Nitrogen-doped Graphene Quantum Dots Research Articles

Machine learning framework for selective and sensitive metal ion sensing with nitrogen-doped graphene quantum dots heterostructure

This study introduces a machine learning (ML) framework to optimize photodetector performance for sensor applications. Using the data from the fabricated photodetector with the heterostructure of nitrogen-doped graphene quantum dot and gold nanoparticles (Au@N-GQDs), various supervised ML models (more than 20 models) are trained and tested for the selection and refinement of the most effective algorithm for our work. Depending on the best-performed ML model, the optimized working wavelength of the photodetector is found for the detection of metal ions. Remarkably, the ML-based sensor shows a high level of selectivity and sensitivity in nM level towards Fe3+ ions in Brahmaputra river water. A strong alignment between model predictions and experimental outcomes validates the efficacy of the proposed ML-based framework. Moreover, data visualization techniques such as heatmaps, classification algorithms, and confusion matrices are introduced to identify the trends in the database. The mechanistic insight of the sensor performance towards Fe3+ ion sensing is further explained with heatmap analysis and experimental verification, which emphasizes the role of photo-induced charge transfer and Fe–O bond formation between metal ions and Au@N-GQDs due to the high electron affinity of Fe3+ ions.

A fluorescent nanocomposite probe of quantum dots and zinc oxide embedded in polymer for smartphone-assisted on-site determination of diflunisal

A fluorescent sensor based on nitrogen-doped graphene quantum dots (N-GQDs) was developed for the smartphone-assisted colorimetric determination of diflunisal. The fluorescence source was embedded with zinc oxide (ZnO) in a molecularly imprinted polymer (ZnO@N-GQDs@MIP). The quantitative analysis was based on the fluorescence quenching caused by electron transfer from the nanoprobe to diflunisal. The sensor demonstrated linearity in the range of 0.10–50.0 μg L−1 with a limit of detection of 0.03 μg L−1. Smartphone-assisted on-site determination produced linearity in the range of 1.0–50.0 µg/L with a limit of detection of 0.30 μg L−1. The developed sensor was applied to determine diflunisal in milk, egg and yogurt samples. Recoveries ranging from 94.8 to 103.7 % were achieved with a RSD below 2.0 % measured by fluorescence spectroscopy, and from 94.9 to 106.9 % with a RSD of <6 % smatphone-assisted measurement. Comparison of the detection outcomes of both methods with those of high-performance liquid chromatography revealed consistent results, demonstrating the accuracy of the developed method, which was also sensitive, selective, and fast. Notably, the portable and easy-to-read smartphone-assisted method is suitable for on-site application.

Nitrogen-doped graphene quantum dot embedded polyaniline for the fabrication of high-performance flexible supercapacitor with enhanced cycling stability

This article explains the synthesis of high surface area nitrogen-doped graphene quantum dots embedded polyaniline (PANI) and its effectiveness in fabricating flexible printed supercapacitors. A noticeable change in polyaniline's morphology and specific surface area suggests the successful incorporation of graphene quantum dots into the polymer matrix. The synergistic interaction of polyaniline with graphene quantum dots is evident in its energy storage performance. The fabricated supercapacitor prototype with PVA/HCl gel electrolyte exhibited a very high areal capacitance of 128.01 mF cm−2, with an areal energy density of 11.40 μWh cm−2, and a power density of 640 μW cm−2 at 1.6 mA cm−2 current density. Most importantly, the developed supercapacitor exhibited 76.70% of original capacitance after 5000 galvanostatic charge-discharge cycles, which was found to be far better result than a supercapacitor fabricated with pristine polyaniline. Furthermore, the developed supercapacitor demonstrated excellent mechanical stability, retaining its performance at diverse angles and even after 4000 bending cycles. These characteristics make PANI/N-GQD-based supercapacitors appropriate for wearable devices requiring flexibility, cycling stability, and mechanical toughness.

