Properties Of Graphene Quantum Dots Research Articles

Analytical control of imatinib in bioanalytical samples using graphene quantum dots sensing.

An analytical method for the determination of imatinib (IMA, the primary treatment for chronic myeloid leukemia), based on the fluorescence properties of graphene quantum dots (GQDs), is reported in this work. The method is addressed to the analytical control of IMA in biological and pharmaceutical samples, due to the present interest in the control of the doses of this anticancer drug, as well as the therapeutic monitoring. The whole method involves the use of a solid-phase extraction (SPE) procedure, followed by an evaporation step, for the treatment of biological samples. For that, tC18 sorbent cartridges were used. After the sample treatment, the solution containing the analyte was mixed with an aqueous solution of GQDs at pH 7.2, and the fluorescent quenching of GQDs was measured. IMA was determined in the 10-250µgL-1 range, with a limit of detection of 21µgL-1 and a precision of 1.5% as relative standard deviation, measured in terms of reproducibility. The recovery for biological samples was in the 84-113% range.

Study on the Terahertz Spectroscopy Properties of Graphene Quantum Dots Based on Microfluidic Chip

Graphene quantum dots are quasi-zero-dimensional nanomaterials with unique physical and chemical properties. This study utilized a terahertz (THz) time-domain spectroscopy system to analyze the absorption characteristics of THz-waves by graphene quantum dots at different concentrations. Additionally, we applied electric fields and magnetic field to explore the THz-wave absorption properties of graphene quantum dots in greater detail. The results indicate that the THz absorbance of graphene quantum dots is positively correlated with sample concentration and applied electric field strength. However, it is negatively correlated with the intensity of the applied magnetic field. This work combines THz technology and microfluidic devices to propose a viable methodology for conducting in-depth study on graphene quantum dots.

Precursor Symmetry Triggered Modulation of Fluorescence Quantum Yield in Graphene Quantum Dots

AbstractAlthough various effective machine‐learning attempts have been made to investigate the photoluminescence properties of graphene quantum dots (GQDs) or carbon dots, the physical correlation behind their mathematical models has not been reasonably elucidated. In this work, the correlation mechanism between the precursor structure and quantum yield of GQDs prepared by a “bottom‐up” method is sufficiently studied. Three decisive factors affecting the quantum yield of GQDs during the two‐component reaction system preparation are revealed, namely structure factor (F1), temperature factor (F2), and concentration factor (F3). The symmetry of precursors in the formation of sp2–sp3 hybrid carbon nanostructures is considered the key factor in the modulation of fluorescence quantum yield in GQDs. Notably, in contrast to previous work, it is first demonstrated that the normal modes of molecular vibration are the core mechanism by which the structural properties of the precursors act on the fluorescence quantum yield of GQDs. The conclusion further proved conducive in obtaining GQDs with a higher absolute quantum yield up to 83.33%.

Tuning optical properties of graphene quantum dots using photoexcited TiO2 for catalytic application

In this work, a simple strategy to tune the emission property of graphene quantum dots (GQDs) from green to blue color using a photochemical method is proposed. Further, the resultant materials are demonstrated to be an efficient and effective catalyst for the reduction of p-nitrophenol to p-aminophenol. Initially, green color emitting GQDs (g-GQDs) is prepared by using a chemical method involving acid reflux of graphene oxide obtained from a modified Hummer's method. Later these g-GQDs are exposed to photochemical excitation with titanium dioxide (TiO2) using UV light at a fixed wavelength of 365 nm and the resultant GQDs are observed to emit blue color (b-GQDs). Basically, the introduction of photochemically excited TiO2 nanoparticles provides excess electrons for g-GQDs to undergo further reduction to form b-GQDs leading to the formation of more sp2 hybridized domains within the carbon network than sp3 in the resultant b-GQDs. Consequently, the emission of GQDs is shifted from green to blue, and significantly ∼4 fold enhancement in the average quantum yield of GQDs is noted. These interesting research findings are analyzed by using zeta potential measurements, spectroscopic (FTIR, UV–visible, and Fluorescence) studies and microscopic investigation. Finally, TiO2 reduced GQDs are subsequently used for the reduction of p-nitrophenol to p-aminophenol, and the results obtained revealed that this material could potentially be employed as an effective catalyst.

