Quantum Dot Nanocomposites Research Articles

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior.

Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4-CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4-CQD composite has been studied using a three-electrode system. The results show that at 1 A g-1, the composite delivers a higher capacitance of 1209 F g-1. The asymmetric supercapacitor (Co3O4-CQD//AC) provided 13.88 W h kg-1 energy and 684.65 W kg-1 power density with a 96% capacitance retention. The Co3O4-CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4-CQD composite is a promising material for commercial energy storage and environmental applications.

Synthesis of Au/Cu2O/graphene quantum dots nanocomposites and its application for glucose oxidation

Synthesis of Au/Cu2O/graphene quantum dots nanocomposites and its application for glucose oxidation

Highly Reliable Performance of Flexible Synaptic Devices Based on PVP-GO QD Nanocomposites Due to the Formation of Directional Filaments.

The metallic conductive filament (CF) model, which serves as an important conduction mechanism for realizing synaptic functions in electronic devices, has gained recognition and is the subject of extensive research. However, the formation of CFs within the active layer is plagued by issues such as uncontrolled and random growth, which severely impacts the stability of the devices. Therefore, controlling the growth of CFs and improving the performance of the devices have become the focus of that research. Herein, a synaptic device based on polyvinylpyrrolidone (PVP)/graphene oxide quantum dot (GO QD) nanocomposites is proposed. Doping GO QDs in the PVP provides a large number of active centers for the reduction of silver ions, which allows, to a certain extent, the growth of CFs to be controlled. Because of this, the proposed device can simulate a variety of synaptic functions, including the transition from long-term potentiation to long-term depression, paired-pulse facilitation, post-tetanic potentiation, transition from short-term memory to long-term memory, and the behavior of the "learning experience". Furthermore, after being bent repeatedly, the devices were still able to simulate multiple synaptic functions accurately. Finally, the devices achieved a high recognition accuracy rate of 89.39% in the learning and inference tests, producing clear digit classification results.

Carbon dots-cadmium sulfide quantum dots nanocomposite for 'on-off' fluorescence sensing of chromium(vi) ions.

This work involves fluorescent probe which is composed of carbon dots (CD) and cadmium sulfide quantum dots (CdS QD) for the sensitive and selective fluorescence detection of chromium(vi) ions. The blue fluorescent carbon dots were synthesized by hydrothermal method from natural precursor apricot. The carbon dots-cadmium sulfide quantum dots (CD-CdS QD) nanocomposite was synthesized and all as-synthesized products were characterized using different characterization techniques. It showed white fluorescence under UV light which was quenched selectively in the presence of chromium(vi) ions due to the inner filter effect (IFE). The linear decrease in the white fluorescence was observed in the concentration range 2-120 μM of chromium(vi) ions with the limit of detection 2.07 μM. This is novel probe for the sensitive, selective and rapid detection of chromium(vi) ions.

MoS2 Quantum Dot-Optimized Conductive Channels for a Conjugated Polymer-Based Synaptic Memristor.

Donor-acceptor-type conjugated polymers are widely used in memristors due to their unique push-pull electron structures and charge transfer mechanisms. However, the inherently inhomogeneous microstructure of polymer films and their low crystallinity produce randomness that destabilizes formed conductive channels, giving polymer-based memristors unstable switching behavior. In this contribution, we prepared a synaptic device based on PM6-MoS2 QD (molybdenum disulfide quantum dot) nanocomposites. In the composites, MoS2 QDs provided the active centers for forming conductive channels via electron trapping and detrapping. They also controlled the directional formation of conductive channels between PM6 and MoS2 QDs, reducing randomness and giving devices a narrow switching voltage range and cycling longevity. The device exhibited continuous multistage conductance states under a direct current voltage sweep and simulated a variety of synaptic functions, including long-term potentiation, long-term depression, short-term potentiation, short-term depression, paired-pulse facilitation, spiking-rate-dependent plasticity, and "learning experience" behavior. The memristor could also perform arithmetic, including "counting" and "subtraction" operations. This work provides a new approach to improving the performance of memristors for neuromorphic computing.

