Ceramics by the solution-sol-gel route

Microfluidic osmotic compression with operando meso-structure characterization using SAXS

We have developed a microfluidic chip for the osmotic compression of samples at the nanoliter scale, enabling the in situ and operando acquisition of structural features through small-angle X-ray scattering throughout the compression process. The design builds upon a previous setup allowing high-throughput measurements with minimal sample quantities. The updated design is specifically tailored for compatibility with a laboratory beamline, taking into account factors such as reduced photon flux and increased beam size compared to synchrotron beamlines. As a proof of concept, we performed on-chip compression of well-documented silica colloidal particles (Ludox TM-50). We demonstrated that the volume fraction could be tracked over time during compression, either by monitoring X-ray absorbance or by modeling the scattered signal. With precise control of the osmotic pressure and salt chemical potential, equations of state can be determined unambiguously from the volume fraction measurements and be interpreted with the help of the scattered intensity. These microfluidic chips will be valuable for understanding the behavior of colloidal suspensions, with applications in areas such as crystallization, nucleation, soil mechanics, control of living matter growth and interaction conditions, as well as the measurement of coarse-grained colloidal interaction potentials.

Bioceramics/Electrospun Polymeric Nanofibrous and Carbon Nanofibrous Scaffolds for Bone Tissue Engineering Applications

Bone tissue engineering integrates biomaterials, cells, and bioactive agents to propose sophisticated treatment options over conventional choices. Scaffolds have central roles in this scenario, and precisely designed and fabricated structures with the highest similarity to bone tissue have shown promising outcomes. On the other hand, using nanotechnology and nanomaterials as the enabling options confers fascinating properties to the scaffolds, such as precisely tailoring the physicochemical features and better interactions with cells and surrounding tissues. Among different nanomaterials, polymeric nanofibers and carbon nanofibers have attracted significant attention due to their similarity to bone extracellular matrix (ECM) and high surface-to-volume ratio. Moreover, bone ECM is a biocomposite of collagen fibers and hydroxyapatite crystals; accordingly, researchers have tried to mimic this biocomposite using the mineralization of various polymeric and carbon nanofibers and have shown that the mineralized nanofibers are promising structures to augment the bone healing process in the tissue engineering scenario. In this paper, we reviewed the bone structure, bone defects/fracture healing process, and various structures/cells/growth factors applicable to bone tissue engineering applications. Then, we highlighted the mineralized polymeric and carbon nanofibers and their fabrication methods.

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO₂-20(1.5Eu³⁺: NaGdF₄) were prepared with sol-gel following the "pre-crystallised nanoparticles route" with promising optical results. The preparation of 1.5 mol % Eu³⁺-doped NaGdF₄ nanoparticles, named 1.5Eu³⁺: NaGdF₄, was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO₂-20(1.5Eu³⁺: NaGdF₄) OxGCs prepared from these nanoparticles' suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF₄ crystalline phases. The optical properties of both nanoparticles' phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the ⁵D₀ state. The emission spectra obtained by exciting the Eu³⁺-O^2- charge transfer band showed similar features in both cases corresponding the higher emission intensity to the ⁵D₀→⁷F₂ transition that indicates a non-centrosymmetric site for Eu³⁺ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu³⁺ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.

Recent Progress in Solution Processed Aluminum and co-Doped ZnO for Transparent Conductive Oxide Applications

With the continuous growth in the optoelectronic industry, the demand for novel and highly efficient materials is also growing. Specifically, the demand for the key component of several optoelectronic devices, i.e., transparent conducting oxides (TCOs), is receiving significant attention. The major reason behind this is the dependence of the current technology on only one material-indium tin oxide (ITO). Even though ITO still remains a highly efficient material, its high cost and the worldwide scarcity of indium creates an urgency for finding an alternative. In this regard, doped zinc oxide (ZnO), in particular, solution-processed aluminum doped ZnO (AZO), is emerging as a leading candidate to replace ITO due to its high abundant and exceptional physical/chemical properties. In this mini review, recent progress in the development of solution-processed AZO is presented. Beside the systematic review of the literature, the solution processable approaches used to synthesize AZO and the effect of aluminum doping content on the functional properties of AZO are also discussed. Moreover, the co-doping strategy (doping of aluminum with other elements) used to further improve the properties of AZO is also discussed and reviewed in this article.

