N-doped Graphene Quantum Dots Research Articles

Graphene Quantum Dots as Hole Extraction and Transfer Layer Empowering Solar Water Splitting of Catalyst-Coupled Zinc Ferrite Nanorods.

Despite the narrow band gap energy, the performance of zinc ferrite (ZnFe2O4) as a photoharvester for solar-driven water splitting is significantly hindered due to its sluggish charge transfer and severe charge recombination. This work reports the fabrication of a hybrid nanostructured hydrogenated ZnFe2O4 (ZFO) photoanode with enhanced photoelectrochemical water-oxidation activity through coupling N-doped graphene quantum dots (GQDs) as a hole transfer layer and Co-Pi as a catalyst. The GQDs not only reduce the surface-mediated nonradiative electron-hole pair recombination but also induce a built-in interfacial electric field leading to a favorable band alignment at the ZFO/GQDs interface, helping rapid photogenerated hole separation and serving as a conducting hole transfer highway, improve the hole transportation into the Co-Pi catalyst for enhanced water oxidation reaction kinetics. The optimized ZFO/GQD/Co-Pi hybrid photoanode delivers a 23-fold photocurrent enhancement at 1.23 V versus the reversible hydrogen electrode (RHE) and a significant 360 mV reduction in the onset potential, reaching 0.65 VRHE compared with the ZFO photoanode under 1 sun illumination in a neutral electrolytic environment. This investigation underscores the mechanism of synergistic interplay between the hole transport layer and cocatalyst in boosting the solar-illuminated water-splitting activity of the ZFO photoanode.

Machine-Learning driven STM images prediction of doped/defective graphene: Towards optimized tools for 2D nanomaterials characterization

Scanning tunneling microscopy (STM) is a key characterization technique that allows for visualization of specific features at nanostructures, given its ability to reveal changes in local charge densities in doping or defective sites. Besides the experimental acquisition of STM data from real samples, there is the theoretical route, which allows for STM images simulation from ab-initio calculations on defined nanostructures. This work presents an alternative route for theoretical STM image prediction by means of Machine Learning (ML) methods, based on the training of deep convolutional neural networks using simulated STM data. The ML-based STM predictions for defective, B- and N-doped graphene quantum dots are compared to ab-initio STM simulations, in terms of accuracy of structural rearrangements, charge density localizations, and computational resources requirements. The results demonstrate that STM images predicted by ML-methods are accurate at doping sites, whereas they show good similarity to simulations of large structural vacancies. This work represents a novel alternative for the use of ML methods in image-based characterization routines of doped/defective graphene, and potentially, for other 2-dimensional nanomaterials.

Absorption and Fluorescence Emission Investigations on Supramolecular Assemblies of Tetrakis-(4-sulfonatophenyl)porphyrin and Graphene Quantum Dots.

The one-pot synthesis of N-doped graphene quantum dots (GQDs), capped with a positively charged polyamine (trien), has been realized through a microwave-assisted pyrolysis on solid L-glutamic acid and trien in equimolar amounts. The resulting positively charged nanoparticles are strongly emissive in aqueous solutions and are stable for months. The interaction with the anionic tetrakis(4-sulphonatophenyl)porphyrin (TPPS4) has been investigated at neutral and mild acidic pH using a combination of UV/vis absorption spectroscopy together with static and time-resolved fluorescence emission. At pH = 7, the experimental evidence points to the formation of a supramolecular adduct mainly stabilized by electrostatic interactions. The fluorescence emission of the porphyrin is substantially quenched while GQDs remain still emissive. On decreasing the pH, protonation of TPPS4 leads to formation of porphyrin J-aggregates through the intermediacy of the charged quantum dots.

Core-shell structure N-doped graphene quantum dots Fe3O4/Co3O4 nanoparticles for colorimetric detection of H2O2