Engineering functionalization and properties of graphene quantum dots (GQDs) with controllable synthesis for energy and display applications.

Graphene quantum dots (GQDs), a new type of 0D nanomaterial, are composed of a graphene lattice with sp2 bonding carbon core and characterized by their abundant edges and wide surface area. This unique structure imparts excellent electrical properties and exceptional physicochemical adsorption capabilities to GQDs. Additionally, the reduction in dimensionality of graphene leads to an open band gap in GQDs, resulting in their unique optical properties. The functional groups and dopants in GQDs are key factors that allow the modulation of these characteristics. So, controlling the functionalization level of GQDs is crucial for understanding their characteristics and further application. This review provides an overview of the properties and structure of GQDs and summarizes recent developments in research that focus on their controllable synthesis, involving functional groups and doping. Additionally, we provide a comprehensive and focused explanation of how GQDs have been advantageously applied in recent years, particularly in the fields of energy storage devices and displays.

Insight into the effect of synthesis parameters on the properties of graphene quantum dots for theranostic application

Ultra-small size and tunable optical properties of graphene quantum dots (GQDs) make them potentially suitable for theranostic applications. This investigation focuses on the effect of process parameters for the synthesis of GQDs of desirable optical properties for biomedical applications. The effect of the raw materials (graphene oxide sheets, glucose, and starch), reaction temperature (170 to 200 °C), and reaction time (3 to 6 h) was investigated on GQDs prepared through hydrothermal treatment. The dispersion of GQDs was characterized using dynamic light scattering (DLS), UV–visible, fluorescence, Raman, and X-ray photon spectroscopic techniques. The effect of the solution temperature and pH on the fluorescence properties of GQDs was also studied. The small hydrodynamic diameter (8.57 ± 1.47 nm) was observed with GQDs prepared from glucose using hydrothermal treatment time of 4 h at 190 °C (GQDs-D). The GQDs-D showed blue fluorescence (λem= 460 nm) with a quantum yield (QY) 67.09 ± 1.25%. The fluorescence characteristic of the GQDs was unchanged up to 6 months during storage at room temperature. GQDs-D revealed their antioxidant nature with a DPPH scavenging activity of 15.08 ± 2.07%. Despite having relatively low DPPH scavenging activity, excellent hemocompatibility (0.23 ± 0.04%) and colloidal stability against bovine serum albumin (BSA) showed GQDs-D as a safe nanocarrier for theranostic application. This was further substantiated with circular dichroism (CD) spectroscopy, which exhibited a preserved α-helical structure of BSA by GQDs-D. High-resolution transmission electron microscopic image of GQDs-D showed an average particle size of 5.70 nm and homogeneous particle distribution between 2–8 nm. Conclusively, all the results revealed the potential of GQDs-D for theranostic application.

Effect of AlN dimers on the electronic properties of graphene quantum dot: DFT investigations

Tuning the electronic properties of engineered graphene quantum dots (GQDs) is used to produce nanoelectronic devices, which are important in many applications. Chemical doping is applied to give GQDs controllable electronic properties. As a model for GQDs, we considered a molecule with 7 benzene rings and a hydrogen atom at the end of each edge carbon atom (written as C24H12). We considered engineering electronic characteristics in a GQD by altering its geometrical pattern of aluminium nitride (AlN) dimers, and so we employed the density function theory (DFT) approach with B3LYP/6-31G level to study the GQD with and without different dopants of AlN dimers. Ortho, meta, and para position dimers of aluminum and nitrogen atoms are used in the making of the three types of AlN dimers. The electronic properties which including DOS resolution, total energies, HOMO and LUMO energies, Fermi level, bandgap, reactivity descriptors, and molecular electrostatic potential are considered. It has been determined that the presence of AlN dimers has a major impact on the bandgap of the GQD. Based on our findings, the electronic characteristics of GQD are affected not only by the number of GQD dimers present but also by the arrangement of AlN dimers within the GQD. By suitably doping AlN dimers, we can tune the bandgap of GQDs. These results contribute to a better understanding of how chemical doping modifies electronic properties of GQDs and inspires the development of nanodevices with enhanced electronic performance.

