Nitrogen-doped Graphene Quantum Dots Research Articles

Tunable Photoluminescent Nitrogen-Doped Graphene Quantum Dots at the Interface for High-Efficiency Perovskite Solar Cells

Tunable Photoluminescent Nitrogen-Doped Graphene Quantum Dots at the Interface for High-Efficiency Perovskite Solar Cells

Operando time and space-resolved liquid-phase diagnostics reveal the plasma selective synthesis of nanographenes.

Coupling atmospheric-pressure low-temperature plasmas to electrochemical reactors enables the generation of highly reactive species at plasma-liquid interfaces. This type of plasma electrochemical reactor (PEC) has been used to synthesize fluorescent nitrogen-doped graphene quantum dots (NGQDs), which are usable for multifunctional applications in a facile, simple, and sustainable way. However, the synthesis mechanism remains poorly understood, as well as the location of synthesis. To research these issues, we present an in situ diagnostics study on liquid phase chemistry during the PEC synthesis of NGQDs from chitosan. Monitoring of the photoluminescence and UV-VIS absorption at different depths in the reaction medium during plasma treatment reveals that the NGQD production initiates at the plasma-liquid interface but its completion and/or accumulation occurs at a few millimetres depth below the interface, where the liquid ceases to flow convectively, as determined by particle image velocimetry. Our study provides insights into the plasma synthesis of fluorescent GQDs/NGQDs from carbon precursors that may prove useful for achieving the scalability of PEC processes up to continuous-flow or array reactors.

Nitrogen-doped graphene quantum dots as a support for Ni–Au nanoparticles: efficient electrocatalysts for ethanol and formate fuel cells using hydrogen peroxide as an oxidant

The obtained results from half-cell and single fuel cell configurations confirm the superiority of the Ni1Au1-NGQD electrocatalyst towards the oxidation of both fuels (ethanol and formate) compared to the two other electrocatalysts.

Hydroquinone colorimetric sensing based on core–shell structured CoFe2O4@N-GQDs@CeO2 nanocomposites as oxidase mimics

The core–shell structured CoFe2O4@N-GQDs@CeO2 nanocomposites were successfully synthesized by co-precipitation method, and CeO2 was uniformly dispersed on the shell layer with the help of nitrogen-doped graphene quantum dots (N-GQDs).

Non-metallic nitrogen-doped graphene quantum dots coupled with g-C3N4 achieve efficient photocatalytic performance

Photocatalysis has been prominently featured as a promising technology for solving environmental problems and energy crises. The incorporation of supported non-metallic cocatalysts is paramount in significantly augmenting the efficiency and performance of semiconductor photocatalysis. N-GQD/CN was successfully prepared and showed excellent performance in terms of light-absorbing capacity, carrier separation efficiency and visible-light driving. The findings underscore the exceptional photocatalytic prowess of the 0.02 wt.% N-GQD/CN composites, particularly in the degradation of RhB, HCl-TC, and BPA under visible light irradiation. The 0.02 wt.% N-GQD/CN composite could eliminate 91.2 % RhB in 90 min, remove 72.4 % of the HCl-TC in 180 min, and degrade 47.9 % of the BPA in 4 h. All of the activities of the 0.02 wt.% N-GQD/CN was superior to that of the monomer g-CN. This elevated photocatalytic performance can be predominantly attributed to the N-GQDs acting as co-catalysts. These N-GQDs possess substantial specific surface areas, effectively enhancing light absorption and facilitating synergistic interactions with g-CN nanosheets. Exploring the utility of N-GQD/CN using ionic interference and pH photocatalysis experiments. The present work provides a rational strategy for designing 0D/2D photocatalysts with improved visible light activity for environmental applications.

