ZnO Quantum Dots Research Articles

Enhanced Luminance of CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO-Oleic Acid/ZnO Quantum Dots Double Electron Transport Layer.

The widely used ZnO quantum dots (QDs) as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) have one drawback. That the balancing of electrons and holes has not been effectively exploited due to the low hole blocking potential difference between the valence band (VB) (6.38 eV) of ZnO ETL and (6.3 eV) of CdSe/ZnS QDs. In this study, ZnO QDs chemically reacted with capping ligands of oleic acid (OA) to decrease the work function of 3.15 eV for ZnO QDs to 2.72~3.08 eV for the ZnO-OA QDs due to the charge transfer from ZnO to OA ligands and improve the efficiency for hole blocking as the VB was increased up to 7.22~7.23 eV. Compared to the QLEDs with a single ZnO QDs ETL, the ZnO-OA/ZnO QDs double ETLs optimize the energy level alignment between ZnO QDs and CdSe/ZnS QDs but also make the surface roughness of ZnO QDs smoother. The optimized glass/ITO/PEDOT:PSS/PVK//CdSe/ZnS//ZnO-OA/ZnO/Ag QLEDs enhances the maximum luminance by 5~9% and current efficiency by 16~35% over the QLEDs with a single ZnO QDs ETL, which can be explained in terms of trap-charge limited current (TCLC) and the Fowler-Nordheim (F-N) tunneling conduction mechanism.

Synthesis and evaluation of composite TiO2@ZnO quantum dots on hybrid nanostructure perovskite solar cell

This research is an interdisciplinary study aimed at helping the environment and producing clean energy. Therefore, one of the goals of this research towards the field of nanotechnology is the application of nanotechnology in the preparation of solar cells and the provision of optimal and efficient cells. Perovskite solar cells are of particular importance because of the high efficiencies that they have achieved in recent years. The use of quantum dots has also played an important role in the efficiency of these cells and their efficiency. The TiO2@ZnO nanocomposite was selected and synthesized for this study. The application of this nanocomposite with different ratios of TiO2 and ZnO quantum dots was investigated and their efficiency was determined. Although the efficiency of the fabricated cell was reported to be about 5% in a solar cell made of TiO2@ZnO composite, the efficiency can be increased by optimizing conditions such as the optimal location for these cells or by compositing with other materials.

Biomediated synthesis of ZnO quantum dots decorated attapulgite nanocomposites for improved antibacterial properties

Abstract Attapulgite (APT) is a natural one-dimensional clay mineral with good biocompatibility and has emerged as a promising nanomaterial for the construction of performance-enhanced nanocomposites. In this study, we developed a ZnO quantum dots-incorporated APT antibacterial nanocomposite by the Aloe vera extract-mediated green route. With the combined assistance of binding interactions of ZnO nuclei with APT and capping effect of active compounds in Aloe vera extract, the quantum-sized ZnO nanoparticles with hexagonal Wurtzite structure and sizes of <5 nm were uniformly decorated on the APT surface, resulting in a high-active antibacterial nanocomposite. The obtained ZnO/APT nanocomposites displayed favorable antibacterial activities, and the minimum inhibitory concentrations of the nanocomposite with ZnO loading of 20% against E. coli and S. aureus were 2.5 and 0.5 mg·mL−1, respectively. This antibacterial performance was far better than that of APT and could almost be comparable to that of pure ZnO. For the green process, the phenolic compounds, proteins, and amino acids in Aloe vera extract were involved in the reduction and capping of ZnO, which contributed to a facile green strategy for preparation of the ZnO-modified APT nanocomposites. The present work provides new insight into the potential applications of APT in the antibacterial fields.

A Flexible and Wearable Nylon Fiber Sensor Modified by Reduced Graphene Oxide and ZnO Quantum Dots for Wide-Range NO2 Gas Detection at Room Temperature.

Reduced graphene oxide (rGO) fiber as a carbon-based fiber sensor has aroused widespread interest in the field of gas sensing. However, the low response value and poor flexibility of the rGO fiber sensor severely limit its application in the field of flexible wearable electronics. In this paper, a flexible and wearable nylon fiber sensor modified by rGO and ZnO quantum dots (QDs) is proposed for wide-range NO2 gas detection at room temperature. The response value of the nylon fiber sensor to 100 ppm NO2 gas is as high as 0.4958, and the response time and recovery time are 216.2 s and 667.9 s, respectively. The relationship between the sensor’s response value and the NO2 concentration value is linear in the range of 20–100 ppm, and the fitting coefficient is 0.998. In addition, the test results show that the sensor also has good repeatability, flexibility, and selectivity. Moreover, an early warning module was also designed and is proposed in this paper to realize the over-limit monitoring of NO2 gas, and the flexible sensor was embedded in a mask, demonstrating its great application potential and value in the field of wearable electronics.

