Composition Of Quantum Dots Research Articles

41.2: High Stability Quantum Dot Composites for Mini LED backlighting

This paper reports a kind of high stability QD composites and their use for Mini LED backlighting. The high stability QD composites was characterized by core‐shell‐shell, expressed as CSS in the following. Mesoporous silica spheres (MSSs), as the cores, were used to adsorb QDs as the first shell; after that, the QD‐adsorbed silica spheres were coated by a silica or alumina oxide layer as the second shell. The QD composite was finally demonstrated with a Mini LED backlighting.

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.

Development of High-Performance Polymer Electrolyte Membranes through the Application of Quantum Dot Coatings to Nafion Membranes

Proton exchange membrane water electrolysis (PEMWE) generates oxygen and hydrogen at the anode and cathode, respectively, by conducting protons generated at the anode to the cathode through a proton exchange membrane (PEM). The performance of PEMWE can be improved with faster catalytic reactions at each electrode; thus, the development of a PEM with excellent ionic conductivity and physicochemical stability is essential. Nafion, a type of perfluoro-sulfonic acid polymer, is the most widely used PEM material. However, despite its excellent conductivity and chemical stability, it exhibits high hydrogen permeability due to its structural characteristics. Quantum dots (QDs) have a hydrophilic functional group that can act as an ion conductor and are extremely compatible with the hydrophilic cluster of Nafion due to their characteristic nanosized structure. In this study, various compositions of N-doped carbon quantum dots (CQDs) containing hydrophilic functional groups were coated on a Nafion-212 membrane. The resulting series of CQD-coated Nafion membranes exhibited improvements in morphology and ionic conductivity as well as reductions in hydrogen permeability. In particular, the Nafion membrane coated with 0.75 wt % of N-doped CQD (CQD-cNafion-0.75) exhibited improved mechanical properties and higher oxidation stability compared to Nafion-212. It also displayed higher ionic conductivity of 240.3 mS cm-1 at 80 °C and reduced hydrogen permeability (about 10% reduction) compared to Nafion-212. In addition, the performance of single-cell PEMWE using the CQD-cNafion-0.75 membrane was found to be approximately 1.2 times higher than Nafion-212.

Simultaneous Detection of Ovarian Cancer-Concerned HE4 and CA125 Markers Based on Cu Single-Atom-Triggered CdS QDs and Eu MOF@Isoluminol ECL.

Simultaneous detection of different disease markers is significant for clinical diagnosis. In this work, a dual-signal electrochemiluminescence (ECL) immunosensor was constructed for the simultaneous detection of carbohydrate antigen 125 (CA125) and human epithelial protein 4 (HE4) markers of ovarian cancer. The results showed that the Eu metal-organic framework-loaded isoluminol-Au nanoparticles (Eu MOF@Isolu-Au NPs) could generate a strong anodic ECL signal through synergistic interaction; as cathodic luminophore, the composite of carboxyl-functionalized CdS quantum dots and N-doped porous carbon-anchored Cu single-atom catalyst could catalyze H2O2 co-reactant to produce a large amount of •OH and O2•-, making the anodic and cathodic ECL signals significantly increase and become stable. Based on the enhancement strategy, a sandwich immunosensor was constructed for the simultaneous detection of ovarian cancer-associated CA125 and HE4 markers by combining antigen-antibody specific recognition and magnetic separation technique. The resulting ECL immunosensor displayed high sensitivity, a wide linear response range of 0.005∼500 ng mL-1, and low detection limits of 0.37 and 1.58 pg mL-1 for CA125 and HE4, respectively. Furthermore, it had excellent selectivity, stability, and practicability in the detection of real serum samples. This work establishes a framework for in-depth design and application of single-atom catalysis in ECL sensing.

One-step synthesis of aqueous CdTe/CdSe composite QDs toward efficiency enhancement of solar cell

Aqueous quantum dots (QDs) have been widely used in photovoltaic devices. However, aqueous QDs usually perform poorly in terms of optical properties and stability. In this paper, CdTe/CdSe composite QDs were synthesized in an aqueous solution by a simple one-step method, obtaining the tunable optical properties with a photoluminescence quantum yield (PLQY) over 80%. The simultaneous addition of Te and Se sources passivates the defects of CdTe while suppressing the overgrowth of CdSe shell, obtaining core–shell structure with small size and high PLQY. The PVA/QDs film was prepared by spin-coating to achieve up to 26.83% efficiency improvement on the surface of crystalline silicon solar cells, due to the excellent antireflection and down-shifting effect.

