Role Of Graphene Quantum Dots Research Articles

Advanced cement composites: Investigating the role of graphene quantum dots in improving thermal and mechanical performance

The investigation of graphene quantum dots (GQDs) at very small nano- and atomic sizes is a novel approach in the fields of structural cement, concrete, and ceramic materials, which have not been thoroughly explored. This study investigates the comparative effects of two variations of GQDs, Qdl and Qdp, against a control mixture to assess the potential of graphene derivatives in enhancing thermal and mechanical properties of cement composites. The research presents their influences across a wide range of attributes, including flowability, bulk density, permeable voids, water absorption, compressive strength, flexural strength, surface temperature, thermal conductivity, thermal diffusivity, specific heat capacity, Brunauer-Emmett-Teller (BET) isotherm, thermogravimetric analysis (TGA), and microstructural characteristics. The empirical data underscore the superior freshness, physical, mechanical, and thermal attributes of GQDs-infused cement composites. Notably, the composites with 0.3 % Qdl show 20.8 % and 50 % increases in compressive and flexural strengths, respectively. On the other hand, the composites with 1.2 % Qdp show significant improvements in both compressive and flexural strengths, being 40 % and 108 % stronger than the control, respectively. Additionally, the thermal properties of the composites exhibit a proportional enhancement with increasing GQDs content. Microstructural analyses reveal a nano-bridging mechanism well-uniformly facilitated by the secondary nucleation and crystallization of calcium silicate hydrate (CSH) gel. This investigation offers innovative insights into the incorporation of GQDs in cement composites, highlighting their potential to create highly conductive structural cement and ceramic.

Insight into the role of graphene quantum dots on the boosted photocatalytic H2 production performance of a covalent organic framework

The photocatalytic activity of covalent organic frameworks (COFs) to evolve hydrogen (H2) triggered by visible light has been promising, but the separation and migration efficiency of photogenerated electron-hole pairs still have to be improved. In the study, we designed and synthesized a kind of graphene quantum dots (GQDs) modified β-ketoenamine-linked COF composite (GQDs/COF) by an in-situ method to improve its photocatalytic H2 evolution for the first time. The resulting 0.44% GQDs/TpPa-1-COF shows a rate of H2 production of 487 μmol g−1h−1 with the illumination of visible light, outperforming those of bare TpPa-1-COF by 2.9 times. It is found that the GQDs serve as a photosensitizer that effectively enhances the optical absorption ability. Moreover, GQDs serve as a means of collecting photoinduced electrons as for preventing the subsequent recombination of carriers excited by visible light. Furthermore, the Ohmic contact effect between the TpPa-1-COF and GQDs facilitates the highly efficient migration of photoinduced electrons, which has been demonstrated by the density functional theory (DFT) calculation results. Overall, this work provides a novel strategy to design COF-based composites and gives some insight into the role of GQDs on enhanced photocatalytic activity.

The role of graphene quantum dots in mitigating lipid peroxidation.

Lipid peroxidation often underlies apoptosis and mitochondrial dysfunction, which are common pathological phenomena in neurodegenerative and lysosomal storage diseases. Graphene quantum dots (GQDs) have garnered considerable interest as a nanomedicine over the last several years due to their biocompatibility and ability to target cellular disorders associated with disease phenotypes. Recent work with cells containing α-synuclein aggregates (i.e., cells mimicking the onset of Parkinson's disease) has demonstrated that GQDs exhibit mitoprotective behavior. In these studies, GQDs were able to permeate the plasma membrane, inhibit mitochondrial deformation, and restore mitochondrial complex I activity. However, the mechanism by which GQDs interacted with mitochondria was neither examined nor understood. It is known that this type of mitochondrial dysfunction is associated with free radical-induced oxidative lipid damage. Therefore, we hypothesize that the observed mitoprotective properties of GQDs arise from the scavenging of reactive oxidative species that would otherwise interact with mitochondrial membranes. To test this hypothesis, we developed a system to examine lipid peroxidation in synthetic membranes while in the presence of GQDs. Here, we used the fluorescent sensor C11-BODIPY to monitor the kinetics of lipid peroxidation in the presence of hydroxyl free radicals. Comparison of peroxidation rates to first principles kinetic models confirmed that GQDs were indeed scavengers of free radicals. When membranes were incubated with GQDs, the lipid peroxidation rate decreased by 90%. Interestingly, when compared to other renowned antioxidants, such as ascorbic acid and Trolox, GQDs exhibited significantly higher antioxidant efficiency. Ascorbic acid and Trolox required substantially higher concentrations than GQDs to achieve comparable levels of reduction to lipid peroxidation rates. These results warrant further investigation of GQDs as a mitochondrial membrane protection agent.

