Single Halide Research Articles

Preparing Methods and Its Influencing Factors about Nanoparticles Based on Dendritic Polymer

Based on the properties, structure and application of dendritic polymer, this paper analysed the methods of the preparation of nanoparticles using dendritic polymer, detailed preparation process, technical parameters and application effect about a single metal nanoparticles, bimetallic nanoparticles, sulfide and halide nanoparticles. The influencing factors of the preparation about nanoparticles were discussed, including the molecular algebra, the molar ratio of the metal ions to the dendritic polymer, and so on.

Composition-dependent dual halide anion-doped bismuth terephthalate hybrids for enhanced pollutants removal

Six dual halide anions made from the combinations of NaF, NaCl, NaBr and NaI, each with 0.25 equiv relative to the molar of Bi(NO3)3, were doped into bismuth terephthalate by a one-pot synthesis method. The hybrid doped by NaF and NaI shows excellent adsorption and significantly enhanced visible-light degradation of rhodamine B. The photodegradation efficiency of this dual halides doped hybrid is approximately 2.2–10 times enhancement in compared to those of similarly single halide doped hybrids. The higher photodegradation activity was attributed to its composition, a regularly lamellar morphology, higher surface-to-volume ratio and an extended light absorption edge. Moreover, O2−, ·OH and h+ are found to be important active species involved in photodegradation process. The dual halide anions doped bismuth terephthalate hybrids reported in the present work are promising visible-light catalysts for organic pollutants removal.

Regulating Carrier Dynamics in Single Crystal Halide Perovskite via Interface Engineering and Optical Doping

High-quality CH3NH3PbI3 single crystals are synthesized with desired intrinsic carrier dynamics revealed by time-resolved photoluminescence spectroscopy and Hall effect measurement. Quantitative anisotropy of electron/hole mobility in CH3NH3PbI3 single crystal is unveiled with a double diode configuration and anisotropic photon illumination. With intentional optical doping, the switching dynamics of the double diode photo­detectors is regulated.

Single Cesium Lead Halide Perovskite Nanocrystals at Low Temperature: Fast Single-Photon Emission, Reduced Blinking, and Exciton Fine Structure.

Metal-halide semiconductors with perovskite crystal structure are attractive due to their facile solution processability, and have recently been harnessed very successfully for high-efficiency photovoltaics and bright light sources. Here, we show that at low temperature single colloidal cesium lead halide (CsPbX3, where X = Cl/Br) nanocrystals exhibit stable, narrow-band emission with suppressed blinking and small spectral diffusion. Photon antibunching demonstrates unambiguously nonclassical single-photon emission with radiative decay on the order of 250 ps, representing a significant acceleration compared to other common quantum emitters. High-resolution spectroscopy provides insight into the complex nature of the emission process such as the fine structure and charged exciton dynamics.

Organic-inorganic interactions of single crystalline organolead halide perovskites studied by Raman spectroscopy.

Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current-voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic-inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3-xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3-NH3(+) embedded in CH3NH3PbBr3 (325 cm(-1)) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3-xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C-N, NH3(+) and CH3 stretching of the CH3NH3(+) as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3(+) interacts with the PbX3(-) octahedral framework via the NH3(+) end through N(+)-HX hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C-N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.

Efficient Perovskite Solar Cells by Temperature Control in Single and Mixed Halide Precursor Solutions and Films

Thermal annealing and precursor composition play critical roles in crystallinity control and morphology formation of perovskite thin films for achieving higher photovoltaic performance. In this study we have systematically studied the role of annealing temperature on the crystallinity of perovskite (CHNH3PbI3) thin films cast from single (without PbCl2) and mixed (with PbCl2) halide precursors. Higher annealing temperature leads to agglomeration of perovskite crystals. The effects of annealing temperature on the performance of perovskite solar cells are different in single and mixed halide processed films. It is observed that the perovskite crystallinity and film formation can be altered with the addition of lead chloride in the precursor solution. We report that single halide perovskite solar cells show no change in morphology and crystal size with increase in annealing temperature, which was confirmed by UV–vis absorption spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). However,...

Two-Dimensional van der Waals Epitaxy Kinetics in a Three-Dimensional Perovskite Halide

The exploration of emerging materials physics and prospective applications of two-dimensional materials greatly relies on the growth control of their thickness, phases, morphologies, and film–substrate interactions. Though substantial progress has been made for the development of two-dimensional films from conventional layered bulky materials, particular challenges remain for obtaining ultrathin, single crystalline, dislocation-free films from intrinsically non-van der Waals-type three-dimensional materials. In this report, with the successful demonstration of single crystalline ultrathin large-scale perovskite halide material, we reveal and identify the favorable role of weak van der Waals film–substrate interaction on the nucleation and growth of the two-dimensional morphology out of nonlayered materials compared to conventional epitaxy. We also show how the bonding nature of the three-dimensional material itself affects the kinetic energy landscape of ultrathin film growth. By studying the formation of fractal perovskites assisted with Monte Carlo simulations, we demonstrate that the competition between the van der Waals diffusion and surface free energy of the perovskite leads to film thickening, suggesting that extra strategies such as surface passivation may be needed for the growth of monolayer and few-layer films.

