Issue 41, 2015

Probing local pH-based precipitation processes in self-assembled silica-carbonate hybrid materials

Abstract

Crystallisation of barium carbonate in the presence of silica can lead to the spontaneous assembly of highly complex superstructures, consisting of uniform and largely co-oriented BaCO3 nanocrystals that are interspersed by a matrix of amorphous silica. The formation of these biomimetic architectures (so-called silica biomorphs) is thought to be driven by a dynamic interplay between the components, in which subtle changes of conditions trigger ordered mineralisation at the nanoscale. In particular, it has been proposed that local pH gradients at growing fronts play a crucial role in the process of morphogenesis. In the present work, we have used a special pH-sensitive fluorescent dye to directly trace these presumed local fluctuations by means of confocal laser scanning microscopy. Our data demonstrate the existence of an active region near the growth front, where the pH is locally decreased with respect to the alkaline bulk solution on a length scale of few microns. This observation provides fundamental and, for the first time, direct experimental support for the current picture of the mechanism underlying the formation of these peculiar materials. On the other hand, the absence of any temporal oscillations in the local pH – another key feature of the envisaged mechanism – challenges the notion of autocatalytic phenomena in such systems and raises new questions about the actual role of silica as an additive in the crystallisation process.

Graphical abstract: Probing local pH-based precipitation processes in self-assembled silica-carbonate hybrid materials

Supplementary files

Article information

Article type
Paper
Submitted
10 Aug 2015
Accepted
08 Sep 2015
First published
28 Sep 2015
This article is Open Access
Creative Commons BY-NC license

Nanoscale, 2015,7, 17434-17440

Probing local pH-based precipitation processes in self-assembled silica-carbonate hybrid materials

J. Opel, M. Hecht, K. Rurack, J. Eiblmeier, W. Kunz, H. Cölfen and M. Kellermeier, Nanoscale, 2015, 7, 17434 DOI: 10.1039/C5NR05399D

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