Enhanced charge storage in supercapacitors using carbon nanotubes and N-doped graphene quantum dots-modified (NiMn)Co2O4

The integration of ternary metal oxides into carbon materials is anticipated to significantly boost the electrochemical performance of supercapacitor electrodes. This article synthesized carbon nanotubes (CNT)/(NiMn)Co2O4 composite materials using a straightforward hydrothermal method and subsequently prepared composite thin films of CNT/P-(NiMn)Co2O4@NGQD by phosphating and incorporating nitrogen-doped graphene quantum dots (NGQD). These films served as the functional electrode material for supercapacitors, enhancing their performance capabilities. The specific capacity of CNT/P-(NiMn)Co2O4@NGQD was measured at 2172.0 F g−1 at a current density of 1 A g−1, maintaining a capacitance of 1954.0 F g−1 at 10 A g−1, thus demonstrating excellent rate performance. Electrochemical impedance spectroscopy (EIS) further revealed enhancements in electrolyte flow dynamics and capacitance behavior post-NGQD introduction. The energy density of the composite material reached 94.4 Wh kg−1 at power density of 800 W kg−1, demonstrating superior electrochemical performance. The enhancement in these electrochemical properties is attributed to the high specific surface area and active sites of CNT/P-(NiMn)Co2O4@NGQD films, along with the synergistic effects of NGQD and metal ions facilitating rapid electrons and charge transfer. This work provides new insights into developing high-performance supercapacitors.

Effect of load on the tribological properties of Si3N4-based composite with N-GQDs

Purpose The purpose of this paper is to improve the mechanical and tribological properties of Si3N4 ceramics and to make the application of Si3N4 ceramics as tribological materials more extensive. Design/methodology/approach Si3N4-based composite ceramics (SN-2L) containing nitrogen-doped graphene quantum dots (N-GQDs) were prepared by hot press sintering process through adding 2 Wt.% nanolignin as precursor to the Si3N4 matrix, and the dry friction and wear behaviors of Si3N4-based composite against TC4 disc were performed at the different loads by using pin-on-disc tester. Findings The friction coefficients and wear rates of SN-2L composite against TC4 were significantly lower than those of the single-phase Si3N4 against TC4 at the load range from 15 to 45 N. At higher load of 45 N, SN-2L/TC4 pair presented the lowest friction coefficient of 0.25, and the wear rates of the pins and discs were as low as 1.76 × 10−6 and 2.59 × 10−4mm3/N·m. The low friction and wear behavior could be attributed to the detachment of N-GQDs from the ceramic matrix to the worn surface at the load of 30 N or higher, and then an effective lubricating film containing N-GQDs, SiO2, TiO2 and Al2SiO5 formed in the worn surface. While, at the same test condition, the friction coefficient of the single-phase Si3N4 against TC4 was at a range from 0.45 to 0.58. The spalling and cracking morphology formed on the worn surface of single-phase Si3N4, and the wear mechanism was mainly dominated by adhesive and abrasive wear. Originality/value Overall, a high-performance green ceramic composite was prepared, and the composite had a good potential for application in engineering tribology fields (such as aerospace bearings). Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0161/

Comparison between pool boiling system of graphene quantum dots and nitrogen-doped graphene quantum dots suspended in binary base fluids

Using nanofluids instead of conventional heat transfer fluids as a passive method is a well-established and widely used technique by researchers to increase the rate and thermal performance of engineering equipment. In this study, the hydrothermal method with a bottom-up approach was used for the synthesis of graphene quantum dots and nitrogen-doped graphene quantum dots. Then, nanofluid samples were prepared in a two-step process, by adding nanoparticles to binary base fluids of deionized water and ethylene glycol in volume concentrations of (50:50) and (60:40), in four concentrations of 100, 200, 500, and 1000 ppm. In order to better understand the boiling heat transfer mechanism and measure its characteristics such as critical heat flux and heat transfer coefficient, an experimental system was designed and built. Nanofluids based on graphene quantum dots have unique features such as compatibility with the environment, economic efficiency, high stability and suitable heat transfer capability. For this reason, their selection in the pool boiling heat transfer process, in addition to saving energy, is introduced as one of the most effective options for improving CHF and HTC. The tests were performed under saturated conditions, atmospheric pressure, and on a vertical flat and polished copper thermal plate. Prepared nanofluids GQDs and N: GQDs based on DI-water maintained their apparent stability for two months. For GQDs nanofluids at an optimal concentration of 500 ppm with a volume ratio of (60:40) DI-water and EG, compared to DI-water, the greatest increase in CHF and HTC is 90.69, 85.011 % and for N: GQDs at a concentration of 500 with a volume ratio (50:50) DI-water and EG, 75.37 and 78.17 % compared to DI-water.

