ZnS Cores Research Articles

Semihollow Core-Shell Nanoparticles with Porous SiO2 Shells Encapsulating Elemental Sulfur for Lithium-Sulfur Batteries.

Lithium-sulfur batteries have shown great promise as next-generation high energy density power sources, but their commercial applications are hindered by short battery cycle life arising from the dissolution and shuttling of polysulfides. To address this shortcoming, we prepared two types of semihollow core-shell nanoparticles in which (1) elemental sulfur is encapsulated within a porous silica shell (S@SiO2) and (2) elemental sulfur is encapsulated within a porous silica shell where the inner surface of the shell is decorated with small Au nanoparticles (S@Au@SiO2). These core-shell nanoparticles, both ∼300 nm in diameter, were generated from analogous zinc sulfide-based core-shell nanoparticles (ZnS@SiO2 and ZnS@Au@SiO2, respectively) by converting the ZnS cores to elemental sulfur upon treatment with Fe(NO3)3. With a high surface area and strong host-polysulfide interaction, the SiO2 shells effectively trap the polysulfides; moreover, the internal void space of these nanostructures accommodates the volume expansion of the sulfur core upon lithiation. By decorating ∼5-7 nm Au nanoparticles evenly on the inner surface of the porous SiO2 shells (i.e., S@Au@SiO2), electron transport is enhanced, with consequently enhanced sulfur conversion kinetics at high current rates. Studies of battery performance showed that the S@SiO2 cathode can deliver an initial capacity of 1153 mA h g-1 under 0.2 C and retain 816 mA h g-1 after 100 cycles. More importantly, the Au-decorated S@Au@SiO2 cathode can deliver a high capacity of 500 mA h g-1 under 5 C.

ZnS@ZIF-8 core-shell nanoparticles incorporated with ICG and TPZ to enable H2S-amplified synergistic therapy.

Abnormal tumor microenvironment, such as hypoxia, interstitial hypertension and low pH, leads to unexpected resistance for current tumor treatment. The development of versatile drug delivery systems which present responsive characteristics to tumor microenvironment (TME) has been extensively carried out, but remains challenging. In this study, zeolitic imidazolate framework-8 (ZIF-8) coated ZnS nanoparticles have been designed and prepared for co-delivery of ICG/TPZ molecules, denoted as ZSZIT, for H2S-amplified synergistic therapy.Methods: The ZSZ nanoparticles were characterized using SEM, TEM and XRD. The in vitro viabilities of cancer cells cultured with ZSZIT under normoxia/hypoxia conditions were evaluated by cell counting kit-8 (CCK-8) assay. In addition, in vivo anti-tumor effect was also performed using male Balb/c nude mice as animal model.Results: ZSZIT shows cascade PDT and hypoxia-activated chemotherapeutic effect under an 808nm NIR irradiation. Meanwhile, ZSZIT degrades under tumor acidic environment, and H2S produced by ZnS cores could inhibit the expression of catalase, which subsequently favors the hypoxia and antitumor effect of TPZ drug. Both in vitro and in vivo studies demonstrate the H2S-sensitized synergistic antitumor effect based on cascade PDT/chemotherapy.Conclusion: This cascade H2S-sensitized synergistic nanoplatform has enabled more effective and lasting anticancer treatment.

Silica-coated ZnS quantum dots as fluorescent probes for the sensitive detection of Pb2+ ions

The silica-coated ZnS quantum dots (ZnS@SiO2 QDs) were prepared via a simple and environmentally friendly process. The oil-soluble ZnS cores were successfully transferred to water by the coating of SiO2 shells. The QDs exhibited satisfying dispersion and luminescent properties in water. The ZnS@SiO2 QDs were directly used as fluorescent probes for heavy metal ions without the addition of any buffer solution. The luminescence of QDs was extremely sensitive to Pb2+ ions, and the fluorescence quenching was well described by the Stern–Volmer equation, with an even quenching constant for the Pb2+ ions samples concentration ranging from 10−9 to 2.6 × 10−4 M. An extended hypothesis based on the traditional cation exchange mechanism is proposed to analyze the most significant fluorescence quenching effect by Pb2+ ions. Studies show that ZnS@SiO2 QDs have great potentials to be a sensor for Pb2+ analysis at low to high concentrations.