In-situ green synthesis of copper tannic acid framework in the presence of graphene quantum dots: Improved colloidal and antibacterial properties

This work reports the preparation of a copper tannic acid MOF (CuTA) and graphene quantum dot (GQD) nanocomposite, GQD/CuTA, by a simple, environmentally friendly, and inexpensive method with exceptionally enhanced antibacterial properties. To end this, GQDs were first fabricated from citric acid using a neoteric, simple and straightforward hydrolysis approach and followed by they effectively anchor MOF nanoparticles (CuTA) by a green hydrothermal in situ synthesizing method. The constructed GQD/CuTA nanomaterials were characterized and validated using XRD, FT-IR, TEM, DLS, UV–vis, and PL techniques. Significant antibacterial activity against E. coli bacteria for both CuTA and GQD/CuTA (0 CFU/mL) and S. aureus bacteria for CuTA and GQD/CuTA (300 and 40 CFU/mL) was observed for the GQD/CuTA nanocomposite. The MTT assay showed good cytocompatibility for the GQD/CuTA nanocomposite against human dermal fibroblast cells (HFF-2). The result suggests that the synthesized GQD/CuTA nanocomposite with improved colloidal and antibacterial properties has the potential to be used as a safe photoluminescent nanoplatform with strong antimicrobial activity.

Comparative electrochemical properties of polyaniline/carbon quantum dots nanocomposites modified screen-printed carbon and gold electrodes

In this study, carbon quantum dots (Cdots) synthesized from a pencil graphite precursor using a bottom-up method were incorporated into polyaniline (PANI) to form Cdots-PANI nanocomposite. Cdots, PANI and Cdots-PANI nanocomposites were characterized using the Fourier-Transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The FT-IR spectra of graphene and Cdots show the emergence of a peak at 3500 cm−1, which was initially absent in graphene, after the formation of Cdots, among other peaks. The peak at 3500 cm−1 and the stretching vibration at 1647 cm−1 suggest the presence of –OH and C=C in the Cdots. The FT-IR spectra of PANI/Cdots and PANI show that the peaks in PANI shifted to higher wavenumbers after composite formation. Similarly, the UV–visible spectra of the PANI/Cdots composite revealed a hypsochromic shift of the characteristic PANI peaks at 320 and 600 nm to 300 and 560 nm, respectively. Electrochemical characterization of Cdots, PANI and Cdots-PANI nanocomposites was done with screen-printed carbon electrodes (SPCE) and screen-printed gold electrodes (SPAuE) modified with the nanomaterials and the nanocomposites. The electrochemical properties of the as-synthesized nanomaterials and the nanocomposite were investigated with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) in 10 mM K3[Fe(CN)6] solution using the bare screen-printed electrodes and the modified electrodes. The modified electrodes gave higher anodic peak current (Ipa) responses and lower charge transfer resistance (Rct) values in the redox probe than the bare electrodes. The SPCE-Cdots-PANI nanocomposite-modified electrode exhibited better redox potentials, faster electron transfer kinetics, larger surface area, and greater stability than the bare electrodes and the other modified electrodes. The outstanding electrochemical properties of SPCE-Cdots/PANI underscores its potentials as a sensitive electrochemical sensor for a wide range of analytes.

Percolation-Modeling Comparison Between the Conductivities of Zinc-Graphene Quantum Dot Nanocomposite and Graphite during Extracellular Electron Transfer in Microbial Fuel Cell Electrodes

Percolation-Modeling Comparison Between the Conductivities of Zinc-Graphene Quantum Dot Nanocomposite and Graphite during Extracellular Electron Transfer in Microbial Fuel Cell Electrodes

Biosynthesis of carbon quantum dot nanocomposite as an advanced material for simultaneous electrochemical sensing of D-glucose and paracetamol

Biosynthesis of carbon quantum dot nanocomposite as an advanced material for simultaneous electrochemical sensing of D-glucose and paracetamol

Covalently linked graphene oxide-transition metal disulfide quantum dots nanocomposites featuring enhanced nonlinear optical absorption

