Inorganic Crystalline Materials Research Articles

ChemInform Abstract: Salt Melt Synthesis of Ceramics, Semiconductors and Carbon Nanostructures

AbstractReview: 201 refs.

Macroscopic chiral crystals can self-segregate

An experiment inspired by the origin of life has uncovered a curious behavior of inorganic crystalline materials. An experiment inspired by the origin of life has uncovered a curious behavior of inorganic crystalline materials.

Salt melt synthesis of ceramics, semiconductors and carbon nanostructures

Materials synthesis in the liquid phase, or wet-chemical synthesis, utilizes a solution medium in which the target materials are generated from a series of chemical and physical transformations. Although this route is central in organic chemistry, for materials synthesis the low operational temperature range of the solvent (usually below 200 °C, in extreme 350 °C) is a serious restriction. Here, salt melt synthesis (SMS) which employs a molten inorganic salt as the medium emerges as an important complementary route to conventional liquid phase synthesis. Depending on the nature of the salt, the operational temperature ranges from near 100 °C to over 1000 °C, thus allowing the access to a broad range of inorganic crystalline materials and carbons. The recent progress in SMS of inorganic materials, including oxide ceramic powders, semiconductors and carbon nanostructures, is reviewed here. We will introduce in general the range of accessible materials by SMS from oxides to non-oxides, and discuss in detail based on selected examples the mechanisms of structural evolution and the influence of synthetic conditions for certain materials. In the later sections we also present the recent developments in SMS for the synthesis of organic solids: covalent frameworks and polymeric semiconductors. Throughout this review, special emphasis is placed on materials with nanostructures generated by SMS, and the possible modulation of materials structures at the nanoscale in the salt melt. The review is finalized with the summary of the current achievements and problems, and suggestions for potential future directions in SMS.

Biomimetic mineralization of calcium phosphates in polymeric hydrogels containing carboxyl groups

Biomimetic processing is an attractive method for the fabrication of inorganic crystalline materials with designed morphology under ambient conditions. Precipitation of inorganic solids in a hydrogel matrix could be regarded as mimicking the process of biomineralization and be called gel-mediated processing. The importance of the functional groups in reaction media and templates has been pointed out for such gel-mediated processing. In the present study, the role of carboxyl groups in hydrogel matrices on precipitation of calcium phosphate was investigated. Carboxyl groups in the hydrogel matrices provided pH buffering action, chelate formation with calcium ions and decreased the diffusion rate of calcium ions. The crystalline phase of the calcium phosphate changed from octacalcium phosphate to hydroxyapatite with increasing carboxyl group concentration in the hydrogels. The crystalline phase change is attributed to a decrease in the activation energy for calcium phosphate formation via a chelate structure involving calcium ions and carboxyl groups.

Shaping Calcite Crystals by Means of Comb Polyelectrolytes Having Neutral Hydrophilic Teeth

Comb polyelectrolytes (CPs) having neutral hydrophilic teeth, similar to double hydrophilic block copolymers, are a powerful tool to modify the chemical-physical properties of inorganic crystalline materials. One of their main applications is in concrete technology, where they work as superplasticizers, particle-dispersing agents. Here, CPs, having the same poly(acrylic acid) (PAA) backbone chain and differing in the grafting with methoxy poly(ethylene glycol) chains (MPEG) of two molecular weights, were used to investigate the influence of tooth chains in polymer aggregation and in control on morphology and aggregation of calcite particles. These polymers aggregate, forming interpolymer hydrogen bonds between carboxylic groups and ether oxygen functionalities. The presence of calcium ions in solution further enhances aggregation. Crystallization experiments of calcite in the presence of CPs show that the specificity of interactions between polymers and crystal planes and control on aggregation and size of particles is a function of the content and chain length of the MPEG in the PAA backbone. These parameters limit and can make specific the electrostatic interactions with ionic crystalline planes. Moreover, the mechanism of crystallization, classical or nonclassical, is addressed by the CP structure and concentration. These findings have implications in the understanding of the complex chemical processes associated to concrete superplasticizers action and in the study of the biomineralization processes, where biological comb polyelectrolytes, the acidic glycoproteins, govern formation of calcitic structures.

