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

A Mini Review on Carbon Quantum Dots: Preparation, Properties, and Electrocatalytic Application

Luminescent carbon quantum dots (CQDs) represent a new form of nanocarbon materials which have gained widespread attention in recent years, especially in chemical sensor, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. CQDs can be prepared simply and inexpensively by multiple techniques, such as the arc-discharge method, microwave pyrolysis, hydrothermal method, and electrochemical synthesis. CQDs show excellent physical and chemical properties like high crystallization, good dispersibility, photoluminescence properties. In particular, the small size, superconductivity, and rapid electron transfer of CQDs endow the CQDs-based composite with improved electric conductivity and catalytic activity. Besides, CQDs have abundant functional groups on the surface which could facilitate the preparation of multi-component electrical active catalysts. The interactions inside these multi-component catalysts may further enhance the catalytic performance by promoting charge transfer which plays an important role in electrochemistry. Most recent researches on CQDs have focused on their fluorescence characteristics and photocatalytic properties. This review will summarize the primary advances of CQDs in the synthetic methods, excellent physical and electronic properties, and application in electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reduction (HER), and CO2 reduction reaction (CO2RR).

Fluorescent carbon dots functionalization

Carbon dots (CDs), as a new type of luminescent zero-dimensional carbon nanomaterial, have been applied in a variety of fields. Currently, functionalization of CDs is an extremely useful method for effectively tuning their intrinsic structure and surface state. Heteroatom doping and surface modification are two functionalization strategies for improving the photophysical performance and broadening the range of applications for fluorescent CDs. Heteroatom doping in CDs can be used to tune their intrinsic properties, which has received significant research interests because of its simplicity. Surface modification can be applied for varying active sites and the functional groups on the CDs surface, which can endow fluorescent CDs with the unique properties resulting from functional ligand. In this review, we summarize the structural and physicochemical properties of functional CDs. We focused our review on the latest developments in functionalization strategies for CDs and discuss the detailed characteristics of different functionalization methods. Ultimately, we hope to inform researchers on the latest progress in functionalization of CDs and provide perspectives on future developments for functionalization of CDs and their potential applications.

DNA supported graphene quantum dots for Ag ion sensing

The use of graphene quantum dots can be extended for bio-sensing and metal ion detection. Synergistic combination of graphene quantum dots (GQDs) with DNA leads to high performance Ag-ion detection system. The thoroughly characterized GQDs were found to have spherical morphology, with dimensions in the range of 5-10 nm. The atomic force microscopy studies proved that the synthesized GQDs were mostly comprised of two to four graphene layers. To make the system biocompatible, GQDs/NGQDs were combined with DNA. Two properties of DNA were exploited, capacity to provide nitrogen to GQDs; and to synergistically contribute to Ag⁺ detection. In addition to Ag⁺, the strong green photoluminescence (PL) of GQDs showed significant quenching, owing to the appearance of associated Förster resonance energy transfer processes. This led to high sensing efficiencies.

The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe3+ and Hg2+. Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe3+ and Hg2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs' surface. Atomic population analysis results show that some charge transfer from Fe3+ and Hg2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg2+ and Fe2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe3+ and Hg2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe3+ and Hg2+ with a detection limit as low as 2.88 and 0.27 nM, respectively.

Recent Advances on Graphene Quantum Dots: From Chemistry and Physics to Applications

Graphene quantum dots (GQDs) that are flat 0D nanomaterials have attracted increasing interest because of their exceptional chemicophysical properties and novel applications in energy conversion and storage, electro/photo/chemical catalysis, flexible devices, sensing, display, imaging, and theranostics. The significant advances in the recent years are summarized with comparative and balanced discussion. The differences between GQDs and other nanomaterials, including their nanocarbon cousins, are emphasized, and the unique advantages of GQDs for specific applications are highlighted. The current challenges and outlook of this growing field are also discussed.

