Functionalized Graphene Quantum Dots Research Articles

GQDs@SiO3Pr Schiff-base complexes Co (II); As an eco-friendly environmental nanocatalyst for the synthesis of the amino carbonitrile chromenes

An effective nanocomposite comprising functionalized graphene quantum dots has been developed for the rapid, one-step production of amino carbonitrile chromenes. To this end, the surface of graphene quantum dots (GQDs) was functionalized with a novel synthetic Schiff-base complex of cobalt (II) prepared by post-synthetic surface modification of the graphene quantum dot surface with a silane coupling agent (3-chloropropyl trimethoxysilane, SiO3PrCl) in order to synthesize GQDs@SiO3PrCl. Then, the Schiff base ligand synthesized from the condensation reaction of 4-aminoantipyrine with ortho-phenylenediamine was immobilized on the surface of the silane-linker grafted GQDs to synthesize the GQDs@SiO3Pr-Schiff base. Finally, the cobalt particles were stabilized on the surface of the graphene quanta functionalized with Schiff bases (GQDs@SiO3Pr-Schiff Base/Co (II)). The GQDs@SiO3Pr-Schiff Base/Co (II) nanocatalyst demonstrated exceptional performance in the synthesis of amino carbonitrile chromenes derivatives, facilitating high product yields using various aromatic aldehydes, 4‑hydroxy coumarin and malononitrile under mild conditions. Additionally, the catalyst exhibited reusability up to seven times without significant loss of productivity, showcasing its environmental friendliness and sustainability in organic synthesis. This versatile nanocatalyst holds promising for efficient and economically viable catalysis in diverse chemical applications.

Construction of Carbon Dioxide Responsive Graphene Point Imbibition and Drainage Fluid and Simulation of Imbibition Experiments

The global oil and gas exploration targets are gradually moving towards a new field of oil and gas accumulation with nanopore throats, ranging from millimeter scale to micro-nano pore throats. The development method of tight oil reservoirs is different from that of conventional oil reservoirs, and the development efficiency is constrained. Therefore, it is necessary to construct a nanoscale fluid with strong diffusion and dispersion and improve its permeability, suction, and displacement capabilities. Under the background of CCUS, carbon dioxide flooding is a better way to develop tight reservoirs. However, in order to solve the problem of gas channeling, this paper developed a carbon dioxide-responsive graphene point type surfactant, which has a good gas–liquid synergistic effect. At the same time, graphene nanomaterials are carbon-based and create no environmental damage in oil reservoirs. In this study, graphene quantum dots (GQDs) were prepared using the hydrothermal method, and functional graphene quantum dots (F-GQDs) responsive to carbon dioxide stimulation were synthesized by covalent grafting of amidine functional groups. By characterizing its structure and physical and chemical properties, and by conducting imbibition simulation experiments, its imbibition and drainage ability in nanopore throats is elucidated. Infrared spectrum measurement shows that after functional modification, the quantum dots exhibited new characteristic peaks at 1600 cm−1 to 1300 cm−1, considering the N-H plane-stretching characteristic peak. The fluorescence spectra showed that the fluorescence intensity of F-GQDs was increased after functional modification, which indicated that F-GQDs were successfully synthesized. Through measurements of interfacial activity and adhesion work calculations, the oil–water interfacial tension can achieve ultra-low values within the range of 10−2 to 10−3 mN/m. Oil sand cleaning experiments and indoor simulations of spontaneous imbibition in tight cores demonstrate that F-GQDs exhibit effective oil-washing capabilities and a strong response to carbon dioxide. When combined with carbon dioxide, the system enhances both the rate and efficiency of oil washing. Imbibition recovery can reach more than 50%. The research results provide a certain theoretical basis and data reference for the efficient development of tight reservoirs.

