Synthesis Of ZnS Quantum Dots Research Articles

Zinc Sulphide Quantum Dots’ Applications in Antibacterial as well as Estimation of E.Coli Concentration by Fabricating Mem-Mode Devices

This paper reports the synthesis of ZnS Quantum Dots (QDs) embedded in PVA by aqueous precipitation method and its application in antibacterial as well as to find or estimation of Escherichia coli (E.coli) concentration by using ZnS/PVA QD based mem-mode nanodevices. The as-synthesized ZnS/PVA samples are characterized by UV-Vis spectroscopy (UV), Photo luminescence (PL), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Antibacterial property of ZnS/PVA QDs against gram positive (S.aureus) as well as gram negative (E.coli) are tested. The antibacterial property is found to be more in S.aureus in comparision to E.coli. Mem-behaviour of the as-fabricated devices is observed through electrical characterization. COMSOL MP Software is used for simulating I-V characteristics. The voltage gap is found to be a promising parameter for estimating E.coli concentration with ZnS/PVA QDs as active material and an electrical circuit is presented

Manganese-Doped ZnS QDs: an Investigation into the Optimal Amount of Doping

In the present study, undoped and Mn-doped ZnS, Zn1 – xMnxS (x = 0, 0.02, 0.06, 0.10) quantum dots (QDs) were successfully synthesized using the simple co-precipitation method. The synthesized samples were thoroughly studied using X-ray diffraction (XRD), UV-visible absorption, high-resolution transmission electron microscopy (HRTEM) with selected area of the electron diffraction, scanning electron microscope with energy dispersive X-ray spectra, photoluminescence emission (PLE), and Fourier transform infrared spectroscopy. The XRD pattern confirmed the cubic zinc-blende phase at low doping concentration; however, at higher Mn-doping concentration hetaerolite phase formation was observed. The calculated particle size using Debye–Scherrer relation was found between 1.90–2.35 nm, which was also confirmed by HRTEM analysis. The blue shift in the absorption peak of all the prepared ZnS QDs as compared to bulk ZnS was indicative of the formation of nanoparticles and the calculated band gap was in the range of 3.94–4.11 eV. The PLE spectroscopy of the synthesized QDs was performed at the excitation wavelength of 280 nm and corresponding emission spectroscopy confirmed the surface defects in synthesized ZnS QDs.

Novel ZnSQDs-SnO2/g-C3N4 nanocomposite with enhanced photocatalytic performance for the degradation of different organic pollutants in aqueous suspension under visible light

We report the synthesis of ZnS quantum dots (ZnSQDs)–SnO2/graphitic C3N4 (g-C3N4) ternary nanocomposites with different mass ratios via solid-state calcination of a mixture of 10 wt% ZnSQDs–SnO2 and g-C3N4. The proposed solid-state procedure does not require any solvent and offers a general route to synthesize composite materials on a large scale. The synthesized products were carefully characterized by traditional analytical techniques such as Fourier transform IR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the nanocomposites was assessed by our studying the degradation of two different chromophoric dyes (rhodamine B and methylene blue) and a colorless pollutant (paracetamol) in aqueous suspension under visible light in the presence of atmospheric oxygen. Among the series of synthesized samples, 7 wt% ZnSQDs–SnO2/g-C3N4 showed significantly improved photocatalytic performance in comparison with the other photocatalysts. In addition, adsorption of dyes onto the surface of the synthesized nanocomposite was studied with different catalyst amounts and time intervals. Moreover, the synthesized material also mineralizes paracetamol, which was measured in terms of depletion of total organic carbon content as a function of time. The remarkable increased photocatalytic efficiency of the synthesized materials could be related to the synergistic interaction between ZnSQDs, SnO2, and g-C3N4 leading to photoseparated electron and hole pairs. The main reactive species involved in the degradation process were determined by our performing quenching experiments with electron donors and acceptors, and a possible mechanistic pathway for the degradation process is proposed.

Biologically synthesized ZnS quantum dots as fluorescent probes for lead (II) sensing.

