Preparation and Characterization of PbS Quantum Dots Doped Ormocers

A new method for the preparation of semiconductor PbS quantum dot-doped Ormocer (Organically Modified Ceramic) has been developed. The Ormocer matrix was prepared through the hydrolysis and condensation of alkoxysilane precursors (sol-gel process). Formation of PbS particles took place in the porous Ormocer through H₂S gas reaction with a lead precursor incorporated at the solution stage. Control of the PbS dot size was achieved through the use of organically substituted trifunctional silanes. Particle formation and growth was studied under different experimental conditions (e.g. temperature and lead precursor concentrations) where nucleation and aggregation processes occurred. Determination of the average particle size was done by XRD. Transmission electron microscopy was also used to determine particle diameter as well as particle size distribution. Optical absorption spectra were measured at the UV-VIS wavelength range. Absorption edge blue shifts showed the quantum confinement effect in these materials. The non-hydrolyzed groups bonded to the silane prevented uncontrolled nucleation and aggregation during the particle formation and growth, i.e. at the solution stage by the homogeneous distribution of the Pb salts or at the xerogel state by the capping of the growing particles.     

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and Bis(4-benzylpiperidine-1-carbodithioato)-lead(II) as Precursors for Lead Sulphide Nano Photocatalysts for the Degradation of Rhodamine B

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and bis(4-benzylpiperidine-1-carbodithioato)-lead(II) were prepared and their molecular structures elucidated using single crystal X-ray crystallography and spectroscopic techniques. The compounds were used as precursors for the preparation of lead sulphide nano photocatalysts for the degradation of rhodamine B. The single crystal structures of the lead(II) dithiocarbamate complexes show mononuclear lead(II) compounds in which each lead(II) ion coordinates two dithiocarbamato anions in a distorted tetrahedral geometry. The compounds were thermolyzed at 180 ℃ in hexadecylamine (HDA), octadecylamine (ODA), and trioctylphosphine oxide (TOPO) to prepare HDA, ODA, and TOPO capped lead sulphide (PbS) nanoparticles. Powder X-ray diffraction (pXRD) patterns of the lead sulphide nanoparticles were indexed to the rock cubic salt crystalline phase of lead sulphide. The lead sulphide nanoparticles were used as photocatalysts for the degradation of rhodamine B with ODA-PbS1 achieving photodegradation efficiency of 45.28% after 360 min. The photostability and reusability studies of the as-prepared PbS nanoparticles were studied in four consecutive cycles, showing that the percentage degradation efficiency decreased slightly by about 0.51–1.93%. The results show that the as-prepared PbS nanoparticles are relatively photostable with a slight loss of photodegradation activities as the reusability cycles progress.     

Synthesis and Characterization of Lead Sulfide Nanoparticles in Zirconia-Silica-Urethane Thin Films Prepared by the Sol-Gel Process

PbS nanocrystals (NCs) ranging between 4–8 nm were incorporated into Zirconium-Silica-Urethane (ZSUR) matrix obtained by the sol-gel method. The sizes of the particles were controlled by temperature treatment and by concentration of PbS in ZSUR matrix. The sizes of PbS NCs were determined by TEM measurements. The quantum size effect could also be extracted from optical absorption and photoluminescence spectra. The new matrix allows incorporation of up to 40% PbS forming a characteristic structure of dendrite by reacting lead acetate with ammonium thiocyanate in sol-gel matrix. The sol precursors of the matrix for Zirconium-Silica-Urethane contained zirconium oxide (ZrO₂) matrix solution, tetramethoxysilane (TMOS), 3-glycid oxypropyl trimethoxysilane (GLYMO) and polyethylene urethane silane (PEUS) synthesized separately. The ZrO₂ matrix solution was obtained from zirconium n-tetrapropoxide in propanol and acetic acid was used as a chelating agent to stabilize the zirconium oxide precursor.     

Photolysis of aqueous solutions of lead thiosulfate thiourea complexes

Photolysis of aqueous solutions of lead thiosulfate thiourea complexes by the action light from a mercury lamp (λ = 253.7 nm) was investigated. The optimal conditions for photolysis of the photosensitive compounds were found. The kinetic parameters for the buildup of photolytic PbS formed on a paper substrate were determined. The morphology of PbS particles was studied by means of microscopic analysis.     

