Introduction Of Graphene Quantum Dots Research Articles

Facile synthesis of V4+-doped and graphene-decorated V2O5/biomass carbon nanocomposite using graphene quantum dots for supercapacitors with wide voltage window and high energy density

This study reports a strategy for synthesis of V4+-doped and graphene-decorated V2O2/biomass carbon nanocomposite using graphene quantum dot. The introduction of graphene quantum dots and cotton significantly improves the supercapacitor performance.

Interfacial Bridging Strategy for Charge Extraction/Injection in the BiVO4/CoSn-Layered Double Hydroxide p-n Heterojunction Approach Using Graphene Quantum Dots for Enhanced Water Oxidation Kinetics.

The design of a photoanode with a bridging strategy that can enhance the charge injection and transport in a heterojunction can be an efficient approach to separate the photogenerated charge carriers and enhance the water oxidation kinetics. Aiming at such issues, herein we propose a BiVO4/GQDs/CoSn-LDH (layered double hydroxide) photoanode, which leads to the formation of a p-n heterojunction with bridged graphene quantum dots (GQDs) to accelerate the photoelectrochemical (PEC) performance. The BiVO4/GQDs/CoSn-LDH photoanode exhibits a maximum photocurrent density of 4.15 mA/cm2, which is ∼3-fold higher than for the pristine BiVO4 photoanode with an ∼250 mV cathodic shift in the onset potential. A faradaic yield of ∼91% confirms that the obtained photocurrent is mainly due to water oxidation. A mechanistic study based on the electrochemical impedance (EIS), charge separation, and charge injection efficacy measurements reveals that the introduction of GQDs between BiVO4 and CoSn-LDH provides a continuous conducting network to extract holes from the BiVO4 surface and efficiently inject into the CoSn-LDH surface for the water oxidation reaction.

Enhanced photocatalytic activity of glyphosate over a combination strategy of GQDs/TNAs heterojunction composites

A photocatalytic process was used to effectively remove glyphosate, an emerging pollutant and contaminant, through advanced oxidation. For this purpose, a feasible combination strategy of two-step anodisation and electrodeposition methods were proposed to fabricate graphene quantum dots (GQDs) supported titanium dioxide nanotube arrays (TNAs). The resultant GQDs/TNAs heterojunction composite exhibited significant degradation reactivity and circulation stability for glyphosate due to its excellent photo-generated electron and hole separation ability. After the introduction of GQDs into TNAs, the photodegradation efficiency of glyphosate increased from 69.5% to 94.7% within 60 min under UV–Vis light irradiation (λ = 320–780 nm). By analysing the intermediate products and through the evolvement of heteroatoms during glyphosate photodegradation, alanine and serine were discovered for the first time, and a detailed degradation mechanism of glyphosate was proposed. This study indicates that GQDs/TNAs heterojunction composite can almost completely degrade the glyphosate into inorganics under the appropriate conditions.

Graphene quantum dots doping SnO2 for improving carrier transport of perovskite solar cells

SnO2 is recognized as an excellent electron transport layer. However, it does not possess the optimal morphology required by perovskite photovoltaic devices, and the conduction band of SnO2 cannot match well with perovskite conduction bands. In the present study, we introduced graphene quantum dots (GQDs) into SnO2. The results show that the introduction of graphene quantum dots effectively improved the morphology of the SnO2 film, reduced the roughness of the surface, and increased the ohmic contact between the SnO2 and perovskite layer. In addition, the conductivity of the SnO2 film was improved, thereby facilitating the transfer of electrons. The optimized SnO2: GQDs layer reduced the density of defect state, suppressed the pinholes appearance to a certain extent, and facilitated the extraction of electrons, thereby ultimately improving the FF, and increasing the efficiency of the perovskite photovoltaic device.

