Nitrogen-doped Graphene Research Articles

Three-dimensional nitrogen-doped graphene quantum dot/Ag leaf/Cu2O-Cu trunk/nickel foam nanocomposites as ultra-high-efficiency cathode electrocatalysts for hydrogen evolution reaction applications

In this study, we developed a three-dimensional (3D) nitrogen-doped graphene quantum dot (NGQD)/Ag leaf/Cu₂O-Cu trunk/nickel foam (NF) structure as a high-performance electrocatalyst for hydrogen evolution reaction (HER) applications. This novel structure exhibited a high surface area, abundant electrochemically active sites, and efficient electronic transmission networks. In alkaline solution, the proposed structure demonstrated an overpotential of 112 mV at a current density of 10 mA/cm2, along with a low Tafel slope of 28 mV dec−1, indicating excellent HER activity. Furthermore, the structure exhibited stability over 100 h during durability testing. Overall, this innovative structure experimentally confirms that Cu-based materials can serve as efficient electrocatalysts for HER applications.

Adsorption and Sensing Performance of Transition Metal Decorated Graphene Quantum Dots for AsH3, NH3, PH3, and H2S.

We have conducted a systematic study employing density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) to explore the gas sensing capabilities of nitrogen-doped single vacancy graphene quantum dots (SV/3N) decorated with transition metals (TM = Mn, Co, Cu). We have studied the interactions between TM@SV/3N and four different target gases (AsH3, NH3, PH3, and H2S) through the computation of adsorption energies, charge transfer, noncovalent interaction, density of states, band gap, and work function for 12 distinct adsorption systems. Our comprehensive analysis included an in-depth assessment of sensors' stability, sensitivity, selectivity, and reusability for practical applications. Our findings indicate that the Co@SV/3N surface strongly interacts with PH3, with the highest adsorption energy (-1.15 eV). It shows remarkable sensitivity and selectivity toward PH3, making it a promising candidate for PH3 gas sensing applications. Similarly, Mn@SV/3N exhibits high sensitivity and selectivity toward NH3, positioning it as a suitable candidate for NH3 gas sensing applications. We believe this study will provide valuable theoretical guidance for developing TM@SV/3N-based gas sensors.

Carbon-based light addressable potential aptasensor based on the synergy of C-MXene@rGO and OPD@NGQDs for low-density lipoprotein detection.

Anovel carbon-based light-addressable potentiometric aptasensor (C-LAPS) was constructed for detection low-density lipoprotein (LDL) in serum. Carboxylated Ti3C2 MXene @reduced graphene oxide (C-MXene@rGO) was used as interface and o-phenylenediamine functionalized nitrogen-doped graphene quantum dots (OPD@NGQDs) as the photoelectric conversion element. The photosensitive layers composed of OPD@NGQDs/C-MXene@rGO exhibit superior photoelectric conversion efficiency and excellent biocompatibility, which contribute to an improved response signal. When LDL reacts with the LDL aptamer (LDLApt) immobilized on the photosensitive layers to form LDL-LDLApt complexes, the reaction process can induce the modification of the surface potential in the photosensitive layer, leading to potential shift observed through the I-V curves. The experimental conditions were successfully optimized with few planned tests by applying the Box-Behnken design and response surface methodology aspects of the Design-Expert software. Under the optimal condition, the potential shift had a linear relationship with concentrations of LDL from 0.02 to 0.30μg/mL. The limit of detection (LOD) was 5.88ng/mL (S/N = 3) and the sensitivity was 315.20mV/μg·mL-1. In addition, the LDL C-LAPS demonstrated excellent specificity, reproducibility, and stability in detecting LDL. Thesensor performed well in quantifying LDL in real samples. Therefore, the LDL C-LAPS has the potential for clinical applications.

What Is the "Other" Site in M-N-C?

