Nitrogen-functionalized Graphene Research Articles

Exploring quantum confinement signature in nitrogen-functionalized graphene quantum dots: Effective mass approximation (EMA) model insights from computational and experimental analyses

A well-established relationship between bandgap energy and Quantum Dots (QDs) dimension, predicted by Effective Mass Approximation (EMA) models, is a cost-effective and reliable method to evaluate the bandgap energy of QDs. The EMA model sheds light on linearity between bandgap energy (Egap) to their inverse square diameter (1/dn), as a signature of the quantum confinement, with the n value reflecting the dimension of the quantum confinement. This study systematically investigated the power parameter "n" dependence in the bandgap energy of Nitrogen-functionalized Graphene Quantum Dots (N-GQDs) with distinct C–N configurations, i.e., Pyridinic-N, Pyrrolic-N, Graphitic-N based on computational and experimental data. The results showed that the calculated bandgap energy values reveal a notable weakening of the size dependence in N-GQDs compared to pristine GQDs, particularly in Pyrrolic-N GQDs, indicative of a unique geometric dimensionality of confinement. This systematic exploration advances our understanding of "n" dependence and bandgap energy in N-GQDs, laying a solid groundwork for modulating the bandgap energy of N-GQDs for optoelectronics and quantum device applications.

Nanostructured polypyrrole nanowires/nitrogen-functionalized graphene composites for supercapacitor electrode

The well-defined polypyrrole (PPy) nanowires are successfully grown on the nitrogen-functionalized graphene (NFG) nanosheets by electrochemical polymerization method (PPy/NFG). The synthesized PPy/NFG composites as supercapacitor electrodes present specific capacitance of 1058 and 910 F g−1 at 0.5 and 10 A g−1, far higher than pristine PPy (309 and 160 F g−1) and NFG (265 and 186 F g−1) electrodes, respectively. Particularly, symmetric supercapacitor device assembled with two PPy10/NFG electrodes delivered 601 F g−1 and 480 F g−1 specific capacitance at 0.5 A g−1 and 20 A g−1, good cycling stability (retaining over 85 % capacitance after 10,000 cycles), large energy density (83.5 Wh kg−1 at 0.5 A g−1). These results indicated the PPy/NFG composites have promising application in supercapacitors.

Exploring Nitrogen-Functionalized Graphene Composites for Urinary Catheter Applications.

Graphene has been broadly studied, particularly for the fabrication of biomedical devices, owing to its physicochemical and antimicrobial properties. In this study, the antibiofilm efficacy of graphene nanoplatelet (GNP)-based composites as coatings for urinary catheters (UCs) was investigated. GNPs were functionalized with nitrogen (N-GNP) and incorporated into a polydimethylsiloxane (PDMS) matrix. The resulting materials were characterized, and the N-GNP/PDMS composite was evaluated against single- and multi-species biofilms of Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Both biofilm cell composition and structure were analyzed. Furthermore, the antibacterial mechanisms of action of N-GNP were explored. The N-GNP/PDMS composite showed increased hydrophobicity and roughness compared to PDMS. In single-species biofilms, this composite significantly reduced the number of S. aureus, P. aeruginosa, and K. pneumoniae cells (by 64, 41, and 29%, respectively), and decreased S. aureus biofilm culturability (by 50%). In tri-species biofilms, a 41% reduction in total cells was observed. These results are aligned with the outcomes of the biofilm structure analysis. Moreover, N-GNP caused changes in membrane permeability and triggered reactive oxygen species (ROS) synthesis in S. aureus, whereas in Gram-negative bacteria, it only induced changes in cell metabolism. Overall, the N-GNP/PDMS composite inhibited biofilm development, showing the potential of these carbon materials as coatings for UCs.

Continuous Production of Functionalized Graphene Inks by Soft Solution Processing.

The continuous production of high-quality, few-layer graphene nanosheets (GNSs) functionalized with nitrogen-containing groups was achieved via a two-stage reaction method. The initial stage produces few-layer GNSs by utilizing our recently developed glycine-bisulfate ionic complex-assisted electrochemical exfoliation of graphite. The second stage, developed here, uses a radical initiator and nitrogen precursor (azobisisobutyronitrile) under microwave conditions in an aqueous solution for the efficient nitrogen functionalization of the initially formed GNSs. These nitrile radical reactions have great advantages in green chemistry and soft processing. Raman spectra confirm the insertion of nitrogen functional groups into nitrogen-functionalized graphene (N-FG), whose disorder is higher than that of GNSs. X-ray photoelectron spectra confirm the insertion of edge/surface nitrogen functional groups. The insertion of nitrogen functional groups is further confirmed by the enhanced dispersibility of N-FG in dimethyl formamide, ethylene glycol, acetonitrile, and water. Indeed, after the synthesis of N-FG in solution, it is possible to disperse N-FG in these liquid dispersants just by a simple washing-centrifugation separation-dispersion sequence. Therefore, without any drying, milling, and redispersion into liquid again, we can produce N-FG ink with only solution processing. Thus, the present work demonstrates the 'continuous solution processing' of N-FG inks without complicated post-processing conditions. Furthermore, the formation mechanism of N-FG is presented.