Enhanced solar photocatalytic degradation of nitric oxide using graphene quantum dots/bismuth tungstate composite catalysts

• A novel method for the preparation of graphene quantum dots/bismuth tungstate (GQDs/BWO) composite photocatalysts. • Performance evaluation of enhanced sunlight responsive photocatalytic performance of GQDs/BWO composite for nitric oxide degradation. • The formation of Z-scheme heterojunction between GQDs and Bi 2 WO 6 . • The mechanism of photocatalysis of the GQDs/BWO photocatalysts. Composite (GQDs/BWO) materials for enhanced photocatalysis are hydrothermally produced by combining graphene quantum dots (GQDs) with bismuth tungstate (Bi 2 WO 6 ). These GQDs/BWO nanomaterials are evaluated for photocatalysis, at different GQDs loadings, for the degradation of gaseous nitric oxide with concentrations of 10–11 ppm. Results show that 10GQDs/BWO has the best photocatalytic performance among competitors for NO degradation. The NO conversion rate reaches 73% during 30 min, which is 3.84 times higher than that of pure Bi 2 WO 6 . This is because GQDs not only have a good electron transfer ability, but also form a direct Z-scheme heterojunction with Bi 2 WO 6 . These features promote electron-hole separation efficiency of the composite catalyst, and inhibit their recombination. This performance results from the increase in the surface area of the composite and to the increase in light absorption. The selectivity for the formation of NO x - ( S N O x - ) increased from 66 to 88%, and the DeNO x index increased from −0.003 to 0.43 after the introduction of GQDs. Active species scavenger experiment, Mott-Schottky (MS) tests and density functional theory (DFT) calculations are used to evaluate the mechanism of photocatalytic NO. Furthermore, cyclic tests show that 10GQDs/BWO catalysts maintain their chemical stability for NO degradation over 8000s.

Recent Advances on Graphene Quantum Dots for Electrochemical Energy Storage Devices

Graphene quantum dots (GQDs) which are nanofragments of graphene with an average size between 2 and 50 nm have attracted much attention due to their outstanding properties such as high conductivity, high surface area, and good solubility in various solvents. GQDs combine the quantum confinement and edges effects and the properties of graphene. Therefore, GQDs offers a broad range of applications in various fields (medicine, energy conversion, and energy storage devices). This review will present the recent research based on the introduction of GQDs in batteries, supercapacitors, and micro‐supercapacitors as electrodes materials or mixed with an active material as an auxiliary agent. Tables, discussed on selected examples, summarize the electrochemical performances and finally, challenges and perspectives are recalled for the subsequent optimization strategy of electrode materials. This review is expected to appeal a broad interest on functional GQDs materials and promote the further development of high‐performance energy storage device.

Interfacial engineering of reduced graphene oxide for high-performance supercapacitor materials

To solve the problems related to the re-stacking of reduced graphene oxides (rGO) and further improve their surface chemical behaviors to satisfy supercapacitor demands. The rGO decorated with graphene quantum dots has been successfully prepared via a facile low-power ultrasonic method. It is demonstrated the graphene quantum dots/reduced graphene oxide electrode has a high specific capacitance of 312 F g −1 , which is nearly three times higher than that of the reduced graphene oxide (132 F g −1 ). The enhanced super-capacitive performances of graphene quantum dots/reduced graphene oxide have been attributed to the introduction of graphene quantum dots, which effectively prevent the aggregation and restacking of reduced graphene oxide sheets, promoting its surface exposed to the electrolyte for sufficient mass transfer. Meanwhile, these features provide more pathways for the transportation of electrons between the interlayer of reduced graphene oxide sheets. Afterward, a detailed energy storage mechanism was analyzed. • Graphene quantum dots reduced the agglomeration of reduced graphene oxide. • More channels for the electrolyte transport into the interlayer of RGO sheets. • The electrode and device exhibit excellent electrochemical performance.

