Reduced Graphene Oxide Quantum Dots Research Articles

Amplified adsorption and photocatalytic degradation of polycyclic aromatic hydrocarbons using biocompatible nanocrystalline reduced graphene oxide quantum dots

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) have been broadly recognized as significant organic pollutants in the environment, which pose a serious threat to both humans and animals. Therefore, there is an urgent need to develop a solution that effectively removes and reduces PAHs present in the environment. In the present work, we synthesized biocompatible nanocrystalline reduced graphene oxide quantum dots in powdered form (rGOQDTs) of crystallite size 2 nm through hydrothermal method and subsequently used for efficient adsorption and degradation of PAHs for the first time. We noticed that the adsorption of PAHs onto rGOQDTs was faster and more efficient as compared to adsorption on graphene oxide (GO). A 40-fold giant enhancement in the adsorption efficiency of Anthracene and Pyrene on rGOQDTs has been observed as compared to that of graphene oxide. We attribute this enormous enhancement in adsorption efficiency to the stacking of PAHs with rGOQDTs and stronger π-π interactions between rGOQDTs and PAHs. Interestingly, rGOQDTs also exhibit efficient photo-degradation of adsorbed PAHs under visible light irradiation and it degrades almost all PAHs after 80 min of visible light illumination. The degradation efficiency of PAHs is also higher for rGOQDTs as compared to GO. Our work paves the way for efficient removal and degradation of polycyclic aromatic hydrocarbons from the environment.

Enhancing Photothermal/Photodynamic Therapy for Glioblastoma by Tumor Hypoxia Alleviation and Heat Shock Protein Inhibition Using IR820-Conjugated Reduced Graphene Oxide Quantum Dots.

We use low-molecular-weight branched polyethylenimine (PEI) to produce cytocompatible reduced graphene oxide quantum dots (rGOQD) as a photothermal agent and covalently bind it with the photosensitizer IR-820. The rGOQD/IR820 shows high photothermal conversion efficiency and produces reactive oxygen species (ROS) after irradiation with near-infrared (NIR) light for photothermal/photodynamic therapy (PTT/PDT). To improve suspension stability, rGOQD/IR820 was PEGylated by anchoring with the DSPE hydrophobic tails in DSPE-PEG-Mal, leaving the maleimide (Mal) end group for covalent binding with manganese dioxide/bovine serum albumin (MnO2/BSA) and targeting ligand cell-penetrating peptide (CPP) to synthesize rGOQD/IR820/MnO2/CPP. As MnO2 can react with intracellular hydrogen peroxide to produce oxygen for alleviating the hypoxia condition in the acidic tumor microenvironment, the efficacy of PDT could be enhanced by generating more cytotoxic ROS with NIR light. Furthermore, quercetin (Q) was loaded to rGOQD through π-π interaction, which can be released in the endosomes and act as an inhibitor of heat shock protein 70 (HSP70). This sensitizes tumor cells to thermal stress and increases the efficacy of mild-temperature PTT with NIR irradiation. By simultaneously incorporating the HSP70 inhibitor (Q) and the in situ hypoxia alleviating agent (MnO2), the rGOQD/IR820/MnO2/Q/CPP can overcome the limitation of PTT/PDT and enhance the efficacy of targeted phototherapy in vitro. From in vivo study with an orthotopic brain tumor model, rGOQD/IR820/MnO2/Q/CPP administered through tail vein injection can cross the blood-brain barrier and accumulate in the intracranial tumor, after which NIR laser light irradiation can shrink the tumor and prolong the survival times of animals by simultaneously enhancing the efficacy of PTT/PDT to treat glioblastoma.

