Activity Of Graphene Quantum Dots Research Articles

Synthesis graphene quantum dots/TiO2 nanocomposite for Rhodamine degradation

The photocatalytic activity of Graphene quantum dots (GQDs)/TiO2 was investigated for the degradation of rhodamine B under UV irradiation. The GQDs/TiO2 was synthesized via chemical method. The synthesized materials have been characterized by photoluminescence (PL), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR–TEM). Under the dark condition GQDs/TiO2 can remove 47,7% RhB. Besides, under the UV light, the removal efficiency of rhodamine B was 99.2%, with thin 50 min. However, the removal efficiency of rhodamine B by using TiO2 was 91.5%, which was lower than that of GQDs/TiO2. Overall, this work provides a novel strategy for the green synthesis of GQDs/TiO2, and its promising application prospect in environmental remediation.

Tuning the photocatalytic activity of graphene quantum dots via decorating the X% (Co3O4) as modern photocatalysts to produce ammonia

The crises related to energy and pollutants in the present century have led to the special look toward clean and sustainable energies. Material science plays a significant role in the way to achieve the world’s envisioned sustainability. This paper introduces an outstanding and facile route for decorating cobalt oxide (Co3O4) on graphene quantum dots (GQDs) to form the X% (Co3O4)/GQDs composites. The 5% Co3O4/GQDs, 10% Co3O4/GQDs, and 20% Co3O4/GQDs composites are formed with the aid of ultrasound irradiation, followed by the pyrolysis of citric acid employing a bottom-up approach. Decoration of Co3O4 nanoparticles with various weight percentages of 5%, 10%, and 20% is uniformly performed into the GQDs with the size distribution of 4.4, 4.6, and 4.8 nm, respectively. The resultant composites are applied as the robust photocatalysts for the conversion of N2 to NH3. In this report, GQDs decorated by three ratios of 5%, 10%, and 20% of Co3O4 are formed to evaluate the effect of decorated Co3O4 weight percentage on the production of ammonia. In addition, the kinetics and the concentration of the produced ammonia are studied using these composites. Based on the comparative analysis, the 5% Co3O4/GQDs photocatalyst not only optimizes the production of ammonia related to 10% Co3O4/GQDs, and 20% Co3O4/GQDs photocatalysts but also indicates the faster kinetics of ammonia production. These results can be attributed to the more uniform distribution and the lower size of nanoparticles in 5% Co3O4/GQDs photocatalyst.

Impact of Photonic Band Edge Enabled Slow Light Effect on Optical Limiting Activity of Graphene Quantum Dots in All Polymer 1-D Photonic Crystals

Impact of Photonic Band Edge Enabled Slow Light Effect on Optical Limiting Activity of Graphene Quantum Dots in All Polymer 1-D Photonic Crystals

Graphene Quantum Dots with Pyrrole N and Pyridine N: Superior Reactive Oxygen Species Generation Efficiency for Metal-Free Sonodynamic Tumor Therapy.

Those responsible for the development of sonosensitizers are faced with a dilemma between high sonosensitization efficacy and good biosecurity that limited the development of sonodynamic therapy (SDT). Herein, inspired by the intriguing therapeutic features of SDT and the potential catalytic activity of graphene quantum dots, the potential of N-doped graphene quantum dots (N-GQDs) to act as a sonosensitizer is demonstrated. The superior sonosensitization effect of N-GQDs is believed to be three to five times higher than that of traditional sonosensitizers (such as porphyrin, porphyrin Mn, porphyrin Zn, TiO2 , etc.). More importantly, the sonochemical mechanism of N-GQDs is revealed. Pyrrole N and pyridine N are believed to form catalytic centers in sonochemical processing of N-GQDs. This knowledge is important from the perspective of understanding the structure-dependent SDT enhancement of carbon nanostructure. Moreover, N-GQDs modified by folic acid (FA-N-GQDs) show a high marker rate for tumor cells (greater than 96%). Both in vitro and in vivo therapeutic results have exhibited high tumor inhibition efficiency (greater than 90%) of FA-N-GQDs as sonosensitizers while the oxidative stress response of tumor cells is activated through the PEX pathway and induced apoptosis via the p53 pathway.

