Nanoclays from an Andisol: Extraction, properties and carbon stabilization Marcela Calabi-Floody a,f , James S. Bendall b , Alejandra A. Jara e,f , Mark E. Welland b , Benny K.G. Theng c , Cornelia Rumpel d , María de la Luz Mora e,f, ⁎ a Programa de Doctorado en Ciencias de Recursos Naturales Universidad de La Frontera, Av. Francisco Salazar 01145, P.O. Box 54-D, Temuco, Chile b Nanoscience Centre, University of Cambridge, Cambridge CB3 0FF, United Kingdom c Landcare Research, Private Bag 11052, Palmerston North 4442, New Zealand d Laboratoire de Biogéochimie et Ecologie des Milieux Continentaux (BIOEMCO, UMR Université Paris VI et XII-CNRS-INRA-IRD), Campus AgroParisTech, Thiverval-Grignon, France e Departamento de Ciencias Químicas y Recursos Naturales, Universidad de La Frontera, Av. Francisco Salazar 01145, P.O. Box 54-D, Temuco, Chile f Scientific and Technological Bioresource Nucleus (BIOREN-UFRO), Universidad de La Frontera. Av. Francisco Salazar 01145, P.O. Box 54-D, Temuco, Chile abstract article info Article history: Received 8 September 2010 Received in revised form 25 November 2010 Accepted 15 December 2010 Available online 15 January 2011 Keywords: Allophane Allophane–organic complexes Andisol Carbon stabilization Clays Nanoclays Soils contain an abundance of nano-size particles. Because of their tendency to aggregate and associate with organic colloids, however, soil nanoparticles are difficult to obtain and characterize. Here we report on a simple and rapid method of extracting mesoporous nanomaterials from the clay fraction of an Andisol with narrow size distribution. The clay and nanoclay were characterized by elemental analysis, pyrolysis GC/MS, electron and atomic force microscopy, infrared spectroscopy, and electrophoresis. The nanoclay dominantly consists of hollow allophane spherules forming globular aggregates of about 100 nm in diameter. The nanoclay contains more organic matter (carbon and nitrogen) with a larger proportion of polysaccharides and nitrogen containing compounds, and has a lower isoelectric point, than the clay. Treatment with hydrogen peroxide causes a large decrease in the organic matter contents of both nanoclay and clay. The aggregates of allophane nanoparticles retain a significant amount (~ 12%) of carbon against intensive peroxide treatment. Thus, besides playing an important role in carbon stabilization, these naturally occurring nanomaterials are potentially useful for developing a low-cost carbon sequestration technology. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Increased burning of fossil fuels and intensive deforestation have released an increasing amount of greenhouse gases into the environment (Angulo-Brown et al., 2009; Glasby, 2006; Schulp et al., 2008; Thomson et al., 2008). It has been suggested that nanoparticles, with their large surface-to-volume ratio, could be highly effective in carbon sequestration (Khedr et al., 2006). Many functional nanoparticles have been synthesized as candidates for environmental applications (Garrido-Ramírez et al., 2010). However, synthetic nanomaterials, especially those with a narrow size distri- bution, can be expensive and difficult to obtain. For this reason, much effort is being directed at developing simple methods for designing and synthesizing low-cost nanomaterials (Bendall et al., 2008, 2010; Plank et al., 2009). Nanoparticles occur widely in the natural environment (Klaine et al., 2008; Yuan, 2004). In this respect, soils can potentially provide an abundance of inexpensive nano-size materials (Besoain and Sepúlveda, 1985; Calabi-Floody et al., 2009; Parfitt et al., 1983, 1988; Theng and Yuan, 2008; Wada, 1987). Soils contain about three times more carbon than the above-ground vegetation, and approximately 75% of the terrestrial carbon pool. As such, soils play a key role in the global carbon cycle (Schlesinger, 1986). The clay fraction of soils derived from volcanic ash (Andisols) contains a range of inorganic nanoparticles, among which allophane is the most abundant (Theng and Yuan, 2008; Wada, 1987). Allophane is a non- crystalline or ‘short-range order’ aluminosilicate with an Al/Si ratio between 1 and 2. Irrespective of chemical composition and origin, the unit particle of allophane is a hollow spherule (Fig. 1) with an outer diameter of 3.5–5.0 nm (Abidin et al., 2007; Creton et al., 2008). The 0.7– 1.0 nm thick spherule wall is composed of an outer Al octahedral (gibbsitic) sheet and an inner Si sheet. Defects in the wall structure give rise to perforations of ~0.3 nm in diameter (Brigatti et al., 2006; Hashizume and Theng, 2007; Parfitt, 1990). The external (interspherule) and internal (intraspherule) surface area of allophane, calculated on the basis of unit particle size and density, is about 1000 m 2 g –1 , while values of 700–900 m 2 g –1 are obtained by retention of ethylene glycol and ethylene glycol monoethyl ether (Hall et al., 1985; Wada, 1989). Allophane spherules (‘nano-balls’) tend to form porous nano-size aggregates (Calabi- Floody et al., 2009; Garrido-Ramírez et al., 2010) with physical characteristics similar to those of synthetic mesoporous silica. Geoderma 161 (2011) 159–167 ⁎ Corresponding author. Tel.: + 56 45 744240; fax: + 56 45 325053. E-mail addresses: mcalabi@ufro.cl (M. Calabi-Floody), jsb53@cam.ac.uk (J.S. Bendall), aljara@ufro.cl (A.A. Jara), mew10@cam.ac.uk (M.E. Welland), Thengb@landcareresearch.co.nz (B.K.G. Theng), rumpel@grignon.inra.fr (C. Rumpel), mariluz@ufro.cl (M.L. Mora). 0016-7061/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2010.12.013 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma