Understanding the role of zinc dithiocarbamate complexes as single source precursors to ZnS nanomaterials

Zinc sulfide is an important wide-band gap semi-conductor and dithiocarbamate complexes [Zn(S₂CNR₂)₂] find widespread use as single-source precursors for the controlled synthesis of ZnS nanoparticulate modifications. Decomposition of [Zn(S₂CNⁱBu₂)₂] in oleylamine gives high aspect ratio wurtzite nanowires, the average length of which was increased upon addition of thiuram disulfide to the decomposition mixture. To provide further insight into the decomposition process, X-ray absorption spectroscopy (XAS) of [Zn(S₂CNMe₂)₂] was performed in the solid-state, in non-coordinating xylene and in oleylamine. In the solid-state, dimeric [Zn(S₂CNMe₂)₂]₂ was characterised in accord with the single crystal X-ray structure, while in xylene this breaks down into tetrahedral monomers. In situ XAS in oleylamine (RNH₂) shows that the coordination sphere is further modified, amine binding to give five-coordinate [Zn(S₂CNMe₂)₂(RNH₂)]. This species is stable to ca. 70 °C, above which amine dissociates and at ca. 90 °C decomposition occurs to generate ZnS. The relatively low temperature onset of nanoparticle formation is associated with amine-exchange leading to the in situ formation of [Zn(S₂CNMe₂)(S₂CNHR)] which has a low temperature decomposition pathway. Combining these observations with the previous work of others allows us to propose a detailed mechanistic scheme for the overall process.

Characterization of visible-light photo-Fenton reactions using Fe-doped ZnS (Fex-ZnS) mesoporous microspheres

PNP was efficiently degraded by a Fe_6%-ZnS catalyst through photo-Fenton-like reactions under visible light irradiation.

Electronic and Structural Study of ZnxSx [x = 12, 16, 24, 28, 36, 48, 96, and 108] Cage Structures

We present a density functional study on the structural and electronic properties of ZnS bubble clusters, specifically, hollow cages whose spontaneous formation was previously observed in classical molecular dynamics simulations by Spano et al. [J. Phys. Chem. B 2003, 107, 10337]. The hollow ZnS cages in our study were modeled as Zn_xS_x [x = 12, 16, 24, 28, 36, 48, 108], and an onionlike structure was modeled as Zn₉₆S₉₆. The study of energetics and stability, performed using large polarized Gaussian basis sets, indicated all structures to be energetically stable with similar binding energy of 5.5-5.6 eV per ZnS pair. Further computation of electronic properties showed that these cages have large vertical ionization energies and relatively low electron affinities in the ranges of 6.8-8.1 and 1.7-3.0 eV, respectively. They have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps between 2.5 and 3.3 eV, and quasi-particle gaps vary from 6.2 eV for Zn₁₂S₁₂ to 4.19 for Zn₁₀₈S₁₀₈. The computed vibrational frequencies for selected cages, that is, Zn₁₂S₁₂, Zn₁₆S₁₆, Zn₂₈S₂₈ (O, S₄, and S₈ point groups), and Zn₃₆S₃₆ indicate that these cage structures correspond to local minima on the potential energy surface. Finally, the infrared spectra calculated using large basis sets are also reported.

A size-dependent structural evolution of ZnS nanoparticles

Recently, ZnS quantum dots have attracted a lot of attention since they can be a suitable alternative for cadmium-based quantum dots, which are known to be highly carcinogenic for living systems. However, the structural stability of nanocrystalline ZnS seems to be a challenging issue since ZnS nanoparticles have the potential to undergo uncontrolled structural change at room temperature. Using the molecular dynamics technique, we have studied the structural evolution of 1 to 5 nm freestanding ZnS nanoparticles with zinc-blende and wurtzite crystal structures. Simulation results revealed that relaxed configurations of ZnS nanoparticles larger than 3 nm consist of three regions: a) a crystalline core, b) a distorted network of 4-coordinated atoms environing the crystalline core, and c) a surface structure made entirely of 3-coordinated atoms. Decreasing the size of ZnS nanoparticle to 2 nm will cause the crystalline core to disappear. Further reducing the size will cause all of the atoms to become 3-coordinated. Dipole moments of zinc-blende and wurtzite nanoparticles are in the same range when the nanoparticles are smaller than 3 nm. Increasing the size makes dipole moments converge to the bulk values. This makes zinc-blende and wurtzite nanoparticles less and more polar, respectively.

Zinc blende versus wurtzite ZnS nanoparticles: control of the phase and optical properties by tetrabutylammonium hydroxide

We demonstrated phase control, mediated by the presence of tetrabutylammonium hydroxide, in the growth of ZnS crystals by using a cost effective MAS method; a very moderate temperature (140 °C) and a very fast reaction time are sufficient to produce nanostructures with a good degree of crystallinity.

