Synthesis Of Graphene Quantum Dots Research Articles

Synthesis of Single-Crystalline Hexagonal Graphene Quantum Dots from Solution Chemistry.

Graphene-based carbon nanostructures with nanometer dimensions have been of great interest due to the existence of a bandgap. So far, well-ordered edge structure and uniformly synthesized graphene quantum dots (GQDs) with a hexagonal single-crystalline structure have not been directly observed owing to the limited precision of current synthesis approaches. Herein, we report on a novel approach not just for the synthesis of the size-controlled single-crystalline GQDs with hexagonal shape but also for a new discovery on constructing 2D and 3D graphene single crystal structures from d-glucose via catalytic solution chemistry. With size-controlled single-crystalline GQDs, we elucidated the crucial role of edge states on luminescence from the correlation between their crystalline size and exciton lifetime. Furthermore, blue-emissive single-crystalline GQDs were used as an emitter on light-emitting diodes and exhibit stable deep-blue emission regardless of the voltage and doping level.

Facile and large-scale synthesis of graphene quantum dots for selective targeting and imaging of cell nucleus and mitochondria

Graphene quantum dots (GQDs) have good biocompatibility, high luminescence, and low photobleaching properties, which make them promising alternatives to fluorescent dyes for cell imaging. However, most of the reported GQDs lack targeted selectivity that limits their applications in biomedicine. To overcome the drawback, novel GQDs modified with polyethyleneimine (PEI) or (3-carboxyl) phenyl bromide phosphine (TPP) were originally synthesized via a facile, low-cost, environmentally friendly, and large-scale preparation method. The GQDs-PEI was synthesized by a simple hydrothermal process, and then TPP was conjugated to the GQDs-PEI via the amide linkage. The physicochemical, optical, biocompatible, and targeted imaging properties were evaluated systematically. The results indicated that the average sizes of the as-produced GQDs-PEI and GQDs-TPP were 3.75 and 3.25 nm, respectively. More significantly, the two composites had excellent optical property, low cytotoxicity and selective targeting and imaging properties for cell nucleus or mitochondria, suggesting their promising applications as the cell nucleus imaging or mitochondria imaging in vivo and in vitro for diagnosis and therapy of some related diseases.

Modification of microencapsulated phase change materials(MPCMs) by synthesizing graphene quantum dots(GQDs) and nano-aluminum for energy storage and heat transfer applications

MPCMs and their suspensions, acting as the thermal storage, heat transfer or temperature constancy mediums, have gained concerns in various energy related sectors. However, problems involving high supercooling degree, low thermal conductivity and suspensions instability are barriers for their energy storage applications. The present study focuses on such properties by adding GQDs/nano-aluminum into MPCMs particles. Paraffin was selected as core material and urea–melamine–formaldehyde polymer as shell to prepare 10 MPCMs samples (no modifiers, GQDs, nano-aluminum, GQDs & nano-aluminum) via in situ polymerization. The morphology, thermal conductivity, thermal property and MPCM/suspensions stability were characterized. It was found, the selected modifiers didn't impact on the microcapsules morphology, but GQDs can make particle size smaller and distribution more uniform. Adversely, the mean particle size can be increased by nano-aluminum. GQDs are much more effective than nano-aluminum in improving thermal conductivity. GQDs can suppress supercooling effectively, however, nano-aluminum has no obvious effect on supercooling suppression. The MPCMs suspension modified by the selected amount of GQDs and nano-aluminum (Al-GQDs(4.5–2)) achieved a high physical stability. No structure instability of modified MPCM sample was observed. To sum up, the combined effort of GQDs and nano-aluminum enabled MPCMs to be more applicable in energy storage applications.

Microwave-assisted synthesis of graphene quantum dots and nitrogen-doped graphene quantum dots: Raman characterization and their optical properties**Report presented at 9th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2018), 7-11 November 2018, Ninh Binh City, Vietnam.

