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Tailoring of graphene quantum dots for toxic heavy metals detection
摘要： The sensitivity of graphene quantum dots towards toxic heavy metals (THMs; Cd, Hg, Pb) can be improved through doping with nitrogen at the vacant site defects. Using density functional theory, we investigate the adsorption of THMs on the graphene quantum dots (GQDs) and nitrogen-coordinated defective GQDs (GQD@1N, GQD@2N, GQD@3N and GQD@4N) surfaces. Thermochemistry calculations reveal that the adsorption of Pb atom on the surfaces is more favorable than Cd and Hg adsorption. The decoration of the vacant defects with nitrogen on the GQD surface substantially increases the charge transfer and adsorption energy values of THMs on the GQD surface (GQD@4N > GQD@3N > GQD@1N > GQD@2N > GQD). The charge transfer and adsorption energy of lead on each of these surfaces are greater than those of cadmium and mercury (Pb > Cd > Hg). Quantum theory of atoms in molecules analysis and non-covalent interaction plots further validate this result while also confirming that Pb atom has a partially covalent and electrostatic nature of interaction at the nitrogen-coordinated vacant site defects. The electron density values—a criterion of bond strength—for the THM...N interactions are greater than for the THM…C interactions, confirming the observed adsorption energy trends of the THMs on the surfaces. The lowering of the HOMO–LUMO energy gap of the surfaces follows the order Pb > Cd > Hg and also results in increased electrical conductivity, which are consistent with the calculated adsorption energy trends. Significant changes in the energy gap and electric conductivity of the surfaces upon THMs adsorption make them promising sensors for metal detection. Finally, time-dependent density functional theory calculations showed that changes such as peak shifts, peak quenching and appearance of new peaks are seen in the UV–visible absorption spectra of the surfaces upon adsorption of THMs, wherein the shifts in peaks correspond to the magnitude of adsorption energy of THMs on the surfaces. These results should motivate the experimentalists towards using rational and systematic modulation of surfaces as sensors for heavy metal detection.
关键词： Adsorption energy,Toxic heavy metals,Charge transfer,UV–visible absorption spectra,Nitrogen doping,Density functional theory,HOMO–LUMO energy gap,Graphene quantum dots
更新于2025-09-16 10:30:52
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Fabrication and characterization of novel cRGD modified graphene quantum dots for chemo-photothermal combination therapy
摘要： In this work, an innovative drug delivery system based on cyclic RGD-modified (as the targeting agent) and doxorubicin-loaded graphene quantum dots (R–GQDs@DOX) was fabricated for chemo-photothermal combination therapy. These tasks include drug loading capacity, photothermal efficiency, cellular uptake and combination therapeutic effect of R–GQDs@DOX. The structure of R–GQDs@DOX was characterized by FT-IR spectrum, UV–vis spectrum and AFM. The results indicated that the doxorubicin (DOX) could be loaded onto graphene quantum dots (GQDs) via van der Waals interaction (π–π stacking) and the drug loading capacity was 96.6 % (wt). The R–GQDs@DOX not only showed obvious pH-responsive release of DOX, but also exhibited great photothermal efficacy for cancer cells. The fluorescence intensity indicated that R–GQDs@DOX was effectively taken up by SK–mel–5 and H460 cells. The combination of chemotherapy and photothermal therapy could more effectively inhibit growth of tumor cells, compared to photothermal therapy or chemotherapy alone.
