PbS Nanoclusters Research Articles

Metal sulfide sub-nanometer clusters formed within calix(8)arene Langmuir-Blodgett films

This work describes the construction of layered Langmuir-Blodgett (LB) films of a calixarene and the use of these as matrices for the synthesis of a range of metal sulfide nanoparticles. CuS, CdS, HgS, and PbS nano-clusters were formed within LB films of an octa-tertbutyl-calix(8)arene substituted with carboxylic acid groups deposited on different substrates (glass, quartz, and silicon) from either: (i) aqueous sub-phases containing 0.5 mM of the respective metal chloride salt (e.g. CuCl2, CdCl2, HgCl2, PbCl2), or (ii) by soaking the LB films in 10 mM solutions of the above salts for 1 h. The formation of metal-sulfide (MeS) nanoparticles was then achieved by exposing samples to H2S gas for 10–12 h.Deposition from salt containing subphases was more reliable and resulted in stoichiometric metal sulfides (CdS, HgS, PbS) being formed within LB films of the calix(8)arene carboxylic acid whereas Cu tended to form polysulfides. UV–vis absorption spectroscopy showed the presence of multiple absorption bands corresponding to electron transitions between energy levels in nanoclusters formed as result of quantum confinement of electrons and holes. The MeS clusters obtained by this process are amongst the smallest reported for LB films, being of the range 0.6–1.2 nm.

Influence of particle size on the magneto-refractive effect in PbS quantum dots-doped liquid core fiber

In this study, magneto-refractive effects of PbS quantum dots (QDs)-doped liquid core fiber with different particle sizes were investigated. Based on the density function theory, the defect structures of PbS nanoclusters were constructed and the spin magnetic moments of sulfur (S) and plumbum (Pb) were analyzed. It indicates that the magnetic moments are mainly induced by the spin interaction between Pb 6s, 6p, and S 3p states, and the spin magnetism shows a weakening trend as the particle size increases. Based on the analysis, we experimentally studied the magneto-refractive effect with different sizes PbS QDs in liquid core fibers through a magneto-refractive index measuring system. The experimental results show that the magneto-refractive effect is strong as the size of PbS QDs decreases when the concentration is 8 mg/mL, exhibiting a maximum magneto-refractive sensitivity of -1.668×10−3 RIU/mT under the magnetic field of 0-7.89 mT, which can be used for magnetic field sensing applications.

Photoluminescence of the PbS quantum dots fabricated by the Langmuir-Blodgett technique

The optical and structure properties of the PbS nanoclusters in the Langmuir-Blodgett matrix as well as their properties after the matrix removal in the ammonium atmospheres have been studied. According to the electron microscopy data, it has been established that there are PbS nanoclusters formed on the surface of the samples. It has been found that the matrix removal results in a significant enlargement of the PbS nanocrystals accompanied by the shift of the luminescence into the infra-red range. It has been shown that the PL intensity of PbS quantum dots (QDs) in the matrix decreases with the temperature decrease due to the carrier transfer into defect QDs whereas the the luminescence intensity of the PbS nanocrystals without a matrix grows at the temperature increase.

Enhanced charge collection and photocatalysis performance of CdS and PbS nanoclusters co-sensitized TiO2 porous film

A novel translucent TiO2 porous film was prepared through etched method. The CdS, PbS and CdS/PbS nanoclusters were imbedded on TiO2 porous film by successive ionic layer adsorption and reaction method. Microstructure, morphology, optical and photoelectron-chemical properties of the as-synthesized thin films were investigated systematically. XRD and morphology analysis showed that PbS or CdS nanoclusters have been attached to the TiO2 porous films. It was found that the energy band gap of TiO2 porous film decreased from 3.46 to 3.2 eV after sensitized with nanoclusters. The photocurrent density of ITO/TiO2 photoelectrode increased from 0.017 to 0.28 mA/cm2 after co-sensitized with CdS and PbS nanoclusters. Besides, the photoelectrode sensitized with two sorts of nanoclusters showed evident higher photocurrent density than which sensitized just one sort of nanoclusters. The photocurrent density of ITO/TiO2/PbS and TO/TiO2/CdS photoelectrode was 0.11 mA/cm2 and 0.22 mA/cm2 respectively. 0.28 mA/cm2 can be obtained by ITO/TiO2/CdS/PbS photoelectrode. The results showed that the optical and photoelectrochemistry properties and phtotcatalysis performance of TiO2 porous film were greatly improved by co-sensitized with CdS and PbS nanoclusters.