Characterization of sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots

In this research we are reporting for the first time the elaboration y characterization of titanium dioxide sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots. Reduced graphene oxide quantum dots were synthesized by microwave assisted cutting of reduced graphene oxide and mixed with protoporphyrin IX previous to be drop-casted on titanium dioxide. Characterization was done by dynamic light scattering, ultraviolet visible spectroscopy, Raman spectroscopy, atomic force microscopy, field electron scanning electron microscopy, impedance spectroscopy and current voltage measurements. There were blue and red shifts of Raman and absorption bands of protoporphyrin+reduced graphene oxide quantum dots nanocomposites, evidencing strong interactions because of π−π electrons stacking, this fact was confirmed by microscopy images showing full coverage of protoporphyrin surface by reduced graphene oxide quantum dots. Electrical characterization of titanium dioxide+protoporphyrin+reduced graphene oxide quantum dots showed one of the highest photo-responses and lowest resistivities, in line with impedance measurements in which these composites presented up to ∼200% increase in capacitance, versus TiO2 alone. Efficiency of the optimized cell was 6.13 %, this was a value 9.4 % higher versus titanium dioxide+protoporphyrin cell. The reasons for the behavior of optimized cells are discussed based on a bands diagram showing the possibility of a rectifier effect and because of the strong affinity between protoporphyrin and reduced graphene oxide quantum dots.

Terahertz Optical Properties and Carrier Behaviors of Graphene Oxide Quantum Dot and Reduced Graphene Oxide Quantum Dot via Terahertz Time-Domain Spectroscopy

Graphene quantum dots (GQDs) with a band gap have been widely applied in many fields owing to their unique optical properties. To better utilize the optical advantages of GQDs, it is important to understand their optical characteristics. Our study demonstrates the optical properties and carrier behaviors of synthesized graphene oxide quantum dot (GOQD) and reduced graphene oxide quantum dot (rGOQD) pellets via Terahertz time-domain spectroscopy (THz-TDS). The complex permittivity and optical conductivity are obtained in the terahertz region, indicating that the optical conductivity of the GOQD is higher than that of the rGOQD. Although rGOQD has a higher carrier density, approximately 1.5-times than that of GOQD, the lower charge carrier mobility of the rGOQD, which is obtained using Drude–Lorentz oscillator model fitting contributes to a decrease in optical conductivity. This lower mobility can be attributed to the more significant number of defect states within the rGOQD compared to GOQD. To the best of our knowledge, our study initially demonstrates the optical property and carrier behaviors of GOQD and rGOQD in the THz region. Moreover, this study provides important information on factors influencing carrier behavior to various fields in which carrier behavior plays an important role.

Smart-Phone-Assisted Optical Biosensors Based on Silk-Fibroin-Decorated Reduced Graphene Oxide Quantum Dots for Fluorescent Turn-On Recognition of l-Dopa

Levodopa (l-dopa) is a gold standard neurological drug for symptomatic medication of Parkinson’s disease. The long-term use of l-dopa therapy frequently leads to l-dopa-induced dyskinesia and several other non-motor flocculants for fluctuating plasma concentration. To alleviate the adverse effect of dopamine replacement therapy, sensitive detection of l-dopa is still challenging. Therefore, this study presents a simple strategy to develop an inexpensive, easy-to-use, smartphone-based fluorescence turn-on sensory system based on the aggregation-induced emission enhancement phenomenon for instant low-level detection of l-dopa in biological samples. The sensor was fabricated using silk-fibroin-decorated reduced graphene oxide quantum dots, which exhibit a progressive increase of fluorescence intensity in the presence of l-dopa. By measuring the turn-on efficiency of the sensor in elevated concentrations of l-dopa, the limit of detection (LOD) was evaluated as 76.18 nM over a linear range of 0–35 μM. We have further designed a smartphone-based electronic device involving a 365 nm light emitting diode attached below the rare camera for capturing the change of fluorescent color of the solution during sensing. From these images, red, green, and blue values are analyzed using a mobile phone application, and the corresponding LOD was found to be 0.29 μM in a similar linear range of concentration. This simple, cost-effective, and rapid screening gadget is very demanding for on-spot detection of the analytes in remote areas where sophisticated instrumentation is not usually available.

