Subcritical solvothermal synthesis of condensed inorganic materials

The solvothermal method has recently been extended from zeolite synthesis to the formation of condensed inorganic solids, which find uses in diverse areas due to properties such as ionic-conductivity, solid-state magnetism, giant magnetoresistance, low thermal expansion and ferroelectricity. This offers specific advantages over the traditional ceramic synthetic routes to inorganic solids and these are highlighted with examples from the recent literature, and the efforts focussed on determining the formation mechanism of solids from the heterogeneous mixtures used in solvothermal procedures are discussed.     

Solvent-free synthesis of reactive inorganic precursors for preparation of organic/inorganic hybrid materials

Prehydrolyzed-condensed precursors containing amino or glycido groups were prepared via sol gel process using various alkoxysilanes in the bulk, without addition of solvent in any step of their preparation. The influence of the experimental set-up, the functionality and ratio of alkoxysilanes, and type of catalyst, on the structure buildup was studied. In the case of amino precursors, the sol–gel process was carried out at weak basic conditions while in the case of glycido precursors the sol–gel process was catalyzed by acid or neutral pH. The sol–gel process was monitored by ²⁹Si NMR in solution and the structure of the prehydrolysed-condensed precursors was characterized by small-angle X-Ray scattering. The systems with high content of tetraethoxysilane led to the fast gel formation. In weak acid medium tetraethoxysilane formed larger, more condensed species as well as small structures (based on Q ₁, Q ₂ and Q ₃ species) with silanol groups. Strong acidic conditions led to the fast formation of insoluble silica particles in liquid (sol) phase containing monomeric alkoxysilanes. The most suitable precursor formulations based on the alkoxysilanes with amino groups, as well as the most efficient set-up, were selected and used to prepare hybrid organic/inorganic networks based on an epoxy matrix. These networks were characterized using dynamic mechanical analysis.     

Design and synthesis of hierarchical materials from ordered zeolitic building units

The crystallization of colloidal silicalite-1 from clear solution is one of the best understood zeolite formation processes. Colloidal silicalite-1 formation involves a self-assembly process in which nanoslabs and nanotablets with a silicalite-1 type connectivity are formed at intermediate stages. During the assembly process, with strongly anisometric particles present, regions appear with orientational correlations, as evidenced with measurements of dynamic light scattering, viscosity, and rotation of polarized light. The presence of such regions rationalizes the unexpected differences between the crystallization kinetics under microgravity and on earth. The discovery of the locally oriented regions sheds new light on currently poorly understood hydrodynamic effects on the zeolite formation processes, such as the influence of stirring on the phases obtained and the subsequent kinetics. Addition of surfactants or polymers modifies the ordering of the zeolitic building units in the correlated regions, and new types of hierarchical materials named zeogrids and zeotiles can be obtained.     

New inorganic materials for medicine

New inorganic materials (metals and their alloys, carbon materials, ceramics, glass, and glass-ceramics) that are used in one of the branches of medicine,viz., bone endoprosthetics and implantology, are considered. Attention is concentrated on calcium- and phosphoruscontaining glassy and glass-ceramic materials that exhibit bioactivity with respect to a living bone. The main statements of the modern theory of bioactivity of these materials are outlined; physicochemical aspects of this theory are considered in detail. Extensive possibilities for controlling the structures, medico-biological, physicochemical, and mechanical properties of bioactive glasses, glass-ceramics, ceramics, and composites based on them are demonstrated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 246–253, February, 1997.     

Organic templates for the generation of inorganic materials

Mankind's fascination with shapes and patterns, many examples of which come from nature, has greatly influenced areas such as art and architecture. Science too has long since been interested in the origin of shapes and structures found in nature. Whereas organic chemistry in general, and supramolecular chemistry especially, has been very successful in creating large superstructures of often stunning morphology, inorganic chemistry has lagged behind. Over the last decade, however, researchers in various fields of chemistry have been studying novel methods through which the shape of inorganic materials can be controlled at the micro- or even nanoscopic level. A method that has proven very successful is the formation of inorganic structures under the influence of (bio)organic templates, which has resulted in the generation of a large variety of structured inorganic structures that are currently unattainable through any other method.     

One-pot synthesis of core-expanded naphthalene diimides: enabling N-substituent modulation for diverse n-type organic materials

A mild and versatile one-pot synthesis of core-expanded naphthalene diimides has been developed, which undergoes a nucleophilic aromatic substitution reaction and then an imidization reaction, allowing an easy and low-cost access to diverse n-type organic materials. Some newly synthesized compounds by this one-pot operation exhibited high electron mobility of up to 0.70 cm(2) V(-1) s(-1) in ambient conditions.     

