Nanocrystal Precursors Research Articles

High-performance bulk Bi0.4Sb1.6Te3.0 thermoelectrics prepared from nanocrystal precursor synthesized via chemical precipitation

Bi0.4Sb1.6Te3.0 is a known p-type thermoelectric material with high thermoelectric performance near room temperature. In this study, bulk Bi0.4Sb1.6Te3.0 materials are synthesized via spark plasma sintering using single nanometer-sized nanocrystals as precursors, which are prepared in the solution phase by chemical precipitation from metallic ions. The obtained bulk material consists of submicron-to-micrometer-sized disk-shaped grains with isotropic distribution. Additionally, structural distortion such as strain and/or defects can be directly introduced into grains upon sintering, presumably due to the incomplete coalescence of the small nanocrystal precursors to form larger grains during the sintering process. The resultant bulk material exhibits high electrical conductivity and considerably low lattice thermal conductivity, due to the utilization of impurity-free nanocrystal precursors and local lattice distortions included inside grains acting as scattering nodes of phonons, respectively. The maximum dimensionless figure of merit (ZT) is achieved to be 1.42 ​at 355 ​K, and, therefore, this work provides effective methodology to fabricate high-performance chalcogenide-based thermoelectric materials.

КВАНТОВЫЕ ТОЧКИ СУЛЬФИДА КАДМИЯ, ПОЛУЧЕННЫЕ С ИСПОЛЬЗОВАНИЕМ БЕЛКОВ-ПОРИНОВ, КАРРАГИНАНОВ, ХИТОЗАНОВ И ЛИПОПОЛИСАХАРИДОВ

Quantum dots (QDs) are a new generation of fluorochromes with significant advantages over traditional organic dyes. QDs based on CdS are promising materials for optics, optoelectronics, biology, and medicine. QDs in the form of colloidal solutions are of great scientific and practical interest. CdS quantum dots were synthesized by chemical condensation in an aqueous solution using Yersinia pseudotuberculosis porin proteins, positively (chitosan) and negatively (carrageenan, lipopolysaccharide) charged polysaccharides. The maxima of the emission spectra for all samples were 450 nm, which indicates the same QD size; is determined by the size of the "cells" of the grid matrix, which limit the size of the QD. It was shown that the fluorescence intensity of QDs synthesized in LPS solutions was two times higher than that of other samples. The fluorescence of the samples and the maxima of the emission spectra (450 nm) are preserved during intensive dialysis against buffers, which indicates the stability of QDs and the possibility of using the obtained labeled preparations. Keeping samples at pH 3 leads to a significant decrease in fluorescence, especially for acidic polysaccharides. Anionic oxygen of phosphate, hydroxyl groups of sugar, nitrogen atoms can interact with metal ions, which are precursors (precursors) for CdS nanocrystals. It was found that the interaction with porin-specific IgG leads to a significant change in the luminescence intensity of QD-porin samples. This is of interest from the point of view of chemical sensing and opens the prospect of using QD-labeled porin-based nanostructures as biosensors.

Transformation of Amorphous Terbium Metal-Organic Framework on Terbium Oxide TbOx(111) Thin Film on Pt(111) Substrate: Structure of TbxOy Film.

The present study is focused on the synthesis and structural properties of amorphous terbium metal–organic framework thin film (TbMOF-TF) and its transformation to terbium oxide by pyrolysis at 450 °C in the air. The crystalline (cTbMOF) and amorphous (aTbMOF) films were prepared by solvothermal synthesis using different amounts (0.4 and 0.7 mmol) of the modulator (sodium acetate), respectively. The powders were characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), Fourier transform infrared (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM). The varied chemical composition of the surface of TbMOFs and TbxOy was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that aTbMOF had been fully transformed to a Tb4O7 phase with a cubic crystal structure at 450 °C. The amorphous aTbMOF-TF film was prepared by dropping a colloidal solution of amorphous precursor nanocrystals on the SiO2/Si substrates covered with Pt as an interlayer. XPS confirmed the presence of Tb in two states, Tb3+ and Tb4+. The amorphous film has a rough, porous microstructure and is composed of large clusters of worm-like particles, while terbium oxide film consists of fine crystallites of cubic fluorite cF-TbOx, c-Tb4O7, and c-Tb2O3 phases. The surface topography was investigated by a combination of confocal (CM) and atomic force microscopy (AFM). The amorphous film is porous and rough, which is contrast to the crystalline terbium oxide film.

