Preparation of uniform colloidal cadmium and lead selenide particles

Colloidal cadmium selenide and lead selenide particles of narrow size distribution were prepared by decomposition of selenourea in solutions of corresponding metal salts. While both salts were crystalline, CdSe powders showed nearly spherical morphology whereas PbSe consisted of particles of cubic symmetry. In the latter case greater uniformity was achieved if homogeneous precipitation was carried out in methanol-water mixtures.     

Unraveling internal structures of highly luminescent PbSe nanocrystallites using variable-energy synchrotron radiation photoelectron spectroscopy

The internal structure of PbSe nanocrystals was deduced using synchrotron X-ray photoemission spectroscopy for three different sizes of nanocrystals. The photoemission data revealed the layered structure of PbSe nanocrystals with the crystalline PbSe core surrounded by a nonstoichiometric Pb(1-x)Se shell, finally passivated by a capping agent in the outermost layer. A detailed analysis of the experimental data yielded quantitative information on the thickness of three different layers, which is unavailable through any other technique; moreover, the overall sizes of the nanocrystals probed by transmission electron microscopy were in agreement with the corresponding quantity obtained in the present experiment. The present results provide a plausible explanation for the strong variation in the photoluminescence intensity with size observed for these nanocrystals.     

Selenide‐chitosan as High‐performance Nanophotocatalyst for Accelerated Degradation of Pollutants

Water pollution is one of the major global challenges today. Water bodies are contaminated by the heavy release of waste effluents of textile industries, which includes intensively colored dye pollutants. Herein, a ternary nanocomposite of bismuth copper selenide with small particle size and ternary metal selenide (TMS)‐chitosan microspheres (TMS‐CM) of the spherical porous surface were successfully synthesized. SEM, XRD, EDX, FTIR, and UV/Vis spectrophotometry analysis revealed the structural and morphological characteristics of the newly synthesized nanocomposites. SEM imaging showed the average diameter of TMS nanoparticle to be 33 nm. The crystal size was calculated as 6.33 nm and crystalline structure as orthorhombic using XRD findings. EDX confirmed the presence of Bi, Cu, and Se in the ternary nanocomposite. The bandgap of 1.8 eV was calculated from Tauc's plot for the TMS nanocomposite. SEM confirmed the successful synthesis of spherical TMS‐CM microspheres of porous surface morphology with an average size of 885.6 μm. The presence of chitosan microspheres in the synthesis of TMS nanocomposite was identified by FTIR spectral analysis. Furthermore, highly efficient photocatalytic degradation (up to 95.4%) of ARS was achieved within 180 min at pH 4.0 using 0.5 g of TMS‐CM in sunlight. The first‐order kinetic model fitted well to the photocatalytic decontamination of ARS using TMS‐CM with a rate constant of 6.1x10^?2 min^?1. The TMS‐CM gave attractive results and high efficiency in photocatalytic degradation of ARS dye after reusing and regeneration of up to seven successive cycles. The newly synthesized nanophotocatalyst could be efficiently used for the decontamination of dye polluted water from textile industries.     

PbSe/CdSe and PbSe/CdSe/ZnSe hierarchical nanocrystals and their photoluminescence

Multiple CdSe and ZnSe semiconductor shells were grown on PbSe semiconductor spherical cores with monolayer control. For CdSe shell coating, we found that there was little room to further increase the quantum yields of freshly-made high-quality PbSe nanocrystals that already owned very high initial values because of their good surface status; but there was great improvement for the PbSe nanocrystals with low initial quantum yields because of the poor surface status. Nonetheless, the quantum yield for the latter case could not reach the former's value. Additional ZnSe shells on PbSe/CdSe could further increase the quantum yield and protect the nanocrystals from air oxidation. The observed phenomena in the synthesis of the PbSe/CdSe and PbSe/CdSe/ZnSe core/shell structures were explained through the carrier wave function expansion and the surface polarization.     

From Atomistic Surface Chemistry to Nanocrystals of Functional Chalcogenides

Synthesis and utilization of nanocrystals are highly active fields of current research, but they require a thorough understanding of the underlying crystal surfaces. In this Minireview, we span the arc from surfaces to free nanocrystals, and onward to their chemical synthesis, using as examples lead selenide (PbSe), tin telluride (SnTe), and their direct chemical relatives. Besides experimental insights, we highlight the increasingly influential role played by quantum‐chemical simulations of surfaces and nanocrystals. What can theory do today, or possibly tomorrow; where are its limits? Answering these questions, and skillfully linking them to experiments, could open up new atomistically (that is, chemically) guided perspectives for nanosynthesis.     