Dual templating synthesis of hierarchical porous silica materials with three orders of length scale

Three-dimensionally interconnected, highly porous silica materials with ordering on three different scales, that is, macropores (10-30 μm), interconnecting windows (3-5 μm), and nanoporous walls (～80 nm), are prepared via a dual-templating approach.     

Synthetic inorganic ion-exchange materials

The change in selectivities by thermal treatment was studied on crystalline (C-SbA) and amorphous (A-SbA) antimonic(V) acids. The equilibrium distribution coefficients (K_d) of Na⁺ and K⁺ ions in HNO₃ solution showed a maximum on the C-SbA heated at 330 °C. An inverse relationship was noticed between the changes in K_d values and in the lattice constants for the heated C-SbA. A-SbA heated at 20–500°C showed two steps of time dependence of adsorption for Na⁺, while a maximum for K⁺. This behavior can be explained in terms of the transformation from amorphous material to C-SbA.     

Multicomponent assembly strategies for the synthesis of diverse tetrahydroisoquinoline scaffolds

Several novel multicomponent assembly processes have been developed for the rapid and efficient assembly of various heterocyclic scaffolds bearing a tetrahydroisoquinoline core, each of which allows for facile derivatization to access a diverse array of compounds. This work led to the serendipitous discovery of a new method for the synthesis of a fused quinazolone ring system, which was applied to a one-step total synthesis of the quinazolinocarboline alkaloid rutaecarpine.     

Microreactors for the synthesis of fluorinated materials

The utility of microreactor for the synthesis of α-fluoro-α,β-unsaturated esters, trifluoromethylation and Michael addition reaction, is described.     

Applications of multicomponent reactions for the synthesis of diverse heterocyclic scaffolds

A four-component coupling process involving sequential reactions of aldehydes, primary amines, acid chlorides, and nucleophiles has been developed to prepare multifunctional substrates that may be employed in subsequent ring-forming reactions to generate a diverse array of functionalized heterocyclic scaffolds. This new approach to diversity-oriented synthesis was then applied to the first total synthesis of the isopavine alkaloid (+/-)-roelactamine.     

Dibenzodioxin adsorption on inorganic materials

Dibenzodioxin adsorption/desorption on solid surfaces is an important issue associated with the formation, adsorption, and emission of dioxins. Dibenzodioxin adsorption/desorption behaviors on inorganic materials (amorphous/mesoporous silica, metal oxides, and zeolites) were investigated using in situ FT-IR spectroscopy and thermogravimetric (TG) analysis. Desorption temperatures of adsorbed dibenzodioxin are very different for different kinds of inorganic materials: approximately 200 degrees C for amorphous/mesoporous silica, approximately 230 degrees C for metal oxides, and approximately 450 degrees C for NaY and mordenite zeolites. The adsorption of dibenzodioxin can be grouped into three categories according to the red shifts of the IR band at 1496 cm(-1) of the aromatic ring for the adsorbed dibenzodioxin: a shift of 6 cm(-1) for amorphous/mesoporous silica, a shift of 10 cm(-1) for metal oxides, and a shift of 14 cm(-1) for NaY and mordenite, suggesting that the IR shifts are proposed to associated with the strength of the interaction between adsorbed dibenzodioxin and the inorganic materials. It is proposed that the dibenzodioxin adsorption is mainly via the following three interactions: hydrogen bonding with the surface hydroxyl groups on amorphous/mesoporous silica, complexation with Lewis acid sites on metal oxides, and confinement effect of pores of mordenite and NaY with pore size close to the molecular size of dibenzodioxin.     

Multicatalytic processes using diverse transition metals for the synthesis of alkenes

A series of cascade processes for the synthesis of alkenes from alcohols is described. Each individual step is catalyzed with a specific transition metal complex. The oxidation-methylenation one-pot procedure took place in the presence of a palladium and a rhodium catalyst to produce the desired terminal alkenes in high yields. A methylenation-ring-closing metathesis allowed the synthesis of cyclic alkenes from carbonyl derivatives, using the second-generation metathesis catalyst. Finally, an oxidation-methylenation-RCM process that involves up to three different transition metal catalysts in the same vessel is presented.     

2-Methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles: versatile starting materials for the synthesis of libraries with diverse heterocyclic scaffolds

Heterocyclic demonstration libraries for agrochemical screening were prepared from the common intermediates 2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles (1), using standard solution-phase techniques. A total of 18 screening libraries were prepared in good to excellent yields. Several members of these libraries were active in the first level of agrochemical screening, especially in the fungicide screen.     