Polyvinyl alcohol fiber with enhanced strength and modulus and intense cyan fluorescence based on covalently functionalized graphene quantum dots

Polyvinyl alcohol fiber with enhanced strength and modulus and intense cyan fluorescence based on covalently functionalized graphene quantum dots

Influence of B, Si, Ge, and As impurities on the electronic properties of graphene quantum dot: A density functional theory study

The electronic features of chemically functionalized graphene quantum dots (GQDs) are investigated using density functional theory (DFT). The fabrication of nanoscale devices needs to enhance- the electronic performance of customized GQDs, which is crucial in many applications. GQDs can be used as a model with the molecule C24H12. We investigated the effects of adding metalloid impurities) boron B, silicon Si, germanium Ge, and arsenic As) on the structure and electronic properties of the dots at the B3LYP/6–31 level using the Gaussian 09 program package. The obtained results show efficient adding impurities B, Si, Ge, and As on the structure and electronic properties of GQDs, where it is noted that the energy gap change with -3.085, -12.340, -13.907, and -66.846 %, respectively.These results not only advance our knowledge of the mechanisms behind chemical doping, which may change the electronic features of quantum dots, but they also provide support for the development of nanodevices that have better electronic performance. As observed with As/GQD, it is anticipated that this system, which has the lowest possible chemical hardness values, will function as an effective corrosion inhibitor.

Synthesis of histidine, serine and folic acid-functionalized and boron and iron-doped graphene quantum dot with excellent optical behavior and peroxidase-like activity for colorimetric and fluorescence detection of H2O2 in food

Low fluorescence under visible light excitation and catalytic activity limit many applications of graphene quantum dots in optical detection, biosensing, catalysis and biomedical. The paper reports design and synthesis of histidine, serine and folic acid-functionalized and boron and iron-doped graphene quantum dot (Fe/B-GQD-HSF). The Fe/B-GQD-HSF shows excellent fluorescence behavior and peroxidase-like activity. Excitation of 330 nm ultraviolet light produces the strongest blue fluorescence and excitation of 480 nm visible light produces the strongest yellow fluorescence. The specific activity reaches 92.67 U g−1, which is higher than that of other graphene quantum dots. The Fe/B-GQD-HSF can catalyze oxidation of 3,3′,5,5′-tetramethylbenzidine with H2O2 to form blue compound. Based on this, it was used for colorimetric and fluorescence detection of H2O2. The absorbance at 652 nm linearly increases with the increase of H2O2 concentration between 0.5 and 100 μM with detection limit of 0.43 μM. The fluorescence signal linearly decreases with the increase of H2O2 concentration between 0.05 and 100 μM with detection limit of 0.035 μM. The analytical method has been satisfactorily applied in detection of H2O2 in food. The study also paves one way for design and synthesis of functional graphene quantum dots with ideal fluorescence behavior and catalytic activity.

Interfacial Bridging Enables High Performance Perovskite Solar Cells with Fill Factor Over 85%

AbstractThe power conversion efficiency (PCE) of perovskite solar cells (PSCs) is approaching their Shockley‐Queisser (S‐Q) limit through numerous efforts in key parameters improvement. To further approaching the limit, it is important to facilitate the fill factor (FF), a parameter closely related to carrier transport and nonradiative recombination. Herein, an interfacial bridging strategy is proposed to improve FF, which utilizes functional graphene quantum dots at the tin oxide (SnO2)/perovskite buried interface. As a result, synergistic effects of enhanced conductivity of SnO2, preferable energy alignment at the buried interface and improved perovskite crystal orientation are realized. The champion FF reaches 85.24% in formamidinium lead iodide (FAPbI3) based PSCs, which ranks among the highest in the n‐i‐p structure. Such strategy is also proven successful in other perovskite systems, where the champion PCE reaches 24.86% in the formamidinium‐cesium (FACs)‐based devices and 24.44% in the flexible devices. Therefore, this work provides a practical design rule for pursuing high FF of PSCs with carbon materials.

High-Performance All-Solid-State on-Chip Planar Micro-Supercapacitors Based on Aminated Graphene Quantum Dots by Photolithography

Rapid development of portable miniaturized electronic devices has put forward higher requirements for microenergy. Functionalized graphene quantum dots combine the properties of both functionalized graphene and quantum dots, and are expected to promote further development of high-performance energy storage devices. Here, all-solid-state on-chip planar micro-supercapacitors (PMSCs) were fabricated based on aminated graphene quantum dots by modified liquid-gas interface self-assembly and photolithography, with the electrode width/gap of 24 μm/8 μm. The electrochemical performance was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectrometry and cycle stability in PVA/H2SO4 gel electrolyte. The results indicated that the fabricated PMSCs showed good capacitive response at the scan rates of 0.01 V s−1 to 10000 V s−1. The CV curves of the PMSCs displayed a typical pseudocapacitive feature at the scan rates of 0.01 V s−1 to 1 V s−1. The PMSCs had ultrahigh rate capability of up to 10000 V s−1, and the GCD curves were near triangle-shaped curves, demonstrating excellent electrochemical reversibility. The PMSCs showed ideal capacitive behavior at the low frequency region of the Nyquist plot. The Nyquist plot of the PMSCs showed a semicircle at the high frequency region. The relaxation time constant of the PMSCs were 3.59 μs, indicating that the PMSCs had fast frequency response. After 10000 charge-discharge cycles at the scan rate of 500 V s−1, the initial capacitance retention rate of the PMSCs were 99.17%, indicating that the PMSCs possessed good long-term electrochemical stability. This study provides an important reference for the application of functional graphene quantum dots in the field of the PMSCs.

