Fabrication of ZnS nanoparticles and nanorods with cubic and hexagonal crystal structures: a simple solvothermal approach

A mechanoluminescent material, ZnS:Mn,Li, with enhanced brightness for visualizing dental occlusion

Mechanoluminescent materials are characterized by high luminescence intensity, high repeatability, no external voltage activation, and a good linear relationship between stress and mechanoluminescence intensity within a certain range. Therefore, mechanoluminescent materials have attracted increasing attention from researchers in the fields of stress sensing, encryption and anti-counterfeiting, structural health monitoring, energy-saving lighting, intelligent wearable devices, and other fields. In this study, ZnS:Mn powders with different Mn2+ ratios and different ion doping were synthesized by a high-temperature solid-phase reaction, and the synthesis of various materials was characterized. Then, the optimal mechanoluminescence effect of the ZnS:1%Mn,1%Li material was obtained. The photoluminescence intensity of ZnS:1%Mn,1%Li was 16.7 times higher than that of the sample without doping with Li+, and the mechanoluminescence intensity was 1.64 times higher. Finally, polyethylene terephthalate (PET) film was combined with ZnS:Mn,Li mechanoluminescent powders to prepare flexible three-layer composite film. Based on this, a feasible strategy for the detection of temporomandibular disorders was proposed. The composite film is easy to use, economical, and safe, and has good mechanoluminescent performance, which has potential application value in the field of occlusal force detection and visualization.

Defect engineering for enhanced optical and photocatalytic properties of ZnS nanoparticles synthesized by hydrothermal method

Defect engineering is a promising method for improving light harvesting in photocatalytic materials like Zinc sulphide (ZnS). By altering the S/Zn molar ratio during hydrothermal processes, Zn and S defects are successfully introduced into the ZnS crystal. The band structures can be modified by adding defects to the crystal structure of ZnS samples. During the treatment process, defects are formed on the surface. XRD and Raman studies are used for the confirmation of the crystallinity and phase formation of the samples. Using an X-ray peak pattern assessment based on the Debye Scherer model, the Williamson-Hall model, and the size strain plot, it was possible to study the influence of crystal defect on the structural characteristics of ZnS nanoparticles. The band gap (Eg) values were estimated using UV-Vis diffuse spectroscopy (UV-Vis DRS) and found that the Eg is reduced from 3.28 to 3.49 eV by altering the S/Zn molar ratio. Photoluminescence study (PL) shows these ZnS nanoparticles emit violet and blue radiations. In keeping with the results of XRD, TEM demonstrated the nanoscale of the prepared samples and exhibited a small agglomeration of homogenous nanoparticles. Scanning electron microscopy (SEM) was used to examine the surface morphology of the ZnS particles. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) were used to evaluate and validate the elemental composition. XPS results indicate the presence of defects on the prepared ZnS nanoparticles. For the investigation of vacancy-dependent catalytic activity under exposure to visible light, defective ZnS with different quantities of Zn and S voids are used as catalysts. The lowest S/Zn sample, ZnS0.67 and the highest S/Zn sample, ZnS3, show superior photocatalytic activity.

Detailed insights into the formation pathway of CdS and ZnS in solution: a multi-modal in situ characterisation approach

The high stability, high availability, and wide size-dependent bandgap energy of sulphidic semiconductor nanoparticles (NPs) render them promising for applications in optoelectronic devices and solar cells. However, the tunability of their optical properties depends on the strict control of their crystal structure and crystallisation process. Herein, we studied the structural evolution during the formation of CdS and ZnS in solution by combining in situ luminescence spectroscopy, synchrotron-based X-ray diffraction (XRD) and pair distribution function (PDF) analyses for the first time. The influence of precursor type, concentration, temperature and heating program on the product formation and on the bandgap or trap emission were investigated in detail. In summary, for CdS, single-source precursor (SSP) polyol strategies using the dichlorobis(thiourea)cadmium(II) complex and double-source precursor approaches combining Cd(CH₃COO)₂·2H₂O and thiourea led to the straightforward product at 100 °C, while the catena((m₂-acetato-O,O')-(acetate-O,O')-(m₂-thiourea)-cadmium) complex was formed at 25 and 80 °C. For ZnS, the reaction between Zn(CH₃COO)₂·2H₂O and thiourea at 100 °C led to the product formation after the crystallisation and dissolution of an unknown intermediate. At 180 °C, besides an unknown phase, the acetato-bis(thiourea)-zinc(II) complex was also detected as a reaction intermediate. The formation of such reaction intermediates, which generally remain undetected applying only ex situ characterisation approaches, reinforce the importance of in situ analysis for promoting the advance on the production of tailored semiconductor materials.