Design 3D hierarchical flower-shaped NH4V4O10/N-GQDs/cellulose nanocomposites as electrode materials for supercapacitor application

In recent years, materials based on carbon dioxide compounds and transition metal oxide nanocomposites with desirable synergistic properties have attracted a great deal of attention as potential candidates for high efficiency electrochemical supercapacitors. Our work presents the development of high-performance supercapacitor electrodes using the 3D-flower-shaped NH4V4O10 microstructures combined with nitrogen-doped graphene quantum dots and cellulose (NHV-NGC). A simple in-situ hydrothermal synthesis was used to synthesize the NHV-NGC. Various methods are employed to characterize the physiochemical properties of the synthesized composite. In addition, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to examine the electrochemical behavior of the materials as designed. According to the GCD profiles, the optimized NHV-NGC electrode has a specific capacitance of 1852.9 Fg−1 (878 Cg−1) at a current density of 2 Ag−1 in 3.0 M KOH aqueous electrolyte. As well, the specific capacitance of the NHV-NGC electrode is about three times greater than the specific capacitance of the NHV electrode (631 Fg−1 (300 Cg−1). The electrode shows a high retention specific capacitance of 83.5% after 3000 charge-discharge cycles at a scanning rate of 100 mVs−1. Additionally, the fabricated supercapacitor exhibits an energy density of 57.8 Whkg−1 at a power density of 473.9 Wkg−1. Based on the GCD plots of the optimized NHV-NGC electrode, the specific capacitance was calculated to be 1852.9, 1224.9, 981.8, and 286.2 Fg−1 (878, 587.1, 466, and 137.1 Cg−1) at 2, 3, 4, and 5 Ag−1, respectively. Synergistic effects between the three-dimensional flower-shaped NH4V4O10 microstructures, nitrogen-doped graphene quantum dots and cellulose in the nanocomposites structure resulted in extraordinary conductivity, excellent electrochemical performance, and the development of suitable routes for rapid ion/electron transport via reversible redox reactions. In terms of electrochemical performance, the NHV-NGC nanocomposite is proving to be a promising candidate for energy storage devices such as supercapacitors.

A magnetic adsorbent of nitrogen-doped graphene quantum dots, zinc metal-organic framework and molecularly imprinted polymer to extract phenylureas

A highly selective composite nano-sorbent was designed and fabricated for the extraction and enrichment of phenylureas. The nano-sorbent was composed of nitrogen-doped graphene quantum dots (N-GQDs), a zinc metal-organic framework (IRMOF-1) and magnetite nanoparticles incorporated in molecularly imprinted polymer (MIP). The fabricated nano-sorbent was characterized and applied to extract and enrich three phenylureas in a dispersive magnetic solid-phase extraction (d-MSPE) process. The developed method was highly sensitive and detected the target phenylureas at trace levels. The linear range was from 1.0 to 150 µg L−1 and the limit of detection was 1.0 µg L−1. The large specific surface area of the nano-sorbent produced highly efficient adsorption. When applied to extract phenylureas in vegetable samples, recoveries were in the range of 80.2–95.8% with relative standard deviations lower than 8.0%. The developed nano-sorbent not only exhibited highly selective and efficient extraction but also good stability which can be reused four times, and ease of fabrication. The developed strategy can also be modified for the extraction and determination of other organic compounds in various complex samples.

Efficient green light-based photocatalytic removal of bilirubin by a biocompatible nanocomposite of nitrogen doped graphene quantum dots/Au

Nitrogen-doped graphene quantum dots/Au (NGQDs/Au) nanocomposite was synthesized by hydrothermal method followed by a photochemical route. The gram-scale nitrogen-doped graphene quantum dot was synthesized by using hydrothermal method from urea and citric acid as a precursor. By adding HAuCl4 to the prepared sample, the nitrogen-doped graphene quantum dots/Au nanocomposite was made in a straightforward photochemical process. The synthesized composite was utilized directly as a biocompatible photocatalyst for bilirubin degradation under green light irradiation.The nanocomposite was characterized using FESEM, Raman, XRD, TEM, UV–Vis spectroscopy, and PL. The quantum yield of the nanocomposite was calculated. The role of surface plasmon resonance (SPR) of Au nanoparticles in reduction of the quantum yield and quantum yield effect on the photodegradation process was investigated. The photocatalytic degradation efficiency of bilirubin in presence of the synthesized nanocomposite was measured to be nearly 74.7 % after 100 min green light irradiation, which is 5 times more than blue light used in clinical phototherapy without any photocatalyst. The optical analysis results reveal that the doping of nitrogen in GQDs and compositing with gold could accelerate the suppression of charge carrier's recombination. The future application of biocompatible photocatalysts in jaundice treatment under the green light irradiation was also approved in this research.