Highly crystalline poly-3-hexylthiophene particles prepared from Pickering emulsions stabilized by alkylamine functionalized graphene quantum dots

Pickering emulsions have received much attention due to their high emulsions stability and ability to form functional emulsions compared to conventional emulsions. The stability of Pickering emulsions is dependent on the geometry and wettability of the particle type emulsifiers, which affect the detachment energy at the interface. Therefore, surface property control of the particle is essential. The graphene quantum dots (GQDs) functionalized with octylamine (C8), dodecylamine (C12), and hexadecylamine (C16) were synthesized and the stability of oil-in-water type Pickering emulsions compared. The detachment energies of the Pickering emulsifiers were calculated by measuring their wettability. Crystalline poly-3-hexylthiopene nanoparticles (P3HT NPs) were synthesized from the Pickering emulsion with C12-GQDs. Among the three GQDs, the C12-GQDs formed the most stable Pickering emulsions at the water-CHCl3 interface because of an appropriate balance between the water and oil phases due to the highest detachment energy. High-crystalline P3HT NPs can be synthesized from the Pickering emulsion with C12-GQDs due to the slower solvent evaporation and enhanced stability.

Tunable dielectric characteristics of the nanocomposite diode based on functionalized graphene quantum dots with and without gadolinium

In this study, we have separately synthesized and characterized solutions of gadolinium (Gd)-free and Gd-doped polyethyleneimine (PEI)-functionalized graphene quantum dots (GQDs) due to the excellent properties of Gd, a rare earth element, in fluorescence and magnetic resonance imaging (MRI). The dielectric properties of Gd-free/doped nanocomposite-based diodes have been compared using impedance spectroscopy (IS) in the frequency range from 1 kHz to 500 kHz and voltage range from −3 V to +5 V at 300 K. From our experimental results, the Gd-free diode was found to have a negative dielectric constant (ε′). In contrast, the Gd-doped nanocomposite diode exhibited positive ε′. The ε′ of the Gd-free diode is −80, while the ε′ of the Gd-doped diode is 35 at 5 V for 1 kHz. The experimental results showed that the dielectric properties of both structures were strongly dependent on the applied voltage and frequency. The Gd doping in the interface has prevented the domination of loss mechanisms within the structure, eliminated negative dielectric at lower frequencies, and conferred a unique micro-capacitor characteristic to the structure. All these efforts will contribute to the development of functional carbon-based materials and the creation of new electronic devices and tunable dielectric properties.

Synthesis, characterization and thermophysical properties of PAG-Amine functionalized graphene quantum dots based nanosuspension

This work presents the synthesis, characterization and evaluation of thermophysical properties of PAG (Polyalkylene glycol)-amine functionalized graphene quantum dots-based nanosuspension. The synthesis is carried out in two steps. In the first step graphene oxide is synthesized using Hummers method and in the next step synthesis of amine functionalized graphene quantum dots is done. The obtained quantum dots are further ultrasonicated in the Polyalkylene glycol resulting in varying concentrations of nanosuspension. For the characterization of graphene oxide Field Emission Scanning Electron Microscopy (FESEM) analysis is done, and for nanosuspension High-Resolution Transmission Electron Microscopy (HRTEM) and ultraviolet (UV)-spectrophotometer analysis is carried out. The thermophysical properties such as thermal conductivity and viscosity are examined using the Hamilton and Maxwell model which are further validated with experimental investigations.