Significant zinc release from widely-used commercial lithopone pigments under solar irradiation

Lithopone pigments are an important group of white inorganic pigments, with production exceeding 240,000 tons/year in China. Nevertheless, our understanding of its environmental behavior is still limited. In this work, we reported the fast and extensive release of Zn²⁺ from the commercial lithopone pigment under solar exposure. The lithopone pigment released 40.97% of its total Zn within 24-h simulated sunlight exposure, generating a significant amount of nanoparticles. The commercial lithopone pigment had bandgap energy of 3.63 eV. It can be excited within the solar spectrum (wavelength <342 nm). As suggested by the photocurrent and surface photovoltage results, the pigment generated electrons and holes with good separation and transfer efficiency upon solar irradiation. The pigment also produced hydroxyl radical and superoxide by the oxidation of surface-bound OH^- and H₂O by the holes and direct transfer of the electrons to oxygen molecules. The photogenerated holes can oxidize the pigment, leading to its photo-dissolution and consequently the release of Zn²⁺. The water chemistry, including pH, coexisting anions, and organic carbons, influenced the photo-dissolution kinetics of the pigment by changing the valence band edge, forming stable precipitates, competing for the holes, and screening effect. The release of Zn²⁺ from the commercial lithopone pigment was fast and extensive under natural conditions, with 35.16% Zn released within 6-h solar exposure. Our results highlighted the crucial role of photochemistry in the environmental risk assessments and regulations of commercial lithopone pigments.

Computational approach to (ZnS)_{i} nanoclusters in ionic liquids

Unique and attractive properties have been predicted for II-VI-type semiconductor nanoclusters within the field of nanotechnology. However, the low reaction kinetics within the usual solvents gives only thermodynamic control during their production process, making the obtention of different metastable polymorphs extremely difficult. The use of ionic liquids as solvents has been proposed to overcome this problem. Identifying how these nanoclusters are solvated within ionic liquids is fundamental if this strategy is to be pursued. While computational chemistry tools are best suited for this task, the complexity and size of the system requires a careful design of the simulation protocol, which is put forward in this work. Taking as reference the (ZnS)_{12} nanocluster and the [EMIM][EtSO_{4}] ionic liquid, we characterize the interactions between the nanoparticle and first solvation shell by density functional theory calculations, considering most of the solvent implicitly. The DFT results are consistent through different theory levels showing a strong interaction between the Zn atoms of the nanocluster and the [EtSO_{4}^{-}] anion of the ionic liquid. A more realistic representation of the system is obtained by classical MD calculations, for which various classical force fields were considered and several atomic interactions parameterized. This new set of parameters correctly describes the interaction of different (ZnS) nanoclusters, supporting its transferability. The resulting MD simulation shows the formation of a structured ionic liquid solvation shell around the nanocluster with no exchange of ions for at least 5 ns, in agreement with the strong interactions observed in the density functional theory calculations.

Emergence and Control of Stacking Fault Formation during Nanoparticle Cation Exchange Reactions

Cation exchange reactions modify the composition of a nanocrystal while retaining other features, including the crystal structure and morphology. In many cases, the anion sublattice is considered to be locked in place as cations rapidly shuttle in and out. Here we provide evidence that the anion sublattice can shift significantly during nanocrystal cation exchange reactions. When the Cu⁺ cations of roxbyite Cu_1.8S nanorods exchange with Zn²⁺ to form ZnS nanorods, a high density of stacking faults emerges. During cation exchange, the stacking sequence of the close-packed anion sublattice shifts at many locations to generate a nanorod product containing a mixture of wurtzite, zincblende, and a wurtzite/zincblende polytype that contains an ordered arrangement of stacking faults. The reagent concentration and reaction temperature, which control the cation exchange rate, serve as synthetic levers that can tune the stacking fault density from high to low, which is important because once introduced, the stacking faults could not be modified through thermal annealing. This level of synthetic control through nanocrystal cation exchange is important for controlling properties that depend on the presence and density of stacking faults.

A straightforward one-pot approach to two new defect energy levels in ZnS

ZnS with double defect energy levels shows an amazing visible light photoactivity.