Role of graphene quantum dots with discrete band gaps on SnO2 nanodomes for NO2 gas sensors with an ultralow detection limit.

NO2 is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO2, but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO2 nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO2 gas with a noticeable response ((Ra/Rg) - 1 = 4.8), which cannot be matched using pristine SnO2 nanodomes. In addition, the GQD@SnO2 nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H2S, CO, C7H8, NH3, and CH3COCH3). The oxygen functional groups in GQDs specifically enhance NO2 accessibility by increasing the adsorption energy. Strong electron transfer from SnO2 to GQDs widens the electron depletion layer at SnO2, thereby improving the gas response over a broad temperature range (RT-150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures.

Sugar moiety driven adsorption of nucleic acid on graphene quantum dots: Photophysical, thermodynamic and theoretical evidence

Integration of biologically important molecules with graphene quantum dots (GQDs) as a new class of luminescent water-soluble carbon materials, has drawn considerable attention for recent exciting progress on its biomedical applications. In order to avoid toxic semiconductor QDs, GQDs have shown great promise in detection of DNA and other biological applications and hence, fundamental understanding of processes of interactions is important and necessary. The present work establishes the significant role of sugar residue of nucleic acids in adsorption of graphene materials through experimental estimation of binding thermodynamics concomitant with density functional theoretical (DFT) simulation and a detailed evaluation of photophysical parameters. Maximum quenching efficiency of adenosine moiety coupled with the shift in the vibrations of the five-member ring of D-ribose demonstrates the adsorption of DNA on GQDs framework through sugar moieties. The observed experimental results are consistent with the favorable Gibb’s free energy calculated through theoretical simulation. DFT presenting orbital interactions and bonding mechanism of DNAs on GQDs confirms that adsorption on GQDs surface involves charge transfer from nucleobases to GQDs and adenosine, in particular, binds strongly through charge transfer of 0.032e from nitrogen atom to carbon of GQDs. The present investigation will provide insights in understanding the possible role of GQDs in cellular imaging, biosensing and as carriers in targeted drug delivery.

Synthesis and Applications of Functional Nanomaterials

The unique physical and chemical properties and variable application potential of nanomaterials are continuously devoted to stimulating scientists’ studying enthusiasm. Extremely fine grains bring quantities excellent properties such as low density, low elastic modulus, high resistance and low thermal conductivity to nanomaterials, which has extensive use in the photoelectric field, environment, bioengineering and other fields. The research progress of graphene quantum dots, transparent reflective coatings and self-assembled nanotubes are mainly demonstrated. This paper shows the role of graphene quantum dots in solar cells, summarizes the synthesis methods of self-assembled nanotubes and their applications in bioengineering, and describes the development of transparent thermal reflective coatings for energy-saving glass attributed to providing relevant reference and basis for the development and research of nanomaterials.

Influence of surface charge of graphene quantum dots on their uptake and clearance in melanoma cells.