Antibacterial property of dual-network hydrogel filled with amino functionalized graphene quantum dots

Bacterial infections seriously impair wound healing, so the development of wound dressings with high antimicrobial activity is of critical importance. In this study, amino functionalized graphene quantum dots (His-GQDs) were prepared via thermal pyrolysis of citric acid and histidine, and doped into a dual-network gelatin/sodium alginate (His-GQDs/G/SA) hydrogel to improve the antibacterial activity. The His-GQDs/G/SA hydrogel exhibited excellent antibacterial activity after 6 h of contact with bacteria. Simultaneously, the composite hydrogel could effectively alleviate the cytotoxicity of His-GQDs. The results of antimicrobial and biocompatibility tests demonstrate that the His-GQDs/G/SA dual-network hydrogel is a promising wound dressing to promote healing of infected wounds.

Unraveling the potential of graphene quantum dots against Mycobacterium tuberculosis infection.

The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) strains has underscored the urgent need for novel therapeutic approaches. Carbon-based nanomaterials, such as graphene oxide (GO), have shown potential in anti-TB activities but suffer from significant toxicity issues. This study explores the anti-TB potential of differently functionalized graphene quantum dots (GQDs) - non-functionalized, L-GQDs, aminated (NH2-GQDs), and carboxylated (COOH-GQDs) - alone and in combination with standard TB drugs (isoniazid, amikacin, and linezolid). Their effects were assessed in both axenic cultures and in vitro infection models. GQDs alone did not demonstrate direct mycobactericidal effects nor trapping activity. However, the combination of NH2-GQDs with amikacin significantly reduced CFUs in in vitro models. NH2-GQDs and COOH-GQDs also enhanced the antimicrobial activity of amikacin in infected macrophages, although L-GQDs and COOH-GQDs alone showed no significant activity. The results suggest that specific types of GQDs, particularly NH2-GQDs, can enhance the efficacy of existing anti-TB drugs. These nanoparticles might serve as effective adjuvants in anti-TB therapy by boosting drug performance and reducing bacterial counts in host cells, highlighting their potential as part of advanced drug delivery systems in tuberculosis treatment. Further investigations are needed to better understand their mechanisms and optimize their use in clinical settings.

Novel palladium nanoparticles/4-aminophenol functionalized nitrogen-doped graphene quantum dots-based nanocomposite electrochemical sensor: Synthesis, characterization, capacitance, and dopamine sensing

In this study, an ultrasensitive electrochemical sensor based on palladium nanoparticles/4-aminophenol functional nitrogen-doped graphene quantum dots (PdNPs/4AP N-GQDs) composite was fabricated to detect dopamine (DA). The sensor was characterized by FTIR, UV–Vis, TEM, EDX, and XRD methods. The electrochemical analysis of the nanocomposite modified glassy carbon electrode (GCE) was conducted by cyclic voltammetry (CV). HOMO-LUMO energy levels and band gap energy was calculated from cyclic voltammograms, and the band gap energy was found to be small at 0.06 eV. The electrode reaction properties of dopamine on this developed ultrasensitive electrode were investigated by CV and differential pulse voltammetry (DPV), which showed that the electrode had electrocatalytic activity for dopamine sensing. Moreover, the developed electrode exhibited good sensitivity and improved performance, and the linear calibration curve for dopamine was calculated to have a LOD (limit of detection) of 21 pM in the range of 250 pM to 10 nM. Finally, the selectivity of the GQDs nanocomposite modified GCE towards dopamine was studied in the presence of several bioactive compounds with inhibitory effects. In addition, the specific capacitance of the nanocomposite material at 5 mV s−1 was found to be as high as 0.777F g−1. Furthermore, the dopamine selectivity of the sensor among some organic and inorganic interfering bioanalytes was investigated and the sensor was found to have excellent DA selectivity despite the bioanalytes.

Theoretical study on the utilization of N, O-functionalized graphene quantum dots in Li-S batteries

Lithium-sulfur (Li-S) batteries have high theoretical capacity and high energy density, and their practical application is difficult because of the “shuttle effect” induced by lithium polysulfides (LiPSs) and the difficulty of insoluble Li2S decomposition. Functionalized graphene quantum dots (GQDs) can anchor LiPSs and suppress the “shuttle effect” because of the various polar functional groups. This work investigates the effect of the size of GQDs and the N/O functional groups on the anchoring performance by first-principles calculations. In addition, the influence on the decomposition of Li2S, the diffusion of Li+, and the Gibbs free energy needed for the sulfur reduction reaction was also studied. The results show that the GQDs can effectively anchor LiPSs when the size is larger than 1.44 nm, and all the N/O-functionalized GQDs can also effectively anchor LiPSs. Among these N/O-functionalized GQDs, GQDs-COOH has the smallest Li+ diffusion energy barrier (0.52 eV) and low Li2S decomposition energy barrier (1.12 eV). It indicates that GQDs-COOH enables the rapid diffusion of Li+, ensures the smooth decomposition of Li2S, and catalyzes the effective conversion of LiPSs. Moreover, this work will promote the application of GQDs in Li-S batteries.

