Nanofibrous Calcite Synthesized via a Solution−Precursor−Solid Mechanism

Abstract

The synthesis of calcite fibers has been confined to nature and is observed most prominently in sea urchin teeth and bacterial deposits. By generating a liquid-phase mineral precursor, induced by the addition of acidic macromolecules to a crystallizing solution, calcite fibers with diameters ranging from 100 to 800 nm have been deposited on existing calcite substrate crystals. A solution-precursor-solid (SPS) mechanism, which has features similar to both the vapor-liquid-solid (VLS) and solution-liquid-solid (SLS) mechanisms, is proposed as the growth mechanism. Because this aqueous-based SPS mechanism occurs under physiological conditions (and down to temperatures as low as 4 °C), it is feasible that it may be used by organisms to form their fibrous biomineral structures. This discovery suggests an interesting link between two seemingly unrelated processes, high-temperature semiconductor fiber formation and biological mineralization.

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

“…However, despite this ubiquity, the origin of calcitic nanofibres still remains unclear (Banerjee and Joshi, 2013). Three hypotheses for their formation have been proposed: (i) physicochemical processes (Jones and Ng, 1988;Jones and Khale, 1993;Borsato et al, 2000); (ii) biomineralization of rod-shaped nano-sized bacteria (Phillips and Self, 1987;Verrecchia and Verrecchia, 1994;Loisy et al, 1999;Gradziński et al, 2012); and (iii) nucleation mediated by an organic template (Benzerara et al, 2003;Olszta et al, 2004;Cailleau et al, 2009a).…”

“…A liquid phase is created at the tip of the fibre, incorporating constituents of the vapour phase. This leads to a rise in the supersaturation level and thus reduces the surface energy for subsequent crystal growth (Olszta et al, 2004;Zhu et al, 2009). They support their hypothesis by the facts that cave atmosphere is saturated with water vapour and that hydro-aerosols as well as dust containing Ca 2+ and CO 2− 3 may be present in the cave environment.…”

“…These latter may act as enhancers of calcite nucleation and/or as crystal growth and shape modifiers (Benzerara et al, 2003;Benzerara et al, 2005;Olszta et al, 2004;Cailleau et al, 2009a;Zhu et al, 2009). This hypothesis lies between physicochemical and biogenic processes, as it involves the presence of organic matter, but the processes of precipitation and crystal growth do not necessarily happen as the direct result of a biological activity.…”

“…This type of process may be defined as organomineralization as discussed in Perry et al (2007) or biologically influenced biomineralization as defined by Dupraz et al (2009). Several studies related to biomimetics have attempted to reproduce the nanofibre shape using template-assisted synthesis and successfully achieved it (Olszta et al, 2004;Homeijer et al, 2008;Zhu et al, 2009). However, it must be pointed out that experimental protocols usually poorly reproduce conditions from the natural environment.…”

“…However, it must be pointed out that experimental protocols usually poorly reproduce conditions from the natural environment. Yet, Olszta et al (2004) have artificially produced monocrystalline calcitic nanofibres with striking The outermost layer, designated the alkali-soluble fraction, is made of amorphous α-glucans and mannans and constitutes an amorphous matrix. It is digested with 5 % KOH (lytic step 1), followed by α-glucanase (lytic step 2).…”