Hydrogen peroxide (H2O2) is an environmentally friendly intermediate in the environmental field and also plays an important role in human metabolism, but the production and accumulation of excessive H2O2 will cause harm to the human body, resulting in serious damage to cells. Therefore, N-doped graphene quantum dots Fe3O4/Co3O4 nanoparticles with core-shell structure were prepared by in-situ synthesis and precipitation. The experimental results show that the prepared Co3O4 nanoparticles have more efficient peroxidase activity than Co3O4 nanoparticles alone. It can catalyze the oxidation of 3, 3, 5, 5-tetramethylbenzidine (TMB) to produce a blue product (TMBox) in the presence of H2O2. In addition, Co3O4 with negative charge in the shell can produce a strong electrostatic driving coordination effect with positively charged TMB, which enhances the affinity between the nanoparticles and the substrate, and selectively catalyzes H2O2 oxidation of colorless TMB to turn it blue. Based on these experimental results, a simple, low-cost, and efficient colorimetric method for H2O2 detection was established, which showed a sensitive response to H2O2 in the range of 0.02–2.5 μM with a detection limit of 2.3 nM. In addition, due to the magnetic properties of the prepared nanoparticles, they could be easily recovered by applying a magnetic field. This research provides a viable approach for magnetic nanomaterials with encouraging prospects for environmental monitoring, biosensing, and more.

OH-Functionalized N-Doped Graphene Quantum Dots as an Efficient Metal-Free Catalysts for Oxygen Reduction Reaction in PEMFCs

OH-Functionalized N-Doped Graphene Quantum Dots as an Efficient Metal-Free Catalysts for Oxygen Reduction Reaction in PEMFCs

Sustainable gambogic acid release via pH/Redox Dual-Responsive C60-Modified magnetic mesoporous nanospheres for antitumor therapy

Traditional cancer treatment modalities such as surgery, chemotherapy, and radiation therapy have seen significant advancements in the past. However, inherent drawbacks, including systemic toxicity and high recurrence rates. Consequently, The nanoparticles, with their targeting and multifunctionality, have captured significant attention. This work synthesizes HMNPs-C60-N-GQDs-SS-PEI (HMNPs:Fe3O4@SiO2@mSiO2-C18) nanoparticles, integrating diverse functionalities for enhanced cancer therapy. The inclusion of SiO2 and C60 significantly improves the loading efficiency of gallic acid (GA). The magnetic properties of HMNPs enable efficient targeting to cancer sites under external magnetic fields. The -SS- linkage ensures drug release exclusively in tumor cells over-expressing glutathione (GSH), minimizing adverse effects on normal tissues. Introduction of Polyethyleneimine (PEI) imparts positive charge to facilitate accumulation on negatively charged tumor surfaces and enhances biocompatibility. Additionally, the fluorescence properties of N-doped graphene quantum dots (N-GQDs) facilitate real-time monitoring of material distribution in vivo during mouse and clinical therapy. Furthermore, the nano-magnetic targeting material demonstrates efficient drug loading and precise control over drug release, addressing issues such as the poor biocompatibility and high biotoxicity associated with traditional materials. This study not only achieves effective tumor treatment but also offers a promising direction for developing efficient multifunctional nano-targeting materials.

A precise flexible printed biosensor based on graphene ink decorated with N-doped graphene quantum dots

The improvement of electrochemical properties of graphene compounds can be achieved by using graphene quantum dots (GQDs) due to their high electron mobility, catalytic property and size corresponding to the active site of the enzyme. In this study, we developed a third-generation enzymatic amperometric biosensor based on nitrogen-doped graphene quantum dots (N-GQDs) and printed graphene electrodes (PGE) for the highly sensitive and selective detection of glucose. The PGEs modified with N-GQDs showed a high potential for the precise and sensitive electrochemical detection of glucose. Due to the high electron mobility and electrical conductivity, excellent electrocatalytic activity, large surface area and size compatibility of PGE and N-GQDs with biomolecules, a high sensitivity of 40.76 mA.mM-1.cm-2 and LOD close to 0.098 mM were achieved. The high enzyme surface coverage measured at 3.33 × 10–7 mol.cm-2 further confirmed the excellent enzyme loading capacity and immobilization tendency of the biosensor. Moreover, the N-GQD-based electrochemical biosensors were found to be highly specific and selective even in complex media, especially human blood serum.

N-Doped Graphene Quantum Dots Incorporated into NiCo Bimetallic-Organic Framework as an Electrocatalyst for Alkaline Water Splitting

N-Doped Graphene Quantum Dots Incorporated into NiCo Bimetallic-Organic Framework as an Electrocatalyst for Alkaline Water Splitting

Solar Hydrogen Production and Biomass Reforming Using Earth-Abundant Non-Toxic Si-Based Photocatalysts