Continuous flow scale-up of biofunctionalized defective ZnO quantum dots: A safer inorganic ingredient for skin UV protection

The versatility of ZnO quantum dots (QDs) exhibiting size-tunable visible photoluminescence has propelled them to the forefront of leading-edge innovations in healthcare. At the nano-bio interface, enhancing the singly-ionized oxygen vacancy defects (VO•) through holistic, sustainable synthesis protocols driven by the synergistic influence of QDs’ nucleation-growth kinetics has implications on their bioactivity, physiochemical, and optical performance. Recently, robust continuous flow platforms have transcended the conventional batch reactors by alleviating the concerns of “hot-spot” formation due to inhomogeneous heat distribution, acute energy consumption, poor quality, and yield. However, complexities exist in translating batch chemistries into flow processes. Here, a unique, rationally designed continuous flow synthesis of luminescent defect-engineered ZnO QDs (E-QDs) via helical-reactor assembly that can adequately synthesize on a large scale is reported. The crux of this lies in the amalgamation of “green chemistry” and flow synthesis, which results in Lamer-mechanism mediated monodispersed E-QDs demonstrating high photoluminescence quantum yield (PLQY) of 89% under an accurately regulated synthesis environment. Process intensification corroborated that the bio-stable E-QDs manifested admirable photostability, broad-spectrum UV-shielding (400–250 nm), colloidal stability, in vitro biocompatibility against L929 and HaCaT cells, and antioxidant activity. These attributes were better compared to the commercial ZnO nanoparticles (ZnOC-NPs) used for skin UV protection. Delving deeper, the main drivers for the high density of intrinsic VO• formation (Iv/Io∼42.5) were revealed to be the reactor's hydrodynamic performance and the improvised heating rate (2.5°C/sec). Hence, these E-QDs have potential as a new, safe, and economical multifunctional active ingredient for skin UV protection and antioxidants for treating ROS-mediated disorders. Statement of significanceUV filters exhibiting questionable UV-attenuation efficacy and phototoxicity are significant impediments to the healthcare industry emphasizing skin cancer prevention. Although least explored, VO•-governed aberrant photoactive, biological, and surface-reactive qualities of engineered ZnO QDs (E-QDs) have created ample room to investigate these hallmarks for skin UV protection. However, the bottlenecks in stereotypical ZnO QDs production confined by inefficient process control are annihilated by continuous flow strategies. Herein, the high-throughput continuous flow helical reactor assembly was designed and fabricated to successfully showcase optimized transport properties, reproducibility, yield, and quality E-QDs. Anticipating a skyrocketing demand for E-QDs as bioactive-sunscreen components, the comprehensive investigation has demonstrated unprecedented biofunctionality and ROS-scavenging behaviour, even upon UVR exposure, contrary to the traditional nanoparticulate ZnO UV filters.

Effect of Antioxidant on ROS Mediated Antifungal Action of ZnO Quantum Dots in Candida albicans

Nanomaterials are increasingly used as new paradigm for treating infectious diseases, wherein redox perturbation using quantum dots (QDs) show tremendous potential in eliminating various multi-drug resistant microbial pathogens. Herein, spherical, monodispersed ZnO QDs of ~5-6 nm size was synthesized. These ZnO QDs significantly inhibited growth of C. albicans cells. The antifungal action of ZnO QDs against C. albicans involved oxidative stress, mediated via augmentation of endogenous reactive oxygen species (ROS). Further, endogenous ROS production by ZnO QDs and their effect on fungal cell killing was investigated in the presence of antioxidant, ascorbic acid. Results showed that antioxidant failed to offer complete protection against ZnO QDs mediated oxidative stress. It is speculated that intracellular ROS alone is not the only mechanism responsible for ZnO QDs mediated microbial toxicity and other mechanisms probably act either in coordinated or parallel manner to induce cell killing, which merit further investigations for medical adoption of ZnO QDs in biomedicine.

The optical properties of Mg-doped ZnO quantum dots

This research found that ZnO doping with Mg2+ can control its fluorescent intensity, energy gap and fluorescent wavelength. The non-high temperature manufacturing process (50 °C) can also avoid the reduction of fluorescent efficiency to a certain extent. A simple sol-gel method is used to prepare a transparent Zn1-XMgXO quantum dot solution, and the product is precipitated by a direct precipitation method. After purification, the Zn1-XMgXO quantum dot powder are obtained, which can be re-dissolved into the solution. The results show that the doping of Mg2+ in ZnO led to the increase of fluorescent intensity and energy gap. Also, with the increase of doping ratios, the PL intensity increases and the emission bands are slightly blue-shifted.