(Invited) Lead Halide Perovskite Nanowire and Nanoplate Lasers with Low Lasing Thresholds and High Quality Factors

The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same physical properties that are ideal for semiconductor lasers. Here we first report new insights on the crystal growth of the perovskite materials and the solution growth of single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide and other perovskites via a dissolution-recrystallization pathway from lead iodide or lead acetate films coated on substrates. We further show room temperature and wavelength tunable lasing from single crystal lead halide perovskite nanowires with the lowest lasing thresholds (220 nJ/cm2) and highest quality factors (Q ~ 3600) reported to date for semiconductor nanowire lasers. The lasing threshold corresponds to a charge carrier density as low as 1.5×1016/cm3. Kinetic analysis based on time-resolved fluorescence reveals little charge carrier trapping in these single crystal nanowires and gives estimated lasing quantum yields approaching 100%. Such lasing performance, coupled with facile solution phase growth of single crystal NWs and broad tunability of emission color from stoichiometry, makes lead halide perovskites ideal materials for the development of nano-photonics, in parallel with the rapid development in photovoltaic technology from the same materials.

Organometallic Lewis Acids, Part LVIIII [1]. Directed Synthesis of Dinuclear Metal Carbonyl Complexes of Rhenium, Iron, Chromium, and Tungsten with a Single Unsupported Halide or Pseudohalide Bridge (Cl-, Br-, I-, CN-, C(CN)3 -, NCS-, PPh2 -, SH-) by Use of Re(CO)5FBF3

Abstract By use of Re(CO)5FBF3 the complexes with a single unsupported halide or pseudohalide bridge [Cp(OC)2Fe-X-Re(CO)5]+ BF4 - (X=Cl, I, PPh2), (OC)5M-X-Re(CO)5 (M=Cr, W; X=Br, I, CN, NCS, SH), (OC)5W-N≡C-C[-C≡N-Re(CO)5]2 + BF4 -, Cp(OC)(NC)Fe-C≡N-Re(CO)5, and [(OC)5Re-N3-Re(CO)5]+ BF4 - have been synthesized.

Survey of Properties of Key Single and Mixture Halide Salts for Potential Application as High Temperature Heat Transfer Fluids for Concentrated Solar Thermal Power Systems

In order to obtain high energy efficiency in a concentrated solar thermal power plant, more and more high concentration ratio to solar radiation are applied to collect high temperature thermal energy in modern solar power technologies. This incurs the need of a heat transfer fluid being able to work at more and more high temperatures to carry the heat from solar concentrators to a power plant. To develop the third generation heat transfer fluids targeting at a high working temperature at least 800 ℃, a research team from University of Arizona, Georgia Institute of Technology, and Arizona State University proposed to use eutectic halide salts mixtures in order to obtain the desired properties of low melting point, low vapor pressure, great stability at temperatures at least 800 ℃, low corrosion, and favorable thermal and transport properties. In this paper, a survey of the available thermal and transport properties of single and eutectic mixture of several key halide salts is conducted, providing information of great significance to researchers for heat transfer fluid development.

Survey of Properties of Key Single and Mixture Halide Salts for Potential Application as High Temperature Heat Transfer Fluids for Concentrated Solar Thermal Power Systems

In order to obtain high energy efficiency in a concentrated solar thermal power plant, more and more high concentration ratio to solar radiation are applied to collect high temperature thermal energy in modern solar power technologies. This incurs the need of a heat transfer fluid being able to work at more and more high temperatures to carry the heat from solar concentrators to a power plant. To develop the third generation heat transfer fluids targeting at a high working temperature at least 800 ℃, a research team from University of Arizona, Georgia Institute of Technology, and Arizona State University proposed to use eutectic halide salts mixtures in order to obtain the desired properties of low melting point, low vapor pressure, great stability at temperatures at least 800 ℃, low corrosion, and favorable thermal and transport properties. In this paper, a survey of the available thermal and transport properties of single and eutectic mixture of several key halide salts is conducted, providing information of great significance to researchers for heat transfer fluid development.