Crystal-Phase Control of Ternary Metal Oxides by Solid-State Synthesis with Nanocrystals.

Ternary metal oxides are materials of interest for many applications, from batteries to catalysis. Their crystalline structure and composition determine their properties, and thus it is important to achieve control over these features. Here, we demonstrate that solid-state chemistry among nanocrystalline precursors is a promising approach for their synthesis. We show that the crystalline phase of nanocrystal precursors direct that of the ternary reaction product. The combination of X-ray and electron microscopy techniques reveals that the spinel and rhombohedral phases of copper iron oxide are obtained by reacting copper nanocrystals with spinel γ-Fe2O3 and corundum α-Fe2O3 nanocrystals, respectively. Considering the available library of nanocrystals with tunable crystal phases, this discovery opens up an alternative pathway toward the synthesis of a wide variety of ternary and quaternary materials, including those with metastable phases.

Sequential, low-temperature aqueous synthesis of Ag-In-S/Zn quantum dots via staged cation exchange under biomineralization conditions.

The development of high quality, non-toxic (i.e., heavy-metal-free), and functional quantum dots (QDs) via 'green' and scalable synthesis routes is critical for realizing truly sustainable QD-based solutions to diverse technological challenges. Herein, we demonstrate the low-temperature all-aqueous-phase synthesis of silver indium sulfide/zinc (AIS/Zn) QDs with a process initiated by the biomineralization of highly crystalline indium sulfide nanocrystals, and followed by the sequential staging of Ag+ cation exchange and Zn2+ addition directly within the biomineralization media without any intermediate product purification. Therein, we exploit solution phase cation concentration, the duration of incubation in the presence of In2S3 precursor nanocrystals, and the subsequent addition of Zn2+ as facile handles under biomineralization conditions for controlling QD composition, tuning optical properties, and improving the photoluminescence quantum yield of the AIS/Zn product. We demonstrate how engineering biomineralization for the synthesis of intrinsically hydrophilic and thus readily functionalizable AIS/Zn QDs with a quantum yield of 18% offers a 'green' and non-toxic materials platform for targeted bioimaging in sensitive cellular systems. Ultimately, the decoupling of synthetic steps helps unravel the complexities of ion exchange-based synthesis within the biomineralization platform, enabling its adaptation for the sustainable synthesis of 'green', compositionally diverse QDs.

Barium and titanium dithiocarbamates as precursors for colloidal nanocrystals of emerging optoelectronic materials.

The synthesis and structures of N,N-dialkyldithiocarbamate complexes of barium are reported; the compounds crystallize as one-dimensional coordination polymers. In combination with a titanium dithiocarbamate precursor, the compounds are demonstrated as competent single-source precursors for the solution-based preparation of colloidal BaTiS3 nanorods.

Pb5Sb8Se17-δ nanocrystals: A new solar absorber material with an optimal bandgap and an efficiency near 6 % under 0.05 sun

