Engineering grain boundaries in monolayer molybdenum disulfide for an efficient water/ion separation

doi:10.21203/rs.3.rs-2630063/v1

Download PDF

Physical Sciences - Article

Engineering grain boundaries in monolayer molybdenum disulfide for an efficient water/ion separation

https://doi.org/10.21203/rs.3.rs-2630063/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Atomically thin two-dimensional (2D) materials have long been considered as ideal platforms for developing separation membranes. However, it is difficult to generate uniform subnanometer pores over large areas on 2D materials. Herein, we report that the well-defined defect structure of monolayer MoS₂, namely, eight-membered ring (8-MR) pores typically formed at the boundaries of two antiparallel grains, can serve as molecular sieves for efficient water/ion separation. The 8-MR pores (4.2 × 2.4 Å) in monolayer MoS₂ allow rapid single-file water transport while rejecting various hydrated ions. Further, the density of grain boundaries and, consequently, the density of pores can be tuned by regulating the nucleation density and size of MoS₂ grains during the chemical vapor deposition process. The optimized MoS₂ membrane exhibited an ultrahigh water/NaCl selectivity of ~6.5 × 10⁴ at a water permeance of 232 mol m⁻² h⁻¹bar⁻¹, outperforming the state-of-the-art desalination membranes. When used for direct hydrogen production from seawater by combining the forward osmosis and electrochemical water splitting processes, the membrane achieved ~40 times the energy conversion efficiency of commercial polymeric membranes. It also exhibited a rapid and selective proton transport behavior desirable for fuel cells and electrolysis. The bottom-up approach of creating precise pore structures on atomically thin films via grain boundary engineering presents a promising route for producing large-area membranes suitable for various applications.

Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials

Physical sciences/Engineering/Chemical engineering

Selective molecular transport through nanoporous membranes forms the basis of many important separation and purification processes. In principle, two-dimensional (2D) materials such as graphene are ideal for preparing high-performance separation membranes. This is because they are extremely thin, thereby maximizing the molecular transport efficiency in the presence of nanopores^1-5. Theoretical studies have suggested that membranes based on 2D materials could be considerably superior to the conventional polymeric membranes in terms of permeability and selectivity in water desalination and gas separation^6-8. However, it is difficult to generate nanopores with precise molecular dimensions on 2D materials, especially over large areas as required for practical applications.

Various methods, including ion or electron irradiation^3,4,9 and chemical or plasma etching^2,10,11, have been used to create nanopores on 2D materials. However, these methods offer poor control of pore size and pore density. The obtained membranes typically have a nonuniform distribution of pore size, resulting in low permeability or poor selectivity when used for molecular separation^9,12,13.

Compared with these posttreatment methods, direct generation of nanopores during the synthesis of 2D materials is more promising for achieving precise pore size control and high pore density. The synthesis of 2D materials via chemical vapor deposition (CVD) typically involves the simultaneous growth of multiple grains having different orientations. As the growth progresses, the grains are connected through grain boundaries (GBs) to form an extensive polycrystalline thin film. The formation of GBs in 2D materials induces structural inhomogeneity, which usually adversely affects the properties that single-crystalline structures are expected to possess. However, the presence of local structures at GBs may also create new opportunities for specific applications. For example, eight-membered rings (8-MRs) formed at graphene GBs can act as pores that allow Li⁺ to pass through¹⁴, whereas the perfect graphene lattice comprising 6-MRs is impermeable to Li⁺. Although 8-MRs at graphene GBs have demonstrated considerable potential for ionic transport, such pores are randomly produced by the uncontrolled growth of graphene, thereby limiting the pore density and, in turn, the permeability of the membrane. The GB structure is primarily determined by the orientation relation of adjacent grains, with the number of pores being directly proportional to the GB density. Hence, controlling the grain orientation and size during the growth of 2D materials is crucial for optimizing the desired pore structure on the GB.

Herein, we intentionally generated a large number of GBs with predesigned porous structures in monolayer molybdenum sulfide (MoS₂) for efficient molecular separation. This was achieved by modifying our recently developed CVD method¹⁵ to precisely control the orientation and size of MoS₂ grains. The MoS₂ grains grown by this method typically exhibit anti-parallel orientations with a 60 degree relationship, resulting in several predictable GB structures. Among these structures, the 8-MR is dominant. The size of 8-MR in monolayer MoS₂ exactly matches the requirement to enable rapid water transport while blocking various hydrated ions. Hence, the prepared films exhibit high water flux and water/ion selectivity when used as separation membranes. The number of 8-MRs can be increased drastically by reducing the average grain size, affording optimized membrane performance that exceeds that of state-of-the-art membranes for osmotically driven water/ion separation. Conversely, monolayer MoS₂ prepared without controlling the grain orientation has less well-defined GB structures with fewer 8-MRs (mainly comprising smaller impermeable rings), thus exhibiting lower water flux and water/ion selectivity.

