Electroassisted Incorporation of Ferrocene within Sol-Gel Silica Films to Enhance Electron Transfer

The sol-gel method is a straightforward technique that allows electrode modification with silica thin films. Furthermore, the silica pores could be functionalized to enhance the electrical conductivity and reactivity of the silica films. In this context, silica thin films were functionalized with ferrocene species. This functionalization was performed by electroassisted accumulation, generating a micro-structured composite electrode (Fc@SiO2 electrode). These modified electrodes were characterized by electrochemical and spectroelectrochemical methods, pointing out that ferrocene species were confined with high stability within the microporous silica thin film, demonstrating the good adsorption capacity of the silica. While the spectroelectrochemical characterization indicates that only a fraction of the confined species within the silica films were electroactive, the electrochemical results demonstrate that the Fc@SiO2 film enhances the electrochemical response of cytochrome c in a solution, which gives rise to further applications of these films for redox-controlled release and electrochemical detection of other redox-active proteins.

Valorization of Starch to Biobased Materials: A Review

Many concerns are being expressed about the biodegradability, biocompatibility, and long-term viability of polymer-based substances. This prompted the quest for an alternative source of material that could be utilized for various purposes. Starch is widely used as a thickener, emulsifier, and binder in many food and non-food sectors, but research focuses on increasing its application beyond these areas. Due to its biodegradability, low cost, renewability, and abundance, starch is considered a "green path" raw material for generating porous substances such as aerogels, biofoams, and bioplastics, which have sparked an academic interest. Existing research has focused on strategies for developing biomaterials from organic polymers (e.g., cellulose), but there has been little research on its polysaccharide counterpart (starch). This review paper highlighted the structure of starch, the context of amylose and amylopectin, and the extraction and modification of starch with their processes and limitations. Moreover, this paper describes nanofillers, intelligent pH-sensitive films, biofoams, aerogels of various types, bioplastics, and their precursors, including drying and manufacturing. The perspectives reveal the great potential of starch-based biomaterials in food, pharmaceuticals, biomedicine, and non-food applications.

Zirconia aerogels for thermal management: Review of synthesis, processing, and properties information architecture

Zirconia aerogels are porous nanomaterials with high specific surface areas and low thermal conductivities that are suitable for a wide range of functions. The applications of zirconia aerogels include numerous uses in thermal management systems that are specifically beneficial in aeronautics and aerospace systems. This review seeks to detail the synthesis, processing, and characterization of these unique materials. However, the many distinctive synthesis pathways and processing conditions of zirconia aerogels can make the optimization of these materials difficult, potentially inhibiting further development. Independent variables in the synthesis process alone include zirconium precursor, rare earth stabilizer, solvent system, gelation agent, and surfactant templating agent. If only two distinct options were available for each synthetic variable, there would be up to 32 different synthetic pathways; if there were three options for each variable, 243 different synthetic pathways would be possible. Apart from the gel synthesis, processing conditions, including drying method, drying temperature, drying solvent, and sintering temperature, as well as various techniques used to characterize aerogels, need to be considered. To mitigate the sheer volume of synthetic parameters, this review uses an architected information structure to contemplate approximately 600 aerogel materials, along with the synthesis and processing conditions that make each material unique. By utilizing this information structure, containing over 10,000 relationships amongst 3,800 nodes, the connection between specific properties of zirconia aerogels and the pathways used to produce them can be more easily visualized, leading to a more effective understanding of the many variables that are used in the synthesis and processing of these materials. This review seeks to utilize data science in a way that can elucidate structure-property relationships in colloidal chemistry, providing a more efficient way to evaluate the synthesis and processing of materials with high experimental dimensionality.

