Influence of graphene oxide nanosheets on the cotransport of cu-tetracycline multi-pollutants in saturated porous media.

Antibiotic-heavy metal multi-pollutants are produced by intensive livestock farming and become an increasingly prominent problem. In this study, the transport behavior of tetracycline (TC) and its chelate with copper ions (Cu-TC) in saturated sand column with and without graphene oxide (GO) prefilled was investigated by laboratory breakthrough experiments. The effects of pH, ionic strength, and the cotransport with GO were studied detailedly. The results showed that the prepared nano-GO had a single- or multilayered sheet structure with a diameter of several µm. The surface of GO contained abundant oxygen-containing functional groups, which imparted it strong hydrophilicity and electronegativity. Pollutant transport experiments showed that decrease of H+ weakened the transport ability of TC and Cu-TC. Both Na+ and Ca2+ promoted the transport of TC, with Ca2+ having a much greater effect. The presence of Na+ inhibited the transport of Cu-TC, while Ca2+ promoted Cu-TC transport. The addition of Cu2+ was more favorable for the transport of Cu-TC than TC alone. In the GO-prefilled column, the effluent concentrations of TC and Cu-TC greatly decreased due to adsorption onto GO surfaces. The transport of Cu-TC was more related to GO concentration than TC alone due to the high affinity between GO and Cu-TC. Moreover, the transport behavior of GO in the sand column was consistent with that of the corresponding TC or Cu-TC, indicating that GO could cotransport with TC and Cu-TC multi-pollutants. Our study showed that the GO would interact with TC and Cu-TC and thus have significant influences on the fate and transport of these pollutions in porous media.

In†Situ Observation of Dynamic Galvanic Replacement Reactions in Twinned Metallic Nanowires by Liquid Cell Transmission Electron Microscopy.

Galvanic replacement is a versatile approach to prepare hollow nanostructures with controllable morphology and elemental composition. The primary issue is to identify its fundamental mechanism. In this study, in situ liquid cell transmission electron microscopy was employed to monitor the dynamic reaction process and to explore the mechanism of galvanic replacement. The detailed reaction process was revealed based on in situ experiments in which small Au particles first appeared around Ag nanowires; they coalesced, grew, and adhered to Ag nanowires. After that, small pits grew from the edge of Ag nanowires to form tubular structures, and then extended along the Ag nanowires to obtain hollowed structures. All of our experimental observations from the viewpoint of electron microscopy, combined with DFT calculations, contribute towards an in-depth understanding of the galvanic replacement reaction process and the design of new materials with hollow structures.