Praseodymium Vanadate-Decorated Sulfur-Doped Carbon Nitride Hybrid Nanocomposite: The Role of a Synergistic Electrocatalyst for the Detection of Metronidazole

The construction of efficient and superior nanostructured materials for the precise determination of contaminants that are hazardous to the environment has gained significant attention by the scientific community. In this regard, we fabricated a nanocomposite consisting of praseodymium vanadate (PrVO₄; PrV) anchored to sulfur-doped carbon nitride (PrV/SCN) and applied it to the electrochemical detection of the antibiotic drug metronidazole (MTZ). The structural and crystalline features of the as-prepared PrV/SCN nanocomposite were characterized by various analytical and spectroscopic methods. More distinctly, the PrV/SCN nanocomposite-modified glassy carbon electrode (GCE) exhibits an outstanding linear range (0.001-2444 μM), high sensitivity (1.386 μA/μM cm²), low detection limit (0.8 nM), good reproducibility, and strong anti-interference ability. Notably, the PrV/SCN sensor can determine MTZ in spiked urine and water samples with high recoveries, suggesting its feasibility for real-time applications. Our findings establish PrV/SCN as a robust and promising platform for electrochemical detection. This promotes innovative design for the synthesis of novel functional nanocomposites.

Nitrogen doped graphene quantum dots as a fluorescent probe for mercury(II) ions

A highly selective fluorescent probe for Hg²⁺ is reported. It consists of nitrogen doped graphene quantum dots (NGQDs) that are nearly spherical in shape, have an average diameter of 2.7 nm and excitation-independent emission. The blue fluorescence of the NGQDs (with maximum excitation/emission at 378/447 nm) is quenched by Hg²⁺ due to both dynamic and static quenching. The probe has a wide detection range (2.5 μM - 800 μM) and a limit of detection of 2.5 μM. The dynamic and static quenching constants are 417 M^-1 and 63500 M^-1, respectively. The probe was used to quantfy Hg²⁺ in spiked real water samples with satisfactory results. Graphical abstract ᅟ.

Promising Fast Energy Transfer System Between Graphene Quantum Dots and the Application in Fluorescent Bioimaging

Tunable photoluminescence performance of graphene quantum dots (GQDs) is one of the most important topics for the development of GQDs. In this paper, we report lattice-doped GQDs (boron-doped GQDs (B-GQDs) and phosphorus-doped GQDs (P-GQDs)). Because of the matched band structure, the fast energy transfer between blue-emitted B-GQDs (emission wavelength: 460 nm) and orange-emitted P-GQDs (emission wavelength: 630 nm) can induce an efficient fluorescence emission in P-GQDs once B-GQDs are excited under the optimal excitation wavelength of 460 nm. Moreover, with the effective energy transfer, the quantum yield of P-GQDs increased to 0.48, which is much higher than that of pure P-GQDs. We also demonstrated the potentials of this system for fluorescent bioimaging in vitro.

Sulfur-doped graphene quantum dot-based paper sensor for highly sensitive and selective detection of 4-nitrophenol in contaminated water and wastewater

4-Nitrophenol (4-NP) is a promulgated priority pollutant, which can cause a negative impact on human health. The development of a direct and effective technique for the rapid detection and screening of 4-NP is, therefore, of urgent need. In this study, the blue luminescent sulfur-doped graphene quantum dots (S-GQDs) with a size of 1–5 nm are fabricated using a one-step pyrolysis procedure in the presence of citric acid and 3-mercaptosuccinic acid. The S-GQDs exhibit a strong emission band at 450 nm under the excitation of 330 nm UV light. 4-NP can serve as the fluorescence quencher by the π–π interaction with S-GQD, resulting in the linear decrease in fluorescence intensity after the addition of various 4-NP concentrations ranging from 10 nM to 200 μM. The S-GQDs serve as the sensing probe to enhance the analytical performance on 4-NP detection with the limit of detection values of 0.7 and 3.5 nM in deionized water and wastewater, respectively. The S-GQD based sensing platform can be used to detect 4-NP in different matrices of water and wastewater. In addition, the detected percentages of spiked 4-NP concentrations in the presence of different matrices and interferences are in the range of (98 ± 5)–(108 ± 2)%. Moreover, the S-GQD based paper sensor can rapidly screen 4-NP in wastewater within 1 min. Results obtained in this study clearly demonstrate the superiority of S-GQDs as a promising fluorescence probe for highly sensitive and selective detection of a wide concentration range of 4-NP in deionized water and wastewater.

Sulfur-doped graphene quantum dots have been prepared for effective and rapid detection of 4-nitrophenol.

Synthesis of carbon quantum dots with green luminescence from potato starch

Water-soluble carbon quantum dots (CQDs) are synthesized via an acid assisted ultrasonic route using the biomass carbon precursor of potato starch as the raw material.