Graphene Quantum Dots Composites Research Articles

Improved Photocatalytic Performance of TiO2-Nitrogen-Doped Graphene Quantum Dot Composites Mediated by Heterogeneous Interactions.

Photocatalysis is typically monitored via analysis of phases in isolation and focuses on the removal of a target analyte from the solution phase. Here we analyze the photocatalytic action of a TiO2-nitrogen-doped graphene quantum dot (NGQD) composite on a target analyte, phenol, using comprehensive multiphase NMR (CMP-NMR) which observes signals in solid, solution, and gel phases in situ. Phenol preferentially interacts with the composite photocatalyst compared to pure TiO2, increasing its effective concentration near the catalyst surface and its degradation rate. The presence of NGQDs in the composite reduced the fouling of the catalyst surface and caused a reduction of photogenerated intermediates. Increased heterogeneous interactions, likely mediated by π-π interactions, are hypothesized to cause each of these improvements in the observed photocatalytic performance by TiO2-NGQDs. CMP-NMR allows the elucidation of how the photocatalytic mechanism is enhanced via material design and provides a foundation for the development of efficient photocatalysts.

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.

Band alignment driven efficient electron transfer and enhanced photoelectric property of gold nanoclusters sensitized graphene quantum dot composites

Gold nanoclusters (Au NCs) have received much attention due to their promising applications in many fields including optical imaging, catalysis, biomedical science and, more recently, energy conversion. Herein, we have constructed a model composite of Au NCs and graphene quantum dots (GQDs), and investigated the band alignment of their energetic levels, efficient electron transfer, and enhanced photoelectric properties of Au NCs/GQDs composites. The introduced Au NCs not only make up for the deficiency of light absorption of GQDs in the visible light region but importantly function as the electron donor to sensitize GQDs and improve the photoelectric properties of the composite. The results from steady-state and time-resolved measurements demonstrate a dramatically quenched fluorescence and a shortened lifetime of Au NCs in the composites, owing to the efficient electron transfer from Au NCs to GQDs. The electron transfer efficiency determined from the dynamical analysis is consistent with that of steady-state fluorescence quenching. The type-II band alignment of Au NCs and GQDs moieties effectively promotes the charge separation of excited Au NCs moieties and the electron transfer to GQDs. As a result, the photoelectric current of Au NCs/GQDs composite is enhanced by 2.69 and 4.80 times that of individual Au NCs and GQDs, respectively. These findings demonstrate a feasible strategy for constructing photoelectric composites with Au NCs as the sensitizer and carbon-based QDs as the electron acceptor and also provide photophysical insights into the structure-property relationship of Au NCs-based composites.

Doped Graphene Quantum Dots Modified Zn0.9Cd0.1Se for Improved Photoelectric Properties

AbstractS‐graphene quantum dots (GQDs), N‐GQDs, P‐GQDs, and Cl‐GQDs are prepared by a solution chemistry method and further incorporated with ZnxCd1−xSe by one‐step hydrothermal method. In the previous study, ZnxCd1−xSe reached the optimal photoelectric performances at the Zn/Cd ratio of 0.9:0.1, so the Zn0.9Cd0.1Se were combined with doped GQDs (D‐GQDs) to form Zn0.9Cd0.1Se/doped‐GQDs. The influence of GQDs doped with different elements on the photoelectric properties of Zn0.9Cd0.1Se composites is discussed. Compared with pristine Zn0.9Cd0.1Se, Zn0.9Cd0.1Se/Cl‐GQDs, and Zn0.9Cd0.1Se/P‐GQDs can improve the photocurrent response and current intensity, therein, Zn0.9Cd0.1Se/Cl‐GQDs reaches the lowest interfacial charge transfer resistance and the highest photocurrent response of 5.48 × 10−6 A cm−2. Mott–Schottky analysis shows that the fitting slope of Zn0.9Cd0.1Se/Cl‐GQDs composites is significantly lower than that of Zn0.9Cd0.1Se/GQDs with other doped elements. The results indicate that Zn0.9Cd0.1Se/Cl‐GQDs composites has the largest carrier density, which is beneficial to charge conduction.