Functionalized graphene quantum dots with ZnO as a humidity sensor

Functionalized graphene quantum dots with ZnO as a humidity sensor

Spectrofluorimetric determination of vitamin D in the serum of autistic and healthy children using functionalized graphene quantum dots

Vitamin D is one of the most essential nutrients for brain development, and deficiencies during pregnancy and early childhood development might be associated with autism. Regular monitoring of serum 25-hydroxyvitamin D3 level could help in early diagnosis and therapy. Analytical measurement of serum 25-hydroxyvitamin D3 level using the traditional matrix-matched calibration technique yields inaccurate results due to absence of serum matrix free from 25-hydroxyvitamin D3. The aim of this work was to develop a validated spectrofluorimetric methodology based on the standard addition approach for quantifying 25-hydroxyvitamin D3 levels in real serum samples of autistic children. The spectrofluorimetric methodology utilizes functionalized graphene quantum dots as a fluorescent probe for selective quantification of 25-hydroxyvitamin D3 level, which is based on measuring the quenching properties of 25-hydroxyvitamin D3 on a fluorescent probe. The standard addition approach exhibits a minimal matrix interference since it identically utilizes the same matrix of each study sample for creating its own calibration curve. The method was validated using the guidelines outlined in ICH M10 draft for endogenous compounds quantification. The method was successfully applied for quantifying the serum 25-hydroxyvitamin D3 levels in autistic and healthy children, and autistic children had significantly lower serum 25-hydroxyvitamin D3 levels (with a mean ± SD of 23.80 ± 17.19) when compared to healthy children (with a mean ± SD of 50.13 ± 18.74, P < 0.001). These results suggested an association between vitamin D deficiency and autism.

Removal of Atrazine from contaminated water by functionalized graphene quantum dots

The limitation of clean water supplies and the increment of water pollution resources, like industrial processes, oil pollution, and herbicides, are urgent reasons for introducing new techniques for treating contaminated water. Atrazine is heavily used as a herbicide due to its high effectiveness and low price. However, its environmental persistence causes water contamination, and human exposure to Atrazine is linked to several health effects. This work presents a simulation study of the possibility of removing the Atrazine from water by functionally activated graphene quantum dots (GQDs), using density functional theory (DFT) at B3LYP/3-21G level. The activity of GQDs C46 with a total dipole moment of 0.9 is enhanced by the attachment of chemical groups; for instance, attaching CN and NO2 groups increases the total dipole moment to 8.744 and 9.123, respectively. The effect of the functionalized groups Carboxyl and cyanide was investigated, and confirmed that there was no structure deformation due to the functionalization process. Analysis of the obtained data shows the remarkable adsorption ability of GQDs activated by CN and NO2 groups toward the removal of atrazine herbicides due to positive adsorption energy 1.31, 128, and 1.3 eV obtained from pristine, carboxyl graphene, and cyanide graphene respectively. According to the calculated total charge on the complexes Atrazine and GQDs and Functionalized GQD, charge transfer mainly depends on the interaction pattern. The values of charges were − 0.02, 0.004, and − 0.004 for pristine, carboxyl, and cyanide graphene, respectively. Therefore, the observed results demonstrated the possibility of applying the chemically modified carbon quantum dots as a potential candidate for the treatment of contaminated water.

Fast proton transport enables the magnetic relaxation response of graphene quantum dots for monitoring the oxidative environment in vivo.

A magnetic relaxation switch (MRS) that targets small molecules such as H2O2 is difficult to realize because of the small size of the targets, which cannot gather enough MRS probes to form aggregates and generate a difference in magnetic relaxation times. Therefore, the development of small molecule-targeted MRS is strongly dependent on changes in the interfacial structure of the probe, which modulates the proton transport behavior near the probe. Herein, functionalized graphene quantum dots (GQDs) consisting of GQDs with disulfide bonds, polyethylene glycol (PEG), and paramagnetic Gd3+ were used as the MRS probe to sense H2O2. The structure of GQDs changed after reacting with H2O2. The PEG assembled a tube for transmitting changes in GQDs via proton transport and thus enabled the magnetic relaxation response of the probe towards H2O2. Pentaethylene glycol was experimentally and theoretically proven to have the strongest ability to transport protons. Such a probe can be applied in the differentiation of healthy and senescent cells/tissues using in vitro fluorescent imaging and in vivo magnetic resonance imaging. This work provides a reliable solution for building a proton transport route, which not only enables the response of the MRS probe towards the targets but also demonstrates the design of carbon nanostructures with proton transport behaviors.

