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Microwave-assisted synthesis of graphene quantum dots and nitrogen-doped graphene quantum dots: Raman characterization and their optical properties
摘要： 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 identi?ed 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 ?uorescence 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 con?rm the shape, size and in-plane spacing lattice of the GQD structure.
关键词： graphene quantum dots (GQDs),PL spectra,nitrogen-doped graphene quantum dots (N-GQD),microwave,Raman spectra,absorption spectra
更新于2025-11-19 16:56:42
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Charge transport and electron recombination suppression in dye-sensitized solar cells using graphene quantum dots
摘要： In this study, TiO2 photoelectrodes were sensitized in different concentration of Graphene Quantum Dots (GQDs) solution to enhance photovoltaic performance and charge transport of DSSC. The performance of pristine TiO2 and TiO2-GQDs photoelectrodes were compared to investigate the effect of GQDs incorporation in DSSC. It was found GQDs increased light absorption of TiO2 photoelectrode at visible spectrum in the range of λ = 375 nm to λ = 600 nm, resulting highest current–density, Jsc and photon-to-current conversion efficiency, ?c. Solar cell sensitized in 7.5 mg/ml concentration of GQDs known as (PG 7.5) cell shown the highest reading by 15.49 mA cm?2 and 6.97%, which indicated an improvement by 28.07% and 70.83% for Jsc and ? compare to pristine TiO2 DSSC at 12.10 mA cm?2 and 4.08%. Photoluminescence property own by GQDs may enhance photon emission to visible region when uv-ray excited on solar cell. Thus, generate more electron-hole pairs in the photoelectrode and enhance the photovoltaic parameters of DSSC. PG 7.5 cell also exhibited lowest series resistance (Rs) of 36.60 Ω, highest charge transfer resistance (Rct2) of 41.98 Ω and electron lifetime of 6.33 ms among other DSSC. These possibly due to suppression of recombination between TiO2/dye/electrolyte interfaces. Hence, resulting highest charge collection efficiency (CCE) of 53.42%. The EIS analysis confirmed the PV performance of the best cell of PG 7.5 since the same cell also generated the best photon-current conversion efficiency (PCE). This study revealed GQDs can enhanced photovoltaic parameter and charge collection efficiency of DSSC.
关键词： Charge collection efficiency,GQDs-DSSC,TiO2-GQDs,Charge transport
更新于2025-11-14 17:04:02
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Dy(III)-induced aggregation emission quenching effect of single-layered graphene quantum dots for selective detection of phosphate in the artificial wetlands
摘要： Carbon quantum dots (CQDs), prepared by one-step hydrothermal treatment of perylene-3,4,9,10-tetra-carboxylic dianhydride (PTCDA) and triethylamine (TEA), could be exfoliated or delaminated into single-layered graphene quantum dots (s-GQDs) with methanol for the first time, with fluorescence (FL) emission at 500 nm when excited at 417 nm. The s-GQDs, with more sufficient carboxyl groups on the surface than CQDs, could be induced to be aggregated by metal ion dysprosium (Dy3+), resulting in aggregation-induced emission quenching effect subsequently. However, the presence of phosphate (PO4 3-) destroys the Dy3+-induced aggregates of s-GQDs owing to the strong coordination between Dy3+ and PO4 3-, inducing the FL emission recovery of the s-GQDs and providing selective detection method of PO4 3- in the artificial wetlands with the linear range of 0.2–30 μM and determination limit of 0.1 μM (3σ).