Aminophenylboronic acid-modified nitrogen-doped graphene quantum dots and their applications in lysine sensing based on interplaying fluorescent mechanisms.

Using nitrogen-doped graphene quantum dots (N-GQDs) and 3-aminophenylboronic acid (APBA), a novel fluorescence nanosensorwas developed. This nanosensor exhibits high selectivity and sensitivity for lysine detection. Its sensing mechanism involves the suppression of electron transfer from APBA to the N-GQDs unit, thereby inhibiting photoinduced electron transfer and initiating internal charge transfer. At an optimal pH of 7, the protonated α-amine and ε-amine groups of lysine interact with the amide and boronic acid moieties, respectively. This interaction results in a redshift of fluorescence, substantially enhancing the response signal. A linear response was observed within a concentration range 0.40-3.01μM, with the detection limit being 0.005μM. A similar linear range was also achieved for the determination of lysine in human serum. Density functional theory calculations correlating molecular orbits and geometries support UV-vis and fluorescence findings. Additionally, the nanosensor wassuccessfully applied to detect lysine in living cells and real samples, including milk and honey. For practical application, we construct a lysine-specific sensing platform using a commercial chip (TCS34725) that collects red, blue, and green signals, thereby facilitating the convenient use of the nanosensor. Overall, this study offers new perspectives on the development and application of fluorescent nanosensors for detecting individual amino acids.

Se-vacancy porous ultrathin ZnSe nanosheet/carbon composite for sodium storage via electron beam irradiation strategy

Zinc selenide (ZnSe) is a next-generation anode material due to its high sodium storage capacity. However, the poor conductivity and volume expansion lead to its capacity attenuation and short cycle life. Herein, Se-vacancy porous ultrathin ZnSe nanosheet/carbon composite (ZnSe@NC/N-GQD) is reported as a high-performance anode material for sodium-ion batteries. Organic-inorganic hybrid ZnSe(en)0.5 ultrathin nanosheets with abundant Se vacancies are rapidly prepared by electron beam irradiation for the first time. Using it as a precursor, Se-vacancy carbon-coated porous ultrathin ZnSe nanosheets loaded with nitrogen-doped graphene quantum dots (N-GQDs) are synthesized via carbonization and electrodeposition process. Through the design of ZnSe@NC/N-GQD, the sodium storage performance can be effectively improved by implementing nanostructure engineering (porous ultrathin nanosheet) via organic–inorganic hybrid, defect engineering (Se vacancy) via electron beam irradiation, and carbon composite (amorphous carbon and N-GQD). Consequently, ZnSe@NC/N-GQD delivers a high capacity of 483 mA h g−1 after 200 cycles at 0.5 A g−1, shows an outstanding rate capability of 381 mA h g−1 at 10.0 A g−1, and exhibits an excellent cycling stability of 86 % retention after 2800 cycles at 5.0 A g−1. This work develops a new method to rapidly prepare organic–inorganic nanohybrids, and proposes an innovative design of high-performance ZnSe-based anodes.

Facile synthesis of N-doped graphene quantum dots as a fluorescent sensor for Cr(vi) and folic acid detection.

The development of stable fluorescent sensors for toxic pollutants and drugs is meaningful to the environment and public health. In this work, nitrogen-doped graphene quantum dots (N-GQDs) were facially synthesized by a one-step hydrothermal method using soluble starch and l-arginine as carbon and nitrogen sources in pure water at 190 °C for 4 h. The as-synthesized N-GQDs were well characterized and displayed blue fluorescence emission at 445 nm with excellent pH stability, salt tolerance, thermostability, photobleaching resistance and reproducibility. Moreover, N-GQDs could serve as an "on-off" sensor for selective detection of Cr(vi) and folic acid with low detection limit (0.80 and 2.1 μM), good linear correlation over wide linear range (0-50 μM and 0-200 μM) as well as short response time (<10 s). The practical applications of N-GQDs for Cr(vi) and folic acid detection in actual samples were further investigated and showed acceptable recoveries (92-105%) with relative standard deviations less than 5%. These results indicated that this N-GQDs-based sensor could be a potential alternative for Cr(vi) and folic acid detection in the fields of environmental monitoring and drug analysis.

