Significance of non-DLVO interactions on the co-transport of levofloxacin and titanium dioxide nanoparticles in porous media.

ABSTRACT

With the application of engineered nanomaterials and antibiotics in the fields of medicine, aerospace, new energy and agriculture, the associated contamination is detected widely in soil-groundwater systems. It is of great scientific and practical significance to deeply explore the environmental interface process between nanoparticles and antibiotics for the scientific assessment of environmental fate and ecological environmental risks, as well as the development of new composite pollution control technologies. In this study, the co-transport behaviors of positively charged titanium dioxide nanoparticles (TiO2-NPs) and negatively charged levofloxacin (LEV) in quartz sand (QS) are investigated in this study. The results show that TiO2-NPs hardly flow out when transported alone in the column because of its positive charge, which creates a strong attraction with the negatively charged quartz sand on the surface. When TiO2-NPs co-migrate with LEV in porous media, the presence of LEV promotes the transport of TiO2-NPs, while the presence of TiO2-NPs inhibits LEV transport. Non-XDLVO interactions based on molecular dynamics (MD) simulations can help explain the observed promotion and inhibition phenomena as well as the correlation between TiO2-NPs and LEV. The results indicate that TiO2-LEV complexes or aggregates can be formed during the co-transportation process of TiO2-NPs and LEV in porous media. As flow velocity increases from 0.204 cm min-1 to 1.630 cm min-1, both the transport capacities of TiO2-NPs and LEV are enhanced significantly. Under the condition of high citric acid (CA) concentration (15 mmol L-1), the transport capacity of TiO2-NPs is slightly inhibited, while the transport capacity of LEV is enhanced. This study provides new insights into the transport of nanometallic oxides and antibiotics in porous media, which suggests that non-XDLVO interactions should be considered together when assessing the environmental risks and fate of nanometallic oxides and antibiotics in soil-groundwater systems.