Synthesis and characterization of zinc di(O-2,2-dimethylpentan-3-yl dithiocarbonates) bearing pyridine or tetramethylethylenediamine coligands and investigation of their thermal conversion mechanisms towards nanocrystalline zinc sulfide

Metal xanthates are versatile single source precursors for the preparation of various metal sulfides. In this study, we present the synthesis of the two novel zinc xanthate complexes bis(O-2,2-dimethylpentan-3-yl-dithiocarbonato)(N,N,N',N'-tetramethylethylenediamine)zinc(ii) and bis(O-2,2-dimethylpentan-3-yl-dithiocarbonato)(pyridine)zinc(ii). A thorough investigation of these compounds revealed distinct differences in their structural and thermal properties. While in the complex containing the chelating tetramethylethylenediamine, the xanthate groups coordinate in a monodentate way, they are bidentally coordinated to the zinc atom in the pyridine containing complex. Both compounds show a two-step thermal decomposition with an onset temperature of 151 °C and 156 °C for the tetramethylethylenediamine and pyridine containing complex, respectively. Moreover, different mechanisms are revealed for the two phases of the decomposition based on high resolution mass spectrometry investigations. By the thermal conversion process nanocrystalline zinc sulfide is produced and the coligand significantly influences its primary crystallite size, which is 4.4 nm using the tetramethylethylenediamine and 11.4 nm using the pyridine containing complex for samples prepared at a temperature of 400 °C.

Phase-dependent structural, optical, phonon and UV sensing properties of ZnS nanoparticles

In order to investigate the influence of crystal structure on the photoresponse properties of ZnS nanoparticles under UV light exposure, electrical measurements on polyvinylpyrrolidone capepd cubic and hexagonal ZnS nanoparticles with average particle size 30-40 nm have been successfully carried out. Low-temperature solvothermal synthesis yields pure and highly crystalline w-ZnS nanoparticles with good stability. Different structures of prepared ZnS nanoparticles have been identified and confirmed with powder x-ray diffraction, high-resolution field-emission transmission electron microscopy and non-resonant Raman spectroscopic techniques, respectively. The energy band gap and emission properties of cubic and hexagonal ZnS have been studied using UV-vis absorption and photoluminescence spectroscopy. The interaction of phonons with free carriers and transport properties has a vital influence on the electronic and optical properties of nanomaterials. Hence, the resonant and non-resonant Raman spectral studies have been carried out for the prepared samples. Studies on the I-V characteristics and the mechanism behind the enhancement of photocurrent for the cubic and hexagonal ZnS nanoparticle-based photodetectors have shown an enhanced photocurrent for hexagonal ZnS nanoparticles rather than the cubic.

Facile synthesis of bovine serum albumin conjugated low-dimensional ZnS nanocrystals

We present a facile synthesis of bovine serum albumin (BSA) conjugated low-dimensional ZnS nanocrystals. The experimental parameters such as effects of BSA concentration and precursor vol ratios of Zn:S on the formation of ZnS nanoparticles in BSA matrix were investigated. The ZnS crystalline sizes of 1.9, 1.8 and 1.6nm were obtained by using the BSA concentrations of 1×10^-4, 5×10^-4 and 10×10^-4g/mL, respectively, with a fixed Zn:S vol ratio of 1:1. The ZnS samples prepared from 1:10 and 10:1 vol ratios of Zn:S at BSA concentration of 5×10^-4g/mL shows the crystalline sizes of ZnS are 2.1 and 1.5nm, respectively. FT-IR analysis suggests that the prepared ZnS nanoparticles might be conjugated through the interactions of hydroxyl and amine groups present in BSA. We evaluate the cytotoxicity of the prepared ZnS nanoparticles, the THP-1 cells showed a good viability (>88%) for all the prepared ZnS samples. The plausible mechanism for the formation of ZnS-BSA composite has also been discussed.

Optical, phonon and efficient visible and infrared photocatalytic activity of Cu doped ZnS micro crystals

We report, the enhanced photocatalytic behaviour of Cu doped ZnS micro crystals. ZnS and different concentrations of Cu doped ZnS microcrystals were prepared. X-ray diffraction confirms the crystalline and phase of the particles. Morphology and sizes were studied using Scanning Electron Microscopy (SEM). Recorded optical absorption spectra show a band for around 365nm for pure ZnS, but there is a broad band in the near infrared regime for the Cu-doped ZnS microcrystals which are attributed to the d-d transitions of Cu²⁺ ions. Phonon properties of as-prepared samples were investigated using Raman spectroscopy. Present work we investigate the potential of ZnS and Cu doped ZnS as a photocatalyst. For this from the degradation of methylene blue dye in aqueous media the photocatalytic activity of pure and highest doped ZnS samples with the irradiation of white light and infrared, enhanced photocatalytic activity were observed. Mechanism of white light an IR light based photocatalytic activity is explained based on the electron-hole pair production.

Synthesis and optical characterization of a high-quality ZnS substrate for optoelectronics and UV solar-energy conversion

A high-grade cubic ZnS substrate crystal with longer range order and a strong band-edge emission was clearly demonstrated.

