Zeolite Crystallization Inside Chemically Recyclable Ordered Nanoporous Co3O4 Scaffold: Precise Replication and Accelerated Crystallization

The synthesis of mesoporous zeolites has garnered attention with regard to improving their catalytic and adsorption performances. While the hard-templating method provides opportunities to design precisely controlled hierarchical micro- and mesoporous structures, synthesizing mesoporous zeolites without external precipitation requires significant work. This is mainly due to the absence of usable templates other than carbon with hydrophobic surfaces. Herein, it is demonstrated that the Co3O4 template is valuable in preparing mesoporous silicalite-1 and ZSM-5 with a precisely controlled porous structure through hydrothermal synthesis. Unlike conventional carbon templates, the Co3O4 template is relatively hydrophilic, effective in suppressing external precipitation, and is reusable by dissolving in an acidic solution. The crystallization process also differs from that of the carbon template, as the silicate precipitates on a 3D ordered nanoporous Co3O4 scaffold, followed by crystallization and crystal growth. Furthermore, it is unexpectedly observed that the zeolite crystallization is accelerated in the Co3O4 template. The synthetic approach utilizing nanoporous metal oxides opens new doors for the control of the hierarchical structure of zeolites, as well as for the design of metal oxide-zeolite nanocomposite catalysts, due to the potential extensibility of the combination of metal oxides and zeolites.

Bioinspired synthesis of bioactive glass nanocomposites for hyaluronic acid delivery to bone and skin

In this study, we present nanocomposites of bioactive glass (BG) and hyaluronic acid (HA) (nano-BGHA) for effective delivery of HA to skin and bone. The synthesis of the nanocomposites has been carried out through the bio-inspired method, which is a modification of the traditional Stober's synthesis as it avoids using ethanol, ammonia, synthetic surfactants, or high-temperature calcination. This environmentally friendly, bio-inspired route allowed the synthesis of mesoporous nanocomposites with an average hydrodynamic radius of ∼190 nm and an average net surface charge of ∼-21 mV. Most nanocomposites are amorphous and bioactive in nature with over 70 % cellular viability for skin and bone cell lines even at high concentrations, along with high cellular uptake (90-100 %). Furthermore, the nanocomposites could penetrate skin cells in a transwell set-up and artificial human skin membrane (StratM®), thus depicting an attractive strategy for the delivery of HA to the skin. The purpose of the study is to develop nanocomposites of HA and BG that can have potential applications in non-invasive treatments that require the delivery of high molecular weight HA such as in the case of osteoarthritis, sports injury treatments, eye drops, wound healing, and some anticancer treatments, if further investigated. The presence of BG further enhances the range to bone-related applications. Additionally, the nanocomposites can have potential cosmeceutical applications where HA is abundantly used, for instance in moisturizers, dermal fillers, shampoos, anti-wrinkle creams, etc.

Investigation of the Mechanism of SiO2 Particle and Capsule Formation at the Oil-Water Interface of Dye-Stabilized Emulsions

In a previous contribution we described the formation of silica nanostructures in dye-stabilized nanoemulsions from tetraethyl orthosilicate droplets in water. Depending on the type of dye, either capsules (crystal violet, CV) or nanoparticles (congo red, CR) are formed. The thorough study of the sol-gel process uses a combination of time- and/or temperature-resolved small-angle X-ray scattering, transmission electron microscopy, and ¹H NMR spectroscopy to elucidate the detailed kinetics and mechanism of structure formation. In both cases, small nuclei of 1.5-2 nm are formed, followed by either a fast cluster-cluster (CV) or a much slower monomer-cluster aggregation (CR). The former leads to a cross-linked network and finally to patchy capsules, while the latter leads to individual nanoparticles (SNPs). From an Avrami plot it can be deduced that the SNPs are formed by an interface-controlled one-dimensional growth process. The mechanisms are based on the different local environments at the oil-water interface, which is either slightly acidic (CV) or fairly basic (CR). The kinetics differ by a factor between 3 and 20 and are presumably caused by the different mobility of the catalyzing species H⁺ or OH^-.

