Nanoporous Graphene Oxide Membranes Research Articles

Magnesium Ion Gated Ion Rejection through Carboxylated Graphene Oxide Nanopore: A Theoretical Study.

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.

Molecular dynamics study on electric field-facilitated separation of H2O/O2 through nanoporous graphene oxide membrane

The application of external stimuli, such as electric fields, could improve gas separation. Molecular dynamics (MD) simulations were conducted to analyze the dynamic electric field-facilitated separation process of H2O/O2 gas molecules through a double-layered nanoporous graphene oxide membrane. The computational results illustrated an enhanced gas permeation rate of 3.26 × 103 mol·m−2·s−1 for H2O molecules with an external electric field of 10−4 V·Å−1, and an enhanced selectivity of 1.44 over O2 molecules, which was 0.33 in the absence of the external electric field. The mechanism of enhanced H2O/O2 separation has also been illuminated by examining the variation in interaction energy with electric field strength. The electric field inhibits the hydrogen bond interactions between H2O molecules and H2O membranes. Accelerating desorption under electric fields would enable more adsorption sites on the membrane, thereby facilitating H2O molecules permeation.

Recent Advances in Graphene Oxide Membranes for Water desalination

Freshwater is one of the most important sources in daily life. However, freshwater resources are very scarce at present. As a consequence, water desalination remains an important challenge in solving the problem of the shortage of freshwater resources. As an effective technique, membrane-based desalination has been developed to be a mature solution to solve the problem of water desalination. Graphene oxide membranes have been considered important membrane materials for water desalination due to their high stability and high hydrophilicity. In such review, this paper will introduce three kinds of recently-developed graphene oxide membranes for water desalination, which respectively are mixed matrix membrane, reduced nanoporous graphene oxide membrane, and GO/C60 membrane. Firstly, the structure and characteristics of each membrane are introduced; then, the processes of how to make these membranes are described. Additionally, this study compares them with other novel methods for water desalination. In the end, on the basis of graphene oxide membranes, it could be seen that these three membranes are more promising.

Thermally Reduced Nanoporous Graphene Oxide Membrane for Desalination.

Graphene-based laminar membranes open new avenues for water treatment; in particular, reduced graphene oxide (rGO) membranes with high stability in aqueous solutions are gaining increased attention for desalination. However, the low water permeability of these membranes significantly limits their applications. In this study, the water permeability of thermally reduced GO membrane was increased by a factor of 26 times by creating in-plane nanopores with an average diameter of ∼3 nm and a high density of 2.89 × 1015 m-2 via H2O2 oxidation. These in-plane nanopores provide additional transport channels and shorten the transport distance for water molecules. Meanwhile, salt rejection of this membrane is dominated by both the Donnan effect and the size exclusion of the interspaces. Besides, the water permeability and salt rejection of the thermally reduced nanoporous GO membrane can also be simply tuned by adjusting the thermal treatment time and membrane thickness. Additionally, the fabricated membrane exhibited a relatively stable rejection of Na2SO4 during the long-term testing. This work demonstrates a novel and effective strategy for fabricating high-performance laminar rGO membranes for desalination applications.

Recent progress in gas separation using functionalized graphene nanopores and nanoporous graphene oxide membranes

Carbon nanomaterials such as nanopores graphene, functionalized graphene and graphene oxide membranes and so forth, have attracted much attention for not only scientific interest but also various application expectations. Gas separation, including gas storage, carbon dioxide capture, flue gas purification and natural gas sweetening through nanopores is of great interest and the porous materials particularly nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes are widely utilized in this phenomenon. Nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes with narrow pore distribution, provide exciting opportunities in gas separation processes. These membranes are an excellent platform for developing size-selective membranes and exhibit unique gas separation properties. This paper reviews potential applications of nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide based membranes for gas separation on the basis of theoretical studies. The properties of porous graphene have been discussed in first section. The second and third sections provide the recent advances in theoretical studies of nanoporous graphene, functionalized graphene nanopores and nanoporous graphene oxide membranes in gas separation, respectively.

