HgS Nanocrystals Research Articles

Fabrication of titanium dioxide (TiO2) and mercury sulfide (HgS) heterojunction for photoelectrochemical study

This work reports a chemical solution sensitization of HgS nanocrystals on mesoporous TiO2 films for different deposition times. The adsorption of the precursor ions and the surface growth of the crystal were found to be affected during the temporal deposition of the HgS over spin-coated TiO2 films. The synthesized electrodes were characterized by structural, morphological, wettability, optical, photovoltaic, and electrochemical performances. The results designate the qualitative confirmation of the TiO2/HgS heterojunction formation, and the combination is explored for the photovoltaic application, which is first of its kind.

Terahertz HgTe Nanocrystals: Beyond Confinement.

We report the synthesis of nanocrystals with an optical feature in the THz range. To do so, we develop a new synthetic procedure for the growth of HgTe, HgSe, and HgS nanocrystals, with strong size tunability from 5 to 200 nm. This is used to tune the absorption of the nanocrystals all over the infrared range up to terahertz (from 2 to 65 μm for absorption peak and even 200 μm for cutoff wavelength). The interest for this procedure is not limited to large sizes since for small objects we demonstrate low aggregation and good shape control (i.e., spherical object) while using nonexpansive and simple mercury halogenide precursors. By integrating these nanocrystals into an electrolyte-gated transistor, we evidence a change of carrier density from p-doped to n-doped as the confinement is vanishing.

Manipulation of structural and optical behaviors in zincblende and wurtzite mercuric sulfide (HgS) nanocrystals: atomistic tight-binding theory

To obtain comprehensive information regarding the effect of size and geometric structure on the associated atomistic properties of mercuric sulfide (HgS) nanocrystals, the structural and optical properties of HgS semiconductor nanocrystals were explored numerically using atomistic tight-binding theory. The optical bandgap, charge density, density of states, electron---hole Coulomb energy, and optical spectrum were evaluated for different sizes and geometric structures. Size-dependent computations were realized by changing the diameter of the HgS nanocrystals. In addition, HgS nanocrystals with wurtzite and zincblende geometric structures were compared numerically. The theoretical results highlight that control of the electronic structure and optical properties of HgS nanocrystals can be achieved by changing their size and geometric structure. The dependence of the optical bandgap on the dimension of the HgS nanocrystals is mainly determined by quantum confinement. Finally, the optical properties of zincblende HgS nanocrystals are more promising than those of wurtzite HgS nanocrystals.

Biomimetic Method Synthesis of HgS/Polyurethane Composite Film and Its Sensing Properties to Ba2+

Polyurethane-conjugated HgS nanocrystals with tunable sizes prepared by using biomimetic method. The obtained HgS nanoparticles with good dispersibility were characterized by Fourier transform infrared. Scanning electron microscopy are used to envisage the binding of nanoparticles with functional groups. The polyurethane molecules can control nucleation and growth of HgS crystals by binding on the surface of nanocrystals to stabilize nanoparticles. Quantum confinement effect of polyurethane-conjugated HgS nanocrystals was confirmed by UV-Vis spectra. The nanoparticles exhibit a well-defined emission feature at about 291 nm. The fluorescence results reveal that the PU/HgS nanoparticles film is sensitive to Ba2+, and a small amount of Ba2+ makes the emissions increase rapidly. The emission is hardly affected by other common ions in water. The nanocomposite film is possible to become a special sensor material for Ba2+.

Highly fluorescent, near-infrared-emitting Cd²⁺-tuned HgS nanocrystals with optical applications.

Bulk HgS itself has proven to be a technologically important material; however, the poor stability and weak emission of HgS nanocrystals have greatly hindered their promising applications. Presently, a critical problem is the uncontrollable growth of HgS NCs and their intrinsic surface states which are susceptible to the local environment. Here, we address the issue by an ion-tuning approach to fabricating stable, highly fluorescent Cd:HgS/CdS NCs for the first time, which efficiently tuned the band-gap level of HgS NCs, pushing their intrinsic states far away from the surface, reducing the strong interaction of the environment with surface states and hence drastically boosting the exciton transition. As compared to bare HgS NCs, the obtained Cd:HgS/CdS NCs exhibited tunable luminescence peaks from 724 to 825 nm with an unprecedentedly high quantum yield up to 40% at room temperature and excellent thermal and photostability. Characterized by TEM, XRD, XPS, and AAS, the resultant Cd:HgS/CdS NCs possessed a zinc-blende structure and was composed of a homogeneous alloyed HgCdS structure coated with a thin-layer CdS shell. The formation mechanism of Cd:HgS/CdS NCs was proposed. These bright, stable HgS-based NCs presented promising applications as fluorescent inks for anticounterfeiting and as excellent light converters when coated onto a blue-light-emitting diode.

