Synthesis of micrometer-sized hard silica spheres with uniform mesopore size and textural pores

Multicomponent oxide microspheres with designed macroporosity (MICROSCAFS®): a customized platform for chemicals immobilization

A novel versatile, easily recoverable, and recyclable material platform is herein presented, consisting of multicomponent oxide microspheres, of silica-titania and silica-titania-hafnia composition, with tailored interconnected macroporosity (MICROSCAFS®). When functionalized or loaded with desired species, they are potential enablers of emerging applications in environmental remediation, among other fields. We combine emulsion templating for the spherical shape of the particles, with an adapted sol-gel technique involving polymerization-induced phase separation by spinodal decomposition. An advantage of our method regards the employed mix of precursors, which prevents the use of specific gelation additives and porogens and allows a high reproducibility of MICROSCAFS®. We present insight into their formation mechanism using cryo-scanning electron microscopy, and a systematic study of the effect of multiple synthesis parameters on the MICROSCAFS® size and porosity. The composition of the silicon precursors has the most significant effect on fine-tuning the pores size, ranging from the nanometer to the micron scale. Mechanical properties are correlated with morphological features. Larger macroporosity (68% open porosity, estimated by X-ray computed tomography) leads to less stiffness, higher elastic recovery, and compressibility values up to 42%. We believe this study creates a base for consistent custom MICROSCAFS® production, with a design for various future applications.

Preparation of Templated Materials and Their Application to Typical Pollutants in Wastewater: A Review

As the pollution and destruction of global water resources become more and more severe, the treatment of wastewater has attracted significant attention. The template method is a synthetic method in which the template is the main configuration to control, influence, and modify the morphology as well as control the dimensions of the material, thus achieving the properties that determine the material. It is simple, highly reproducible, and predictable, and more importantly, it can effectively control the pore structure, size, and morphology of the material, providing a novel platform for the preparation of adsorbent materials with excellent adsorption properties. This review focuses on the classification of the templates according to their properties and spatial domain-limiting capabilities, reviews the types of hard and soft template materials and their synthetic routes, and further discusses the modulation of the morphological structure of the materials by the introduction of templates. In addition, the application and adsorption mechanisms of heavy metal ions and dyes are reviewed based on the regulatory behavior of the template method.

Macroporosity Control by Phase Separation in Sol-Gel Derived Monoliths and Microspheres

Macroporous and hierarchically macro/mesoporous materials (mostly monoliths and microspheres) have attracted much attention for a variety of applications, such as supporting or enabling materials in chromatography, energy storage and conversion, catalysis, biomedical devices, drug delivery systems, and environmental remediation. A well-succeeded method to obtain these tailored porous materials relies on the sol-gel technique, combined with phase separation by spinodal decomposition, and involves as well emulsification as a soft template, in the case of the synthesis of porous microspheres. Significant advancements have been witnessed, in terms of synthesis methodologies optimized either for the use of alkoxides or metal-salts and material design, including the grafting or immobilization of a specific species (or nanoparticles) to enable the most recent trends in technological applications, such as photocatalysis. In this context, the evolution, in terms of material composition and synthesis strategies, is discussed in a concerted fashion in this review, with the goal of inspiring new improvements and breakthroughs in the framework of porous materials.

Synthesis of fully porous silica microspheres with high specific surface area for fast HPLC separation of intact proteins and digests of ovalbumin

Fully porous silica microspheres (FPSM) with high specific surface area and hierarchical pore as matrix for HPLC were prepared. First, the porous silica nanospheres with controllable particle size and pore diameter were successfully synthesized using a dual-templating approach, the pore size of nanospheres can be increased to 18.4 nm by changing the molar ratios of octyltrimethylammonium bromide (TOMAB) and cetyltrimethyl ammonium bromide (CTAB), which is suitable for separation and analysis of biomolecules without pore enlargement. Then, the micron FPSM with hierarchical pore were synthesized by polymerization-induced colloid aggregation (PICA) using the porous nanospheres as a silicon source, which has a large mesoporous structure (35.2 nm) and high specific surface area (560 m² g^-1). Subsequently, the FPSM modified with octadecyltrichlorosilane were studied as stationary phase for separation of cytochrome C, lysozyme, ribonuclease A, and ovalbumin, bovine serum albumin, and the baseline separation of five proteins was achieved within 1 min. The prepared column was also applied to the fast separation of digests of ovalbumin, and more chromatographic peaks were obtained compared to a commercial column under the same gradient elution conditions. In addition, the static-binding capacity of the functionalized FPSM for bovine serum albumin (BSA) was measured to be 276 mg g^-1, which was nearly twice the static adsorption given in literature. Therefore, these FPSM with high specific surface area and hierarchical pore structure are expected to have great potential for the separation of complex biological samples using HPLC. Graphical abstract A synthetic strategy was provided towards FPSM with hierarchical pores and high specific surface area using porous nanospheres as silicon source. The outstanding performance of the FPSM is that it has a high specific surface area while maintaining a large mesoporous size, which overcomes the disadvantage of sacrificing the specific surface area when increasing the pore size of porous silica microspheres prepared by using the traditional PICA method.

