One-pot synthesis of silica monoliths with hierarchically porous structure (original) (raw)
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One-pot synthesis of bimodal (macro-meso, micro-mesoporous) silica by polyHIPE: parameter studies
Journal of Porous Materials, 2019
Porous silica with hierarchical organization of pore structure is desired for a variety of applications such as, chromatography, sensing, control release, scaffold for biomedical applications and catalysis. Highly porous polymers obtained from high internal phase emulsion (HIPE) templating route have attracted increasing attention of researchers due to their hierarchical porous and interconnected structure with high porosity and low density. The novel method adopted in our approach combines redox initiated polymerization using HIPE polymerization and an in-situ sol-gel processing technique followed by calcination to obtain highly porous materials. The obtained materials have reminiscent of polyHIPE morphology containing pores and interconnected pore throats in micrometer size range with mesopores on the wall of macropores. The effect of concentration of TEOS, volume of dispersed phase, crosslinker concentration, shear rate and surfactant concentration as well as variation in calcination temperatures on the properties of silica materials were examined.
A novel way for preparing high surface area silica monolith with bimodal pore structure
Journal of Materials Science, 2008
The crack-free silica monolith with macropores and mesopores has successfully been achieved in the presence of citric acid as nonsurfactant via sol-gel reactions of tetramethoxysilane (TMOS). Citric acid was removed by calcination to afford monolithic bodies with high specific surface area of 648 m 2 /g, pore volume of 0.9 cm 3 /g. Poly (ethyl glycol) has been used together with citric acid to control the particle aggregation and internal structure. Macropores in the micrometer range originate from the spinodal phase separation and gelation kinetics. Textural mesopores in the 2-8 nm range are controlled through adding citric acid and postsynthesis treatment in ammonia solution. By employing the glycerol as drying control chemical additives (DCCA), cracks of the materials can be successfully avoided.
The Journal of Physical Chemistry C, 2018
Mesoporous materials of tailored pore size, structure, and morphology are of interests for a wide range of applications. It is important to develop synthetic methods that will allow for easy processing and facile structure modification. Here, we present the preparation of hierarchically structured bimodal mesoporous silicas using water soluble poly(lactic acid-co-glycolic acid)-b-poly(ethylene oxide) (PLGA-b-PEO) diblock copolymer and a poly(lactic acid-co-glycolic acid)b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(lactic acid-co-glycolic acid) (PLGA-b-PEOb-PPO-b-PEO-b-PLGA) pentablock copolymer as templates. The block copolymers were synthesized through a step-growth polymerization method using a commercial Pluronic F68 macro-initiator. Mesoporous silica samples were obtained by solgel chemistry in acidic aqueous solutions. Hexagonally (p6mm) ordered mesoporous silica particles were obtained in the presence of a PLGA-PEO diblock copolymer and exhibited bimodal pore size distributions in the range of 2-9 nm. Coreshell type mesoporous silica particles were obtained in the presence of PLGA-PEO-PPO-PEO-PLGA pentablock copolymer and exhibited large pore diameter up to 20 nm with distinct bimodal pore size distributions. The pore size increased when using longer pentablock copolymer template in strong acid. The physicochemical properties were investigated using smallangle X-ray scattering (SAXS), nitrogen adsorption-desorption, transmission electron microscope (TEM), solid-state 29 Si nuclear magnetic resonance (NMR), and scanning electron microscope (SEM), respectively.
Catalysis Today, 2001
Hierarchically structured porous materials are of great interest to catalysis, where an accurately controlled pore texture at different length scales can help to reduce or otherwise control transport limitations. A method is presented to synthesize bimodal structured silicas, with an independently controlled small meso-and large meso-to macroporosity. Small primary MCM-41 particles assemble around micelles formed by a tri-block copolymer surfactant that is added as a low-concentration ethanolic solution to the particles, while these still form a flexible gel. Cross-linking of the particles in an autoclave, followed by drying and calcination, leads to bimodal materials with the controlled small mesopores of MCM-41, and a larger meso-to macropore size distribution that depends on the micelle shape and size. The latter is a function of the conditions in the second step, such as the amount and composition of the surfactant, the aging time, the temperature, the pH and the type of solvent. Fine tuning of this procedure, application to other primary structured particles, and combination with other structuring methods, should enable to construct multi-structured hierarchical materials with a desired texture at all scales.