Diffusion/Reaction Limited Aggregation Approach for Microstructure Evolution and Condensation Kinetics during Synthesis of Silica-Based Alcogels

A base-catalysed methyltrimethoxysilane (MTMS) colloidal gel formation was implemented as a cellular automaton (CA) system, specifically diffusion and/or reaction-limited aggregation. The initial characteristic model parameters were determined based on experimental synthesis of MTMS-based, ambient-pressure-dried aerogels. The applicability of the numerical approach to the prediction of gels' condensation kinetics and their structure was evaluated. The developed model reflects the kinetics properly within the investigated chemical composition range (in strongly reaction-limited aggregation conditions) and, to a slightly lesser extent, the structural properties of aggregates. Ultimately, a relatively simple numerical model reflecting silica-based gel formation was obtained and verified experimentally. The CA simulations have proved valid for understanding the relation between the initial chemical composition and kinetics constants of MTMS-based synthesis and their impact on secondary particle aggregation process kinetics.

Review on Sol-Gel Synthesis of Perovskite and Oxide Nanomaterials

Sol-Gel is a low cost, well-established and flexible synthetic route to produce a wide range of micro- and nanostructures. Small variations in pH, temperature, precursors, time, pressure, atmosphere, among others, can lead to a wide family of compounds that share the same molecular structures. In this work, we present a general review of the synthesis of LaMnO3, SrTiO3, BaTiO3 perovskites and zinc vanadium oxides nanostructures based on Sol-Gel method. We discuss how small changes in the parameters of the synthesis can modify the morphology, shape, size, homogeneity, aggregation, among others, of the products. We also discuss the different precursors, solvents, working temperature, reaction times used throughout the synthesis. In the last section, we present novel uses of Sol-Gel with organic materials with emphasis on carbon-based compounds. All with a perspective to improve the method for future applications in different technological fields.

Copper-containing bioactive glasses and glass-ceramics: From tissue regeneration to cancer therapeutic strategies

Copper is one of the most used therapeutic metallic elements in biomedicine, ranging from antibacterial approaches to cancer theranostics. This element could be easily incorporated into different types of biomaterials; specifically, copper-doped bioactive glasses (BGs) provide great opportunities for biomedical engineers and clinicians as regards their excellent biocompatibility and regenerative potential. Although copper-incorporated BGs are mostly used in bone tissue engineering, accelerated soft tissue healing is achievable, too, with interesting potentials in wound treatment and skin repair. Copper can modulate the physico-chemical properties of BGs (e.g., reactivity with bio-fluids) and improve their therapeutic potential. Improving cell proliferation, promoting angiogenesis, reducing or even prohibiting bacterial growth are counted as prominent biological features of copper-doped BGs. Recent studies have also suggested the suitability of copper-doped BGs in cancer photothermal therapy (PTT). However, more research is needed to determine the extent to which copper-doped BGs are actually applicable for tissue engineering and regenerative medicine strategies in the clinic. Moreover, copper-doped BGs in combination with polymers may be considered in the future to produce relatively soft, pliable composites and printable inks for use in biofabrication.

Hierarchically structured porous materials: synthesis strategies and applications in energy storage