Elucidating the role of etchants induced photo- and electro-activity in holey graphene oxide and graphene quantum dots composites for textile electrode applications

Holey graphene oxide (HGO) can unlock the potential of graphene oxide (GO) by providing high surface area, increased surface reactivity, and fast electrolyte flow. Generally, HGOs are prepared by etching GO, and graphene quantum dots (GQDs) are formed as a byproduct during the etching. GQDs are active materials to increase charge mobility and reduce charge recombination. Previous studies employed strong and high boiling point etchants (e.g., H2SO4), and a filtration process is required for purification. GQDs remained in the filtrate and were lost during the purification because of their small size. To avoid the wastage of GQDs, we tested the low boiling point etchants, which can be separated via vacuum drying to retain GQDs. Considering easy recovery, H2O2, NH4OH, and HNO3 were used for etching, and the resulting composite of GQDs and HGO was characterized and tested for photocatalytic and electrocatalytic activity. The active composite materials were loaded on carbon cloth and reduced to fabricate a stable electrode for performance evaluation. Amongst all etchants, NH4OH could generate the highest surface roughness and nitrogen doping. The NH4OH etched HGO & GQDs composite demonstrated excellent photocatalytic and electrocatalytic activity due to its enhanced surface reactivity, despite its reduced surface area. Compared to negligible photocatalysis of rGO, the optimized composite of GQDs and HGO showed nearly complete dye degradation in 4 h.

Flexible Transient Resistive Memory Based on Biodegradable Composites.

Physical transient electronics have attracted more attention as the basis for building green electronics and biomedical devices. However, there are difficulties in selecting materials for the fabricated devices to take into account both biodegradability and high performance. In this paper, a physically transient resistive random-access memory (RRAM) device was fabricated by using egg protein and graphene quantum dot composites as active layers. The sandwich structure composed of Al/EA:GQD/ITO shows a good write-once-multiple-read memory characteristic, and the introduced GQD improves the switching current ratio of the device. By using the sensitivity of GQDs to ultraviolet light, the logic operation of the “OR gate” is completed. Furthermore, the device exhibits a physical transient behavior and good biodegradability due to the dissolution behavior in deionized water. These results suggest that the device is a favorable candidate for the construction of memory elements for transient electronic systems.

Ultrasensitive luteolin electrochemical sensor based on zeolitic imidazolate frameworks-derived cobalt trioxide @ nitrogen doped carbon nanotube/amino-functionalized graphene quantum dots composites modified glass carbon electrode

The accurate determination of luteolin is of great significance for food and pharmaceutical industry. Herein, an ultrasensitive electrochemical sensor for luteolin based on zeolitic imidazolate frameworks (ZIF)-derived cobalt trioxide @ nitrogen doped carbon nanotube/amino-functionalized graphene quantum dots composites modified glass carbon electrode (Co3O4@N-CNTs/NH2-GQDs/GCE) was constructed. The Co3O4@N-CNTs composites were synthesized through direct pyrolysis of ZIF-67 in the N2 atmosphere, which exhibited outstanding electrochemical performance for luteolin due to the conductivity of N-CNTs and the catalytic action of Co3O4. Under optimized conditions, the Co3O4@N-CNTs /NH2-GQDs/GCE exhibited a linear range of 0.5–1000 nM for detecting luteolin, with a low detection limit (LOD) of 0.1 nM (S/N = 3). Furthermore, the sensor was successfully applied for the detection of luteolin in Chrysanthemum extracts.