Enhanced photocatalytic activity of hierarchical C/ZnO nanocomposite derived from solvothermally restructured Zn-BTC microspheres

Single step solvothermal synthesis of hierarchical and hollow microspheres (HHMs) assembly of 1D zinc-trimesic acid (Zn-BTC) MOF nanospikes, without using any external stabilizer as shape modifier is reported here. Detailed electron microscopy imaging revealed that the Zn-BTC HHMs form through a self-templating mechanism due to the typical reaction conditions. The Zn-BTC HHMs were annealed to form ZnO/C hierarchical nanocomposite microspheres (HNMs). HNMs were found to be quite active for the photocatalytic water remediation through the photo-oxidation of dyes as well as photo-reduction of Cr (VI). Thorough characterization revealed that the HNMs exhibited three-dimensional (3D) hierarchical morphology with comparatively higher mesoporosity, extended visible light absorption, and better separation of photogenerated charges (e-/h+), resulting in enhanced photocatalytic performance (0.40 and 1.89 mg·g−1·min−1 removal efficiency for MV and Cr (VI) respectively). The enhanced photocatalytic activities of the HNMs were found to be due to the synergism between carbon matrix and the well-dispersed ZnO quantum dots.

Facile synthesis of MoS[formula omitted]/ZnO quantum dots for enhanced visible-light photocatalytic performance and antibacterial applications

MoS 2/ZnO quantum dots (QDs) were synthesized in aqueous media via a facile hydrothermal route. QDs have attracted great interest for the effective photocatalytic removal of environmental pollutants due to their outstanding visible-light harvesting and electron mobility properties. The capability of the visible-light activity system of these QDs make them a highly suitable candidate for the degradation of organic compounds and for antibacterial applications. The photocatalytic activity was improved for the QDs, with an antibiotic removal of 96.5%, compared to bare MoS 2 (38.4%) and ZnO (25.6%). The highly practical antibacterial ability could be realized by the heterojunction QDs within 5 min of visible light activity, being 99.9% for Escherichia coli (E. coli). The large surface area with sufficient reactive oxygen species decontaminated large amounts of E. coli. The results proved that the QDs can be used to degrade organic pollutants and remove harmful bacteria in water environments.

Surface modification of ZnO quantum dots coated polylactic acid knitted fabric for photocatalytic application

AbstractIn this work, ZnO quantum dots (ZnOQD) were synthesized by Sol–gel synthesis and impregnated on polylactic acid (PLA) knitted fabric through self‐assembly of different cycles from layer‐by‐layer (LBL) using cationic agent Poly(diallydimethylammonium chloride) (PDDA). Then, morphological, chemical and photocatalytic properties were studied. The results demonstrate that the synthesis provided 8 nm Wurtzite‐type ZnO nanoparticles. In addition, X‐ray photoelectron spectroscopy (XPS) spectra, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) proved the inclusion of ZnOQD on the surface of PLA matrix, which allowed the evaluation of its photocatalytic properties, therefore, coated PLA with five cycles of ZnOQD obtained the best result for degrading 85% of the dye Rhodamine B (RhB) in 360 min under UV radiation, in addition to its reusability for another five cycles of photocatalytic activity.

Distinctive roles of graphene oxide, ZnO quantum dots, and their nanohybrids in anti-corrosion and anti-fouling performance of waterborne epoxy coatings

In this research, the amino-silane functionalized ZnO quantum dots (F-ZnO QDs), graphene oxide (F-GO), and their nanohybrids (F-GO@ZnO QDs) are used as effective nanofillers to improve the anti-corrosion and anti-fouling properties of waterborne epoxy coatings. The synthesized nanomaterials before and after silane functionalization are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Then, the nanocomposite waterborne epoxy coatings loaded with 0.1 wt% F-ZnO QDs, F-GO, and F-GO@ZnO QDs are prepared through solution mixing method. The effects of different nanofillers on the surface roughness, water contact angle, pull-off adhesion strength, fracture surface, and corrosion resistance of the nanocomposite coatings are considered. The results reveal that the uniformly dispersed F-GO@ZnO QDs in the fracture surface of the coating could provide the highest barrier and corrosion resistance on the steel substrates. Meanwhile, the nanocomposite coatings have higher water contact angle and higher adhesion strength to the substrates. The anti-bacterial and anti-fouling properties of the nanocomposite coatings have also been confirmed. The multifunctional performance of the epoxy/F-GO@ZnO QDs is assigned to the synergy effect between the GO, ZnO QDs, and amino-silane; exhibiting the importance of the nanohybrids to combine the advantages of different nanomaterials in one coating system.

