Preparation of POSS-based organic–inorganic hybrid mesoporous materials networks through Schiff base chemistry

Evolutionary Progress of Silica Aerogels and Their Classification Based on Composition: An Overview

Aerogels are highly porous materials with fascinating properties prepared using sol-gel chemistry. Due to their unique physical and chemical properties, aerogels are recognized as potential candidates for diverse applications, including thermal insulation, sensor, environmental remediation, etc. Despite these applications, aerogels are not routinely found in our daily life because they are fragile and have highly limited scale-up productions. It remains extremely challenging to improve the mechanical properties of aerogels without adversely affecting their other properties. To boost the practical applications, it is necessary to develop efficient, low-cost methods to produce aerogels in a sustainable way. This comprehensive review surveys the progress in the development of aerogels and their classification based on the chemical composition of the network. Recent achievements in organic, inorganic, and hybrid materials and their outstanding physical properties are discussed. The major focus of this review lies in approaches that allow tailoring of aerogel properties to meet application-driven requirements. We begin with a brief discussion of the fundamental issues in silica aerogels and then proceed to provide an overview of the synthesis of organic and hybrid aerogels from various precursors. Organic aerogels show promising results with excellent mechanical strength, but there are still several issues that need further exploration. Finally, growing points and perspectives of the aerogel field are summarized.

Facile Fabrication of Flexible, Robust, and Superhydrophobic Hybrid Aerogel

Silica aerogels, which are constructed with silica nanoparticles and numerous nanoscale pores, have many outstanding attributes, but they are usually brittle and hydrophilic. For the construction of a robust aerogel, the novel polyhedral oligomeric silsesquioxane (POSS) was introduced to prepare a series of aerogels possessing particles covered with elastic cushion to improve the mechanical property. The multialkoxy POSS, which possessed stiff Si-O-Si nanocages and flexible alkyl chains, was synthesized via thiol-ene click chemistry. After a facile and efficient approach, a partially ordered structure of SiO₂ nanoparticles and organic elastic cushion would form spontaneously within the aerogels. With the POSS as the only precursor, several outstanding attributes were achieved in a single aerogel such as high specific surface area (SSA), high compression strength, high compression modulus, and noticeable compression flexibility. Meanwhile, the aerogel was superhydrophobic of which the contact angle (CA) was higher than 153°. Moreover, the potential application of oil-water separation is also presented.

Organic-Inorganic Hydrophobic Nanocomposite Film with a Core-Shell Structure

A method to prepare novel organic-inorganic hydrophobic nanocomposite films was proposed by a site-specific polymerization process. The inorganic part, the core of the nanocomposite, is a ternary SiO₂–Al₂O₃–TiO₂ nanoparticles, which is grafted with methacryloxy propyl trimethoxyl silane (KH570), and wrapped by fluoride and siloxane polymers. The synthesized samples are characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrscopy, X-ray diffractometry (XRD), contact angle meter (CA), and scanning electron microscope (SEM). The results indicate that the novel organic-inorganic hydrophobic nanocomposite with a core-shell structure was synthesized successfully. XRD analysis reveals the nanocomposite film has an amorphous structure, and FTIR analysis indicates the nanoparticles react with a silane coupling agent (methacryloxy propyl trimethoxyl silane KH570). Interestingly, the morphology of the nanoparticle film is influenced by the composition of the core. Further, comparing with the film synthesized by silica nanoparticles, the film formed from SiO₂–Al₂O₃–TiO₂ nanoparticles has higher hydrophobic performance, i.e., the contact angle is greater than 101.7°. In addition, the TEM analysis reveals that the crystal structure of the particles can be changed at high temperatures.

Organosilica hybrid nanomaterials with a high organic content: syntheses and applications of silsesquioxanes

Organic-inorganic hybrid materials garner properties from their organic and inorganic matrices as well as synergistic features, and therefore have recently attracted much attention at the nanoscale. Non-porous organosilica hybrid nanomaterials with a high organic content such as silsesquioxanes (R-SiO_1.5, with R organic groups) and bridged silsesquioxanes (O_1.5Si-R-SiO_1.5) are especially attractive hybrids since they provide 20 to 80 weight percent of organic functional groups in addition to the known chemistry and stability of silica. In the organosilica family, silsesquioxanes (R-SiO_1.5) stand between silicas (SiO₂) and silicones (R₂SiO), and are variously called organosilicas, ormosil (organically-modified silica), polysilsesquioxanes and silica hybrids. Herein, we comprehensively review non-porous silsesquioxane and bridged silsesquioxane nanomaterials and their applications in nanomedicine, electro-optics, and catalysis.