Facile synthesis of hierarchical porous Li2FeSiO4/C as highly stable cathode materials for lithium-ion batteries

Journal of Solid State Electrochemistry - Lithium iron silicate has caught tremendous attentions as an appealing cathode for future lithium-ion batteries due to high capacity, low cost, and...     

From microfluidics to hierarchical hydrogel materials

Over the past two decades, microfluidics has made significant contributions to material and life sciences, particularly via the design of nano-, micro- and mesoscale materials such as nanoparticles, micelles, vesicles, emulsion droplets, and microgels. Unmatched in control over a multitude of material parameters, microfluidics has also shed light on fundamental aspects of material design such as the early stages of nucleation and growth processes as well as structure evolution. Exemplarily, polymer hydrogel particles can be formed via microfluidics with exact control over size, shape, functionalization, compartmentalization, and mechanics that is hardly found in any other processing method. Interestingly, the utilization of microfluidics for material design largely focuses on the fabrication of single entities that act as reaction volume for organic and cell-free biosynthesis, cell mimics, or local environment for cell culturing. In recent years, however, hydrogel design has shifted towards structures that integrate a large variety of functions, e.g., to address the demands for sensing tasks in a complex environment or more closely mimicking architecture and organization of tissue by multiparametric cultures. Hence, this review provides an overview of recent literature that explores microfluidics for fabricating hydrogel materials that go well beyond common length scales as well as the structural and functional complexity of microgels necessary to produce hierarchical hydrogel structures. We focus on examples that utilize microfluidics to design microgel-based assemblies, on microfluidically made polymer microgels for 3D bioprinting, on hydrogels fabricated by microfluidics in a continuous fashion, like fibers, and on hydrogel structures that are shaped by microchannels.     

Hydrophobicityand collectorless flotation of inorganic materials

Hydrophobicity and floatability of solids have been analyzed from the standpoint of properties of solid-water and solid-water vapors interfaces, chemical bonds, bulk properties, crystal structure of the solid, and reactivity of the solid with water. Although the hydrophobicity results from complex interactions in the solid-water-air system, simple equations and rules for predicting hydrophobicity and floatability are presented. The applicability of the Gaudin-Miaw-Spedden theory which states that molecular and sheet crystals, if their structure is controlled by the residual bonds across their basal planes, are floatable was confirmed. It was also shown that elements and compounds with different degrees of ionic-covalent and metallic-nonmetallic characters of bonds in the absence of residual bonds can be either hydrophilic, hydrophobic, or change their properties from hydrophobic to hydrophilic and vice versa. For some materials, hydrophobidty was found to be time-dependent. Decreasing hydrophobicity occurs with the oxidation and hydroxylation of the surface (oxides, metals), while increasing hydrophobicity takes place due to non-dissociative adsorption of water vapors on the surface (noble metals). Increased hydrophobicity can also be due to the formation of hydrophobic species such as sulfur species on the surface of Sulfides. It was demonstrated that the potential hydrophobicity of solids, expressed as the contact angle formed between the three involved (solid, water, and air) phases, can be evaluated from the Hamaker constants.This work supplements the Gaudin-Miaw-Spedden theory by showing that not only molecular crystals (paraffin, I₂, S₈, As₄O₆, As₂S₂) and non-ionic sheet crystals (MoS₂, Sb₂S₃, talc, graphite, As₂S₃, boric acid, BN) but also elements and crystalline compounds without residual bonds can be hydrophobic and floatable. A partial list of such materials includes Hg, Ge, Si, SiC, AgI, CaF₂, and diamond (whose hydrophobidties are already well known) as well as BaSO₄, FeTiO₃, In, and Sn (whose hydrophobidties have been established in this work). It was also demonstrated that the hydrophobidty of some solids changes as a result of reaction of the surface with constituents of the air.     

Gas-phase synthesis of inorganic fullerene-like structures and inorganic nanotubes

Following the discovery of fullerenes (C₆₀) and carbon nanotubes, it was shown that nanoparticles of inorganic layered compounds, like WS₂ and MoS₂, are unstable in the planar form and they form closed cage structures with polyhedral or nanotubular shapes. Although initially the method of synthesis for the formation of such closed caged structures and nanotubes involved starting from the respective oxides, it is now well established that the gas-phase synthetic route (using metal chlorides, carbonyls etc) provides an alternative which is suitable for the synthesis of very many closed caged structures and nanotubes hitherto unknown. Various issues with this method of synthesis, including its fundamentals, mechanism, and the properties of the inorganic fullerene-like structures produced are reviewed, together with some possible applications.