Biomimetic synthesis and assembly of HgS nanocrystals via a protein inducing process

In this contribution, we report a simple protein-directed biomimetic strategy for fabricating HgS nano-assemblies in pepsin and bovine hemoglobin (BHb) aqueous solutions. Powder X-ray diffraction, transmission electron microscopy (TEM) and high-resolution transmission microscopy were used to characterize the structure and morphology of the nanocrystals, and track the whole growth process of HgS nano-assemblies. The prepared cubic phase HgS nano-assemblies were uniform and monodispersed with homogeneous sizes of around 60 nm (pepsin) and 50 nm (BHb), respectively. Time-dependent TEM results showed that the final products were formed via multi-level assembly by a large number of smaller nanoparticles under the confinement of protein molecules. The interaction between proteins and Hg2+/HgS was assessed by Fourier transform infrared and circular dichroism spectroscopy. Pepsin and BHb molecules have multiple functional groups, such as O–H, C=O and N–H, which could coordinate with Hg2+ ions to induce nucleation and control the growth of HgS nanocrystals. The formation of HgS–protein nanoconjugates resulted in the change of the secondary structure of the protein molecules. In addition, the HgS nanocrystals assembly process is discussed to investigate the growth mechanism.

Synthesis and Optical Characteristics of PAM/HgS Nanocomposites

Polyacrylamide (PAM) -HgS nanocomposites were successfully prepared in polyacrylamide (PAM) matrix. From TEM and XRD characterizations, the synthesized HgS nanocrystals were chain-like spherical in shape with a diameter of about 40-60 nm and high crystalline quality. The quantum-confined effect of HgS nanocrystals was confirmed by UV-vis diffuse reflection spectra. The optical properties of products were investigated by using photoluminescence (PL) spectra, which showed that HgS nanocrystals exhibited good optical properties with maximum emission peak at about 640 and 650 nm at different reaction temperatures. The interaction of HgS nanocrystals with PAM was studied through FT-IR spectroscopy and TG analysis, which suggested that <TEX>$Hg^{2+}$</TEX> could interact with functional groups of PAM. The experimental results indicated that PAM not only induced nucleation, but also inhibited further growth of HgS crystals and play an important role in the formation of PAM/HgS nanocomposites. In addition, the possible mechanism of HgS nanoparticles growth in PAM solution was also discussed.

Air-Stable n-Doped Colloidal HgS Quantum Dots.

HgS nanocrystals show a strong mid-infrared absorption and a bleach of the near-infrared band edge, both tunable in energy and reversibly controlled by exposure to solution ions under ambient conditions. The same effects are obtained by applying a reducing electrochemical potential, confirming that the mid-infrared absorption is the intraband transition of the quantum dot. This is the first time that stable carriers are present in the quantum state of strongly confined quantum dot in ambient conditions. The mechanism by which doping is achieved is attributed to the rigid shifts of the valence and conduction band with respect to the environment, similar to the sensitivity of the work function of surfaces to adsorbates.

Phase transfer-based synthesis of HgS nanocrystals.

Phase transfer techniques possess remarkable advantages for the synthesis of inorganic nanomaterials. In contrast to the abundant reports on the preparation of noble metal nanoparticles using phase transfer, the number of semiconductor nanocrystals syntheses based on phase transfer techniques is still limited. Herein, we report a systematic study of the phase transfer-based synthesis of HgS nanocrystals, including the tuning of their morphology/shape by either solvent choice or temperature. This strategy involves the transfer of Hg(ii) ions from aqueous solution to toluene, oleic acid or oleylamine and subsequent sulfidation at room or elevated temperature. Furthermore, we have extended this phase-transfer based strategy to the fabrication of HgS-Au nanocomposites. The studies in this work might provide a facile route for producing HgS nanocrystals with desirable properties and offer an effective strategy to investigate the influence of the morphology of HgS on the physical/chemical properties of various HgS-based materials.