Synthesis of reduced graphene oxide quantum dots from graphene oxide via hydrothermal process and theirs structural, luminescence and magnetic properties

BackgroundReduced graphene oxide quantum dots (rGO-QDs) have attracted much interest because of its exceptional chemical and physical properties and novel applications in a new technology and devices such as, energy storage, electrochemical, photocatalysis, sensing, drug delivery, bioimaging and anticancer therapy. MethodsIn this work, we reported a correlation study of the structural, morphological, luminescence and magnetic behavior of rGO-QDs as a function of hydrothermal reduction temperatures (such as 90 °C, 120 °C, 150 °C and 180 °C) of GO sheets precursor via hydrothermal process. GO precursor and the obtained rGO-QDs samples were confirmed and analyzed by several techniques such as, XRD, Raman, XPS, TEM, PL, UV–Visible, Fluorescence and EPR. Significant findingsInfluence of hydrothermal cutting process with different temperatures (90 °C, 120 °C, 150 °C and 180 °C) on the evolution of structural, morphologies, luminescence and magnetic behavior for the changes of large GO sheets into ultra-small rGO-QDs is presented. XRD result confirmed the effect of increasing temperature on the hydrothermal cutting process which led to a decrease in d-spacing values of rGO-QDs products. While Raman results indicates the trend of ID/IG ratio decreases along with increasing hydrothermal reduction temperatures. XRS analysis revealed that the percentage of carbon content of GO precursor (∼64%) was shifted value to ∼83% for obtained rGO-QDs sample prepared at 180 °C. TEM images shown that a very thin plate-like shape with ultrasmall average diameter of rGO-QDs samples in rage of 22±2 nm to 8 ± 2 nm. The optical and PL results well-confirmed the characteristic quantum size effect of all rGO-QDs samples. Finally, the EPR signals indicate the crossover between paramagnetic and diamagnetic are depended on the reduction temperature. The rGO-QDs prepared at 180 °C do not give any EPR signal, signify the nonmagnetic nature. This indicate that the basal plane of rGO-QDs at 180 °C has nearly perfect sp2 network of graphene.

Reduced Graphene Oxide Quantum Dot Light Emitting Diodes Fabricated Using an Ultraviolet Light Emitting Diode Photolithography Technique.

Graphene quantum dots usually suffer from serious fluorescence quenching in aggregates and the solid state due to easy agglomeration and aggregation-induced quenching, which seriously restrict their practical applications. An ingenious strategy to kill three birds with one stone, the ultraviolet (UV) photolithography technique, was studied, and blue-emitting reduced graphene oxide quantum dot (rGOQD)-based light emitting diodes (LEDs) with efficient solid state emission were first fabricated using UV photolithography. First, rGOQDs were prepared by the in situ photoreduction of GOQDs by using the photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide with 395 nm UV LED exposure. Furthermore, rGOQD/photoresist patterns were prepared under the same conditions. Meanwhile, the in situ photoreduction of GO in the aforementioned photoresist to rGO was realized by UV photolithography to improve the conductivity of the rGOQD/photoresist films. Additionally, the in situ photoreduction of GOQDs in different surroundings was studied, with the results showing that GOQDs are more easily photoreduced in ionic liquids and that the photoluminescence spectrum obtained for rGOQDs exhibits a 70 nm blueshift with a narrow full-width at half-maximum compared to GOQDs.

Characterization of Sensitized Solar Cells Based on Nanocomposites of Protoporphyrin Ix and Microwave Reduced Graphene Oxide Quantum Dots

Characterization of Sensitized Solar Cells Based on Nanocomposites of Protoporphyrin Ix and Microwave Reduced Graphene Oxide Quantum Dots

A CdS/rGO QDs/TiO2nanolawn photoanode co-decorated with reduced graphene oxide quantum dots and CdS nanoparticles with photoinduced cathodic protection characteristics of 316L SS and Cu

A ternary CdS/rGO QDs/TiO2nanobranched photoanode synergistically boosted the simulated sunlight-driven and visible light-driven photoinduced cathodic protection characteristics.