A selective approach towards synthesis of poly (3‑bromo thiophene)/graphene quantum dot composites via in-situ and ex-situ routes: Application in light emission and photocurrent generation

This article elucidates fabrication of a smart composite from poly (3-bromothiophene) (PTBr) and graphene quantum dot (GQD) through facile in-situ and ex-situ routes and demonstrates their photo-physical and photo-electrochemical behaviors. 3-bromothiophene was first polymerized to poly (3-bromothiophene) (PTBr) in presence of graphene oxide (GO) and then converted into PTBr/GQD composite through solvo-thermal route in the in-situ process while in the ex-situ process, both graphene oxide (GO) and poly (3-bromothiophene) (PTBr) were first combined ex-situ and then solvo-thermally treated to fabricate the PTBr/GQD composite. Spectroscopic findings indicate safe formation of the composites however, alteration in both precursor and fabrication route had simultaneously created a demonstrable difference in interfacial interaction between poly (3-bromothiophene) (PTBr) and graphene quantum dot (GQD) which eventually impacted their application behavior. Microscopy, Energy dispersive X-Ray (EDX) mapping and X-ray diffraction study mutually elucidated the formation of uniformly thin, fibrillar (8 nm) over-growth of amorphous poly (3-bromothiophene) (PTBr) over graphene quantum dot (GQD) in the ex-situ composite while in the in-situ composite a comparatively non-uniform and thicker over-growth (12 nm) of poly (3-bromothiophene) (PTBr) over graphene quantum dot (GQD) was noticed. Both the composites had shown quenched photoemission but exhibited a much improved photocurrent generation than the pristine components. However, relatively high concentration of poly (3-bromothiophene) (PTBr) coupled with its stronger interaction with graphene quantum dot (GQD) in the in-situ composite had produced a stronger red shift and much higher photocurrent efficiency than that in the ex-situ sample.

Au-Nitrogen-Doped Graphene Quantum Dot Composites as "On-Off" Nanosensors for Sensitive Photo-Electrochemical Detection of Caffeic Acid.

Herein, gold–nitrogen-doped graphene quantum dot (Au/NGQD) composite modified electrodes were fabricated and applied as “on–off” nanosensors for the photo-electrochemical (PEC) detection of caffeic acid under visible-light irradiation. An effective and simple strategy was established for the preparation of Au/NGQD composites by hydrothermal and calcination methods. Owing to the quantum confinement effect of NGQDs, the local surface plasmon resonance (LSPR) effect of Au nanoparticles (NPs), and the synergistic effect between Au and NGQDs NPs, the Au/NGQDs showed excellent PEC performance, with wide linear concentration ranges (0.11 to 30.25 μM and 30.25 to 280.25 μM), a low detection limit (0.03 μM), excellent sensitivity, and high stability. The present study may provide an advanced strategy for the simple design of Au/NGQD composites to allow their effective application for selective and sensitive sensing of small biological molecules.

GFP Plasmid and Chemoreagent Conjugated with Graphene Quantum Dots as a Novel Gene Delivery Platform for Colon Cancer Inhibition In Vitro and In Vivo.

Scientists have studied intensively the gene delivery carriers for treating genetic diseases. However, there are challenges that impede the application of naked gene-based therapy at the clinical level, such as quick elimination of the circulation, lack of membrane penetrability, and poor endosome trapping. Herein, we develop graphene quantum dots (GQDs)-derivative nanocarriers and introduce polyethylenimine (PEI) to equip the system with enhanced biocompatibility and abundant functional groups for modification. In addition to carrying green fluorescent protein (GFP) as an example of gene delivery, this system covalently binds colon cancer cells targeted antibody and epidermal growth factor receptor (EGFR) to enhance cell membrane penetrability and cell uptake of nanocarriers. To achieve multistrategy cancer therapy, the anticancer drug doxorubicin (Dox) is noncovalently encapsulated to achieve pH-induced drug release at tumor sites and leaves space for further functional gene modification. This nanoparticle serves as a multifunctional gene delivery system, which facilitates improved cytotoxicity and longer-sustained inhibition capacity compared to free Dox treatments in colon cancer cells. Moreover, our GQD composites display compatible tumor suppression ability compared with the free Dox treatment group in xenograft mice experiment with significantly less toxicity. This GQD nanoplatform was demonstrated as a multifunctional gene delivery system that could contribute to treating other genetic diseases in the future.