关键词： s-GQDs-Dy3+ system,Phosphate detection,Single-layered graphene quantum dots,Carbon quantum dots
更新于2025-11-14 17:04:02
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Determination of Thiourea by On–Off Fluorescence Using Nitrogen-Doped Graphene Quantum Dots
摘要： A thiourea-detecting fluorescence sensor with Hg2t as a switch was developed using nitrogen-doped graphene quantum dots (N-GQDs). The surface of N-GQDs had many organic functional groups on which Hg2t was effectively bound and turned off the fluorescence of the N-GQDs. The fluorescence of N-GQDs was turned on by the thiol functional group of thiourea that bound strongly with Hg2t and formed Hg2t/thiourea complexes. After constructing the sensor, the experimental conditions and parameters, such as the pH and Hg2t concentration, were investigated and optimized. Under the optimum conditions, the constructed fluorescence sensor showed high sensitivity to thiourea at concentrations from 0.5 to 14 mM with a low detection limit of 41.7 nM. The sensor also exhibited high specificity, excellent stability, and good reproducibility so that the determination of thiourea in various samples had acceptable values with good recoveries from 99% to 106%. The relative standard deviation was less than 4.1% (n ? 3).
关键词： thiourea,Fluorescence,nitrogen-doped graphene quantum dots (N-GQDs),Hg2t,sensor
更新于2025-11-14 17:04:02
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Developing an Analytical Method Based on Graphene Quantum Dots for Quantification of Deferiprone in Plasma
摘要： In the world of nanotechnology, graphene quantum dots (GQDs) have been considerably employed in numerous optical sensing and bioanalytical applications. Herein, a simple and cost-efficient methodology was developed to the quantification of deferiprone in plasma samples by utilizing the selective interaction of the GQDs and drug in the presence of Fe3+ ions. GQDs were synthesized by a bottom-up technique as an advantageous fluorescent probe. Increasing levels of deferiprone ranging from 5 to 50 mg.L?1, leads to significant fluorescence quenching of GQDs. In addition, the calibration curve was revealed a linear response in this range with a sensitivity of 5 mg.L?1. The method validation was carried out according to the FDA guidelines to confirm the accuracy, precision, stability and selectivity of the developed method. The results show that this green and low-cost fluorescent probe could be used for the analysis of deferiprone.
关键词： Graphene quantum dots (GQDs),Fluorescent,Plasma,Deferiprone,Iron
更新于2025-09-23 15:21:01
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Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media
摘要： Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4–5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe3+, Pb+2, and Cr3+ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe3+, Cr3+ and Pb2+ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions.
关键词： GQDs,Lead and chromium ions,Iron,Fluorescence
更新于2025-09-23 15:19:57
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Biomemristic Behavior for Water-Soluble Chitosan Blended with Graphene Quantum Dot Nanocomposite
摘要： Bionanocomposite has promising biomemristic behaviors for data storage inspired by a natural biomaterial matrix. Carboxylated chitosan (CCS), a water-soluble derivative of chitosan avoiding the acidic salt removal, has better biodegradability and bioactivity, and is able to absorb graphene quantum dots (GQDs) employed as charge-trapping centers. In this investigation, biomemristic devices based on water-soluble CCS:GQDs nanocomposites were successfully achieved with the aid of the spin-casting method. The promotion of binary biomemristic behaviors for Ni/CCS:GQDs/indium-tin-oxide (ITO) was evaluated for distinct weight ratios of the chemical components. Fourier transform infrared spectroscopy, Raman spectroscopy (temperature dependence), thermogravimetric analyses and scanning electron microscopy were performed to assess the nature of the CCS:GQDs nanocomposites. The ?tting curves on the experimental data further con?rmed that the conduction mechanism might be attributed to charge trapping–detrapping in the CCS:GQDs nanocomposite ?lm. Advances in water-soluble CCS-based electronic devices would open new avenues in the biocompatibility and integration of high-performance biointegrated electronics.