La-Doped CeO2 Quantum Dots: Novel Dye Degrader, Antibacterial Activity, and In Silico Molecular Docking Analysis.

The current work demonstrates a novel synthesis of different concentrations of La-doped (2, 4, and 6 wt %) CeO2 quantum dots (QDs) using a hydrothermal approach. This research aimed to examine the dye degradation efficiency, antibacterial activity, and in silico molecular docking analysis of La-doped CeO2 QDs. The structure, elemental composition, optical properties, d-spacing, and morphological features of QDs were examined using various methods. XRD spectra exhibited the cubic structure of CeO2, and the crystallinity was suppressed upon La doping. TEM revealed the formation of cubic-shaped QDs of CeO2, and the incorporation of La decreased agglomeration. UV-vis absorption spectra showed a red shift upon La doping, assigned to a decrease in band gap energy. 6% La-doped CeO2 showed significant antibacterial activity against Escherichia coli at higher concentrations in comparison to ciprofloxacin. La-CeO2 was proposed as a putative inhibitor of β-lactamase E.coli and DNA gyrase E.coli relying on the outcomes of a molecular docking analysis that was in improved accord with in vitro bactericidal activity. Moreover, the prepared QDs exhibited a remarkable photocatalytic degradation of methylene blue in a basic medium.

Highly fluorescent composite of boron nitride quantum dots decorated on cellulose nanofibers for detection and removal of Hg(II) ions from waste water

To address the challenge of heavy-metal ions in wastewater, boron nitride quantum dots (BNQDs) were synthesized in-situ on rice straw derived cellulose nanofibers (CNFs) as substrate. The composite system exhibited strong hydrophilic-hydrophobic interactions, as corroborated by FTIR, integrated the extraordinary fluorescence properties of BNQDs with fibrous-network of CNFs (BNQD@CNFs) yielding a surface of 35.147 m2 g−1 of luminescent fibers. Morphological studies revealed uniform distribution of BNQDs on CNFs due to hydrogen bonding, according high thermal stability with peak degradation occurring at 347.7 °C and quantum yield of 0.45. The nitrogen-rich surface of BNQD@CNFs exhibited strong affinity for Hg(II), quenching the fluorescence intensity due to combined inner-filter effect and photo-induced electron transfer. The limit of detection (LOD) and limit of quantification (LOQ) were 4.889 nM and 11.1 5 nM, respectively. BNQD@CNFs concomitantly exhibited adsorption of Hg(II) owing to strong electrostatic interactions, confirmed by X-ray photon spectroscopy. Presence of polar BN bonds favoured 96 % removal of Hg(II) at 10 mg L−1 with maximum adsorption capacity of 314.5 mg/ g. Parametric studies corresponded to pseudo-second order kinetics and Langmuir isotherm with R2 ≈ 0.99. BNQD@CNFs exhibited recovery rate between 101.3 %–111 % for real water samples and recyclability upto 5 cycles, demonstrating high potential in wastewater remediation.

Strongly Confined CsPbBr3 Quantum Dots as Quantum Emitters and Building Blocks for Rhombic Superlattices.

The success of the colloidal semiconductor quantum dots (QDs) field is rooted in the precise synthetic control of QD size, shape, and composition, enabling electronically well-defined functional nanomaterials that foster fundamental science and motivate diverse fields of applications. While the exploitation of the strong confinement regime has been driving commercial and scientific interest in InP or CdSe QDs, such a regime has still not been thoroughly explored and exploited for lead-halide perovskite QDs, mainly due to a so far insufficient chemical stability and size monodispersity of perovskite QDs smaller than about 7 nm. Here, we demonstrate chemically stable strongly confined 5 nm CsPbBr3 colloidal QDs via a postsynthetic treatment employing didodecyldimethylammonium bromide ligands. The achieved high size monodispersity (7.5% ± 2.0%) and shape-uniformity enables the self-assembly of QD superlattices with exceptional long-range order, uniform thickness, an unusual rhombic packing with an obtuse angle of 104°, and narrow-band cyan emission. The enhanced chemical stability indicates the promise of strongly confined perovskite QDs for solution-processed single-photon sources, with single QDs showcasing a high single-photon purity of 73% and minimal blinking (78% "on" fraction), both at room temperature.