Fabrication of symmetric hierarchical hollow PbS microcrystals via a facile solvothermal process

Symmetric hierarchical hollow PbS structures consisting of nanowalls were successfully fabricated by a facile solvothermal process in ethylenediamine at 120 degrees C for 12 h, employing lead acetate trihydrate and dithizone as precursors; the thickness of the nanowalls is about 80 nm. No surfactants or other templates were used in the process. The synthesized product was characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), ultraviolet-visible spectrometer (UV-vis), near-infrared absorption spectroscopy (near-IR), and fluorescence spectrophotometer. The effect of the reaction conditions on the size and morphologies of PbS structures was investigated. The results show that the temperatures, solvent, and sulfur sources are crucial factors on the morphologies and sizes of the symmetric hierarchical hollow PbS microcrystals. A possible growth mechanism of hierarchical hollow PbS structures is presented. UV-vis absorption spectrum holds a weak peak at 253 nm; the near-infrared absorption spectrum of PbS microcrystals has the two absorption peaks centered at 9613 cm(-1) (1040 nm) and 6771 cm(-1) (1477 nm), showing a blue shift compared with the bulk PbS (approximately 3020 nm). And the fluorescence spectrum of PbS microcrystals consists of an emission peak with a maximum at 305 nm. These PbS microcrystals may have potential applications in the fundamental study of nanostructures as well as fabricating nanodevices.     

Synthesis and photophysics of leadsulphide nanocrystallites

Nanoparticles of lead sulphide have been stabilized in the presence of excess Pb²⁺ in aqueous basic medium by a simple chemical route of synthesis. These PbS nanoparticles were synthesized very conveniently at room temperature using hexametaphosphate as stabilizer. These nanoparticles have an absorption extending into the NIR region. A significant quantum confinement effect made the bandgap of lead sulphide nanoparticles produce a blue shift from 0.41 eV to about 1.5 eV. The size and morphology of the particles were studied by TEM. Particles were relatively small sized (about 6 nm) having narrow size distribution. XRD data analysis indicate that the product is a mixture of PbS, PbO and Pb(OH)₂. Both XRD pattern and HRTEM images confirm the crystalline structure of lead sulphide crystals. IR spectroscopy indicates the formation of PbS. PbS nanoparticles were fairly stable and could be stored for about three weeks at room temperature and for about two months at 5°C without agglomeration. These particles were photoactive and sensitized the reaction of aniline by light leading to the formation of azobenzene.     

Formation of SnS,SnS<Subscript>2</Subscript>, and PbS films from thiourea coordination compounds

Deposition of semiconductor tin and lead sulfide films from thiourea coordination compounds was examined. The nature of the ligands in the intermediate complexes formed was determined, and the influence of these precursors on the formation and phase composition of SnS, SnS₂, and PbS thin layers was examined.     

Zeolite-modified paraffin-impregnated graphite electrode

This paper describes a new kind of zeolite-modified electrodes (ZMEs) based on the physical immobilization of zeolite particles onto the surface of paraffin-impregnated graphite electrodes (PIGEs). Their electrochemical behavior was first evaluated by ion-exchange voltammetry using methylviologen as a model redox probe, indicating better performance in comparison to the corresponding zeolite-modified carbon paste electrodes. The zeolite-modified-PIGEs were then applied to the study of lead(II)-loaded zeolites to monitor their reaction with sulfide ions at various sulfidation levels. Both Pb(II) ions and PbS nanoparticles gave rise to well-defined voltammetric signals, but peak currents due to the more mobile Pb(II) ions were much higher than those recorded for PbS nanoparticles. This is due to the fact that Pb(II) ions underwent ion exchange for the electrolyte cation prior to the electron transfer whereas the PbS nanoparticles are immobilized in the microporous structure of the zeolite particles and thus less available for the redox reactions. Nevertheless, these signals were useful to discriminate between the various sulfidation levels, as ascertained by additional X-ray photoelectron spectroscopy measurements.     

聚合物对硫化铅钠米微粒的稳定作用

以含铅聚合物微凝胶与Ｈ２Ｓ气体反应制得ＰｂＳ纳米微粒／聚合物复合体系，利用小角Ｘ光散射方法对复合在聚合物中的ＰｂＳ纳米微粒的粒度及分布进行了表征，研究了不同反应条件对其粒度及复合体系稳定性的影响。     

Fabrication of polystyrene–PbS core-shell and hollow PbS microspheres with sulfonated polystyrene templates

Uniform inorganic- (PbS) coated polymer core-shell and hollow PbS microspheres were prepared by an easy and economical approach. Monodisperse polystyrene (PS) microspheres were used as templates, as well as the core of the composite spheres; lead sulfide shells were obtained through the reaction of lead acetate (Pb(CH₃COO)₂) and thioacetamide (TAA) at room temperature. The morphologies and structures of the as-synthesized products were systematically characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), and Fourier transform infrared spectra (FTIR). The fluorescence property of the as-synthesized product was also investigated. A reasonable mechanism for the formation of PS–PbS core-shell and hollow PbS microspheres was discussed. According to a series of parallel experiments, effects of related experimental parameters were also carefully investigated, such as the molar ratio of Pb(CH₃COO)₂ to TAA, reaction temperature, etc.     