Tuning optical excitations of graphene quantum dots through selective nitrogen doping

Our research has revealed that the nitrogen doping configuration has a significant impact on the absorption properties and band gap of nitrogen doped graphene quantum dots (NGQDs). By analyzing the composition and character of optical transitions, we have observed that nitrogen doping causes a redistribution of oscillator strength between significant peaks and the emergence of new optical features. These changes lead to broken molecular orbital degeneracies, optical peak splitting, and activation of dark states in the visible to near-infrared (NIR) region. These findings shed light on the mechanisms that govern alterations in the spectral properties of NGQDs within the visible and near-infra red (NIR) absorption bands. Furthermore, selective manipulation of optoelectronic properties via distinct N-doping patterns could pave the way for the development of novel optoelectronic nanodevices and functional materials.

Constructing nitrogen-doped graphene quantum dots embedded in CNT supported layered (Ni0.5Co0.5)3V2O8 self-supporting film for high-performance supercapacitor

To improve the electrochemical performance of positive electrode materials, constructing graded nanostructures is a worthwhile approach. This study successfully synthesized nitrogen-doped graphene quantum dots (NGQD) modified (Ni0.5Co0.5)3V2O8 on a carbon nanotube (CNT) substrate to construct self-supporting electrodes for high-performance supercapacitors. The (Ni0.5Co0.5)3V2O8 nanosheets were successfully wrapped onto the CNT surface through a solution impregnation process, which increased the specific surface area and interlayer spacing of the material. Furthermore, the electrochemical properties of the electrode material underwent significant enhancement due to the synergistic interplay between metal ions and the numerous redox centers. The embedding of the NGQD enriched the materials with active sites and further improved its specific capacity without compromising the structure intergrity of the layer configuration. Using CNT as the substrate ensured the self-supporting nature of the electrode. Consequently, the (Ni0.5Co0.5)3V2O8/NGQD@CNT composite exhibits an ultra-high specific capacitance of 3018.2 F g−1 at 1 A g−1 and 2332 F g−1 at 10 A g−1. The asymmetric supercapacitor constructed with (Ni0.5Co0.5)3V2O8/NGQD@CNT and activated carbon (AC) presented an impressive energy density of 160.2 Wh kg−1 at a power density of 800 W kg−1. After 8000 charge–discharge cycles, the capacity retention rate was 78.5 %, with a Coulo mbic efficiency consistently above 98 %.

Coal derived highly fluorescent N-Doped graphene quantum dots with graphitic and chemisorbed nitrogen

Graphene quantum dots (GQDs) constitute a novel category of quantum dots distinguished by their distinctive properties. The introduction of nitrogen heteroatom in GQD is an effective strategy for tuning its intrinsic properties and band gap toward its optoelectronic application. This work explores the synthesis and characterization of nitrogen-doped graphene quantum dots (N-GQDs) derived from low-cost precursor coal. The synthesized N-GQD contains both graphitic and chemisorbed nitrogen states along with pyrollic and pyridinic nitrogen states which is the key responsible factor for excellent photoluminescence properties. The excitation dependent photoluminescence of the synthesized N-GQD exhibited excellent emission at 520 nm in neutral and basic pH due to the additional conjugation provided by the doped nitrogen on the surface and functional groups as well. The pH dependent photophysical properties support the existence of doped graphitic and chemisorbed nitrogen states which is also well supported by the high resolution N1s XPS peaks at 402 eV (graphitic N) and 406 eV (chemisorbed N/N2). DFT calculations further showed the decrease in fermi energy level by introducing chemisorbed-N. TEM analysis evident the formation of quantum dots with an average diameter of 3 - 7 nm with d-spacing of 0.20 - 0.34 nm. Additionally, the cyclic voltammetry analysis of the synthesized N-GQDs sheds light on the participation of doped nitrogen in redox reactions.