To address the growing energy demands of sustainable development, it is crucial to develop new materials that can improve the efficiency of energy storage systems. Hierarchically structured porous materials have shown their great potential for energy storage applications owing to their large accessible space, high surface area, low density, excellent accommodation capability with volume and thermal variation, variable chemical compositions and well controlled and interconnected hierarchical porosity at different length scales. Porous hierarchy benefits electron and ion transport, and mass diffusion and exchange. The electrochemical behavior of hierarchically structured porous materials varies with different pore parameters. Understanding their relationship can lead to the defined and accurate design of highly efficient hierarchically structured porous materials to enhance further their energy storage performance. In this review, we take the characteristic parameters of the hierarchical pores as the survey object to summarize the recent progress on hierarchically structured porous materials for energy storage. This is the first of this kind exclusively to survey the performance of hierarchically structured porous materials from different porous characteristics. For those who are not familiar with hierarchically structured porous materials, a series of very significant synthesis strategies of hierarchically structured porous materials are firstly and briefly reviewed. This will be beneficial for those who want to quickly obtain useful reference information about the synthesis strategies of new hierarchically structured porous materials to improve their performance in energy storage. The effect of different organizational, structural and geometric parameters of porous hierarchy on their electrochemical behavior is then deeply discussed. We outline the existing problems and development challenges of hierarchically structured porous materials that need to be addressed in renewable energy applications. We hope that this review can stimulate strong intuition into the design and application of new hierarchically structured porous materials in energy storage and other fields.

A sol-gel synthesis to prepare size and shape-controlled mesoporous nanostructures of binary (II-VI) metal oxides

A base-catalyzed sol–gel approach combined with a solvent-driven self-assembly process at low temperature is augmented to make manganese oxide (Mn₃O₄), copper oxide (CuO), and magnesium hydroxide (Mg(OH)₂) nanostructures with size- and shape-controlled morphologies. Nanostructures of Mn₃O₄ with either hexagonal, irregular particle, or ribbon shape morphologies with an average diameter ranged from 100 to 200 nm have been prepared in four different solvent types. In all morphologies of Mn₃O₄, the experimental XRD patterns have indexed the nanocrystal unit cell structure to triclinic. The hexagonal nanoparticles of Mn₃O₄ exhibit high mesoporocity with a BET surface area of 91.68 m² g⁻¹ and BJH desorption average pore diameter of ∼28 nm. In the preparation of CuO nanostructures, highly nanoporous thin sheets have been produced in water and water/toluene solvent systems. The simulated XRD pattern matches the experimental XRD patterns of CuO nanostructures and indexes the nanocrystal unit cell structure to monoclinic. With the smallest desorption total pore volume of 0.09 cm³ g⁻¹, CuO nanosheets have yielded the lowest BET surface area of 18.31 m² g⁻¹ and a BHJ desorption average pore diameter of ∼16 nm. The sol of magnesium hydroxide nanocrystals produces highly nanoporous hexagonal nanoplates in water and water/toluene solvent systems. The wide angle powder XRD patterns show well-defined Bragg's peaks, indexing to a hexagonal unit cell structure. The hexagonal plates show a significantly high BET surface area (72.31 m² g⁻¹), which is slightly lower than the surface area of Mn₃O₄ hexagonal nanoparticles. The non-template driven sol–gel synthesis process demonstrated herein provides a facile method to prepare highly mesoporous and nanoporous nanostructures of binary (II–IV) metal oxides and their hydroxide derivatives, enabling potential nanostructure platforms with high activities and selectivities for catalysis applications.

A base-catalyzed sol–gel approach combined with a solvent-driven self-assembly process at low temperature is augmented to make highly mesoporous metal oxide nanostructures of manganese and copper, and hydroxide nanostructures of magnesium.

Structural transformation caused by pyridine carboxylate in rosebengal-modified metal framework: Synthesis and spectral analysis

In this paper, luminescent metal-organic framework was modified with a rosebengal dye. This resulting composite structure was confirmed with XRD, IR, TGA/DTG and photophysical spectroscopy. Detailed analysis suggested that it was responsive towards pyridine carboxylate (PC), a bio-indicator. Two responsive modes were found, which are absorption-based sensing (named colorimetric one) and emission-based sensing (named fluorescent ratiometric one), respectively. The sensing nature was explored as rosebengal structural transformation triggered by PC and energy transfer between metal framework and PC. These two responsive modes both obey linear performance against PC concentration, showing detection limit of 2.4 μM. Especially, fluorescent ratiometric sensing rendered high selectivity. Their practical sensing performance was discussed as well.