This manuscript presents a robust strategy for selective Pb(II) sensing based on a fluorescence turn-off mechanism using ZnS quantum dots (QDs) biosynthesized using Aspergillus sp. The biogenic nanoprobe displayed marked sensing efficiency in the presence of Pb ions over concentration ranges from 5 to 100 μM with limits of detection of around 2.45 μM. Performance optimization studies revealed that the maximum fluorescence quenching efficiency was obtained in the presence of [ZnS NPs] at 4 mg/ml, and alkaline pH of 10 recorded under stable ambient temperature for approximately 5 min for the quenching process. Advanced morphological analysis indicated that the bio-sensing mechanism was essentially a surface-based phenomenon in which the Pb ions were in very close proximity to the QDs and formed stable ground-state Pb-ZnS complexes, resulting in a quenched fluorescence of the QDs. Simultaneously, a larger fraction of Pb ions interacted via collisions with the excited ZnS QDs and resulted in an effective energy transfer from the excited QDs to the Pb ions, therefore resulting in an obvious decrease in QD fluorescence. These insights were well supported by theoretical analysis using Stern-Volmer plots and sphere-of-action models.

Photocatalytic and catalytic degradation of organic dye by uncapped and capped ZnS quantum dots

ZnS quantum dots were prepared with different concentrations of 2-mercaptoethanol as a capping agent by simple and fast co-precipitation method. The synthesized nanopowders were characterized using various analytical chemistry as well as image visualizing techniques to elucidate the changes in structure and shape of quantum dots. The lowest average estimated crystallite size of ZnS quantum dot was 4.2 nm that showed relevancy to 2-Mercaptoethanol amount. X-ray diffraction (XRD) confirmed purity of nanosized ZnS with cubic and rhombohedral crystalline structures. Upon capping increased absorption around 300 nm was recorded by UV–vis spectroscopy that suggests ZnS interaction with 2-mercaptoethanol. The surface morphology of capped ZnS showed nanorod shape with agglomeration of particles confirmed by field emission electron microscopy (FESEM). The presence of functional groups and strong chemical bonding at the interface of quantum dots was confirmed by fourier transform infrared spectroscopy (FTIR). However, thermal analysis revealed no decomposition till 200 °C evidenced by DSC-TGA that suggests its high temperature stability. Moreover, uncapped ZnS quantum dot showed extensive methylene blue (MB) dye degradation with maximum absorption peak (λmax) at 664 nm that suggests visible light activity. The synthesized ZnS quantum dots has strong potential to be used as effective dye degradation agents in textile, tanneries and leather industries.

Bio-inspired ZnS quantum dots as efficient photo catalysts for the degradation of methylene blue in aqueous phase

ZnS quantum dots are semiconductor nanoparticles characterized by superior optoelectronic properties. The amenability of these nanoparticles in initiating efficient photo-redox reactions enable their use as photocatalysts for environmental remediation. In the present study, ZnS quantum dots were biosynthesized from Zn tolerant Penicillium sp. under ambient reaction conditions. The biogenic ZnS quantum dots were characterized using TEM, SEM, XRD, FTIR and UV–Vis absorption studies that revealed the formation of spherical particles of average diameter 11.08 nm with a zinc blend crystal structure and the optical properties were in par with chemically synthesized ZnS. The biogenic ZnS were then used for the photodegradation of methylene blue (MB) dye. It was found that the green synthesized ZnS quantum dots exhibited good photocatalytic activity with a half-life of 4 h. Further, the dye degradation efficiency was enhanced as the ZnS nanocatalyst/dye ratio increased and reached equilibrium within 6 h. The present study reports an inexpensive and scalable method to fabricate ZnS nano hybrids with practical applicability in the remediation of pollutants in textile, paper and dyeing industry.