Formation and x-ray and electron diffraction study of Cds and Pbs particles inside fatty acid matrix

Langmuir-Blodgett films of lead and cadmium stearate were treated by exposure to H₂S atmosphere. Such treatment lead to formation of CdS and PbS particles and protonation of stearic acid head-groups. The process was studied by small-angle X-ray scattering. The reaction was shown to be completed after 5 hours of treatment.     

Controlled synthesis of high-quality PbS star-shaped dendrites, multipods, truncated nanocubes, and nanocubes and their shape evolution process

Well-defined single-crystalline PbS nano- and microstructures including dendrites, multipods, truncated nanocubes, and nanocubes were synthesized in high yield by a simple solution route. Novel star-shaped PbS dendrites with six symmetric arms along the 100 direction, each of which shows one trunk (long axis) and four branches (short axes), have been achieved using Pb(AC)2 and thioacetamide (TAA) as precursors, under the molar ratio Pb(AC)2/TAA = 2/1, at initial reaction temperature 80 degrees C, refluxing for 30 min at 100 degrees C, in the presence of cetyltrimethylammonium bromine (CTAB). The "nanorods" in each branch are parallel to each other in the same plane and are perpendicular to the trunk. The truncated nanocubes mainly bounded by the {100} plane were prepared under a different Pb(AC)2/TAA molar ratio, at initial reaction temperature 40 degrees C, refluxing for 12 h at 100 degrees C. Based on the systematic studies on their shape evolution, a possible growth mechanism of these PbS nano- and microstructures was proposed. The shapes of PbS nanocrystals with face-centered cubic (fcc) structure are mainly determined by the ratio (R) between the growth rates along the (100) and (111) directions. The Pb(AC)2/TAA molar ratio and the initial reaction temperature influence the growth ratio R in the formation of PbS nuclei at an early stage, which results in the final morphology of PbS nanocrystals. Under the current experimental conditions, we can control the PbS shape evolution by simply tuning the molar ratio, the initial reaction temperature, and the period of reaction. Based on the systematic studies on the shape evolution, this approach is expected to be employed for the control-shaped synthesis of other fcc structural semiconductor nanomaterials. The photoluminescence properties were investigated and the prepared nano- and microstructures displayed a very strong luminescence around 600-650 nm at room temperature.     

Preparation of ultrasmall, uncapped PbS quantum dots via electroporation of vesicles

Electric-field-induced transient pore formation (electroporation) in synthetic unilamellar dioleoylphosphatidylcholine vesicles of 178-nm diameter is utilized for the preparation of subnanometer-size PbS quantum dots. With Pb2+ ions originally entrapped in the vesicles and S2- ions placed in the bulk, their reaction is initiated by the opening of pores and occurs in the bulk. The ensuing self-aggregation of PbS is slowed to the hour and day time scales by its adsorption at the exterior surface of the vesicles. The growth of the particles in the molecular size regime is found to exhibit novel, time-dependent, oscillating red and blue shifts of the characteristic UV absorption band. On the basis of similarities between the oscillating trend of the experimentally observed transition energy and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital gap of (PbS)n clusters with n = 1-9, the wavelengths of the sequential spectral peaks can be assigned to the PbS monomer (237.5 nm), dimer (282 nm), tetramer (232 nm), hexamer (281 nm), octamer (234.5 nm), and nonamer (278-280 nm). Growth beyond the octamer is associated with the customary monotonic red shift of the absorption band. Under the experimental conditions used, a stable system is reached with unchanging spectral features after 20 days. This solution is estimated to contain 1.82 x 10(-5) M (PbS)9 particles, each with a greatest dimension of <9 A.     

Controlled synthesis of bionic microstructure PbS crystals by mixed cationic/anionic surfactants

Hexagonal starfish-like PbS crystals have been synthesized by the reaction of lead acetate and thioacetamide (TAA) controlled by mixture of cetyltrimethylammonium bromide/sodium dodecyl sulfate (STAB/SDS) at the molar ratio of 5: 1 through a hydrothermal process at 80°C. It has been found that the hexagonal starfish-like PbS single crystal is in cubic phase, and the six arms of the star extend along the six 〈100〉 directions. By changing reaction conditions, such as the molar ratio of CTAB/SDS, temperature, and reaction time, the amounts of TAA and lead sources, the morphology and structure of the PbS crystals can be controlled. Furthermore, possible formation mechanism was preliminarily illustrated. The room-temperature photoluminescence spectra in solid state of the PbS single crystals obtained after different reaction times were investigated, which demonstrated that the PbS single crystals presented excellent optical properties. This work may open a novel route to the shaped-controllable synthesis of semiconductor crystals with various morphologies.     

