Separation and identification of soil nanoparticles by conventional and synchrotron X-ray diffraction

Separation and collection of environmental nanoparticles (ENPs) in natural systems are of paramount importance in research on their nature and physicochemical properties for understanding their associated properties of adsorbing or binding to organic and trace metal contaminants. However, efficient separation and collection of ENPs in nature system remain obscure. This study aimed to use an automated ultrafiltration device (AUD) to demonstrate efficient collection of ENPs from highly weathered red soils. Synchrotron and conventional X-ray diffraction (XRD) with oriented and random powder specimens were employed to identify the composition of clay minerals with various particle-size fractions (PSFs, < 2000, 450–2000, 100–450, and 1–100 nm). The AUD was used successfully to overcome the problem of efficiently collecting ENPs in large quantities in red soils. This study showed that the major clay minerals in the < 2000 and 450–2000 nm size fractions were illite, kaolinite, and minor constituents of goethite and hematite by synchrotron and conventional XRD analyses. Illite and kaolinite were confirmed to be presented in the 1–100 nm size fraction by conventional XRD analysis with oriented specimens. From synchrotron random powder XRD analysis, illite, kaolinite, goethite, and hematite nanoparticles were present. Synchrotron XRD patterns and transmission electron microscopy (TEM) images provided unequivocal evidence of goethite and hematite existence in the 1–100 nm size fraction. The AUD has the characteristics of automation, easy operation, and high efficiency in the separation of nanoparticles and would, thus, facilitate future research and developments in environmental nanoscience, nanotechnology and their impacts on the ecosystem.