Grain boundary engineering in monolayer MoS₂

A single-crystalline defect-free monolayer MoS₂ comprising 6-MRs is impermeable to any atoms or molecules¹⁶. Structural defects with ring sizes exceeding the intrinsic 6-MR can provide channels for selective molecular transport. However, to achieve high selectivity, the generated structural defects should have appropriate channel diameters (i.e., ring sizes), depending on the requirements of specific applications. Molecular dynamics (MD) simulations were performed to explore appropriate MoS₂ ring sizes for water/ion separation based on the density functional theory (DFT)–optimized structural models (Supplementary Fig. 1). The results revealed that 7-MR is still too small to transport water molecules or ions (Fig. 1a), whereas 8-MR exhibits the desired pore size (~4.2 × 2.4 Å), allowing fast water permeation while completely rejecting hydrated Na⁺ and Cl^– ions (Fig. 1b). The MD simulations also revealed the single-file transport of water in MoS₂ 8-MRs. The average number of hydrogen bonds (H-bonds) per water molecule in 8-MRs was considerably lower than that of bulk water (1.6 vs. 3.3, Fig. 1c), similar to water transport through protein aquaporin channels^17,18.

Notably, 8-MR is a typical defect structure of polycrystalline monolayer MoS₂, which is commonly found at the boundaries between two grains with a 60° orientation relationship^19,20. To gain insights into this phenomenon, we performed DFT calculations to compare the formation energies of the GB structures that were previously observed between grains with a 60° orientation relationship, including 4, 8-4, 8-4-8-4, 12-4, 12-4-12-4, and 4-8-4-4-12 structures (the numbers refer to ring sizes; see Fig. 1d). The calculation results showed that 8-4 (i.e., 8-MR combined with 4-MR) is the most stable configuration with the lowest formation energy, regardless of the S concentration; moreover, structures involving 12-MR generally exhibited high formation energies, suggesting that the formation of 12-MR is energetically less favorable than the formation of 8-MR (Fig. 1e). Therefore, polycrystalline monolayer MoS₂ films exclusively comprising grains with a fixed orientation relationship (0° or 60°) are expected to have abundant 8-MRs suitable for water/ion separation.

We successfully fabricated such films on sapphire (α-Al₂O₃ (0001)) substrates using our recently developed CVD-based method¹⁵. The key to this method is a two-step process that facilitates the alignment of MoS₂ seed crystals before further growth (see experimental section for details). For comparison, we also prepared monolayer MoS₂ films comprising randomly oriented grains (denoted as R-MoS₂) by omitting the prior alignment step. The films with controlled and random grain orientations are denoted as C-MoS₂ and R-MoS₂, respectively. The difference in grain orientation between C-MoS₂ and R-MoS₂ can be clearly identified from optical microscopy images showing triangular MoS₂ flakes recorded at an early stage of the CVD process (Figs. 2a, 2d). As the CVD process proceeded, the triangular MoS₂ flakes continued to grow and connected to each other through GBs, eventually forming continuous films (Figs. 2b, 2e). The as-prepared MoS₂ films exhibited excellent uniformity throughout the substrate (diameter: 2 inch), as seen from the Raman and photoluminescence spectra as well as atomic force microscopy (AFM) images (Supplementary Figs. 2-4).

The GB structures on C-MoS₂ and R-MoS₂ films were probed using atomic-resolution annular dark-field scanning transmission electron microscopy (ADF-STEM). The images revealed that 7-MR is the main defect structure of R-MoS₂, prevalent at GBs between grains with non-60° orientation relationships. Figure 2c shows a typical example, where many 7-MRs are observed along the boundary between two grains misaligned by 19°. This observation is consistent with the conclusions of previous theoretical studies that the formation of 7-5 rings in non-mirror-twin boundaries (or tilt boundaries) is energetically favorable^21-23. Interestingly, when the two interconnected grains have a 60° orientation relationship, as in the case of C-MoS₂, a string of 8-MRs is observed along the mirror-twin boundaries (Fig. 2f and Supplementary Fig. 5). This observation is consistent with the expectation that building GBs with MoS₂ grains with a 60° orientation relationship can yield abundant 8-MRs in the film. Statistics based on ADF-STEM imaging revealed that 8-MRs accounted for ~97% of all the pores observed in the GBs of C-MoS₂ (4-MRs were not included in the statistics because of their impermeability), while pores of sizes >1 nm were rare, accounting for only ~2.3% of all the observed pores (Supplementary Fig. 6).

The grain sizes and grain boundary numbers in C-MoS₂ and R-MoS₂ films can be roughly determined by visualizing GBs using an established method. Specifically, heating the films at 100°C for 1 h in humid air (60% relative humidity) caused the accumulation of contaminants (water, oxygen, and hydrocarbon molecules) along the GB, allowing the easy identification of GBs using scanning electron microscopy (SEM)²⁴. The SEM results show that R-MoS₂and C-MoS₂films grown under standard conditions exhibit similar average grain sizes of ~7.4 and ~6.8 µm², respectively; however, the intersection of multiple GBs was observed in R-MoS₂ but not in C-MoS₂, confirming the difference in grain orientation (i.e., random vs. fixed) between the two films (Supplementary Fig. 7).

