Evidence for an organic origin of pedogenic calcitic nanofibres

Abstract

a b s t r a c tCalcium carbonate nanofibres are found in numerous terrestrial environments, often associated with needle fibre calcite. This study attempts to mimic the natural system and generate comparable crystalline structures. A comparison of natural and synthesized nanofibre structures, using HRTEM as well as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), has demonstrated that this type of nanocrystal can result from precipitation on organic templates, most likely cellulose nanofibres. This study emphasizes the fundamental role of organic templates in the precipitation of calcium carbonate in vadose environments, even at the nanoscale.

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).…”

“…Therefore, a fungal origin for organic nanofibres is rational. Moreover, other authors have already put forward the hypothesis of an indirect biogenic origin, involving "organic nanofibres coming from a cell wall" (Klappa, 1979;Cailleau et al, 2009a;Bindschedler et al, 2010). Both fungi and plants harbour a cell wall composed partly of fibrous polymers and thus can be a source of organic nanofibres (Carlile et al, 2001;Paul, 2007).…”

“…Nanofibres exhibit an average width of 50-150 nm and length from 10 up to 10 4 times their width (Table 1). They reveal a monocrystalline nature using Transmission Electron Microscopy (TEM) microdiffraction analyses (Loisy et al, 1999;Borsato et al, 2000;Cailleau et al, 2009a). However, due to their tiny dimensions they are highly versatile under an electron beam and it has not been possible to accurately determine whether or not the calcite c axis corresponds to the morphological nanofibre orientation (Cailleau et al, 2009a).…”

“…They reveal a monocrystalline nature using Transmission Electron Microscopy (TEM) microdiffraction analyses (Loisy et al, 1999;Borsato et al, 2000;Cailleau et al, 2009a). However, due to their tiny dimensions they are highly versatile under an electron beam and it has not been possible to accurately determine whether or not the calcite c axis corresponds to the morphological nanofibre orientation (Cailleau et al, 2009a). Vergès et al (1982) and Phillips and Self (1987) suggested a similar crystallographic orientation for both nanofibres and NFC as a result of their equivalent morphology.…”

“…Richter et al (2008) were not able to measure crystallographic orientations of nanofibres with Electron Backscatter Diffraction (EBSD) due to their small sizes. As a result, no clear answer regarding the crystallographic orientations of nanofibres is available at present, due to the technical limitations put forth by Cailleau et al (2009a) and Richter et al (2008), as well as the contradictory results obtained by Loisy et al (1999) and Borsato et al (2000). Nanofibres correspond to the M-type micro-rods described by Verrecchia and Verrecchia (1994) as proposed by Borsato et al (2000) and later summarized by Cailleau et al (2009a).…”