A 31P CP/MAS NMR study of PbS surface O,O'-dialkyldithiophosphate lead(II) complexes

31P CP/MAS NMR spectroscopy was used to study the adsorption of six different O,O'-dialkyldithiophosphate ions on the surface of synthetic galena (PbS). The 31P CP/MAS NMR spectra of the surface lead(II) dithiophosphates were compared with the 31P CP/MAS NMR spectra of polycrystalline lead(II) dithiophosphate complexes of the same ligands. Surface complexation of the dialkyldithiophosphate ions was established on the surface of PbS. A terminal S,S(')-chelating coordination is suggested for the surface complexes. The bulkier alkyl groups lead to surface precipitation in addition to the surface adsorption. Derivatives of monothiophosphoric and phosphoric acids were displayed as hydrolysis products of dialkyldithiophosphates on the synthetic PbS, the amount of which depends on the type of alkyl group.     

花生酸单分子膜诱导PbS晶体取向生长的研究

以花生酸单分子膜为模板，诱导沉积了PbS半导体纳米粒子，粒径为30～50 nm.实验发现， 由于花生酸单分子膜的诱导作用， 使得PbS晶体在膜上发生取向生长，可以形成三角形、四边形和棒状的PbS纳米粒子.通过改变单分子膜的表面压，考察了表面压对PbS晶体取向生长的影响，结合透射电镜及电子衍射实验，对PbS晶体的生长机制进行了初步的分析和探讨.     

用软刻蚀方法制备PbS纳米晶复合聚丙烯酸微图形

PbS microstructures have several applications such as Pb2+ion-selective sensors and IR detector.The method to prepare PbS nanocrystal embed in poly(acrylicacid) (PAA) microstructures produced by means of soft lithography and solid state polymerizatio n by γ-ray irradiation was described. PbS micro patterns were prepared by Micro molding in Capillaries (MIMIC) with aqueous solution of acrylic acid lead monomer, and then solid state polymerized by γ-ray irradiation. Finally, the sample was treated with aqueous solution of Na2 Stoconvert the Pb2+ to PbS in the matrix. High-resolution micro structures of PAA, which have PbS nanocrystals embedded in them, could be produced successfully in this way. The final products were characterized by TEM, XRD, and XPS. TEM image indicated that the PbS particles embedded in PAA had a diameter of smaller than 20nm. X-ray powder diffraction method was also used to characterize the PbS/PAA nanocomposite film. The XPS analysis showed the element Pb has been converted to PbS nanoparticles in the composite films.     

Synthesis of single‐core and multiple‐core core‐shell nanoparticles by RAFT emulsion polymerization: Lead sulfide‐copolymer nanocomposites

We report here a simple and direct route for the preparation of lead sulfide (PbS) quantum dots (QDs) embedded into polymeric nanospheres by emulsion polymerization. In this process, QDs are first dispersed in an aqueous solution containing a statistical oligomer constituted of five butyl acrylate and ten acrylic acid units prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a trithiocarbonate as RAFT agent. Then, the dispersion of PbS QDs is engaged into an emulsion polymerization process to form core‐shell nanoparticles. Transmission electron microscopy reveals the presence of single‐core core‐shell particles at low concentration of PbS QD, whereas multiple‐core core‐shell particles containing either well separated or aggregated PbS QDs are formed at high concentration of PbS QDs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The solventless syntheses of unique PbS nanowires of X-shaped cross sections and the cooperative effects of ethylenediamine and a second salt

Unique PbS nanowires with x-shaped cross sections, with diameters in the range of 300-800 nm with an average of 598 nm (sigma = +/-21.7% ), and lengths of up to several tens of micrometers, have been made by a solventless method. Such nanowires show high adsorptivities of the PbS nanooctahedra, which can be washed off by ultrasound. The suitable precursor is obtained from a Pb(NO3)2/octanoate/ethylenediamine/dodecanethiol molar ratio of 1:2:1:1.6, and the PbS nanowires are produced by the thermolysis of such precursors at 280 degrees C for 1 hour. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations of the products and the keys of the morphological control have been reported. For the formation of such products, two cooperative effects are found to be crucial, the roles of ethylenediamine and a second salt, lead octanonate.     

Considering the polynuclear complexes in the ionic equilibria of the Pb2+-H2O system

Analysis of conditions of the lead hydroxide and sulfide formation in the Pb²⁺-H₂O system was carried out with accounting for the formation of polynuclear hydroxo-complexes. This allows predicting a possibility of the lead hydroxide formation in the solution before the beginning of the synthesis of lead sulfide. The domains of the stable formation of Pb(OH)₂ and PbS were calculated for the systems containing lead citrate complexes and hydroxo-complexes. The proposed calculation method can be used for the quantitative determination of the reaction mixture composition and development of the chemical deposition technology of lead chalcogenides in different morphological forms: nanocrystalline powders (hydrophobic sol), quantum dots, heterostructures of the core@shell type or films. The proposed calculation method is applicable to other chalcogenide systems containing metal ions forming mononuclear and polynuclear hydroxo-complexes.