抄録
Environmental nanoparticles exist in the hydrosphere, pedosphere, biosphere and atmosphere. However, efficiently collecting nanoparticles in large quantities of time consuming from both pure and natural systems is a major challenge in nanoscience. This review paper aimed to use zeolite A and highly weathered red soils as examples, employed an automated ultrafiltration device (AUD) to fractionate nanoparticles (i.e., 1-100nm) from aqueous suspensions, and characterized the properties of nanoparticles. We have successfully overcome the problems and collected large quantities of nanoparticles with AUD system. Freeze-dried zeolite A and soil nanoparticles were characterized by conventional and synchrotron X-ray diffraction (XRD) with petrographic glass slides of oriented samples and random powder samples, as well as by synchrotron powder XRD analysis. The chemical properties of a zeolite are dependent on its framework structure, which is formed by connecting truncated octahedra (sodalite) through the simple double four rings (D4-R) with external linkage in each sodalite. With decreasing particle size, the T(Si, Al)-O asymmetric and symmetric stretching vibrations shifted toward higher frequencies and the Si to Al molar ratio increased consistently from 1.8 to 5.2. Comparing the various particle-size fractions (PSFs) showed significant differences in surface area, Si to Al molar ratio, morphology, crystallinity, framework structure, and surface atomic structure of nanoparticles from those of the bulk sample (i.e., <2000nm) prior to particle-size fractionations. Our results reveal the degree of crystallinity of the soil particles, and they can be used to identify the presence or absence of minerals at various PSFs (450-2000, 100-450, and 1-100nm). Kaolinite, illite, goethite and hematite were identified in the 1-100nm size fraction by synchrotron high-resolution XRD and by transmission electron microscopy (TEM). The XRD patterns of the various PSFs, shows that synchrotron XRD is better at identifying soil nanoparticles (1-100nm) than conventional XRD using powder samples due to its use of higher photon energies. Synchrotron XRD analysis is also a more straightforward and powerful technique for identifying mineral nanoparticles, particularly those of phyllosilicate minerals.