Optical, dielectric, electronic and morphological study of biologically synthesized zinc sulphide nanoparticles using Moringa oleifera leaf extract and quantitative analysis of chemical components present in the leaf extract

The biosynthesis of zinc sulphide nanoparticles with ∼30 nm diameter using the leaf extract of Moringa oleifera is reported here.

Visible light-driven photocatalytic degradation performance for methylene blue with different multi-morphological features of ZnS

SEM images of synthesized 3D ZnS microspheres self-assembled with various precursor substances by different hydrothermal synthesis methods: (a) dandelion-ZnS, (b) raspberry-ZnS, (c) ball-ZnS and (d) flower-ZnS.

Photochemical synthesis of size-tailored hexagonal ZnS quantum dots

ZnS quantum dots were synthetized at room temperature using a simple photochemical process involving ketyl radicals. Through the simple adjustment of reagent concentration, the method allows the control of nanoparticle size. Transmission electron microscopy confirmed that the nanomaterial adopts the hexagonal structure.

One-pot, template-free syntheses of spherical ZnS nanocrystals using a new S2−source and their photocatalytic study

A facile, one-pot solvothermal method for the syntheses of template-free ZnS NCs (~3–6 nm) using (C₇H₇)S₂as a newin situsource of S²⁻ions without and with the use of MCE-capping agent has been demonstrated. Photocatalytic investigation of the NCs revealed very good activity for degradation of MO under UV light irradiation.

ZnS nanoparticles well dispersed in ethylene glycol: coordination control synthesis and application as nanocomposite optical coatings

The study of the preparation and application of ZnS nanoparticles (NPs) has been one of the most prominent hotspots in the domain of semiconductor NPs. The ZnS NPs usually exist in two crystallographic forms: zinc blende (cubic) and wurtzite (hexagonal). However, controlled preparation of ZnS NPs with specified crystallographic forms is still a difficult problem. Herein, zinc blende type ZnS NPs have been prepared by coordination control with diethanolamine (DEA) in ethylene glycol (EG). The prepared ZnS NPs can be well dispersed in EG without precipitation. The effect of DEA on the crystal form of the ZnS NPs was studied. We conclude that in EG, when no strong coordinating agent exists for the zinc ion, hexagonal crystal ZnS nanoparticles may be obtained, while coordinating agents such as acetate and DEA coordinated with the zinc(II) ion can inhibit the formation of the hexagonal ZnS crystal nucleus and the more stable zinc blende can be obtained. Moreover, transparent nanocomposite coatings of ZnS in PU matrix were prepared. This demonstrates that the incorporation of ZnS NPs can improve the refractive index of the optical coatings.

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%.

A hybrid photocatalytic system comprising ZnS as light harvester and an [Fe(2)S(2)] hydrogenase mimic as hydrogen evolution catalyst

Photo opportunity: A highly efficient and stable hybrid artificial photosynthetic H(2) evolution system is assembled by using a semiconductor (ZnS) as light-harvester and an [Fe(2)S(2)] hydrogenase mimic ([(μ-SPh-4-NH(2) )(2) Fe(2) (CO)(6)]) as catalyst for H(2) evolution. Photocatalytic H(2) production is achieved with more than 2607 turnovers (based on [Fe(2)S(2)]) and an initial turnover frequency of 100 h(-1) through the efficient transfer of photogenerated electrons from ZnS to the [Fe(2)S(2)] complex.

ZnS, CdS and HgS nanoparticles via alkyl-phenyl dithiocarbamate complexes as single source precursors

The synthesis of II-VI semiconductor nanoparticles obtained by the thermolysis of certain group 12 metal complexes as precursors is reported. Thermogravimetric analysis of the single source precursors showed sharp decomposition leading to their respective metal sulfides. The structural and optical properties of the prepared nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) UV-Vis and photoluminescence spectroscopy. The X-ray diffraction pattern showed that the prepared ZnS nanoparticles have a cubic sphalerite structure; the CdS indicates a hexagonal phase and the HgS show the presence of metacinnabar phase. The TEM image demonstrates that the ZnS nanoparticles are dot-shaped, the CdS and the HgS clearly showed a rice and spherical morphology respectively. The UV-Vis spectra exhibited a blue-shift with respect to that of the bulk samples which is attributed to the quantum size effect. The band gap of the samples have been calculated from absorption spectra and werefound to be about 4.33 eV (286 nm), 2.91 eV (426 nm) and 4.27 eV (290 nm) for the ZnS, CdS and HgS samples respectively.

