Synergistic catalysis of Au@Ag core-shell nanoparticles stabilized on metal-organic framework

For the first time, this work presents Au@Ag core-shell nanoparticles (NPs) immobilized on a metal-organic framework (MOF) by a sequential deposition-reduction method. The small-size Au@Ag NPs reveal the restriction effects of the pore/surface structure in the MOF. The modulation of the Au/Ag ratio can tune the composition and a reversed Au/Ag deposition sequence changes the structure of Au-Ag NPs, while a posttreatment process transforms the core-shell NPs to a AuAg alloy. Catalytic studies show a strong bimetallic synergistic effect of core-shell structured Au@Ag NPs, which have much higher catalytic activities than alloy and monometallic NPs.     

Growth and characterization of unidirectional (100) KDP single crystal by Sankaranarayanan-Ramasamy (SR) method

Unidirectional (100) potassium dihydrogen orthophosphate (KDP) single crystals were grown by Sankaranarayanan-Ramasamy (SR) method. The (100) oriented seed crystals were mounted at the bottom of the glass ampoules and the crystals of 20mm diameter, 30 mm height and 15 mm diameter, 65 mm height were grown by SR method. The grown crystals were characterized by high-resolution X-ray diffractometry anlaysis, UV-vis spectroscopy, dielectric and microhardness studies. The high-resolution X-ray diffractometry anlaysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. The SR method-grown unidirectional KDP has 15% higher transmittance compared to conventional method-grown crystals. The dielectric constant was higher and the dielectric loss was less in SR method-grown crystal. The crystals grown by SR method have much higher hardness value than conventional method-grown crystals. The quality of the crystal grown by SR method is better than conventional method-grown crystal.     

Noncontact atomic force microscopy of perfect single crystals of pentacene prepared by crystallization from solution

Nearly perfect single crystals of pentacene were grown from trichlorobenzene solution. The surface structure of pentacene single crystals has been investigated by frequency modulation atomic force microscopy. Molecularly flat and extraordinarily wide terraces, extended over the width of more than a few micrometers with monomolecular steps, were consistently observed, suggesting that those pentacene crystals were nearly perfect single crystals. Molecular packing arrangements were revealed by FM-AFM for the first time.     

Fabrication of a Kagomé-type MOF Membrane by Seeded Growth on Amino-functionalized Porous Al2O3 Substrate

In this study, we report an efficient fabrication method for the membrane of a metal-organic framework (MOF) (Kgm−OEt) which is one kind of kagomé-type MOF with a two-dimensional (2D) sheet structure having one-dimensional (1D) channels suitable for separation of H₂ from other larger gases. The Kgm−OEt seed layer was created on an Al₂O₃ substrate using layer-by-layer (LBL) growth, then a membrane was fabricated by secondary growth. The membrane on a 3-aminopropyltriethoxysilane (APTEs)-treated substrate obtained in this method was continuous and defect-free with the crystal orientation suitable for gas transportation, while the membrane grown on an unmodified substrate was loosely packed with unfavorable crystal orientation.     

Synthesis, growth and characterization of a new nonlinear optical material: 4-phenylpyridinium hydrogen squarate (4PHS)

A novel organic non-linear optical organic single crystal of 4-phenylpyridinium hydrogen squarate (4PHS) has been synthesized and successfully grown from aqueous solutions by slow evaporation solution growth method. In the present investigation the title compound has been synthesized by taking equimolar quantity of 4-phenylpyridine and squaric acid and mixed thoroughly using double distilled water as the solvent. The prepared concentrated solution was placed in an undisturbed condition, and then the solution was periodically inspected. The good quality single crystals have been harvested in a time span of 3 weeks. Then the grown crystal was characterized as single crystal XRD, differential thermal analysis, thermogravimetric analysis, FTIR, UV-vis-NIR, SHG, (1)H NMR and (13)C NMR analyses, respectively. The observed results from the characterization analyses show its suitability for NLO applications when compared with some of the existing organic crystals. The relative second harmonic generation of this grown crystal was found to be five times higher than that of KDP crystal. The UV cut-off wavelength and decomposition temperature of this grown crystal were also comparatively better. (1)H NMR and (13)C NMR spectroscopic studies were employed to elucidate the structure of the grown specimen.     

