Sulfur Co-doped Graphene Quantum Research Articles

Simultaneous detection of iodide and mercuric ions by nitrogen-sulfur co-doped graphene quantum dots based on flow injection “turn off-on” chemiluminescence analysis system

A simple, rapid and sensitive nitrogen and sulfur co-doped graphene quantum dots (NSGQD) based on flow injection chemiluminescence (FI-CL) technique for the determination of iodide and mercuric ions was reported. Strong CL signal was observed from the reaction of NSGQD and Ce(IV) under acidic condition. The mechanism was investigated by the spectra of CL, fluorescence and UV–vis. Moreover, the CL of the NSGQD-Ce(IV) system was found to be quenched by I−, and then recovered by Hg2+. In this way, a NSGQD-based CL “off-on” nanosensor for the simultaneous detection of I− and Hg2+ was designed. The “turn-off” mode was used for the determination of I− in a linear range of 0.04–3.0 μM with a detection limit of 4.23 nM. And the linear range for Hg2+ detection based on the “turn-on” process was from 0.3 to 7.0 μM with a 24.7 nM detection limit. The methods have been applied to the analysis of kelp, tea and water samples.

Facile synthesis of defect-rich nitrogen and sulfur Co-doped graphene quantum dots as metal-free electrocatalyst for the oxygen reduction reaction

Carbon-based metal-free nanomaterials have attracted immense and persistent attention as electrocatalysts for oxygen reduction reaction (ORR) in fuel cells, due to their high electrocatalytic activity, long-term stability and low cost. Here, a facile hydrothermal treatment in the presence of ammonium hydroxide (NH4OH) and sodium sulfide (Na2S), as precursors, has been developed to synthesize heteroatom-doped graphene quantum dots (GQDs). For comparison, undoped graphene quantum dots (GQDs), nitrogen doped graphene quantum dots (N-GQDs), sulfur doped graphene quantum dots (S-GQDs) and nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs) have been synthesized with the same method. The as-obtained N,S-GQDs possess a high N-doping content up to 9.36% and low S-doping content up to 0.78%, with a uniform size distribution similar to that of GQDs, N-GQDs and S-GQDs. Interestingly, the multi-types of NC or CSC bonding in metal free N,S-GQDs can significantly enhance the electrocatalytic activity for the oxygen reduction reaction (ORR), with the electron transfer number as good as 3.82, which verify the importance of our facile synthesis method to fabricate metal-free electrocatalysts for ORR and other electrochemical applications.

Sulfur and Nitrogen Co-Doped Graphene Quantum Dots as a Fluorescent Quenching Probe for Highly Sensitive Detection toward Mercury Ions

Sulfur and nitrogen codoped graphene quantum dots (SN-GQDs) were synthesized through an efficient infrared (IR)-assisted pyrolysis of glucose, urea, and ammonia sulfate at 260 °C. These served as a...

Nitrogen and sulfur Co-Doped graphene quantum dots decorated CeO2 nanoparticles/ polyaniline: As high efficient hybrid supercapacitor electrode materials

Recently, hybrid supercapacitor due to high energy/power density and long cycle life has been attractive field for energy researchers. In this work, we demonstrated the decoration of graphene quantum dots on metal oxide/polyaniline to form efficient electrode materials for a hybrid supercapacitor for the first time. Ultrafine N and S co-doped graphene quantum dots (N,S-GQDs) were grown on CeO2 nanoparticles via in situ hydrothermal method. Then, PANI-N,S-GQDs@CeO2 nanocomposites have been prepared by the chemical oxidation polymerization process. The simultaneous incorporation of S and N species in GQDs provides a larger active surface and greatly increases the contact area with the CeO2 in polymer nanocomposite. The as prepared material was analyzed by spectroscopic techniques and electron microscopy analysis. Electrochemical properties of the PANI-N,S-GQDs@CeO2 as supercapacitor electrodes were investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy experiments. The maximum specific capacity of 189 C g−1was obtained for PANI/5 wt % N,S-GQDs@CeO2 nanocomposite at current density of 1 A g−1 in comparison with 175 and 115 C g−1 for PANI/10 wt% N,S-GQDs@CeO2 and PANI/5 wt% CeO2 respectively. Value of specific capacity remained at 75% after 1000 cycles under the current density of 1 A g−1.