Synthesis, characterization and hydrogen sorption studies of mixed sodium‐potassium alanate

AbstractThe aim of the present investigation is to synthesize mixed sodium potassium alanate (K2NaAlH6) and to explore its hydrogen sorption characteristics. K2NaAlH6 is synthesized through ball milling of KH and NaAlH4 in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K2NaAlH6 has peak desorption temperature of ∼352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl3 and TiF3) on K2NaAlH6. In the case of graphene and SWCNT catalyzed K2NaAlH6, the peak desorption temperature gets reduced to ∼347°C and ∼341°C respectively. The catalytic effects of CNS and titanium halide on K2NaAlH6 are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF3 is found to be the best catalyst for hydrogen sorption in K2NaAlH6. The peak desorption temperature decreases significantly from 352°C to ∼324°C for TiF3 catalyzed K2NaAlH6. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K2NaAlH6) to 88.05 kJ/mol for TiF3 catalyzed K2NaAlH6.

Molecular and crystal assembly inside the carbon nanotube: encapsulation and manufacturing approaches

Encapsulation of different guest-species such as molecules and ions inside carbon nanotubes (CNTs) has been reported in the literatures during the last 15 years and represents an exciting development of nanoengineering of novel materials and composites. The reported nanocomposite materials show the semi-conducting properties with potential applications in nanosensors, nanounits and nanocircuits as well as advanced energy transfer and storage properties, and encompass manufacturing for novel nanowires, nanoelectronic devices with properties designed with optoelectronic, spintronic and nanomagnetic qualities. This review reports on a wide range of encapsulation references with particular focus on single molecules, atomic chains, metal halides and polymers encapsulated inside CNTs. The encapsulation methods and the chemical and physical qualities of these novel materials are crucial for the future manufacturing of novel innovations in nanotechnology, and represent therefore the current state-of-the-art of encapsulation methods in advanced manufacturing.

Temperature Dependence and Energetics of Single Ions at the Aqueous Liquid–Vapor Interface

We investigate temperature-dependence of free energetics with two single halide anions, I(-) and Cl(-), crossing the aqueous liquid-vapor interface through molecular dynamics simulations. The result shows that I(-) has a modest surface stability of 0.5 kcal/mol at 300 K and the stability decreases as the temperature increases, indicating the surface adsorption process for the anion is entropically disfavored. In contrast, Cl(-) shows no such surface state at all temperatures. Decomposition of free energetics reveals that water-water interactions provide a favorable enthalpic contribution, while the desolvation of ion induces an increase in free energy. Calculations of surface fluctuations demonstrate that I(-) generates significantly greater interfacial fluctuations compared to Cl(-). The fluctuation is attributed to the malleability of the solvation shells, which allows for more long-ranged perturbations and solvent density redistribution induced by I(-) as the anion approaches the liquid-vapor interface. The increase in temperature of the solvent enhances the inherent thermally excited fluctuations and consequently reduces the relative contribution from anion to surface fluctuations, which is consistent with the decrease in surface stability of I(-). Our results indicate a strong correlation with induced interfacial fluctuations and anion surface stability; moreover, resulting temperature dependent behavior of induced fluctuations suggests the possibility of a critical level of induced fluctuations associated with surface stability.

On the origin of frequency dispersion at the interface between mercury electrode and aqueous solutions of alkali halides

The origin of frequency dispersion of electrochemical impedance is investigated at the interface of mercury and aqueous solutions of single alkali halides. It is found that in the presence of each one of KI, CsI, CsF and CsBr salts, the interface presents certain potential regions where frequency dispersion effects are detected and others where the ideal capacitor behavior is closely approximated. Frequency dispersion effects are contributed by interfacial processes such as anion and cation adsorption, mercury halide film formation and dissolution and charge transfer reactions. The discrimination between frequency dispersion due to charge transfer processes occurring at the Hg/solution interface and that due to reactant adsorption itself is generally difficult and depends on the reaction mechanism, provided that a discrete adsorption step is anticipated.

Thermal conductivity in molten alkali halides: composition dependence in mixtures of (Na–K)Cl

The thermal conductivities of molten (Na–K)Cl systems have been evaluated using equilibrium molecular dynamics simulation within the framework of Fumi–Tosi potential models. An expression for the thermal conductivity of binary ionic mixtures was derived from the phenomenological equations between flux densities and their conjugate forces in the related transport processes. Each transport coefficient was evaluated using the Green–Kubo formula. The statistical errors of thermal conductivity evaluated using six kinds of the coefficients in these mixtures were estimated to be ca. 7–12%, depending on composition, which is comparable with the case for single molten NaCl evaluated using three kinds of the coefficients. The calculation results for the equimolar mixture show that the thermal conductivity depends strongly on density, but only weakly on temperature. Furthermore, all the calculated thermal conductivities of the mixtures scale with m − 1/2 (N/V)2/3, where m is the average ionic mass and N/V is the number density. These results regarding temperature and density dependencies and scaling with m − 1/2 (N/V)2/3 are common to the previous results for a series of single molten alkali halides.