Enhancement of sensitivity for dichlorvos detection by a low-weight gelator based on bolaamphiphile amino acid derivatives decorated with a hybrid graphene quantum dot/enzyme/hydrogel

The use of fluorescent gel blends with GQDs provides new insights into gel formation and hydrogen peroxide detection utilizing the peroxidase-like catalytic activity of graphene quantum dots. This hybrid hydrogel enhances the performance of hybrid hydrogel properties by a low molecular weight gelator with the assistance of GQDs and phosphate buffer and taking an advantage of sensing application with a highly potential sensitivity and stability.

The effects of various molecular weight of passivator on the photoluminescence properties of graphene quantum dots

Here, we realize manipulation of photoluminescence (PL) intensity of GQDs through various molecular weight of surface passivator. With the increase of passivator molecular weight, only the PL intensity increases. However, the peak positions and half-peak width of spectral line remain unchanged. Our results reveal that surface passivation with larger molecular weight only weakens the chemical activity of graphene quantum dots (GQDs) and the π-π stacking interaction between GQDs, but exerts less impact on GQDs intrinsic energy gap. Therefore, the weaker π-π stacking interaction and chemical activity induce the weaker non-radiative recombination, leading to enhanced fluorescence from radiative recombination.

On the Factors behind the Photocatalytic Activity of Graphene Quantum Dots for Organic Dye Degradation

AbstractGraphene quantum dots (GQD) are promising visible‐light photocatalysts for organic dye degradation. Besides having improved visible‐light activity compared with commercial TiO2, GQD are versatile photocatalysts as their chemical composition and, consequently, optical properties can be tuned synthetically, with a direct impact on photoactivity. However, there is a lack of systematic comparative studies to benchmark GQD photocatalytic performance and relate it to their intrinsic properties. This is undertaken in this work for three types of GQD, which are prepared using well‐established synthetic methods representative of top‐down and bottom‐up approaches using different precursors. Resulting GQD are similar in size but differ in chemical composition, crystallinity, bandgap (ranging from 2.63 to 3.63 eV) and visible‐light absorptivity. Photoactivity measurements under comparable experimental conditions (visible‐light illumination) reveal enormous activity differences for rhodamine B (RhB) degradation, with up to tenfold higher degradation yields at the same time for certain GQD types. The enormous influence of intrinsic and tunable GQD factors, like visible‐light absorptivity and surface charge, on their photoactivity for the degradation of organic dyes is demonstrated, highlighting the importance of tailoring such parameters for enhanced photocatalytic performance. A plausible mechanism for GQD‐catalyzed photodegradation of RhB is also proposed.

Antioxidant Activity of Graphene Quantum Dots Prepared in Different Electrolyte Environments.

Antioxidants can reduce or inhibit damage such as oxidative decay caused by elevated levels of free radicals. Therefore, pursuing antioxidants with excellent properties has attracted more and more attention. Graphene quantum dots (GQDs) are considered a promising material because of their good free radical scavenging activity, low toxicity, and excellent water solubility. However, their scavenging efficiency, antioxidant mechanism, and effective control methods need to be improved. Herein, in order to further reveal the antioxidant mechanism of GQDs, the role of electrolytes in improving the antioxidant activity of GQDs is explored. In addition, 1,1-diphenyl-2-picrazine (DPPH∙), hydroxyl (∙OH), and superoxide (∙O2−) free radicals are used to evaluate the antioxidant activity of the as-prepared GQDs. Combined with transmission electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and cyclic volt–ampere characteristic curves, the effects of an electrolytic environment on the surface functional groups, charge transfer capability, and defect states of GQDs are obtained. The antioxidant mechanism of GQDs and how to improve their antioxidant activity are further elucidated.

Lanthanide-Boosted Singlet Oxygen from Diverse Photosensitizers along with Potent Photocatalytic Oxidation.

Singlet oxygen (1O2) plays a central role in photochemical and photobiological research. Although many photosensitizers for efficient 1O2 generation were reported, further improving its yield and oxidation power is still highly desirable. Instead of developing new ones, current photosensitizers might be boosted by mediators to facilitate energy transfer. Taking advantage of the long triplet state lifetime of lanthanide ions (Ln3+), we herein demonstrate their roles as potent oxidation mediators. Using oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) at neutral pH as a difficult model reaction, based on the fluorescence, phosphorescence, and metal-binding properties, various dyes and nanomaterials were classified into four types. The 1O2 emission of carbon dots and rose bengal was enhanced 4 times in the presence of Ce3+. Some nonphosphorescent, but strongly fluorescent dyes that are not known as photosensitizers can still be mediated by Ln3+ to produce 1O2, but metal-chelating calcein was not enhanced. Finally, nonemissive dyes failed to show activity. As mediators, the excited Ln3+ can migrate a long distance and transfer energy to O2, resulting in high 1O2 yield. Since redox-active Ce3+ and Eu3+ had the highest activity, participation of oxidation involving excited lanthanides might be possible too. In addition, Ln3+ also enhanced the activity of graphene quantum dots, graphene oxide, and g-C3N4. Rapid degradation of organic dyes was demonstrated, further supporting a high photocatalytic activity of the Ln3+-mediated system.