关键词： Cellular imaging,Graphene quantum dots,Synergetic therapy,Composite drug-loaded carrier,Drug delivery
更新于2025-09-16 10:30:52
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Graphene Quantum Dots: Efficient Mechanosynthesis, White-Light and Broad Linearly Excitation-Dependent Photoluminescence and Growth Inhibition on Bladder Cancer Cells
摘要： Heteroatom-doped graphene quantum dots (GQDs) have attracted considerable attention due to their potential applications in luminescent materials and biology. In this work, we developed a solvent-free gram-scale mechanochemical method for the preparation of nitrogen-doped graphene quantum dots (N-GQDs) with the highest solubility (31 mg/mL) in water reported to date. Commercial graphite was sheared and cut through grinding with solid melamine, then ground with solid KOH to get sub-5-nm-sized, 1-3-layered N-GQDs. Notably, these N-GQDs exhibit white-light emission and a broad excitation-dependent full-color photoluminescence from 463 nm to 672 nm. When the excitation light ranged from 325 nm to 485 nm, these mechanochemically-obtained N-GQDs exhibited bright white-light emission. Intriguingly, the change of emission wavelength has two-stage linear relationships with the change of the excitation, and the inflection point is at 580 nm (excited at 550 nm). The difference between the emission and excitation wavelength decreases from 138 to 12 nm, which also shows two-stage linear relationships with the change of the excitation wavelength. It is notable that the PL quantum yields of them are high, up to 26.6%. Furthermore, we studied the inhabitation of as-obtained N-GQDs on bladder cancer cells (UMUC-3); as a result, with the increase of the concentration of N-GQDs, the proliferation of cancer cells was obviously prohibited.
关键词： bladder cancer cells,nitrogen-doped,mechanochemical method,photoluminescence,graphene quantum dots
更新于2025-09-16 10:30:52
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Electrochemical sensing of mercury ions in electrolyte solutions by nitrogen-doped graphene quantum dot electrodes at ultralow concentrations
摘要： Electrochemical detection of mercury ions in aqueous solution was investigated at indium tin oxide (ITO) conducting glass electrode modified by nitrogen-doped graphene quantum dots (N-doped GQDs). The N-doped GQDs with an average particle size of 4.5 nm were synthesized through an infrared-assisted pyrolysis of citric acid and urea at 250°C. The GQD sample contains high oxidation and amidation level, i.e., O/C and N/C atomic ratios: 37.6% and 30.7%, respectively. The electrochemical sensing toward Hg2+ ions was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on the CV and EIS analyses, both the reductive and oxidative peak currents as well as the equivalent series resistance demonstrate a decreasing trend with increased Hg2+ concentration. The detection limit of N-doped GQD/ITO electrodes toward Hg2+ ions reached 10 ppb with the accumulation time of 32 s. The GQD/ITO electrodes also exhibit superior selectivity toward the target contaminant (i.e. Hg2+ ion). Accordingly, the functionalized GQDs pave the way for engineering the electrochemical sensors capable of detecting toxic Hg2+ ions with superb sensitivity and selectivity.
关键词： Nitrogen doping,Electrolyte solution,Infrared-assisted synthesis,Graphene quantum dots,Mercury ions
更新于2025-09-16 10:30:52
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A Dual Role of Amino-functionalized Graphene Quantum Dots in NiOx Films for Efficient Inverted Flexible Perovskite Solar Cells
摘要： NiOx has been widely used as an effective hole transport material for inverted perovskite solar cells (PSCs), particularly flexible PSCs, owing to its low-temperature processing, low cost, and good electron blocking ability. However, the band structure alignment between low-temperature-processed NiOx and the perovskite layer is not satisfactory, resulting in reduced photovoltaic performance. Herein, we report a novel strategy to tune the NiOx hole transport layer for achieving high-performance flexible PSCs. Amino-functionalized graphene quantum dots (AGQDs) are employed in the NiOx film as a dual-role additive. On the one hand, the added AGQDs can provide abundant N atoms at the modified NiOx layer surface to enhance the crystallization of the perovskite film by a Lewis base-acid interaction. On the other hand, the AGQDs can optimize the band structure alignment between the NiOx and perovskite layers, facilitating hole extraction at the NiOx/perovskite interface. As a result, the inverted flexible PSCs exhibit a champion efficiency of 18.10%, which is comparable to the values reported for the current state-of-the-art inverted flexible PSCs. In addition to good air stability, our best flexible device has excellent mechanical stability, retaining 88% of its initial efficiency after continuously bending 1000 times. This new strategy highlights a promising way to enhance the performance of inverted flexible PSCs.