Single metal atoms embedded in nitrogen-doped graphene (M-N-C) have emerged as a promising catalyst for a wide variety of reactions. In addition to the pyridinic site, there is another site responsible for the catalytic activity, but its structure is under debate. Here, we resolve its structure using first-principles calculations. Using Fe-N-C as a representative example, we systematically explore numerous possible structures and discover a new moiety with comparable energy to the pyridinic. This moiety features a hybrid coordination environment between pyridinic and porphyrinic and is located at the edge of graphene sheets or pores. We further calculate its X-ray absorption spectrum, catalytic thermodynamics for oxygen reduction reaction (ORR), and stability under ORR conditions, all of which support its existence. Lastly, we show that this site also exists in other M-N-C with different M elements. This study uncovers a new and important structure in M-N-C and paves a critical step toward site engineering for improved catalytic performance.

Study on the Synthesis and Electrochemical Properties of Nitrogen-Doped Graphene Quantum Dots

Nitrogen-doped graphene quantum dots (N-GQDs) are widely used in biosensing, catalysis, and energy storage due to their excellent conductivity, high specific surface area, unique quantum size effects, and optical properties. In this paper, we successfully synthesized N-GQDs using a facile hydrothermal approach and investigated the effects of different hydrothermal temperatures and times on the morphology and structure of N-GQDs. The results indicated that the size of N-GQDs gradually increased and they eventually aggregated into graphene fragments with increasing temperature or reaction time. Notably, N-GQDs synthesized at 180 °C for 6 h exhibited the most uniform size, with an average diameter of approximately 3.48 nm, a height of 5–6 graphene layers, as well as favorable fluorescence properties. Moreover, the surface of N-GQDs contained abundant oxygen- and nitrogen-containing functional groups, which could provide numerous active sites for electrode reactions. The assembled electrode exhibited typical pseudocapacitive behavior with exceptional electrochemical performance, achieving a specific capacitance of 102 F g−1 at a current density of 1 A g−1. In a 10,000-cycle test, the electrode demonstrated excellent cycling stability with a capacitance retention rate of 78.5%, which laid the foundation for practical application of the electrode. This work successfully applied N-GQDs in supercapacitors, offering new insights into their development for the energy storage field.

Exploring the electronic and mechanical properties of the recently synthesized nitrogen-doped amorphous monolayer carbon.

The recent synthesis of nitrogen-doped amorphous monolayer carbon (NAMC) opens new possibilities for multifunctional materials. In this study, we have investigated the nitrogen doping limits and their effects on NAMC's structural and electronic properties using density functional-based tight-binding simulations. Our results show that NAMC remains stable up to 35% nitrogen doping, beyond which the lattice becomes unstable. The formation energies of NAMC are higher than those of nitrogen-doped graphene for all the cases we have investigated. Both undoped MAC and NAMC exhibit metallic behavior, although only MAC features a Dirac-like cone. MAC has an estimated Young's modulus value of about 410 GPa, while NAMC's modulus can vary around 416 GPa depending on nitrogen content. MAC displays optical activity in the ultraviolet range, whereas NAMC features light absorption within the infrared and visible ranges, suggesting potential for distinct optoelectronic applications. Their structural thermal stabilities were addressed through molecular dynamics simulations. MAC melts at approximately 4900 K, while NAMC loses its structural integrity for temperatures ranging from 300 K to 3300 K, lower than graphene. These results point to potential NAMC applications in flexible electronics and optoelectronics.

Electrochemical paper-based sensor based on molecular imprinted polymer and nitrogen-doped graphene for tetracycline determination

In this work, an electrochemical paper-based analytical device (ePAD) based on molecular-imprinted polymer (MIP) and nitrogen-doped graphene (NG) was developed for sensitive electrochemical detection of tetracycline in wastewater. The NG was in-situ synthesized on the paper-based screen-printed carbon electrode (pSPCE) by potentiostatic method to improve the conductivity of the sensor. Subsequently, the MIP were electropolymerized on NG using o-phenylenediamine (oPD) as a functional monomer and tetracycline (TC) as template molecule by cyclic voltammetry (CV) to deliver the specific recognition of TC. The electrode modification process was highly controllable, and the detection efficiency was improved. The electrochemical properties of MIP/NG/ePAD were evaluated by CV, differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the fabricated ePAD sensor showed a good linear relationship with TC concentration ranging from 5 × 10−9 to 1 × 10−5 mol/L with a correlation coefficient (R2) of 0.995 and a detection limit of 3.29 × 10−9 mol/L. The ePAD sensor was successfully applied to TC detection in real water samples with satisfied recoveries from 94.0 % to 106.9 %. The low-cost, portable, high specificity, and reliable ePAD sensor proposed here has promising potential for application in point-of-care testing (POCT) in environmental monitoring.