Synthesis of lead chalcogenide nanocrystals and study of charge transfer in blends of PbSe nanocrystals and poly(3-hexylthiophene)

Nearly monodisperse lead chalcogenide (PbE, E = S, Se, or Te) semiconductor quantum dots of controllable shape have been produced via a novel synthesis which includes the occurrence of in situ formed Pb(0) particles. Tunable size and shape are achieved through appropriate choice of the precursor type and the stabilizer. As precursor, we use, on the one hand, lead oxide or lead acetate, on the other hand, tellurium, selenium, or sulfur powder dissolved in trioctylphosphine (TOP), tributylphosphine (TBP), or 1-octadecene (ODE). Oleic acid (OA) and various amines, as well as TOP and TBP are used for stabilization. With respect to possible application in hybrid solar cells, the surface of as-synthesized spherical PbSe nanocrystals was investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS) and thermogravimetric analysis (TGA). As an important result, it was found that the surface is not mostly covered by oleic acid after synthesis, but by a phosphorus compound. We also applied a ligand exchange procedure with hexylamine and found evidence for the successful attachment of hexylamine to the nanocrystal surface. Additionally, charge separation between these nanoparticles and the conjugated polymer poly(3-hexylthiophene) (P3HT) is studied by electron spin resonance and photoinduced absorption spectroscopy. The spectra obtained suggest that charges can be produced successfully by photoinduced charge transfer.     

两种不同Pb源对PbSe纳米晶生长的影响

采用有机相合成法, 分别以PbO和醋酸铅[Pb(Ac)₂]作为铅源, 研究了在不同反应温度和反应时间下, 不同铅源对PbSe纳米晶生长的影响. 实验结果表明, 以PbO作为铅源, 油酸(OA)作为配体时, 在不同的反应温度下得到了球形PbSe纳米晶和截角八面体PbSe纳米晶; 选择Pb(Ac)₂作为铅源时, 在不同的温度下得到了PbSe纳米花和PbSe纳米星. 选择不同铅源得到的PbSe纳米晶形貌完全不同, 这主要是由于醋酸根的引入产生了不同的空间位阻, 引起纳米晶导向吸附并形成纳米花. 而随着反应温度的升高和反应时间的延长, 这些不同形貌的PbSe纳米晶最终会演变成纳米立方块, 这主要是由PbSe的晶体特性决定的.     

Synthesis of Barium Lithium Fluoride Nanocrystals Using Reverse Micelles as Microemulsion

Barium lithium fluoride nanocrystals were synthesized in cetyltrimethylammonium bromide (CTAB)/2-octanol/water microemulsion systems. The impurity peaks in XRD patterns were not determined. The result of SEM confirmed that the average sizes and shape of the BaLiF3 nanocrystals. The formation of BaLiF3 and particles size were strongly affected by water content. With increasing water content and reaction times, the size of the particle increases.Meanwhile, the solvent was also found to play a key role in the synthesis of the BaLiF3 nanocrystals.     

Solvothermal Synthesis and Characterization of PbSe Nanostructures with the Aid of Schiff-base Ligand

In this work, Pb(II)N,N-bis(salicylidene)-ethylenediamine; [Pb(salen)]; was applied as lead precursor to synthesis PbSe nanostructures. Besides [Pb(salen)], SeCl₄ and reducing agents like N₂H₄·H₂O have been employed for the production of PbSe nanostructures via a solvothermal route at 180 °C for 3 h in propylene glycol. The effect of preparation factors such as temperature, reaction time, and surfactant on the morphology of PbSe nanostructures was investigated. The experimental results indicated that PbSe synthesized at 150 and 210 °C was composed of agglomerated particles. On the other hand, the use of KBH₄ as reducing agent led to produce PbSe with higher particle size and agglomeration. The as-prepared PbSe nanostructures were characterized by XRD, SEM, TEM, EDS, and FT-IR.     

Electrodeposition and characterization of PbSe films on indium tin oxide glass substrates

Electrodeposition of lead selenide (PbSe) thin films on indium tin oxide (ITO) covered glass is described. While disodium salt of ethylenediaminetetraaceticacid was used to complex the lead ions, well crystallized, nearly stoichiometric and mirror-like PbSe films were deposited on ITO glass in potentiostatic mode using aqueous acidic electrolyte containing Pb and Se precursors at different bath temperature. The improvement of crystallinity of the PbSe films deposited at different temperature was studied using X-ray diffraction and Raman scattering. The morphology and composition of the films were characterized by scanning electron microscopy and energy disperse analysis by X-ray, respectively. The optical property of the film was studied by optical measurement techniques.     