New trends in the synthesis of crystalline microporous materials

Zeolites and related microporous materials form the most important class of microporous solids due to their practical importance in different technological areas. In spite of the extensive research carried out in previous decades, it is surprising to realize that there is still space for innovation in this area, making microporous crystalline solids special among all classes of materials known today. We illustrate here the most recent advances in the field, focusing on the research topics that, in our opinion, are most likely to provide results of practical interest. Three main topics are discussed: (1) the synthesis of new framework topologies, with particular attention to those having extra-large and/or multidimensional pore systems; (2) the modification of the morphological and textural properties of known zeolites, including the discussion on two-dimensional structures and on the synthesis of nanocrystals and of the hierarchical porous structures; (3) the still poorly explored field of silica-based hybrid organic–inorganic porous crystalline materials (hybrid zeolites). For each of these topics, a selection of the most relevant results reported in the literature is provided together with some considerations on the potentialities and future perspectives.

Macroscopic chiral crystals can self-segregate

<xhtml:span xmlns:xhtml="http://www.w3.org/1999/xhtml" xml:lang="en"> An experiment inspired by the origin of life has uncovered a curious behavior of inorganic crystalline materials. </xhtml:span>

Biomimetic peptoid oligomers as dual-action antifreeze agents

The ability of natural peptides and proteins to influence the formation of inorganic crystalline materials has prompted the design of synthetic compounds for the regulation of crystal growth, including the freezing of water and growth of ice crystals. Despite their versatility and ease of structural modification, peptidomimetic oligomers have not yet been explored extensively as crystallization modulators. This report describes a library of synthetic N-substituted glycine peptoid oligomers that possess "dual-action" antifreeze activity as exemplified by ice crystal growth inhibition concomitant with melting temperature reduction. We investigated the structural features responsible for these phenomena and observed that peptoid antifreeze activities depend both on oligomer backbone structure and side chain chemical composition. These studies reveal the capability of peptoids to act as ice crystallization regulators, enabling the discovery of a unique and diverse family of synthetic oligomers with potential as antifreeze agents in food production and biomedicine.

Patterning Hierarchy in Direct and Inverse Opal Crystals

Biological strategies for bottom-up synthesis of inorganic crystalline and amorphous materials within topographic templates have recently become an attractive approach for fabricating complex synthetic structures. Inspired by these strategies, herein the synthesis of multi-layered, hierarchical inverse colloidal crystal films formed directly on topographically patterned substrates via evaporative deposition, or "co-assembly", of polymeric spheres with a silicate sol-gel precursor solution and subsequent removal of the colloidal template, is described. The response of this growing composite colloid-silica system to artificially imposed 3D spatial constraints of various geometries is systematically studied, and compared with that of direct colloidal crystal assembly on the same template. Substrates designed with arrays of rectangular, triangular, and hexagonal prisms and cylinders are shown to control crystallographic domain nucleation and orientation of the direct and inverse opals. With this bottom-up topographical approach, it is demonstrated that the system can be manipulated to either form large patterned single crystals, or crystals with a fine-tuned extent of disorder, and to nucleate distinct colloidal domains of a defined size, location, and orientation in a wide range of length-scales. The resulting ordered, quasi-ordered, and disordered colloidal crystal films show distinct optical properties. Therefore, this method provides a means of controlling bottom-up synthesis of complex, hierarchical direct and inverse opal structures designed for altering optical properties and increased functionality.

Synthesis, structure and non-linear optical properties of l-argininium perrhenate crystal

A new hybrid organic–inorganic non-linear optical crystalline material, L-argininium perrhenate has been synthesized. The crystal belongs to P212121 space group, has a good optical quality and high transmission in the visible and near infra-red spectral regions. L-argininium perrhenate has high birefringence and is more than four times as efficient as KDP in second harmonic generation, making it a potentially attractive material for non-linear optical applications.

Prediction of Microporous Aluminophosphate AlPO4 -5 Based on Resampling Using Partial Least Squares and Logistic Discrimination.

In this paper, Partial Least Squares (PLS) regression and Logistic Discrimination (LD) are employed to predict the formation of microporous aluminophosphate AlPO4 -5 based on the database of AlPO synthesis, which aims to provide a useful guidance to the rational synthesis of microporous materials as well as other inorganic crystalline materials. To deal with the problem of class imbalance, four guided resampling methods considering not only the between-class imbalance but also the within-class imbalance are proposed. Experimental results indicate that the presented methods are competent for predicting the formation of microporous aluminophosphate AlPO4 -5. Specially, compared with some existing resampling methods, our proposed resampling methods exhibit much better predictive results.

Hematite (α-Fe2O3) with Various Morphologies: Ionic Liquid-Assisted Synthesis, Formation Mechanism, and Properties

The alpha-Fe(2)O(3) with various morphologies has been successfully synthesized via an ionic liquid-assisted hydrothermal synthetic method. The samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscope (FE-SEM), transmission electron microscopy, and high-resolution transmission electron microscopy. The results indicate that the as-prepared samples are alpha-Fe(2)O(3) nanoparticles, mesoporous hollow microspheres, microcubes, and porous nanorods. The effects of the ionic liquid 1-n-butyl-3-methylimidazolium chloride ([bmim][Cl]) on the formation of the alpha-Fe(2)O(3) with various morphologies have been investigated systematically. The proposed formation mechanisms have also been investigated on the basis of a series of FE-SEM studies of the products obtained at different durations. Because of the unique porous structure, the potential application in water treatment of the alpha-Fe(2)O(3) porous nanorods was investigated. The UV-vis measurements suggest that the as-synthesized pure alpha-Fe(2)O(3) with various morphologies possess different optical properties depending on the shape and size of the samples. The magnetic hysteresis measurements indicate the interesting magnetic property evolution in the as-prepared alpha-Fe(2)O(3) samples, which is attributed to the superstructure or the shape anisotropy of the samples. This method is expected to be a useful technique for controlling the diverse shapes of crystalline inorganic materials for a variety of applications, such as sensors, gas and heavy metal ion adsorbents, catalytic fields, hydrogen and Li ion storage, and controlled drug delivery, etc.

Computational prediction of the formation of microporous aluminophosphates with desired structural features

A better understanding of the relationship between the synthetic factors and the resulting structures is of great importance to rationalizing the synthesis of the target zeolitic materials. We present a computational study for predicting the formation of (6,12)-ring-containing microporous aluminophosphates (AlPOs), using a data classification approach. Through analyses of a database of AlPO synthesis with ca. 1600 reaction data, we identified a number of synthetic parameters such as three gel molar ratios of Al 2O 3, P 2O 5 and the organic amine template, as well as eleven parameters associated with the geometric and electronic characteristics of the templates deemed to be useful in distinguishing (6,12)-ring-containing AlPOs from the other AlPOs. Using these parameters, we have trained a support vector machine (SVM)-based classifier on a training dataset containing 360 (6,12)-ring-containing AlPOs and 1069 AlPOs without such rings. Analysis results revealed that the geometric size of the organic template, particularly the second longest distance of the template along with the gel molar ratios, has good predictive power for microporous aluminophosphates containing (6,12)-rings. This work demonstrates the general feasibility in establishing a relationship between the synthetic parameters and the structural features of the synthesized microporous materials, providing a useful guidance to the rational design and synthesis of such materials as well as other inorganic crystalline materials.

Novel Liquid Crystalline Organic−Inorganic Hybrid for Highly Sensitive Photoinscriptions

A new class of organic−inorganic liquid crystalline hybrid materials consisting of an azobenzene derivative and titanium oxide (6Az5COO-TiO and 6Az1COO-TiO) was synthesized. 6Az5COO-TiO with a C5 spacer showed a smectic liquid crystalline phase. The organic 6Az5COO and TiO inorganic components in the hybrid film were oriented perpendicular and parallel to the substrate plane, respectively, to form a layered structure. The structure of the liquid crystalline hybrid material was formed via nanophase separation of the organic and inorganic components. This film was then subjected to the inscription of surface relief structure formation by patterned UV irradiation. The efficiency of the phototriggered mass transfer showed a clear temperature dependency. The optimal temperature range was around 130 °C, which corresponds to the lower edge of the endothermic peak in the differential scanning calorimetric profile. The mass transfer was initiated at a surprisingly small energy dose of irradiation [40 mJ cm−2 (8 mW...

Contribution of calcium-containing crystals to cartilage degradation and synovial inflammation in osteoarthritis

The role of calcium phosphate and pyrophosphate crystals in osteoarthritis (OA) is unclear: are they a symptom of the damage that occurs to the joint or a key intermediate in the progression of inflammation and joint damage that occurs in OA? The proinflammatory and catabolic response of synthetic calcium phosphate and pyrophosphate crystals and crystals extracted from human osteoarthritic knee cartilage has been investigated. The crystal forms eliciting a response have been characterised allowing a comparison of the biological effects of synthetic and native calcium crystals on human osteoarthritic chondrocytes and synoviocytes to be carried out. Calcium phosphate and pyrophosphate crystals were synthesised in vitro and their crystal forms characterised by X-ray powder diffraction (XRPD). The inorganic crystalline material present in human osteoarthritic cartilage was extracted and its structural composition elucidated by XRPD. These crystals were applied to human primary osteoarthritic chondrocytes and synoviocytes and the production of proinflammatory and catabolic mediators measured. The crystals extracted from human osteoarthritic knee cartilage were identified as consisting of a mixture of monoclinic and triclinic calcium pyrophosphate dihydrate (m-CPPD and t-CPPD). These crystals elicited an inflammatory and catabolic response in human primary osteoarthritic chondrocytes and synoviocytes as measured by an increase in nitric oxide (NO), matrix metalloproteinase 13 (MMP-13) and prostaglandin E2 (PGE(2)) production. NO, MMP-13 and PGE(2) production was also increased when the synthetic calcium hydrogen phosphate dihydrate (DCPD) and calcium pyrophosphate hydrates were applied to the cells. Crystals extracted from human osteoarthritic knee cartilage induce the production of proinflammatory and catabolic mediators (NO, MMP-13 and PGE(2)) in human primary chondrocytes and synoviocytes. Synthetic calcium phosphate and pyrophosphate crystals elicit a similar response in those cells. Our findings suggest that these crystals could contribute to cartilage degradation and synovitis in OA.

Marrying gas power and hydrogen energy: A catalytic system for combining methane conversion and hydrogen generation

Ceria-based catalysts are good candidates for integrating methane combustion and hydrogen generation. These new, tuneable catalysts are easily prepared. They are robust inorganic crystalline materials, and perform well at the 400 °C–550 °C range, in some cases even without precious metals. This makes them attractive for practical applications in the energy conversion market.

Advances in Structural Analysis of Fluoroaluminates Using DFT Calculations of 27Al Electric Field Gradients

Based on the analysis of 23 aluminum sites from 16 fluoroaluminates, the present work demonstrates the strong potential of combining accurate NMR quadrupolar parameter measurements, density functional theory (DFT)-based calculations of electric field gradients (EFG), and structure optimizations as implemented in the WIEN2k package for the structural and electronic characterizations of crystalline inorganic materials. Structure optimizations are essential for compounds whose structure was refined from usually less accurate powder diffraction data and provide a reliable assignment of the 27Al quadrupolar parameters to the aluminum sites in the studied compounds. The correlation between experimental and calculated EFG tensor elements leads to the proposition of a new value of the 27Al nuclear quadrupole moment Q(27Al) = 1.616 (+/-0.024) x 10(-29) m2. The DFT calculations provide the orientation of the 27Al EFG tensors in the crystal frame. Electron density maps support that the magnitude and orientation of the 27Al EFG tensors in fluoroaluminates mainly result from the asymmetric distribution of the Al 3p orbital valence electrons. In most cases, the definition of relevant radial and angular distortion indices, relying on EFG orientation, allows correlations between these distortions and magnitude and sign of the Vii.

1D and 3D Ionic Liquid–Aluminum Hydroxide Hybrids Prepared via an Ionothermal Process

AbstractRoom‐temperature ionic liquids (RTILs) are used as hierarchically multifunctional components by employing them not only as templates and co‐solvents for fabricating nanostructured materials but also proton conductors for electrochemical devices. RTIL/aluminum hydroxide (RTIL–Al) hybrids containing various nanometer‐sized shapes, including 1D nanorods with hexagonal tips, straight and curved nanofibers, nanofibers embedded in a porous network, and 3D octahedral‐, polyhedral‐, and angular spherical shapes are synthesized via a one‐pot ionothermal process. The structures or shapes of the RTIL–Al hybrids are related to the anionic moieties, alkyl chain length of the RTILs, and the humidity during fabrication. In particular, the introduction of water molecules into the interface led to 3D isotropic growth of the hybrids by influencing intermolecular interactions between the RTILs and the building blocks. The shapes of the nanohybrids fabricated from RTILs containing short alkyl chains were dependent on the types of anions and on the level of humidity. These results indicate that the cooperative interactions between RTILs and aluminum hydroxides induces emerging shape‐controlled hybrids. The shape‐controlled nanohybrids show enhanced electrochemical properties compared to those of a conventional hybrid prepared by mixing RTILs and aluminum hydroxides, exhibiting tenfold or higher proton conductivity under anhydrous condition and thermal stability as a result of the continuous proton conduction channel and the one‐pot‐assembled nanoconfinement. This method is expected to be a useful technique for controlling the diverse shapes of nanometer‐sized crystalline inorganic materials for a variety of applications, such as fuel cells, solar cells, rechargeable batteries, and biosensors.

Microheterogeneous Electrocatalytic Chiral Recognition at Monoclinic Vanadium-Doped Zirconias: Enantioselective Detection of Glucose

Synthetic tetragonal and monoclinic vanadium-doped zirconias (t- and m-VxZr1-xO2, 0.005 < x < 0.150) exert an effective catalytic effect toward the electrochemical oxidation of glucose in aqueous alkaline media. The catalytic effect of monoclinic specimens attached to carbon and fluorine-doped tin oxide electrodes exhibits a remarkable enantioselectivity, so that catalytic currents for the oxidation of L-glucose at +0.92 V vs AgCl/Ag are considerably larger than those obtained for the oxidation of D-glucose. This enantioselectivity can be associated with the existence of a noncentrosymmetric coordination of vanadium centers in the monoclinic crystalline form of zirconia. From the electrochemical results, it can be suggested that the electrocatalytic mechanism includes the formation of glucose-vanadium surface adducts and electron transfer between catalytic centers and the substrate. The interference from chloride ions in the electrocatalytic process is significantly decreased by covering the zirconia particles with a layer of amorphous silica. These results propose that incorporation of catalytically active centers into nonsentrosymmetric sites of inorganic crystalline materials can be taken as a plausible strategy for chiral recognition via electrocatalysis.

Crystallization in Hybrid Organic−Inorganic Materials Induced by Self-Organization in Basic Conditions

Hybrid organic−inorganic crystalline materials have been obtained from a simple solvent-free synthesis in highly basic conditions. The formation of an organized hybrid structure has been achieved for the first time via sol−gel without employing bridged organosilica precursors. 3-glycidoxypropyltrimethoxysilane, which is an organically modified alkoxide bearing a terminal epoxy group, has been used for the synthesis. The opening of the epoxy has been observed to produce poly/oligo(ethylene oxide) chains or p-dioxane species. In the second case crystalline hybrids have been formed by self-organization during gelation. Analysis performed by wide-angle X-ray scattering and X-ray diffraction have confirmed the crystalline nature of the aggregates, epoxy ring opening/self-condensation which resulted in a pillared-type organic−inorganic hybrid structure with Si-substituted 2,5-bis(propoxymethyl)-1,4-dioxane organic spacer as pillar.