Green synthesis, characterisation, optical properties of graphene quantum dots with anti bacterial characteristics

Green synthesis, characterisation, optical properties of graphene quantum dots with anti bacterial characteristics

Theoretical insights into tunable electronic properties of graphene quantum dots through ZnO doping

Quantum dots are interesting systems because they can be tuned electronically. We used graphene quantum dots (GQDs) known as the formula C24H12 as a model for studying the effect of zinc oxide (ZnO) dimers on the structural and electronic properties of GQDs by density functional theory (DFT) investigation. By modifying a GQD geometrical pattern with ZnO dimers, three different forms of ZnO dimers are used to create the zinc and oxygen atoms in the ortho, meta, and para positions. Based on our findings, it has been found that the bandgap values of the GQD structure are significantly influenced by the presence and form of ZnO dimers. the electronic characteristics of GQD are affected not only by the number of GQD dimers present but also by the arrangement of ZnO dimers within the GQD. By suitably doping ZnO dimers, we can tune the bandgap of GQDs. These findings provide insight into how chemical doping affects the electronic characteristics of GQDs and motivate the design of nanodevices with improved electronic performance.

Advances in Structural Modifications and Properties of Graphene Quantum Dots for Biomedical Applications.

Graphene quantum dots (GQDs) are carbon-based, zero-dimensional nanomaterials and unique due to their astonishing optical, electronic, chemical, and biological properties. Chemical, photochemical, and biochemical properties of GQDs are intensely being explored for bioimaging, biosensing, and drug delivery. The synthesis of GQDs by top-down and bottom-up approaches, their chemical functionalization, bandgap engineering, and biomedical applications are reviewed here. Current challenges and future perspectives of GQDs are also presented.

Effect of hetero-atom doping on the electrocatalytic properties of graphene quantum dots for oxygen reduction reaction

Oxygen reduction is an important reaction involved in a diverse variety of energy storage devices and also in many chemical and biological processes. However, the high cost of suitable catalysts like platinum, rhodium, and iridium proves to be a major obstacle for its commercialization. Consequently, many new materials have emerged in recent years such as various forms of carbon, carbides, nitrides, core–shell particles, Mxenes, and transition metal complexes as alternatives to platinum and other noble metals for oxygen reduction reaction (ORR). Among these, Graphene Quantum Dots (GQDs) as metal-free alternatives have captured universal attention, since electrocatalytic properties can be tuned not only by size and functionalization but by heteroatom doping also. We discuss electrocatalytic properties of GQDs (approximate size 3–5 nm) with specific dopants such as N and S focusing on their synergistic effects of co-doping, prepared by solvothermal routes. Cyclic Voltammetry shows benefits of doping as lowering of the onset potentials while steady-state Galvanostatic Tafel polarization measurements show a clear difference in the apparent Tafel slope, along with enhanced exchange current densities, suggesting higher rate constants.

First-principles studies the optical properties of defective-GQDs and -fullerene

We demonstrate the size effect of quantum dots and discuss the effect of defect on the luminescence properties of graphene quantum dots (GQDs) and fullerene (C60) in this paper. Results show that the smaller the GQDs, the more difficult it is to prepared. The absorption peak of visible light region can be attained from large-size GQDs and small-size GQDs mainly show the luminescence performance of UV region. The band gap of GQDs become narrower and narrower with increasing size and adjusting symmetry. And then C60 (0.7 nm) with higher symmetry exhibits better optical and electronic conductivity. The defective GQDs and C60 have better adsorption capacity for functional group –OH and -NMP than non-defective structure. And the effect of defect and adsorbed functional group on the optical properties is clearly different, which C defect and functional group adsorption can improve its optical properties for large size GQDs and completely weaken its optical properties for C60.

Paper-based electrodes with nitrogen-doped graphene quantum dots for detection of copper ions via electrochemiluminescence