Unveiling the impact of nitrogen-doped graphene quantum dots on improving the photocatalytic performance of CuWO4 nanocomposite

Unveiling the impact of nitrogen-doped graphene quantum dots on improving the photocatalytic performance of CuWO4 nanocomposite

Theoretical studies of nitrogen-doped graphene loaded transition metal single-atom catalysts for electrochemical CO reduction

Theoretical studies of nitrogen-doped graphene loaded transition metal single-atom catalysts for electrochemical CO reduction

Oxygen Reduction Reaction Activity of Pt on Various Carbon Supports in OH- conducting Ionic Liquids

The intermediate temperature operation above 100 °C is one of important targets of next generation fuel cell development from both points of view of the activity enhancement and carbon monoxide poisoning mitigation of catalysts. To tackle this challenge, we have synthesized and applied OH- conducting ionic liquids as new fuel cell electrolytes, in which the progress of oxygen reduction reaction (ORR) has been successfully confirmed at temperatures above 100 °C under non-humid conditions. However, there is a problem to be solved that the overpotential for ORR is high due to the strong adsorption of ionic species on Pt catalyst. In this study, the electronic state of Pt catalyst was designed by applying heterogeneous atom-doped graphene materials as catalyst supports to reduce the ORR overpotential.A 1:1 mixture of tetrabutylphosphonium hydroxide (TBPOH) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (P4441TFSI) was prepared and used as OH- conducting ionic liquid. As Pt catalyst supports, reduced graphene oxide (RGO) and nitrogen-doped graphene (NG) were synthesized. The deposition of Pt catalyst on these graphene materials were carried out by a conventional reduction method of platinum chloride with ethylene glycol.The ORR activity of Pt catalysts supported on various carbon materials was evaluated by cyclic voltammetry in O2 saturated TBPOH/ P4441TFSI at 120 °C, and the positive shift of ORR onset potential from 0.4 V to 0.6 V and then 0.7 V vs. RHE was observed by changing the support from commercial Ketjen Black to RGO and then NG, accompanied by an increase in the ORR current density. X-ray photoelectron spectroscopy (XPS) revealed that this improvement is related to the different electronic state of Pt catalyst, and it was suggested that the supports with higher electron donating properties such as NG are suitable for Pt catalyst to enhance the ORR activity. Figure 1

(Invited) Anion-Intercalated Cathode Concept for Fast and Stable Cycling of LIC and Batteries