ZnS Quantum Dots Based Voltage-Sensing Light-Emitting Device

This article reports the synthesis of ZnS quantum dots (QDs) embedded in polyvinylpyrrolidone matrix via a simple chemical technique and its novel application as a nano-light-emitting device. The synthesized specimen has been characterized by using UV/Vis spectroscopy, X-ray diffraction study, atomic force microscopy, and high-resolution transmission electron microscopy. These studies indicate the sizes of QDs to be within 8 nm. The prepared QD samples have been examined in a fabricated ZnO/QD-based nano-light-emitting device by exploring the variation of electroluminescence (EL) (light emission phenomenon) with supply voltage at room temperature. The almost linear variation of EL intensity with voltage is obtained for a specific range of voltage, which makes ZnS nanoparticles suitable for light-emitting devices.

Microwave-assisted synthesis, characterization and photoluminescence interaction studies of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS quantum dots

Here, we report the simple and low-cost synthesis of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS quantum dots (QDs) by a microwave-assisted method. We study the compositional, structural, and optical properties by XRD, SEM-EDX, TEM, FTIR, UV–vis and PL spectroscopy. The quantum confinement effect of the products was confirmed by means of spectroscopic measurements. XRD and TEM show that the synthesized ZnS quantum dots have cubic structures with a diameter of about less than 10 nm. The fluorescence interaction studies suggest that L-Cysteine was effectively quenched the fluorescence intensity of ZnS QDs and form stable Cys-ZnS complex using fluorescence spectroscopy.

Synthesis of ZnS Quantum Dots for QDs-LED hybrid device with different cathode materials

In this study, a chemical method was used to synthesise ZnS quantum dots (QDs) with low cost and simple process. A fixed molar ratio 1:1 of zinc chloride and sodium sulfide has been used for preparing two samples A and B. The X-ray diffraction (XRD) analyses prove the cubic phase of ZnS with an average particles size of (3-29) nm According to UV-Vis. spectra analyses, a large blue shift over 32 and 48 nm was observed, while the band gaps energy (Eg) were 3.55 and 3.8 eV for A and B samples respectively. The emission spectrum of quantum dots carries more evidence on the presence of shallow at 373 and 367 nm originated from the interstitial Zn and traps at 428 and 439 nm, whose origin ascribed to defects zinc vacancy (VZn), while 541 nm was due to sulfide vacancy (VS). QDs-LED hybrid devices were fabricated using ITO/PEDOT: PSS/Poly-TPD/ZnS-QDs/layers with two types of cathode materials LiF and Al. Using LiF as cathode in addition to the Al gives good enhancement to light generation in compares with that of Al cathode only. The spectra 350-700 nm appeared a wide emission band according to the EL measurement.

Au/ZnS and Ag/ZnS nanoheterostructures as regenerated nanophotocatalysts for photocatalytic degradation of organic dyes

Although several groups have reported the synthesis of ZnS quantum dots, only a few have developed methods to prepare potentially nontoxic, noble metal loaded ZnS QDs. In this study, we devised a gram scale, environmentally benign, room temperature, aqueous solution based method for the synthesis of renewable and eco-friendly, well dispersed ZnS quantum dots along with noble metal loaded ZnS QDs (loading amount 4 wt%). The properties of the nanophotocatalysts were determined by using XRD, XPS, TEM and SEM techniques. The ZnS QDs were found to have small sizes of ca. 4.5 nm and to display quantum effects in terms of blue shifts in their absorption maxima associated with an optical band gap, Eg, of 4.63 eV. The photocatalytic activities of ZnS QDs, Au/ZnS and Ag/ZnS were assessed using photodegradation of methylene blue. The results demonstrate that a significant increase in the photocatalytic efficiency takes place upon the loading of Ag and Au nanoparticles on ZnS QDs. An in-depth investigation was carried out to uncover information about the effects of noble metals on band gap energies and surface charges of the QDs. Finally, a new surface reactivation procedure was developed for the reactivation of nanophotocatalysts. Consequently, the newly synthesized photocatalysts are renewable, a property that should make their use in practical applications cost effective.