PARTICLE SIZE DISTRIBUTION OF POLYMER POWDERS BY ANALYSIS OF SORPTION KINETICS

A method has been proposed for determination of particle size distributions of polymer powders via analysis of the Fickian sorption and desorption kinetics of organic vapors. The basis for this method is a model describing the kinetics of sorption in homogeneous spherical particles having diameters distributed a-mong a finite set of diameters. A computation procedure has been developed for determining the weight fractions of each particle diameter which optimize the fit between the model and experimental sorption data. This procedure has been applied to gravimetric sorption data for several organic vapors in PVC powders ranging in diameter from 0.2 to 80 μm. For samples whose particle structure meets the assumptions of the model, the procedure yields histographic distributions closely approximating the particle size distributions determined by conventional microscopic and sedimentation methods. For porous or agglomerated particles, the method yields an “equivalent spherical size distribution” which adequately describes the sorption kinetics, but may differ significantly from size distributions measured by other methods.     

Modulating Hierarchical Micro/Mesoporosity by a Mixed Solvent Approach in Al-MOF: Stabilization of MAPbBr3 Quantum Dots

Various hierarchical micro/mesoporous MOFs based on {[Al(μ-OH)(1,4-NDC)]⋅H₂O} ( MOF1 ) with tunable porosities (pore volume and surface area) have been synthesized by assembling Al^III and 1,4-NDC (1,4-naphthalenedicarboxylate) under microwave irradiation by varying water/ethanol solvent ratio. Water/ethanol mixture has played a crucial role in the mesopore generation in MOF1M₂₅ , MOF1M₅₀ , and MOF1M₇₅ , which is achieved by in situ formation of water/ethanol clusters. By adjusting the ratio of water/ethanol, the particle size, surface area and micro/mesopore volume fraction of the MOFs are controlled. Furthermore, reaction time plays a critical role in mesopore formation as realized by varying reaction time for the MOF with 50 % ethanol ( MOF1M₅₀ ). Additionally, hierarchical MOF ( MOF1M₅₀ ) has been used as a template for the stabilization of MAPbBr₃ (MA=methylammonium) perovskite quantum dots (PQDs). MAPbBr₃ PQDs are grown inside MOF1M₅₀ , where mesopores control the size of PQDs which leads to quantum confinement.     

MOF‐5‐Polystyrene: Direct Production from Monomer,Improved Hydrolytic Stability,and Unique Guest Adsorption

An unprecedented mode of reactivity of Zn₄O‐based metal–organic frameworks (MOFs) offers a straightforward and powerful approach to polymer‐hybridized porous solids. The concept is illustrated with the production of MOF‐5‐polystyrene wherein polystyrene is grafted and uniformly distributed throughout MOF‐5 crystals after heating in pure styrene for 4–24 h. The surface area and polystyrene content of the material can be fine‐tuned by controlling the duration of heating styrene in the presence of MOF‐5. Polystyrene grafting significantly alters the physical and chemical properties of pristine MOF‐5, which is evident from the unique guest adsorption properties (solvatochromic dye uptake and improved CO₂ capacity) as well as the dramatically improved hydrolytic stability of composite. Based on the fact that MOF‐5 is the best studied member of the structure class, and has been produced at scale by industry, these findings can be directly leveraged for a range of current applications.     

MOF‐5‐Polystyrene: Direct Production from Monomer,Improved Hydrolytic Stability,and Unique Guest Adsorption

An unprecedented mode of reactivity of Zn₄O‐based metal–organic frameworks (MOFs) offers a straightforward and powerful approach to polymer‐hybridized porous solids. The concept is illustrated with the production of MOF‐5‐polystyrene wherein polystyrene is grafted and uniformly distributed throughout MOF‐5 crystals after heating in pure styrene for 4–24 h. The surface area and polystyrene content of the material can be fine‐tuned by controlling the duration of heating styrene in the presence of MOF‐5. Polystyrene grafting significantly alters the physical and chemical properties of pristine MOF‐5, which is evident from the unique guest adsorption properties (solvatochromic dye uptake and improved CO₂ capacity) as well as the dramatically improved hydrolytic stability of composite. Based on the fact that MOF‐5 is the best studied member of the structure class, and has been produced at scale by industry, these findings can be directly leveraged for a range of current applications.     

Preparation and characterization of a bis thiourea sodium iodide (BTSI)

A semi-organic nonlinear optical single crystal of bis thiourea sodium iodide (BTSI) has been successfully grown from aqueous solution using the slow evaporation solvent technique (SEST) at room temperature. Obtained crystals using the SEST method were characterized by using different characterization techniques. Structural studies of the grown crystals have been carried out by single-crystal XRD to confirm the crystal system and functional groups by FT-IR spectroscopy. Single-crystal XRD reveals orthorhombic structure of semi-organic BTSI single crystals and its unit cell parameters. Metal complex coordination of the single crystal is studied by FT-IR spectroscopy. The optical absorption study revealed excellent optical transparency of BTSI crystal in the entire visible region with a sharp lower cutoff wavelength 298 nm. The energy band gap of BTSI is found to be 4.16 eV. Thermal stability and thermal decomposition of BTSI single crystals were investigated by TGA–DTA and DSC analysis. The surface appearance of BTSI crystals by scanning electron microscopy reveals the formation of layer growth pattern. The structural perfection and growth features of the grown crystal were analyzed by wet chemical etching studies. The above studies reveal the effect of incorporation of sodium iodide into the lattice of thiourea crystals. The as-grown BTSI single crystals can be used as a potential candidate for NLO material as well as in electronic and optoelectronic devices.     