Performance evaluation of energy efficient lighting associated with renewable energy applications

Energy efficiency is a primary consideration when designing off-grid renewable energy systems including portable micro-grids. This study focuses on characterizing the potential benefits associated with using energy efficient exterior area lighting commonly associated with remote installations. Light emitting diode (LED) luminaires are becoming more commercially available, and this study compares two LED products designed for exterior lighting to traditional metal halide lamps. The characterization focuses on the use of a diesel generator, battery bank, and a bank of ultra capacitors (UCAPs) to power the lights because these systems are also used to generate or store energy at renewable energy-powered micro-grids. This field-based study quantifies the illuminance provided by each lighting system, diesel consumption rates associated with powering the lights and/or charging the batteries and UCAPs, and the time of operation for each lighting system when powered by a single discharge cycle of the batteries and UCAPs. The energy efficiency benefit of the LED luminaires is offset by their lower illuminance. However, a comparison of lighting standards for specific purposes such as security lighting indicates that LEDs may be appropriate for applications where a metal halide system would provide significantly more illumination than required at a much higher energy cost. For those purposes where higher levels of illuminance are required, the data presented in the paper may be useful in designing a renewable energy-powered micro-grid that uses multiple LED fixtures to illuminate an exterior area that is currently illuminated by a single metal halide light stand.

Use of Mordenite Surface Acidity Properties for the Selective Separation of Halide Salts: Modification of Dielectric Effects

The Mordenite membrane was synthesized onto commercial ceramic tubular support (α-alumina), and surface characterizations were carried out on Mordenite powder. The surface charge density remains stable when Mordenite was in contact with monovalent or divalent salts. Pore diameter was estimated in the range of 8−10 nm. Filtrations tests were performed using the Mordenite membrane with single monovalent halide salt solutions. No rejection was observed. Then, the Mordenite membrane was treated with a divalent anionic salt (Na2CO3). Weak rejections were observed according to the order of hydration energy (NaF > NaCl > NaBr > NaI). After an acid cleaning, the membrane recovered its initial properties. A new estimation of average pore radius proved that steric effects were not responsible for rejection themselves. A new filtration test of mixed monovalent salt solution was carried out. The fluoride ion was retained by a majority. A preferential transfer was observed for chloride, bromide, and iodide ions.

Synthesis and characterization of neutral and anionic carbonyl derivatives of palladium(ii)

The action of CO on the solvento-complexes cis-[PdR2(thf)2] [R = C6F5 (1), C6Cl5 (2)] at low temperature gives cis-[PdR2(CO)2] [R = C6F5 (3), C6Cl5 (4)] in good yield by simple replacement of the highly labile thf molecules. These are rare cases of Pd(II) dicarbonyl compounds, whose characterization relies on spectroscopic and analytic data. The crystal structure of the square-planar platinum homologue cis-[Pt(C6Cl5)2(CO)2] is also presented. CO can split the double bridging-system in the dinuclear species [{PdR2}2(mu-X)2]2- giving the homologous series of anionic monocarbonyl Pd(II) derivatives with formula [cis-PdR2X(CO)]- (5-10: R = C6F5, C6Cl5; X = Cl, Br, I), which were isolated (except for the R = C6F5 and X = I) and suitably characterized. Characterization includes the crystal and molecular structure of [PPh3Me][cis-Pd(C6F5)2Br(CO)] (6'). The anionic species [NBu4][cis-Pd(C6F5)2Cl(CO)] (5) reacts with neutral cis-[Pd(C6F5)2(CO)2] (3) under CO extrusion, affording the dinuclear derivative [NBu4][{Pd(C6F5)2(CO)}2(mu-Cl)] (11), which contains a single unsupported halide bridge (X-ray diffraction). Complex 11 can be considered as modelling a possible intermediate step in intermolecular CO substitution reactions that are easily undergone by Pd(II) halo carbonyl species.

Synthesis of Methyl Halides from Biomass Using Engineered Microbes

Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synthesized all 89 putative MHT genes from plants, fungi, bacteria, and unidentified organisms present in the NCBI sequence database. The set was screened in Escherichia coli to identify the rates of CH(3)Cl, CH(3)Br, and CH(3)I production, with 56% of the library active on chloride, 85% on bromide, and 69% on iodide. Expression of the highest activity MHT and subsequent engineering in Saccharomyces cerevisiae results in productivity of 190 mg/L-h from glucose and sucrose. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass (Panicum virgatum), corn stover, sugar cane bagasse, and poplar (Populus sp.). These results demonstrate the potential of producing methyl halides from non-food agricultural resources.