Nitrogen-doped graphene quantum dots for extensive production of hydrogen: A hybrid density functional study

Photocatalytic water splitting has emerged as a promising approach for storing solar energy in the form of chemical energy, which can solve the energy crisis and environmental issues. Herein we have explored the potentiality of nitrogen-doped graphene quantum dots for solar-driven hydrogen evolution. The motivation behind applying quantum dots as a photocatalyst is to utilize a major portion of the solar energy spectrum to enhance hydrogen yield. The alignment of frontier molecular orbitals (FMOs) in comparison to the redox potential of water reveals that all the studied quantum dots are eligible for photocatalytic hydrogen evolution. The energy gap between FMOs varies with the size of quantum dots from 3.01 to 2.32 eV, showing absorption of light in the visible range. The Gibbs free energy calculation shows that the formation of intermediate species is energetically unfavorable without exposure to light at pH=7, except for hydrogen adsorption. However, the photogenerated electron and hole drive the steps of oxygen and hydrogen evolution by making those a downhill process. The optical absorption spectra show that all the studied quantum dots absorb visible light.

Fabrication of Ti3+/N/B-TiO2@NGQDs composite photocatalyst with significantly enhanced visible light catalytic activity

A two-step hydrothermal process was used to successfully create Ti3+, N, and B co-doped TiO2 modified with nitrogen doped graphene quantum dots (Ti3+/N/B-TiO2@NGQDs (TNBTN)) composite photocatalyst for photodegradation of bisphenol A (BPA) and methyl orange (MO) under visible-light illumination. The prepared TNBTN composite demonstrated significantly enhanced visible light catalytic performance. Especially, the apparent rate constant of BPA degradation with TNBTN was approximately 56.9 times that of pure TiO2, which was attributed to broader visible light absorbance and faster transmission and separation of photoinduced charge. In addition, the mechanism of BPA and MO degradation with TNBTN was distinct.

Enhancing photoluminescence performance and pH photostability of nitrogen-doped graphene quantum dots via surface-passivated by polyethylene glycol

The photoluminescence (PL) properties of nitrogen-doped graphene quantum dots (NGQDs) are highly dependent on reaction parameters. In this study, we developed new and fast protocols to surface passivate NGQDs with polyethylene glycol (PEG) using microwave irradiation. The resulting NGQDs-PEG exhibited highly stable PL with an emission peak at 424 nm when excited at 325 nm. The PL intensity of NGQDs with PEG increased with the volume of capping agents due to the enhancing luminescence effect of the surface functional group of polyethylene glycol. The optimal PEG amount of 2 wt% was found to improve the PL effect of NGQDs. Interestingly, the surface passivation of NGQDs with PEG enabled the NGQDs to exhibit strong PL performance across varying pH environments (from acidic to alkaline), addressing the issue of quenching of quantum dots in biological environments. Our research also focused on the ultrafast synthesis of NGQDs, where process parameters such as power value, catalyst volume, and reaction time were identified as important factors affecting NGQD luminescence. Our results showed that the optimal microwave power was 640 W, lower than that used in previous synthesis methods. Increasing the volume of catalyst promoted faster NGQD formation. The optimal reaction time was found to be 5 min, catalyst volume of 5 ml resulted in the highest PL intensity of NGQDs.