Influence of Nd:Zn codoping in near-stoichiometric lithium niobate

Near-stoichiometric lithium niobate (SLN) crystals doped with up to 1.6 mol % Zn and codoped with various Nd concentrations in the melt (0.2, 0.5, 0.9, and 1.5 mol %) (Nd:Zn:SLN) are grown from 58.6 mol % Li(2)O using conventional Czochralski technique. Crystals are pulled at the rate of 0.35 mmh with seed rotation at 9 rpm. Concentrations of Zn and Nd in the crystal are varied by adding appropriate amounts of ZnO and Nd(2)O(3) to the starting composition. Unit cell parameters of the grown crystals are calculated by Rietveld refinement method using FULLPROFF software. Domain structure studies are carried out by chemical etching followed by microscopic examination. Dielectric studies reveal the existence of piezoelectric resonance at high frequencies. Enhancement in dielectric constant and tan delta in Nd doped samples has been attributed to the space charge polarization. Nd doped samples exhibit reduction in the relative permittivity after oxygen annealing. Transmission spectra of Nd:Zn:SLN crystals in the UV region exhibit blueshift in the cutoff wavelength. In Mid Infrared (MIR) region crystals doped with 1.6 mol % Zn have shift in the OH absorption peak from 2873 to 2833 nm. Judd-Ofelt analysis carried out on the absorption spectra of codoped crystal yields the lifetime of 104 mus for the metastable state (4)F(32). The branching ratio for the electronic transition from (4)F(32) to (4)I(112) is high compared to that for (4)F(32) to (4)I(132), indicating a higher emission cross section for the former transition. Laser damage threshold evaluated using 532 nm, 5 ns pulsed neodymium doped yttrium aluminum garnet laser, shows an increase by two orders of magnitude for crystals doped with 1.6 mol % Zn. Photorefractive damage threshold for these crystals shows an enhancement of four orders of magnitude due to increase in the photoconductivity.     

Self-propagating high-temperature synthesis as a promising method for the utilization of technical lignins

The self-propagating high-temperature synthesis method has been used for technical lignin utilization after long-term storage under atmosphere conditions. For the first time a new allotropic form of carbon, carbonized lignin, has been obtained and analyzed. It has been shown that, in terms of its parameters (dispersity, surface groups), the carbonized lignin is a suitable alternative to conventional brands of technical carbon in resin compounds.     

Synthesis, growth, and characterization of iminodiacetic acid monohydrochloride

The title compound of iminodiacetic acid hydrochloride (IDAAMHCL) has been successfully synthesized by adopting conventional chemical reaction and the single crystals have been grown by solvent evaporation method at room temperature and studied its various properties and reported for the first time. The lattice dimension and the crystal structure were identified from the powder X-ray diffraction analysis. The crystalline perfection assessed by high resolution X-ray diffraction technique shows that the specimen is free from structural grain boundaries. The presence of functional groups and the protons in IDAAMHCl was confirmed by Fourier transform infra-red and NMR (¹H and ¹³C) spectroscopic techniques. The presence of carbon, hydrogen, and nitrogen was confirmed by elemental analysis. The optical behavior of IDAAMHCl was assessed by UV-visible spectroscopy and it is found that there is no absorption in the entire visible region of the spectrum. The Z scan measurements at 532 nm with 5 ns laser pulses show that IDAAMHCL is a very good candidate for optical limiting applications.     

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo‐Polymerization Reaction

Getting suitable crystals for single‐crystal X‐ray crystallographic analysis still remains an art. Obtaining single crystals of metal–organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single‐crystal‐to‐single‐crystal manner. The spacer ligands with trans,trans,trans‐conformation in the pillared‐layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans‐conformation prior to [2+2] photo‐cycloaddition reaction and yield single crystals of MOF containing two‐dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.     

Mechanical Alloying of Metal–Organic Frameworks

The solvent‐free mechanical milling process for two distinct metal–organic framework (MOF) crystals induced the formation of a solid solution, which is not feasible by conventional solution‐based syntheses. X‐ray and STEM‐EDX studies revealed that performing mechanical milling under an Ar atmosphere promotes the high diffusivity of each metal ion in an amorphous solid matrix; the amorphous state turns into the porous crystalline structure by vapor exposure treatment to form a new phase of a MOF solid solution.     