关键词： flexible,amino functionalization,graphene quantum dots,NiO,inverted perovskite solar cells
更新于2025-09-16 10:30:52
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Controlled Nitrogen Doping of Graphene Quantum Dots Through Laser Ablation in Aqueous Solutions for Photoluminescence and Electrocatalytic Applications
摘要： Nitrogen-doped graphene quantum dots (N-GQDs) have promising applications in catalysis and photoluminescence, but many existing synthetic methods require uses of harsh chemicals, long reaction times, and complicated purification steps and have poor control over the surface functional groups. Laser ablation in liquid (LAL) is a promising alternative method to prepare nanomaterials because of its fast production, use of fewer chemicals, simple purification, and fewer byproducts and its control of the product by precise tuning of laser ablation parameters. We report the use of LAL to produce N-GQDs from carbon nano-onions in aqueous solutions of ammonia, ethylenediamine, and pyridine. The choice of these dopants allowed for tuning the overall nitrogen content and the distribution of functional groups that led to the control over the photoluminescence emission wavelengths and lifetimes. High concentrations of amine groups tended to red shift emission and exhibit shorter lifetimes, whereas pyridinic groups would blue shift the emission and exhibit longer lifetimes. The N-GQDs also showed a promising performance as electrocatalysts for reducing oxygen to hydrogen peroxide, an important chemical widely used in industrial applications. The N-GQDs exhibited both low overpotentials and high selectivity for a two-electron oxygen reduction pathway.
关键词： electrocatalysis,photoluminescence,lifetime,laser ablation in liquid,oxygen reduction reaction,Graphene quantum dots
更新于2025-09-16 10:30:52
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Orange photoluminescent N-doped graphene quantum dots as an effective co-sensitizer for dye-sensitized solar cells
摘要： In this research, nanocoral (NC) film of TiO2 was decorated with nitrogen-doped graphene quantum dots (NGQDs, average size of ～ 9 nm) and photovoltaic properties were investigated for dye-sensitized solar cell application. TiO2 NCs and NGQDs synthesized separately using the hydrothermal method and TiO2 NCs were decorated with NGQD solution by spin coating. FESEM images prove that TiO2 NCs are composed from nanorods, with an average diameter of about 60 nm. Optical characterization shows that the NGQDs are highly orange-luminescent (emission at 590 nm) and absorb UV and visible light photons. Using NGQDs together with N719 dye as co-sensitizers led to an improvement in efficiency of DSSC, as investigated by photoelectrical measurements. The experimental analysis reveals that this improvement arises from enhancement of charge separation and collection due to the cascaded energy levels because of presence of NGQDs. By addition of NGQDs into TiO2 NC photoanode, we were able to increase the short-circuit current density and efficiency by 40% (from 12.61 to 17.65 mA/cm2) and 31% (from 5.72 to 7.49%), respectively.