Sequential Thermal Decomposition of the Shell of Cubic ZnS/Zn(OH)2 Core–Shell Quantum Dots Observed With Mn2+ Probing Ions

Thermally induced changes in the structure and composition of the shell of tightly aggregated cubic ZnS/Zn(OH)2 core–shell quantum dots of 1.9 nm average core size were investigated by multifrequency electron paramagnetic resonance of Mn2+ probing ions. The observed three-steps temperature induced transformation of the Mn2+ surface centers in the 80–450 °C temperature range was attributed to the sequential decomposition by dehydration of the disordered ε-Zn(OH)2 shell into ZnO, with the formation of the Zn2O(OH)2 and Zn4O3(OH)2 intermediate nanocompounds. The presence of a 0.3 to 1.9 nm thick surface layer of disordered nanomaterial separating the cubic ZnS cores and its shrinking to a few atomic layers by mass loss after annealing up to 350 °C was observed by high resolution transmission electron microscopy. Unlike the single step dehydration around 120 °C of the bulk ε-Zn(OH)2, the complex decomposition of the ε-Zn(OH)2 shell is attributed to its nanosized, disordered structure.

Fabrication and luminescence properties of In 2O 3-capped ZnS nanowires

ZnS-core/In 2O 3-shell nanowires have been prepared by using a two-step process: thermal evaporation of ZnS powders on Si(1 0 0) substrates coated with Au thin films and sputter-deposition of In 2O 3. The ZnS nanowires were a few tens of nanometers in diameter and a few hundreds of micrometers in length. ZnS nanowires have an emission band centered at approximately 570 nm in the yellow region. The yellow emission has been enhanced in intensity by capping the ZnS nanowires with In 2O 3 presumably due to the increase in the concentrations of indium and oxygen interstitials in the very surface region of the ZnS cores and further enhanced by annealing in a reduction atmosphere maybe because of the increase in the concentration of Au Zn − in the ZnS cores. In contrast, the yellow emission intensity has been decreased by annealing in an oxidation atmosphere due to the conversion of ZnS into ZnO as a result of the reaction of ZnS in the cores with oxygen.

Structure and photoluminescence properties of ZnS nanowires sheathed with SnO2 by atomic layer deposition

Influence of the thermal annealing atmosphere on the photoluminescence properties of ZnS-core/SnO2-shell coaxial nanowires was investigated. ZnS nanowires were synthesized by a two-step process: the thermal evaporation of ZnS powders and the atomic layer deposition of SnO2. Transmission electron microscopy and X-ray diffraction analyses reveal that two crystalline ZnS phases: one with a zinc blende structure and the other with an wurtzite structure coexist in the cores whereas the SnO2 cores in the as-prepared coaxial nanowires are amorphous. The SnO2 shells are found to be crystallized by thermal annealing. Photoluminescence (PL) measurements at room temperature show that the green emission of the ZnS/SnO2 coaxial nanowires is enhanced in intensity by thermal annealing regardless of the annealing atmosphere. The PL emission is more significantly enhanced in intensity by annealing in a reducing atmosphere than in an oxidative atmosphere since AuZn− is more easily generated in the ZnS cores in the former atmosphere.

Effects of coating and thermal annealing on the photoluminescence properties of ZnS/ZnO one-dimensional radial heterostructures

Influence of the thermal annealing atmosphere and the ZnO layer thickness on the photoluminescence properties of ZnS-core/ZnO-shell one-dimensional (1D) radial heterostructures was investigated. ZnS nanowires were synthesized by thermal evaporation of ZnS powders and then coated with ZnO by using the sputter-deposition technique to form the nanostructures. TEM and XRD analysis results reveal that a crystalline ZnS phase with a zinc blende structure and a crystalline ZnS phase with an wurtzite structure coexist in the cores whereas amorphous ZnO exists in the shells. Photoluminescence (PL) measurements at room temperature show that the green emission of the ZnS/ZnO 1D radial heterostructures is enhanced by annealing in an oxygen atmosphere due to the decrease in the concentration of oxygen vacancies in the ZnO shells, which normally absorbs the light emitted from the core, during the annealing process. In contrast, the green emission is degraded by annealing in an argon atmosphere since the light emitted from the core is absorbed more efficiently by the defects in the shell due to the crystallization of the ZnO shells during annealing. The PL emission intensity of the ZnS/ZnO 1D radial heterostructures is decreased by increasing the thickness of the ZnO shell layers due to the absorption of the light emitted from the ZnS cores by the ZnO shells or some interfacial effects.