Increasing the efficiency and cycle life of Na-O2 batteries based on graphene cathodes with heteroatom doping

To overcome the challenges of Na-O2 batteries with respect to efficiency, capacity, and cycle life as well as to develop cheap, metal-free, and abundant electrocatalysts, we explored boron and nitrogen-functionalized graphene aerogels prepared by the hydrothermal self-assembly of graphene oxide with subsequent thermal reduction. The results showed an improve of both the cycling overpotential and the coulombic efficiency for the functionalized graphene aerogels. However, the nitrogen-containing cathode presented a shortened cycle life and decreased charging stability. The postmortem analysis of the full discharge, and the full discharge and charge cathodes demonstrated that nitrogen functionalization triggered the formation of solid parasitic products that passivate the cathode surface, thus resulting in a poorer electrochemical performance. By contrast, functionalization with boron-containing groups demonstrated to be a more promising strategy due to minimized parasitic products, leading to lower oxygen reduction and evolution overpotentials with a concomitantly enhanced cell efficiency vs. the undoped cathodes. This resulted in a cycle life of 70 cycles at a relatively high current density of 0.1 mA cm−2 with a capacity cut-off of 0.5 mAh cm−2. Our study underscores that functionalization with heteroatoms simultaneously alters multiple characteristics of graphene-based materials, including their chemistry, texture and morphology, which in turn presents a critical impact on the electrochemical response of the resultant Na-O2 cells.

Nitrogen-functionalized graphene quantum dot incorporated GelMA microgels as fluorescent 3D-tissue Constructs.

Biopolymer microgels present many opportunities in biomedicine and tissue engineering. To understand their in vivo behavior in therapeutic interventions, long-term monitoring is critical, which is usually achieved by incorporating fluorescent materials within the hydrogel matrix. Current research is limited due to issues concerning the biocompatibility and instability of the conventional fluorescent species, which also tend to adversely affect the bio-functionality of the hydrogels. Here, we introduce a microfluidic-based approach to generate nitrogen-functionalized graphene quantum dot (NGQD) incorporated gelatin methacryloyl (GelMA) hydrogel microspheres, capable of long-term monitoring while preserving or enhancing the other favorable features of 3D cell encapsulation. A multilayer droplet-based microfluidic device was designed and fabricated to make monodisperse NGQD-loaded GelMA hydrogel microspheres encapsulating skeletal muscle cells (C2C12). Control over the sizes of microspheres could be achieved by tuning the flow rates in the microfluidic device. Skeletal muscle cells encapsulated in these microgels exhibited high cell viability from day 1 (82.9 ± 6.50%) to day 10 (92.1 ± 3.90%). The NGQD-loaded GelMA microgels encapsulating the cells demonstrated higher metabolic activity compared to the GelMA microgels. Presence of sarcomeric α-actin was verified by immunofluorescence staining on day 10. A fluorescence signal was observed from the NGQD-loaded microgels during the entire period of the study. The investigation reveals the advantages of integrating NGQDs in microgels for non-invasive imaging and monitoring of cell-laden microspheres and presents new opportunities for future therapeutic applications.

CsPbI3/N-GQDs dual layer phosphor-converted white-LEDs with ultrahigh luminous efficiency and color rendering index

Phosphor-converted LEDs or pc-LEDs, as a solid-state lighting source, are attractive for next-generation display technologies because of their energy savings, and green environmentally friendly nature. Recently, white LEDs are being produced commercially by coating blue LED (440–470 nm) chips with various yellow-emitting phosphors. However, the LEDs produced by this technique often exhibit high correlated color temperature (CCT) and low color rendering index (CRI) values, due to sufficient red spectral components not being present, and thus aren’t suitable for commercial grade white illumination. To circumvent this drawback, our work reports for the first time the use of blue and green-emitting nitrogen-functionalized graphene quantum dots (GQDs) coupled with red-emitting CsPbI3 NCs for phosphor-based LED applications. We deployed near-UV to visible excitable red-emitting perovskite CsPbI3 nanocrystals which contribute toward the red spectral component, thus greatly improving the CRI of the LEDs. CsPbI3 nanocrystals are optically excited by nitrogen-functionalized GQD with blue and green emissions in a remote double-layer phosphor stack technique. This double phosphor layer stacking greatly improves both the CRI and luminous efficiency of radiation (LER), which usually has a trade-off in previously reported phosphor stacks. A CCT of ∼5182 K providing daylight white tonality, with superior CRI (∼90%) and ultrahigh LER (∼250 lumens/watt) are reported, which are significantly higher than the established benchmarks.