Ternary semiconductor Pb5Sb8S17 has been shown to be a candidate solar absorber. This work presents a new solar absorber of the same group – Pb5Sb8Se17. Pb5Sb8S17 precursor nanocrystals (NCs) are first synthesized using solution processing. A subsequent S to Se ion exchange transforms the Pb5Sb8S17 precursor into the monoclinic Pb5Sb8Se17-δ phase. The substitution of S by Se reduces the band gap Eg from 1.75 (Pb5Sb8S17) to 1.41 eV (Pb5Sb8Se17-δ), increasing the optical absorption band from 300 to 750 (Pb5Sb8S17) to 300–900 nm (Pb5Sb8Se17-δ). The Eg of 1.4 eV equals to the ideal Eg for the Shockley-Queisser-limit. Liquid-junction quantum dot-sensitized solar cells (QDSSCs) are fabricated from the Pb5Sb8Se17-δ NCs with three types of counter electrode (CE): Pt, Au and NiSe. The cell using NiSe CE yields the best PCE of 2.73% (1 sun). Under reduced sun intensities, the PCE increases to 5.47% (0.1 sun) and further to 5.91% (0.05 sun). The external quantum efficiency (EQE) spectrum yields an EQE-integrated photocurrent Jph of 26.8 mA/cm2. The PCE of Pb5Sb8Se17 is 50% higher than that of the host Pb5Sb8S17 (3.95%). The optimal Eg, a high Jph and a high PCE suggest that Pb5Sb8Se17-δ has potential to be an efficient solar absorber.

Nanocrystals as Precursors in Solid-State Reactions for Size- and Shape-Controlled Polyelemental Nanomaterials

Solid-state reactions between micrometer-size powders are among the oldest, simplest, and still widely used methods for the fabrication of inorganic solids. These reactions are intrinsically slow because, although the precursorsare "well mixed" at the macroscale, they are highly inhomogeneous at the atomic level. Furthermore, their products are bulk powders that are not suitable for device integration. Herein, we substitute micrometer-size particles with nanocrystals. Scaling down the size of the precursors reduces the reaction time and temperature. More importantly, the final products are nanocrystals with controlled size and shape that can be used as active materials in various applications, including electro- and photocatalysis. The assembly of the nanocrystal precursors as ordered close-packed superlattices enables microscopy studies that deepen the understanding of the solid-state reaction mechanism. We learn that having only one of the two nanocrystal precursors dissolving and diffusing toward the other is crucial to obtain a final nanocrystalline product with homogeneous size and shape. The latter are regulated by the nanocrystal precursor that is the most stable at the reaction temperature. Considering the variety of controlled nanocrystals available, our findings open a new avenue for the synthesis of functional and tunable polyelemental nanomaterials.

Nanocrystal Precursor Incorporating Separated Reaction Mechanisms for Nucleation and Growth to Unleash the Potential of Heat-up Synthesis.

A heat-up method for quantum dots (QDs) synthesis holds distinctive benefits for large-scale production with its simplicity, scalability, and high reproducibility. Its applications, however, have been limited because it inevitably yields a strong overlap between the nucleation and the growth stages. We addressed this long-standing problem by introducing a precursor having separated reaction paths for nucleation and growth. Unlike existing precursors, which employ a shared intermediate for both reactions, 9-mercapto-9-borabicyclo[3.3.1]nonane (BBN-SH) induces growth via surface-assisted conversion and drives nucleation via cluster formation in solution. Furthermore, this precursor chemistry embeds an efficient mechanism to suppress nucleation during growth. As such, BBN-SH allows heat-up-based growth of high-quality shells that are comparable to those created by the injection method. It is also notable that BBN-SH-based heat-up synthesis shows mitigated sensitivity to temperature fluctuation; therefore, it is highly suitable for industrial-scale reactions. We established a simple, scalable, and economic scheme for core/shell QDs by streamlining quantitative core synthesis and heat-up-based shell growth and showed that the scheme produces QDs of comparable quality to those produced by the traditional method. Here, we introduce a precursor that drives a distinctive mode of nanoparticle growth. We anticipate our study to inspire the design of other precursors and unleash the full potential of heat-up synthesis.