Temperature driven morphological changes of hydrothermally prepared copper oxide nanoparticles

The size and shape of nanocrystals have a strong effect on the optical, electrical and catalytic properties. Therefore, controlling the size, shape and structure of nanocrystals is technically important. The controlled synthesis of CuO nanostructures was achieved using a hydrothermal process by simply controlling the precipitation reaction temperature between copper nitrate trihydrate and sodium hydroxide. The Scanning Electron Microscopy (SEM), EDS, XRD, and FTIR analysis revealed that the synthesized product at 200 °C is of pure copper oxide particles. From Scherrer formula, the prepared CuO particles varied approximately 3–7 nm in size simply by varying the reaction temperature. The synthesized particles exhibited a regular flake like morphology and had a uniform size distribution. The morphology and size depend on the reaction conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface chemistry of colloidal PbSe nanocrystals

Solution nuclear magnetic resonance spectroscopy (NMR) is used to identify and quantify the organic capping of colloidal PbSe nanocrystals (Q-PbSe). We find that the capping consists primarily of tightly bound oleic acid ligands. Only a minor part of the ligand shell (0-5% with respect to the number of oleic acid ligands) is composed of tri- n-octylphosphine. As a result, tuning of the Q-PbSe size during synthesis is achieved by varying the oleic acid concentration. By combining the NMR results with inductively coupled plasma mass spectrometry, a complete Q-PbSe structural model of semiconductor core and organic ligands is constructed. The nanocrystals are nonstoichiometric, with a surface that is composed of lead atoms. The absence of surface selenium atoms is in accordance with an oleic acid ligand shell. NMR results on a Q-PbSe suspension, stored under ambient conditions, suggest that oxidation leads to the loss of oleic acid ligands and surface Pb atoms, forming dissolved lead oleate.     

The hidden role of acetate in the PbSe nanocrystal synthesis

Monodisperse spherical, star-shaped, and octahedral PbSe nanocrystals were synthesized via a hot injection method. We show that the shape and size of the colloidal PbSe nanocrystals are determined by the concentration of acetate and that only acetate-free reaction mixtures result in spherical nanocrystals. The presence of acetate leads to efficient oriented attachment of smaller PbSe nanoparticles along the 100 crystal axis. Comparing different synthesis procedures from the recent literature with our observations, we propose that the acetate, naturally present in insufficiently dried reaction mixtures, is responsible for many of the PbSe crystal shapes reported in the literature. In addition we show that it is possible to synthesize these star-shaped nanocrystals so monodisperse that they form ordered monolayers with crystal alignment.     

Aqueous-Phase Synthesis of Size-Tunable PbSe Nanocubes at Room Temperature for Optical Property Characterization

A simple aqueous-phase synthesis of PbSe nanocubes with tunable sizes has been developed by first preparing a Na₂SeSO₃ stock solution through dissolution of selenium powder in a solution of Na₂SO₃ at 90–100 °C for 30 min, and adding part of this solution to a mixture of lead acetate and acetic acid at room temperature with stirring for only 5–8 min to complete the nanocrystal growth. Adjusting the volume of acetic acid and Na₂SeSO₃ solution added enabled the size of the nanocrystals to be tuned, with average edge lengths of 13 to 121 nm attained. Changes in solution color revealed very different crystal growth rates for the 13 and 121 nm nanocubes. The PbSe cubes exhibit size-dependent absorption bands in the ultraviolet and visible-light region; the band positions show progressive redshifts with increasing particle size. Slight photocatalytic activity upon 532 nm laser irradiation of the nanocubes suggests the presence of higher energy levels in the band structure of PbSe. The synthetic conditions can be easily scaled up to obtain a large quantity of PbSe nanocubes for applications.     

PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.     

Electrodeposition of micro- and nanocrystalline lead selenide from alkaline selenosulfate solutions

Cathodic electrodeposition of PbSe is carried out in aqueous alkaline selenosulfate (SeSO ₃ ^2? ) bath of lead complex ions at various conditions of electrolysis. Micro- and nanocrystalline PbSe thin films were grown onto glassy carbon (GC) substrates by potentiostatic and cyclic voltammetric (CV) methods respectively. Structure and surface morphology of thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction indicates that the PbSe films have cubic structure without any impurities. The SEM micrograph showed the films cover GC substrate completely and consisted of irregular shaped grains.     