Photoluminescence and Electron Paramagnetic Resonance Spectroscopy for Revealing Visible Emission of ZnO Quantum Dots

AbstractBoth PL and EPR are simultaneously adopted to systematically elucidate the defect centers of green luminescence (GL) as well as the EPR peak g = 1.96 of ZnO and the relationship between them. The PL of ZnO QDs reveals that GL of 2.21–2.31 eV disappears at excitation wavelengths > 400 nm. This is related to the electronic transition from conduction band (CB), or shallow donor defect centers, to deep defects of VZn‐H complexes at ≈0.9 eV above the valence band (VB). The EPR peak g = 1.96 emerged only when irradiated with light shorter than 400 nm, which is explicitly correlated with the electrons trapped in the CB or the shallow donors participating in the GL. A spin‐spin relaxation time (T2) estimated from the peak‐to‐peak line width ΔHpp in the EPR signal is ≈17.5–52.5 ns, which is two orders of magnitude longer than known values for bulk or thin‐film ZnO.

Interplay between multipole expansion of exchange interaction and Coulomb correlation of exciton in colloidal II–VI quantum dots

We study the effect of Coulomb correlation on the emission properties of the ground state exciton in zincblende CdSe/ZnS core–shell and in wurtzite ZnO quantum dots (QDs). We validate our theory model by comparing results of computed exciton energies of CdSe/ZnS QDs to photoluminescence and scanning near-field optical microscopy measurements. We use that to estimate the diameter of the QDs using a simple model based on infinitely deep quantum well and compare the results with the statistics of the atomic force microscopy scans of CdSe/ZnS dots, obtaining excellent agreement. Thereafter, we compute the energy fine structure of exciton, finding striking difference between properties of zincblende CdSe/ZnS and wurtzite ZnO dots. While in the former the fine structure is dominated by the dipole terms of the multipole expansion of the exchange interaction, in the latter system that is mostly influenced by Coulomb correlation. Furthermore, the correlation sizeably influences also the exciton binding energy and emission radiative rate in ZnO dots.

ZnO QDs and three-dimensional ordered macroporous structure synergistically enhance the photocatalytic degradation and hydrogen evolution performance of WO3/TiO2 composites

Using polystyrene microspheres as the template, a sol–gel method combined with a vacuum impregnation method was used to successfully prepare ZnO quantum dots (QDs) modified three-dimensional ordered microporous (3DOM) WO3/TiO2 composite material (ZnO QDs 3DOM WO3/TiO2). The material has a good crystal structure and a macroporous structure with open and transparent periodic arrangement. The introduction of ZnO QDs in the composite not only increases the specific surface area of the material, but also improves separation and migration efficiencies of photogenerated carriers. Moreover, the light-induced recombination of e−–h+ pairs is effectively inhibited with the help of ZnO QDs. The photocatalytic results show that ZnO QDs 3DOM WO3/TiO2 composite has enhanced photocatalytic activity in multi-mode photocatalytic experiments, and the hydrogen evolution capacity of the 2.0 ZnO QDs 3DOM WO3/TiO2 composite is ca. 3.4 times that of pure TiO2. The cycle results reflect that the ZnO QDs 3DOM WO3/TiO2 composite material has good cycle stability. After five cycles of experiments, the composite material still maintains a similar hydrogen production activity. Finally, the possible photocatalytic reaction mechanism of ZnO QDs 3DOM WO3/TiO2 was proposed.

UV-enhanced NO2 sensor using ZnO quantum dots sensitized SnO2 porous nanowires

ZnO quantum dots sensitized SnO2 porous nanowires were fabricated and designed for UV excitation gas sensor. The ZnO/SnO2 composite (SZQ1%) with the molar proportion of 1:100 exhibits excellent sensing properties to NO2 gas under UV irradiation at 40 °C. The limits of detection of the SZQ1% sensor is 100 ppb. The humidity stability of SZQ1% was also measured and discussed by DC reversed circuit and complex impedance curves. The gas sensing mechanism is well discussed and illustrated to the ZnO quantum dots sensitized and the increased photo-generated carriers under UV irradiation.

