Attachment of cerium oxide nanoparticles of different surface charges to kaolinite: Molecular and atomic mechanisms

Sustainable applications of nanotechnology in agriculture require insights into the interactions between engineered nanoparticles (ENPs) and clay minerals, a key component in soil that governs the soil properties and functions. This study investigated the charge-dependent interactions of cerium oxide nanoparticles (CeO(2)NPs) with kaolinite at atomic level with several complementary surface characterization techniques. High resolution transmission electron microscope (HRTEM) and atomic force microscope (AFM) images showed strong attachment of positively charged and neutral CeO(2)NPs to the surface of kaolinite while the negatively charged CeO(2)NPs demonstrated low affinity to the surface of kaolinite, indicating strong electrostatic interactions between CeO(2)NPs and kaolinite surface. Attached CeO(2)NPs on kaolinite surface displayed charge-dependent aggregation, with neutral CeO(2)NPs showing the most substantial aggregation on kaolinite surface. The variation in hydrodynamic size and surface charge of kaolinite with the charge on CeO(2)NPs was observed. The attachment of CeO(2)NPs also changed the surface charge density distribution on the surface of kaolinite, converting a relatively homogenously charged basal plane into a heterogeneously charged plate. The change on kaolinite surface charge density may markedly affect the interactions of clay minerals with surrounding macro- and micro-nutrients in soil pore water and affect their bioavailability to plants.