Surfactant-mediated transport of copper oxide nanoparticles in porous media: Effects of electrolytes, phosphate and organic matter

This study investigates the transport behavior of copper oxide nanoparticles (nCuO) in saturated porous media mediated by the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecyl sulfate (SDS). The effects of ion types and concentrations, humic acid (HA), and phosphate on nCuO mobility were systematically examined. Under CTAB conditions, low ion concentrations enhanced nCuO transport by reducing interfacial tension (IFT), with calcium ions (Ca^2 +) exhibiting a stronger promotive effect than sodium ions (Na⁺). However, higher ion concentrations subsequently inhibited nCuO transport. The addition of HA and phosphate promoted nCuO deposition by diminishing the electrostatic repulsion between nCuO and quartz sand. In SDS-mediated systems, increasing ion concentrations suppressed nCuO transport and exhibited "ripening" phenomena. The introduction of HA in SDS systems initially inhibited and then enhanced nCuO transport, with breakthrough curves under inhibitory conditions also showing "ripening". Notably, phosphate enhanced nCuO transport by increasing the electronegativity of quartz sand, with the promotive effect being more pronounced at low phosphate concentrations compared to high concentrations. Overall, the type of surfactant significantly influences the mobility of nCuO under various environmental conditions. These findings advance the understanding of nanoparticle behavior in environmental systems and provide valuable insights for the development of strategies in environmental protection and pollution remediation.