In this report we will present completely new results on the improvement of the graphene quantum dots (GQDs) and nitrogen-doped graphene quantum dots (N-GQD) production method, using the microwave with different power levels and durations, from citric acid and urea. This is a new and unprecedented method of fabrication. The use of microwave has allowed ultra-fast fabrication of GQDs and nitrogen doped GQDs. These GQDs had their characteristics identified by Raman scattering spectra for the characteristic C–C graphene vibration mode (G-peak) and defects of GQDs (D-peak). The absorption spectra of GQDs samples were fabricated under different conditions, with the expectation of different sizes, to be compared and analyzed. These absorption spectra were also compared with those of the N-GQD produced under the same conditions. The absorption mechanism of GQDs and N-GQD will be presented in detail. Measurements of the photoluminescence (PL) spectra in GQDs and N-GQD have also been recorded and analyzed. The fluorescence mechanism will be presented, explained, and compared with other international publications of other authors. Some of the TEM and HR-TEM images of these two samples were also presented to confirm the shape, size and in-plane spacing lattice of the GQD structure.

A Hydrothermal Synthesis of Graphene Quantum Dots Modified Carbon Paste Electrode as an Efficient Electro Sensor Towards L-Ascorbic Acid

The tremendous electronic assets of graphene, with its charge carriers parroting relativistic graphene quantum dots and its potential in numerous applications, have ensured a hasty evolution of interest in this ground-breaking material. The graphene quantum dots, in the size range of 1-5 nm, showed 0 D morphology, which exists with few atomic layers of wideness and have zigzag edge structure. Herein, We report on electrochemical behaviour of graphene quantum dots modified electrode that hold edges and basal plane content, accelerated the anodic peak current with a sensitivity of about 0.68 mA mM–1 and offers 1.4 times higher sensitivity towards the oxidation of ascorbic acid.

Graphene quantum dots unraveling: Green synthesis, characterization, radiolabeling with 99mTc, in vivo behavior and mutagenicity

Graphene is one of the crystalline forms of carbon, along with diamond, graphite, carbon nanotubes, and fullerenes, and is considered as a revolutionary and innovating product. The use of a graphene-based nanolabels is one of the latest and most prominent application of graphene, especially in the field of diagnosis and, recently, in loco radiotherapy when coupled with radioisotopes. However, its biological behavior and mutagenicity in different cell or animal models, as well as the in vivo functional activities, are still unrevealed. In this study we have developed by a green route of synthesizing graphene quantum dots (GQDs) and characterized them. We have also developed a methodology for direct radiolabeling of GQDs with radioisotopes.Finally; we have evaluated in vivo biological behavior of GQDs using two different mice models and tested in vitro mutagenicity of GQDs. The results have shown that GQDs were formed with a size range of 160-280 nm, which was confirmed by DRX and Raman spectroscopy analysis, corroborating that the green synthesis is an alternative, environmentally friendly way to produce graphene. The radiolabeling test has shown that stable radiolabeled GQDs can be produced with a high yield (>90%). The in vivo test has demonstrated a ubiquitous behavior when administered to healthy animals, with a high uptake by liver (>26%) and small intestine (>25%). Otherwise, in an inflammation/VEGF hyperexpression animal model (endometriosis), a very peculiar behavior of GQDs was observed, with a high uptake by kidneys (over 85%). The mutagenicity test has demonstrated A:T to G:C substitutions suggesting that GQDs exhibits mutagenic activity.

Optimum Electrochemical Production Method of Few-Layers and Few-Defective Graphene

Among the different synthesizing method of graphene, besides having a most suitable and cost-effective method, it is essential to have high-quality graphene. For this reason, the effects of the cathode electrode, the time and type of voltage variation, dispersion time, the electrolyte salt and washing solvent on process performance of electrochemical exfoliation of graphite (EE-G) were investigated. Here, we show great promise for few-layer and few-defective graphene by optimum EE-G. The most suitable condition to produce graphene is performing the process in (NH4)2SO4. Moreover, the NaOH as salt is suitable in the synthesis of graphene quantum dots. Raman analysis clearly showed the G, D band, and 2D band of carbon for samples.

Green Synthesis of Graphene Quantum Dots from Cotton Cellulose

AbstractFabrication of graphene quantum dots (GQDs) often requires strong acids or organic solvents, and their green synthesises on sustainable routes still face challenges. Herein, an eco‐friendly synthetic process has been developed, in which the natural polymer cellulose has been utilized as a new precursor for the first time. The reaction system is only composed of cellulose and water, in absence of any other chemical reagents. Moreover, the products contain only GQDs, carbide precipitates, and water, leading to easy separation and avoiding complicated post‐processes. In addition, the synthetic mechanism is presented that the formation process of GQDs consists of the first hydrolyzation and the following cyclic condensation. With highly photoluminescent (PL) properties, favourable hydrophilicity, low cytotoxicity and excellent biocompatability, the as‐synthesized GQDs have been successfully applied in bioimaging. This work not only develops a sustainable route for the green synthesis of GQDs, but also finds a renewable resource as the raw material, which significantly facilitates the extensive applications of GQDs in biological fields.

Size-Dependent Electronic Properties of Uniform Ensembles of Strongly Confined Graphene Quantum Dots.

The electronic structure of a series of bottom-up synthesized graphene quantum dots (GQDs) smaller than 2 nm was investigated by spectroelectrochemistry, yielding insights not previously available from ensemble-level studies. The results show that for the strongly confined GQDs the dependence of the band gap on the GQD size deviates from the prediction of the standard Dirac Fermion model but agrees well with the models explicitly accounting for the electron-electron and electron-hole interactions. The HOMO/LUMO energy levels are found to be distributed nearly symmetrically around the 0 V value versus normal hydrogen electrode (NHE), becoming more positive/negative, respectively, with increasing GQD size. The exciton binding energies are found to follow power dependence on the number of carbon atoms per GQD, with the experimental values falling within the range of ∼0.1 to ∼0.6 eV. Given the broad accessibility of the described experimental tools and methods, our work opens a path to a more systematic examination of quantum confinement effects in GQDs.

Hydrothermal Synthesis of Graphene Quantum Dots Supported on Three-Dimensional Graphene for Supercapacitors.

Incorporation of new functional components into a three-dimensional graphene (3DG) framework improves the performance of supercapacitors based on 3DG as electrodes by tailoring the framework’s structure and properties. In this work, graphene quantum dots (GQDs) were incorporated into 3DG via one-step hydrothermal treatment of GQDs and graphene oxide (GO). By simply adjusting the GQDs/GO feeding ratio by weight, various GQDs/3DG composites were formed. The maximum feeding ratio was 80%, and the prepared composites possessed saturated GQDs loading on the 3DG framework, whereas composites obtained with a GQDs/GO feeding ratio of 40% as electrodes exhibited optimal specific capacitance of 242 F·g−1 for supercapacitors, an increase of 22% compared with that of pure 3DG electrodes (198 F·g−1). This improved performance was mainly due to better electrical conductivity and larger surface area for GQDs/3DG composites with moderate GQDs content. The fabricated GQDs/3DG composites as electrodes for supercapacitors revealed high electrochemical stability. Their capacitance kept 93% of the initial value after 10,000 charge-discharge cycles.

An Optimum Electrochemical Production Method of Few-Layers and Few-Defective Graphene

Among the different synthesizing method of graphene, besides having a most suitable and cost-effective method, it is essential to have high-quality graphene. For this reason, the effects of the cathode electrode, the time and type of voltage variation, dispersion time, the electrolyte salt and washing solvent on process performance of electrochemical exfoliation of graphite (EE-G) were investigated. Here, we show great promise for few-layer and few-defective graphene by optimum EE-G. The most suitable condition to produce graphene is performing the process in (NH4)2SO4. Moreover, the NaOH as salt is suitable in the synthesis of graphene quantum dots. Raman analysis clearly showed the G, D band, and 2D band of carbon for samples.

Synthesis of graphene quantum dot-stabilized gold nanoparticles and their application.

Herein, we report an in situ synthesis of graphene quantum dots (GQDs), which have been synthesized from only starch and water and stabilize AuNPs in water. The construction of six gold nanocomposites, i.e. AuNPs 1–6, with sizes ranging from 13.4 nm to 32.6 nm, was accomplished by only mixing the GQDs and chloroauric acid in different amounts without any additional reductants and surfactants. HRTEM has confirmed that the AuNPs have been stabilized by the GQDs, and a core/shell AuNPs@GQD structure has formed. In addition, the as-synthesized AuNPs show excellent catalytic performance in the reduction of 4-nitrophenol, a pertinacious pollutant occurring in industrial wastewater.

Raman spectroscopy of bottom-up synthesized graphene quantum dots: size and structure dependence.

Graphene quantum dots (GQDs) have attracted significant interest as synthetically tunable optoelectronic and photonic materials that can also serve as model systems for understanding size-dependent behaviors of related graphene structures such as nanoribbons. We present a Raman spectroscopy study of bottom-up synthesized GQDs with lateral dimensions between 0.97 to 1.62 nm, well-defined (armchair) edge type, and fully benzenoid structures. For a better understanding of observed size-dependent trends, the study is extended to larger graphene structures including nano-graphene platelets (>25 nm) and large-area graphene. Raman spectra of GQDs reveal the presence of D and G bands, as well as higher order modes (2D, D + G, and 2G). The D and G band frequencies and intensity were found to increase as GQD size increases, while higher order modes (2D, D + G, and 2G) also increased in intensity and became more well-defined. The integrated intensity ratios of D and G bands (ID/IG) increase as the size of the GQDs approaches 2 nm and rapidly decrease for larger graphene structures. We present a quantitative comparison of ID/IG ratios for the GQDs and for defects introduced into large area graphenes through ion bombardment, for which inter-defect distances are comparable to the sizes of GQDs studied here. Close agreement suggests the ID/IG ratio as a size diagnostic for other nanographenes. Finally, we show that Raman spectroscopy is also a good diagnostic tool for monitoring the formation of bottom-up synthesized GQDs.

Facile synthetic Photoluminescent Graphene Quantum dots encapsulated β-cyclodextrin drug carrier system for the management of macular degeneration: Detailed analytical and biological investigations

Drug administration by effective nano-carriers is an emerging and growing technology in the field of bio-medicine and particularly Age –related macular degeneration (AMD). This developed nanomaterials based methods with drug administration maximizes the biocompatibility and systemically increases drug delivery profile for the drugs. Herein, we described the effective drug molecules delivery profiles by the hydrothermally synthesized graphene quantum dots (GQDs) encapsulated with supramolecular β-cyclodextrin (β-CD) as a drug delivery system for AMD. The drug release profiles were analysed and plotted by two different types of drugs ((Bevacizumab (Bev) and Ranibizumab (Ran))) and compounds displayed an initial burst delivery percentage of 55.7 ± 1.6% and 52.2 ± 2.6, respectively, within 15 min. After 1 h, 94.2% (Ran) and 93.1% (Bev) of loaded drug molecules were released from the β-CD encapsulated GQDs in sustained manner. The biocompatibility of the synthesized carriers was investigated quantitatively and qualitatively with the mouse Fibroblast L929 cell line. The biological cell analysis observed by calculated cell count and green fluorescence visualization has been clearly confirmed the samples are non-toxic and highly compatible to the cells with more than 90% cell viability after 5 days cell culture. The observed material properties and biological results demonstrated that the suitability of the developed nano-carriers for the drug delivery system in the AMD.

Facile synthesis of graphene quantum dots based on electrochemical method and their application for specific Fe3+ detection

Facile synthesis of graphene quantum dots based on electrochemical method and their application for specific Fe3+ detection

Direct Synthesis of Graphene Quantum Dots with Different Fluorescence Properties by Oxidation of Graphene Oxide Using Nitric Acid

Graphene quantum dots (GQDs) play a critical role in many applications in the electrical and optical fields. We develop a simple three-step hydrothermal etching method to prepare GQDs by adopting graphene oxide (GO) as a precursor and nitric acid as an oxidant. We discuss the formation mechanism of GQDs by the characterization of products and intermediates with Scanning electronic microscopy (SEM), Transmission electron microscopic (TEM), Raman, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Two kinds of GQDs have been obtained after the treatment of GO with different concentrations of nitric acid. The sizes of GQDs are small, with diameters of 3.38 nm and 2.03 nm on average, respectively. When excited with 365 nm UV light, the two kinds of GQDs exhibit green and yellow luminescence; the different optical properties can be attributed to the differences in degree of oxidation and nitrogen doping. The result is important for GQDs in synthesizing and optical field.

One-Pot Facile Synthesis of Graphene Quantum Dots from Rice Husks for Fe3+ Sensing

In this work, graphene quantum dots (GQDs) with an average size of 3.9 nm were synthesized using rice husk biomass as the raw material via a facile one-step one-pot hydrothermal method. The size and morphology of the rice husk-derived GQDs were characterized by transmission electron microscopy and atomic force microscopy. The GQDs exhibit bright blue photoluminescence under 365 nm ultraviolet irradiation and can be well dispersed in water. The GQDs reach the strongest photoluminescence excitation intensity at ca. 360 nm under an emission wavelength of 466 nm, suggesting that the GQDs were oxidized with oxygenous groups attached. The quenching tests showed that the synthesized GQDs were highly and selectively sensitive toward Fe3+ ions and thus can potentially be used for Fe3+ sensing.