Insights on salting-out triggering aggregation-induced emission in nitrogen-doped graphene quantum dots

A straightforward methodology for obtaining Nitrogen-doped Graphene Quantum Dots (N-GQDs) with aggregation-induced emission (AIE) using salting-out purification processes is presented in this work. Various salts, including NaCl at concentrations of 50 mM, were found to be effective for stratification of graphene-based materials (GBMs) by salting-out treatments. These salts were shown to be safer, more cost-effective, and environmentally sustainable alternatives to (NH4)2SO4 reported in previous works. Remarkably, this method demonstrated the ability to promote the self-assembly of N-GQDs into stable J-aggregates-like arrays with an average fluorescence decay time of ca. 4 ns and absolute quantum yield with values of 3.5 % and 6.9 % for 100 mM and 2 M, respectively. In contrast to a typical quenching effect caused by π-stacking, these arrays exhibited aggregation-induced emissions, as evidenced by the presence of new excitation and emission bands at 532 and 600 nm, respectively. The scalability of the process, along with the absence of additional purification steps, renders these results of great scientific and technological interest. Furthermore, the modulable fluorescence, size, and stability of these GBMs suggest their potential application in energy cells, sensors, and biomedical imaging.

Plasma-engineered GQD-inorganic membranes with tunable interactions for ultrahigh-efficiency molecular separations

Ultrahigh-efficiency molecular separation (MS) membranes with tunable size-selective molecular separation, chemical-mechanical robustness, and long-term stabilities are useful for fundamental studies and applications. However, conventional MS membranes are hampered by the problems of uncontrolled molecular interactions, low separation efficiency, and energy and time-consuming fabrications. Here, we show an effective plasma engineering of nitrogen doped graphene quantum dot (NGQD)-inorganic nanocomposites composed with NGQDs and alumina-based hollow fibers (AHFs) with controlled properties and tunable local physicochemical environments for size-selective molecular separations. Detailed spectroscopic study and membrane characterization suggest that the plasma-synthesized NGQDs with defined zero-dimensional (0D) carbon-based sp2 hybridization, tunable nitrogen dopants and surface functional groups can affect the properties of the GQD-inorganic nanocomposites, therefore controlling molecular separation between the nanocomposites and molecules with different dye molecular weights (MWs). Moreover, the NGQDs can further induce the formation of nanochannel and control the nanopore structures of the nanocomposites, leading a significant molecular separation performance with a high 92.68 separation factor (S) for the mixed molecules with a 200 Da MW difference and a high water permeability up to 36.64 L m−2 h−1 bar−1. Our work provides a step for the engineering of functional nanocomposites for fundamental studies of molecular transport and emerging applications including catalysis, green energy, optoelectronics, biomedical and environmental applications.

Application of surface nitrogen-doped graphene quantum dots in the sensing of ferric ions and glutathione: Spectroscopic investigations and DFT calculations

Developing a sensing platform that can quickly and accurately measure glutathione (GSH) is crucial for the early detection of various human diseases. GQDs have shown great potential in many technological and biological applications. This study focused on synthesizing nitrogen-doped GQDs (NGQDs) with stable blue fluorescence using a simple and easy hydrothermal method in one step. The bamboo fiber was used as the green source for this synthesis. The NGQDs had a tiny particle size of 4.7 nm and emitted light at 405 nm when excited. They displayed a remarkable quantum yield of 40.36 % and were effectively used as fluorescent probe to specifically detect Fe3+. The energy transfer mechanism led to the NGQDs' fluorescence being deactivated by Fe3+ ions (turn- “off”). However, with the addition of GSH to the system, the fluorescence intensity of NGQDs was reactivated (turn- “on”). Thus, a fluorescence turn “off–on” system was developed for the sensitive detection of Fe3+ and GSH. Using density functional theory (DFT), it was theoretically calculated that the surface of the fabricated NGQDs possess lone pairs of electrons on oxygens and doped nitrogen causing a photo-induced electron transfer (PET) process to occur. This PET process was suppressed previously owing to complex formation between oxygen atoms of modeled structure and ferric ions. The sensing platform displayed a sensitive response to Fe3+ in the 1–1000 μM range with LOD of 34 nM and GSH in the range of 1–50 μM, with a detection limit of 45 nM. Furthermore, the NGQDs exhibited high selectivity towards Fe3+ and GSH over other electrolytes and biomolecules. Additionally, the probe exhibited non-cytotoxicity and was practically applicable for the detection of GSH in HeLa cells.