Preparation of mesoporous nitrogen-doped titania comprising large crystallites with low thermal conductivity

Reducing the thermal conductivity (κ) of mesoporous N-doped titania (TiO2) is crucial for the development of TiO2-based materials that exhibit excellent electronic, photochemical, and thermoelectric properties. Mesopores can contribute to the reduction of κ via phonon scattering, and the scattering effect due to the randomness of crystal interfaces should be significantly reduced to clarify the role of mesopores in reducing thermal conductivity. Highly ordered mesoporous N-doped TiO2 comprising large crystallites was prepared with silica colloidal crystals as a template into which a Ti source was introduced, followed by calcination with urea. N-doped samples comprising large crystallites exhibiting random mesopores were also prepared and used for the investigation of the effects of the shape and arrangement of the mesopore on phonon scattering. The mesostructures of the two separately prepared N-doped TiO2 samples were retained after sintering at 873 K and 80 MPa to fabricate pellets. Furthermore, the effective suppression of the long mean-free-path phonon conduction by the thin pore walls at a nanometer scale thickness significantly reduced the thermal conductivities of both samples. The presence of ordered mesopores further contributed to the reduction of κ, which was probably due to the enhanced contribution of the backscattering of phonons caused by ordered pore wall surfaces.

Preparation of Ordered Nanoporous Indium Tin Oxides with Large Crystallites and Individual Control over Their Thermal and Electrical Conductivities

Metal oxides are considered suitable candidates for thermoelectric materials owing to their high chemical stabilities. The formation of ordered nanopores within these materials, which decreases thermal conductivity (κ), has attracted significant interest. However, the electrical conductivity (σ) of reported nanoporous metal oxides is low, owing to electron scattering at the thin pore walls and many grain boundaries formed by small crystallites. Therefore, a novel synthesis method that can control pore walls while forming relatively large crystallites to reduce κ and retain σ is required. In this study, we used indium tin oxide (ITO), which is a typical example among metal oxides with high σ. Nanoporous ITOs with large crystallite sizes of several hundred nanometers and larger were successfully prepared using indium chloride as a source of indium. The pore sizes were varied using colloidal silica nanoparticles with different particle sizes as templates. The crystal phase and nanoporous structure of ITO were preserved after spark plasma sintering at 723 K and 80 MPa. The κ was significantly lower than that reported for bulk ITO due to the phonon scattering caused by the nanoporous structure and thin pore walls. There was a limited decrease in σ even with high porosity. These findings show that κ and σ are independently controllable through the precise control of the structure. The control of the thickness of the pore walls at tens of nanometers was effective for the selective scattering of phonons, while almost retaining electron mobility. The remarkable preservation of σ was attributed to the large crystallites that maintained paths for electron conduction and decreased electron scattering at the grain boundaries.

Improvement of the Centrifugal Force in Gravity Driven Method for the Fabrication of Highly Ordered and Submillimeter-Thick Colloidal Crystal

In this paper, we propose a modified gravity method by introducing centrifugal force to promote the stacking of silica particles and the order of formed colloidal crystals. In this method, a monodispersed silica colloidal solution is filled into empty cells and placed onto rotation arms that are designed to apply an external centrifugal force to the filled silica solution. When sample fabrication is in progress, silica particles are forced toward the edges of the cells. The number of defects in the colloidal crystal decreases and the structural order increases during this process. The highest reflectivity and structural order of a sample was obtained when the external centrifugal force was 18 G. Compared to the samples prepared using the conventional stacking method, samples fabricated with centrifugal force possess higher reflectivity and structural order. The reflectivity increases from 68% to 90%, with an increase in centrifugal force from 0 to 18 G.

