Issue 42, 2022

Preparation of ZIF-8-coated silica hard-shell microcapsule by semi-batch operation

Abstract

This paper reports the selective fabrication of a zeolitic imidazolate framework-8 (ZIF-8) cover layer over the outer surface of silica hard-shell microcapsules (HSMC) to improve the microencapsulation technique of phase change materials for heat storage materials. ZIF-8 was formed not only over the HSMC but also in the synthesis solution side when using a conventional batch operation owing to the rapid formation rate of ZIF-8 in the aqueous solution at 293 K. In this study, a semi-batch operation, which can control the concentration of the components in the synthesis solution by gradually dropping the components, was employed to decrease the formation rate of ZIF-8. X-ray diffraction results suggested that dropping ingredients strongly affected the obtained products; the addition of the Zn2+ aqueous solution into a 2-methylimidazole (Hmim) aqueous solution was suitable for the formation of ZIF-8, whereas the addition of an aqueous solution of Hmim into the Zn2+ aqueous solution formed Zn hydroxides as unfavorable by-products. Field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy results confirmed that the semi-batch operation with the addition of Zn2+ into the Hmim aqueous solution selectively formed a ZIF-8 cover layer over the HSMC. We conclude that the semi-batch operation is an effective procedure for suppressing the unfavorable homogeneous nucleation on the solution side and making heterogeneous nucleation dominant without any additives to fabricate the ZIF-8 cover layer.

Graphical abstract: Preparation of ZIF-8-coated silica hard-shell microcapsule by semi-batch operation

Supplementary files

Article information

Article type
Paper
Submitted
07 Apr. 2022
Accepted
10 Sept. 2022
First published
15 Sept. 2022

CrystEngComm, 2022,24, 7378-7386

Author version available

Preparation of ZIF-8-coated silica hard-shell microcapsule by semi-batch operation

S. Kawada, T. Otsubo, T. Horie, Y. Komoda, N. Ohmura, H. Asano, R. Hidema, H. Suzuki, K. Taniya, Y. Ichihashi and S. Nishiyama, CrystEngComm, 2022, 24, 7378 DOI: 10.1039/D2CE00488G

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