One-step synthesis of nitrogen-functionalized graphene aerogel for efficient removal of hexavalent chromium in water.

The efficient removal of hexavalent chromium (Cr(VI)) with high toxicity has attracted widespread concern since it causes serious harm to ecological environment and public health. Herein, we report a novel nitrogen-functionalized graphene aerogel with stereoscopic structure through a simple hydrothermal method and freeze drying for Cr(VI) removal from water. Graphene oxide (GO) and nitrogenous organics polyethyleneimine (PEI) and pyrrole are used as raw materials for preparing PEI/polypyrrole/GO aerogel (PPGA) adsorbent. PEI and pyrrole act as nitrogen sources to introduce nitrogenous functional groups, and also take on the role of cross-linkers for helping GO sheets to form stereoscopic structure. The obtained PPGA has a fast adsorption rate, excellent reusability, and shows a remarkable adsorption capacity for Cr(VI) up to 458.24mg/g under the optimal conditions (pH 2.0, 298K, Cr(VI): 600mg/L, dosage: 0.4g/L). The adsorption process of Cr(VI) on PPGA can fit the pseudo-second-order kinetic model well. Analysis of intraparticle diffusion shows that the Cr(VI) removal process is a multi-step process. Adsorption thermodynamic and isotherm results demonstrate Cr(VI) adsorption on PPGA is a spontaneous endothermic process. The adsorption mechanism involves electrostatic attraction, redox, and chelation. In general, this work provides a simple and eco-friendly way to prepare PPGA, which has a great potential for actual application of Cr(VI) removal in effluent.

Fast, eco-friendly synthesis of blue luminescent nitrogen-doped graphene quantum dots in glycerol

Nitrogen-functionalized graphene quantum dots (N-GQDs) were synthesized by hydrothermal transformation of glycine precursors in glycerol. Functionalization of GQDs with nitrogen was confirmed with FTIR spectroscopy. Atomic force microscopy (AFM) analysis revealed that the thickness of the quantum dots is around ~ 1 nm while the lateral dimensions are in the range from 20 to 80 nm. N-GQDs exhibit strong fluorescence in the blue (420 nm) region and they are suitable for bioimaging applications.

Up-conversion and Tunable Up-conversion Emission from Nitrogen Functionalized Graphene Quantum Dots

In amidst of conflicts of opinion regarding the presence of up-conversion in carbonaceous nanostructure. We have critically and precisely asserted that there is a real up-conversion in the nitrogen functionalized graphene quantum dots (NGQDs), which is found to be its inherent feature and not a measurement artefact. We have demonstrated that NGQDs exhibit real up-conversion in the blue-green region. To define the perspective of the study a variant of GQDs, NGQDs was synthesized using facile, one-pot synthetic methods. We have critically examined the up-conversion emission in NGQDs, interestingly, N-GQDs exhibited very superior optical properties such as high quantum yield of 97%, up-conversion emission at 535 nm and tunable up-conversion that exhibited a red shift of 12 nm. The two-photon excitation process is the governing phenomenon behind the real up-conversion in NGQDs which is suggested by the quadratic dependence of the integrated intensity on excitation power. Up-conversion can enhance the efficiency of the photovoltaic solar cell by even converting infrared region of sunlight to electricity. Moreover, tunable up-conversion open the door for promising applications of NGQDs in tunable fibre lasers, multicolour displays and multiphoton optical data storage.

N-functionalized graphene derivatives as hole transport layers for stable perovskite solar cell

In this work, three Nitrogen-functionalized graphene (NGs): amino-graphene (G-NH2), graphene-ethanolamine (G-EA), and graphene ethylenediamine (G-EDA) have been synthesized and tested as hole transport layers (HTL) for perovskite solar cells (PSCs) applications. Among the evaluated graphene-based derivatives, the PSCs fabricated with graphene-ethylenediamine (G-EDA) showed best power conversion efficiency of 12.9%. The enhanced PCE of G-EDA based PSCs as compared to other NGs are attributed to the uniform coverage, faster hole transportation, and a template for larger perovskite crystal growth. Moreover, the PCE of the PSCs fabricated with G-EA and G-EDA based HTLs remain stable even after 200 h of light-soaking.