Behavior of Graphene-like Graphite Cathode in Ionic Liquid Electrolytes Research and development of energy storage devices with higher energy densities than those of ordinary supercapacitors is underway. In the field of rechargeable batteries, a rechargeable battery that utilizes anion intercalation between graphite layers for charge compensation is being considered as one of the post-lithium ion batteries1). Anion intercalation is the insertion and desorption of anions between the layers of cathode materials during charging and discharging. The wider the interlayer of the cathode material, the greater the amount of anion insertion, leading to higher battery capacity. Generally, graphite is used as the cathode material for secondary batteries that utilize anion insertion. However, graphite has narrow interlayer spaces, making it impossible to increase intercalation capacity. Therefore, the use of graphene-like graphite (GLG), which has been reported to have wider interlayer space than graphite, is expected to provide high-speed operating performance and high capacity equivalent to that of ordinary capacitors2). In a previous study by the presenter, a two-electrode cell was constructed with GLG as the working electrode, Li metal as the counter electrode, and 1.0M LiFSI / Pyr13FSI ionic liquid electrolyte as the electrolyte, and a high discharge capacity of approximately 200mAh g-1 was demonstrated3).In this study, we attempted to examine and develop a LIC using GLG as a cathode material. Since both the cathode and anode are carbon materials, the LIC is lighter, safer, and more environmentally friendly than conventional LIBs. In addition, the operating voltage per cell is high due to the large redox potential difference. Therefore, the energy density of the LIC can be expected to be comparable to that of a conventional LIB using transition metal oxides for the cathode. However, the reversible capacity of graphite as a cathode material depends on the type of anion and is lower than that of conventional LIB cathodes with transition metal oxides4). In addition, the high redox potential may cause undesirable side reactions such as oxidative decomposition of the electrolyte, so an electrolyte with oxidation resistance is required. Therefore, we focused on GLG as a cathode material to replace graphite and ionic liquid electrolyte as an oxidation-resistant electrolyte. LICs were fabricated using GLG as the cathode, graphite as the anode, and LiFSI/Pyr13FSI ionic liquid electrolyte as the electrolyte. The results showed that the initial discharge capacity and electrolytic efficiency in the first cycle were lower than those of the GLG cathode-Li half cell. Therefore, we analyzed the structure of each electrode and conducted charge-discharge tests under various conditions to investigate the improvement of discharge capacity and initial coulombic efficiency. Development of LICs using Nitrogen-Doped Graphene Conventional dual carbon energy storage devices use graphite with narrow interlayer space as the cathode active material, and the capacity was limited by the reduced utilization of the graphene layer due to the insertion of anions5) . To solve this problem, reduced nitrogen-doped graphene (N-rGO), in which nitrogen is doped into graphene with wider interlayer space than graphite, was applied as cathode active material in LIC and dual carbon batteries. The results showed that N-rGO exhibited higher specific capacitance than graphite. In general, a plateau region originating from the step structure of graphite was observed in the charge-discharge curve of anion insertion-desorption reaction using graphite as the cathode active material6), but no plateau region originating from the step structure was observed in the charge-discharge curve using N-rGO as the cathode active material. This result suggests that the anion insertion/desorption reaction of N-rGO has different reactivity between cathode active materials. References T. Ishihara et al., J. Phys. Chem. C., 120 (2016) 22887.J. Inamoto, Y. Matsuo et al., J. Electrochem. Soc., 168(2021) 010528.M. Yoshie, M. Ishikawa et al., of the 62nd battery Symposium in Japan (2021) 3A13.J.A. Read et al., Energy Environ. Sci., 7 (2014) 617.X. Qi et al., J. Mater. Sci., 56 (2021) 10555.W. Zhou et al., ACS Omega, 5 (2020) 18289.

