Molecular mechanisms of mesoporous silica formation from colloid solution: Ripening-reactions arrest hollow network structures.

Bahanur Becit,Patrick Duchstein,Dirk Zahn,Yogendra Kumar Mishra

doi:10.1371/journal.pone.0212731

Bahanur Becit, Patrick Duchstein + Show 2 more

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https://doi.org/10.1371/journal.pone.0212731

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Journal: PloS one	Publication Date: Mar 7, 2019
Citations: 9	License type: CC BY 4.0

Affiliation: University of Erlangen-Nuremberg

Abstract

The agglomeration of silica nanoparticles in aqueous solution is investigated from molecular simulations. Mimicking destabilization of colloidal solutions by full removal of protective moieties or surface charge, association of SiO2/Si(OH)4 core/shell particles leads to rapid proton transfer reactions that account for local silanole → silica ripening reactions. Yet, such virtually barrier-less binding is only observed within a limited contact zone. Agglomeration hence leads to the formation of oligomers of nanoparticles, whilst full merging into a compact precipitate is hampered by the need for extended structural reorganisation. Implementing sufficiently fast supply from colloidal solution, our simulations show the development of silica networks comprised of covalently bound, yet not fully merged nanoparticles. Within the oligomerized nanoparticle network, coordination numbers range from 2 to 5 –which is far below closest packing. Our simulations hence rationalize the formation of covalently bound network structures hosting extended pores. The resulting interfaces to the solvent show water immobilization only for the immediate contact layers, whilst the inner pores exhibit solvent mobility akin to bulk water.

Highlights

In the past few decades, silica particles and nanocomposites thereof were used in many applications ranging from catalysts to coatings and reinforced plastics.[1,2,3,4] In addition to this, more recent developments suggest silica nanomaterials for medical and biotechnological applications.[5,6,7] In bionanotechnological terms, colloidal amorphous silica is taken as a base material to form mesoporous silica
Its large surface area is ideal for hosting molecules, empowering mesoporous silica to be used as biocatalysts and drug/gene delivery vehicles, and for biomimetic processes like bone tissue engineering.[8,9,10,11,12]
We find the corresponding density profiles in line with the comparable simulation studies of Wendland[32] and Singer[33]. This holds for the interactions with water molecules, once the colloid is immersed into aqueous solution

Summary

Introduction

In the past few decades, silica particles and nanocomposites thereof were used in many applications ranging from catalysts to coatings and reinforced plastics.[1,2,3,4] In addition to this, more recent developments suggest silica nanomaterials for medical and biotechnological applications.[5,6,7] In bionanotechnological terms, colloidal amorphous silica is taken as a base material to form mesoporous silica. Its large surface area is ideal for hosting molecules, empowering mesoporous silica to be used as biocatalysts and drug/gene delivery vehicles, and for biomimetic processes like bone tissue engineering.[8,9,10,11,12]. Despite such broad interest, our in-depth (i.e. atomic scale) understanding is rather limited.

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