Growth of PbS nanoclusters on specific sites of programmed oligodeoxynucleotides**Project supported by the National Natural Science Foundation of China (Grant Nos. 11104328, 10904164, and 11004234) and the Knowledge Innovation Program of Chinese Academy of Sciences (Grant No. kjcx3.syw.n8).

We develope a method to synthesize PbS nanoclusters (NCs) using guanine-containing oligodeoxynucleotides (ODNs) as templates. The NCs on the ODNs are ultra small (ranging from ∼ 0.5 nm to 2.1 nm) and luminescent in the visible region. They are characterized by photoluminescence (PL) spectra, transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). The ODN–NC complexes can be used as customer-designed fluorophores which do not have the problem of multiple conjugations. The same method enables us to fabricate PbS quantum dot molecules and connect them into nanowires, expanding their potential applications in molecule electronics and quantum computing.

Novel Visible Emission and Mechanism Investigation from PbS Nanoclusters‐Doped Borosilicate Glasses

Borosilicate glasses doped with PbO, ZnS, or PbS were fabricated to investigate the visible emissions (one located at 370 nm and another at 550 nm) observed in the PbO and ZnS codoped glass. Several series of glassy systems were designed to investigate the mechanism of above visible emissions. The absorption, photoluminescence (PL), photoluminescence excitation (PLE) spectra, and lifetime measurements were used to characterize all the emissions. The nanosecond level lifetimes for all the samples' 370 nm emissions ascribed the 370 nm emission to the glass defects. Measured lifetimes for the PbS quantum dots (QDs) in the glasses with an emission in the near‐infrared region which was about 8 μs was close to the values for the yellow emission, which confirmed the formation of PbS nanoclusters in the codoped glass was responsible for the yellow emission.

Biotin-avidin-conjugated metal sulfide nanoclusters for simultaneous electrochemical immunoassay of tetracycline and chloramphenicol

We report on a protocol for a simultaneous competitive immunoassay for tetracycline (TC) and chloramphenicol (CAP) on the same sensing interface. Conjugates of TC and of CAP with bovine serum albumin were first co-immobilized on a glassy carbon electrode modified with gold nanoparticles. In parallel, monoclonal anti-TC and anti-CAP antibodies were conjugated onto CdS and PbS nanoclusters, respectively. In a typical assay, the immobilized haptens and the added target analytes competed for binding to the corresponding antibodies on the nanoclusters. Subsequently, Cd(II) and Pb(II) ions are released from the surface of the corresponding nanoclusters by treatment with acid and then were detected by square wave anodic stripping voltammetry. The currents at the peak potentials for Cd(II) and Pb(II) were used as the sensor signal for TC and CAP, respectively. This multiplex immunoassay enables the simultaneous determination of TC and CAP in a single run with dynamic ranges from 0.01 to 50 ng mL−1 for both analytes. The detection limits for TC and for CAP are 7.5 pg mL−1 and 5.4 pg mL−1, respectively. No obvious nonspecific adsorption and cross-reactivity was observed in a series of analyses. Intra-assay and inter-assay coefficients of variation were less than 10 %. The method was evaluated by analyzing TC and CAP in spiked samples of milk and honey. The recoveries range from 88 % to 107 % for TC, and from 91 % to 119 % for CAP.

Facile and Room Temperature Preparation and Characterization of PbS Nanoparticles in Aqueous [EMIM][EtSO4] Ionic Liquid Using Ultrasonic Irradiation

At room-temperature, a facile, seedless, and environmentally benign green route for the synthesis of star like PbS nanoclusters at 7 min in aqueous solution of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM] [<TEX>$EtSO_{4}$</TEX>], room-temperature ionic liquid (RTIL), via ultrasonic irradiation is proposed. The X-ray diffraction studies display that the products are excellently crystallized in the form of cubic structure. An energy dispersive X-ray spectroscopy (EDX) investigation reveals the products are extremely pure. The absorption spectra of the product exhibit band gap energy of about 4.27 eV which shows an enormous blue shift of 3.86 eV that can be attributed to very small size of PbS nanoparticles produced and quantum confinement effect. A possible formation mechanism of the PbS nanoparticles using ultrasonic irradiation in aqueous solution of the RTIL is presented.