Hierarchically Ordered Micro-/Mesoporous Material Assembled by a Zeolite W Nanocrystal and Its Hydro-Upgrading Performance for FCC Gasoline

A novel micro-/mesoporous composite material W-MCM-41 was synthesized through self-assembly of the zeolite W nanocrystal precursor. The hierarchical structure material inherited the combining advantages of the ordered mesopores of MCM-41 and the modulated acid properties of zeolite W. Different crystallization times of zeolite W and various molar ratios of CTAB/SiO2 were optimized to achieve good physicochemical properties of micro-/mesoporous materials, which were used to prepare the corresponding CoMo-supported catalysts. Various characterization methods were adopted to analyze the relationship between the catalytic performance and physicochemical properties of series catalysts. The CoMo/WMA catalyst presented the highest hydrodesufurization activity (93.4%) and the best octane number preservability (ΔRON = −1.3 unit), which could be attributed to desirable texture of support, moderate metal–support interaction, and highest sulfidation degree of active phases. The distribution of sulfide compounds in hy...

Orthorhombic Nb2O5-x for Durable High-Rate Anode of Li-Ion Batteries.

SummaryLi4Ti5O12 anode can operate at extraordinarily high rates and for a very long time, but it suffers from a relatively low capacity. This has motivated much research on Nb2O5 as an alternative. In this work, we present a scalable chemical processing strategy that maintains the size and morphology of nano-crystal precursor but systematically reconstitutes the unit cell composition, to build defect-rich porous orthorhombic Nb2O5-x with a high-rate capacity many times those of commercial anodes. The procedure includes etching, proton ion exchange, calcination, and reduction, and the resulting Nb2O5-x has a capacity of 253 mA h g−1 at 0.5C, 187 mA h g−1 at 25C, and 130 mA h g−1 at 100C, with 93.3% of the 25C capacity remaining after cycling for 4,000 times. These values are much higher than those reported for Nb2O5 and Li4Ti5O12, thanks to more available surface/sub-surface reaction sites and significantly improved fast ion and electron conductivity.

Hydrothermal synthesis of Mn2+ doped titanate nanotubes: Investigation of their structure and room temperature ferromagnetic behavior

Hydrothermal synthesis of Mn2+ doped titanate nanotubes (TNTs), which exhibited room temperature ferromagnetism (RTFM), is reported. Dispersions of 1 and 5 at.% Mn2+ doped anatase TiO2 nanocrystals were used as precursors. Size and shape of Mn2+ doped TNTs and precursor nanocrystals were studied by transmission electron microscopy (TEM). The relatively uniform size distribution of transverse dimension of nanotubes of about 10 nm was observed while their lengths varied up to few hundred nanometers. The X-Ray Diffraction (XRD) analysis and Raman spectroscopy of resultant powder confirmed the hydrogen dititanate (H2Ti2O5 x H2O) crystal phase of Mn2+ doped TNTs with the presence of small amount of sodium titanates. Electron paramagnetic resonance (EPR) experiments were performed to probe the local atomic and electronic structure of Mn in the nanotubes. Room temperature ferromagnetic ordering with saturation magnetic moment (Ms) in the range of 0.6–1.5 μB per Mn atom was observed.

Tris(dithiocarbamato)iron(III) complexes as precursors for iron sulfide nanocrystals and iron sulfide-hydroxyethyl cellulose composites

ABSTRACTIron(III) complexes of dimethyldithiocarbamate and imidazolyl dithiocarbamate were synthesized and characterized by elemental analyses, FTIR, UV–VIS and the ligands by NMR spectroscopy. The complexes were thermolysed as single molecule precursors at 180°C to prepare octadecylamine (ODA) capped iron sulfide nanocrystals and iron sulfide-hydroxyethyl cellulose (HEC) composites. UV–VIS, PL, FTIR, P-XRD, HRTEM, FESEM and EDS were used to characterize the iron sulfide nanocrystals and corresponding HEC nanocomposites. XRD confirmed iron sulfide nanocrystal (NP1) from dimethyldithiocarbamate to be hexagonal pyrrhotite-5H, Fe9S10 crystalline phase while iron sulfide nanocrystals (NP2) from imidazolyl dithiocarbamate is in pyrrhotite, Fe11S12 crystalline phase. TEM images show that the iron sulfide nanocrystals have particle sizes in the range 24–32 nm for NP1 and 18–25 nm for NP2 iron sulfide nanocrystals. The optical band gaps of the iron sulfide nanocrystals obtained from Tauc plots are 3.83 and 4.16 eV for NP1 and NP2, respectively. IR spectra, FESEM surface morphology and EDS spectra of iron sulfide/HEC composites confirmed dispersion of the iron sulfide nanocrystals within the hydroxyethyl cellulose (HEC) matrix.