Electrochemical Production of Exfoliated Graphene: Scale-up and Applications

We have previously reported on the production of high quality graphene nanoplatelets by anodic electrochemical intercalation / exfoliation of graphite in simple aqueous salt solutions [1-3]. The process is attractive as it operates under ambient conditions, achieves a relatively high yield, and the graphene product does not require thermal or chemical reduction. In addition, heteroatom doping and surface functionalization ensure effective dispersion (enabling simple processing) and excellent performance for a range of applications, including supercapacitors [4,5], redox flow batteries [6], CO2 capture [7], and water treatment [8]. A key step for widespread implementation of electrochemically exfoliated graphene in these applications is the scale up of the process for cost effective production. In this study, a range of scale-up challenges have been evaluated, including the applied current density, temperature control, electrode dimensions and thickness, current connections, electrolyte volume and flow conditions, water purity, electrolyte recycling. The results demonstrate the scalability of the process, but also highlight critical issues that must be considered to enable successful scale-up. In particular, selection of the electrode dimensions must consider the potential and current distribution in the graphite working electrode. Temperature control is also important, since significant joule heating of the electrolyte occurs as the process is scaled up. A material and energy balance reveals that electrolyte management / recycling will be important for reducing waste. Economic analysis suggests that more than half of the cost of production is associated with the graphite foil raw material, and significantly lower cost may be achieved by changing to the process to a packed bed graphite flake electrode.[1] Sharif et al. Synthesis of a high-temperature stable electrochemically exfoliated graphene. Carbon 157 (2020) 681-692[2] Momodu et al. Mixed-acid intercalation for synthesis of a high conductivity electrochemically exfoliated graphene. Carbon 171 (2021) 130-141[3] Roberts and Singh, Electrochemical graphene exfoliation with hydroxide intercalation. US Patent Application 17174552 (2021)[4] Cao et al., A Flexible Nanocomposite Film of Electrochemically Exfoliated Graphene @ Ti3CNTx for Supercapacitors with high Volumetric Capacitance. ACS Materials Letters 6 (2024) 2360-2368[5] Momodu et al. Hybrid energy storage using nitrogen-doped graphene and layered-MXene (Ti3C2) for stable high-rate supercapacitors. Electrochimica Acta 388 (2021) 138664[6] Pahlevaninezhad et al. Exfoliated Graphene Composite Membrane for the All-Vanadium Redox Flow Battery. ACS Applied Energy Materials 6 (2024), 6505-6517[7] Pal et al. Sustainable CO 2 adsorbent via amine–phosphate coupling of glycated chitosan and electrochemically exfoliated graphene Journal of Materials Chemistry A 12 (2024) 10216-10228[8] Abuhatab et al. Electrochemical regeneration of highly stable and sustainable cellulose/graphene adsorbent saturated with dissolved organic dye. Langmuir 40 (2024), 3606-3616

Study on Enhanced Electron Field Emission Properties of Graphene Quantum Dots Synthesized By Pulsed Laser Ablation

Graphene quantum dots (GQDs) and nitrogen-doped graphene quantum dots (N-GQDs) were synthesized by the Pulsed LASER Ablation method. The nanostructure and chemical composition of the GQDs were analyzed by means of TEM, HRTEM, Raman, XPS, and FT-IR spectra. Field emission is a quantum mechanical phenomenon where electrons tunnel from the cathode to the anode through vacuum under an applied electric field. So far, the field emission properties of two-dimensional (graphene) and one-dimensional (CNT) carbon nanostructures have been extensively studied. For the first time, to the best of our knowledge, the field emission behavior of GQDs and N-GQDs, deposited on n-Si (100) substrates, is studied. As a candidate of cold cathode, the GQDs display good field emission performance. The field emission properties of GQDs and N-GQDs were studied by measuring turn-on field (E) and field enhancement factor β.The results show that nitrogen doping improved the field emission properties of GQDs by reducing the turn-on field from 13.1V/μm (GQDs) to 7.9V/μm (N-GQDs) and enhancing the field enhancement factor β from 1427 (GQDs) to 2511 (N-GQDs). The field emission behavior of pristine GQDs and N-GQDs is explained in terms of change in the effective microstructure as well as a reduction in the work function, as probed by measured characterizations. The enhanced emission properties of N-GQDs are mainly attributed to the upshifting of fermi energy level and defects produced as a result of nitrogen doping. The good emission performance of the GQDs field emitters suggests promising applications in next-generation vacuum micro and nano-electronic devices.

Ultrahigh Loading of Copper Single Atoms through Pyrolysis of Nitrogen-Doped Graphene Quantum Dots for Oxygen Reduction Reaction

Major bottlenecks against the widespread utilization of proton-exchange-membrane fuel cells are (i) the sluggish kinetics of oxygen reduction reaction (ORR) and (ii) economic viability associated with the extensive use of Pt group metal (PGM) catalysts,. Therefore, non-PGM single-atom catalysts (SACs) have received a considerable attention as alternatives to PGM catalysts for ORR. In this presentation, we will share our recent studies that investigate the synthesis and characterization of copper single atom catalysts (Cu-SACs) for ORR. Ultrahigh loading (10 – 40 wt%) of Cu-SACs was achieved through a simple pyrolysis of nitrogen-doped graphene quantum dots derived from small organic molecules like pyrene and citric acid. Graphene quantum dots have abundant functional groups, facilitating the incorporation of nitrogen and Cu single atoms during pyrolysis. Abundant nitrogen sites (pyridinic-N and pyrrolic-N) effectively chelated Cu atoms by forming Cu-N complexes (Cu-Nx). The effects of Cu loading and pyrolysis temperature on ORR activities were investigated. Interestingly, after the removal of co-synthesized metallic Cu by acid-washing, Cu-SAC demonstrated a noticeable enhancement of ORR activity with 4-electron transfer pathway. High-resolution scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS) and electrochemical characterization results will be presented. This bottom-up approach of utilizing graphene quantum dots demonstrates promise for developing high-density, non-PGM-based SAC sites for efficient and economically viable electrocatalysis.