The efficient production of electrochemical hydrogen and biomass refinement is crucial for the decarbonization of various industries. However, their low efficiency and high energy requirements make them impractical. In this talk, we propose using earth-abundant and non-toxic photocatalysts that can produce hydrogen and reform biomass efficiently by utilizing solar energy. Our approach involves using low bandgap Si flakes (SiF) for efficient light absorption. SiF was further modified with Ni-coordinated N-doped graphene quantum dots (Ni-NGQDs) to enable stable light-driven biomass reforming and hydrogen production. SiF/Ni-NQGDs enabled a record hydrogen productivity and concurrent vanillin production when using kraft lignin as model biomass under simulated sunlight without any buffering agent or sacrificial electron donors. SiF/Ni-NQGDs can also be easily recycled without noticeable performance degradation due to the prevention of Si deactivation through oxidation. Our findings provide valuable insights into the practical application of biomass refinement and electrochemical hydrogen production and efficient use use of solar energy.Reference)1. Y. Choi, S. Choi, I. Lee, T. V. T. Nguyen, S. Bae, J. Ryu, Y. H. Kim, S. Park, J. Ryu, Solar Biomass Reforming and Hydrogen Production with Earth-Abundant Si-Based Photocatalysts. Advanced Materials 2023, Accepted. Figure 1

Blue-light-driven photoactivity of L-cysteine-modified graphene quantum dots and their antibacterial effects

The widespread abuse of traditional antibiotics has led to a global rise in antibiotic-resistant bacteria, which give in return unprecedented health risks. Therefore, there is a large and urgent need for the development of new, smart antibacterial agents able to efficiently kill or inhibit bacterial growth. In this study, we investigated the antibacterial activity of S, N-doped Graphene Quantum Dots (GQDs) as a light-triggered antibacterial agent. Gamma irradiation was employed as a tool to achieve one-step modification of GQDs in the presence of L-cysteine amino acid as a source of heteroatoms. X-ray Photoelectron Spectroscopy (XPS), nuclear magnetic resonance (NMR), and zeta potential measurements provided the necessary data to clarify the structure of modified dots and verify the introduction of both S- and N-atoms in GQDs structure, but also severe changes in the aromatic, sp2 domains. Namely, γ-irradiation caused a bonding of S atoms in 1.14 at.% mainly as thiol groups, and N in 1.81 at.% as amino groups, but sp2 contribution in GQD structure was lowered from 63.00 to 4.86 at.%, as measured in dots irradiated at a dose of 200 kGy. Fluorescence quenching measurements showed that L-cysteine-modified dots are able to bind to human serum albumin. The antibacterial activity of GQDs combined with 1 and 6 h of blue light (470 nm) irradiation was tested against 8 bacterial strains. GQD-cys-25 sample provided the best results, with minimum inhibitory concentration (MIC) as low as 125 μg/mL against S. aureus, E. faecalis, and E. coli after only 1 h of blue light exposure.

Facile synthesis and modifying of Nitrogen-doped graphene quantum dots (N-doped GQDs) as fluorescent probes for detection of nitrite ions

Modifying of graphene quantum dots (GQDs) by adding heteroatoms to them improves their structural and optical properties and also makes them applicable in different areas. In this work, we synthesized nitrogen- doped GQDs (N-GQDs) by green method. They were used as fluorescence probes for the recognition and determination of nitrite. The reaction between the nitrogen groups of N-GQDs sensors and the analyte caused quenching fluorescence to increase linearly with increasing nitrite concentration due to an electron transfer mechanism. Under the ideal tested conditions, the response of N-GQDs to nitrite showed a concentration range of 0.3–1400 µM and R2 = 0.9956 with a LOD of 0.1 µM, with (S/N = 5).

Surface restructuring Prussian blue analog-derived bimetallic CoFe phosphides by N-doped graphene quantum dots for electroactive hydrogen evolving catalyst

As a crucial stage of electrochemical water splitting, hydrogen evolution reaction (HER) favour catalyst to attain rapid kinetics for its broader application, alternating Pt in the acidic environment. Transition metal phosphides (TMPs) are one kind of earth-abundant, nonprecious-based catalyst which has been classified as a viable alternative and active for HER. While the performance remains inferior to Pt which primarily targets durability under high current density, pinpointing the reconfiguration strategy would be critical to their catalytic competency. Herein, we reported engineered N-doped graphene quantum dots (NGQD) on the surface of bimetallic CoFe phosphide (CoFeP) derived from cobalt iron Prussian blue analogue (CoFePBA) as an efficient HER. By introducing the NGQD, the surface architect and electronic state of the transition metal are altered through an adjusted electronic configuration and thus, improving the electrocatalytic activity for HER. The X-ray absorption spectroscopy (XAS) highlighting the role of NGQD, which successfully induced the electron density of Co atoms, further expedites its conductivity and electroactivity. The optimized NGQD/CoFeP substantially surpasses an overpotential of 70 mV (vs. RHE) at the current density of 10 mA cm−2 in 0.5 M H2SO4. Furthermore, the NGQD/CoFeP maintains its exceptional stability under an extremely high current density of 600 mA cm−2 after 12 h of continuous operation. Our findings show that NGQD/CoFeP might demonstrate as a viable alternative to the conventional Pt electrocatalyst in commercial water splitting for hydrogen generation.