Supramolecular Assembly of Single-Source Metal–Chalcogenide Nanocrystal Precursors

In this feature article, we discuss our recent work in the synthesis of novel supramolecular precursors for semiconductor nanocrystals. Metal chalcogenolates that adopt liquid-crystalline phases are employed as single-source precursors that template the growth of shaped solid-state nanocrystals. Supramolecular assembly is programmed by both precursor chemical composition and molecular parameters such as the alkyl chain length, steric bulk, and the intercalation of halide ions. Here, we explore the various design principles that enable the rational synthesis of these single-source precursors, their liquid-crystalline phases, and the various semiconductor nanocrystal products that can be generated by thermolysis, ranging from highly anisotropic two-dimensional nanosheets and nanodisks to spheres.

Synthesis and Investigation of Solid Solutions Based on Indium Oxide in In2O3–MeO2 (Me = Zr, Sn, Ti) Systems

Solid solutions in In2O3–MeO2 (Me = Zr, Sn, Ti) systems based on indium oxide are synthesized by the coprecipitation method. It is found that the ultrasound treatment of the coprecipitation products reduces the degree of agglomeration of the initial particles by a factor of 3 and initiates the crystallization process of the precipitates. Nanocrystal (5–8 nm) precursor powders are obtained at 400°C. The optimal regime for sintering powders based on In2O3 to form a ceramic with a dense microstructure is chosen. The influence of the temperature, alloying additives, and the partial pressure of oxygen on the specific conductivity of indium oxide solid solutions is studied.

Tuning of the active phase structure and hydrofining performance of alumina-supported tri-metallic WMoNi catalysts via phosphorus incorporation

The effects of phosphorus on the structure and hydrofining performance of tri-metallic WMoNi/Al2O3 catalysts prepared with W/Mo-based hybrid precursor nanocrystals were investigated. The incorporation of phosphorus weakened the metal-support interactions (MSIs) and facilitated the formation of more synergetic NiWMoS phases with higher stacks. Catalytic tests using a fluid catalytic cracking diesel fuel showed that the changes in the MSIs and the morphology of the active phases had a more positive effect on the hydrodenitrogenation activity than on the hydrodesulfurization activity. In contrast, when phosphorus was incorporated into a tri-metallic WMoNiP/ Al2O3 catalyst prepared by a conventional incipient impregnation method, the MSIs decreased causing aggregation of the metal species which resulted in poorer hydrofining performance of the catalyst. These results show that incorporating phosphorus into a WMoNi/Al2O3 catalyst can finely tune the structure of the active phase to enhance the hydrogenation and hydrodenitrogenation activity of the resulting tri-metallic catalyst.

Metal complexes of alkyl-aryl dithiocarbamates: Structural studies, anticancer potentials and applications as precursors for semiconductor nanocrystals

Dithiocarbamates are versatile ligands able to stabilize wide range of metal ions in their various oxidation states with the partial double bond character of CN and CS of thioureide moiety. Variation of the substituents attached to the nitrogen atom of dithiocarbamate moiety generates various intermolecular interactions, which lead to different structural arrangement in the solid state. The presence of bulky substituents on the N atom obviates the supramolecular aggregation via secondary MS interactions whereas smaller substituents encourage such aggregation that results in their wide properties and applications. Over the past decades, the synthesis and structural studies of metal complexes of dithiocarbamates have received considerable attention as potential anticancer agents with various degree of DNA binding affinity and cytotoxicity and as single molecule precursors for the preparation of semiconductor nanocrystals. In this paper, we review the synthesis, structural studies, anticancer potency and the use of alkyl-phenyl dithiocarbamate complexes as precursors for the preparation of semiconductor nanocrystals. The properties of these compounds and activities are ascribed to be due to either the dithiocarbamate moieties, the nature or type of the substituents around the dithiocarbamate backbone and the central metal ions or combination of these factors.