Carbon monoxide gas sensor based on an α-Fe2O3/reduced graphene oxide quantum dots composite film integrated Michelson interferometer

A carbon monoxide (CO) sensor based on a Michelson interferometer combined with α-Fe2O3/reduced graphene oxide quantum dots (rGOQDs) composite film is proposed and fabricated. First, a waist-enlarged taper is formed between the single-mode fiber (SMF) and the no-core fiber (NCF), then the other end of the NCF is spliced with a section of thin-core fiber (TCF). The end of the TCF is coated with a layer of silver film to enhance the reflection. Thus, a Michelson interferometer comprising SMF–NCF–TCF is formed. The α-Fe2O3/rGOQDs composite film is deposited on the outside surface of the TCF. The specific adsorption of CO by the composite film leads to a change in the sensor’s effective refractive index, realizing the detection of CO. The results show that the interference intensity of the monitoring valley decreases with increase in the concentration of CO. The sensitivity of the sensor is 0.057 dBm ppm−1, the detection limit of the sensor is 105 ppb and the response time and recovery time are 70 s and 100 s, respectively. The sensor has the advantages of high sensitivity, high selectivity and simple structure, and it is expected to be used for the detection of low concentrations of CO gas.

Room temperature photoluminescent study of thermally grown reduced graphene oxide quantum dots

In this work, we describe the formation of rGO nanomaterial from GO using a simple, eco-friendly, cost-effective, and template-free modified Hummer's approach followed by thermal reduction. X-ray diffraction, Scanning electron microscopy, UV–VIS spectroscopy, photoluminescence, Fourier transform infrared, Raman technique and Thermogravimetric (TGA) analysis are used to investigate the features of the rGO nanomaterial. Structural characteristics of rGO nanomaterial revealed that they grow in a hexagonal phase and within the quantum range. Morphological studies show the production of wrinkled and smooth-like structures with nanoscale thickness. TGA demonstrated that the nanomaterial is extremely stable at elevated temperatures. The optical characteristics of the rGO quantum dots indicated that they are suited for optoelectronic devices with room-temperature photoluminescence. Photoluminescence (PL) investigation revealed that rGO absorbs ultraviolet light and emits green color. The color coordinates of nanomaterials are determined using the Comission Internationale de I'E'clairage CIE diagram, which indicates their compatibility for biological applications.

Synthesis of Nanocrystalline Reduced Graphene Oxide Quantum Dots

Reduced graphene oxide quantum dots (rGOQDTs) play a vital role in a variety of biological, optoelectronics, and environmental applications. The quality of 0D nanodots is compromised when they are cut from big 2D nanosheets. As a result, it is necessary to maintain a balance between quality and yield. Here, we developed a two-step hydrothermal process for producing nanocrystalline rGOQDTs by employing graphene oxide (GO) as an initial precursor. UV-Visible spectroscopy was used to explore the optical properties of rGOQDTs. XRD, Raman, and FTIR spectroscopic experiments were performed to better understand the crystalline and chemical properties and composition of rGOQDTs. The nanocrystalline rGOQDTs have an average crystallite size of 1.67[Formula: see text]nm. Using GO as an initial precursor implies a simple two-step approach for producing nanocrystalline rGOQDTs in a low-cost, highly efficient, and scalable manner.

Nitrogen-Doped Graphene Quantum Dots and Reduced Graphene Oxide Quantum Dots As Intracellular Temperature Sensors

Non-invasive temperature sensing is necessary for the analysis of biological processes occurring in the human body including cellular enzyme activity, protein expression, and ion regulation. In order to probe temperature-sensitive processes at the nanoscale we develop novel luminescence nanothermometers based on graphene quantum dots (GQDs) synthesized via top-down (RGQDs) and bottom-up (N-GQDs) approaches from reduced graphene oxide and glucosamine precursors. Because of their small 3-6 nm size, non-invasive optical sensitivity to temperature change, and high biocompatibility, GQDs enable biologically safe sub-cellular resolution sensing. Both GQD types exhibit temperature-sensitive, yet photostable fluorescence in the visible and near-infrared for RGQDs, utilized as a sensing mechanism in this work. Distinctive linear and reversible fluorescence quenching with temperature by up to 19.3 % is observed for the visible and near-infrared GQD emission in aqueous suspension, in a small temperature range from 25 to 49℃. An even more pronounced trend is observed with GQD nanothermometers internalized into the cytoplasm of HeLa cells as they are tested in vitro in the temperature range of 25℃ to 45℃ with over 40% quenching response. Our findings suggest that the temperature-dependent fluorescence quenching of bottom-up and top-down-synthesized GQDs studied in this work can serve as non-invasive reversible photostable deterministic mechanism for temperature sensing in microscopic sub-cellular biological environments.