Low-Temperature and Catalyst-Free Plasma Synthesis of Plastics-Derived Graphene Quantum Dots

The advanced industrial, social, and technological developments in modern society have rendered the production of around 300 million tons of plastic annually, yet only 50% or even less are being recycled. Moreover, the current recycling process is limited to the conversion of plastic wastes (PWs) into hydrocarbon fuels, which also requires the use of high temperatures and energies, long reaction time, and high-cost platinum-based catalysts. Therefore, there is an urgent need to develop a more sustainable and environmentally friendly method to recycle these PWs and possibly into functional materials for diverse applications.We introduce non-equilibrium and low-temperature microplasma technologies to convert PWs into graphene quantum dots (GQDs) at ambient conditions without any additional toxic chemicals, expensive catalysts, and sophisticated vacuum technologies. The reactive species generated by the plasma enables not only rapid deconstruction of PWs into small hydrocarbons moieties, but also simultaneous reconstruction of nanographene domain and nucleation into GQDs. GQDs are zero-dimensional carbon nanomaterials with unique quantum confinement and edge effects, which are hybridized by sp2 carbon in a honeycomb network. The quantum confinement and edge effects bestow GQDs with unique, tunable, and stable photoluminescence (PL) properties. Coupled with the biocompatibility, low toxicity, large surface area, and chemical inertness, GQDs can be employed in various applications, including imaging, sensing, optoelectronics, drug delivery, catalysis, and energy related applications. Nevertheless, the current syntheses of GQDs still need the use of high temperatures, strong acids or reducing agents, long reaction time, and tedious synthesis procedures.Here the utilization of microplasma enables the degradation and conversion of various plastics into functional GQDs with well-controlled structures in one-step at ambient conditions and catalyst-free manner, alleviating the current drawbacks in the GQDs synthesis. Among various PWs, polyethylene terephthalate-derived GQDs (PET-GQDs) exhibit enticing and bright white emission under 365 nm UV irradiation with a Commission Internationale de l’Eclairage 1931 of (0.29, 0.35). Moreover, the colloidal PET-GQDs can be exploited for heavy metal ions detection with a low limit of detection of 8.4 nM, while the composite film state is usable as sensitive temperature tag from 10 – 80 °C and LED panel. Our work provides an insight into the novel technologies for PWs recycling into functional nanomaterials in cost-effective, scalable, and environmentally friendly way.

Recent Progress on Functionalized Graphene Quantum Dots and Their Nanocomposites for Enhanced Gas Sensing Applications.

Gas-sensing technology has witnessed significant advancements that have been driven by the emergence of graphene quantum dots (GQDs) and their tailored nanocomposites. This comprehensive review surveys the recent progress made in the construction methods and applications of functionalized GQDs and GQD-based nanocomposites for gas sensing. The gas-sensing mechanisms, based on the Fermi-level control and charge carrier depletion layer theory, are briefly explained through the formation of heterojunctions and the adsorption/desorption principle. Furthermore, this review explores the enhancements achieved through the incorporation of GQDs into nanocomposites with diverse matrices, including polymers, metal oxides, and 2D materials. We also provide an overview of the key progress in various hazardous gas sensing applications using functionalized GQDs and GQD-based nanocomposites, focusing on key detection parameters such as sensitivity, selectivity, stability, response and recovery time, repeatability, and limit of detection (LOD). According to the most recent data, the normally reported values for the LOD of various toxic gases using GQD-based sensors are in the range of 1-10 ppm. Remarkably, some GQD-based sensors exhibit extremely low detection limits, such as N-GQDs/SnO2 (0.01 ppb for formaldehyde) and GQD@SnO2 (0.10 ppb for NO2). This review provides an up-to-date perspective on the evolving landscape of functionalized GQDs and their nanocomposites as pivotal components in the development of advanced gas sensors.