Synthesis of HgS nanocrystals in the Lysozyme aqueous solution through biomimetic method

In the present work, it is reported for Lysozyme-conjugated HgS nanocrystals with tunable sizes prepared at Lysozyme (Lyso) aqueous solutions by using biomimetic method. The obtained HgS nanoparticles with good dispersibility have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission microscopy (HRTEM) and energy-dispersive X-ray spectrum (EDS). The Lysozyme molecules can control nucleation and growth of HgS crystals by binding on the surface of nanocrystals to stabilize protein-capped nanoparticles. Quantum confinement effect of Lyso-conjugated HgS nanocrystals has been confirmed by UV–vis spectra. The nanoparticles exhibit a well-defined emission feature at about 470nm. Fourier transform infrared (FT-IR) data are used to envisage the binding of nanoparticles with functional groups of Lysozyme. The results of circular dichroism (CD) spectra indicated that the formation of HgS nanocrystals can lead to conformational change of Lysozyme.

One-Step Synthesis and Assembly of Two-Dimensional Arrays of Mercury Sulfide Nanocrystal Aggregates at the Air/Water Interface

Ordered two-dimensional (2D) arrays of β-HgS nanocrystal aggregates were prepared successfully at the air/water interface through the interfacial reaction between Hg(2+) ions in the subphase and H(2)S in the gaseous phase under the direction of liquid-expanded monolayers of arachidic acid (AA). These 2D arrays are composed of hexagonal or quasi-hexagonal aggregates with the size of several hundreds of nanometers that consist of several tens of HgS nanocrystals with the size of several nanometers. The formed HgS nanocrystals together with AA molecules self-assembled into round aggregates due to the interactions between the species, and the aggregates self-assembled into 2D arrays further due to the attractions between them. During the self-assembly process, the soft round aggregates transformed into hexagonal or quasi-hexagonal ones. The experimental conditions, especially the phase states of the AA monolayers and temperature, have great influences on the formation of the 2D arrays. To the best of our knowledge, this is the first case to get 2D ordered arrays at the air/water interface through a one-step synthesis and assembly process.

Moderate temperature synthesis of flower- and dot-shaped HgS nanocrystals

We report a simple, robust, reproducible and phosphine-free approach to synthesize zinc-blende HgS nanocrystals with both flower and dot shapes at moderate temperatures. 1-Octadecylamine was used to effectively adjust the activity of mercury ions. HgS nanoflowers were synthesized with S precursors prepared at temperatures between 100 °C and 210 °C, while individual dot-shaped HgS nanocrystals were obtained when the temperature to prepare S precursors was higher than 210 °C. We proposed that the structure difference of S molecules due to different heating temperatures might affect the final shape of nanocrystals. The as-prepared HgS nanocrystals were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis absorption spectroscopy .

Biomimetic synthesis of HgS nanoparticles in the bovine serum albumin solution

HgS nanocrystals conjugated with protein were synthesized in aqueous solution of Bovine Serum Albumin (BSA) at room temperature. The obtained HgS nanoparticles with average diameter about 20–40 nm were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The quantum-confined effect of the HgS nanoparticles is confirmed by the ultraviolet-visible (UV-vis) and photoluminescence (PL) spectrum. The rescults indicate that the BSA not only induce the nucleation, but inhibit the further growth of HgS nanoparticles. The effect of Hg2+ on BSA and the change of BSA conformation were studied through Fourier transform infrared (FTIR) spectroscopy and Circular dichroism (CD) spectroscopy. The possible mechanism of HgS nanoparticles growth in the BSA solution was also discussed.

Formula omitted]-HgS nanocrystals: Synthesis, structure and optical properties

Well-separated mercury sulfide (HgS) nanocrystals are synthesized by a wet chemical route. Transmission electron microscopy studies show that nanocrystals are nearly spherical in shape with average size of 9 nm. Grazing angle X-ray diffraction confirms that HgS nanocrystals are in cinnabar phase. Particle induced X-ray emission and Rutherford back scattering spectrometry analysis reveal HgS nanocrystals are stoichiometric and free from foreign impurities. The optical absorption measurements show two excitonic peaks corresponding to electron-heavy hole and electron-light hole transitions, which are blue shifted by 0.1 and 0.2 eV, respectively, from its bulk value, due to quantum size effect. The experimental data obtained by optical absorption measurement is simulated with a theoretical model considering the particle size distribution as Gaussian.