The effect of graphene-nanoplatelets on gelation and structural integrity of a polyvinyltrimethoxysilane-based aerogel

Aerogels suffer greatly from poor mechanical properties resulting from their particulate structure. They also experience noticeable pore shrinkage during drying due to their low structural integrity. These shortfalls limit their broad application. To enhance the mechanical properties and improve the structural integrity of silica-based aerogels, graphene nanoplatelets (GnPs), as a nanofiller, were embedded into the solution of polymerized vinyltrimethoxysilane (VTMS) to prepare P-VTMS-based silica/GnP (PE-b-Si/GnP) hybrid aerogel monoliths based on sol–gel synthesis and supercritical drying. The inclusion of GnPs in our polymer-based silica aerogel processes reinforced the nanostructure and suppressed PE-b-Si nanopore shrinkage during supercritical drying, thus acting as an effective anti-shrinkage nanofiller. Accordingly, the GnPs significantly contributed to the PE-b-Si solution's uniform gelation and to the change of the hydrophilic nature to a hydrophobic one even with 1 wt% addition. In this study, the influence of the GnP content on the sol–gel process, structure, and physical properties of PE-based silica aerogels is studied.

Aerogels suffer greatly from poor mechanical properties resulting from their particulate structure.

Poly(Urethane-Acrylate) Aerogels via Radical Polymerization of Dendritic Urethane-Acrylate Monomers

The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur RE) triisocyanate core. The terminal acrylate groups (three at the tip of each of the three branches, nine in total) were polymerized with 2,2'-azobis(isobutyronitrile) (AIBN) via free radical chemistry. The resulting wet-gels were dried with supercritical fluid (SCF) CO₂. Aerogels were characterized with ATR-FTIR and solid-state 13C NMR. The porous network was probed with N₂-sorption and scanning electron microscopy (SEM). The thermal stability of aerogels was studied with thermogravimetric analysis (TGA). Most aerogels were macroporous materials (porosity > 80%), with high thermal stability (up to 300 °C). Aerogels were softer at low monomer concentrations and more rigid at higher concentrations. The material properties were compared with those of analogous aerogels bearing only one acrylate moiety at the tip of each branch and the same cores, and with those of analogous aerogels bearing norbornene instead of acrylate moieties. The nine-terminal acrylate-based monomers of this study caused rapid decrease of the solubility of the growing polymer and made possible aerogels with much smaller particles and much higher surface areas. For the first time, aliphatic/flexible triisocyanate-based materials could be made with similar properties in terms of particle size and surface areas to their aromatic/rigid analogues. Finally, it was found that with monomers with a high number of crosslinkable groups, material properties are determined by multifunctionality and thus aerogels based on 9-acrylate- and 9-norbornene-terminated monomers were similar. Materials with aromatic cores are carbonizable with satisfactory yields (20⁻30% w/w) to mostly microporous materials (BET surface areas: 640⁻740 m² g-1; micropore surface areas: 360⁻430 m² g-1).

Millimeter-Size Spherical Polyurea Aerogel Beads with Narrow Size Distribution

We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying the resulting wet spherical gels with supercritical fluid (SCF) CO₂ afforded spherical aerogel beads with a mean diameter of 2.7 mm, and a narrow size distribution (full width at half maximum: 0.4 mm). Spherical PUA aerogel beads had low density (0.166 ± 0.001 g cm⁻3), high porosity (87% v/v) and high surface area (197 m² g⁻1). IR, ¹H magic angle spinning (MAS) and 13C cross-polarization magic angle spinning (CPMAS) NMR showed the characteristic peaks of urea and the isocyanurate ring. Scanning electron microscopy (SEM) showed the presence of a thin, yet porous skin on the surface of the beads with a different (denser) morphology than their interior. The synthetic method shown here is simple, cost-efficient and suitable for large-scale production of PUA aerogel beads.

Scalable, hydrophobic and highly-stretchable poly(isocyanurate–urethane) aerogels

Scalable, low-density and flexible aerogels offer a unique combination of excellent mechanical properties and scalable manufacturability. Herein, we report the fabrication of a family of low-density, ambient-dried and hydrophobic poly(isocyanurate–urethane) aerogels derived from a triisocyanate precursor. The bulk densities ranged from 0.28 to 0.37 g cm⁻³ with porosities above 70% v/v. The aerogels exhibit a highly stretchable behavior with a rapid increase in the Young's modulus with bulk density (slope of log–log plot > 6.0). In addition, the aerogels are very compressible (more than 80% compressive strain) with high shape recovery rate (more than 80% recovery in 30 s). Under tension even at high strains (e.g., more than 100% tensile strain), the aerogels at lower densities do not display a significant lateral contraction and have a Poisson's ratio of only 0.22. Under dynamic conditions, the properties (e.g., complex moduli and dynamic stress–strain curves) are highly frequency- and rate-dependent, particularly in the Hopkinson pressure bar experiment where in comparison with quasi-static compression results, the properties such as mechanical strength were three orders of magnitude stiffer. The attained outcome of this work supports a basis on the understanding of the fundamental mechanical behavior of a scalable organic aerogel with potential in engineering applications including damping, energy absorption, and substrates for flexible devices.