Water desalination through fluorine-functionalized nanoporous graphene oxide membranes

Abstract This study evaluates the application of fluorinated graphene-based water desalination membranes using molecular dynamics simulations. The studied membranes are fluorinated nanoporous graphene oxide (F–NPGO) and nanoporous graphene (F–NPG) sheets. The applied pressure, as a driving force, was used in the range of 5–150 MPa in order to transfer the water molecules through the reverse osmosis (RO) membranes. The obtained results show that the water permeability of F–NPGO membranes (G1 and G2) is much greater than that of F–NPG membranes (G3 and G4) due to the existence of hydrophilic groups on their surface. The maximum value of water permeability was obtained for the G2 system (i.e., 3345 L/(m2 hr bar)) at 150 MPa applied pressure. By fluorine functionalization of the pore edge, the passage of ions through the membrane, especially Cl− ions was prevented. This is the main issue of salt rejection performance. The minimum of obtained salt rejection percentage for F–NPGO membranes with the large pore (G2) was 94.31%, and small pore (G1) did not allow for crossing all of the ions. Many analyses such as water density map, water density profile, RDF, and PMF were computed for precisely understand and prove the performance of membrane systems.

Improving the performance of water desalination through ultra-permeable functionalized nanoporous graphene oxide membrane

Abstract Molecular dynamics simulations were performed to investigate the water desalination performance of nanoporous graphene oxide (NPGO) membranes. The simulated systems consist of a NPGO as a membrane with a functionalized pore in its center immersed in an aqueous ionic solution and a graphene sheet as a barrier. The considered NPGO membranes are involved four types of pore with different size and chemistry. The results indicated that the NPGO membrane has effective efficiency in salt rejection as well as high performance in water flux. For all types of pore with the radius size of 2.9–4.5 A, the NPGO shows salt rejection of >89%. Functional groups on the surface and edge of pores have a great effect on water flux. To precisely understand the effect of functional groups on the surface of nanostructured membranes, nanoporous graphene was simulated under the same condition for comparison. Hydrophilic groups on the surface make the NPGO as an ultra-permeable membrane. As a result, the obtained water flux for NPGO was about 77% greater than graphene. Also, it was found that the water flux of NPGO is 2–5 orders of magnitude greater than other existing reverse osmosis membranes. Therefore, the investigated systems can be recommended as a model for the water desalination.

Molecular Perspective of Radionuclides Separation by Nanoporous Graphene Oxide Membrane

Abstract Graphene-derived membranes has gained much interest recently due to its promising potential in filtration and separation applications. Molecular Sieving phenomena of gas molecules in the interlayer of graphene oxide nanopore have been investigated using molecular dynamic (MD) simulation. We explore I-129 gas radionuclides sequestration from natural air in nanoporous graphene oxide membranes in which different sizes and geometries of pores were modeled on the graphene oxide sheet. In the present work, mean-squared displacement (MSD), diffusion, flow of gas and the number of crossed gas molecules through graphene oxide nanopore membrane have been calculated and the results showed, selective proper nanopores in graphene oxide membrane could dramatically improve separation. The aim of this paper is to show that for the well-defined pore size called P-12, it is possible to separate I-129 from a gas mixture containing I-129, O2 and N2. The results would be benefited by the oil industry and others.

Nanoporous graphene oxide membrane and its application in molecular sieving

Gas transport through graphene-derived membranes has gained much interest recently due to its promising potential in filtration and separation applications. In this work, we explore Kr-85 gas radionuclide sequestration from natural air in nanoporous graphene oxide membranes in which different sizes and geometries of pores were modeled on the graphene oxide sheet. This was done using atomistic simulations considering mean-squared displacement, diffusion coefficient, number of crossed species of gases through nanoporous graphene oxide, and flow through interlayer galleries. The results showed that the gas features have the densest adsorbed zone in nanoporous graphene oxide, compared with a graphene membrane, and that graphene oxide was more favorable than graphene for Kr separation. The aim of this paper is to show that for the well-defined pore size called P-7, it is possible to separate Kr-85 from a gas mixture containing Kr-85, O2 and N2. The results would benefit the oil industry among others.