Journal of Materials Chemistry, 2008
We have obtained a new class of porous silica with good structural order and additional corrugated nanopores clustered around the primary mesopores from the co-condensation of TEOS and adamantylphenol-grafted trimethoxysilane (adam-graft SQ) using a triblock Pluronic P123 (EO 20 PO 70 EO 20 , M w ¼ 5800) copolymer as a structure-directing agent. Thermally activated removal of pore-generating moieties (i.e., adamantylphenol groups) in adam-graft SQ involves the generation of secondary micro-to-small mesopores, while the block copolymer template generates 2D-hexagonal mesopores. We found that the mesostructural characteristics and the generation of secondary indented pores right next to the mesopores can be tailored by the addition order of the two silica precursors (TEOS and adam-graft SQ), varying the molar ratio between TEOS and adam-graft SQ in the starting sol mixture, and the degree of silica polymerization. The increase in the hexagonal unit cell parameters is attributed to the increment of pore size originating from the removal of adamantylphenol moieties. It is believed that the hydrophobicity of adamantylphenol groups plays a key role in its selective incorporation into the region near the PPO core blocks and the subsequent generation of corrugated pores along the silica channels resulting in the increase of pore diameter.
Journal of Non-crystalline Solids, 2008
Macroporous (1-5 lm) monolithic silica aerogels consisting of both random but also ordered mesoporous walls have been synthesized via an acid-catalyzed sol-gel process from tetramethoxysilane (TMOS) using a triblock co-polymer (Pluronic P123) as a structure-directing agent and 1,3,5-trimethylbenzene (TMB) as a micelle-swelling reagent. Pluronic P123 was removed by Soxhlet extraction, and materials in monolithic form were obtained by extracting the pore filling solvent with liquid CO 2 , which eventually was taken out supercritically. Although these monoliths are more robust than base-catalyzed silica aerogels of similar density, nevertheless, the mechanical properties can be improved dramatically by letting an aliphatic di-isocyanate (Desmodur N3200) react with the silanols on the macro-and mesoporous surfaces. As it turns out, the polymer fills the mesopores and coats conformally the macropores of templated samples, so that BET surface areas decrease dramatically, from 550-620 m 2 g À1 to <5 m 2 g À1 . By comparison, polymer nano-encapsulation of non-templated acid-catalyzed aerogels preserves a large fraction of their mesoporous surface area, and BET values decrease from 714 m 2 g À1 to 109 m 2 g À1 . Finally, since polymer nano-encapsulation preserves the macroscopic physical dimensions of the monoliths before drying, comparative analysis of the physical dimensions against XRD data of native versus polymer nano-encapsulated samples provides evidence that upon drying macropores (micron size regime) shrink less than mesopores (nanometer size regime).
Hierarchically porous silica monoliths with tuneable morphology, porosity, and mechanical stability
Colloids have been used as sacrificial templates to produce porous materials with controllable morphology and pore sizes. Ceramic particles were employed to prepare porous ceramics and strong composite materials by freeze-casting. However, highly porous monodisperse microspheres have been rarely used as building blocks to obtain hierarchically porous structures. In the present study, porous monodisperse silica microspheres were prepared by a modified St€ ober method and then used as building blocks to produce porous silica with meso-/micro-pores and macropores by a controlled freezing approach. The macropore morphologies could be tuned with the addition of surfactants in the silica colloidal suspensions during the freezing process. The engineering of porosity and improvement on mechanical stability of the silica materials were achieved via a further soaking and sol–gel process. It was also possible to enhance the mechanical stability through the thermal treatment of the materials.
Large-pore mesoporous silica: template design, thin film preparation and biomolecules infiltration
Materials Chemistry Frontiers, 2023
Nanopores have been applied in the development of artificial biocatalytic systems, controlled drug delivery, and solid-state sensing devices. The interaction of biomacromolecules with surfaces show a dependence on the nanopore diameter, crucial in their ability to infiltrate porous materials. In this context, ordered mesoporous materials obtained by evaporation-induced self-assembly are model materials to test pore-biomolecule interactions. Nevertheless, these materials are generally restricted to pore diameters within the 2-10 nm range, therefore, new polymers as templating agents hold potential to provide an easy reproducible route for the synthesis of mesoporous silica thin films (MTF) with pore diameters above 10 nm without the use of swelling or additional structuring agents. Here, we present a novel and simple approach towards large pore MTF through the combination of supramolecular templating and phase separation with tailor-made block co-polymers. Accurate tuning of the oxide pore size distribution (with small mesopores between 13-18 nm diameter) is achieved by controlling the length and the nature of the hydrophilic polymer block used as a template through a simple reversible addition-fragmentation chain transfer (RAFT) polymerization approach. The importance of these features is highlighted by showing the capability that these new materials offer for biomolecule infiltration benchmarked against the widespread MTF prepared using pluronic F127 as a template. Effect of protein to pore diameter ratio, protein location and effect of pH and ionic strength is briefly tested and discussed.