Nanocomposites composed of different nanomaterials are a promising class of optoelectronic materials, owing to their interfacial electronic interactions. Compared to van der Waals forces, covalent bond-based linkages may endow nanocomposites with promoted electronic interactions and reinforced nonlinear optical (NLO) responses. In this study, we constructed covalently linked, mixed-dimensional nanocomposites by combining graphene oxide (GO) with MoS2 and WS2 quantum dots (QDs). These nanocomposites were prepared by employing a bifunctional molecule, 4-mercaptobenzenediazonium tetrafluoroborate, which carries a reactive diazonium group and a thiol group. The reactive diazonium group allowed for the attachment of thiophenol to GO via a radical addition reaction, while the thiol group enabled the subsequent passivation of sulfur vacancies in MoS2 and WS2 QDs. The resulting nanocomposites, denoted as GO-MoS2 and GO-WS2, respectively, exhibited significant fluorescence quenching, indicating effective electron and/or energy transfer from MoS2 or WS2 QDs to GO. Importantly, these covalently linked nanocomposites demonstrated superior two-photon absorption (TPA) responses compared to the individual components (GO, MoS2 and WS2 QDs) as well as the corresponding physical blends, presumably resulting from the efficient electron and/or energy transfer within these nanocomposites. This study not only demonstrates the significant promise of covalently linked GO-MoS2 and GO-WS2 nanocomposites in optical limiting applications, but also opens up new opportunities for the advancement of nanocomposites in ultrafast photonic devices.

Efficiency performance of Ag-CdSe quantum dots nanocomposite sensitized solar cells

An in-depth analysis of a solar cell with a photoanode made of glass/FTO/TiO2, and Ag- CdSe quantum dots (QD) nanocomposite, an electrolyte of iodide and triiodide, and a Pt electrode is presented in this work. We looked at how CdSe QD filling factors and Ag nanoparticles affect the solar cell's ability to absorb light. Additionally, the effects of nanocomposite layer thicknesses, Iodide/triiodide layer thicknesses, and TiO2 layer thicknesses on the absorption are investigated. It has been discovered that the Ag nanoparticles have an effect on the absorbance around 700 nm, dropping around 800 nm while keeping the range from 400 nm to 600 nm constant as the fraction of silver increases. With the switch to CdSe, the solar cell's performance was only marginally altered. When the composite thickness is increased to 200 nm, the value of A has the highest values and is expanded to include longer wavelengths. While altering the thickness of the iodide/triiodide layer (di) causes the highest values of A to expand at di = 200 nm. However, the performance of the solar cell is unaffected by the TiO2 layer's thickness (dt). As a result, we gave a solar cell the variables that impacted its performance.

A novel successful strategy for the detection of antibiotics and toxic heavy metals based on fluorescence silver/graphene quantum dots nanocomposites

A novel successful strategy for the detection of antibiotics and toxic heavy metals based on fluorescence silver/graphene quantum dots nanocomposites

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.

Efficient removal of anionic and cationic dyes from waste water using green ZnO/NiO/graphene quantum dots nano photocatalyst

For its detrimental environmental and health impact, water pollution with organic contaminants has found more attention. In this research, a series of nanostructures were prepared and applied as catalysts for the photodegradation of methylene blue and methyl orange as organic pollutants. In this regard, ZnO nanoparticles (NPs), NiO NPs, ZnO/NiO nanocomposites (NCs), and ZnO/NiO/Graphene quantum dots NCs (ZnO/NiO/GQDs NCs) were prepared by a novel and green co-precipitation and hydrothermal route. The crystallinity and morphological properties of samples were studied via X-ray diffraction pattern (XRD), transmittance electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) analysis. The results showed that the applied synthesis routes successfully produced pure nanostructures with uniform shapes and sizes. The optical properties studied with diffuse reflectance measurement-ultraviolet (DRS-UV) analysis revealed that the synthesized green GQDs have an important effect on the optical band gap of the prepared nanostructures. In this regard, the optical band gaps were determined 3.04, 3.07, 2.98, and 2.88 eV for prepared ZnO NPs, NiO NPs, ZnO/NiO NCs, and ZnO/NiO/GQDs NCs, respectively. Photocatalytic tests showed that prepared ZnO/NiO/GQDs NCs is a better catalyst than ZnO NPs, NiO NPs, ZnO/NiO NCs, and photodegraded methylene blue (93.42 %) better than methyl orange (75.68 %) after 90 min. It was also found that the increase in solution acidity reduces photocatalytic performance. As a result, the optimum photocatalytic activity was recorded on pH = 9. Also, the impact of irradiation light on the photocatalytic efficiency was studied.

