Highly Selective Room Temperature Trimethylamine Gas Sensor Fabricated Using Conducting Polyaniline, Electrospun Yttrium Doped Tin Oxide, and Nitrogen Doped Graphene Quantum Dot

The synthesis of nitrogen-doped Graphene Quantum Dots (N-GQDs) employing Pennisetum purpureum (elephant grass) as the carbon precursor and ethylenediamine (EDA) as the nitrogen source was conducted. This study highlights the potential applications of nitrogen-doped multi-fluorescent graphene quantum dots (N-GQDs) in the detection of Fe3+. The synthesized N-GQDs have been studied using UV–vis spectrophotometry, fluorescence spectrometry, Raman spectrometry, FT-IR spectrometry, x-ray spectroscopy, selected-area electron diffraction, transmission and high-transmission electron microscopy. The acquired N-GQDs were observed to have an almost hexagonal shape with a lateral size of 2.42 nm and exhibited a comparable quantum yield of approximately 26%. The N-GQDs that have been prepared with consistent size distribution and a significant amount of nitrogen and oxygen-based functional groups showcase outstanding water dispersity. The N-GQDs exhibited the capability to identify the Fe3+ ions in a broad range concentration of 1–600 μM by creating an N-GQDs-Fe3+ complex through the occurrence of functional groups like nitrogen, carbonyl, and carboxyl on N-GQDs surface, has a lower limit of detection at approximately 60 nM. Our study provides evidence that the N-GQDs produced a strong and persistent fluorescence, which is highly soluble in water, notably the precise and selective detection of Fe3+ in water-based solutions.

Nitrogen-doped graphene and graphene quantum dots: A review onsynthesis and applications in energy, sensors and environment

In this study, the newly synthesized polyaniline (PANI)/polyethylenimine modified nitrogen doped graphene quantum dot (PN‐GQD)/tungsten oxide (WO3) ternary composites were used as ammonia (NH3) gas sensor detected the NH3 at room temperature. Fourier transform infrared spectrometer, field‐emission scanning electron microscopy, transmission electron microscopy, and x‐ray photoelectron spectroscopy were applied to illustrate the chemical structure and morphology of the fabricated ternary composites. The NH3 gas‐sensing performances of PANI/PN‐GQD/WO3 composite sensor were determined in the concentration between 0.6 and 2.0 ppm at room temperature and the response value of the ternary composite sensor with an exposure of 1.0 ppm NH3 was 19.9, which was much better than those of PANI and PANI/WO3 sensors. Because their highly sensitive detection of NH3 ranging from the concentration between 0.6 and 2.0 ppm at room temperature, the PANI/PN‐GQD/WO3 composite sensor was confirmed to be extremely effective to detect the kidney or hepatic disease from the human breath. This ternary composite sensor with an exposure of 1.0 and 2.0 ppm NH3 also displayed extraordinary repeatability and selectivity at room temperature. According to these findings, this fabricated PANI/PN‐GQD/WO3 composite sensor will be an excellent gas‐sensing material to detect the kidney or hepatic disease from the human breath.

GO/Cu2O nanocomposite based QCM gas sensor for trimethylamine detection under low concentrations

In this work, we investigate the adsorption process of CO2 in graphene quantum dots from the electronic structure and spectroscopic properties point of view. We discuss how a specific doping scheme could be employed to further enhance the adsorbing properties of the quantum dots. This is evaluated by considering the depth of the potential well, the spectroscopic constants, and the lifetime of the compound. Electronic structure calculations are carried out in the scope of the density functional theory (DFT), whereas discrete variable representation (DVR) and Dunham methodologies are employed to obtain spectroscopic constants and hence the lifetimes of the systems. Our results suggest that nitrogen-doped graphene quantum dots are promising structures as far as sensing applications of CO2 are concerned. Graphical Abstract Adsorption mechanism of the CO2 molecule in (a) a pristine and (b) a nitrogendoped Graphene Quantum Dot.

Facile and highly effective synthesis of nitrogen-doped graphene quantum dots as a fluorescent sensing probe for Cu2+ detection

Functionalized nitrogen doped graphene quantum dots and bimetallic Au/Ag core-shell decorated imprinted polymer for electrochemical sensing of anticancerous hydroxyurea

Nitrogen-doped graphene quantum dots (N-GQDs) perturb redox-sensitive system via the selective inhibition of antioxidant enzyme activities in zebrafish

Boron regulated dual emission in B, N doped graphene quantum dots

A novel, highly sensitive and selective fluorescent sensor based on water‐soluble nitrogen‐doped graphene quantum dots (N‐GQDs) coupled with molecularly imprinted polymers (MIPs) was developed to detect tetracycline (TC). Unique N‐GQDs@MIPs nanomaterials were synthesized via the simple sol‐gel method due to its advantages of saving time and costs. The prepared N‐GQDs were fairly uniform and the fluorescence quantum yield (QY) was up to 58.2%. Results of transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) confirmed that the N‐GQDs@MIPs nanomaterial was prepared successfully. The imprinted factor (IF) of the synthesized N‐GQDs@MIPs was 3.42. Under the optimized experimental conditions, the fluorescence intensity and concentration of TC maintained a good linear range. The recovery experiment indicated this method can be applied to detecting TC in animal‐derived food. In summary, the proposed method provided a new and effective way for simple and rapid analysis of specific components in complex matrix samples.

Graphene quantum dots have been widely studied owing to their unique optical, electrical, and optoelectrical properties for various applications in solar devices. Here, we investigate the optoelectronic properties of hexagonal and nitrogen-doped graphene quantum dots using the first-principles method. We find that doping nitrogen atoms to hexagonal graphene quantum dots results in a significant red shift toward the visible light range as compared to that of the pristine graphene quantum dots, and the doped nitrogen atoms also induce a clear signature of anisotropy of the frontier orbitals induced by the electron correlation between the doped nitrogen atoms and their adjacent carbon atoms. Moreover, time-dependent density functional theory calculations with the M06-2X functional and 6-311++G(d,p) basis set reproduce well the experimental absorption spectra reported recently. These results provide us with a novel approach for more systematic investigations on next-generation solar devices with assembled quantum dots to improve their light selectivity as well as efficiency.

Nitrogen doped graphene quantum dots (N-GQDs) were synthesized to explore and extend their potential applications in biomedical field. The hemocompatibility and cytotoxity of the obtained N-GQDs were primarily assessed at concentrations ranging from 10 to 100 μg/ml. From the results, it was found that the proliferation of rat Bone Mesenchymal Stem Cells (rBMSCs) was depressed to a certain extent after incubating with the high concentration (100 μg/ml) of N-GQDs. The nanoscale size and superior dispersibility endow N-GQDs with good cell permeability. Meanwhile, owing to their intrinsic photoluminescence characteristic, the N-GQDs can be used to label cells with high uniformity and light stability in absence of chemical dyes. More importantly, the up-regulated expression of alkaline phosphate (ALP), extracellular matrix, osteopontin (OPN) and osteocalcin (OCN) in rBMSCs cultured with N-GQDs, indicating N-GQDs have the abilities to promote rBMSCs osteogenic differentiation. This work would help give a new insight into the advantages of N-GQDs and pave the way for application of N-GQDs in regenerative medicine fields.

Giant femtosecond nonlinear optical response in bi-metallic GO nanocomposites for photonic applications

Preparation of blue- and green-emissive nitrogen-doped graphene quantum dots from graphite and their application in bioimaging

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.