Precipitation and optical properties of PbSexS1-x quantum dots in glasses

Lead chalcogenide quantum dots have particular optoelectronic properties induced by the quantum confinement effects and have promising potentials towards applications in infrared spectral range. Modulation of the optoelectronic properties of lead chalcogenide quantum dots is mainly based on the thermal treatment. In this work, precipitation and optical properties of alloyed PbSexS1-x quantum dots in glasses are investigated. Composition, size, absorption, and photoluminescence properties of PbSexS1-x quantum dots are modulated by chalcogen elements in glasses and thermal treatment. By adjusting the concentration of ZnSe and ZnS in the glasses, average diameters of the PbSexS1-x quantum dots are tuned in the range of 8.1–16.1 nm, their absorption peak wavelengths are tuned in the range of 724–2497 nm, and photoluminescence bands are tuned in the range of 1016–2165 nm with full width at half maximum in the range of 167–517 nm. Fraction of Se in the PbSexS1-x quantum dots precipitated in glasses is dependent on the concentrations of ZnSe and ZnS in the glass and heat-treatment temperature. Increase in concentration of S in the glasses results in the reduction of relative fraction of Se in the PbSexS1-x quantum dots formed in glasses. More importantly, high heat-treatment temperature promotes the enrichment of Se in PbSexS1-x quantum dots, and Se fraction in PbSexS1-x quantum dots increases from 0.69 to 0.89, from 0.53 to 0.85, from 0.47 to 0.79, and from 0.45 to 0.76 for those precipitated in glasses with ZnSe/(ZnSe+ZnS) molar ratios of 0.545, 0.375, 0.286, and 0.231, respectively. Increase in ZnSe/(ZnSe+ZnS) molar ratios in glasses also leads to reduction in diameter of PbSexS1-x quantum dots formed in glasses. These alloyed PbSexS1-x quantum dots also exhibit improved photoluminescence quantum yields and enhanced resistance to thermal quenching of photoluminescence.

Label-free electrochemical detection of cancer biomarkers DNA and anti-p53 at tin oxide quantum dot-gold-DNA nanoparticle modified electrode

Lung cancer is one of the deadliest types of cancer and accounts for 8.1% of all cancer related deaths. To prevent a growing death rate, it is crucial to identify lung cancer at an early stage by single polynucleotide morphism detection. In this paper, we present a novel label-free electrochemical biosensor based on composites of tin oxide quantum dots and gold nanoparticles (SnO2-QD-Au) for the sensitive and precise detection of lung cancer DNA. The SnO2-QD and SnO2-QD-Au nanoparticles were characterized using Scanning and Transmission Electron Microscopes (SEM and TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis spectroscopy (UV), Fourier transmission infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Gold thiol covalent bonding was used for immobilising probe DNA on the surface of SnO2-QD-Au nanoparticles followed by target DNA hybridization and detected electrochemically in presence of 1 mM [Fe(CN6)]3−/4−as a redox couple probe. Under ideal circumstances, the sensor showed the lowest detection limit of 3.2 × 10−20 M with a linear range of 1 × 10−6 − 1 × 10−20 M. Additionally, the sensing method was applied to find a cancer biomarker, Anti-P53 antibody.

The interface microenvironment mediates the emission of a semiconductor nanocluster via surface-dopant-involving direct charge transfer.

The interface microenvironment of doped quantum dots (QDs) is crucial in optimizing the properties associated with the photogenerated excitons. However, the imprecision of QDs' surface structures and compositions impedes a thorough understanding of the modulation mechanism caused by the complex interface microenvironment, particularly distinguishing the contribution of surface dopants from inner ones. Herein, we investigated interface-mediated emission using a unique model of an atomically precise chalcogenide semiconductor nanocluster containing uniform near-surface Mn2+ dopants. Significantly, we discovered that Mn2+ ions can directly transfer charges with hydrogen-bonding-bound electron-rich alkylamines with matched molecular configurations and electronic structures at the interface. This work provides a new pathway, the use of atomically precise nanoclusters, for analyzing and enhancing the interface-dependent properties of various doped QDs, including chalcogenides and perovskites.

