Competition/Cooperation between Humic Acid and Graphene Oxide in Uranyl Adsorption Implicated by Molecular Dynamics Simulations

Abstract

Molecular dynamics (MD) simulations were performed to investigate the influence of curvature and backbone rigidity of an oxygenated surface, here graphene oxide (GO), on its adsorption of uranyl in collaboration with humic acid (HA). The planar curvature of GO was found to be beneficial in impeding the folding of HA. This, together with its rigidity that helps stabilize the extended conformation of HA, offered rich binding sites to interact with uranyl with only marginal loss of binding strength. According to our simulations, the interaction between uranyl and GO was mainly driven by electrostatic interactions. The presence of HA not only provided multiple sites to compete/cooperate with GO for adsorption of free uranyl but also interacted with GO acting as a “bridge” to connect uranyl and GO. The potential of mean force (PMF) profiles implied that HA significantly enhanced the interaction strength between uranyl and GO and stabilized the uranyl-GO complex. Meanwhile, GO could reduce the diffusion coefficients of uranyl and HA and retard their migrations in aqueous solution. This work provides theoretical hints on the GO-based remediation strategies for the sites contaminated by uranium or other heavy metal ions and oxygenated organic pollutants.

Surface Properties of Nanoparticles Dictate Their Toxicity by Regulating Adsorption of Humic Acid Molecules

“…The all-atom model of the Leonardite HA was transferred to the CG model using the four-to-one mapping rule (Figure S1a,b), similar to the martinize.py script provided by the Martini force field . Although it is hard to expect a single type of model compound to represent the full features of HAs, the model used in our simulations has the typical features of real HAs, such as aromatic rings, hydroxy groups, and carboxyl groups that enable it to be amphiphilic with a flexible backbone. − NP was constructed by arranging CG beads into a sphere of 10 nm in diameter. Types of CG beads on the NP surface were set according to the defined surface property (Figure S1c–f).…”

Molecular Dynamics Study on the Mechanism of Graphene Oxide to Destabilize Oil/Water Emulsion

“…28−32 The model for GO (C 106 H 26 O 20 ) was based on experimental characterizations and simulations in previous studies. 33,34 All the carboxyl and hydroxyl groups have net zero charge to mimick an acidic environment, where GO has been shown to be effective in demulsification. 18 Molecular structures of VO-79 and GO are shown in Figure 1.…”

“…Violanthrone-79 (VO-79, C 50 H 48 O 4 ) was chosen as the model for asphaltene. VO-79 has one central polyaromatic core (PAC) and two side chains, resembling the island-type structure of asphaltene proposed in the literature and has been employed widely to study the behavior of asphaltenes at the oil/water interface. − The model for GO (C 106 H 26 O 20 ) was based on experimental characterizations and simulations in previous studies. , All the carboxyl and hydroxyl groups have net zero charge to mimick an acidic environment, where GO has been shown to be effective in demulsification . Molecular structures of VO-79 and GO are shown in Figure .…”

A contribution of molecular modeling to supramolecular structures in soil organic matter#

“…The TNB monomeric model was used in FFMD simulation of interactions of HAs with several explosive species (e.g., trinitrotoluene) by Schutt and Shukla (2020). The older Stevenson HA model (Stevenson, 1994) was used in the FFMD simulation of HA interactions with uranyl and graphene oxide (Lan et al, 2016(Lan et al, , 2019.…”