Dimethyl carbonate production via transesterification reaction using nitrogen functionalized graphene oxide nanosheets

Nitrogen-functionalized graphene oxide (GO) nanocatalysts were prepared using ammonia, methylamine, ethylamine, and hydrazine hydrate as a nitrogen source. Nanocatalysts samples were thoroughly characterized using XRD, Raman, FTIR, XPS, FESEM, TEM, and TGA techniques. Quantitative and qualitative analyses of surface acidic and basic sites were done by NH3- and CO2-TPD techniques. Nanocatalysts were further examined for DMC production via transesterification reaction of propylene carbonate (PC) with CH3OH. Quantitative analysis of nitrogen-containing functional groups in the prepared sample with respect to other functional moieties was performed. Among various nanocatalysts, ammonia functionalized GO (AGO) was found to be the best for DMC production. At optimized reaction conditions of temperature (180 °C), time (6 h), and catalyst dose (1 wt% with respect PC), the highest DMC yield of ∼50% was observed. Reusability studies using AGO nanocatalyst were conducted up to four consecutive test cycles to evaluate catalysts' potentiality towards DMC synthesis. Thus, N-functionalized GO is a useful metal-free nanocatalyst that could also be explored for other chemical processes.

Charge Transport through Functionalized Graphene Quantum Dots Embedded in a Polyaniline Matrix

Nitrogen-functionalized graphene quantum dots embedded in a polyaniline matrix (NGQD–PANI) are extremely promising candidates for the development of next-generation sensors and for thermoelectric m...

Ternary metal-metalloid-nonmetal alloy nanowires: a novel electrocatalyst for highly efficient ethanol oxidation electrocatalysis

We report rational design and syntheses of ternary noble metal-metalloid-nonmetal alloy nanowires (NWs) as a novel electrocatalyst for electrochemical ethanol oxidation reaction (EOR). This novel electrocatalyst is formed in an aqueous solution via anisotropic nucleation and growth of ternary PdBP alloy NWs along assembled cylinder template of Plurolic F127 on a nitrogen-functionalized graphene support (denoted as PdBP NWs@N-G). We find that uniformly alloying B and P intrinsically modulates the electronic states of Pd catalyst and also introduces new functions into the catalyst, while NW structure supported on the N-G exposes more electrocatalytic active sites and accelerates electron/mass transfers. Such add-in synergies of PdBP NWs@N-G kinetically facilitate the removal and/or further oxidation of CO-based poisoning intermediates, thus remarkably enhancing the electrocatalytic EOR performance. They exhibit a high mass activity of 4.15 A mgPd−1 and superior cycling and chronoamperometric stability for electrocatalytic EOR, much better than previously reported monometallic Pd-based nanocatalysts. More interestingly, this design strategy can be easily extended to develop more sophisticated NWs catalysts with more compositions (for example quaternary PdCuBP NWs@N-G) that further tunes the electronic and bifuntional effects for various desired catalysis and electrocatalysis.

Asymmetric PdPtCu mesoporous hemispheres on nitrogen-functionalized graphene for methanol oxidation electrocatalysis

This work reports an easy solution-phase synthesis of asymmetric metallic mesoporous hemispheres on nitrogen-functionalized graphene for fuel cell electrooxidation.

Nitrogen-Functionalized Graphene Quantum Dots: A Versatile Platform for Integrated Optoelectronic Devices.

Over the past 10 years, graphene quantum dots (GQDs) have grown into a highly innovative optical material in various research fields, including electronics, photonics, biotechnologies, etc. With the increasing implementation of GQDs in these fields, GQDs with tunable optical properties will emerge that could be especially suitable for applications in the field of integrated photonics. Herein, a short summary of the recent state of our research on the development of nitrogen-functionalized GQDs with tunable optical properties and their integration into photodetectors is given.

Emission-wavelength-dependent photoluminescence decay lifetime of N-functionalized graphene quantum dot downconverters: Impact on conversion efficiency of Cu(In, Ga)Se2 solar cells