Carbon-based light addressable potential sensor based on nitrogen-doped graphene quantum dots for detection of low-density lipoprotein

Cardiovascular diseases have become the number one killer of human health. Early diagnosis and treatment of cardiovascular diseases can effectively improve the treatment effect and reduce the disease death rate. As an important marker of cardiovascular disease, Low-Density Lipoprotein (LDL) can be used for the early detection of cardiovascular disease. In this study, a novel carbon-based Light Addressable Potentiometric Sensor (C-LAPS) for determination LDL has been constructed based on o-phenylenediamine modified nitrogen-doped graphene quantum dots/reduce graphene oxide (OPD@NGQDs/rGO) photosensitive layer. The OPD@NGQDs/rGO photosensitive layer has excellent photoelectric conversion efficiency, large specific surface area and good biocompatibility to enhance the response signal. For the determination LDL by the C-LAPS system, LDL binding to LDL aptamer causes a change in the surface potential of the photosensitive layer, producing a response signal that can be detected by the I-V curve. Under optimal conditions, the C-LAPS had a good linear relationship with LDL concentration in the range of 0.01 μg/mL- 0.15 μg/mL. The sensitivity was 1819 mV/µg·mL−1 and the limit of detection (LOD) was 6.43 ng/mL (S/N = 3). In addition, the C-LAPS showed good specificity, reproducibility, stability and satisfactory relative error for detecting LDL in human serum samples. Therefore, the C-LAPS has good performance and demonstrates potential clinical value.

Nitrogen-Doped Graphene Quantum Dot-Passivated δ-Phase CsPbI3: A Water-Stable Photocatalytic Adjuvant to Degrade Rhodamine B.

Inorganic halide perovskite CsPbI3 is highly promising in the photocatalytic field for its strong absorption of UV and visible light. Among the crystal phases of CsPbI3, the δ-phase as the most aqueous stability; however, directly using it in water is still not applicable, thus limiting its dye photodegradation applications in aqueous solutions. Via adopting nitrogen-doped graphene quantum dots (NGQDs) as surfactants to prepare δ-phase CsPbI3 nanocrystals, we obtained a water-stable material, NGQDs-CsPbI3. Such a material can be well dispersed in water for a month without obvious deterioration. High-resolution transmission electron microscopy and X-ray diffractometer characterizations showed that NGQDs-CsPbI3 is also a δ-phase CsPbI3 after NGQD coating. The ultraviolet-visible absorption spectra indicated that compared to δ-CsPbI3, NGQDs-CsPbI3 has an obvious absorption enhancement of visible light, especially near the wavelength around 521 nm. The good dispersity and improved visible-light absorption of NGQDs-CsPbI3 benefit their aqueous photocatalytic applications. NGQDs-CsPbI3 alone can photodegrade 67% rhodamine B (RhB) in water, while after compositing with TiO2, NGQDs-CsPbI3/TiO2 exhibits excellent visible-light photocatalytic ability, namely, it photodegraded 96% RhB in 4 h. The strong absorption of NGQDs-CsPbI3 in the visible region and effective transfer of photogenerated carriers from NGQDs-CsPbI3 to TiO2 play the key roles in dye photodegradation. We highlight NGQDs-CsPbI3 as a water-stable halide perovskite material and effective photocatalytic adjuvant.

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).

