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While nanoporous graphene oxide (GO) is recognized as one of the most promising reverse osmosis desalination membranes, limited attention has been paid to controlling desalination performance through the large GO pores, primarily due to significant ion leakage resulting in the suboptimal performance of these pores. In this study, we employed a molecular dynamics simulation approach to demonstrate that Mg2+ ions, adhered to carboxylated GO nanopores, can function as gates, regulating the transport of ions (Na+ and Cl−) through the porous GO membrane. Specifically, the presence of divalent cations near a nanopore reduces the concentration of salt ions in the vicinity of the pore and prolongs their permeation time across the pore. This subsequently leads to a notable enhancement in salt rejection rates. Additionally, the ion rejection rate increases with more adsorbed Mg2+ ions. However, the presence of the adsorbed Mg2+ ions compromises water transport. Here, we also elucidate the impact of graphene oxidation degree on desalination. Furthermore, we design an optimal combination of adsorbed Mg2+ ion quantity and oxidation degree to achieve high water flux and salt rejection rates. This work provides valuable insights for developing new nanoporous graphene oxide membranes for controlled water desalination. [ABSTRACT FROM AUTHOR]

The scarcity of freshwater is of great challenge that the world is facing nowadays. The advances of nanomaterial based on the reverse osmosis (RO) technology provide new possibilities for desalination. In this study, using molecular dynamics simulation, we propose and design an excellent RO membrane composed of fluorinated graphene (F-GRA) nanochannels, by which the exceptionally high water permeation (reaching up to 61.1 L/cm2/day/MPa) and the almost complete ion rejection are achieved. Notably, F-GRA nanochannel membranes exhibit a desalination performance much more promising than many other nanomaterials in previously theoretical studies. This superior desalination performance of F-GRA channels is attributed to the negatively charged surface and hydrophobicity of F-GRA, where the electrostatic interactions (attraction or repulsion) between ions and F-GRA surface cause the ideal ion rejection and the ultralow water friction on F-GRA mediated by its hydrophobicity results in the excellent water penetration. Moreover, potential of mean force calculations further reveal that the water molecule reflects the lowest free energy barrier relative to ions when traversing through the F-GRA channel, indicating the energetical favorability of the successful water transport instead of ions. Our theoretical study offers a fascinating approach of molecular sieving design usable for future desalination. • Fluorinated graphene (F-GRA) nanochannel based membrane is constructed. • The F-GRA membrane presents an excellent desalination performance with the high water permeability and the high ion rejection. • The superior water permeability and ion rejection are resulted from the negatively charged surface and hydrophobicity of F-GRA. • The desalination performance of F-GRA nanochannel is investigated from the molecular level. [ABSTRACT FROM AUTHOR]

Combining the molecular dynamics (MD) simulations and the free-energy-based thermodynamic analysis, we analyze the role of alkyl chain length on the nucleation of alcohol molecules with the mono-hydroxyl in nanoconfined solution. The free energy formulae and thermodynamic equilibrium equation are parameterized by fitting the theoretical equilibrium equation to MD simulation results. We find that alcohol molecules with the varied alkyl chain length show different nucleation states, i.e. , dispersion, reversible and aggregation states, corresponding to the total free energy G c o n f i n e (n , N) with a single minimum at n ∼ 1, two minima at n ∼ 1 and N separated by a maximum, and a local minimum at n ∼ N , respectively. The alcohol molecule with a longer alkyl chain tends to aggregate into a cluster at a lower solute number in nanoconfined solution. Besides, the free energy of cluster formation in nanoconfined solution G c l u s t e r (n) also depends on the alkyl chain length, and three regions can be identified: For the shorter alkyl chain, such as ethanol, there is no local maximum on G c l u s t e r (n), indicating that alcohol molecules tend to be dispersed in water; For the intermediate alkyl chain length, such as 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol, the critical nucleation number n c and nucleation barrier G b monotonically decrease with the increase of alkyl chain length; For the longer alkyl chain, n c ∼ 1 and G b ∼ 0 k B T suggest that alcohol molecules, such as 1-heptanol, can aggregate into clusters easily. Our work deepens the understanding of the alkyl chain length effect on the nucleation behavior of alcohol molecules in nanoconfined solution. [ABSTRACT FROM AUTHOR]

Abstract: Using all-atom molecular dynamics (MD) simulation, we have investigated the adsorption of protein GA module (GA53) onto graphene oxide (GO), compared with similar adsorption onto pristine graphene (PG). We find that: (1) the protein GA53 can be easily and firmly adsorbed onto the surface of GO and PG, but the binding sites are not specific; the main difference is that the secondary structure of GA53 can be well preserved in protein–GO system, while GA53 will partially lose its secondary structure after adsorbed on PG. (2) in protein–GO system, hydroxyl and epoxy groups increase the distance between protein and GO, which weaken their vdW interactions, meanwhile, hydrogen bonds and electrostatic interactions enhance their binding affinity. In protein–PG system, strong vdW interactions between residues of GA53 and PG have destroyed its secondary structure. (3) π–π stacking interactions still exist between aromatic residues and both the basal plane of GO and PG. In comparison with PG, our results suggest that GO presents better biocompatibility to preserve protein secondary structure when simultaneously absorbing protein. [Copyright &y& Elsevier]

[Display omitted] • A prior exploration of the potential biological effect of a carbon nitride (C 3 N 3). • The moderate adsorption of C 3 N 3 nanosheet to membrane. • The molecular insights and mechanism of the interaction between C 3 N 3 and membrane. • The specific attraction between C 3 N 3 pores and lipid heads. Recently, the novel hole-containing carbon nitride C 3 N 3 nanomaterial was successfully synthesized, featuring outstanding and unique mechanical and electrical properties. However, to fully exploit this nanomaterial in biomedical applications, information regarding its biocompatibility is necessary. Herein, by using all-atom molecular dynamics simulations, we evaluate the interactions between a C 3 N 3 nanosheet and a critical cellular component, that is, a lipid membrane bilayer. Our results indicate that the C 3 N 3 nanosheet is able to interact with the lipid bilayer surface without affecting the membrane's structural integrity. Moreover, our results showed that the C 3 N 3 nanosheet is adsorbed on the surface of the lipid bilayer without inflicting any structural damage to the membrane, regardless of the conditions of the system (that is, with and without restrains in the C 3 N 3 nanosheet). Also, we found that both energy contributions, namely vdW and Coulomb energies, conjointly mediated the C 3 N 3 adsorption process. In comparison and as expected, pristine graphene significantly disturbed the membrane structure. Perpendicularly-oriented-sheet simulations described the significance of the surface charges of the C 3 N 3 nanosheet in prohibiting its insertion into the membrane. Detailed analysis indicated that the electrostatic attraction between the pores in the C 3 N 3 structure and the lipid head amino groups stabilized the interaction restricting the insertion of the C 3 N 3 structure deeper into the membrane. Our results suggested the importance of the negatively charged C 3 N 3 pores when interacting with lipid membranes. Our findings shed light on the potential compatibility of C 3 N 3 with biomembranes and its underlying molecular mechanism, which might provide a useful foundation for the future exploration of this 2D nanomaterial in biomedical applications. [ABSTRACT FROM AUTHOR]