关键词： biomemristic behavior,water-soluble CCS:GQDs nanocomposites,CCS-based,binary biomemory
更新于2025-09-23 15:19:57
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Study on the interactions between graphene quantum dots and Hg(II): Unraveling the origin of photoluminescence quenching of graphene quantum dots by Hg(II)
摘要： The present investigation reveals that when Hg(II) interacts with the colloidal solution of graphene quantum dots (GQDs), initially it forms complex with GQDs and then reduces to Hg(0) and Hg(I) resulting the complete quenching of GQDs blue luminescence. This is in contradiction with the earlier reports in which the quenching of GQDs by Hg(II) is attributed to complexation alone. In order to understand the reasons for the quenching of GQDs by Hg(II), a detailed study was undertaken by varying the pH of GQDs solution, incubation time and concentration of Hg(II). The emission studies indicate that formation of Hg(0) is less favorable at pH 7 whereas its formation is more favorable at pH 13. It is assumed that the formation of Hg(OH)2 in alkaline pH facilitates Hg(II) reduction easier than at neutral pH. The SEM and TEM images confirm the presence of spherical Hg(0) particles with different sizes depending upon Hg(II) concentration, pH and incubation time. The results obtained from emission, XPS and differential pulse voltammetry (DPV) studies reveal that Hg(II) was reduced to Hg(0) via Hg(I) on GQDs surface. The differential pulse voltammogram of 40 min incubated Hg(II)-GQDs coated GC electrode shows three oxidation peaks at 0.34, 0.48 and 0.65 V, corresponding to Hg(I) to Hg(II) and Hg(0) to Hg(II), respectively.
关键词： metallic Hg,incubation time,mechanism for quenching,effect of pH,Interaction of GQDs with Hg(II)
更新于2025-09-19 17:13:59
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Selective and Sensitive Visible-Light-Prompt Photoelectrochemical Sensor of Cu2+ Based on CdS Nanorods Modified with Au and Graphene Quantum Dots
摘要： Nowadays, increasing the risk for copper leaching into the drinking water in homes, hotels and schools has become unresolved issues all around the countries such as Canada, the United States, and Malaysia. The leaching of copper in tap water is due to a combination of acidic water, damaged pipes, and corroded plumbing fixtures. To remedy this global problem, a triple interconnected structure of CdS/Au/GQDs was designed as a photo-to-electron conversion medium for a real time and selective visible-light-prompt photoelectrochemical (PEC) sensor for Cu2+ ions in real water samples. The synergistic interaction of the CdS/Au/GQDs enabled the smooth transportation of charge carriers to the charge collector and provided a channel to inhibit the charge recombination reaction. Thus, a detection limit of 2.27 nM was obtained, which is 10,000 fold lower than that of WHO’s Guidelines for Drinking-water Quality (~30 μM). The photocurrent reduction was negligible after 30 days of storage under ambient conditions, suggesting the high stability of photoelectrode. Moreover, the real-time monitoring of Cu2+ ions in real samples was performed with satisfactory results, confirming the capability of the investigated photoelectrode as the most practical detector for trace amounts of Cu2+ ions.
关键词： Copper sensing,Photo-to-electron conversion,High stability,Photoelectrochemistry,CdS/Au/GQDs
更新于2025-09-19 17:13:59
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Silver nanoparticles on graphene quantum dots as nanozyme for efficient H <sub/>2</sub> O <sub/>2</sub> reduction in a glucose biosensor
摘要： In this work, we developed graphene quantum dot-supported silver nanoparticles (AgNPs@GQDs) as Nanozyme for efficient electrocatalytic reduction of H2O2. We applied this composite material in a glucose oxidase-based glucose sensor, by drop casting a mixture of AgNPs@GQDs and chitosan (CS) on glassy carbon electrodes (GCE). Various conditions such as thickness of the AgNPs@GQDs/CS film, pH and temperatures were optimized. The proposed sensor presented excellent selectivity and sensitivity, a linear dependence on glucose concentration in the range 0.1–10 mM and a limit of detection of ca. 0.01 mM.
关键词： hydrogen peroxide reduction,electrochemical sensor,graphene quantum dots (GQDs),silver nanoparticles (AgNPs),glucose oxidase (GOx)
更新于2025-09-19 17:13:59