Synthesis of Cristobalite Containing Ordered Interstitial Mesopores using Crystallization of Silica Colloidal Crystals

Cristobalite with ordered interstitial dual-sized mesopores was synthesized through the crystallization of silica colloidal crystals composed of monodispersed amorphous silica nanoparticles. An aqueous solution containing both a flux (Na₂ O) and a carbon precursor (an aqueous low-molecular weight phenolic resin) was infiltrated into the interstices of silica colloidal crystals. The organic fraction in the nanocomposite was further polymerized and subsequently carbonized in an Ar flow at 750 °C to reinforce the colloidal crystal structure. The thermal treatment resulted in the crystallization of the colloidal crystals into cristobalite while retaining the porous structure. The cristobalite-carbon nanocomposite was calcined in air to remove the carbon and create interstitial ordered mesopores in the cristobalite. The surfaces of crystalline mesoporous silica are quite different from those of various ordered mesoporous silica with amorphous frameworks; thus, the present findings will be useful for a precise understanding and control of the interfaces between the mesopores and silica networks.

Preparation of periodic mesoporous organosilica with large mesopores using silica colloidal crystals as templates

Organosiloxane-based mesoporous materials with periodically ordered pores (periodic mesoporous organosilica, PMO) have many applications due to their various organic functions, high surface areas, and large pore volumes. Conventional methods using surfactant templates (soft templates) are limited in terms of the diversity of organosilane precursors and precise control over the pore size in a relatively large mesopore region (10-50 nm). This paper demonstrates the preparation of PMOs with precisely controlled pore sizes (>10 nm in diameter) and various organosiloxane frameworks, using colloidal crystals of monodisperse silica nanospheres as a template. An inverse opal structure with interconnected spherical mesopores was obtained through polycondensation of hydrolyzed organoalkoxysilanes [(EtO)₃Si-R-Si(OEt)₃, R = C₂H₄, CH[double bond, length as m-dash]CH, and C₆H₄; PhSi(OEt)₃], within the voids of silica colloidal crystals, followed by the preferential dissolution of silica under well-controlled basic conditions. The pore size varied depending on the size of the silica nanospheres. The versatility of this method will allow for the wide tuning of the physical and chemical properties of organosiloxane-based mesoporous materials.

Green Chemistry in Red Emulsion: Interface of Dye Stabilized Emulsions as a Powerful Platform for the Formation of sub-20-nm SiO2 Nanoparticles

Dye stabilized nanoemulsions offer the unique possibility of creating both silica capsules and sub-20-nm particles with precise control of particle size and narrow dispersity from the same system by the choice of the proper dye. The large o/w interface enhances the kinetics of particle formation significantly over macroscopic interfaces which enables the synthesis of silica nanoparticles without any catalyst or elevated temperatures under static conditions. This is in contrast to syntheses for sub-20-nm silica nanoparticles described until now which can normally not be conducted at neutral pH and/or room temperature without stirring. Furthermore, the synthesis can be run without any additional organic solvent and the dyes can be easily removed from the dispersion which opens the pathway to silica dispersions containing only particles, traces of ethanol and water at neutral pH without centrifugation, washing, or redispersion in accordance with the idea of "green chemistry".

Solid-state synthesis of ordered mesoporous carbon catalysts via a mechanochemical assembly through coordination cross-linking

Ordered mesoporous carbons (OMCs) have demonstrated great potential in catalysis, and as supercapacitors and adsorbents. Since the introduction of the organic–organic self-assembly approach in 2004/2005 until now, the direct synthesis of OMCs is still limited to the wet processing of phenol-formaldehyde polycondensation, which involves soluble toxic precursors, and acid or alkali catalysts, and requires multiple synthesis steps, thus restricting the widespread application of OMCs. Herein, we report a simple, general, scalable and sustainable solid-state synthesis of OMCs and nickel OMCs with uniform and tunable mesopores (∼4–10 nm), large pore volumes (up to 0.96 cm³ g⁻¹) and high-surface areas exceeding 1,000 m² g⁻¹, based on a mechanochemical assembly between polyphenol-metal complexes and triblock co-polymers. Nickel nanoparticles (∼5.40 nm) confined in the cylindrical nanochannels show great thermal stability at 600 °C. Moreover, the nickel OMCs offer exceptional activity in the hydrogenation of bulky molecules (∼2 nm).

Ordered mesoporous carbons have shown promise in a range of applications, but sustainable methods to achieve their large scale production are lacking. Here, Dai and coworkers produce OMCs via the mechanochemical assembly of non-toxic polyphenol-metal complexes and triblock copolymers, followed by pyrolysis.