High Throughput Synthesis of Multifunctional Oxide Nanostructures within Nanoreactors Defined by Beam Pen Lithography

Reliably obtaining nanostructures of complex oxides over large area with nanoscale resolution and well-controlled shape, spacing, and pattern symmetry remains a major challenge. In this article, millions of nanowells have been routinely generated by beam pen lithography. Each attoliter volume nanowell functions as a "nanoreactor", inside which oxide nanostructures are synthesized from their sol-gel precursors. Importantly, these nanometer scale entities are in single crystalline or textured forms and epitaxial to the underlying substrates, which promises functionalities including ferroelectricity, ferromagnetism, and multiferroicity. This method provides a general solution which allows one to rapidly screen structural parameters of oxide nanostructures comprising of three or more elements for prominent properties.

Hierarchically porous materials: synthesis strategies and structure design

This review addresses recent advances in synthesis strategies of hierarchically porous materials and their structural design from micro-, meso- to macro-length scale.

Orientation-controlled BaTiO3 thin films fabricated by chemical solution deposition

We synthesized orientation-controlled (100), (110), and (111) BaTiO₃ films by the CSD method and revealed the dielectric properties the films.

Effects of inorganic acids and divalent hydrated metal cations (Mg2+, Ca2+, Co2+, Ni2+) on γ-AlOOH sol–gel process

In-depth understanding of the sol–gel process plays an essential role in guiding the preparation of new materials.

Thin Anisotropic Coatings Based on Sol-Gel Technology

Using sol-gel technology, thin organic/ceramic (ceramer) coatings have been applied to metal surfaces in order to enhance such surface properties as adhesion promotion and corrosion prevention. Isotropic coatings have been found to be effective in certain applications such as corrosion prevention, but the formation of anisotropic coatings permits greater flexibility over the resulting properties. Isotropic coatings derived from tetraethoxysilane, for example, effectively inhibit corrosion while being only 100 to 1000 Å thick. These coatings do not, however, promote adhesion. Thin coatings made from traditional silane adhesion promoters alone are unable to prevent corrosion of metallic substrates.

Using monomers with appropriate reactivities permits the single-step synthesis of anisotropic coatings that can both promote adhesion and prevent corrosion. These types of anisotropic coatings allow the physical and chemical properties of a coating to be varied as a function of distance from the substrate and confer properties to the substrate that would not be possible from a single isotropic coating. The principle behind the construction of these anisotropic coatings is general enough that it can be used in many applications where microengineering of surface structures is important.

Oxide and Metal Intercalated Clay Nanocomposites

Truly nanocomposite materials that are stable to about 400 to 700°C can be prepared by intercalating oxides or metal clusters of about 0.4 to 2.0 nm in between ∼1.0 nm layers of smectite clays. Both the chemistry and size of intercalates (pillars) can be varied to introduce unique catalytic, molecular sieving, dehumidifying and adsorption properties in these materials. The intercalated clays also provide opportunities to prepare compositionally and stoichiometrically diverse nanocomposite precursors to high temperature structural and electronic ceramics. Although montmorillonite is the most widely used host, further designing in properties can be achieved by using other members of smectite family having subtle crystal chemical and compositional variations, such as beidellite, nontronite, saponite or hectorite. The sol-gel chemistry involving the preparation of positively charged mono- or multiphasic solution-sol or colloidal-sol particles is a viable approach to introduce chemically diverse oxide particles in the interlayers of smectite. Reduction of transition metal ions or complexes in the interlayers of smectite to zerovalent metal clusters/particles using polar liquids is another novel approach to develop catalytically active, high surface area materials.

Pyrolysis of Organometallic Precursors As A Route to Novel Ceramic Materials

Homogeneously mixed nanocrystalline composites incorporating SiC, Si3N4, AIN, BN and TiN, and SiC/AIN solid solutions were prepared from mixtures of known precursors to the separate components and specially prepared singlesource precursors. These novel materials are of potential interest as tough, abrasion-resistant coatings, continuous fibers and matrices for high temperature composites and, possibly, superplastic ceramics. Solid state NMR spectroscopy along with other chemical and materials characterization methods have been employed in studies of the precursor-to-ceramic conversion process and the characterization of the final ceramic products. The results of these studies are described and their implications with respect to the relationship between precursor structure, pyrolysis chemistry and the final ceramic composition and microstructure are discussed.