Enhanced defect emission of TiO2-doped transparent glass-ceramics embedding ZnO quantum dots with optimized heat-treatment schedule

This work mainly concentrated on the structural and optical properties of TiO 2 -doped transparent glass-ceramics embedding ZnO quantum dots (QDs). The results show that the concentration of non-bridging oxygen and related defects in the glasses increases and thermal parameters decreases by the introduction of TiO 2 . The surface defect concentration of ZnO QDs is greatly improved and the size of ZnO QDs is reduced by heat treatment below the T g and the introduction of TiO 2 . The green emission of glasses is mainly derived from oxygen vacancy defects and the yellow emission of glass-ceramics primarily originated from oxygen interstitial defects which show a tendency of enhancing first and then reducing with the increase of TiO 2 content. Among them, the optimal content for the strongest emission intensity of TiO 2 -doped glasses and glass-ceramics was determined to be 1.0 mol%, and the relative exceeds 10 times and 5.4 times that of TiO 2 -free glasses and glass-ceramics, respectively. The average size of ZnO QDs (∼2.1 nm) remarkably close to its exciton Bohr radius is successfully prepared by the optimal heat treatment condition (630 °C/8 h, below the T g ). The results show that these glass-ceramics embedding ZnO QDs are good yellow emission materials and have application prospects in WLEDs.

Preparation of pro-angiogenic, antibacterial and EGCG-modified ZnO quantum dots for treating bacterial infected wound of diabetic rats

The complex wound environment and abnormalities in self-metabolism of diabetic skin defects lead to impaired angiogenesis, which can easily lead to bacterial infection and increased inflammation. Therefore, there is an urgent need for multifunctional composites with antimicrobial and pro-angiogenic properties to improve the current therapeutic outcomes of diabetic wounds. In this study, we described an EGCG-modified zinc oxide quantum dots (ZnO QDs) hydrogel (ZnO-EGCG@H) for the treatment of delayed diabetic wounds. In vitro antimicrobial assays showed that ZnO-EGCG@H effectively cleared 95.6% of MRSA and 97% of AmprE. coli with good bactericidal activity. Western blotting assay analysis showed that ZnO-EGCG@H downregulated trauma inflammatory factors (TNF-α, IL-6) by 46.9% and 57%, respectively, while upregulating 1.7-fold VEGF and 2-fold EGF, accelerating wound healing by reducing inflammatory response and promoting proliferation of vascular endothelial cells and skin epidermal cells. After 15 days of ZnO-EGCG@H treatment, the rate of skin lesion closure in rats was 96.3%, which was much better than that of 65.4% in the control group. Safety experiments showed that ZnO-EGCG@H was reassuringly biocompatible and harmless to vital organs. The obtained results suggested that ZnO-EGCG@H had the potential to be a safe and effective treatment method with a promising future as a diabetic wound treatment material.

Excitons in ZnO Quantum Dots: The Role of Dielectric Confinement

Quantum dots (QDs) grown by chemical synthesis methods are relatively unstable and present difficulties in dispersion and preservation. The most common way of surpassing the stability issues is to embed (and passivate) the QDs in a matrix material. However, some fundamental questions concerning the influence of the dielectric confinement caused by the matrix environment on the exciton energy and exciton binding energy of the QDs have not yet been properly addressed. Here we explore the exciton fine structure of wurtzite ZnO QDs by means of plane-wave million-atom atomistic pseudopotential calculations and a configuration interaction approach taking into account the dielectric confinement from the surrounding material. Our results indicate that the exciton energy increases and the exciton binding energy decreases as the dielectric constant of the surrounding material increases. The behavior of the exciton binding energy is caused by the presence of self-polarization potential induced by the dielectric mismatch in the surface of the QD. This mainly alters the localization of the hole charge density and thus reduces the electron–hole overlap and inevitably the exciton binding energy.

Dengue NS1 antigen detection using photoluminescence of solution phase biotylinated anti-NS1 antibody conjugated ZnO quantum dots

Biotinylated anti-NS1 antibody of dengue was conjugated on the streptavidin functionalized ZnO quantum dots (QD) by EDC-NHS chemistry. Photoluminescence spectra of the ZnO QDs showed band edge peak (∼366 nm, peak 1) and a defect related peak (∼470 nm, peak 2). The defect related peak was present only for Zn/Li ratio below 0.5. The change in the luminescence intensity of peak 1 and peak 2 was studied with negative and positive serum of suspected dengue cases. A 14% decrease of the average intensity of peak 1 and peak 2 was observed per 20 μl addition of negative serum. In the case of dengue positive serum, the average intensity was increased by 7% per 20 μl of serum sample. This suggests that the prepared solution phase ZnO QDs could be applied in the detection of dengue antigen in suspected patients’ serum.

MoS2 Nanoflake and ZnO Quantum Dot Blended Active Layers on AuPd Nanoparticles for UV Photodetectors

MoS₂ Nanoflake and ZnO Quantum Dot Blended Active Layers on AuPd Nanoparticles for UV Photodetectors