Synthesis and characterization of optically active polyimides and their octa(aminophenyl)silsesquioxane nanocomposites

New optically active diamine (3,5-diaminophenyl)((R)-3,4-dihydro-1-phenylisoquinoline-2(1H)-yl)methanone was successfully prepared. Optically active polyimides (PIs) were synthesized by reacting the prepared diamine with the aromatic tetracarboxylic dianhydrides, namely, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride/pyromelltic dianhydride by thermal imidization method and characterized using Fourier transform infrared and nuclear magnetic resonance spectral techniques. Additionally, PI nanocomposites were also prepared by incorporating amino-functionalized polyhedral oligomeric silsesquioxane named as octa(aminophenyl)silsesquioxane (OAPS). The cut-off wavelengths of PIs and their nanocomposites were found to be less than 350 nm, indicating that the PIs are transparent. The PIs and their nanocomposites were found to have glass transition temperature between 204°C and 269°C (differential scanning calorimetric analysis). The 10% weight loss temperature and char yield were found to be 319.5–420.3°C and 26.3–62.7%, respectively. The PIs were found to be amorphous as indicated by X-ray analysis. The scanning electron microscopic images of the nanocomposites also reveal uniform distribution of the nanoparticles in the nanocomposite. PIs and PI/OAPS nanocomposites were found to have low dielectric constant in the range of 2.59–3.36.

Synthesis of a novel hierarchical mesoporous organic–inorganic nanohybrid using polyhedral oligomericsilsesquioxane bricks

A novel mesoporous silica with high surface area and ordered porosity has been developed using N-methylamino POSS and dichloromethylsilane.

Mesostructured nanomagnetic polyhedral oligomeric silsesquioxanes (POSS) incorporated with dithiol organic anchors for multiple pollutants capturing in wastewater

A functionalizable organosiliceous hybrid magnetic material was facilely constructed by surface polymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) on the Fe3O4 nanoparticles. The resultant Fe3O4@POSS was identified as a mesoporous architecture with an average particle diameter of 20 nm and high specific surface area up to 653.59 m(2) g(-1). After it was tethered with an organic chain containing dithiol via thiol-ene addition reaction, the ultimate material (Fe3O4@POSS-SH) still have moderate specific area (224.20 m(2) g(-1)) with almost identical porous morphology. It turns out to be a convenient, efficient single adsorbent for simultaneous elimination of inorganic heavy metal ions and organic dyes in simulate multicomponent wastewater at ambient temperature. The Fe3O4@POSS-SH nanoparticles can be readily withdrawn from aqueous solutions within a few seconds under moderate magnetic field and exhibit good stability in strong acid and alkaline aqueous matrices. Contaminants-loaded Fe3O4@POSS-SH can be easily regenerated with either methanol-acetic acid (for organic dyes) or hydrochloric acid (for heavy metal ions) under ultrasonication. The renewed one keeps appreciable adsorption capability toward both heavy metal ions and organic dyes, the removal rate for any of the pollutants exceeds 92% to simulate wastewater with multiple pollutants after repeated use for 5 cycles. Beyond the environmental remediation function, thanks to the pendant vinyl groups, the Fe3O4@POSS derived materials rationally integrating distinct or versatile functions could be envisaged and consequently a wide variety of applications may emerge.

Conceptual design of large surface area porous polymeric hybrid media based on polyhedral oligomeric silsesquioxane precursors: preparation, tailoring of porous properties, and internal surface functionalization

We report on the preparation of hybrid, organic-inorganic porous materials derived from polyhedral oligomeric vinylsilsesquioxanes (vinylPOSS) via a single-step molding process. The monolithic, large surface area materials are studied with a particular focus on morphology and porous properties. Radical vinyl polymerization of the nanometer-sized POSS building blocks is therefore utilized via a thermally initiated route and in porogenic diluents such as tetrahydrofuran and polyethylene glycols of varying composition. Careful choice of these porogenic solvents and proper choice of initiator concentration lead to highly porous monolithic building entities which show a rigid, 3D-adhered, porous structure, macroscopically adapting the shape of a given mold. The described materials reflect Brunauer-Emmett-Teller (BET) surface areas of 700 m2/g or more and maximum tunable mesopore volumes of up to 2 cm3/g. Experimental investigations demonstrate the option to tailor nanoporosity and macroporosity in the single-step free-radical polymerization process. While studies on the influence of the used porogenic solvents reveal tuneability of pore sizes due to the unique pore formation process, tailored existence of residual vinyl groups allows facile postpolymerization modification of the highly porous, large surface area hybrid materials exploited via thiol-ene "click" chemistry. Our developed, simply realizable preparation process explores a new route to derive porous organic-inorganic hybrid adsorbents for a wide variety of applications such as extraction, separation science, and catalysis.