Cotransport of titanium dioxide nanoparticles and formaldehyde in saturated and unsaturated columns packed with quartz sand

Abstract Laboratory‐scale experiments were conducted to investigate the simultaneous transport of titanium dioxide (TiO 2 ) nanoparticles and formaldehyde (FA) in columns packed with quartz sand under water saturated and unsaturated flow conditions. The effects of interstitial velocity and solution ionic strength on the TiO 2 and FA cotransport were examined. The experimental results indicated that substantial retention of TiO 2 nanoparticles occurs in both saturated and unsaturated porous media. The solution ionic strength was found to have a noticeable effect on the retention of TiO 2 nanoparticles in the packed columns. Moreover, the results from the TiO 2 nanoparticle transport experiments in water‐saturated packed columns suggested that the TiO 2 nanoparticle mass recoveries increased with increasing flow rate. The results from the TiO 2 nanoparticles and FA cotransport experiments in both water saturated and unsaturated packed columns did not reveal a distinct relationship between mass recoveries and flow rate. The transport of FA in both saturated and unsaturated packed columns was hindered in the presence of TiO 2 nanoparticles, especially at high ionic strength. This work provides useful insights into fate and transport of TiO 2 nanoparticles and FA in saturated and unsaturated porous media.