Ball mill-hydrothermal method for one-step synthesis of zinc oxide/carbon quantum dot (ZnO-CQD) nanocomposites as photocatalyst for degradation of organic pollutants

In this work, we report a cost-effective, green, one-step, and new method without any extra materials to prepare ZnO/CQD photocatalyst. Hence, ZnO nanoparticles and zinc oxide/carbon quantum dot (Z-CQD) nanocomposites were synthesized using zinc salt, KOH, and sucrose through the new green ball mill-hydrothermal method. The prepared nanomaterials were characterized by FT-IR, TEM, XRD, FE-SEM, TGA, and UV–Vis absorption. The analysis of the TGA result shows the presence of around 6 wt% of CQD in Z-CQD nanocomposite. The presence of CQD in ZnO nanoparticles decreased the bandgap. The photocatalytic performance of ZnO and Z-CQD were compared by evaluating the degradation of phenazopyridine (PhP), a drug pollutant, and rhodamine B (RhB), an organic dye pollutant, under UV light. The results showed that the degradation rate of RhB is higher than that of PhP. In addition, in the case of RhB, the degradation rate by Z-CQD is higher than that of pure ZnO. Therefore, the presence of carbon quantum dots showed a positive effect on the rate of photocatalytic degradation.

Flower-like nanocomposite of carbon quantum dots, MoS2, and dendritic Ag-based Z-scheme type photocatalysts for effective tartrazine degradation

Nanocomposites of carbon quantum dots, molybdenum disulfide, and dendritic silver (MoS2/CQD/dendritic Ag) were synthesized via a facile and inexpensive procedure and utilized to investigate photocatalytic degradation of tartrazine (TZN) in aqueous medium. The nanocomposites and their individual components were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), mapping, X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS). The optimum conditions for TZN degradation obtained were TZN concentration of 20 mg/L and a solution pH of 6.5. Electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) analysis were employed to evaluate the TZN degradation by the prepared MoS2/CQD/dendritic Ag nanocomposites. XRD of CQDs, MoS2 and Ag NPs showed amorphous, hexagonal phase and face-centered cubic structures, respectively. Band gaps of 3.3 and 1.9 eV for CQDs and MoS2, respectively as obtained from UV–Vis DRS.The enhanced photo-degradation of TZN was achieved due to the synergistic effects between the nanocomposite constituents. Complete degradation of TZN occurred within 30 min with a rate constant value of 0.172 min−1, wherein oxygen radicals played a significant role compared to other species during the process of degradation.

Hyaluronic acid-graphene oxide quantum dots nanoconjugate as dual purpose drug delivery and therapeutic agent in meta-inflammation

Type 2 diabetes mellitus (T2DM) predominantly considered a metabolic disease is now being considered an inflammatory disease as well due to the involvement of meta-inflammation. Obesity-induced adipose tissue inflammation (ATI) is one of the earliest phenomena in the case of meta-inflammation, leading to the advent of insulin resistance (IR) and T2DM. The key events of ATI are orchestrated by macrophages, which aggravate the inflammatory state in the tissue upon activation, ultimately leading to systemic chronic low-grade inflammation and Non-Alcoholic Steatohepatitis (NASH) through the involvement of proinflammatory cytokines. The CD44 receptor on macrophages is overexpressed in ATI, NASH, and IR. Therefore, we developed a CD44 targeted Hyaluronic Acid functionalized Graphene Oxide Quantum Dots (GOQD-HA) nanocomposite for tissue-specific delivery of metformin. Metformin-loaded GOQD-HA (GOQD-HA-Met) successfully downregulated the expression of proinflammatory cytokines and restored antioxidant status at lower doses than free metformin in both palmitic acid-induced RAW264.7 cells and diet induced obese mice. Our study revealed that the GOQD-HA nanocarrier enhanced the efficacy of Metformin primarily by acting as a therapeutic agent apart from being a drug delivery platform. The therapeutic properties of GOQD-HA stem from both HA and GOQD having anti-inflammatory and antioxidant properties respectively. This study unravels the function of GOQD-HA as a targeted drug delivery option for metformin in meta-inflammation where the nanocarrier itself acts as a therapeutic agent.Graphical