Synthesis of ZnS quantum dots and CoFe 2 O 4 nanoparticles co-loaded with graphene nanosheets as an efficient broad band EM wave absorber

Abstract In order to obtain the high-performance electromagnetic (EM) wave absorber, nanocomposites have been applied to absorbing field. In our research, hybrid reduced graphene oxide (RGO)/CoFe 2 O 4 /ZnS nanocomposites were successfully synthesized via a facile hydrothermal process in combination with the co-precipitation route. The crystal structure, chemical composition and morphology of the as-prepared nanocomposites have been detailedly investigated. The ZnS quantum dots and CoFe 2 O 4 nanoparticles with an average diameter of 3–8 nm and 10–20 nm, respectively, were homogeneously anchored on graphene sheets. Moreover, the EM parameters of both RGO/CoFe 2 O 4 and RGO/CoFe 2 O 4 /ZnS nanocomposites were measured using a vector network analyzer. The EM wave absorption properties of RGO/CoFe 2 O 4 /ZnS nanocomposites are significantly improved compared with RGO/CoFe 2 O 4 nanocomposites, with the maximum reflection loss as high as −43.2 dB at only 1.8 mm and the maximum absorption bandwidth (

Single step synthesis of ZnS quantum dots and their microstructure characterization and electrical transport below room temperature

Low dimensional cubic phase ZnS quantum dots (QDs) are formed by mechanical alloying the stoichiometric mixture of Zn and S powders at room temperature. During milling process the primary mixed phase ZnS is formed at about 3.5 h of milling and strain less single phase (cubic) ZnS QDs are formed with ∼4.5 nm in size after 20 h of milling. Detailed microstructure study has been done by both Rietveld analysis of x-ray diffraction pattern and high resolution transmission electron microscope images. Dc resistivity decreases with increasing temperature which can be explained by three-dimensional hopping conduction mechanisms. Observed negative magnetoconductivity has been analyzed by wave function shrinkage model. Alternating current conductivity can be described by the correlated barrier hopping conduction mechanism. Analysis of complex impedance indicates that the grain boundary resistance is found to be dominating over the grain resistance. Relaxation behavior has been explained by the analysis of the electric modulus.

Controlled synthesis of ZnS quantum dots with cubic crystallinity by laser ablation in solution

In this work, we propose using the pulsed laser ablation technique in solution as a ‘chemical-free’ method for forming biatomic or multiatomic semiconductor quantum dots. In particular, we present the results of the formation and characterization of ZnS nanoparticles by laser ablation in solution as a case study for all semiconductors of the III and IV groups. We obtain results comparable to those obtained by chemical methods without the use of surfactants and without changing the crystallinity of the precursor target. Colloidal solutions of nanoparticles with different dimensions were obtained by varying the irradiation time during laser ablation. A study of the morphology and changes in the band edge indicates the formation of ZnS quantum dots with dimensions <4 nm for an irradiation time of less than 10 s. The changes in the band edge were studied in terms of the effective mass approximation model, which indicates, for low irradiation times, the formation of quantum dots with radii ranging from 2.5–2.8 nm and band edges ranging from 4.21–4.15 eV. Raman measurements indicate that quantum dots have the same crystallinity as bulk grains, while photoluminescence measurements clearly show a rearrangement of Zn and S atoms, eliminating the vacancies defects of the bulk material.

Observation of two-photon absorption at UV radiation in ZnS quantum dots

Research studies on quantum dots (QDs) of semiconductor materials are of potential interest in present days having promising applications in different optoelectronic devices. Among other materials, ZnS is a direct bandgap semiconductor material having a wide bandgap of 3.6 eV for its cubic phase at room temperature and it shows excellent optical properties. However, here the nonlinear optical (NLO) properties of chemically synthesized ZnS QDs of average size of ∼1.5 nm have been reported which are measured by using an indigenously developed Z-scan technique. The pump radiation is 355 nm which is the third harmonic of the Q-switched Nd:YAG laser radiation having pulsed duration of 10 ns with the repetition rate of 10 Hz. The measured experimental data have been analysed by using analytical models and two-photon absorption coefficients of the ZnS QDs at 355 nm have been extracted.