N-Doped Graphene Quantum Dots Confined within Silica Nanochannels for Enhanced Electrochemical Detection of Doxorubicin.

Herein, we describe a fast and highly sensitive electrochemical sensor for doxorubicin (DOX) detection based on the indium tin oxide (ITO) modified with a binary material consisting of vertically-ordered mesoporous silica films (VMSFs) and N-doped graphene quantum dots (NGQDs). VMSFs, with high permeability and efficient molecular transport capacity, is attached to the ITO electrode via a rapid and controllable electrochemical method, which can serve as a solid template for the confinement of numerous NGQDs through facile electrophoresis. By virtue of the excellent charge transfer capacity, π-π and electrostatic preconcentration effects of NGQDs, as well as the electrostatic enrichment ability of VMSF, the presented NGQDs@VMSF/ITO shows amplified electrochemical signal towards DOX with a positive charge, resulting in good analytical performance in terms of a wide linear range (5 nM~0.1 μM and 0.1~1 μM), high sensitivity (30.4 μA μM-1), and a low limit of detection (0.5 nM). Moreover, due to the molecular sieving property of VMSF, the developed NGQDs@VMSF/ITO sensor has good selectivity and works well in human serum and urine samples, with recoveries of 97.0~109%, thus providing a simple and reliable method for the direct electrochemical analysis of DOX without complex sample pretreatment procedures.

Employing novel N-doped graphene quantum dots to improve chloride binding of cement

One of the most primary reasons for durability deterioration of reinforced concrete (RC) structures is reinforcement corrosion caused by chloride ion invasion. However, there is still a lack of efficient additives to enhance the anti-chloride-corrosion behavior of RC structures. Herein, highly dispersed and cost-efficient N-doped graphene quantum dots (N-GQDs) are firstly applied to significantly increase the chloride binding performance of cement. Specifically, N-GQDs with high dispersity and low cost are successfully synthesized by one-step hydrothermal method. And the typical equilibrium test determines that after 14-day exposure to 3 M NaCl solution, the incorporation of 0.2 wt% (by weight of cement) N-GQDs makes the chloride binding ability of cement paste sharply boost by 134%. Moreover, in light of phase compositions analyses from XRD, TGA and SEM, the chloride binding mechanism of cement pastes modified by N-GQDs is rationally ascribed to the fact that the addition of N-GQDs enormously increases the physically adsorbed chloride ions and slightly promotes chemically bound chloride ions. This work firstly provides a novel carbon-based nanomaterial to efficiently enhance the chloride binding of cement, expected to improve the durability of RC structures.

An Ultrasensitive Photoluminescent Immunosensing of Lipovitellin by Using N-doped Graphene Quantum Dots

The increasing levels of environmental estrogens (EEs) have caused harmful effects on wildlife and human beings. Constructing a sensitive detection technique for EEs is meaningful. For intrinsic high specificity and sensitivity, immunosensing technique is a good choose for estrogeneous chemicals test in complex environment. As the main cleavage composition of vitellogenin (Vtg), a biomarker of EEs, lipovitellin (Lv) was proved to have same immunogenicity as Vtg, while better thermal stability than Vtg, thus Lv is more suitable than Vtg to be used as a standard matter to establish standard test curve. Upon the fluorescence resonance energy transfer (FRET) between N-doped graphene quantum dots (N-GQDs) coupled with anti-lipovitellin monoclonal antibody (anti-Lv-mAb) and reduced graphene oxide (rGO), a free-labelled photoluminescent immunosensing of Lv was developed and validated to quantify Lv of Paralichthys olivaceus. The assay obtained a large linear measuring range of 1 pg/mL- 2 µg/mL, high sensitivity of 9910.67 CPS/(ng/mL), low limit of detection (LOD) of 9.4 pg/mL and relative standard deviation of 1.19%. For 1 ng/mL Lv dispersed in drink water and sea water, the error of the recovery ratio is 1.65% and 10. 27% respectively. Our results demonstrated that the N-GQDs prepared by ultrasonic-assisted hydrothermal method could be effectively used to construct a nano photoluminescent immunosensor, which possesses the advantages of simplicity, rapidity, high specificity and anti-interference.