Nanocomposites: Retrospecr and Prospect

In this paper we make clear distinctions from the terms nanophase, nanocrystalline and deal only with nanocomposites defined as an interacting mixture of two phases, one of which is in the nanometer size range in at least one dimension. The author's origins of development of the idea that nanocomposites are a virtually infinite class of new materials are described.

Then we refer to the results of our extensive studies of nanocomposites derived by solution-solgel techniques to illustrate the properties of such materials in the area of chemical and thermal reactivity.

Finally it is pointed out that in the last few years nanocomposite materials have become a major part of new materials synthesis all over the world for applications ranging from mechanical to optical, to magnetic to dielectric.

Designing Zeolites As Novel Precursors To Electronic Ceramics

The decomposition of zeolites is a novel route for the synthesis of aluminosilicate-based ceramic materials. Zeolites offer a number of advantages as ceramic precursors which allow the formation of dense ceramics at lower temperatures than by conventional methods. Using various cation-exchanged zeolites, ceramics and ceramic composites containing anorthite (CaAl2Si2O8). mullite (Al6Si2O11) cordierite (Mg2Al4Si5O18). celsian (BaAl2Si2O8), and ß-spodumene (LiAlSi2O6) have been formed. Using Extended X-ray Absorption Fine Structure (EXAFS), we have studied the reconstructive transformation of strontium-exchanged zeolite A to Sr-anorthite and have shown that the primary coordination of strontium remains intact during conversion.

Sol-gel-derived epitaxial nanocomposite thin films with large sharp magnetoelectric effect

Nanostructures of multiferroic materials have drawn increasing interest due to the enhanced magnetoelectric coupling and potential for next-generation multifunctional devices. Most of these structures are typically prepared by thin film evaporation approaches. Herein, however, we report a novel sol-gel-based process to synthesize epitaxial BaTiO(3)-CoFe(2)O(4) nanocomposite thin films via phase separation and enhanced heterogeneous nucleation. The magnetoelectric coupling effect is investigated by examining the temperature-dependent magnetization of the composite film, which manifests as a sharp and significant drop (>50%) of the magnetization at the vicinity of a BaTiO(3) ferroelectric phase transition. We propose that the phase transition in BaTiO(3) is mediated by the tensile strain due to intimate coupling to CoFe(2)O(4) phase, which has rarely been reported before. The significant coupling effect is attributed to the small substrate clamping, and the large areal distribution of intimate heteroepitaxial interfaces between the three-dimensionally distributed ferroelectric and magnetic nanostructured phases.

Novel Materials through Non-Hydrolytic Sol-Gel Processing: Negative Thermal Expansion Oxides and Beyond

Low temperature methods have been applied to the synthesis of many advanced materials. Non-hydrolytic sol-gel (NHSG) processes offer an elegant route to stable and metastable phases at low temperatures. Excellent atomic level homogeneity gives access to polymorphs that are difficult or impossible to obtain by other methods. The NHSG approach is most commonly applied to the preparation of metal oxides, but can be easily extended to metal sulfides. Exploration of experimental variables allows control over product stoichiometry and crystal structure. This paper reviews the application of NHSG chemistry to the synthesis of negative thermal expansion oxides and selected metal sulfides.

Characterization of the structure of ultra dilute sols with remarkable biological properties

Most natural waters are probably "ultra dilute": aquasols. While the composition of such waters is routinely characterized thoroughly with respect to composition, very little attention has been paid to the solid phases which are certainly suspended in most, if not all, such. Our recent work having established the importance of the structure of water on its properties, [[1]; R. Roy, W.A. Tiller, I. Bell, M.R. Hoover; Mater Res Innov. 9 (2005) 577.] we have examined the structures of many waters with easily demonstrated (e.g. silver aquasols) or long-claimed (e.g. homeopathic remedies) biological effects. The results show that such materials can be easily distinguished from the pure solvent, and from each other, by the use of UV-VIS and Raman spectroscopy, while FTIR is insensitive to these differences. This opens up a whole new field of endeavor for inorganic materials scientists interested in biological effects.

