Insights into the transport of pristine and photoaged graphene oxide-hematite nanohybrids in saturated porous media: Impacts of XDLVO interactions and surface roughness.

The transport behaviors of nanomaterials, in especial multifunctional nanohybrids have not been well disclosed until now. In this study, environmentally relevant conditions, including cation types, ionic strength and pH, were selected to investigate the transport and retention of graphene oxide-hematite (GO-Fe 2 O 3) nanohybrids and a photoaged product in saturated sandy columns. Results show that more hybridization of hematite led to decreased negative surface charge, while increased particle size and hydrophobicity of the nanohybrids, which depressed their transport according to extented Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. However, the inhibitory transport of photoaged nanohybrids was attributed to their distinct surface roughness caused by relatively high hybridization and photoirradiation. Notably the restrained transport was alleviated in the CaCl 2 saturated media, since the less surface O-functional groups of the corresponding nanohybrids reduced the cation bridging effect caused by Ca2+. Similarly, increasing pH promoted the transport of the nanohybrids in NaCl saturated media, particularly for the nanohybrids that contained rich O-functional groups, but exerted inconspicuous effect on mobility of the nanohybrids in CaCl 2 saturated media. These observations highlight that both XDLVO interactions and surface roughness may work together to impact the transport and fate of the burgeoning, versatile nanohybrids in the environment. [Display omitted] • Nanohybrids mobility decreased in the order of NH-Low > NH-High > rNH-High. • Hybridization led to less negative charge, larger particle size and hydrophobicity of the nanohybrids. • Irradiation-induced surface roughness aggravated the inhibitory transport of rNH-High. • Depressed transport of low O-functionalized NH-High and rNH-High was alleviated in CaCl 2. • Higher pH facilitated transport of nanohybrids in NaCl, but not in CaCl 2 electrolytes. [ABSTRACT FROM AUTHOR]