Synthesis, structural, and optical properties of type-II ZnO–ZnS core–shell nanostructure

We demonstrate a facile one-step method for the preparation of ZnO–ZnS core–shell type-II nanostructures, pure ZnS quantum dots and pure ZnO nanoparticles with different experimental conditions. Treatment with sodium hydroxide as a capping agent is investigated systematically during the synthesis of ZnS quantum dots (QDs). The thickness of the ZnS shell is controlled by the concentration of the sodium sulphide during the synthesis of ZnO–ZnS core–shell nanostructures. The morphology and structure of samples are verified by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis (EDX). The UV–vis absorption spectra of the pure ZnS QDs exhibit a blue shift in the absorption edge due to the quantum confinement effect. The PL emission spectra of the ZnO–ZnS core–shell nanostructure are compared with the ZnO nanoparticles. The ZnO–ZnS core–shell nanostructures show decrease in the UV and green emissions with the appearance of a blue emission, which are not found in the ZnO nanoparticles.

Facile synthesis of water-soluble ZnS quantum dots with strong luminescent emission and biocompatibility

ZnS quantum dots (QDs) are among the most promising emerging fluorescent materials for biolabeling. High-quality colloidal ZnS QDs were synthesized via a new facile chemical precipitation method using the mixture of ethylene glycol (EG) and water as the solvent. The phase structure and morphology of the ZnS QDs were characterized by X-ray powder diffraction and high resolution transmission electron microscopy. The synthesized ZnS QDs have a cubic zinc blende structure with monodispered and small particles. ZnS QDs easily dispersed in water to form stable and clear colloids and the strong tunable trap state emissions from 452 to 516nm were achieved by varying the reaction time. The hemolysis assay was performed to evaluate the biocompatibility of the ZnS QDs.

RETRACTED: Low temperature method for synthesis of ZnS quantum dots and its luminescence characterization studies

RETRACTED: Low temperature method for synthesis of ZnS quantum dots and its luminescence characterization studies

Microwave assisted synthesis of ZnS quantum dots using ionic liquids

In this work we report results from microwave (MW) assisted synthesis of highly crystalline ZnS quantum dots (QDs) using ionic liquid (ILs) as MW absorbing medium. Two types of ionic liquids, imidazolium and phosphonium based, were used. The QDs are less than 5nm in size and of wurtzite ZnS type, as characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern. The optical properties were investigated by UV–vis absorption and show a blue shift in absorption as compared to bulk wurtzite ZnS due to quantum confinement effects. The photoluminescence (PL) spectra of the QDs show different trap state emissions.

Controlled Synthesis of ZnS Quantum Dots and ZnS Quantum Flakes with Graphene as a Template

Novel ZnS quantum dots (QDs) and ZnS quantum flakes (QFs) were successfully prepared with graphene nanosheets (GNs) as a special template, and two unique heterostructures of ZnS/GNs were also obtained. Due to the structure-directing template effect of GNs, the as-synthesized ZnS with different morphologies, dots or flakes, were uniformly distributed on the surface of GNs by controlling nucleation and growth. The two different heterostructures of ZnS/GNs exhibited obvious photovoltaic response, and ZnS/GN QFs-on-sheet heterostructures show higher photovoltage than that of ZnS/GN QDs-on-sheet.

Low temperature synthesis of cubic phase zinc sulfide quantum dots

Abstract In this study, we report on a new method for the synthesis of ZnS quantum dots (QDs). The synthesis was carried out at low temperature by a chemical reaction between zinc ions and freshly reduced sulfide ions in ethanol as reaction medium. Zinc chloride and elemental sulfur were used as zinc and sulfur sources, respectively and hydrazine hydrate was used as a strong reducing agent to convert elemental sulfur (S8) into highly reactive sulfide ions (S2−) which react spontaneously with zinc ions. This facile, less toxic, inexpensive route has a high yield for the synthesis of high quality metal sulfide QDs. Transmission electron microscopy (TEM) image analysis and selected area electron diffraction (SAED) reveal that ZnS QDs are less than 3 nm in diameter and are of cubic crystalline phase. The UV-Vis absorption spectrum shows an absorption peak at 253 nm corresponding to a band gap of 4.9 eV, which is high when compared to the bulk value of 3.68 eV revealing strong quantum confinement. PL emission transitions are observed at 314 nm and 439 nm and related to point defects in ZnS QDs.