Forces between Surfaces across Nanoparticle Solutions: Role of Size, Shape, and Concentration

Using a surface force apparatus, we have measured the normal forces between mica surfaces across various types of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dispersed in organic solvents. We focused on the effects of nanoparticle size, shape, and concentration on the force-distance profiles. Forces were exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles and were roughly linear when there was adhesion between the nanoparticle cores, i.e., when the surfactant layers detached from the nanoparticles. In both cases, the range and magnitude of the forces were dependent upon the particle size, shape, and solution concentration. Fine details in the otherwise smooth force-distance profiles indicate specific effects due to particle chemistry and geometry and the existence of first-order disorder-order phase transitions upon confinement. Small amounts of water in the (hydrophobic) organic solvents had dramatic effects on the measured forces. Understanding and controlling the effects of particle shape, size, and concentration and the presence of water (or other surface-active solutes) on particle-particle and particle-surface interactions are important for the processing of nanoparticles into ordered superstructured materials.

II–VI semiconductor quantum dot quantum wells: a tight‐binding study

AbstractWe have studied the electronic structure, exciton states and optical spectra of spherical semiconductor quantum dot quantum wells (QDQW's) by means of a symmetry‐adapted tight‐binding (TB) method. We have investigated two classes of QDQW's: CdS/HgS/CdS, based on a CdS core which acts as a barrier, with a thin HgS well layer intercalated between the core and a clad layer of CdS. The second class of QDQW's is based on ZnS cores covered with CdS layers which act in this case as a well. The calculated values of the absorption onset show a good agreement with the experimental data. Large photoluminescence Stokes shifts are also predicted. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of ZnS∕SiC nanocables, SiC-shelled ZnS nanoribbons (and sheets), and SiC nanotubes (and tubes)

Here we report on the synthesis of ZnS∕SiC nanocables and SiC nanotubes and other relevant structures via a controllable two-stage thermal process using ZnS nanowires, nanoribbons, and sheets as templates. Within the cables, the ZnS cores are polytypes of fcc- and hcp-ZnS with ∼50–130nm diameter, and the SiC shells are polycrystalline β-SiC with ∼15–50nm thickness. SiC nanotubes were formed through simple removal of ZnS cores from the cables. Room-temperature photoluminescence of the SiC nanotubes displays a strong green emission band centered at ∼517nm. The nanostructures described herewith may be valuable in the blocks of advanced semiconducting devices.

Exciton fine structure in semiconductor nanocrystals in the tight‐binding method

We present a symmetry-based tight-binding (TB) method for calculating the exciton states and optical spectra in spherical semiconductor quantum dots (QD's). Here we focus on the resonant photoluminescence (PL) Stokes shift between the first optically active level and the “dark” exciton ground state for nanocrystals (NC's). The method has so far been applied to CdSe and CdTe NC of diameter up to 6 nm. The experimental gaps and Stokes shifts show satisfactory agreement with the theoretical results. We have also investigated two series of quantum dot quantum wells (QDQW's). One of them is based on CdS cores which act as energy barrier; HgS well layers are intercalated between the core an additional CdS clad. The second serie of QDQW's is based on ZnS cores and CdS layers as wells. The experimental absorbance edges in the latter are quantitatively reproduced by our model which allows us to confidently predict the corresponding Stokes shifts.

New Zinc and Cadmium Chalcogenide Structured Nanoparticles

ABSTRACTThe growth of 2D quantum dot quantum well (QDQW) nanocrystals in which a shell of CdSe is grown onto cores of ZnS and capped with a further shell of ZnS is reported. The red shift in the interband absorption and photoluminescence spectrum of the quantum dots (QDs) indicates relocalization of carriers from confinement in the ZnS core to the CdSe shell. The change in interband absorption energy utilizing the effective mass approximation with spherical symmetry was modeled, enabling an estimate of the CdSe thicknesses grown. 1.8nm and 2.5nm ZnS cores were selected as the base on which to grow the CdSe shells. Despite the 12% lattice mismatch between ZnS and CdSe, our results indicate that we have successfully grown CdSe shells approximately three monolayers thick onto 2.5nm ZnS core. Anything beyond a single monolayer of CdSe could not be grown onto the 1.8nm core, although some success was observed by incorporating a CdS graded layer in-between the ZnS core and CdSe shell. The effect of ZnS shell thickness on photoluminescence efficiency has also been studied with optimum shell thicknesses showing quantum yields as high as 52%. Growth of these nanocrystals represents a significant step in the development of strained nanocrystalline heterostructures.