Development of High-Performance Lithium-Ion Capacitor Using Reduced Nitrogen-Doped Graphene as Capacitor-Type Cathode Material Exhibiting Anomaly Anion Storage Mechanism

1.IntroductionLithium-ion capacitor (LIC) is a capacitor with improved energy density by applying a battery-type active material capable of lithium storage as the anode material. However, a typical cathode of LIC applies a capacitor-type active material that adsorbs anions, limiting its specific capacity as LIC. Therefore, we synthesized and applied reduced nitrogen-doped graphene (N-rGO) as a new cathode active material to achieve high energy density in LIC. The N-rGO cathode exhibits capacitance via an anion intercalation mechanism, a faradaic reaction, and initial charge-discharge characteristics in the N-rGO/Li half-cell showed a high specific capacitance exceeding 160 mAh g-1 in a 2.0 - 4.8 V voltage range and a current density of 150 mA g-1. We also reported that N-rGO cathode exhibits high rate characteristics due to a unique anion storage mechanism in which the capacity increases proportionally to the voltage after the first charge cycle. [1, 2] This suggests that it is suitable as a new cathode material for LIC. This unconventional anion storage mechanism would be ascribed to a change in the N-rGO morphology due to anion intercalation during the initial charging, but there have been still many unresolved points. In this study, we further analyzed the anion storage mechanism in N-rGO cathode and constructed a LIC device using N-rGO, which exhibits an anomaly anion storage mechanism, and examined the possibility of achieving high capacity.2.Experimental sectionN-rGO was synthesized by a hydrothermal reaction of ball-milled graphene oxide (GO) as a N-rGO precursor with urea as a nitrogen source and distilled water as a solvent in an autoclave at 180°C in 12 hours under high pressure conditions. N-rGO and graphite electrodes were prepared by mixing each active material with acetylene black (AB), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) in the weight ratio of 90:5:3:2, respectively. The slurry was coated onto Al and Cu current collector, respectively. Cathode half-cells were assembled with the N-rGO cathode, Li-metal as the counter electrode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte to analyze the anion storage mechanism of N-rGO cathode. Full-cells were assembled with the N-rGO cathode, graphite anode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte, and its performance as LIC was evaluated.3.Results and discussionIn our previous report, a conventional anion intercalation mechanism undergoes expansion and shrinking of the interlayer distance of carbon as anions are inserted and removed, whereas the N-rGO cathode goes through expanding the interlayer distance of carbon due to anion insertion at the initial charging, and then the expanded interlayer distance is maintained during subsequent charge-discharge cycles. Morphology difference between these materials may have altered the anion storage mechanism. The microstructure within the interlayer was investigated using XANES. Details will be explained in this poster presentation. Constant current charge-discharge tests were conducted to investigate the performance of LIC with this N-rGO as a capacitor-type cathode. With the previous LIC, we pre-doped Li in the graphite anode and constructed a full cell. The specific capacity was almost the same as the N-rGO/Li half cell, but the capacity retention was poor and the capacity was significantly reduced after 10 cycles. We speculated that this was due to a plateau in the charge curve even after the initial charge, and that the morphological change due to sufficient anion insertion had not occurred. Therefore, in addition to pre-doping Li into the graphite anode, we pre-cycled the N-rGO cathode as a single cycle prior to constructing full cell. As a result, the plateau in the charge process almost disappeared, and the specific capacity and high capacity-retention were almost the same as those of the N-rGO/Li half-cell, and long-term cycling was achieved.Reference[1] J. Ishikawa et al., The 64th Battery Symposium Japan, 1F01 (2023).[2] M. Zhang et al., Energy Stor. Mater., 16 (2019) 65-84.