关键词： Nitrogen,Hydrothermal,Graphene quantum dots,Dye-sensitized solar cell
更新于2025-09-16 10:30:52
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Highly porous self-assembly of nitrogen-doped graphene quantum dots over reduced graphene sheets for photo-electrocatalytic electrode
摘要： Nitrogen-doped graphene quantum dots (NGQDs) are a diverse organic catalyst, competitive with other metallic catalysts due to their low cost, high stability, biocompatibility, and eco-friendliness. Highly functional multi-edge surfaces of NGQDs play a key role in imparting superb photocatalytic and electrocatalytic activity. However, when coating NGQDs by conventional techniques, such surfaces are not exposed for catalysis, due to the unwanted overlap of NGQDs sheets. To avoid this issue, here we propose a facile technique to orient NGQDs in a three-dimensional (3D) self-assembled foam-like structure, over reduced graphene oxide coated woven carbon fabric. This 3D assembled structure provides highly exposed active surfaces, which are readily available for catalytic reactions: however, in the conventional uniformly coated NGQDs layer, catalytic activity was limited by complex diffusion. The superb catalytic activity of the assembled NGQDs was utilized for the degradation of organic pollutant (methylene blue dye) from water. Additionally, the proposed electrode revealed much higher electrocatalytic activity than the rare Pt catalyst, owing to the easy diffusion of electrolyte and fast quenching of charges through the porous structure. The assembled NGQDs showed 50% higher photocatalytic degradation compared to uniformly coated NGQDs, which was further accelerated (50%) by application of the biased potential of 2 V; i.e. photo-electrocatalysis. The novel photo-electrocatalytic electrode offers high conductivity, stability, and flexibility, which make this complete carbon electrode highly attractive for other catalytic applications such as fuel cells, supercapacitors, and water splitting.
关键词： Reduced graphene oxide,Photo-electrocatalysis,Stable electrode,Three-dimensional self-assembly,Nitrogen-doped graphene quantum dots
更新于2025-09-12 10:27:22
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Folic Acid-conjugated nitrogen-doped graphene quantum dots as fluorescent diagnostic material for MCF-7 cells
摘要： This paper reports the preparation and application of folic acid-conjugated nitrogen-doped graphene quantum dot as a fluorescent diagnostic material for MCF-7 cells of breast cancer. Nitrogen-doped graphene quantum dots (N-GQD) were prepared by hydrothermal method using citric acid as carbon source and diethylamine as nitrogen source. The doping of different nitrogen contents was effectively controlled by diethylamine. As the amount of nitrogen increased, more binding sites on the nitrogen-doped graphene quantum dots were supplied to the folic acid. Laser confocal scanning microscopy showed that the more folic acid binding facilitated the recognition and swallowing by cancer cells, which made the labeled cells emit stronger fluorescence and thus cancer cells could be better detected. Cytotoxicity tests showed that the material was low cytotoxic, making it a promising prospect for fluorescent probes.
关键词： fluorescent diagnostic material,nitrogen-doped graphene quantum dots,folic acid
更新于2025-09-12 10:27:22
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Modified graphene quantum dots-zinc oxide nanocomposites for photocatalytic degradation of organic dyes and commercial herbicide
摘要： The high crystallinity of graphene quantum dots-ZnO nanocomposites is considered to have a significant effect in improving the carrier lifetime for enhanced photocatalytic degradation. The graphene quantum dots-ZnO nanocomposites were synthesized by adding graphene quantum dots solution into starting precursors during the precipitation. Characterization was performed using various techniques. High crystallinity of graphene quantum dots-ZnO nanocomposites is obtained in terms of increased crystal size and decreased dislocation density. The improved crystallinity increases the carrier lifetime on the material surface for the functional improvement of photocatalytic material. Photocatalytic test of methylene blue and methyl orange was performed under UV irradiation. Degradation rate constant reaches the maximum value for both organic dyes for the appropriate preparing condition of graphene quantum dots-ZnO nanocomposites. The graphene quantum dots-ZnO nanocomposites were then applied to degrade commercial glyphosate herbicide contaminants for an agricultural wastewater treatment investigation. The investigation aims to demonstrate a facile useful way of herbicide contaminant reduction for the better health of farmers. The graphene quantum dots-ZnO nanocomposites show an enhancement of the photocatalytic process with improved degradation rate constant (23% increased) in comparison to pure ZnO. Therefore, this work demonstrates that graphene quantum dots-ZnO nanocomposites can be used as a photocatalytic material for degrading organic dyes and commercial herbicide contaminants owing to its low-cost and environmental-friendly properties.
关键词： graphene quantum dots,ZnO,organic dye,photocatalytic degradation,herbicide
更新于2025-09-12 10:27:22