Preparation of β-Cyclodextrin Conjugated, Gelatin Stabilized SBA 15-CuInS2/ZnS Quantum Dot Nanocomposites for Camptothecin Release

Camptothecin (CPT) is a potential anticancer drug. However, it faces challenges due to its poor water solubility and the need for an efficient drug release system. Herein, we developed a novel system composed of gelatin stabilized, mesoporous silica SBA15 encapsulated CuInS2/ZnS (CIS/ZnS) quantum dots (QDs) conjugated with β-cyclodextrin (β-CDs) for its potential use in the release of CPT. In this multifunctional system, β-CDs served as the drug carrier, SBA15 encapsulated QDs is capable of imaging and the gelatin was used to enhance the carrier-drug interaction. Fourier transform infrared (FTIR) analysis confirmed the successful conjugation of β-CDs to the Gel-SBA15 CIS/ZnS QDs, while optical analyses revealed excellent emission properties and high photostability. The β-CD-conjugated Gel-SBA15-CIS/ZnS QD nanocomposite was used to obtain the soluble derivate of CPT which further demonstrated a drug release profile following the triphasic model. Overall, the improved photostability and acceptable drug release profile of the β-CD conjugated Gel-SBA15-CIS/ZnS QD nanocomposite hold great promise for both imaging and therapeutic applications.Graphical

Effect of Gadolinium on Electrical Properties of Polyethyleneimine Functionalized and Nitrogen‐Doped Graphene Quantum Dot Nanocomposite Based Diode

AbstractCarbon, especially graphene quantum dots (GQDs) based electronics have become an attractive technology in recent years. The controlled modification of the electrical and optoelectronic properties of GQDs by physical/chemical processes or synthetic methods may lead to new applications. Gadolinium‐doped polyethyleneimine (PEI) functionalized and nitrogen‐doped graphene quantum dots (GdNPs‐PEI@N‐GQDs) are synthesized by a hydrothermal method to determine how doping carbon‐based materials with Gd alters the electrical properties of the structure. The electrical properties of the GdNPs/PEI@N‐GQDs nanocomposite‐based diode are investigated using the current–voltage (I–V) technique and the capacitance and conductance voltage (C–V & G/ω–V) technique at 300 K in the frequency range of 0.5 to 500 kHz at ± 5 V. The rectification ratio (RR) is found to be 14 at a voltage of ±5 V. The rectifying behavior of the diode changes to an ohmic behavior after doping with Gd, compared to the Gd‐free PEI@N‐GQDs sample (2.8 × 104 at ±5 V). The results are expected to have an impact on the understanding of carbon‐based electronics technology.

Environmentally friendly g-C3N4/carbon quantum dots nanocomposites as fluorescent and anti-spoofing inks

The major goal of this research is to examine fluorescence (FL) features and application of graphitic carbon nitride/carbon quantum dots (GCN/CQD) nanocomposites as invisible and anti-spoofing inks. GCN/CQD nanocomposites were used for an environmentally friendly synthesis method. To achieve this, starch and urea were, respectively, applied as a natural source of carbon and a nitrogen resource. The mixtures of starch and urea with a weight ratio of 1:5 and 1:10 were synthesized using a two-step pyrolysis and microwave-assisted method. FL behavior of the GCN/CQD aqueous colloids indicated that a change in the urea concentration could result in FL emission in the various areas of visible light. FL emission spectra of the synthesized sample with low amount urea and in the sample including extra urea were, respectively, observed at blue and green regions. Anti-spoofing function of these nanocomposites as inks were confirmed via optical spectroscopy testing and digital photos taken from UV cabinet. The photos and patterns taken from the ink made of GCN/CQD nanocomposites are nearly invisible under daylight but clear and observable open to UV, as a result one could conclude that these are potentially usable in anti-spoofing function of the secure inks.