Chicken IgY based electrochemical immunosensor for the detection of bacterial pathogen E. coli in water

On a global scale, approximately 1 in 8 (13.6 %) of worldwide mortalities have been associated with bacterial infections. Therefore, the necessity for rapid and cost-effective diagnostic kits is paramount to accurately diagnose bacterial infections. Besides, the utilization of IgY antibodies emerges as a natural and economical option for effective sensing of pathogens. Notably, electrochemical IgY-based immunosensors amalgamate the inherent specificity of immunoreactions with highly sensitive electrochemical sensors, thereby facilitating the advancement of next generation Point-of-Care (POC) devices. In this work, a label-free IgY-based immunosensor for the detection of E. coli, employing Boron and Nitrogen-doped Graphene Quantum Dots (B, N-doped GQDs) nanomaterial as the electrode interface was successfully devised. This developed immunosensor has demonstrated commendable sensitivity of 0.0395 µA. (CFU/mL)−1 & 0.0491 µA. (CFU/mL)−1 from Cyclic Voltammetry (CV) & Amperometry (Amp) techniques across various E. coli concentrations (0.5 x 101 – 107 CFU/mL) and exhibited exceptional selectivity of < 5.88 %, thereby ensuring precise E. coli detection while mitigating interference from other agents. Moreover, real sample analysis with the developed sensor displayed exemplary recoveries, affirming its efficacy in detecting E. coli. The immunosensor’s promising results in terms of its figures-of-merit underscore the potential diagnostic utility of IgY in E. coli screening bacterial sensing applications.

Preparation of SnOx/N-GQDs composites with oxygen-rich vacancies for enhanced photoelectric properties

SnOx with oxygen-rich vacancies and SnOx/N-GQDs (Nitrogen-doped graphene quantum dots) composites were prepared by high temperature annealing and hydrothermal method, respectively. The annealing process introduced a large number of oxygen vacancies and produced defect energy levels in the band gap. The existence of the defect level effectively reduced the band gap of SnOx, enlarged the optical absorption range, and improved the light utilization. The introduction of N-GQDs also improved the carrier density and electron transport rate, and extended the carrier lifetime (τ = 7.44 ms). I-T (Transient photocurrent response) analysis results showed that when the mass ratio of Sn/SnO2 was 1:4 and N-GQDs doping content was 1 wt%, the transient photocurrent response of SnOx/N-GQDs could reach 5.51 × 10−4 A/cm2, which was 25 times higher than that of pure SnO2, and the photocurrent response value maintained 80.1 % within 500 s. EIS (Electrochemical impedance) and M-S (Mott-Schottky) analyses indicated that the appropriate amount of oxygen vacancies and N-GQDs were beneficial to reducing the charge transport resistance, inhibiting the electron-hole pair recombination, and increasing the carrier density of SnOx. The results show that SnOx/N-GQDs composites present the improved photoelectric properties with the addition of oxygen vacancies and N-GQDs, which provides a new idea for promoting the properties of semiconductors.

Green emissive nitrogen-doped graphene quantum dots for fluorescence off–on probing methimazole via palladium (II) mediated assay

A palladium ion ([Formula: see text])-mediated nitrogen-doped graphene quantum dots (N-GQDs/Pd[Formula: see text]) was developed as a fluorescent “off–on” probe for methimazole (MZ). Fluorescent N-GQDs interact with Pd[Formula: see text] through coordination interactions, leading to weak photoluminescence (PL) owing to the quenching ability of Pd[Formula: see text]. Upon introducing MZ, the stronger binding between N-GQDs and Pd[Formula: see text] destroys the N-GQDs/Pd[Formula: see text] complex and restores the PL of N-GQDs. The probe exhibits a linear PL response to MZ concentrations from 3.0 to 50.0 [Formula: see text]M with a detection limit down to 4.5 nM. In addition, the probe has been used to detect MZ in real samples including natural water sources and human urine.

Design of Polymeric Nanoparticles for Theranostic Delivery of Capsaicin as Anti-Cancer Drug and Fluorescent Nitrogen-Doped Graphene Quantum Dots.

