Preservation of the allophanic soils structure by supercritical drying

Allophanic soils are interesting in terms of environmental properties especially because of their potentialities as sinks for “greenhouse gases”: Allophane clays are natural mesoporous materials exhibiting organic carbon and nitrogen contents 3–4 times higher than those measured in other clay soils. We present results on the preservation of the porous features of allophanic soils, at the nanometer scale, by supercritical drying technique (SD).We show that textural properties such as specific surface area are systematically higher for the supercritical dried samples compared to the classical dried samples, indicating the preserving effect of supercritical drying. Pore size distribution and small angle X-rays scattering data confirm specific surface area results. The structure at the nanometer scale is affected by classical dying, which reveals the interest of the SD method to correctly characterize natural and complex mesoporous material such as allophane. Thanks to this approach we show correlation between the true specific surface area and the carbon content, in allophanic soils.