N, S co-doped graphene quantum dot–decorated Fe3O4 nanostructures: Preparation, characterization and catalytic activity

The sonocatalytic decolorization of the dye methylene blue was considered in the present study. In this regard, as a novel approach, Fe3O4 nanoparticles synthesized through a coprecipitation method were decorated with nitrogen and sulfur co-doped graphene quantum dots (NS-GQDs) and used as a sonocatalyst. The use of NS-GQD-decorated/Fe3O4 (NS-GQD/Fe3O4) nanoparticles significantly increased the decolorization efficiency (99.0%) compared with the use of pure Fe3O4 nanoparticles (43.7%). The band gap of the nanostructured NS-GQD/Fe3O4 (1.923 eV) was lower than that of pure Fe3O4 nanoparticles (2.147 eV). An optimal dopant amount of 3 wt% was used in the experiments. The highest sonocatalytic decolorization of 99.0% was attained at an initial pH of 8. As a result, the adverse effect of scavenging compounds on the sonocatalytic decolorization was in the following order: sulfate < carbonate < chloride. In the case of enhancers, the presence of potassium persulfate and hydrogen peroxide resulted in complete decolorization in a reaction time of 60 min. A drop in the decolorization efficiency of only 4% was observed after the fifth consecutive cycle, thereby implying the appropriate reusability potential of the NS-GQD/Fe3O4 sonocatalyst for use in full-scale operation. Gas chromatography–mass spectrometry analysis was used for the identification of intermediate by-products generated during the sonocatalytic decolorization of methylene blue.

Femtomolar Detection of Dengue Virus DNA with Serotype Identification Ability.

Dengue surveillance trusts only on reverse transcription-polymerase chain reaction (RT-PCR) type methodologies for confirmation of dengue virus serotypes; however, its real time application is restricted due to the expensive, complicated, and time-consuming process. In search of a new sensing system, here, we have reported a two-way-detection method for Dengue virus (DENV) serotype identification along with DNA quantification by using a new class of nanocomposite of gold nanoparticles (AuNP) and nitrogen, sulfur codoped graphene quantum dots (N,S-GQDs). The N,S-GQDs@AuNP has been used for serotype detection via a simple fluorescence technique using four dye-combined probe DNAs which is further validated by confocal microscopy. The quantification of the DNA has been measured by the differential pulse voltammetric (DPV) technique using methyelene blue as a redox indicator. Results obtained in this study, clearly demonstrate that the N,S-GQDs@AuNP can efficiently detect the four serotypes of DENV individually in the concentration range of 10-14 to 10-6 M with the LOD of 9.4 fM. In addition, to confirm its applicability in long chained complex DNA system, the sensor was also applied to the clinically isolated DENV DNA and showed satisfactory performances for serotype identification as well as quantification. We hope this simple and reliable method can pave an avenue for the development of sensitive and robust sensing probes in biomedical applications.

Photo‐and Electroluminescence from Nitrogen‐Doped and Nitrogen–Sulfur Codoped Graphene Quantum Dots

AbstractAs opposed to inorganic counterparts, organic quantum dots often exhibit lower fluorescence efficiencies and are complex to synthesize. Here we develop nitrogen‐doped (N‐GQDs) and nitrogen–sulfur codoped (NS‐GQDs) graphene quantum dots exhibiting high‐yield visible and near‐IR emission that are synthesized via a single‐step microwave‐assisted hydrothermal technique with a single glucosamine‐HCl starting material (thiourea precursor used for NS‐GQDs). As‐synthesized N‐GQDs and NS‐GQDs are well‐dispersed (average sizes of 5.50 and 3.90 nm) with high crystallinity and pronounced G‐band. Formed by the bottom‐up assembly of glucosamine, they contain amine linkage and a variety of oxygen‐containing functional groups assessed by Fourier‐transform infrared spectroscopy with ≈2% sulfur for NS‐GQDs. The synthetic procedure allows varying their size and the bandgap. Unlike other graphene‐based quantum dots, these GQDs exhibit bright, stable fluorescence both in the visible and near‐IR with high quantum yields of up to 60%. Excitation‐dependent visible fluorescence is attributed to size‐dependent bandgaps, with near‐IR emission potentially arising from the emissive defect states/their arrangements. Advantageous properties of these GQDs are utilized to develop exciton recombination layer for organic light‐emitting devices exhibiting both photoluminescence and electroluminescence in the visible. Produced by ecofriendly one‐step scalable synthesis brightly‐emissive N‐GQDs and NS‐GQDs become a promising material for novel organic optoelectronics.

Nitrogen and sulfur co-doped graphene quantum dots for the highly sensitive and selective detection of mercury ion in living cells

In this work, a novel nitrogen and sulfur co-doped graphene quantum dots (N,S/GQDs) were synthesized by a simple and green pyrolysis method with citric acid as carbon source, d‑penicillamine as doped molecule. The obtained N,S/GQDs shows good water solubility, low cytotoxicity and high quantum yield of 56.4%. The doping of N and S can efficient promoted the coordination between the residual group of N,S/GQDs and Hg2+, thus, the fluorescence of N,S/GQDs can be dramatically and selectively quenched by Hg2+. Under the optimum conditions, the quenching effect of Hg2+ to N,S/GQDs was lined with its concentrations in the range of 0.9 to 30 nM with a detection limit of 0.69 nM. 100 fold of common metals had no influence for the determination of Hg2+. When Hela cells were incubated into the N,S/GQDs solutions for 2 h, more than 85% Cells still kept living even at a high concentration of 400 μg/mL suggesting the good biocompatibility and low toxicity of the obtained N,S/GQDs. Besides this, the N,S/GQDs also showed good cell permeability and could enter into the cell and showed bright blue light. Thus, they were successfully applied as a powerful fluorescent nano-sensor for imaging detection of mercury ions in the living cells.

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.

CdS QDs Amplified Electrochemiluminescence of N,S Co-doped Graphene Quantum Dots and Its Application for Pb(II) Determination

An electrochemiluminescence (ECL) system based on cadmium sulfide quantum dots (CdS QDs) amplified the ECL of nitrogen and sulfur co-doped graphene quantum dots (N,S:GQDs) was established and applied for lead ion (Pb2+) determination. The anodic ECL signal of N,S:GQDs was enhanced greatly by CdS QDs; furthermore, the enhanced ECL signal could be quenched by Pb2+. Based on the quenching effect, a simple method for the selective ECL determination of Pb2+ was proposed.

Sensitive recognition of ethion in food samples using turn-on fluorescence N and S co-doped graphene quantum dots

To achieve a fast, sensitive and inexpensive method for the detection of ethion in the presence of Hg2+ ions, a nitrogen and sulfur co-doped graphene quantum dot (N,S/GQD)-based fluorescence sensing system was developed.

Tuning the photoluminescence of graphene quantum dots by co-doping of nitrogen and sulfur

Nitrogen and sulfur co-doped graphene quantum dots (NS-GQDs) were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of aqueous ammonia, S powder, and graphene quantum dots. The NS-GQDs with oxygen-rich functional groups have a high quantum yield of 41% and a diameter of 1–5 nm. The photoluminescence (PL) properties of the nitrogen-doped graphene quantum dots (N-GQDs) and NS-GQD were investigated. The results showed that the PL emission of the NS-GQD exhibits a clear blue shift of 54 nm compared to that of the N-GQDs.

Highly fluorescent nitrogen and sulfur co-doped graphene quantum dots for an inner filter effect-based cyanide sensor

In this work, nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs), exhibiting bright blue fluorescence with an excellent quantum yield of 67%, were facilely prepared by one-pot pyrolysis of citric acid (carbon source) and cysteine (N and S sources). Compared to conventional GQDs, the doping of nitrogen/sulfur had significantly altered and uniformed the surface state, and the as-obtained N,S-GQDs displayed an excitation-independent emission behavior, where the fluorescence decay curve was nearly a single exponential. On the basis of the well-known inner filter effect of silver nanoparticles (AgNPs) and cyanide (CN−)-induced etching of AgNPs, the fluorescence of N,S-GQDs could be quenched by AgNPs, and the nonfluorescence state of the as-prepared N,S-GQD-AgNP ensemble would be switched on in the presence of CN−. Meanwhile, the addition of N,S-GQDs has almost ignorable effect on the absorption spectrum of the AgNP solution, however, the subsequent introduction of CN− would significantly decrease the absorbance value owing to the aforementioned etching behavior of CN−. Therefore, a N,S-GQD-based fluorescent and AgNP-related colorimetric dual-mode analytical system for efficacious determination of CN− has been rationally designed and successfully developed for the first time. Furthermore, the detection limits were found to be 0.52μM and 0.78μM for fluorescent and colorimetric sensors individually under the optimal experiment conditions. The proposed N,S-GQD-AgNP-based assay can be successfully utilized to the quantitative determination of CN− in spiked tap water samples.

Time-efficient syntheses of nitrogen and sulfur co-doped graphene quantum dots with tunable luminescence and their sensing applications

N,S co-doped GQDs with fast preparation and tunable fluorescence were developed and employed as fluorescence probe for selective detection of Fe3+.

Significantly enhanced electrochemical performance of lithium titanate anode for lithium ion battery by the hybrid of nitrogen and sulfur co-doped graphene quantum dots

ABSTRACT The paper reported a facile synthesis of lithium titanate/nitrogen and sulfur co-doped graphene quantum dots(LTO/N,S-GQDs). Tetrabutyl titanate was dissolved in tertbutanol and heated to refluxing state by microwave irradiation. Then, lithium acetate was added into the mixed solution to produce LTO precursor. The precursor was hybridized with N,S-GQDs in ethanol. Followed by drying and thermal annealing at 500 °C in Ar/H 2 to obtain LTO/N,S-GQDs. The synthesis creates fully crystalline interconnected porous framework composed of nanoscale LTO crystals. The unique architecture achieves to maximize the high-rate performance and enhance the power density. More importantly, the introduction of N,S-GQDs don't almost influence on the electrolyte transport, but greatly improve the electron transfer and the storage lithium capacity. The LTO/N,S-GQDs anode exhibits remarkably enhanced electrochemical performance for lithium ion battery. The specific discharge capacity is 254.2 mAh g −1 at 0.1C and 126.5 mAh g −1 at 10C. The capacity remains 96.9% at least after 2000 cycles at 2C. The battery performance is significantly better than that of pure LTO electrode and LTO/graphene electrode.

Nitrogen and sulfur codoped graphene quantum dots as a new fluorescent probe for Au3+ ions in aqueous media

The N and S codoped GQDs can be used as a promising label free fluorescent probe for the sensitive and selective detection of Au3+ in aqueous media, which provides a new application of the functionalized GQDs to the detection of metal ions.

Synthesis and optical properties of nitrogen and sulfur co-doped graphene quantum dots

Schematic and digital photos of the preparation for water-soluble nitrogen (N) and sulfur (S) co-doped graphene quantum dots (NS-GQDs). Sulfur enhances the photoluminescence of NS-GQDs.