New Insight into GO, Cadmium(II), Phosphate Interaction and Its Role in GO Colloidal Behavior.

This study establishes the relationship between the graphene oxide (GO) colloidal behavior and the co-adsorption of Cd(II) and phosphate (P(V)) on GO. Results reveal that the interactions among GO, Cd(II), and P(V) exhibit a significant dependence on solution chemistry and addition sequences and that these interactions subsequently affect the GO colloidal behavior. The GO aggregation is pH-dependent at pH < 4.0 and depends apparently on the binding ability of Cd(II) to GO at pH > 4.0. When the components were added simultaneously, the presence of P(V) enhances the GO binding capacity toward Cd(II), confirmed by theoretical calculation, resulting in the greater destabilizing influence of Cd(II) + P(V) on GO than Cd(II) at pH 3.0-9.5, while the formation of Cd3(PO4)2 precipitate leads to a lower destabilizing influence of Cd(II) + P(V) on GO than Cd(II) at pH > 9.5. Both pH and addition sequence affect the destabilizing ability of Cd(II) + P(V). These new insights are expected to provide valuable information not only for the application of GO as a potential adsorbent in multicomponent systems for heavy metal ion and oxyanion co-removal but also for the fate and risk assessment of GO after serving as heavy metal ion and oxyanion carrier.