Liquid-phase laser ablation synthesis of graphene quantum dots from carbon nano-onions: Comparison with chemical oxidation

Graphene quantum dots (GQDs) have been synthesized reproducibly by chemical oxidation (CO) of carbon nano-onions (nCNOs) and a one-step pulsed laser ablation (LA) of nCNOs in deionized water. The photoluminescence (PL) spectra show that the LA-GQDs have blue shifted emission relative to the CO-GQDs which is attributed to the effects of both particle sizes and surface functional groups. The CO-GQDs have an average diameter of 4.1(8) nm and a thickness corresponding to two or three graphene layers, while the LA-GQDs have an average diameter of 1.8(6) nm and a thickness comparable to a single layer of graphene. The CO-GQDs favor the presence of carboxylic groups and have a higher fraction of sp2 carbons, while the LA-GQDs prefer the presence of hydroxyl groups and have a higher fraction of sp3 carbons. PL lifetime data suggests that surface functional groups are the main source of radiative deactivation and the sp2 carbon domains are mainly responsible for non-radiative decay. PL lifetimes are measured to be 7.9(6) ns for the emission from the carboxylic groups and 3.18(10) ns from the hydroxyl groups. Compared to CO, liquid-phase LA is a faster and cleaner one-step method for producing GQDs with fewer starting chemicals and byproducts.

Coal-derived nitrogen, phosphorus and sulfur co-doped graphene quantum dots: A promising ion fluorescent probe

N, P, S co-doped graphene quantum dots (NPS-GQDs) were prepared via a one-step wet chemical plus dialysis method directly using anthracite coal as raw material. This facile oxidation process simultaneously synthesized graphene quantum dots (GQDs) and doped N, P and S atoms on edges or forming functional groups of GQDS. X-ray photoelectron spectroscopy (XPS) proved that the involved heteroatoms were successfully doped on GQDs. The local doping of N, P and S on GQDs can reach high levels as 5.6%, 3.7% and 3.7% (by atomic) during XPS detection, respectively. Raman spectra showed that the amount of defects or disorders of prepared GQDs increased during the transition of the coal hunk toward the nano-GQDs. The effect of graphitizing degree of applied coals (varied coal ranks) on the formation of GQDs implied that raw coals with too high or too low graphitizing degree were not optimizing for the formation of high-quality GQDs. The prepared NPS-GQDs showed excellent properties on the excitation-dependent fluorescence and the quench by some trace metals. Thus, the NPS-GQDs were applied to detect of Pb2+ in both a DI water and a multi-elements analysis matrix, exhibited wide linear detection range (1–20 μM) and a detection limit of 0.75 μM.

Facile and Highly Effective Synthesis of Controllable Lattice Sulfur-Doped Graphene Quantum Dots via Hydrothermal Treatment of Durian.

Recently, the biomass "bottom-up" approach for the synthesis of graphene quantum dots (GQDs) has attracted broad interest because of the outstanding features, including low-cost, rapid, and environmentally friendly nature. However, the low crystalline quality of products, substitutional doping with heteroatoms in lattice, and ambiguous reaction mechanism strongly challenge the further development of this technique. Herein, we proposed a facile and effective strategy to prepare controllable sulfur (S) doping in GQDs, occurring in a lattice substitution manner, by hydrothermal treatment of durian with platinum catalyst. S atoms in GQDs are demonstrated to exist in the thiophene structure, resulting in good optical and chemical stabilities, as well as ultrahigh quantum yield. Detailed mechanism of the hydrothermal reaction progress was investigated. High-efficiency reforming cyclization provided by platinum was evidenced by the coexistence of diversified sp2-fused heterocyclic compounds and thiophene derivatives. Moreover, we also demonstrated that saccharides in durian with small molecular weight (<1000 Da) is the main carbon source for the forming GQDs. Because of the desulfurizing process, controllable photoluminescence properties could be achieved in the as-prepared GQDs via tuning doping concentrations.