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Silica-based microspheres with interconnected macroporosity by phase separation

  • Original Paper: Nano- and macroporous materials (aerogels, xerogels, cryogels, etc.)
  • Published:
Journal of Sol-Gel Science and Technology Aims and scope Submit manuscript

Abstract

This work reports on a novel method which combines emulsion templating with an adapted sol–gel technique, to create silica-based microspheres with tailored interconnected porosity at the nano, but mostly at the macroscale, due to phase separation by spinodal decomposition. These new materials have potential application in many domains, as support materials, or microscaffolds for (photo)catalysis, biomedical materials, energy storage, or separation, etc. In order to achieve microspheres with the desired coexisting porosity, a water-in-oil (W/O) emulsion is prepared, and phase separation between siloxane-rich domains and water-rich phase is promoted to occur within the aqueous droplets of the emulsion. No specific gelation promoting additives are employed in this work, contrary to other works present in the state of the art. Instead, the silane combination was selected to provide an inherent gelation capability, through the oxirane group of the epoxy silane employed. The obtained microspheres display a diameter and a characteristic size ranging from 26 to 130 µm and 149 ± 11 to 485 ± 38 nm, respectively, as well as a large amount of interconnected macropores, peaked at 164–405 nm, depending on the sample, i.e., on the hydrolysis and emulsification parameters. Longer hydrolysis time and lower hydrolysis pH were found to lead to smaller but more porous microspheres, and higher amount of surfactant was found to lead to smaller microspheres. The achieved microspheres are silica based, of hybrid nature with some organic epoxy functionality, if dried at 150 °C, or of inorganic nature, if heat treated at 700 °C.

Highlights

  • Silica-based microspheres with interconnected macroporosity by emulsion templated sol–gel method.

  • Tailored macroporosity through polymerization induced phase separation by spinodal decomposition.

  • No gelation promoting additives employed.

  • 3-(glycidyloxypropyl)trimethoxysilane (GPTMS) acts as an inherent gelation promoting agent.

  • More viscous sols (hydrolysates) lead to smaller microspheres with larger characteristic size.

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Acknowledgements

We are grateful to Dr. Flávio Ferreira for the viscosity measurements, to Prof. J. G. Martinho for fruitful discussions on polymer phase separation and to Prof. Carlos Henriques, Dr. Carmen Bacariza, and Prof. Laura Ilharco for achieving the nitrogen adsorption–desorption isotherms. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project no. 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). We thank Fundação para a Ciência e a Tecnologia (FCT) through the support of CERENA (strategic project FCT-UID/ECI/04028/2019) and the grants SFRH/BD/138717/2018 (MV) and SFRH/BD/140700/2018 (MVL). We are also grateful to the Dow Chemical Company (Dow) for the kind supply of the silanes for this study, such as (3-glycidyloxypropyl)trimethoxysilane (Xiameter OFS-6040).

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  1. Centro de Recursos Naturais e Ambiente (CERENA), Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal

    Mário Vale, Mónica V. Loureiro & Ana C. Marques

  2. Centro de Química Estrutural (CQE), Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal

    M. João Ferreira

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  1. Mário Vale
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Correspondence to Ana C. Marques.

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Vale, M., Loureiro, M.V., Ferreira, M.J. et al. Silica-based microspheres with interconnected macroporosity by phase separation. J Sol-Gel Sci Technol 95, 746–759 (2020). https://doi.org/10.1007/s10971-020-05257-4

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