Nitrogen-doped graphene quantum dots (N-GQDs) were prepared using pyrolysis, with citric acid and urea as the carbon and nitrogen sources, respectively, to be used for Cu2+ ion detection in a paper-based ECL sensor. Existing methods for Cu2+ detection require expensive equipment, specialized experimental chambers, or complex sample pretreatment procedures, which limit their functionality. Using first principles, the electronic and optical properties of graphene quantum dots (GQDs) and N-GQDs were calculated and analyzed. The N-GQDs showed clearer green fluorescence under long-wave ultraviolet light and a better, more stable electrochemiluminescence (ECL) performance. Using first principles, the electronic and optical properties of the GQDs and N-GQDs were calculated and analyzed, and A theoretical mechanism for the observed ECL enhancement in the N-GQDs was proposed. A paper-based ECL sensor with N-GQDs was then developed, using a screen-printing technique, to detect Cu2+ ions. The results showed that the ECL intensity of the sensor increased as the Cu2+ ion concentration increased, and the sensor demonstrated a linear detection range of 0.01–1000 μM. Overall, the sensor exhibited excellent ECL stability, reproducibility, and selectivity. This simple, inexpensive, and effective monitoring technique can be used to detect Cu2+ to prevent negative effects on human health and the environment.

Effect of defects on optical and electronic properties of graphene quantum dots: a density functional theory study.

The effects of different types of defects (vacancy, Stone-Wales defects, and heteroatom doping) and varying defect concentrations (single and double defects) on the structure, electronic, and optical properties of graphene quantum dots (GQDs) are systematically investigated using time-dependent density functional theory (TD-DFT). The results reveal that most defects induce noticeable structural distortions, with increasing deformation at higher defect concentrations. Compared to pristine GQD model C96 (with a maximum absorption peak at 592 nm), the absorption spectra of 6 defective C96 exhibit blue shifts ranging from 554 to 591 nm, while 12 defective C96 lead to red shifts (598-668 nm). The HOMO-LUMO gaps vary from 0.62 to 2.04 eV (2.10 eV for pristine C96). Quantitative analysis of the absorption spectra and molecular orbital energy levels demonstrate that the electronic and optical properties of defective C96 strongly depend on the types, concentrations, and locations of defects. NTO analysis illustrates that higher electron localization exists in defective C96, which is attributed to the disruption of the original π-conjugation caused by structural distortions and different orbital hybridizations. These findings offer a comprehensive insight into the impact of defects on GQDs and provide valuable guidance for exploiting the unique features of GQDs to expand new applications in various fields.

Recent advances in the graphene quantum dot-based biological and environmental sensors

• Unique properties of graphene quantum dots (GQDs). • Syntheses of GQDs with controlled structures. • Advances in GQD-based biological and environmental sensors. Graphene quantum dots (GQDs) are zero-dimensional (0D) materials having unique luminescence properties due to quantum confinement and edge effect. Coupled with their large surface area, chemical- and photostability, biocompatibility, and low-toxicity, GQDs have enchanted many attentions for fundamental researches and applications. In particular, the broad synthesis methods with ease of functionalization and controlled-synthesis as well as large variety of naturally available precursors, have made GQDs to be suitable for the development of advanced, rapid, and versatile optical-based biological and environmental sensors with high sensitivity and selectivity. In this review, we summarize the intrinsic knowledge about GQDs related to what properties that make them interesting as nanosensors and further highlight the recent advances in their synthesis methods particularly from naturally available resources. Furthermore, fundamental sensing mechanisms will also be given to provide basic knowledge and more comprehensive understanding to the readers about GQDs as luminescence-based biological and environmental nanosensors. The current limitations and future prospects of GQDs are highlighted as the final conclusion of this review, hoping that the readers from various multidisciplinary natures to contribute their expertise and collaborate not only to improve the currently available GQD-based sensors but also developing a new sensing concepts which have never been realized. Graphical Abstract. .

Effect of surface modification on optical and electronic properties of graphene quantum dots

Optical and electronic properties of graphene quantum dots (GQDs) could be modified either by introducing heteroatoms on their surface or by covalently linking these with certain groups. In this work, time-dependent density functional theory (TD-DFT) with functional B3LYP/6-31G* has been used to study the effects of boron doping and surface-modified configurations of GQDs on the HOMO-LUMO gap and absorption spectra. The photoluminescence properties and quantum yield of GQDs have also been explored. Doping as well as a surface modification with boron configurations resulted in a decrease in the band gap and a red shift in absorption and photoluminescence/fluorescence spectra. As compared to surface modified GQDs, the presence of B atom in the edge modified GQDs has a pronounced effect on the tuning of the energy bandgap. Also, BCO2 is found to affect the electrical structures of GQDs more significantly as compared to BC2O. The fluorescence of surface-modified GQD is found fall in the near-infrared region with a quantum yield of 29 % rendering them suitable for bio-imaging applications. The results thus obtained are in good consonance with those reported in the literature.