Synthesis of new functionalized reduced graphene oxide quantum dot composite for high-performance NO2 gas sensor

In this research, synthesis of a novel magnetic 2-naphthalenesulfonic acid-grafted reduced graphene oxide quantum dot (Fe3O4-rGOQD-naphthalene-2-SO3H) via a five-step procedure has been described. The structure of this newly prepared Fe3O4-rGOQD-naphthalene-2-SO3H was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive spectroscopy (EDX), thermogravimetric analytical (TGA), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM) analysis. Synthesized Fe3O4-rGOQD-naphthalene-2-SO3H has been explored as a highly efficient and recoverable nanosensor and was prepared with different weight percentages of Fe3O4 (X = 99, 95, 90, 85% wt). The efficiency of Fe3O4-rGOQD-naphthalene-2-SO3H as a sensor was explored in nitrous oxide (NO2) gas probe at the concentration of 2.5–50 ppm NO2 at room temperature. Detection of NO2 by Fe3O4-rGOQD-naphthalene-2-SO3H was investigated under a series of different experimental conditions and the obtained results were compared with previously published methods. The results show that the detection range, the responsiveness, and the optimum temperature of Fe3O4-rGOQD-naphthalene-2-SO3H sensor were improved compared to other works.

Hollow molecularly imprinted microspheres made by w/o/w double Pickering emulsion polymerization stabilized by graphene oxide quantum dots targeted for determination of l-cysteine concentration

A double Pickering emulsion was designed to fabricate hollow imprinted microspheres (H-IMMs) for the detection of l-Cysteine (l-Cys). In a w1/o/w2 double emulsion, the main o/w2 emulsion droplets stabilized by hydrophilic partially reduced graphene oxides (r-GOs) encapsulating smaller w1/o emulsion droplets stabilized by hydrophobic reduced graphene oxide quantum dots (r-GOQDs). The results revealed that size distribution and calculated volume-surface mean diameter (d3,2) of main droplets were narrowed and decreased from 48.2 to 16.7 μm with pH variation from 4 to 12 ; the reason lies in the pH-sensitivity of r-GOs. Polymerization of methacrylic acid and ethylene glycol dimethacrylate in the presence of l-Cys, as a target molecule, at the oil phase led to the synthesize of H-IMMs. Investigations by cyclic voltammetry and differential pulse voltammetry methods demonstrated that the prepared H-IMMs is responsive to l-Cys. The response of H-IMMs leach/CPE displayed a linearity range of 0.01 μM to 1 μM Cys with a limit of detection of 15.5 nM.

A facial synthesis of nitrogen-doped reduced graphene oxide quantum dot and its application in aqueous organics degradation

N-doped reduced graphene oxide quantum dots (N-rGQDs) have attracted more and more attention in efficient catalytic degradation of aqueous organic pollutants. However, the synthesis of N-rGQDs is generally a complex and high energy required process for the reduction and N-doping steps. In this study, a facile and green fabrication approach of N-rGQDs is established, based on a metal-free Fenton reaction without additional energy-input. The N structures of N-rGQDs play a significant role in the promotion of their catalytic performance. The N-rGQDs with relatively high percentage of aromatic nitrogen (NAr-rGQDs) perform excellent catalytic activities, with which the degradation efficiency of pollutant is enhanced by 25 times. Density functional theory (DFT) calculation also indicates aromatic nitrogen structures with electron-rich sites are prone to transfer electron, presenting a key role in the catalytic reaction. This metal-free Fenton process provides a green and cost-effective strategy for one-step fabrication of N-rGQDs with controllable features and potential environmental catalytic applications.