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation.

It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best ORR activity is measured with the catalyst at a size of 50 nm. Further size reduction to 20 nm leads to significant particle agglomeration, thus decreasing the activity. Using the homogeneous atomic Fe model catalysts, we elucidated the active site formation process through correlating measured ORR activity with the change of chemical bonds in precursors during thermal activation up to 1100 °C. The critical temperature to form active sites is 800 °C, which is associated with a new Fe species with a reduced oxidation number (from Fe3+ to Fe2+) likely bonded with pyridinic N (FeN4) embedded into the carbon planes. Further increasing the temperature leads to continuously enhanced activity, linked to the rise of graphitic N and Fe-N species. The new atomic Fe catalyst has achieved respectable ORR activity in challenging acidic media (0.5 M H2SO4), showing a half-wave potential of 0.85 V vs RHE and leaving only a 30 mV gap with Pt/C (60 μgPt/cm2). Enhanced stability is attained with the same catalyst, which loses only 20 mV after 10 000 potential cycles (0.6-1.0 V) in O2 saturated acid. The high-performance atomic Fe PGM-free catalyst holds great promise as a replacement for Pt in future PEMFCs.

CdTe Nanocrystal Hetero-Junction Solar Cells with High Open Circuit Voltage Based on Sb-doped TiO₂ Electron Acceptor Materials.

We propose Sb-doped TiO2 as electron acceptor material for depleted CdTe nanocrystal (NC) hetero-junction solar cells. Novel devices with the architecture of FTO/ZnO/Sb:TiO2/CdTe/Au based on CdTe NC and TiO2 precursor are fabricated by rational ambient solution process. By introducing TiO2 with dopant concentration, we are able to tailor the optoelectronic properties of NC solar cells. Our novel devices demonstrate a very high open circuit voltage of 0.74 V, which is the highest Voc reported for any CdTe NC based solar cells. The power conversion efficiency (PCE) of solar cells increases with the increase of Sb-doped content from 1% to 3%, then decreases almost linearly with further increase of Sb content due to the recombination effect. The champion device shows Jsc, Voc, FF, and PCE of 14.65 mA/cm2, 0.70 V, 34.44, and 3.53% respectively, which is prospective for solution processed NC solar cells with high Voc.

Formation of CuInSe2 films from metal sulfide and selenide precursor nanocrystals by gas-phase selenization, an in-situ XRD study

In this work phase pure CuInSe2 thin flms were obtained by selenization of ternary CuInSe2 and CuInS2 nanocrystals and mixtures of binary nanocrystals such as CuS, In2S3, Cu2Se and In2Se3. The temperature of the selenium source was kept at 400°C during selenization. Monitoring the process using in-situ x-ray diffraction, the effect of selenization on the phase formation and grain growth in the precursor film was investigated. Whereas CuInSe2 and CuInS2 nanocrystals exhibit little grain growth, we found that mixtures of binary nanocrystals can show significant sintering depending on the reaction conditions. For the mixture of CuS and In2S3 nanocrystals, the crystallinity and the morphology of the obtained fims strongly depends on the Cu/In ratio, with a Cu excess strongly promoting grain growth. With mixtures of Cu2Se and In2Se3 nanocrystals the selenium partial pressure plays a crucial role. Selenium evaporation from the mixed compounds results in CuInSe2 films composed of relatively small crystallites. Higher selenium partial pressures however resulted in improved sintering. Incomplete propagation of the selenization reaction through the layer was observed though, only leading to a well sintered CuInSe2 top layer above a fine grained bottom layer.