Abstract

Chemical surface fuctionalization and surface structuring particularly on the nanometer scale play an increasing role in many fields of technological application. However, the production of nanoparticle with small diameters and a narrow size distribution is challenging and expensive. Therefore, natural nanoparticles are a cheap alternative if the size distribution is narrow and the extraction of the particles from soil material is economically efficient. Our goal is to provide nanostructured surfaces based on natural nanoparticles particularly for agricultural application (e.g. Biofertilizer or pesticides of controlled release). The first stage of our study contemplates the extraction and characterization of nanoparticles from two Andisols belonging from Piedras Negras and Temuco series of southern Chile. To obtain the nanometric fraction of soils (nanoclays covered with organic matter), first we separate the < 0.02 mm fraction by a sedimentation method based on Stokes's law. From this fraction, the nanoparticles were obtained according the methodology described by Li and Hu (2003). The nanoparticles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and also, were determinated the isoelectric point (PIE) and specific surface area Brunauer-Emmett-Teller (SSABet) of both materials. Transmission electron microscopy micrographs revealed more or less condensed aggregates of nanoparticle and the obtaining material corresponds to nanoclays with a particle average size less than 50 nm for Andisols series Piedras Negras and less than 100 nm for Temuco series, which displaying homogeneous elemental compositions, with Al/Si molar ratios ranging ~ 2:1. SEM showed aggregates of nanoclays with variable pore size, which can adsorb high quantity of water generating microenvironments benefit for an adequate mass transfer. The FTIR spectra showed characteristic bands of the soil organic matter (fulvic and humic acids). Low values of PIE (3.2) are attributed to the organic matter covering of nanoclays. Variations in SSABet and in mesoporous and microporous between both materials were observed (14 m2 g-1 and 8 m g-1 for Piedras Negras and Temuco series respectively). The shape of the nitrogen adsorption-desorption isotherms allows two types of curves BET, nanoparticles from Piedras Negras series presented a curve Type II that suggest the presence of a relatively well-calibrated pore and a narrow pore-size distribution, and nanoparticles from Temuco series presented a curve Type III suggesting high microporosity and relatively low nitrogen-adsorbed volumes. From the results, we can conclude that both nanomaterials are promising to be used in biocatalysis or in other technological application, because of suitable confinement and enzymatic stabilization that those support nanomaterial can provide.