Patterning micron-sized features in a cross-linked poly(acrylic acid) film by a wet etching process

This paper describes a photolithographic method to create sub-micron-scale patterns of cation-cross-linked poly(acrylic acid) (CCL-PAA). PAA can be cross-linked with a wide range of metal cations-including, but not limited to, Ag, Ca, Pd, Al, La, and Ti. Upon patterning a positive photoresist (diazonaphthoquinone-novolac resin) on a film of CCL-PAA, the exposed regions of CCL-PAA were etched by either an aqueous NaOH or EDTA solution. The initial cross-linking cation could be exchanged for a second cation that could not be patterned photolithographically. We used these patterned films of CCL-PAA i) to host and template the reduction of metallic cations to metallic nanoparticles, and ii) to fabricate porous, low- dielectric substrates.

Glass and bioglass nanopowders by flame synthesis

The preparation of amorphous nanopowders by flame synthesis opens access to common soda-lime, metal-doped glasses or bioglasses in the range of 20-80 nm and offers an alternative to conventional wet-phase preparation, solid state reactions or melting.

A general process for in situ formation of functional surface layers on ceramics

Ceramics are often prepared with surface layers of different composition from the bulk, in order to impart a specific functionality to the surface or to act as a protective layer for the bulk material. Here we describe a general process by which functional surface layers with a nanometre-scale compositional gradient can be readily formed during the production of bulk ceramic components. The basis of our approach is to incorporate selected low-molecular-mass additives into either the precursor polymer from which the ceramic forms, or the binder polymer used to prepare bulk components from ceramic powders. Thermal treatment of the resulting bodies leads to controlled phase separation ('bleed out') of the additives, analogous to the normally undesirable outward loss of low-molecular-mass components from some plastics; subsequent calcination stabilizes the compositionally changed surface region, generating a functional surface layer. This approach is applicable to a wide range of materials and morphologies, and should find use in catalysts, composites and environmental barrier coatings.

Atmospheric weathering and silica-coated feldspar: analogy with zeolite molecular sieves, granite weathering, soil formation, ornamental slabs, and ceramics

Feldspar surfaces respond to chemical, biological, and mechanical weathering. The simplest termination is hydroxyl (OH), which interacts with any adsorption layer. Acid leaching of alkalis and aluminum generated a silica-rich, nanometers-thick skin on certain feldspars. Natural K, Na-feldspars develop fragile surfaces as etch pits expand into micrometer honeycombs, possibly colonized by lichens. Most crystals have various irregular coats. Based on surface-catalytic processes in molecular sieve zeolites, I proposed that some natural feldspars lose weakly bonded Al-OH (aluminol) to yield surfaces terminated by strongly bonded Si-OH (silanol). This might explain why some old feldspar-bearing rocks weather slower than predicted from brief laboratory dissolution. Lack of an Al-OH infrared frequency from a feldspar surface is consistent with such a silanol-dominated surface. Raman spectra of altered patches on acid-leached albite correspond with amorphous silica rather than hydroxylated silica-feldspar, but natural feldspar may respond differently. The crystal structure of H-exchanged feldspar provides atomic positions for computer modeling of complex ideas for silica-terminated feldspar surfaces. Natural weathering also depends on swings of temperature and hydration, plus transport of particles, molecules, and ionic complexes by rain and wind. Soil formation might be enhanced by crushing granitic outcrops to generate new Al-rich surfaces favorable for chemical and biological weathering. Ornamental slabs used by architects and monumental masons might last longer by minimizing mechanical abrasion during sawing and polishing and by silicifying the surface. Silica-terminated feldspar might be a promising ceramic surface.