Preparation and characterization of PbS nanoclusters made by using a powder method on ionomers

By using a powder method, a new method for producing semiconductor/polymer nanocomposites, lead sulfide (PbS) nanoparticles were prepared and dispersed in either poly(methylmethacrylate- co-methacrylic acid) or poly(styrene- co-styrenesulfonic acid). The size of the nanoclusters was less than 2 nm, and the size distribution was rather sharp, determined by UV–vis absorption spectroscopy. The absorption spectra of the PbS-containing sheets showed a blue shift and the absorption edges were steep, reflecting the formation of nano-sized PbS clusters. The spectra also exhibited an absorption maximum, which is an indication of a narrow particle size distribution. The glass transition temperature ( T g) of the PbS-containing nanocomposites was higher than that of the corresponding ionomer. The effect of heat treatment on the aggregation of PbS is also discussed. The dissolution of powder samples, followed by neutralization of acidic groups, led to reduction of particle sizes, suggesting the usefulness of ionic groups for stabilizing PbS nanoclusters.

Effect of the organic solvent on the formation and stabilization of CdS and PbS nanoclusters

Nanoclusters of CdS and PbS were prepared using two different organic solvents as stabilizers in order to understand the factors affecting their formation and stabilization. Growth of the nanoclusters was monitored by optical absorption spectroscopy at regular intervals of time. Mean cluster size was characterized by X-ray diffraction (XRD). The surface structure of nanoclusters was analyzed using infrared (IR) spectroscopy. Spectroscopic studies under identical experimental conditions reveal interesting correlations between the stability of the nanoclusters formed, the nature of the solvent and the size of metal ion involved, leading to a better understanding of nanocluster formation.

Theoretical Study of the Electronic Structure of PbS Nanoclusters

The semiempirical tight-binding method was used to study the electronic structure of spherical PbS nanocrystals. The effects of spin-orbit coupling were included, and the calculated band gaps were found to agree well with previously published experimental values for PbS clusters. The size dependence of the band gaps was studied for clusters containing as many as 912 atoms (35-A diameter). Direct diagonalization was used for small clusters, and Lanczos recursion was used to determine the band gaps and the eigenfunctions for the larger clusters. Analysis of the eigenfunctions revealed that the HOMO and LUMO states were spread throughout the cluster. Densities of states for the PbS nanoclusters converged to the bulk density of states, and the joint densities of states were computed as an approximation to the absorption spectra of the nanoclusters.

Synthesis of PbS Nanoclusters within Block Copolymer Nanoreactors

We have demonstrated the synthesis of PbS nanoclusters within the microphase-separated films of diblock copolymers containing carboxylic acid units on one of the blocks. Lead was selectively sequestered into the acid containing domains by treating the polymer films with tetraethyllead, and PbS was formed by subsequently treating the films with H2S. The PbS nanoclusters were characterized by X-ray diffraction, X-ray fluorescence, electron microscopy, and UV−vis spectroscopy. The cluster size could be controlled by varying processing parameters such as temperature, the presence of coordinating bases, and the H2S exposure time. Increasing the size of the nanoreactors increased the cluster size. The universal cluster synthesis scheme enabled multiple passes through the process, which were used to increase the cluster size and which could in principle be used to passivate the surface of the PbS cluster or to produce mixed semiconductor clusters.

Synthesis of PbS Nanoclusters within Microphase-Separated Diblock Copolymer Films

Synthesis of PbS Nanoclusters within Microphase-Separated Diblock Copolymer Films

Optical Properties of Lead Sulfide Nanoclusters: Effects of Size, Stoichiometry and Surface Alloying

ABSTRACTThe optical absorption and photoluminescence properties of nanosize PbS clusters synthesized in inverse micelles are presented. Relative to bulk crystals, the bandgap of PbS nanoclusters is significantly blue shifted from the near-IR into the visible and near-UV region with decreasing cluster size. The optical absorption spectra for clusters with a diameter of ∼2.5-3 nm contain a molecular-like feature at 284 nm (4.37eV) which matches the absorption of diatomic PbS. The main photoluminescence band occurs at 520 nm and is due to recombination at surface states. The PLE spectrum of the 520 nm band has a minimum which coincides with the absorption peak. The absorption line is interpreted to arise from a pre-dissociative excitation of PbS molecules on the surface. The PLE band is interpreted to be an excitation of molecular-like levels in the interior of the cluster. Evidence from size, stoichiometry and surface alloy (Au) dependent properties supports this interpretation.