skip to main content

Explore Research Products in the NSF-PAR

Title: Growth kinetics determine the polydispersity and size of PbS and PbSe nanocrystals
A library of thio- and selenourea derivatives is used to adjust the kinetics of PbE (E = S, Se) nanocrystal formation across a 1000-fold range ( k r = 10 −1 to 10 −4 s −1 ), at several temperatures (80–120 °C), under a standard set of conditions (Pb : E = 1.2 : 1, [Pb(oleate) 2 ] = 10.8 mM, [chalcogenourea] = 9.0 mM). An induction delay ( t ind ) is observed prior to the onset of nanocrystal absorption during which PbE solute is observed using in situ X-ray total scattering. Density functional theory models fit to the X-ray pair distribution function (PDF) support a Pb 2 (μ 2 -S) 2 (Pb(O 2 CR) 2 ) 2 structure. Absorption spectra of aliquots reveal a continuous increase in the number of nanocrystals over more than half of the total reaction time at low temperatures. A strong correlation between the width of the nucleation phase and reaction temperature is observed that does not correlate with the polydispersity. These findings are antithetical to the critical concentration dependence of nucleation that underpins the La Mer hypothesis and demonstrates that the duration of the nucleation period has a minor influence on the size distribution. The results can be explained by growth kinetics that are size dependent, more rapid at high temperature, and self limiting at low temperatures.  more » « less
Award ID(s):
2004008
NSF-PAR ID:
10375760
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Chemical Science
Volume:
13
Issue:
16
ISSN:
2041-6520
Page Range / eLocation ID:
4555 to 4565
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ( , Environmental Science: Water Research & Technology)
    null (Ed.)
    This study investigated the reaction kinetics on the oxidative transformation of lead( ii ) minerals by free chlorine (HOCl) and free bromine (HOBr) in drinking water distribution systems. According to chemical equilibrium predictions, lead( ii ) carbonate minerals, cerussite PbCO 3(s) and hydrocerussite Pb 3 (CO 3 ) 2 (OH) 2(s) , and lead( ii ) phosphate mineral, chloropyromorphite Pb 5 (PO 4 ) 3 Cl (s) are formed in drinking water distribution systems in the absence and presence of phosphate, respectively. X-ray absorption near edge spectroscopy (XANES) data showed that at pH 7 and a 10 mM alkalinity, the majority of cerussite and hydrocerussite was oxidized to lead( iv ) mineral PbO 2(s) within 120 minutes of reaction with chlorine (3 : 1 Cl 2  : Pb( ii ) molar ratio). In contrast, very little oxidation of chloropyromorphite occurred. Under similar conditions, oxidation of lead( ii ) carbonate and phosphate minerals by HOBr exhibited a reaction kinetics that was orders of magnitude faster than by HOCl. Their end oxidation products were identified as mainly plattnerite β-PbO 2(s) and trace amounts of scrutinyite α-PbO 2(s) based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. A kinetic model was established based on the solid-phase experimental data. The model predicted that in real drinking water distribution systems, it takes 0.6–1.2 years to completely oxidize Pb( ii ) minerals in the surface layer of corrosion scales to PbO 2(s) by HOCl without phosphate, but only 0.1–0.2 years in the presence of bromide (Br − ) due the catalytic effects of HOBr generation. The model also predicts that the addition of phosphate will significantly inhibit Pb( ii ) mineral oxidation by HOCl, but only be modestly effective in the presence of Br − . This study provides insightful understanding on the effect of residual disinfectant on the oxidation of lead corrosion scales and strategies to prevent lead release from drinking water distribution systems. 
    more » « less
  2. ; ; ; ; ; ( , Small)
    Abstract

    Next‐generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)‐free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials’ design with multi‐phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead‐free piezoelectric materials (1‐x)Ba0.95Ca0.05Ti0.95Zr0.05O3‐(x)Ba0.95Ca0.05Ti0.95Sn0.05O3, are reported, which are represented as (1‐x)BCZT‐(x)BCST, with demonstrated excellent properties and energy harvesting performance. The (1‐x)BCZT‐(x)BCST materials are synthesized by high‐temperature solid‐state ceramic reaction method by varyingxin the full range (x= 0.00–1.00). In‐depth exploration research is performed on the structural, dielectric, ferroelectric, and electro‐mechanical properties of (1‐x)BCZT‐(x)BCST ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X‐ray diffraction (XRD) analyses, which also reveals that the Ca2+, Zr4+, and Sn4+are well dispersed within the BaTiO3lattice. For all (1‐x)BCZT‐(x)BCST ceramics, thorough investigation of phase formation and phase‐stability using XRD, Rietveld refinement, Raman spectroscopy, high‐resolution transmission electron microscopy (HRTEM), and temperature‐dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2+P4mm) phases at room temperature. The steady transition ofAmm2crystal symmetry toP4mmcrystal symmetry with increasingxcontent is also demonstrated by Rietveld refinement data and related analyses. The phase transition temperatures, rhombohedral‐orthorhombic (TR‐O), orthorhombic‐ tetragonal (TO‐T), and tetragonal‐cubic (TC), gradually shift toward lower temperature with increasingxcontent. For (1‐x)BCZT‐(x)BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constantεr≈ 1900–3300 (near room temperature),εr≈ 8800–12 900 (near Curie temperature), dielectric loss, tanδ≈ 0.01–0.02, remanent polarizationPr≈ 9.4–14 µC cm−2, coercive electric fieldEc≈ 2.5–3.6 kV cm−1. Further, high electric field‐induced strainS≈ 0.12–0.175%, piezoelectric charge coefficientd33≈ 296–360 pC N−1, converse piezoelectric coefficient ≈ 240–340 pm V−1, planar electromechanical coupling coefficientkp≈ 0.34–0.45, and electrostrictive coefficient (Q33)avg≈ 0.026–0.038 m4C−2are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT‐(0.4)BCST composition (x= 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead‐free piezoelectric (1‐x)BCZT‐(x)BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1‐x)BCZT‐(x)BCST ceramics as a potentially strong contender within the family of Pb‐free piezoelectric materials for future electronics and energy harvesting device technologies.