Solar Biomass Reforming and Hydrogen Production with Earth-Abundant Si-Based Photocatalysts.

Efficient electrochemical hydrogen production and biomass refinery are crucial for the decarbonization of various sectors. However, their energy-intensive nature and low efficiency have hindered their practical application. In this study, earth-abundant and non-toxic photocatalysts that can produce hydrogen and reform biomass efficiently, utilizing unlimited solar energy, are presented. The approach involves using low-bandgap Si flakes (SiF) for efficient light-harvesting, followed by modification with Ni-coordinated N-doped graphene quantum dots (Ni-NGQDs) to enable efficient and stable light-driven biomass reforming and hydrogen production. When using kraft lignin as a model biomass, SiF/Ni-NQGDs facilitate record-high hydrogen productivity at 14.2mmolgcat -1 h-1 and vanillin yield of 147.1mgglignin -1 under simulated sunlight without any buffering agent and sacrificial electron donors. SiF/Ni-NQGDs can be readily recycled without any noticeable performance degradation owing to the prevention of deactivation of Si via oxidation. This strategy provides valuable insights into the efficient utilization of solar energy and practical applications of electro-synthesis and biomass refinement.

Conductive thin-film nanocomposite nanofiltration membrane comprising N-doped graphene quantum dots with relieved concentration polarization for sulfate separation from high-salinity solution

Conductive thin-film nanocomposite nanofiltration membrane comprising N-doped graphene quantum dots with relieved concentration polarization for sulfate separation from high-salinity solution

A simple fluorescent “Turn off-on” sensor based on P, N-doped graphene quantum dots for Hg2+ and Cysteine determination

A simple fluorescent “Turn off-on” sensor based on P, N-doped graphene quantum dots for Hg2+ and Cysteine determination

Enhanced electro-optical properties of nematic liquid crystal doped with Nitrogen doped graphene quantum dots

The first step of this study was to prepare mixtures that contained different concentrations of N doped graphene quantum dots (NGQDs) into nematic liquid crystals (NLCs). Then, through the Z-scan technology, the optical measurements in the nonlinear regime were conducted with a continuous wave (CW) at 632 nm wavelength and a low power laser beam. The nonlinear absorption (NLA) coefficient, nonlinear refractive (NLR) index, and third-order nonlinear susceptibility of NLCs doped with different concentrations of the NGQDs at distinctive laser powers and diverse applied voltages of external electric field was experimentally measured. The Z-scan results demonstrate that prepared cells have two photon absorption (2PA) and self-focusing effects. As the result, the concentration of the NGQDs in E7 and power of laser were optimum at 1% wt. and 11 mW, respectively. The effect of a DC electric field on optical nonlinearity was also investigated in the mixtures of NLCs and NGQDs at the concentration of 1% wt. Based on these findings, this sample can be used in both nonlinear optics and ultrafast broadband photonics.

Crystalline F-doped titanium dioxide nanoparticles decorated with graphene quantum dots for improving the photodegradation of water pollutants

Carbon dots are emerging photoactive materials with high chemical stability, aqueous solubility, abundant surface functional groups and low-cost production. Their great advantages, incorporated into the high photocatalytic activity of the TiO2, result in hybrid systems that overcome some of the photocatalytic drawbacks associated with TiO2. In this work, a facile synthesis of hybrids of F-doped TiO2 and N-doped graphene quantum dots (F-TiO2@N-GQDs) is reported. These systems have demonstrated efficient photocatalytic properties in light-driven pollutant reduction from water. Therefore, using a simple and low-cost synthesis method, the N-GQDs act as electron reservoirs improving the pairs e--h+ lifetime in TiO2 by decreasing charge recombination, increasing their photocatalytic capacity. The photocatalysts showed very effective degradations of different contaminants such as methylene blue (90% degradation) ciprofloxacin (62% degradation) and naproxen (60% degradation) in short periods of up to 15 min and 4-chlorophenol (59% degradation) in 30 min using UV light (300 W).