Scalable, low-density and flexible aerogels offer a unique combination of excellent mechanical properties and scalable manufacturability.

Mechanical reinforcement of a cellulose aerogel with nanocrystalline cellulose as reinforcer

The NCC reinforced cellulose aerogel exhibited better mechanical properties, as well as good adsorption performance and reusability.

Synthesis and characterization of partially fluorinated aerogels and xerogels from environmentally-compatible precursors

A new fluorocyclic monomer, prepared from environmentally benign starting materials, was used to synthesize the first known fluorocyclic aero- and xerogels.

Robust urethane-bridged silica aerogels available for water-carved aerosculptures

Novel in situ bridged silica precursors were used to synthesize robust aerogels for aerosculptures carved with aqueous solvents.

Synthesis of aerogels: from molecular routes to 3-dimensional nanoparticle assembly

Colloidal nanocrystals are extensively used as building blocks in nanoscience, and amazing results have been achieved in assembling them into ordered, close-packed structures. But in spite of great efforts, the size of these structures is typically restricted to a few micrometers, and it is very hard to extend them into the macroscopic world. In comparison, aerogels are macroscopic materials, highly porous, disordered, ultralight and with immense surface areas. With these distinctive characteristics, they are entirely contrary to common nanoparticle assemblies such as superlattices or nanocrystal solids, and therefore cover a different range of applications. While aerogels are traditionally synthesized by molecular routes based on aqueous sol-gel chemistry, in the last few years the gelation of nanoparticle dispersions became a viable alternative to improve the crystallinity and to widen the structural, morphological and compositional complexity of aerogels. In this Review, the different approaches to inorganic non-siliceous and non-carbon aerogels are addressed. We start our discussion with wet chemical routes involving molecular precursors, followed by processing methods using nanoparticles as building blocks. A unique feature of many of these routes is the fact that a macroscopic, often monolithic body is produced by pure self-assembly of nanosized colloids without the need for any templates.

A robust salt-tolerant superoleophobic aerogel inspired by seaweed for efficient oil–water separation in marine environments

A robust salt-tolerant superoleophobic aerogel was fabricated by a simple combined freeze-drying and ionic cross-linking method for oil–seawater separation.

Direct solvothermal preparation of nanostructured fluoride aerogels based on AlF3

AlF3-based aerogels, a new class of inorganic aerogels, are prepared in a novel direct process that combines fluoride sol-gel synthesis with high temperature supercritical drying. The bulk structure of the solid products depends decisively on the applied solvent(s); very voluminous bulk aerogels are obtained only with MeOH that is used either alone or in combination with some other polar solvents. MeOH acts as a methoxylation agent; and formed methoxy (MeO) species are remarkably stable and deactivate the surface acidic sites. Removal of MeO species under moderate conditions results in catalytically active fluorides with a preserved nanostructure. In preparations with MeOH, preferential growth of anisotropic nanoparticles (nanorods) is the key step that leads to the formation of very open aerogel structures. Another process, dehydration of alcohols, results in some hydroxylation and hydration that lead to the formation of distinctive surface and bulk OH/H2O species. The structure of AlF3-based aerogels is consistent with the hexagonal tungsten bronze (HTB) β-AlF3 although their composition corresponds to a formula AlF3-x(OH, OMe)x·yH2O (x = 0.1 ± 0.05). Some other characteristics of the fluoride nanoparticles, like crystallinity, particle size, and uniformity, can be effectively controlled by the temperature of the solvothermal process. The described methodology allows a controllable preparation of catalytically active fluorides in the form of regularly shaped and uniformly sized nanoparticles.

Highly flexible silica aerogels derived from methyltriethoxysilane and polydimethylsiloxane

The rapid synthesis of low-density, highly hydrophobic silica aerogels was performedviaambient pressure drying.