Graphene quantum dots (GQDs) continue to draw interest in biomedical applications. However, their efficacy gets compromised due to their rapid clearance from the body. On one hand, rapid clearance is desired and considered advantageous in terms of their cytocompatibility, but on the other hand, it is a major limitation for their prolonged use as imaging and therapeutic probes. The uptake and clearance of GQDs have been described in vivo, however, their clearance in vitro is still not understood, one of the main reasons being that their uptake and clearance are a cell type-dependent phenomena. Studies on other types of quantum dots revealed the importance of surface charge in their uptake and retention in different cell types. However, the role of surface chemistry in GQD uptake and clearance has not been described previously. Here, we studied the influence of surface charge on GQDs (anionic and cationic) on their uptake and clearance in melanoma cells. Both cationic and anionic GQDs were synthesized using a hydrothermal method to have a relatively consistent size with an aim to study the role of surface charge in their uptake and clearance in isolation by avoiding size-dependent uptake bias. Both GQDs exhibited excellent biocompatibility with cell viability over 90% even at a high concentration of 200 μg mL−1. Using confocal microscopy and flow cytometry, we observed significantly faster and higher uptake of cationic GQDs compared to anionic GQDs. Consequently, relatively rapid clearance was observed in cells treated with anionic GQDs compared to those treated with cationic GQDs, highlighting the role of surface charge on GQDs in their uptake and clearance. Raman analysis of the cleared exocytosed GQDs revealed no sign of biodegradation of either type.

Revisiting the Role of Graphene Quantum Dots in Ternary Organic Solar Cells: Insights into the Nanostructure Reconstruction and Effective Förster Resonance Energy Transfer

Recent studies have introduced the graphene quantum dot (GQD) as a third material for the bulk-heterojunction polymer:fullerene solar cell (PSC) to improve light conversion efficiency. Although exciton generation/dissociation and carrier transport in the GQD-incorporated light-absorbing layer are strongly influenced by the ternary component, detailed analysis on the role of GQD in the light-absorbing layer is lacking. In this study, a perspective on origin of improved photovoltaic performance of GQD-incorporated PSC is provided. The Forster resonance energy transfer (FRET) from GQD to polymer:fullerene and reorganization of the ternary-component film are analyzed. The GQD chemical nature difference after controlling nitrogen functionality affects the quantum yield (QY) and surface energy. Because the GQD is distributed in the fullerene-rich domain, actual improvements in the FRET to polymer-rich phase are not great, despite the improved QY and red-shifted photoluminescence. However, changes in the surface...

Dual Role of Graphene Quantum Dots in Active Layer of Inverted Bulk Heterojunction Organic Photovoltaic Devices.

Graphene quantum dots (GQDs) have shown broad application prospects in the field of photovoltaic devices due to their unique quantum confinement and edge effects. Here, we prepared GQDs by a photon-Fenton reaction as reported in our previous work, which has great advantage in the preparation scale. The photoelectric properties of the inverted hybrid solar cells based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methylester (PCBM):GQDs and P3HT:GQDs with different contents of GQDs as the active layers are demonstrated, as well as their morphology and structure by atomic force microscopy images. Then, the different roles of GQDs played in the ternary (P3HT:PCBM:GQDs) and binary (P3HT:GQDs) hybrid solar cells are studied systematically. The results indicate that the GQDs provide an efficient excition separation interface and charge transport channel for the improvement of hybrid solar cells. The preliminary exploration and elaboration of the role of GQDs in hybrid solar cells will be beneficial to understand the interfacial procedure and improve device performance in the future.

Second-Order Nonlinear Optical Switch Manipulation of Photosensitive Layer by an External Electric Field Coupled with Graphene Quantum Dots.

The main purpose of this work is to explore the effect of graphene quantum dots (GR) filling the photosensitive layer. The multibranched dye JH-1 as the photoactive layer material was used to analyze the non-negligible role of graphene quantum dots from the perspectives of optimized structure, electrochemical parameters, optical properties, nonlinear optical (NLO) switch, and external electric field. The results demonstrated that the graphene quantum dots not only improve the optical properties of solar cells but also control the electron transfer in the photosensitive layer molecules under the manipulation of a specific external electric field. When the external electric field intensity is below 20 × 10-4 au, the excess electron orbital does not change. When the external electric field reaches 25 × 10-4 au, the excess electron orbital on the graphene quantum dots evolves. This discovery allows the electron transfer from the photosensitive layer, which should be controlled by the NLO switch. In addition, the optical properties of sensitizers showed regular evolution in the external electric field, which provides an effective way to improve the performance. Comprehensive analysis indicated that the doping of graphene quantum dots with the photosensitive layer can be used as a new way to improve the photoelectric conversion efficiency of solar cells.