Graphene quantum dots (GQDs) have several advantages over inorganic quantum dots owing to their beneficial properties. Recently, GQDs have been used as downconverters in photovoltaic devices. However, the application of GQDs in most emergent thin-film-based Cu(In, Ga)Se2 (CIGS) photovoltaic cells is limited because of either low photoluminescence (PL) quantum yield (QY) or a small Stokes shift (Δλ). Therefore, GQDs with an ultrahigh QY and large Δλ are essential to realizing the two emergent fields, i.e., the application of GQDs in CIGS photovoltaic solar cells. In this regard, we synthesized nitrogen-functionalized GQDs (NGQDs) with an ultrahigh QY (77–99%) and a large Δλ (95–155 nm) via tailoring of the nitrogen and oxygen moieties. The NGQDs were applied in CIGS solar cells to evaluate their downconversion efficiency. Our study shows that the emission wavelength (λem)-dependent photoluminescence decay lifetime (τem) determines the down-conversion efficiency of the nitrogen-functionalized graphene quantum dots. With the increase in τem at λem > 500 nm, the conversion efficiencies of the NGQDs coated-CIGS solar cells increased by 12.22%. Thus, the increase in τem at λem > 500 nm significantly increased the maximum current output and thus enhanced the solar-cell performance.

Nitrogen-Doped Graphene-Based Catalyst with Metal-Reduced Organicframework: Chemical Analysis and Structure Control

Here we report an advanced nitrogen-doped graphene-based catalyst with metal-reduced organic framework structure (N-G/MOF) prepared by functionalizing ZIF-8 and nitrogen-functionalized graphene oxide using the nanoscale high energy wet ball milling method. The chemical structure control of N-G/MOF was studied by characterizing the variation of the chemical structure of synthesized samples throughout targeted grinding speeds. The results proved that the chemical interaction between ZIF-8 and N-G caused the reduction of nitrogen, oxygen and zinc atoms, and the variation of chemical bonding composition in N-G/MOF. The reduction rate of zinc was gradually increased with the increasing grinding speed and reached 82% of zinc loss at 650 RPM. The characterization of carbon and nitrogen bonding composition confirmed that the reduction of nitrogen, oxygen and zinc atoms was caused by the decomposition of C-N-Zn heteroatom contents in ZIF-8 and the O-containing functional groups in N-G which were influenced by the grinding speed. The decomposition of ZIF-8 not only affected the framework and the pore structure but also modified the chemical structure and the surface distribution of C-N-containing functional groups-constituted active sites. The variation of physical and chemical properties enhanced the electrochemical performance of N-G/MOF and made it comparable to the 10 wt% Pt/C catalyst.

Highly-efficient Peroxymonosulfate Activation for Sulfacetamide Degradation over Nitrogen-functionalized Graphene: the Effect of Thermal Annealing Temperature on Reactive Functional Groups

Nitrogen-doped graphene (NG) prepared through thermal annealing of graphene oxide (GO) and urea was employed as a peroxymonosulfate (PMS) activator to degrade sulfacetamide (SAM). The fine tuning of the concentrations of functionalities and catalytic performance of NG was realized via tweaking thermal annealing temperature. NG600 (NG prepared at 600 °C) with the controlled N bonding configurations (a high N doping level (16.0 wt%) and a most optimum amount of pyridinic N (38.4 %N), pyrrolic N (31.8 %N), graphitic N (25.9 %N)) performed best as PMS activator. Quenching experiments disclosed that radical pathway contributed more to SAM degradation than non-radical pathway. SO4•- was the key reactive species for the SAM degradation in the NG/PMS system.Key words: metal-free catalysis, nitrogen-doped graphene, peroxymonosulfate, sulfacetamide, sulfate ra

Thermal Stability and Potential Cycling Durability of Nitrogen-Doped Graphene Modified by Metal-Organic Framework for Oxygen Reduction Reactions

Here we report a nitrogen-doped graphene modified metal-organic framework (N-G/MOF) catalyst, a promising metal-free electrocatalyst exhibiting the potential to replace the noble metal catalyst from the electrochemical systems; such as fuel cells and metal-air batteries. The catalyst was synthesized with a planetary ball milling method, in which the precursors nitrogen-functionalized graphene (N-G) and ZIF-8 are ground at an optimized grinding speed and time. The N-G/MOF catalyst not only inherited large surface area from the ZIF-8 structure, but also had chemical interactions, resulting in an improved Oxygen Reduction Reaction (ORR) electrocatalyst. Thermogravimetric Analysis (TGA) curves revealed that the N-G/MOF catalyst still had some unreacted ZIF-8 particles, and the high catalytic activity of N-G particles decreased the decomposition temperature of ZIF-8 in the N-G/MOF catalyst. Also, we present the durability study of the N-G/MOF catalyst under a saturated nitrogen and oxygen environment in alkaline medium. Remarkably, the catalyst showed no change in the performance after 2000 cycles in the N2 environment, exhibiting strong resistance to the corrosion. In the O2 saturated electrolyte, the performance loss at lower overpotentials was as low compared to higher overpotentials. It is expected that the catalyst degradation mechanism during the potential cycling is due to the oxidative attack of the ORR intermediates.