Hydrothermal synthesis of quantum dots dispersed on conjugated polymer as an efficient electrodes for highly stable hybrid supercapacitors

Hydrothermal synthesis of graphene quantum dots (GQDs) composited with conjugated polymer were investigated the high specific capacitance and cyclic stability of supercapacitor. The situ chemical polymerization method was employed to synthesize the polypyrrole - graphene quantum dots (PPY-GQDs) composite at different concentrations of GQDs. The size, morphology and structural phase of the PPY- GQDs composites was studied by using Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM), Atomic Force Microscope (AFM) and X-ray diffractometry (XRD) techniques respectively. The optical and electrochemical measurements were carried out by using Ultraviolet-Visible (UV--Vis) Absorption spectroscopy, Photoluminescence Spectroscopy (PL) and electrochemical work station. The cyclic voltammetry (CV) results show enhanced current density and area of CV loop with increasing scan rate and the concentration of GQDs. The Supercapacitor was fabricated by two electrodes owns a high energy density 67.8 Wh/kg and 93 Wh/kg at a power density of 1210 W/kg and 1430 W/kg for PGC1 and PGC3 composites. The highest specific capacitance values 467.32 and 647.54F/g are achieved by PGC1 and PGC3 composite compare to pure PPY. The PPY-GQDs composites achieved excellent cycle stability until the 2000 cycle. Thus, it demonstrates that GQDs is playing a unique and important role in improving the performance of a hybrid supercapacitor device.

Ultrathin BiOCl/nitrogen-doped graphene quantum dots composites with strong adsorption and effective photocatalytic activity for the degradation of antibiotic ciprofloxacin

Photocatalysis, as a green chemical technology for the removal of antibiotics, has attracted great interest recently. This study proposed a facile one-step hydrothermal process to fabricate ultrathin two dimensional (2D) BiOCl/nitrogen-doped graphene quantum dots (BiOCl/NGQDs) composites. Compared to pure BiOCl, the BiOCl/NGQDs composites exhibited enhancement in both adsorption and photodegradation for antibiotic ciprofloxacin (CIP). The optimized content of NGQDs was 6.9% and this optimized composite showed a degradation efficiency of 82.5% within 60 min under visible-light irradiation, which was considerably better than that of pure BiOCl (34.9%). Meanwhile, most of CIP was efficiently mineralized into CO2, H2O and other inorganic products, as revealed by a total organic carbon (TOC) removal efficiency of 95.5% within 5 h. The improved photocatalytic activity was attributed to excellent adsorption capability, enhanced visible-light response and efficient separation of the photoinduced electron-hole pairs in BiOCl/NGQDs composite. The active species trap experiments and electron spin resonance revealed that O2− and hole mainly participated in the CIP degradation process. Such an effective strategy to design ultrathin 2D composite photocatalysts would provide a new approach for application in wastewater purification.

Graphene quantum dot induced tunable growth of nanostructured MnCo2O4.5 composites for high-performance supercapacitors

A method that adapts graphene quantum dots (GQDs) as structural inducing agents to tune the morphology of MnCo2O4.5/GQDs composites is developed, and utilized to enhance their electrochemical performance for supercapacitor applications.

Graphitic carbon nitride co-modified by zinc phthalocyanine and graphene quantum dots for the efficient photocatalytic degradation of refractory contaminants

