Aggregation, Adsorption, and Morphological Transformation of Graphene Oxide in Aqueous Solutions Containing Different Metal Cations

Abstract

The colloidal behavior of graphene oxide (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 have not been investigated. We observed that heavy metal cations (Cr, Pb, Cu, Cd, Ag) destabilized GO suspension more aggressively than common cations (Ca, Mg, Na, K). In addition to electric double-layer (EDL) suppression, 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. According to aggregation kinetics, the destabilizing ability of cations follows the order of Cr ≫ Pb > Cu > Cd > Ca > Mg ≫ Ag > K > Na. The destabilizing capability of metal cations is consistent with their adsorption affinity with GO, which is determined by their electronegativity and hydration shell thickness. 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. Therefore, the aggregation of GO 2D nanosheets follows the Schulze-Hardy rule, which is usually used for spherical particles. An integrative process of adsorption-transformation-aggregation is proposed to better understand the nanomaterial (e.g., GO) colloidal behavior, environmental risk, self-assembly process, and application as a novel adsorbent.

Ionic strength induced electrodeposition of two-dimensional layered MoS 2 nanosheets

“…Thus, aggregation of PAA-MoS 2 is dependent on the charge of the cations as well as the specific binding by the metal ions. This observed behaviour of PAA-MoS 2 aggregation is similar to other colloidal particles including graphene oxide [30,31] and can be understood by the well-established DLVO theory and the Schulze-Hardy rule [29]. According to the latter, the minimum concentration of ions nec- Where n is the Schulze-Hardy exponent, typically ranges from ca.…”

“…It can be seen, that the CCC ratio of divalent and trivalent cations to CCC K + are in line with the Schulze-Hardy rule. Therefore, it is demonstrated that the PAA-MoS 2 dispersion followed the SchulzeHardy rule even though its shape is not spherical [30,31]. The above DLS measurement also provides a good estimate of ionic strength concentration and type of ion that can decrease the stability of colloidal PAA-MoS 2 dispersion.…”

“…The latter is vital for the stability of the colloids and depends on the ionic strength of electrolyte. It has been shown that increasing the ionic strength of electrolyte induces the aggregation/destabilization of dispersed colloidal particles [29][30][31]. This aggregation capacity of the electrolyte is principally depended upon the ionic strength, that is, on the valence and concentration of the ions in the electrolyte.…”

Separation-free Al-Mg/graphene oxide composites for enhancement of urban stormwater runoff quality

“…An enhancement and slight wavelength shift of epoxy groups was observed in the ATR-FTIR spectra of copper (II)-laden Al-Mg/GO, which indicates the epoxy groups were involved in the metal cation adsorption. Also, the C=C stretching peak was strengthened and slightly shifted from 1575 to 1566 cm −1 , indicating that copper (II) ions can interact with Al-Mg/GO aromatic framework directly through cation-π interactions [65]. Similar variations of the C=C peak were also observed in the ATR-FTIR spectra of DCF-laden composites due to π-π interactions.…”

Untitled

“…It could be said that negatively charged areas of ptPO residues could be suppressed by Na + cations. Moreover, existed cations in the same mediums exhibit different effects on adsorbents (Yang, Chen, Zhu, & Xing, 2016). Since slight effect of ionic strength was observed, hydrophobic-hydrophobic interaction and hydrogen bonding might have been effective in the adsorption of tetracycline by ptPO.…”