Role of Polyelectrolytes in Crystallogenesis of Calcium Carbonate

The effects anionic polyelectrolytes, having various molecular weights and repeating unit structures, on the crystallization of calcium carbonate in supersaturated solutions are studied. The induction times of the crystals grown in the presence of the polymers were optically evaluated; X-ray diffraction and Scanning Electronic Microscopy (SEM) analyses were performed to determine, respectively, their crystalline structures and morphologies. The polyelectrolyte is found to lengthen the induction time and to reduce the size of CaCO₃ nanocrystallites, to an extent depending on the interaction efficiency between the polymer anionic repeating units and the calcium ions. Further, depending on their sizes and their crystalline structures (calcite, vaterite) the nanocrystallites aggregate and yield final calcium carbonate particles having various sizes and morphologies. The data indicate that nanocrystals having vaterite structure, as determined by X-ray analysis, give spherical CaCO₃ final particles, while nanocrystals having calcite structure lead to either acicular or flower shapes of CaCO₃ final particles.     

Microwave-assisted aqueous synthesis: a rapid approach to prepare highly luminescent ZnSe(S) alloyed quantum dots

In this paper, we present a new procedure for the rapid synthesis of luminescent ZnSe nanocrystals in aqueous phase by microwave irradiation with controllable temperature. The effects of microwave irradiation and experimental conditions on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of pH value of reaction solutions, molar ratio of precursors, and heating time of microwave irradiation on the optical properties of the ZnSe nanocrystals. A series of nanocrystals with different size was prepared in 1 h, and the photoluminescence quantum yield reached up to 17% at the optimal reaction condition. The results of HRTEM and XRD showed that the as-prepared nanocrystals had high crystallinity. The characterizations of EDS spectra and elemental analysis showed that the sulfur content of nanocrystals increased with the growth of nanocrystals. We speculated that the structure of nanocrystals was an alloy ZnSe(S) shell on the surface of the ZnSe particles core. Furthermore, we found that the oxygen from air in the reaction vessel played an important role in the decomposition of the thiol group under microwave irradiation.     

Biosynthesis and characterization of lead selenide semiconductor nanoparticles (PbSe NPs) and its antioxidant and photocatalytic activity

The current study fabricated novel lead selenide nanoparticles (PbSe NPs) by a simple biological benign process with Trichoderma sp. WL-Go. Ultraviolet–visible spectroscopy (UV–vis), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transfer infra-red (FTIR) spectroscopic analysis, Raman spectroscopy and Photoluminescence (PL) were used to characterize the physicochemical properties of the fabricated NPs. Synthesis at pH 8 with 0.5 g biomass of strain WL-Go and (1:1) mM of SeO₂: Pb(NO₃)₂ were the optimal synthesis conditions to achieving 10–30 nm cubic faced centered NPs. The PbSe NPs served as catalyst for investigating the antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and photodegradation ability of rhodamine B dye (10 mg/L). The results indicated that the NPs could eliminate up to 88.60% of free radicals after adding 600 g/mL NPs and could photodegrade 82% of rhodamine B in 30 min. Thus, this study provides new knowledge and strategies for the future use of an environmentally benign bio- catalytic PbSe NPs to efficiently eliminate free radicals and in treatment of persistent organic pollutants in wastewaters.     

Structure and optoelectronic properties of PbSe quantum dots /PVA. Does the polymer molecular weight matter?

Polyvinyl alcohol (PVA) with different molecular weights (8000, 14,000, and 132,000 g/mol) capped lead selenide (PbSe) quantum dots (QDs) are prepared. The nanocomposites are characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM studies show that the particle size of PbSe QDs decrease with the increase in PVA molecular weight and/or PVA amount. This may be due to the increase in molecular weight inhibiting further growth of PbSe into the polymer matrix. Thermogravimetric analysis showed that the introduction of PbSe QDs into PVA decreases the crystallinity of the polymer. The optical absorption spectroscopy of prepared nanocomposites showed that the absorption peaks are strongly shifted to the lower wavelength (blue shift) from near infrared region to visible region by increasing the PVA molecular weight. The (I–V) characteristic curves of the PVA/PbSe nanocomposite films under illumination showed a photovoltaic cell‐like behavior. The results indicated that as the molecular weight of polymer increases, the conversion efficiency increases. Copyright © 2010 John Wiley & Sons, Ltd.