Solar-excited graphene quantum dots for bacterial inactivation via generation of reactive oxygen species

Nanoscale photocatalysts have attracted abundant research attention in the solar-activated disinfection. In this work, we find that solar irradiation significantly improves the antimicrobial activity of graphene quantum dots (GQDs), accompanied by severe oxidative stress and membrane damage. By using electron spin resonance (ESR) technique, we confirm that different reactive oxygen species (ROS), including singlet oxygen (1O2), hydroxyl radical (•OH), and superoxide anion (O2•−) were generated by GQDs upon irradiation with simulated sunlight. Additionally, these generated ROS will further facilitate lipid peroxidation of cell membrane and suppress bacterial antioxidant systems, enhancing the phototoxicity of GQDs. These findings will bring major advancements of GQDs in applications of solar-driven bacterial disinfection.

Anti-Biofilm Activity of Graphene Quantum Dots via Self-Assembly with Bacterial Amyloid Proteins.

Bacterial biofilms represent an essential part of Earth's ecosystem that can cause multiple ecological, technological, and health problems. The environmental resilience and sophisticated organization of biofilms are enabled by the extracellular matrix that creates a protective network of biomolecules around the bacterial community. Current anti-biofilm agents can interfere with extracellular matrix production but, being based on small molecules, are degraded by bacteria and rapidly diffuse away from biofilms. Both factors severely reduce their efficacy, while their toxicity to higher organisms creates additional barriers to their practicality. In this paper, we report on the ability of graphene quantum dots to effectively disperse mature amyloid-rich Staphylococcus aureus biofilms, interfering with the self-assembly of amyloid fibers, a key structural component of the extracellular matrix. Mimicking peptide-binding biomolecules, graphene quantum dots form supramolecular complexes with phenol-soluble modulins, the peptide monomers of amyloid fibers. Experimental and computational results show that graphene quantum dots efficiently dock near the N-terminus of the peptide and change the secondary structure of phenol-soluble modulins, which disrupts their fibrillation and represents a strategy for mitigation of bacterial communities.

Graphene quantum dots-based electrochemiluminescence detection of DNA using multiple cycling amplification strategy

In this study, a novel strategy for amplified electrochemiluminescence (ECL) detection of DNA was proposed based on excellent ECL activity of graphene quantum dots (GQDs) coupled with multiple cycling amplification technique. A new type of graphene QDs with well ECL property and uniform size were firstly synthesized, then the graphene QDs were assembled on the electrode by poly (diallyldimethylammonium chloride) (PDDA)-graphene oxide (GO) nanocomposites, which could greatly improve ECL signal and stability of QDs. A novel signal-on ECL biosensor for DNA analysis was designed by using ECL quenching of gold nanoparticles (NPs) to graphene QDs combined with endonuclease–aided cyclic amplification strategy. As a result, the proposed strategy can be conveniently expanded to other biosensing application, especially in clinical diagnoses.

Tuning the antioxidant activity of graphene quantum dots: Protective nanomaterials against dye decoloration

The antioxidant activity of graphene quantum dots (GQD) with different chemical composition and sp2-hybridized carbon content has been evaluated and compared to that of a standard antioxidant, ascorbic acid. GQD were prepared by top down and bottom up synthetic approaches from three different precursors (carbon black, glucose and pyrene) in order to vary significantly the chemical composition, electron density and sp2-hybridized carbon content. For a given radical, the three types of GQD exhibited very different radical scavenging activity (RSA). Moreover, the RSA varied with the type of free radical and reactive oxygen species (ROS) tested, indicating different radical inhibition mechanisms. Overall, GQD with strong hydrogen donor behavior and large content of sp2–hybridized carbon domains were the most effective radical scavengers. Thus, highly graphitic GQD with abundant edge functional groups produced from pyrene exhibited an extraordinary high antioxidant activity, with inhibition effective concentrations much lower than those of ascorbic acid. The great potential of highly antioxidant GQD as protective films against organic dye decoloration by ROS was demonstrated with two model target molecules, methylene blue and rhodamine B.

Modulating the Photocatalytic Activity of Graphene Quantum Dots via Atomic Tailoring for Highly Enhanced Photocatalysis under Visible Light

Precise control over doping of photocatalysts is required to modulate their photocatalytic activity in visible light‐driven reactions. Here, a single precursor‐employing bottom‐up approach is developed to produce different heteroatom‐doped graphene quantum dots (GQDs) with unique photocatalytic activities. The solvothermal reaction of a norepinephrine precursor with redox active and condensable moieties effectively produces both nitrogen/sulfur codoped GQDs (NS‐GQDs) and nitrogen‐doped GQDs (N‐GQDs) by simply varying solvents (from dimethyl sulfoxide to water) under microwave irradiation. As‐prepared NS‐GQDs and N‐GQDs show similar lateral sizes (3–4 nm) and heights (1–2 nm), but they include different dopant types and doping constitution and content, which lead to changes in photocatalytic activity in aerobic oxidative coupling reactions of various amines. NS‐GQDs exhibit much higher photocatalytic activity in reactions under visible light than N‐GQDs and oxygen‐doped GQDs (O‐GQDs). The mechanism responsible for the outstanding photocatalytic activity of NS‐GQDs in visible light‐driven oxidative coupling reactions of amines is also fully investigated.

Colorimetric detection of cholesterol based on highly efficient peroxidase mimetic activity of graphene quantum dots

In the present study, we report graphene quantum dots (GQDs), an enzyme mimetic of horse radish peroxidase (HRP), for unprecedented detection of free cholesterol. Synthesized directly from graphite using simple and quick one step wet chemical method, these GQDs in the presence of H2O2 exhibit highly efficient catalytic activity toward the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) to produce a blue colored product. The proposed detection system based on GQDs allows wide range (0.02–0.6mM) of cholesterol sensing with a detection limit as low as 0.006mM. Further, higher Vmax (7.3×10−6Ms−1) along with lower Km (0.01mM) attest enhanced peroxidase like catalytic activity and better binding affinity of cholesterol oxidase (ChOx) to cholesterol resulting in good biosensor stability and resistance to environmental interferences. The proposed method without the use of sophisticated instruments perceives the cholesterol using naked eye with blue color compound formation. The potential of the method to be applied on field is shown by the proposed cholesterol measuring color wheel, where the shades of color are related to actual levels of cholesterol in the sample.

Graphene Quantums Dots Combined with Endonuclease Cleavage and Bidentate Chelation for Highly Sensitive Electrochemiluminescent DNA Biosensing

A novel strategy for highly sensitive electrochemiluminescence (ECL) detection of DNA was proposed based on site-specific cleavage of BamHI endonuclease combined with the excellent ECL activity of graphene quantum dots (GQDs) and bidentate chelation of the dithiocarbamate DNA (DTC-DNA) probe assembly. The difference between photoluminescence and ECL spectral peaks suggested that a negligible defect existed on the GQDs surface for generation of an ECL signal. The formed DTC-DNA was directly attached to the gold surface by bidentate anchoring (S-Au-S bonds), which conferred a strong affinity between the ligands and the gold surface, increasing the robustness of DNA immobilization on the gold surface. BamHI endonuclease site-specifically recognized and cleaved the duplex symmetrical sequence, which made the double-stranded DNA fragments and GQDs break off from the electrode surface, inducing a decrease of the ECL signal. Using hepatitis C virus-1b genotype complementary DNA (HCV-1b cDNA) as a model, a novel signal-off ECL DNA biosensor was developed based on variation of the ECL intensity before and after digestion of the DNA hybrid. Electrochemical impedance spectroscopy confirmed the successful fabrication of the ECL DNA biosensor. This ECL biosensor for HCV-1b cDNA determination exhibited a linear range from 5 fM to 100 pM with a detection limit of 0.45 fM at a signal-to-noise ratio of 3 and showed satisfactory selectivity and good stability, which validated the feasibility of the designed strategy. The proposed strategy may be conveniently combined with other specific biological recognition events for expansion of the biosensing application, especially in clinical diagnoses.