Binary Short-Range Colloidal Assembly of Magnetic Iron Oxides Nanoparticles and Fullerene (nC60) in Environmental Media

Colloidal assembly of nC(60) fullerene with naturally abundant magnetic iron oxide NPs will affect their fate and transformation in environmental media. In solution, fullerene association to aggregating iron oxide NPs/clusters greatly enhanced the overall colloidal stability. Development of depletion-mediated structured fullerene layers between pure and surface modified gamma Fe2O3 NPs possibly resulted in such stabilization. Here, we also report that on air-water interface, association of fullerene to pure and humic acid (HA7) coated gamma Fe2O3 NPs led to the formation of ordered assemblies, e.g., binary wires and closed-packed crystalline and glassy structures in the presence and absence of electrolytes suggesting immobilization of the former. The interaction of fullerene to Fe3O4 NPs and clusters also produced ordered assemblies along with amorphous aggregates. Fullerene interaction with Fe3O4 NPs in low concentration of HA1 and Na+ at pH 6 formed dendritic growth and polycrystalline circular assemblies on air-water interface. HRTEM study further revealed that the monolayer circular assemblies were highly ordered but structural degeneracy was evident in multilayers. Therefore, interfacial assemblies of fullerene with iron oxide NPs resulted in short-range periodic structures with concomitant immobilization and reduction in availability of the former, especially in soils or sediments rich in the latter.