STRUCTURAL TRANSFORMATION IN PbS AND HgS NANOCRYSTALS UNDER HIGH PRESSURE

The phase transition induced by pressure in the PbS and HgS nanocrystals was studied by in situ high pressure X-ray powder diffraction measurements. PbS underwent a phase transition from B1-B16 at 7 GPa whereas no transition was observed in HgS up to 15 GPa. The transition remained unaltered on the release of pressure. The volume decreased with an increase in pressure. There is a shift in transition pressure towards the higher side when compared with the bulk materials.

Microwave heating synthesis of HgS and PbS nanocrystals in ethanol solvent

A novel route was developed to prepare PbS and HgS nanocrystals in ethanol solvent in the presence of sodium hydroxide by microwave heating method. PbS and HgS nanocrystals were obtained with an average size of approximately 10 and 6 nm, respectively. In the reaction, mercury acetate and lead acetate were used as mercury and lead source; sulfur powder was employed as chalcogenide source. The products were characterized by X-ray powder analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis absorption spectroscopy. The probable mechanism was presented.

Synthesis of HgS and PbS nanocrystals in a polyol solvent by microwave heating

A novel and quick method for the synthesis of PbS and HgS semiconductor nanoparticles using mercury acetate and lead acetate as source materials and sulfur powder employed as chalcogenide source by microwave heating in polyethylene glycol (PEG) solvent is presented in this paper. HgS and PbS nanoparticles were obtained with average sizes from 20 to 30 nm in PEG, which acts as both solvent and reducing agent. The products were characterized by powder X-ray analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The probable mechanism was presented.

Synthesis and Characterization of Colloidal β-HgS Quantum Dots

High-quality colloidal mercury sulfide quantum dots (QDs) are synthesized at room temperature using a strategy combining the effects of strongly binding Hg(II) ligands and metal/chalcogen precursor phase separation. This combination prevents both the rapid precipitation of bulk HgS in preparations involving only weak Hg(II) ligands and the reduction of mercury that takes place when only strongly binding ligands are used to slow the growth kinetics. Both the linear absorption and complementary band edge emission of the synthesized HgS QDs exhibit narrow, size-dependent transitions between 500 and 800 nm for sizes ranging from 1 to 5 nm in diameter. The metastable zinc blende phase of HgS is verified by wide-angle X-ray diffraction experiments and suggests potentially large tunable band edges if larger HgS nanocrystals that approach the bulk (zero energy) gap can be made. Growth of HgS QDs can be arrested by subsequent addition of Cd or Zn to the surface, after which the QDs can be stabilized with long-chai...

Inorganic: Organic Hybrid Nanocomposites for Photorefractivity at Communication Wavelengths

This paper reports new photorefractive polymeric nanocomposites photosensitized with HgS or PbS nanocrystals and operating at the communication wavelength of 1.3 μm. To our knowledge, it is the first report of a polymeric photorefractive medium with spectral response at a communication wavelength. The nanocomposites involving HgS are prepared by an in-situ nanochemistry approach, whereas those involving PbS were prepared using competitive nanochemistry. Photoconductivity experiments were employed in the characterization of photocharge generation quantum efficiency provided by the semiconductor nanocrystals. The photorefractive nature of the composites is confirmed using electric field dependent two-beam coupling. In the case of nanocomposite containing PbS nanocrystals, a net gain in excess of the associated absorption loss is observed.

A microwave assisted heating method for the rapid synthesis of sphalrite-type mercury sulfide nanocrystals with different sizes

A novel method for the preparation of sphalrite-type HgS ( β-HgS) nanocrystals by microwave irradiation is reported in this paper. Mercury acetate and thiourea were used as mercury source and sulfur source, respectively. It was found that the HgS with different average crystal sizes from 8 to 23 nm were obtained by using different solvents. The products were characterized by powder X-ray diffraction, transmission electron microscopy, electron diffraction, X-ray photoelectron spectroscopy, energy-disperseive X-ray analysis and UV–Visible absorption spectroscopy. The probable mechanism of the formation of β-HgS nanocrystal is discussed.