Novel microwave assisted synthesis of ZnS nanomaterials

A novel ambient pressure microwave assisted technique is developed in which silver and indium-modified ZnS is synthesized. The as-prepared ZnS is characterized by x-ray diffraction, UV-vis spectroscopy, x-ray photoelectron spectroscopy and luminescence spectroscopy. This procedure produced crystalline materials with particle sizes below 10 nm. The synthesis technique leads to defects in the crystal which induce mid-energy levels in the band gap and lead to indoor light photocatalytic activity. Increasing the amount of silver causes a phase transition from cubic blende to hexagonal phase ZnS. In a comparative study, when the ZnS cubic blende is heated in a conventional chamber furnace, it is completely converted to ZnO at 600 °C. Both cubic blende and hexagonal ZnS show excellent photocatalytic activity under irradiation from a 60 W light bulb. These ZnS samples also show significantly higher photocatalytic activity than the commercially available TiO(2) (Evonik-Degussa P-25).

Size- and shape-dependent phase transformations in wurtzite ZnS nanostructures

This paper describes the equilibrium morphologies of zinc sulfide nanoparticles in the wurtzite phase as a function of size, determined using ab initio Density Functional Theory (DFT) simulations and a shape-dependent thermodynamic model predicting the Gibbs free energy of a nanoparticle. We investigate the relative stabilities of a variety of nanoparticle shapes based on the wurtzite structure and show how the aspect ratio of wurtzite nanorods moderates the size-dependent phase transformation to the zinc blende phase. We find that while wurtzite nanoparticles are thermodynamically unstable with respect to the low energy rhombic dodecahedron morphology in the zinc blende phase at all sizes, shape- and size-dependent phase transformations occur when other zinc blende morphologies are present. Despite popular synthesis of zinc sulphide nanoparticles in the wurtzite phase, an in-depth thermodynamic study relating to the relative stability of wurtzite shapes and comparison with the zinc blende phase does not exist. Therefore this is the first thermodynamic study describing how shape can determine the solid phase of zinc sulfide nanostructures, which will be of critical importance to experimental applications of nanostructured zinc sulfide, where phase and shape determines properties.

ZnS nanocrystals and nanoflowers synthesized by a green chemistry approach: rare excitonic photoluminescence achieved by the tunable molar ratio of precursors

In the present work, we demonstrated a simple and green synthesis route for shape-controlled ZnS nanocrystals, where only environmentally benign chemicals, namely sulfur, zinc oxide and olive oil, were employed. By controlling the experimental conditions, we were able to tune the band edge and trap state photoluminescences of ZnS nanocrystals and obtain pure excitonic photoluminescence that was rarely observed in literature. The trap state emission was derived from sulfur vacancies and would be eliminated when an excess of sulfur was used during the synthesis. Additionally, the morphology of ZnS nanocrystals could be tuned to appear like flowers, where the formation mechanism was systematically discussed.

Atomistic theory and simulation of the morphology and structure of ionic nanoparticles

Computational techniques are widely used to explore the structure and properties of nanomaterials. This review surveys the application of both quantum mechanical and force field based atomistic simulation methods to nanoparticles, with a particular focus on the methodologies available and the ways in which they can be utilised to study structure, phase stability and morphology. The main focus of this article is on partially ionic materials, from binary semiconductors through to mineral nanoparticles, with more detailed considered of three examples, namely titania, zinc sulphide and calcium carbonate.

ZnS nanostructure arrays: a developing material star

Semiconductor nanostructure arrays are of great scientific and technical interest because of the strong non-linear and electro-optic effects that occur due to carrier confinement in three dimensions. The use of such nanostructure arrays with tailored geometry, array density, and length-diameter-ratio as building blocks are expected to play a crucial role in future nanoscale devices. With the unique properties of a direct wide-bandgap semiconductor, such as the presence of polar surfaces, excellent transport properties, good thermal stability, and high electronic mobility, ZnS nanostructure arrays has been a developing material star. The research on ZnS nanostructure arrays has seen remarkable progress over the last five years due to the unique properties and important potential applications of nanostructure arrays, which are summarized here. Firstly, a survey of various methods to the synthesis of ZnS nanostructure arrays will be introduced. Next recent efforts on exploiting the unique properties and applications of ZnS nanostructure arrays are discussed. Potential future directions of this research field are also highlighted.

Morphological and phase stability of zinc blende, amorphous and mixed core-shell ZnS nanoparticles

Zinc sulfide (ZnS) nanoparticles are of interest for their luminescent and catalytic properties which are being considered for the next generation of optical, electronic and photovoltaic devices. However, ZnS nanoparticles undergo reversible and irreversible phase transformations under ambient conditions, so a detailed understanding of the nanomorphology is critical in ensuring these desirable properties can be controlled and maintained. Anticipating the structure and transformations in ZnS nanoparticles experimentally is difficult, since selectivity among competing phases, shapes and sizes is intrinsically linked. Presented here are the results of first principle computer simulations and advanced theoretical modelling used to investigate the relationship between size and shape in determining the crystallinity of ZnS nanoparticles. We find that the equilibrium morphology is characterised by {220} facets, irrespective of the size of the particle, but that the presence of different high energy facets introduced kinetically may significantly influence the zinc blende to amorphous ZnS transformation size, as well as the agglomeration behaviour. In addition to this, we model the relationship between transformation size, morphology and the ratio of crystalline core to amorphous shell and show that at small sizes, a core-shell crystalline/amorphous structure is thermodynamically favourable.