Graphene nanosheet (GNS) is a member of the carbonaceous nanomaterial family with a honeycomb structure that is sp2-hybridized with a thickness of one atom. Graphene oxide (GO), a unique soft 2D amphiphilic material, which has widely be applied in various areas but is acute toxic to microorganism and human cells. Widely applications and large-scale production lead its inevitable release to environment. An integrative process of adsorption-transformation-aggregation is proposed to better understand the nanomaterial (e.g., GO and GNS) colloidal behavior, environmental risk, self-assembly process and application as a novel adsorbent. The colloidal behavior of GO has been extensively studied in the presence of common environmental cations, but the aggregation, adsorption and morphological transformation of GO under heavy metal ions has not been investigated. We observed that heavy metal cations (Cr3+, Pb2+, Cu2+, Cd2+, Ag+) destabilized GO suspension more aggressively than common cations (Ca2+, Mg2+, Na+, K+). Heavy metal cations can easily cross the EDL, bind to GO surface, and then change the surface potential, which is a more efficient pathway for GO aggregation. GO nanosheets can be transformed to 1D tube-like carbon material, 2D multiple overlapped GO plane and 3D sphere-like particles during aggregation, thereby combined to form a sphere-like aggregated GO, which is for the first time observed by TEM and AFM images. The adsorption of naphthalene, phenanthrene and pyrene onto GNS and GO nanosheets was investigated to probe the potential adsorptive sites and molecular mechanisms. The TEM and SEM images initially revealed that after loading with PAH, the conformation and aggregation of GNS and GO nanosheets dramatically changed, which explained the observations that the potential adsorption sites of GNS and GO were unusually altered during the adsorption process. The flexibilities of graphene and graphene oxide nanosheets were sufficient for conformational change to occur, and interactions with the pollutant molecules might change the conformation of GNS and GO, thus influencing the adsorption sites. More studies are needed to recognize the potential adsorption behaviors, aggregation process of graphene nano-materials at a molecular level.

Adsorption, aggregation, and morphological transformation of graphene and graphene oxide with binding pollutants in water

253rd National Meeting (2017)

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