Preparation of Fe3O4Spherical Nanoporous Particles Facilitated by Polyethylene Glycol 4000

Much interest has been attracted to the magnetic materials with porous structure because of their unique properties and potential applications. In this report, Fe3O4nanoporous particles assembled from small Fe3O4nanoparticles have been prepared by thermal decomposition of iron acetylacetonate in the presence of polyethylene glycol 4000. The size of the spherical nanoporous particles is 100-200 nm. Surface area measurement shows that these Fe3O4nanoporous particles have a high surface area of 87.5 m2/g. Magnetization measurement and Mössbauer spectrum indicate that these particles are nearly superparamagnetic at room temperature. It is found that the morphology of the products is greatly influenced by polyethylene glycol concentration and the polymerization degree of polyethylene glycol. Polyethylene glycol molecules are believed to facilitate the formation of the spherical assembly.

Nanoporous Pt with high surface area by reaction-limited aggregation of nanoparticles

Nanoporous structures with high active surface areas are critical for a variety of applications. Here, we present a general templateless strategy to produce such porous structures by controlled aggregation of nanostructured subunits and apply the principles for synthesizing nanoporous Pt for electrocatalytic oxidation of methanol. The nature of the aggregate produced is controlled by tuning the electrostatic interaction between surfactant-free nanoparticles in the solution phase. When the repulsive force between the particles is very large, the particles are stabilized in the solution while instantaneous aggregation leading to fractal-like structures results when the repulsive force is very low. Controlling the repulsive interaction to an optimum, intermediate value results in the formation of compact structures with very large surface areas. In the case of Pt, nanoporous clusters with an extremely high specific surface area (39 m2/g) and high activity for methanol oxidation have been produced. Preliminary investigations indicate that the method is general and can be easily extended to produce nanoporous structures of many inorganic materials.

Engineering biodegradable polyester particles with specific drug targeting and drug release properties

Poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres and nanoparticles remain the focus of intensive research effort directed to the controlled release and in vivo localization of drugs. In recent years engineering approaches have been devised to create novel micro- and nano-particles which provide greater control over the drug release profile and present opportunities for drug targeting at the tissue and cellular levels. This has been possible with better understanding and manipulation of the fabrication and degradation processes, particularly emulsion-solvent extraction, and conjugation of polyesters with ligands or other polymers before or after particle formation. As a result, particle surface and internal porosity have been designed to meet criteria-facilitating passive targeting (e.g., for pulmonary delivery), modification of the drug release profile (e.g., attenuation of the burst release) and active targeting via ligand binding to specific cell receptors. It is now possible to envisage adventurous applications for polyester microparticles beyond their inherent role as biodegradable, controlled drug delivery vehicles. These may include drug delivery vehicles for the treatment of cerebral disease and tumor targeting, and co-delivery of drugs in a pulsatile and/or time-delayed fashion.

Facile synthesis of monodisperse microspheres and gigantic hollow shells of mesoporous silica in mixed water-ethanol solvents

Mesoporous silica materials with a variety of morphologies, such as monodisperse microspheres, gigantic hollow structures comprising a thin shell with a hole, and gigantic hollow structures consisting of an outer thin shell and an inner layer composed of many small spheres, have been readily synthesized in mixed water-ethanol solvents at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained mesoporous silica generally shows a disordered mesostructure with typical average pore sizes ranging from 3.1 to 3.8 nm. The effects of the water-to-ethanol volume ratio (r), the volume content of tetraethyl orthosilicate TEOS (x), and the CTAB concentration in the solution on the final morphology of the mesoporous silica products have been investigated. The growth process of gigantic hollow shells of mesoporous silica through templating emulsion droplets of TEOS in mixed water-ethanol solution has been monitored directly with optical microscopy. Generally, the morphology of mesoporous silica can be regulated from microspheres through gigantic hollow structures composed of small spheres to gigantic hollow structures with a thin shell by increasing the water-to-ethanol volume ratio, increasing the TEOS volume content, or decreasing the CTAB concentration. A plausible mechanism for the morphological regulation of mesoporous silica by adjusting various experimental parameters has been put forward by considering the existing state of the unhydrolyzed and partially hydrolyzed TEOS in the synthesis system.