Broad solar light absorption and rapid photogenerated electron-hole pair separation are two critical factors for the efficient enhancement of catalytic performance in a g-C3N4-based photocatalytic system. This study developed a facile method to construct a ternary graphitic carbon nitride/zinc tetracarboxyphthalocyanine/graphene quantum dots (g-C3N4/ZnTcPc/GQDs) composite photocatalyst. Graphene quantum dots (GQDs) were used to modify g-C3N4/ZnTcPc through hydrothermal method, where g-C3N4/ZnTcPc was fabricated by immobilizing zinc tetracarboxyphthalocyanine (ZnTcPc) onto g-C3N4 covalently via amido bonds. The photocatalyst was characterized by transmission electron microscopy, ultraviolet-visible diffuse reflectance spectrum, and X-ray photoelectron spectroscopy. The g-C3N4/ZnTcPc/0.1GQDs composites presented an increased photocatalytic activity by using Rhodamine B, sulfaquinoxaline sodium and carbamazepine as the model pollutants under solar light irradiation. ZnTcPc bonding on the g-C3N4 broadens its visible-light spectral response, and GQDs promotes the photogenerated electron-hole-pair separation efficiency because of its efficient electrons-transfer property. Experiments confirmed that superoxide radicals, photogenerated holes and singlet oxygen are the primary active species. The photocatalytic degradation pathway of Rhodamine B, sulfaquinoxaline sodium and carbamazepine was proposed on the basis of ultra-performance liquid chromatography and high-definition mass spectrometry.

Graphene Quantum Dots Decorated Al-doped ZnS for Improved Photoelectric Performance.

Graphene quantum dots (GQDs) decorated Al-doped ZnS composites were prepared using the solvothermal process, and the hydrothermal method was used to prepare GQDs. Various spectroscopic techniques were used to characterize the products, and the results show that Al-ZnS attached GQD composites present lattice fringes that can be assigned to ZnS and GQDs, respectively. The absorption peaks of Al-ZnS/GQDs are red-shifted because of the doping of aluminum and the incorporation of GQDs. The luminescence intensity of Al-ZnS/GQDs shows a downward trend with the addition of GQDs. As the GQD content changes from 0.6 wt % to 1.8 wt %, the photocurrent density achieves a maximum at the addition of 1.2 wt %. The photocurrent of Al-ZnS/GQDs composites are about 700% and 200% of pure ZnS and Al-ZnS, respectively. The results indicate that Al doping can reduce the energy bandgap of ZnS and produce more photogenerated electrons. The photogenerated electrons from Al-ZnS can be extracted and transferred to GQDs, which act as conducting materials to decrease the recombination rate and improve the photogenerated electron-transfer.

Facile synthesis of Ag3PO4 modified with GQDs composites with enhanced visible-light photocatalytic activity

In this work, the Ag3PO4 modified with graphene quantum dots composites (GQDs–Ag3PO4) were synthesized via a facile precipitation method to further improve the photocatalytic performance of Ag3PO4. Interestingly, these GQDs–Ag3PO4 exhibited improved visible light photocatalytic performance for the degradation of rhodamine B than pure Ag3PO4. The composite with GQDs weight percentage of 0.48 showed the most excellent performance, which was completely almost 11.25 times than that of pure Ag3PO4. Furthermore, this composite also showed excellent photocatalytic performance for the photodegradation of para-chlorophenol, levofloxacin and negatively charged aromatic dye methyl orange. The remarkable enhancement of photocatalytic performance should be attributed to the larger surface area, the enhanced light absorption property and the effective suppression of electron–hole recombination.

Direct Formation of Reduced Graphene Oxide and Graphene Quantum dot Composites by Using Ascorbic Acid as High-Performance Binder-Free Supercapacitor Electrodes

Direct Formation of Reduced Graphene Oxide and Graphene Quantum dot Composites by Using Ascorbic Acid as High-Performance Binder-Free Supercapacitor Electrodes

One-step synthesis of band-tunable N, S co-doped commercial TiO2/graphene quantum dots composites with enhanced photocatalytic activity

N, S co-doped commercial TiO2/N, S-GQDs graphene quantum dots (NSTG) composites with band tunability are synthesized via a facile solvothermal treatment in the presence of thiourea, which acts as a precursor for the dopants.

Selective oxidation of veratryl alcohol with composites of Au nanoparticles and graphene quantum dots as catalysts.

Veratryl alcohol can be oxidized to veratryl aldehyde or veratric acid with excellent selectivity and efficient conversion under acidic and alkaline conditions using Au nanoparticles and graphene quantum dot composites (Au/GQDs) as catalysts.