Role of graphene quantum dots synthesized through pyrolysis in the release behavior of temperature responsive poly (N,N-diethyl acrylamide) hydrogel loaded with doxorubicin

We have reported the synthesis and characterization of new drug carrier using Poly (N,N-diethyl acrylamide) (PDEA) and graphene quantum dots (GQDs). PDEA is a stimuli-responsive, macroporous polymer which has the ability to respond to change in surrounding temperature and addition of GQDs will help in improving the inherent characteristics of PDEA. In this research work, PDEA hydrogels along with GQDs have been synthesized by free radical polymerization. The effect of various concentrations of GQDs on the property of PDEA hydrogel was studied. The structural analysis of synthesized hydrogels was done using Fourier transform infrared spectroscopy (FT–IR). The internal surface morphology of porous hydrogels was observed using scanning electron microscope (SEM) micrographs. From the analysis, it has been observed that the equilibrium swelling ratio (ESR) and reswelling kinetics of the hydrogel significantly increased as the GQDs content was varied. The cancer drug (an anthracycline that is used for cancer chemotherapy) Doxorubicin (DOX) release behavior was studied and found that the performance of hydrogel is dependent on hydrogel composition, time, and surrounding temperature. The cytotoxicity of GQDs incorporated PDEA hydrogels gave a significant report which supports the potential application of hydrogel as an intelligent drug carrier.

Charge and energy transfer interplay in hybrid sensitized solar cells mediated by graphene quantum dots

We explored the role of graphene quantum dots (GQDs) as co-sensitizers in hybrid dye sensitized solar cell (DSSC) architectures, focusing on various concurring mechanisms, such as: charge transfer, energy transfer and recombination rate, towards light harvesting improvement. GQDs were prepared by the hydrothermal method that allows the tuning of electronic levels and optical properties by employing appropriate precursors and synthesis conditions. The aim was to realize a type II alignment for TiO2/GQD/dye hybrid configuration, using standard N3 Ru-dye in order to improve charge transfer. When GQDs were used as co-sensitizers together with N3 Ru-dye, an improvement in power conversion efficiency was achieved, as shown by electrical measurements. The experimental analysis indicates that this improvement arises from the interplay of various mechanisms mediated by GQDs: (i) enhancement of charge separation and collection due to the cascaded alignment of the energy levels; (ii) energy transfer from GQDs to N3 Ru-dye due to the overlap between GQD photoluminescence and N3 Ru-dye absorption spectra; and (iii) reduction of the electron recombination to the redox couple due to the inhibition of the back electron transfer to the electrolyte by the GQDs.

Enhancement of electro-optical response of ferroelectric liquid crystal: the role of graphene quantum dots

We present a pioneer study depicting a significant improvement in the photoluminescence (PL) intensity and display of an expeditious electro-optic response of ferroelectric liquid crystal (FLC) when doped with graphene quantum dots (GQDs). Significant threefold enhancement in PL intensity of GQDs/FLC composite material can be ascribed to the additive combination of emissions from GQDs and FLCs. Furthermore, promptness in electro-optical response by a factor of 34% can be attributed to the lowering of rotational viscosity of the FLC material due to the incorporation of GQDs. These results would certainly be helpful in realisation of highly luminescent and faster generation of LC systems.

Efficiency Enhancement of Perovskite Solar Cells through Fast Electron Extraction: The Role of Graphene Quantum Dots

We report on a significant power conversion efficiency improvement of perovskite solar cells from 8.81% to 10.15% due to insertion of an ultrathin graphene quantum dots (GQDs) layer between perovskite and TiO2. A strong quenching of perovskite photoluminescence was observed at ∼760 nm upon the addition of the GQDs, which is pronouncedly correlated with the increase of the IPCE and the APCE of the respective cells. From the transient absorption measurements, the improved cell efficiency can be attributed to the much faster electron extraction with the presence of GQDs (90-106 ps) than without their presence (260-307 ps). This work highlights that GQDs can act as a superfast electron tunnel for optoelectronic devices.