One solvent, one pot and free capping ligands: Synthesis of alloyed multipod-branched Cd(x)Zn(1-)(x)S nanocrystals

The solvent ethanolamine with the assistance of cationic doping has been applied to synthesize alloyed multipod-branched Cd(x)Zn(1-)(x)S (0<x<1) nanocrystals through a simple solvothermal route. During the growth of the alloyed multipod-branched nanocrystals, for one thing, the cationic doping enlarges the energy difference between wurtzite and zinc-blende phases; for another thing, the -OH groups of ethanolamine favor the thorough alloying effects and the formation of the zinc-blende-structured seeds, while the -NH(2) groups facilitate the subsequent preferential growth of the wurtzite-phased arms. The composition x of the alloyed multipod-branched Cd(x)Zn(1-)(x)S nanocrystals can be facilely tuned by Cd/Zn initial molar ratios. Furthermore, the absorption edges (corresponding to optical band gaps E(g)) and the near-band-edge emission peaks are varied with the doping Cd(2+) content x. It is reasonable for us to believe that ethanolamine can also be employed to fabricate other alloyed multipod-branched nanocrystals such as CdS(x)Se(1-)(x), CdSe(x)Te(1-)(x) and CdS(x)Te(1-)(x).

Fabrication and Optical Behaviors of Core-Shell ZnS Nanostructures

Novel core-shell nanostructures comprised of cubic sphalerite and hexagonal wurtzite ZnS have been synthesized at 150°C by a simple hydrothermal method. The results of HR-TEM and SAED investigation reveal that the cores of hexagonal wurtzite ZnS (ca. 200 nm in average diameter) are encapsulated by a shell of cubic sphalerite ZnS. The FE-SEM image of the nanomaterials shows a surface tightly packed with nanoparticles (<10 nm in size). The optical properties of the fabricated material have been studied in terms of ultraviolet-visible absorption and photoluminescence. Furthermore, a possible mechanism for the fabrication of the core-shell nanostructures has been presented.

Luminescence in Sulfides: A Rich History and a Bright Future

Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce³⁺ and Eu²⁺, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl₂S₄:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu²⁺-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles.

Effect of Cationic Surfactant Head Groups on Synthesis, Growth and Agglomeration Behavior of ZnS Nanoparticles

Colloidal nanodispersions of ZnS have been prepared using aqueous micellar solution of two cationic surfactants of trimethylammonium/pyridinium series with different head groups i.e., cetyltrimethylammonium chloride (CTAC) and cetyltrimethylpyridinium chloride (CPyC). The role of these surfactants in controlling size, agglomeration behavior and photophysical properties of ZnS nanoparticles has been discussed. UV-visible spectroscopy has been carried out for determination of optical band gap and size of ZnS nanoparticles. Transmission electron microscopy and dynamic light scattering were used to measure sizes and size distribution of ZnS nanoparticles. Powder X-ray analysis (Powder XRD) reveals the cubic structure of nanocrystallite in powdered sample. The photoluminescence emission band exhibits red shift for ZnS nanoparticles in CTAC compared to those in CPyC. The aggregation behavior in two surfactants has been compared using turbidity measurements after redispersing the nanoparticles in water. In situ evolution and growth of ZnS nanoparticles in two different surfactants have been compared through time-dependent absorption behavior and UV irradiation studies. Electrical conductivity measurements reveal that CPyC micelles better stabilize the nanoparticles than that of CTAC. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11671-009-9377-8) contains supplementary material, which is available to authorized users.

Rapid synthesis of core/shell ZnS:Mn/Si nanotetrapods by a catalyst-free thermal evaporation route

We report the fabrication of a hybrid all semiconductor core/shell nanotetrapod structure consisting of crystalline ZnS:Mn core and amorphous Si shell for the first time. The nanostructures were produced via a catalyst-free rapid thermal evaporation technique. Core/shell nanotetrapods were formed in two steps: (i) formation of the crystalline ZnS:Mn tetrapods and (ii) simultaneous surface adsorption of the in situ formed Si vapor species providing the amorphous shell. Crystalline tetrapod formation was guided by the formation of cubic structured ZnS octahedrons with four active (111) polar growth planes, which served as the favored growth site for the four wurtzite structured legs of the tetrapods. Choice of chloride salt as the source of dopant ion was crucial for the in situ generation of Si vapor. At elevated temperature, chloride salt reacted with the sulfur vapor to produce S2Cl2 gas that etched the Si wafers, generating Si vapor. Suppression of the surface-state-related blue emission was observed in the core/shell structures that clearly supported the formation of a shell layer. Elimination of the surface states ensured efficient energy transfer to the dopant Mn ionic state, resulting in the strong orange emission via (4)T(1)-(6)A(1) electronic transition.