     
    more » « less
  3. ; ; ; ; ; ; ; ; ( , Digital Discovery)
    We present a complete open-hardware and software materials acceleration platform (MAP) for sonochemical synthesis of nanocrystals using a versatile tool-changing platform (Jubilee) configured for automated ultrasound application, a liquid-handling robot (Opentrons OT2) and a well-plate spectrometer. An automated high-throughput protocol was developed demonstrating the synthesis of CdSe nanocrystals using sonochemistry and different combinations of sample conditions, including precursor and ligand compositions and concentrations. Cavitation caused by ultrasound fields causes local and transient increases in temperature and pressure sufficient to drive the decomposition of organometallic precursors to drive the chemical reaction leading to nanocrystal formation. A total of 625 unique sample conditions were prepared and analyzed in triplicate with an individual sample volume of as little as 0.5 mL, which drastically reduced chemical waste and experimental times. The rapid onset of cavitation and quick dissipation of energy result in fast nucleation with little nanocrystal growth leading to the formation of small nanocrystals or magic-size clusters (MSCs) depending on composition. Using the effective mass approximation, the calculated QD diameters obtained under all our experimental conditions ranged between 1.3 and 2.1 nm, which was also validated with small angle X-ray scattering (SAXS). Polydispersity, QD shape and optical properties largely varied depending on the concentration of ligands present in solution. Statistical analysis of the spectroscopic data corroborates the qualitative relationships observed from the optical characterization of the samples with the model-agnostic SHAP analysis. The complete workflow relies on relatively low-cost and open-source systems. Automation and the reduced volumes also allow for cost-efficient experimentation, increasing the accessibility of this MAP. The high-throughput capabilities of the automated sonication platform, the extensible nature of the Jubilee system, and the modular nature of the protocol, make the workflow adaptable to a variety of future studies, including other nanocrystal design spaces, emulsification processes, and nanoparticle re-dispersion or exfoliation. 
    more » « less
  4. ; ; ; ( , Journal of Materials Chemistry C)
    We report a synthesis procedure for dodecanethiol capped wurtzite ZnO nanocrystals with an average diameter of 4 nm that are monodisperse, highly soluble, and shelf-stable for many months. Compared to previous ZnO ink recipes, we demonstrate improved particle solubility and excellent ink stability, resulting in ZnO nanocrystal inks that are optimized for printed electronics applications. The ZnO nanocrystal solution exhibits an absorption peak at 341 nm (3.63 eV), which represents a blue-shift of approximately 0.3 eV from the bulk ZnO bandgap (∼3.3 eV). This blue shift is consistent with previously reported models for an increased bandgap due to quantum confinement. We used variable-angle spectroscopic ellipsometry (VASE) to determine the optical properties of solution-processed thin films of ZnO nanocrystals, which provides valuable insight into the changes in film composition and morphology that occur during thermal annealing treatments ranging from 150–300 °C. The ZnO nanocrystals maintain their quantum confinement when deposited into a thin film, and the degree of quantum confinement is gradually reduced as the thermal annealing temperature increases. Using infrared absorption measurements (FTIR) and X-ray photoelectron spectroscopy (XPS), we show that the dodecanethiol ligands are removed from the ZnO films during annealing, resulting in a high-purity semiconductor film with very low carbon contamination. Furthermore, we show that annealing at 300 °C results in complete ligand removal with only a slight increase in grain size. Thin-film transistors (TFT) using ZnO nanocrystals as the channel material annealed at 300 °C show moderate mobility (∼0.002 cm 2 V −1 s −1 ) and good on/off ratio >10 4 . These results demonstrate the distinct advantages of colloidal nanocrystals for printed electronics applications: the composition and morphology of the solution-processed film can be carefully tuned by controlling the size and surface coating of the nanocrystals in the ink. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al ( , Chemical Science)
    We report a method to control the composition and microstructure of CdSe 1−x S x nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents ( k E ) spanning 1.3 × 10 −5 s −1 to 2.0 × 10 −1 s −1 . Depending on the relative reactivity ( k Se / k S ), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe 1−x S x alloys ( k Se / k S = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email