Enhanced mobility and controlled transparency in multilayered reduced graphene oxide quantum dots: a charge transport study

Reduced graphene oxide (rGO) layers are known to be significantly conductive along the basal plane throughout delocalized sp2 domains. Defects present in rGO implies in disordered systems with numerous localized sites, resulting in a charge transport governed mainly by a 2D variable range hopping (VRH) mechanism. These characteristics are observed even in multilayered rGO since the through-plane conduction is expected to be insubstantial. Here, we report on the multilayer assembly of functionalized rGO quantum dots (GQDs) presenting 3D VRH transport that endows elevated charge carrier mobility, ca ∼ 236 cm2 V−1 s−1. Polyelectrolyte-wrapped GQDs were assembled by layer-by-layer technique (LbL), ensuring molecular level thickness control for the formed nanostructures, along with the adjustment of the film transparency (up to 92% in the visible region). The small size and the random distribution of GQDs in the LbL structure are believed to overcome the translational disorder in multilayered films, contributing to a 3D interlayer conduction that enhances the electronic properties. Such high-mobility, transparency-tunable films assembled by a cost-effective method possess interesting features and wide applicability in optoelectronics.

Performance and stability of counter electrodes based on reduced few-layer graphene oxide sheets and reduced graphene oxide quantum dots for dye-sensitized solar cells

Graphene-based materials represent an attractive alternative to platinum in dye-sensitized solar cells (DSSC) counter electrodes to contribute to an efficient conversion of solar energy into electricity. Despite the slower kinetics of carbon for the reduction of triiodide compared to platinum, they are characterized by low cost and promising stability. In this work, two different materials are investigated: reduced few-layer graphene oxide (rFLGO) and reduced graphene oxide quantum dots (rGOQD). The electrochemical performance of DSSC assembled with either rFLGO or rGOQD at the counter electrode is correlated to their most important physico-chemical features. The domain size of graphene sheets had an important effect on the performance at the counter electrode, with quantum dots performing 13% higher efficiency than rFLGO, correlated with a higher density of active sites. Both graphene nanostructures exhibited a better stability behavior upon electrochemical cycling and seasoning of the cells as compared to Pt counter electrode.

Synergistic Enhancement of H2and CH4Evolution by CO2Photoreduction in Water with Reduced Graphene Oxide–Bismuth Monoxide Quantum Dot Catalyst

Photocatalytic water splitting or CO2 reduction is one of the most promising strategies for solar energy conversion into hydrogen-containing fuels. However, these two processes typically compete with each other, which significantly decreases the solar energy conversion efficiency. Herein, we report for the first time this competition can be overcome by modulation of reactive sites and electron transfer pathway of heterogeneous photocatalysts. As a prototype, BiO composite reduced graphene oxide quantum dots (RGO-BiO QDs) were synthesized, which can provide large amounts of photogenerated electrons as well as individual reactive sites for H+ and CO2 reduction. The productivity of H2, CH4, and CO by the RGO-BiO QDs catalyst were 102.5, 21.75, and 4.5 μmol/(g·h), respectively, in pure water without the assistance of any cocatalyst or sacrificial agent. The apparent quantum efficiency at 300 nm reached to 4.2%, which is more than 10 times higher than that of RGO-TiO2 QDs (0.28%) under the same conditions. In situ DRIFT, ESR, and photoelectrochemical studies confirmed that the unique circled electron transfer pathway (Evb(BiO) → Ecb(BiO) → Ef(RGO) → EVo•(BiO)) and the large amount of separated different reactive sites are responsible for the highly efficient simultaneous H2 evolution and CO2 reduction performance.

A Reduced Graphene Oxide Quantum Dot-Based Adsorbent for Efficiently Binding with Organic Pollutants

This paper, for the first time, presents a novel, robust, and efficient high-quality reduced graphene oxide quantum dot (GQD)-based adsorbent for addressing the alarming environmental pollution iss...