In recent years, multifunctional nanocarriers that provide simultaneous drug delivery and imaging have attracted enormous attention, especially in cancer treatment. In this research, we designed a biocompatible fluorescent multifunctional nanocarrier for the co-delivery of capsaicin (CPS) and nitrogen-doped graphene quantum dots (N-GQDs) using the pH sensitive amphiphilic block copolymer (poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone), PEtOx-b-PCL). The effects of the critical formulation parameters (the amount of copolymer, the concentration of poly(vinyl alcohol) (PVA) as a stabilizing agent in the inner aqueous phase, and volume of the inner phase) were evaluated to achieve optimal nanoparticle properties using Central Composite Design (CCD). The optimized nanoparticles demonstrated a desirable size distribution (167.8±1.4nm) with a negative surface charge (-19.9±0.4) and a suitable loading capacity for capsaicin (70.80±0.05%). The CPS & N-GQD NPs were found to have remarkable toxicity on human breast adenocarcinoma cell line (MCF-7). The solid fluorescent signal was acquired from cells containing multifunctional nanoparticles, according to the confocal microscope imaging results, confirming the significant cellular uptake. This research illustrates the enormous potential for cellular imaging and enhanced cancer therapy offered by multifunctional nanocarriers that combine drug substances with the novel fluorescent agents. This article is protected by copyright. All rights reserved.

Nitrogen-Doped Graphene Quantum Dots Incorporated into MOF-Derived NiCo Layered Double Hydroxides for Nonenzymatic Lactate Detection in Noninvasive Biosensors

Nitrogen-Doped Graphene Quantum Dots Incorporated into MOF-Derived NiCo Layered Double Hydroxides for Nonenzymatic Lactate Detection in Noninvasive Biosensors

An ammonia-sensitive fluorescence sensor based on polyvinyl alcohol-graphene quantum dots/halloysite nanotubes hybrid film for monitoring fish freshness

A fluorescent hybrid film composed of nitrogen-doped graphene quantum dots (N-GQDs) loaded on halloysite nanotubes (HNTs) (N-GQDs/HNTs nanocomposite) as a sensitive element and polyvinyl alcohol (PVA) as a film-forming matrix was designed for freshness detection. The PVA-N-GQDs/HNTs hybrid film exhibited significantly enhanced fluorescence attributed to the loading of N-GQDs onto the surface of HNTs through electrostatic interactions and hydrogen bonding, effectively reducing their aggregation. The fluorescence of the hybrid film could be quenched by ammonia via photoinduced electron transfer (PET), with good linearity in the range of 20 ppm to 500 ppm ammonia and a limit of detection (LOD) of 0.63 ppm. In addition, the hybrid film was applied to monitor the freshness of seawater fish and freshwater fish stored at refrigeration and room temperature to evaluate the practicality of this approach. The developed hybrid film showed promise for nondestructive and on-site monitoring of fish spoilage.

A magnetic imprinted polymer nano-adsorbent with embedded quantum dots and mesoporous carbon for the microextraction of triazine herbicides

A magnetic molecularly imprinted polymer (MMIP) adsorbent incorporating amino-functionalized magnetite nanoparticles, nitrogen-doped graphene quantum dots and mesoporous carbon (MIP@MPC@N-GQDs@Fe3O4NH2) was fabricated to extract triazine herbicides from fruit juice. The embedded magnetite nanoparticles simplified the isolation of the adsorbent from the sample solution. The N-GQDs and MPC enhanced adsorption by affinity binding with triazines. The MIP layer provided highly specific recognition sites for the selective adsorption of three target triazines. The extracted triazines were determined by high-performance liquid chromatography (HPLC) coupled with diode-array detection (DAD). The developed method exhibited linearity from 1.5 to 100.0 µg L−1 with a detection limit of 0.5 µg L−1. Recoveries from spiked fruit juice samples were in the range of 80.1– 108.4 %, with a relative standard deviation of less than 6.0 %. The developed MMIP adsorbent demonstrated good selectivity, high extraction efficiency, ease of fabrication and use, and good stability.

Nitrogen-Doped Graphene Quantum Dots for Efficient Detection of Toxic Gas

Nitrogen-Doped Graphene Quantum Dots for Efficient Detection of Toxic Gas