Yitzhak Mastai

Hybrid Organic–Inorganic Perovskites (HOIPs): Opportunities and Challenges

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

Silica-carbon nanocomposites : a new concept for the design of solar absorbers

To create materials that are composites or hybrids structured on the nanometer scale or the meso-domain, respectively, is one of the major tasks in modern materials science. In this paper, we demonstrate general strategies on how to obtain these nanocomposites founded on the knowledge about ordered mesoporous materials. One strategy involves the formation of the composite by performing a chemical reaction in the pores of a pre-formed ordered mesoporous silica while the other strategy uses compounds that first mold their porous environment in the silica and in a succeeding step react to the final composite. As a model system, here, we present the formation of porous silica–carbon hybrid materials. Besides this more general question, we also tackle the task of finding a suitable application for the obtained nanocomposites. We chose an application as selective solar-absorber materials.

Chiral silicate zeolites

Chiral zeolites are porous materials of prime importance because of their enantioselective potential applications in catalysis, in separation-science and in chromatography. We report a surprising observation made: as many as many 20 chiral silicate zeolites, none of which were recognized as such in their original publication, exist. In other words, the “holy grail” of having a library of such silicates was right under our nose. To be of practical use, such zeolites must reveal molecular level enantioselectivity; we show, for the first time, that chiral silicate zeolites are capable of enantioselective recognition of enantiomers, as revealed from comparative adsorption calorimetry experiments with either D- or L-histidine. The question of how to assign handedness to a chiral zeolite is addressed.

Amino-Acid-Based Chiral Nanoparticles for Enantioselective Crystallization

Chiral polymer nanoparticles based on amino acids are prepared by miniemulsion polymerization and are demonstrated to serve as nucleating agents for the enantioselective crystallization of racemic mixtures of amino acids. The synthesized chiral nanoparticles are suited for the development of enantioselective processes and also contribute to a better understanding of chiral recognition on polymer surfaces.

Chiral-mesoporous-polypyrrole nanoparticles: Its chiral recognition abilities and use in enantioselective separation

Chiral-mesoporous-polypyrrole (CMPPy) nanoparticles are synthesized by templating chiral block copolymers (CBCs) of poly(ethylene oxide), (PEO) and chiral L-/D- glutamic acid [PEO-b-(L-/D-GluA)10] and blocks of chiral L-/D-phenylalanine [PEO-b-(L-/D-Phe)10]. The well ordered chiral mesopores of nanoparticles are characterized by HRTEM and BET. The CMPPy nanoparticles have well organized pores with sizes ca. 3.5–3.7 nm in diameter and with a high surface area. These CMPPy nanoparticles are able to recognize chiral molecules. Using the selective chiral recognition abilities, the chiral resolution of the copolymer-extracted CMPPy nanoparticles and the chiral separation kinetics using a racemic mixture of valine are probed by circular dichroism (CD) and optical polarimetry. Further, the chiral resolution of the CMPPy is confirmed with a racemic mixture of alanine. The chiral selectivity factor is 5.05 for a specific enantiomer which is adsorbed preferably by the CMPPy. These results allow a new approach towards the enantiomeric separation and other enantiomeric applications of novel CMPPy.

Sonochemical synthesis of tungsten sulfide nanorods

Amorphous WS2 has been prepared by ultrasound irradiation of W(CO)6 solution in diphenylmethane (DPhM) in the presence of a slight excess of sulfur at 90 °C under argon. Heating the amorphous powder at 800 °C under argon yields WS2 nanorods and their packings. The average size of WS2 nanorods was found to be 3–10 nm and 1–5 µm in thickness and length, respectively. The prepared WS2 has been characterized by elemental analysis, X-ray powder diffraction measurements, FTIR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and energy dispersive X-ray analysis.

The Separation of Racemic Crystals into Enantiomers by Chiral Block Copolymers

A series of chiral double hydrophilic block copolymers (DHBCs) was synthesized and employed as additives in the crystallization of calcium tartrate tetrahydrate (CaT). We found that appropriate polymers can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of the pure enantiomeric crystals so that chiral separation by crystallization occurs even when racemic crystals can be formed. In addition, the presence of DHBCs results in major modifications of crystal morphology, creating unusual morphologies of higher complexity. Our study demonstrates the potential application of chiral DHBCs in the control of chirality throughout crystallization, in particular for racemic crystal systems, and also shows that enantiomeric excess of one enantiomer can be maximized by the kinetic control of crystallization.

Enantioselective Separation Using Chiral Mesoporous Spherical Silica Prepared by Templating of Chiral Block Copolymers

In this work, we synthesized chiral mesoporous silica (CMS) spheres, which can be used as a potential candidate for chiral separation. The CMS spheres with controllable pore sizes (of 2-3 nm) and high surface areas of ca. 614 m(2) g(-1) were synthesized by chiral templating with chiral block copolymers based on poly(ethylene oxide) and dl-glutamic acid [PEO(113)-b-(GluA)(10)]. The ordered structure of the chiral mesopores was characterized by high-resolution transmission electron microscopy, and the average pore diameters of chiral mesopores were estimated from the nitrogen adsorption-desorption measurements. The enantioselectivity properties and chiral resolution kinetics of the mesopores of silica spheres, after extraction of chiral polymers of PEO(113)-b-(l/d-GluA)(10), were scrutinized using a racemic solution of valine and measuring the circular dichroism and optical polarimetery. A chiral selectivity factor of 5.22 was found with a specific enantiomer of valine adsorbed preferably. These results raise the new possibilities of CMS spheres for enantiomeric separation and other enantioselective applications.

Deposition of tellurium films by decomposition of electrochemically-generated H2Te : application to radiative cooling devices

Abstract The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H 2 Te. Pre-treatment of the polyethylene substrates with KMnO 4 to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H 2 Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.

Effect of solvents on the growth morphology of DL-alanine crystals

Solvents have a significant effect on crystal morphology, particularly for polar organic crystals. However, the role played by solvents in enhancing or inhibiting crystal growth is still not completely understood. In this paper we investigated the morphologies of DL-alanine as a model of organic polar crystals grown from a mixture of aqueous solutions, with organic solvents such as isopropyl alcohol (IPA) and ethanol. DL-alanine crystals were grown from pure water for a large range of supersaturation in various solutions of water-isopropyl alcohol (IPA) and water–ethanol. The crystal morphology formed under different crystallization conditions was analyzed using an electron microscope and X-ray diffraction to determine the specific effects of each solvent. It was found that the quantity of the solvents in the crystallization solutions has a large influence on the crystal tip morphology, and on the crystal aspect ratio. Molecular dynamic simulations were used to determine the relative growth rates of different crystallographic planes and crystal morphology. A combination of experimental morphology and simulated morphology calculated using a theoretical method allows us to understand the role played by solvents on crystal growth and crystal morphologies of DL-alanine crystals.