Ordered mesoporous silica prepared by quiescent interfacial growth method - effects of reaction chemistry.

Hatem M Alsyouri,Malyuba A Abu-Daabes,Jerry Ys Lin,Ayah Alassali

doi:10.1186/1556-276x-8-484

Hatem M Alsyouri, Malyuba A Abu-Daabes + Show 2 more

Open Access

https://doi.org/10.1186/1556-276x-8-484

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Abstract

Acidic interfacial growth can provide a number of industrially important mesoporous silica morphologies including fibers, spheres, and other rich shapes. Studying the reaction chemistry under quiescent (no mixing) conditions is important for understanding and for the production of the desired shapes. The focus of this work is to understand the effect of a number of previously untested conditions: acid type (HCl, HNO3, and H2SO4), acid content, silica precursor type (TBOS and TEOS), and surfactant type (CTAB, Tween 20, and Tween 80) on the shape and structure of products formed under quiescent two-phase interfacial configuration. Results show that the quiescent growth is typically slow due to the absence of mixing. The whole process of product formation and pore structuring becomes limited by the slow interfacial diffusion of silica source. TBOS-CTAB-HCl was the typical combination to produce fibers with high order in the interfacial region. The use of other acids (HNO3 and H2SO4), a less hydrophobic silica source (TEOS), and/or a neutral surfactant (Tweens) facilitate diffusion and homogenous supply of silica source into the bulk phase and give spheres and gyroids with low mesoporous order. The results suggest two distinct regions for silica growth (interfacial region and bulk region) in which the rate of solvent evaporation and local concentration affect the speed and dimension of growth. A combined mechanism for the interfacial bulk growth of mesoporous silica under quiescent conditions is proposed.

Highlights

Discovery of the surfactant-based supramacromolecular templating assembly over the past two decades added new dimensions for material synthesis with tuned properties
The growth starts with a thin amorphous layer at the interface of the two-phase mixture within 2 days of induction followed by slow growth of a white matrix of fibers attached to the thin amorphous layer in the water phase
We have recently demonstrated that mixing of the water phase while quiescent interfacial growth using Tetrabutyl orthosilicate (TBOS) alters the linear supply of TBOS and leads to gyroidal shapes [47]

Summary

Introduction

Discovery of the surfactant-based supramacromolecular templating assembly over the past two decades added new dimensions for material synthesis with tuned properties. The distinct feature lies in mixing while adding the silica source to the surfactant solution. A silica precursor is added without mixing it to a premixed water phase containing the surfactant, while in static conditions, a silica precursor is mixed well with the water phase before holding the solution static. Upon aging, the silica species are available homogenously all over the solution in the static growth medium and grow in the bulk, while they have to diffuse across an interface in quiescent conditions and grow in the interface and/or the bulk regions. The growth time in both cases is remarkably longer (days) than mixed conditions (minutes to hours), but it is obviously longer under quiescent conditions due to diffusion limitations

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