Scalable preparation of high-dispersion g-C3N4via GQDs-assisted ultrasonic exfoliation for accelerating cement hydration

Tremendous progress has been made in the employment of two-dimensional (2D) nanomaterials in cement composites. However, high cost and poor dispersion of 2D nanomaterials immensely hinder their extensive use. To address these issues, in this work, a scalable, simple, and eco-friendly graphene quantum dots (GQDs)-assisted ultrasonic exfoliation approach was elaborately designed to efficiently delaminate and disperse bulk g-C3N4 (B–CN), thereby obtaining low-cost and high-dispersion CN (G-CN). And the effect of B–CN, B–CN exfoliated without GQDs (U–CN) and G-CN on cement hydration was comprehensively investigated for the first time. Specifically, G-CN possessed a remarkably higher dispersion and a larger specific surface area (32.92 m2 g−1) increasing by 44.45% and 183.55% than U–CN and B–CN, respectively. And based on characteristics of G-CN and properties of GQDs, the exfoliation mechanism of g-C3N4 was ascribed to intercalation, exfoliation, and surfactant effects of GQDs. More importantly, highly dispersed G-CN was more propitious to accelerate cement hydration and refine microstructure, thereby dramatically boosting the compressive strength of cement paste at 7-day curing by 10.1% and 25.0% compared with that of U–CN and B–CN, respectively. This work not only provided a scalable, facile and environmentally-friendly approach to efficiently fabricate well dispersive g-C3N4, but also firstly testified their evident accelerating effect on cement hydration. These findings would be conducive to advancing the application of 2D nanomaterials in cement composites.

Polarity, intramolecular charge transfer, and hydrogen bond co-mediated solvent effects on the optical properties of graphene quantum dots

Polarity, intramolecular charge transfer, and hydrogen bond co-mediated solvent effects on the optical properties of graphene quantum dots

Ultrafast electron dynamics of graphene quantum dots: High harmonic generation

We study theoretically nonlinear optical properties of graphene quantum dots placed in a field of a short and strong linearly polarized optical pulse. We address the problem of high harmonic generation in quantum dots and how such nonlinear effect is affected by dephasing processes in a quantum dot. The dephasing makes the ultrafast electron dynamics more irreversible with a large residual population of the excited quantum dot levels. In relation to the high-harmonic spectrum, with increasing the dephasing time, the intensities of the low-frequency harmonics increase while the cutoff energy decreases. The dependence of the cutoff energy on the amplitude of the optical pulse is also sensitive to the frequency of the pulse. When the frequency of the optical pulse is much less than the quantum dot band gap, this dependence is almost linear, but when the frequency of the pulse is comparable to the band gap, the cutoff energy shows saturation behavior at large field amplitude, $>0.4$ V/\AA{}.

Nonradiative electron-hole recombination dynamics in edge-selective phosphorus-doped graphene quantum dots for energy conversion applications

Doping with heteroatoms is an effective way to modify the electronic structures and photophysical properties of graphene quantum dots (GQDs). However, there are few studies on phosphorus-doped GQDs (P-GQDs), especially with respect to the dynamics of electron-hole recombination, which plays a crucial role in the energy conversion performance of P-GQDs. In the current study, we investigate the effect of phosphorus-containing groups (i.e., phosphine oxide, phosphonic acid, phosphate, and phosphinic acid) on the electronic structures, optical properties, and dynamics of nonradiative recombination of P-GQDs with different edge coverages and structural symmetries. Our results show that P-doping disrupts the integrity of the conjugated π-skeleton of carbon system, leading to the localization of electrons in P-GQDs. The phosphine oxide has a stronger effect on the sp2 bonding environment of the carbon skeleton, leading to a greater impact on the geometrical and electronic structures of the P-GQDs than in the other P-functionalized systems. The increase in the passivation density of phosphinic acid leads to localization of electron and hole densities at the periphery of the GQDs. In addition, the PC bond in phosphonic acid dramatically increases the electronic coupling, leading to the fastest non-radiative decay rate. The overall photovoltaic performance of phosphate- and phosphine oxide-functionalized GQDs are better than the other P-functionalized GQDs. Our calculations provide guidance for the rational design of P-doping configurations in P-GQDs to improve their energy conversion efficiency.