Cotransport of multi-walled carbon nanotubes and titanium dioxide nanoparticles in saturated porous media.

The cotransport of multi-walled carbon nanotubes (MWCNTs) and nanoscaled titanium dioxide (nano-TiO2) in porous media were investigated in 1 and 10 mM NaCl at both pH 5 and 7. Nano-TiO2 decreased MWCNTs transport under all conditions. The increased MWCNTs deposition at pH 5 was due to MWCNTs deposition onto previously deposited nano-TiO2 and codeposition of nano-TiO2-MWCNTs aggregates; whereas, codeposition of nano-TiO2-MWCNTs aggregates contributed to the increased MWCNTs deposition at pH 7. MWCNTs increased nano-TiO2 transport under all conditions except in 10 mM NaCl at pH 5. MWCNTs facilitated transport drove to the increased nano-TiO2 transport in 1 mM NaCl at pH 5; whereas, competition of deposition sites and stabilization of nano-TiO2 by MWCNTs mainly caused the increased nano-TiO2 transport at pH 7. Although MWCNTs didn't affect nano-TiO2 breakthrough curve in 10 mM NaCl at pH 5, concurrent aggregation induced straining yet shifted nano-TiO2 retained profile from log-linear to hyper-exponential decreases.