High Performance Self-Powered UV Photodetector Based on Nitrogen-Doped Graphene Quantum Dot Schottky Diode

We report a straightforward bottom-up approach for the synthesis of high-quality nitrogen-doped graphene quantum dots (NGQDs). This approach is cost-effective, environmentally friendly, and suitable for the production of high-quality NGQDs on a large scale. The as-synthesized NGQDs have high crystalline quality with an average size of 3.26 nm, are water soluble, and show strong fluorescence. The UV-vis spectra indicate that N-doping introduces new energy levels into the electronic structure of graphene, which tune the optical properties, resulting in a photoluminescence quantum yield (PLQY) of 73%. The NGQDs show excitation wavelength-dependent fluorescence with a maximum excitation and emission at 340 and 431 nm, respectively. Using the as-synthesized NGQDs, we fabricated a high-efficiency and fast-response self-powered UV photodetector. Under the illumination of 365 nm UV light with a power density of 25 mW/cm, the NGQD photodetector shows a high photoresponsivity of 37 A/W, detectivity of 1 * 10 Jones, and external quantum efficiency (EQE) of 12.6 * 10%. This UV photoresponse is fast, with rise time of 0.29 s and fall time of 0.33 s. This work paves the way for the development of graphene-based high-performance optoelectronic devices.

Nanochannel confined graphene quantum dots/platinum nanoparticles boosts electrochemiluminescence of luminal-O2 system for sensitive immunoassay

Sensitive detection of tumor biomarkers is of great significance for early cancer diagnosis, treatment evaluation, and recurrence monitoring. Development of convenient electrochemiluminescence (ECL) immunosensor using dissolved oxygen (O2) as an endogenous co-reactant of luminol combined with efficient nanocatalysts to boost ECL signal in neutral media is highly desirable. Herein, sensitive detection of tumor biomarker using ECL of luminal-O2 enhanced by confinement of nitrogen-doped graphene quantum dots (N-GQDs) and platinum nanoparticles (PtNPs) on nanochannel array was demonstrated. A high-density nanochannel array-modified electrode was achieved by rapidly growing an amino-functionalizedvertically-ordered mesoporous silica film (NH2-VMSF) on the inexpensive and readily available indium tin oxide (ITO) electrode. Through simple electrodeposition, N-GQDs were confined and PtNPs were in-situ synthesized in nanochannels of NH2-VMSF. These confined nanocomposites catalyzed the electroreduction of O2 at negative potentials to generate a large amount of reactive oxygen species (ROS) and facilitated luminol oxidation, enhancing the ECL signal of luminol by 25 times. Two immunosensors were fabricated after covalent immobilization of the recognition antibody of carbohydrate antigen 199 (CA199) or carbohydrate antigen 125 (CA125) on the outer surface of the NH2-VMSF and blocking of non-specific sites. When tumor biomarkers bind to the corresponding antibodies on the recognition interface, the formed immunocomplex hindered the diffusion of luminol to the underlying electrode, resulting in a decrease in the ECL signal and sensitive detection of tumor biomarker. The constructed CA199 immunosensor exhibited a linear detection range for CA199 from 0.5 mU mL−1 to 50 U mL−1, with a detection limit (DL) of 0.03 mU mL−1. For CA125 detection, linear detection ranged from 0.5 mU mL−1 to 500 U mL−1, with a DL of 0.005 mU mL−1. The fabricated immunosensors demonstrated good selectivity and high reproducibility. This study provides great potential for the development of efficient luminol ECL systems in neutral media and expands the biological application in sensitive detection of tumor biomarker.

Mechanistic insight into the catalytic activities of metallic sites on nitrogen-doped graphene quantum dots for CO2 hydrogenation

The origin of selectivity and activity of the CO2 hydrogenation reaction on single-atom catalysts composed of three adjacent 3d transition metals (Fe, Co, and Ni) supported on N-doped graphene quantum dots were systematically investigated and compared using density functional theory (DFT) calculations, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM) analysis. This study reveals that π-backbonding between the metal and CO2* does not occur and [CO2]δ+ species drive the reaction. The CO2* reacts with H2 via the Eley-Rideal (ER) mechanism by using the synergistic effects of the N site. The higher the partial positive charge on the C atom, the lower the Ea of the reaction. Subsequently, a tautomerization reaction, which is facilitated by hydrogen bonding, occurs and hydrogen is transferred to HCOO* resulting in the formation of CHOOH*. This study shows the selective formation of formic acid from CO2 is accessible on these SACs and Fe-SAC is the best one between these three catalysts. Although CO2 is more inert than formic acid the H2 molecule reacts with the adsorbed formic acid more difficult than the adsorbed CO2. It is because the hydrogenation of formic acid causes C-H bond formation resulting in failure of the coordinated O atom's octet and the unstable H2COOH* is formed. This step is the rate-determining step of HOCH2OH formation from CO2, with Ea of 1.94, 2.03, and 2.23 eV for Fe, Co, and Ni, respectively. Finally, the system undergoes another tautomerization reaction resulting in the formation of HOCH2OH (formaldehyde monohydrate).

Preparation, Characterization, and Cytotoxicity Study of Nitrogen-Doped Graphene Quantum Dots Functionalized Hyaluronic Acid Loaded with Docetaxel-Catalyzed Nanoparticles for Breast Cancer Imaging and Targeting In Vitro

Many women worldwide are impacted by breast cancer that also claims many lives every year. Docetaxel (DOC) is the natural chemotherapeutic agent used most commonly for the treatment of breast cancer. However, it has some drawbacks including low water solubility, a long half-life, an unregulated rate of discharge from the target site, etc. The objective of our present research reported here was to formulate DOC-loaded hyaluronic acid (HA)-functionalized nitrogen-doped graphene quantum dots (N-GQDs) nanoconjugate (DOC@HA-SDH-NGQDs) by using the adhesive properties of succinic acid dihydrazide (SDH) as a hopeful nanocarrier system for potential breast cancer imaging and targeting. The prepared DOC@HA-SDH-NGQDs nanoparticles (NPs) demonstrated 87.58 % drug loading, 97 % drug release, and −14.5 zeta potential indicating excellent stability. The outcomes of our MTT assay showed the full biocompatibility of the produced nanoconjugate and the significant reduction in MCF7 breast cancer cell viability observed in samples of DOC-loaded HA-SDH-NGQDs NP when we compared to other formulations. The MCF7 cancer cell line was found to respond better to the DOC@HA-SDH-NGQDs nanocomposite than to the standard drug, according to the cellular uptake studies. Conclusively, our described study, we believe, is the first to describe HA-NGQDs nanotherapeutics (NTCs) with the added adhesive qualities of SDH for breast cancer imaging and treatment via pH-triggered targeted anticancer drug delivery.

A Two-Step Synthesis of Porous Nitrogen-Doped Graphene for Electrochemical Capacitors.

Porous nitrogen-doped graphene (PNG) materials with high conductivity, high surface area, and chemical stability have displayed superior performance in electrochemical capacitors. However, previously reported methods for fabricating PNG render the processes expensive, hard to control, limited in production, and unsafe as well, thus largely restricting their practical applications. Herein, we present a facile two-step calcination method to prepare PNG using petroleum asphalt as the carbon source to provide the original three-dimensional porous structure directly and using environmentally friendly and high nitrogen content urea as the nitrogen source without adding any etching agent. The porous structure in PNG can largely increase its specific surface area, and the introduction of nitrogen atoms can effectively increase the degree of defects and improve the wettability of PNG. As a result, PNG displays a high specific capacitance of 157 F g-1 at a current density of 1 A g-1 and cycling stability while maintaining 98.68% initial capacitance after 10,000 cycles.