heated RuO2-Decorated Nitrogen- and Sulfur-Doped Graphene Fibers for Flexible Fiber-type Supercapacitors.

Graphene-based fiber-shaped supercapacitors (FSSCs) have received considerable attention as potential wearable energy storage devices owing to their simple operating mechanism, flexibility, and long-term stability. To date, energy storage capacities of supercapacitors have been significantly improved via strategies such as heteroatom doping and the incorporation of pseudocapacitive metal oxides. Herein, we develop a novel and scalable direct-hybridization method that combines heteroatom doping and metal oxide hybridization for the fabrication of high-performance FSSCs. Using porous and highly conductive nitrogen and sulfur co-doped graphene fibers (NS-GFs) as self-heating units, we successfully convert ruthenium hydroxide anchored to the surface into ruthenium oxide nanoparticles after programmed sub-second electrothermal annealing without structural damage of the fibers. The resulting fibers show an increased gravimetric capacitance of 68.88 F g-1 compared to that of the pristine NS-GF (8.32 F g-1), excellent cyclic stability maintaining 96.67% of the initial capacitance after 20 000 continuous charging/discharging cycles, and good mechanical flexibility. The findings of this work advocate a successful Joule heating strategy for preparing high-performance graphene-based metal oxide hybrid FSSCs for use in energy storage applications.

Visible active enhanced adsorptive performance of the green synthesized Sulphur and Nitrogen codoped reduced graphene Oxide towards Degradation of reactive blue 4

The present study proposed a green way to synthesize Sulphur (S) and Nitrogen (N) codoped reduced graphene oxide (SN-rGO) employing a simple, efficient, and environmentally effective method. The graphene oxide (GO) sheets were integrated with S and N heteroatoms and were synthesized in an ecological manner employing bone meal extract (BME) as a green reducing agent. FTIR, FESEM, EDX, XPS and UV–Visible spectroscopy were used to evaluate the functional chemical bonding, surface morphology, chemical structure, and elemental compositions of the SN-rGO nanomaterial. The outcomes of the experiment have notably proved that SN-rGO possesses uncountable remarkable catalytic properties. In brief, UV–visible and Fourier transform infrared (FTIR) spectroscopies demonstrated the efficient synthesis of SN-rGO. The FESEM and HRTEM results indicated the crumbled, folded, and interconnected geometries of the networks that verified the surface modification and integration in the rGO sheets. The elemental composition of the SN-rGO nanomaterial was validated simultaneously by the EDAX and XPS analysis. The S and N doping may give additional carriers for reactive sites, hence enhancing the absorption of Reactive Blue 4 (RB4) was researched and addressed.

Enhanced hydrogen gas adsorption properties of B, N, and Au co-doped graphene in o-, m-, and p-configurations: DFT study

The adsorption of hydrogen gas molecules on boron, nitrogen, gold co-doped graphene has been investigated for different configurations using Density Functional Theory. Co-doped graphene systems outperform single doped graphene systems due to combined influence of hetero-atoms. Different configurations studied in present study include gold doped graphene (Au-G); boron‐gold (BAu); nitrogen‐gold (NAu); and boron‐nitrogen‐gold (BN-Au) co-doped graphene. In case of BN-Au co-doped graphene, the aspect of relative sites of boron and nitrogen has also been determined. Despite the fact that all configurations were confirmed to have interaction with hydrogen molecule, relative sites of boron and nitrogen resulted in distinct responses to hydrogen adsorption. The sensing performance has been evaluated by calculating adsorption energies and changes observed in electronic properties following geometry optimization. The primary goal of this research is to better interpret structure, stability, and prospective capability of hydrogen molecule detection by diverse combinations of boron, nitrogen, gold co-doped graphene geometries.

Theoretical analysis of the NH3, NO, and NO2 adsorption on boron-nitrogen and boron-phosphorous co-doped monolayer graphene - A comparative study

In this work, a density functional theory (DFT) based detailed theoretical study has been performed on the Boron/Nitrogen (B/N) and Boron/Phosphorous (B/P) codoped monolayer Graphene for molecular adsorptions and co-adsorptions of three Nitrogen-based environmental pollutant gasses, namely Ammonia (NH3), Nitrogen Di-Oxide (NO2) and Nitric Oxide (NO). The B acts as a localized electron deficit site in the codoped lattice and subsequently offers a suitable adsorption site for electron-enriched gas molecules like NH3 and NOx. The work systematically explores the influence of introducing Nitrogen or Phosphorus impurities in the same and different sub-lattice sites of boron-doped Graphene in the context of molecular adsorption. In this context, six doping configurations are identified that demonstrate distinct electronic properties and characteristic responses towards individual gas molecule adsorption. The molecular adsorption strongly influences the spatial distribution of electronic states near the band edges due to orbital overlaps from the adsorbed gas molecules, which leads to significant modulations in the energy band gaps and effective masses of the codoped lattices. The co-doping strategies appear highly advantageous for electrochemical gas sensing as it leads to appreciable semiconducting bandgap opening while retaining the intrinsic nature of the Graphene. The subsequent molecular adsorptions and co-adsorptions result in notable charge transfer between the gas molecules and the host lattice and considerably enhance the density of electronic states around the Fermi-level for codoped lattices.

Fabrication and Characterization of Planar on-Chip Micro-Supercapacitors Based on Nitrogen and Oxygen Co-Doped Graphene Quantum Dots by Modified Liquid-Air Interface Self-Assembly Method

Planar micro-supercapacitors stand out among micro/nano energy storage components for their high power, high energy, long life and fast time response. In this paper, all-solid-state planar on-chip micro-supercapacitors with high power characteristics were prepared by modified liquid-air interface self-assembly method, photolithography and sputtering gold. The nitrogen and oxygen co-doped graphene quantum dots electrode films are continuous and uniform, and the surface contains a large number of nitrogen and oxygen chemical bonds and functional groups. The finger width of the supercapacitors is 50 μm, the gap width is 50 μm and a number of electrode fingers is 100. In terms of performance, the supercapacitors had a very short time constant (2.16 μs), high power density (15.80 μW cm−2) and excellent cycle stability (94.5% capacity retention after 10000 cycles).