Atomic force microscopy investigation of the mechanism of calcite microcrystal growth under Kitano conditions

A combined atomic force microscopy (AFM)-inverted optical microscopy technique has been used to image the surface of calcite single microcrystals, with dimensions of 10-20 microm, at high resolution. The microcrystals were grown on a glass substrate using the Kitano method, a process that involves the outgassing of carbon dioxide from a saturated solution of calcium carbonate. The resulting increase in the supersaturation of the solution, with respect to calcium carbonate, induces crystallization. It is demonstrated, for the first time, that calcite microcrystals formed in this way exhibit a single spiral growth hillock on the (104) surface, as evidenced by a spiral step pattern, indicating that growth occurs at steps arising from an individual screw dislocation. The subsequent reactivity of these crystals under Kitano conditions has been followed in situ using AFM imaging.     

Microwave-Assisted Synthesis and Characterization of Polyurethanes from TDI and Starch

In this work, a microwave-assisted method was developed to prepare polyurethanes from starch or maltodextrin and tolylene-2,4-diisocyanate (TDI). As compared to conventional heating, this new synthetic procedure saves energy, significantly reduces reaction time, and yet entails product yields that are comparable to those of the conventional heating procedure. The reaction products were characterized with NMR, FT-IR, thermogravimetric analysis, and scanning electron microscopy. From these analyses, the polyurethanes made with the conventional and microwave methods are shown to be similar in chemical structure and physical morphology. Furthermore, the ¹H and ¹³C NMR spectra of the starch polyurethanes have been fully assigned for the first time.     

Shish-kebab structures of nylon-6 obtained from quiescent solutions by application of self-seeding

A study has been made of the morphology and structure of nylon-6 crystals grown from diluted 1,4-butanediol solution. Isothermal crystallization from homogeneous solution resulted in smooth ribbons or lath-shaped crystals aggregated into sheaves. Shish-kebab structures of nylon-6 could be grown from the quiescent solution by self-seeding techniques. Electron microscopic investigations and small-angle x-ray measurements showed that the molecules in the lath-shaped backbones of the shish kebab are folded and oriented perpendicular to the long axis of the crystals. The polyamide laths have the α-monoclinic crystal structure with the hydrogen bonds parallel to the long axis. It is suggested that due to the anisotropic type of bonding in the crystal lattice the crystals fragment laterally during the heating stage in the self-seeding technique. Structural defects, e.g., twinning sites introduced during the dissolution and subsequent crystallization may cause the growth of shish-kebab structures from quiescent solution.     

Growth dynamics of isotactic polypropylene single crystals during isothermal crystallization from a miscible polymeric solvent

The present article presents a spatiotemporal growth of isotactic polypropylene (iPP) single crystals, melt crystallized from a polymeric solvent, i.e., poly (ethylene octene) copolymer that is known to be miscible with iPP. Optical and atomic force microscopic investigations reveal that the melt grown single crystals of iPP develop in the form of two parallel rows of crystal lamellae, but these crystals merge at the tips. To elucidate the mechanism of these emerging parallel rows of iPP crystals, a phase field model pertaining to solidification phenomena has been employed that involves a nonconserved crystal order parameter and a chain-tilting angle. This phase field model is based on the free energy of crystallization, having an asymmetric double well, and a tensorial surface free energy of the crystal interface coupled with a curvature elastic free energy that is possessed by the solid-liquid interface. The spatiotemporal simulation of iPP single crystal growth has been carried out on a square lattice based on the finite difference method for spatial steps and an explicit method for temporal steps with a periodic boundary condition. The appearance of the seemingly twin crystal is captured in the simulation, which may be attributed to the sector demarcation that is taking place in the anisotropically growing single crystal of iPP.     

A Universal Strategy toward Ultrasmall Hollow Nanostructures with Remarkable Electrochemical Performance

A facile and versatile microwave‐assisted and shell‐confined Kirkendall diffusion strategy is used to fabricate ultrasmall hollow nanoparticles by modulating the growth and thermal conversion of metal–organic framework (MOF) nanocrystals on graphene. This method involves that the adsorption of microwave by graphene creates a high‐energy environment in a short time to decompose the in situ grown MOF nanocrystals into well‐dispersed uniform core–shell nanoparticles with ultrasmall size. Upon a shell‐confined Kirkendall diffusion process, hollow nanoparticles of multi‐metal oxides, phosphides, and sulfides with the diameter below 20 nm and shell thickness below 3 nm can be obtained for the first time. Ultrasmall hollow nanostructures such as Fe2O3 can promote much faster charge transport and expose more active sites as well as migrate the volume change stress more efficiently than the solid and large hollow counterparts, thus demonstrating remarkable lithium‐ion storage performance.