Plasma-engineered graphene quantum dot-based nanocomposites as smart CO2-philic membranes with extremely high separation performance

Carbon dioxide (CO2) capture, separation and utilization with membrane-based technologies are important for the development of carbon neutral society. However, conventional membranes are facing the difficulties of energy-consuming fabrication, expensive and toxic chemicals, and low efficient performance. Here, we report the CO2-Philic, optical-active nitrogen-doped graphene quantum dot (NGQD)-embedded polyether-block-amide (Pebax)-based membranes for highly efficient CO2 separation and sensitive on-line CO2 detection. The NGQDs with abundant surface functionalities are synthesized from bioresource chitosan using a customized microplasma process. The plasma-engineered NGQDs with defined zero-dimensional (0D) geometry, surface functional groups and nitrogen dopants can enhance the CO2-philicity for CO2 capture and separation. Moreover, the NGQDs can not only generate the angstrom (Å)-level channels, but also tune the morphologies, pore structures, crystallinities of the nanophases, and functional groups of the Pebax-based membranes, leading to extremely high CO2 separation performance with a 415 Barrer CO2 permeability and a 125 CO2/N2 selectivity. Furthermore, the stable solid-state PL emission of the fabricated GQD@Pebax membranes enables the sensitive on-line monitoring of CO2 concentrations during the CO2 separation. Our work provides an understanding of the CO2 capture and transport with nanomaterials-based composites and a plasma engineering of advanced functional materials for clean energy, environmental and biomedical applications.

A melanin-integrated graphene quantum dots embedded molecularly imprinted polymer: A nano-fluorescence sensing probe for trace determination of prometryn

A nanocomposite fluorescence sensing probe was successfully designed and utilized for the ultrasensitive and highly selective determination of prometryn. The nanoprobe incorporated melanin nanoparticles, as an affinity material, and nitrogen-doped graphene quantum dots (N-GQDs) as fluorophores in molecularly imprinted polymers (MIP). Multiple techniques were employed to characterize the synthesized essential precursors and MIP fluorescent nanoprobe. The developed nanoprobe was then applied to detect prometryn, demonstrating linearity from 1.0 to 100.0 μg kg−1 with a limit of detection of 0.63 μg kg−1. When used to determine prometryn in real samples, the developed nanoprobe achieved recoveries from 92.4 % to 102.8 % with RSDs less than 5.4 %. The simplicity, reliability, selectivity and sensitivity of the proposed sensor indicated that the combination of MIP and eco-friendly materials produced an excellent fluorescent sensor for the detection of trace analytes.

Nitrogen-Doped Graphene Quantum Dots as Electrochemiluminescence-Emitting Species for Sensitive Detection of KRAS G12C Mutation via PET-RAFT.

The levels of KRAS G12C point mutation is recognized to be closely related to the earlier diagnosis of non-small cell lung cancer (NSCLC). Here, based on nitrogen-doped graphene quantum dots (NGQDs) and photo-induced electron/energy transfer reversible addition-fragment chain transfer (PET-RAFT) signal amplification strategy, we fabricated a novel electrochemiluminescence (ECL) biosensor for the detection of KRAS G12C mutation for the first time. NGQDs as ECL-emitting species with cathodic ECL were prepared by a simple calcination method. Firstly, KRAS G12C mutation DNA, i. e., target DNA (tDNA), was captured by specific identification with hairpin DNA (hDNA). Then, PET-RAFT was initiated by blue light, and large numbers of monomers were successfully polymerized to form controllable polymer chains. Lastly, massive NGQDs was introduced via amidation reaction with N-(3-aminopropyl)methacrylamide hydrochloride (APMA), which significantly amplified the ECL signal intensity. Under optimal conditions, this biosensor achieved a good linear relationship between ECL intensity and logarithm of the levels of KRAS G12C mutation in the range from 10 fM to 10 nM. Moreover, this strategy exhibited high selectivity and excellent applicability for KRAS G12C mutation detection in the serum samples. Therefore, this biosensor has great potential in clinical diagnosis and practical application.