Computational investigation of graphene quantum dot and tridentate Au(iii) complex composites

We studied Au(iii) complex decay using DFT and TDDFT to understand the impact of graphene quantum dot (GQD) ligands on emission properties and phosphorescence quantum yields.

Hollow nanocages of vanadium nitride-based electrode material designed for superior charging/discharging stability supercapacitors

Vanadium nitride quantum dot composites are prepared by in situ replacement using a ZIF-8 dodecahedral structure, resulting in a material with good electrochemical performance and enhanced cycling stability.

Electrochemical and optical dual-mode detection of phenolic compounds using MnO2/GQD nanozyme

Phenolic compounds (PCs) have been widely employed in industrial activities and have also been found at threatening levels in natural environments, posing risks to human health and the environment. As a consequence, there is an increasing demand for the development of simple and sensitive detection methods of such pollutants. In this work, we report the use of manganese dioxide and graphene quantum dot (MnO2/GQD) composites as a dual-functional sensing platform for the electrochemical and colorimetric detection of catechol (CC) and dopamine (DA), two important PCs. Regarding the electrochemical detection, differential pulse voltammetry showed a linear relationship between current signal intensity and concentration of DA and CC over the linear ranges of 0.5–100 μM and 5–150 μM, with limits of detection of 0.05 µM and 0.09 µM for DA and CC, respectively. In addition, the composite was employed for the colorimetric detection of CC and DA through the oxidase mimic activity of the MnO2/GQD in the presence of 3,5,3,5-tetramethylbenzidine (TMB). Analysis in real samples showed that the MnO2/GQD composite can be used for the sensitive detection of CC and DA in river samples. The high surface area and improved electrochemical properties of the MnO2/GQD were demonstrated to be beneficial for dual sensing applications of phenolic compounds.

Platinum nanoparticle-graphene quantum dot nanocage as a promising Schottky heterojunction electrocatalyst for electrochemical detection of vanillin in baby milk powder

Facile synthesis of platinum nanocrystal and its improvement in catalytic activity still face great challenges. The paper reports one strategy for synthesis of platinum nanoparticle-serine-functionalized and boron-doped graphene quantum dot composite (Pt-Ser-B-GQD). The Ser-B-GQD was prepared by pyrolysis of serine, boric acid and citric acid at 180 °C for 3 h and then reacted with chloroplatinic acid to form platiunm nanocrystal. The resultant Pt-Ser-B-GQD offers a nanocage-like structure composing of tiny graphene sheets connecting many ultrasmall platinum nanocrystals with an average particle size of 8.2 ± 0.32 nm. The combination of Pt nanocrystal with Ser-B-GQD results in the formation of Schottky heterojunction at the interface. The unique structure achieves to an improved catalytic activity. Pt-Ser-B-GQD was further used as Schottky heterojunction electrocatalyst for the construction of electrochemical sensor for the detection of vanillin. Because of excellent electrochemical properties, the sensor based on Pt-Ser-B-GQD exhibits a high sensitivity for electrochemical detection of vanillin. Differential pulse voltammetric peak current will increase linearly with increasing vanillin concentration in the range of 1 × 10−9-1 × 10−4 M with the detection limit of 2.8 × 10−10 Μ (S/N = 3). The proposed analytical method provides advantage of sensitivity, selectivity and reproducibility and was successfully applied in the detection of vanillin in baby milk powder.

Shuttle-inhibited 3D sandwich MXene/SnO2QDs sulfur host for high-performance lithium-sulfur batteries

Herein, sandwich-like Ti3C2Tx MXene/SnO2 quantum dots composites were synthesized as sulfur host, aiming to alleviate the shuttle effect of polysulfides present in lithium-sulfur batteries. SnO2 quantum dots (SnO2QDs) were introduced into the interlayer of MXene through a simple electrostatic self-assembly method, and the mass fraction of SnO2QDs was controlled to construct sandwich MXene/SnO2QDs. While SnO2QDs effectively alleviating the stacking tendency of MXene, Ti and Sn co-chemisorb polysulfides and the interlayer structure physically confines polysulfides. Significantly, the synergistic effect between MXene with SnO2QDs effectively alleviates the shuttle effect of polysulfides and buffers the volume expansion. Meanwhile, with the help of the catalysis of SnO2QDs, the liquid-solid reaction kinetics of lithium polysulfides converting to Li2S2/Li2S is accelerated. Electrochemical test results showed that the MXene/SnO2QDs/S cathode has a high initial discharge specific capacity (1147.6 mAh g−1 at 0.1 C, while MXene/S is only 615.4 mAh g−1), as well as excellent rate performance and cycling stability in Li-S batteries.

