Extraction and characterization of natural soil nanoparticles from Chinese soils

Natural nanoparticles are present in soils but their abundance, properties and interactions with other soil components have not been studied widely. We used an ultrasonic-centrifugal method to disperse and extract nanoparticles from 12 soils sampled in different regions of China. Various techniques were used to study the characteristics of the nanoparticles obtained, including particle size and zeta potential analysis, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The results showed that not all soils released nanoparticles by ultrasonic perturbation. For most Mollisols and Alfisols, large amounts of nanoparticles of relatively small size (around 25 nm) and simple composition (only muscovite and montmorillonite) were released preferentially at low ultrasonic energy. The suspension conditions (34 g kg-1 nanoparticle in solution with 0.40.6 mm ionic strength) were unfavourable for nanoparticle aggregation and the suspensions remained stable for up to 100 days. In contrast, it was difficult to release nanoparticles from Ultisols and Entisols. Ultisols and Entisols released small amounts of nanoparticles (size around 70 nm) and the suspension was very unstable, and some released no nanoparticles unless the dispersant was added. The study also indicated that the characteristics of the isolated nanoparticles were directly related to their respective matrix soils.