Preparation and electrochemical properties of graphene quantum dots/biomass activated carbon electrodes

Graphene quantum dots and biomass activated carbon have enormous potential for electrochemical application, which composites as anode materials for lithium ion battery are rarely reported. Here, the rice husk based activated carbon was modified by graphene quantum dots, exhibiting excellent electrochemical performance as an electrode for lithium ion battery. The results show that, with the introduction of graphene quantum dots, the charge transfer resistance of the electrode was reduced from 577.7 Ω to 123.9 Ω, and the lithium ion diffusion coefficient was increased by 175 times. Meanwhile, the introduction of graphene quantum dots plays an important role in improving the cycle stability of the battery.

Heterostructured graphene quantum dot/WSe2/Si photodetector with suppressed dark current and improved detectivity

A high-performance heterojunction photodetector is formed by combining an n-type Si substrate with p-type monolayer WSe2 obtained using physical vapor deposition. The high quality of the WSe2/Si heterojunction is demonstrated by the suppressed dark current of 1 nA and the extremely high rectification ratio of 107. Under illumination, the heterojunction exhibits a wide photoresponse range from ultraviolet to near-infrared radiation. The introduction of graphene quantum dots (GQDs) greatly elevates the photodetective capabilities of the heterojunction with strong light absorption and long carrier lifetimes. The GQDs/WSe2/Si heterojunction exhibits a high responsivity of ∼ 707 mA·W–1, short response time of 0.2 ms, and good specific detectivity of ∼ 4.51 × 109 Jones. These properties suggest that the GQDs/WSe2/Si heterojunction holds great potential for application in future high-performance photodetectors.

Synthesis of porous materials of high mechanical strength with graphene quantum dots

A series of porous materials with good mechanical and fluorescence properties enhanced by graphene quantum dots (GQDs) were prepared using surfactant reverse micelle swelling method with acrylamide (AAM) and 1-vinylimidazole (VIM) as monomers, ethylene glycol dimethacrylate (EGDMA) as crosslinking agent and azobisisobutyronitrile(AIBN) as initiator. Effects of additional amount of GQDs on the pore structure, fluorescence property, zeta potential and mechanical properties of the porous materials were systematically investigated. The surface area and pore volume increased as introduction of GQDs, while average pore width increased at first and then decreased with the amount of GQDs increasing, verifying the successful preparation of the porous materials. The fluorescence intensity changed to certain degree by the introduction of GQDs, which might resulted from photoelectron transfer between the GQDs and polymer matrices. The mechanical strength of the porous materials was greatly enhanced with introduction of GQDs due to the increase in storage modulus and permeability. The present work will shed light on the preparation of porous materials with high mechanical strength and fluorescence.

Enhanced Performance of GaN-based Ultraviolet Light Emitting Diodes by Photon Recycling Using Graphene Quantum Dots

Graphene quantum dots (GQDs) with an average diameter of 3.5 nm were prepared via pulsed laser ablation. The synthesized GQDs can improve the optical and electrical properties of InGaN/InAlGaN UV light emitting diodes (LEDs) remarkably. An enhancement of electroluminescence and a decrease of series resistance of LEDs were observed after incorporation of GQDs on the LED surface. As the GQD concentration is increased, the emitted light (series resistance) in the LED increases (decreases) accordingly. The light output power achieved a maximum increase as high as 71% after introducing GQDs with the concentration of 0.9 mg/ml. The improved performance of LEDs after the introduction of GQDs is explained by the photon recycling through the light extraction from the waveguide mode and the carrier transfer from GQDs to the active layer.

Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries

Lithium–sulfur (Li–S) batteries are expected to overcome the limit of current energy storage devices by delivering high specific energy with low material cost. However, the potential of Li–S batteries has not yet been realized because of several technical barriers. Poor electrochemical performance is mainly attributed to the low electrical conductivity of the fully charged and discharged species, the irreversible loss of polysulfide anions and the decrease in the number of electrochemically active reaction sites during battery operation. Here, we report that the introduction of graphene quantum dots (GQDs) into the sulfur cathode dramatically enhanced sulfur/sulfide utilization, yielding high performance. In addition, the GQDs induced structural integrity of the sulfur–carbon electrode composite by oxygen-rich functional groups. This hierarchical architecture enabled fast charge transfer while minimizing the loss of lithium polysulfides, which is attributed to the physicochemical properties of GQDs. The mechanisms through which excellent cycling and rate performance are achieved were thoroughly studied by analyzing capacity versus voltage profiles. Furthermore, experimental observations and theoretical calculations further clarified the role played by GQDs by proving that C–S bonding occurs. Thus, the introduction of GQDs into Li–S batteries will provide an important breakthrough allowing their use as high-performance and low-cost batteries for next-generation energy storage systems. High-capacity cathodes with enhanced stability have been prepared by using graphene quantum dots (GQDs). Lithium–sulphur batteries are considered one of the most promising candidates for future battery systems. However, intermediate compounds readily dissolve into the electrolyte during battery operation, which results in a loss of active materials. A team led by Yung-Eun Sung and Byung Hee Hong of Seoul National University introduced a hierarchical structure with GQDs via wet chemical techniques. Oxygen-rich functional groups of GQDs gave rise to a tightly packed structure between carbon black and sulphur, enabling fast charge transfer. Moreover, experimental observations and theoretical analysis helped to clarify the role of GQDs. In particular, the introduction of GQDs significantly was found to improve cycling performance and rate capability through the formation of carbon–sulphur bonds. Graphene quantum dots (GQDs) decorated sulfur–carbon hierarchical structure serve as a high sulfur/sulfide utilization in Li–S battery. The oxygen rich functionalities of the GQDs induced structural integrity of the sulfur–carbon electrode composite. This hierarchical structure enables fast charge transfer, minimizes the loss of soluble polysulfides and completes reaction of sulfur/sulfide.

Enhancing the short-circuit current and power conversion efficiency of polymer solar cells with graphene quantum dots derived from double-walled carbon nanotubes

Derived from double-walled carbon nanotubes, graphene quantum dots (GQDs) with a uniform size distribution were prepared through solution chemistry. The GQDs in chlorobenzene exhibited bright blue emission upon UV excitation. The introduction of the GQDs into a bulk heterojunction polymer solar cell based on poly(3-hexylthiophene):(6,6)-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) resulted in a significant enhancement of the power conversion efficiency (PCE). The efficiency was further improved by adjusting the PCBM content in the active layer, reaching a maximum PCE of 5.24%. This ternary system based on blended P3HT:PCBM:GQDs represents a new method to enhance the efficiency of polymer solar cells. Fushan Li, Tailiang Guo and co-workers from Fuzhou University, China, have constructed an efficient polymer solar cell by adding graphene quantum dots to a conventional design. Lighter than their silicon-based counterparts, easier to fabricate and more environmentally friendly, polymer solar cells show particular promise but do not yet convert enough of the sunlight they absorb for practical application. The active layer of such solar cells comprises an electron-donating material — often the conjugated polymer poly(3-hexylthiophene) — and an electron-accepting one, such as a fullerene derivative. The use of graphene quantum dots as the electron acceptor has recently been shown to endow a photovoltaic device with good stability and low cost but also a relatively poor performance. Li, Guo and their colleagues have now incorporated graphene quantum dots — prepared from double-walled carbon nanotubes — in addition to, rather than instead of, the fullerene-based electron acceptor of a polymer solar cell, significantly enhancing its energy conversion efficiency. Graphene quantum dots (GQDs) derived from double-walled carbon nanotubes with strong emission were prepared through solution chemistry. The introduction of GQDs in a bulk heterojunction polymer solar cell based on Poly (3-hexylthiophene):(6,6)-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) resulted in the significant enhancement of power conversion efficiency (PCE). The efficiency can be further improved by adjusting the PCBM content in the active layer, with the highest PCE of 5.24%.