Statistical Analysis of Photoluminescence Decay Kinetics in Quantum Dot Ensembles: Effects of Inorganic Shell Composition and Environment.

Discerning the kinetics of photoluminescence (PL) decay of packed quantum dots (QDs) and QD-based hybrid materials is of crucial importance for achieving their promising potential. However, the interpretation of the decay kinetics of QD-based systems, which usually are not single-exponential, remains challenging. Here, we present a method for analyzing photoluminescence (PL) decay curves of fluorophores by studying their statistical moments. A certain combination of such moments, named as the n-th order moments' ratio, R n , is studied for several theoretical decay curves and experimental PL kinetics of CdSe quantum dots (QDs) acquired by time-correlated single photon counting (TCSPC). For the latter, three different case studies using the R n ratio analysis are presented, namely, (i) the effect of the inorganic shell composition and thickness of the core-shell QDs, (ii) QD systems with Förster resonance energy transfer (FRET) decay channels, and (iii) system of QDs near a layer of plasmonic nanoparticles. The proposed method is shown to be efficient for the detection of slight changes in the PL kinetics, being time-efficient and requiring low computing power for performing the analysis. It can also be a powerful tool to identify the most appropriate physically meaningful theoretical decay function, which best describes the systems under study.

LaCoxFe1‐xO3‐δ‐QDs/CNTs Composite as an Efficient Electrocatalyst for Oxygen Evolution Reaction

AbstractOxygen evolution reaction (OER) is a critical half‐reaction in the process of electrochemical water splitting, which has been researched a lot in last few years. Nevertheless, OER has high overpotential and sluggish reaction kinetics. Therefore, preparing non‐noble metal catalysts with high surface activity to decrease the activation energy of the reaction is the key to solving these problems. Herein, we report a facile development of an electrocatalyst for OER. The composites of perovskite oxide quantum dots with abundant oxygen vacancies attached to oxidized carbon nanotubes (LaCoxFe1‐xO3‐δ‐QDs/CNTs) were manufactured by sodium borohydride reduction method. The results evidence that the optimized LaCo0.5Fe0.5O2.603‐QDs/CNTs sample exhibits optimal electrocatalytic performance (with an overpotential of 210 mV at 10 mA/cm2) and prominent stability towards OER. It should attribute to quantum dots structure, suitable Co/Fe ratio, fitting calcination temperature, appropriate oxygen vacancy concentration. This work will offer novel inspiration for the research and evolution of non‐precious metal catalysts with improved performance.

Facet-dependent photocatalytic and photoelectric properties of CQDs/TiO2 composites under visible irradiation

The construction of photocatalytic heterostructures and the study of carrier kinetics are significant for developing novel functional materials and understanding catalytic mechanisms. Here, we synthesized the heterostructural composites of carbon quantum dots (CQDs) and TiO2 nanoparticles with (101) or (001) as the main exposed facets by hydrothermal method, named CQDs/TiO2(101) and CQDs/TiO2(001). The facet-dependent sensitization and photocatalysis properties of these composites have been investigated using steady-state and time-resolved spectroscopy. The results indicate that the electron transfer process between CQDs and TiO2 is associated with the exposed facet of TiO2. The electron transfer rate from CQDs to TiO2(101) is two orders of magnitude larger than that to TiO2(001). The CQDs/TiO2(101) composite also demonstrates three times higher photoelectric conversion than CQDs/TiO2(001). The facet-dependent catalytic performances of CQDs/TiO2 composites have been evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The rate constant of CQDs/TiO2(101) for the degradation of intermediates (Rh-110) shows 1.82 times higher than that of CQDs/TiO2(001). These findings indicate the effective loading of CQDs on TiO2(101) nanoparticles can be expected to efficiently improve the photoelectric and photocatalytic properties of TiO2-based heterostructure under visible irradiation, and are significant for deep understanding the facet-dependent photocatalytic mechanism and property.

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.