We fabricated three other C-MoS₂ films exhibiting different average grain sizes by varying the CVD conditions to tune the nucleation density (see experimental section). Their average grain sizes, which were determined using the aforementioned method, were ~443.4, ~87.3, and ~0.26 µm², respectively (Supplementary Fig. 8). Thus, a total of five films were fabricated, hereinafter denoted as “C-MoS₂-X” or “R-MoS₂-X,” where “X” indicates the average grain size. The 8-MR density of the film increases with decreasing grain size. From the ADF-STEM imaging results, the density of 8-MR pores in C-MoS₂-0.26 was estimated to be ~5.5–7.6 × 10¹¹ cm⁻²(Supplementary Note 1).

MoS₂ membranes for water/ion separation

To fabricate separationmembranes, the CVD-grown monolayer MoS₂ films were transferred from sapphire to porous polycarbonate (PC) substrates using the polydimethylsiloxane-assisted technique^24,25 (Fig. 3a and Supplementary Fig. 9). PC was chosen as the substrate because its smooth surface and high surface energy (~40 mJ m⁻²) can provide a strong adhesion with the supported MoS₂film^26,27. The top-view SEM image shows that the MoS₂ film is continuous and devoid of cracks (Fig. 3b), while the cross-sectional ADF-STEM image confirms the monolayer nature and homogeneity of the film (Fig. 3c).

The water and ion transport properties of the fabricated MoS₂ membranes were first verified using a forward osmosis (FO) configuration. When pure water was used as the feed solution and 2 M NaCl was used as the draw solution, the C-MoS₂-6.8 membrane exhibited a water flux of ~1.2 × 10⁵ mol m⁻² h⁻¹ (Supplementary Fig. 10a). Its water/ion separation capability was evaluated using various salt solutions (K⁺, Na⁺, Ca²⁺,Mg²⁺, and Al³⁺; 0.1 M) as the feed solution and a sucrose solution (2 M) as the draw solution. In all the tests, the ion flux of the C-MoS₂-6.8 membrane was ultralow; it was more than five orders of magnitude lower than that of the bare PC substrate (Supplementary Fig.10b), corresponding to extremely high water/ion selectivity. For example, when tested with 0.1 M NaCl, the membrane had a water permeance of ~118.9 mol m⁻² h⁻¹ bar⁻¹ and a water/NaCl selectivity of ~4.6 × 10⁴. The nonzero ion fluxes (<0.16 mol m⁻² h⁻¹) can be attributed to the presence of a few large pores (Supplementary Fig. 6), which are only occasionally observed along the GBs (Supplementary Fig.11) but are absent inside the MoS₂ grains (Supplementary Fig.12). Under identical test conditions, the R-MoS₂-7.4 membrane showed considerably lower water permeance (~10.5 mol m⁻² h⁻¹ bar⁻¹) and water/NaCl selectivity (~4418) than the C-MoS₂-6.8 membrane despite having similar average MoS₂ grain sizes (Fig. 3d). This result is consistent with the expectations and is attributed to the presence of the impermeable 7-MR as the primary defect structure on the randomly grown MoS₂ film.

The C-MoS₂-87.3 and C-MoS₂-443.4 membranes showed lower permeability and water/NaCl selectivity compared to the C-MoS₂-6.8 membrane, while the C-MoS₂-0.26 membrane outperformed all the tested membranes, exhibiting a water permeance of ~232 mol m⁻¹ h⁻¹ bar^-1and a water/NaCl selectivity of ~6.5 × 10⁴ (Fig. 3d). These results demonstrate that the water/ion separation performance of the C-MoS₂ membranes is dependent on the number of 8-MRs, which increases as the grain size decreases. Unlike the conventional water desalination membranes that have a tradeoff between water permeance and water/ion selectivity, C-MoS₂ membranes show positively correlated water permeance and water/ion selectivity, both of which increase with the number of 8-MRs, suggesting a molecular sieving–based separation mechanism.

Notably, the optimized C-MoS₂ (i.e., C-MoS₂-0.26) membrane outperforms advanced membranes made of various nanomaterials (Fig. 3f). The water/NaCl selectivity and water permeance of C-MoS₂-0.26 are approximately five times and more than 10 times the corresponding values of commercial polyamide thin-film composite membranes (Fig. 3f and Supplementary Table 1)^28,29. Seven membranes fabricated using C-MoS₂-0.26 collected from different regions of a sapphire substrate (diameter: 2 inch) showed consistent water/ion separation properties (Supplementary Fig.13), demonstrating the structural homogeneity of monolayer MoS₂ and reliability of the water separation tests. Because C-MoS₂-0.26 membranes delivered the best performance, these membranes were used in subsequent studies.

During 30 days of continuous testing with 0.6 MNaCl in the feed (similar to the ionic strength of seawater) and 2 M sucrose as the draw solution, the C-MoS₂-0.26 membrane showed a steady NaCl rejection of >99% and only slightly reduced water permeance, demonstrating long-term mechanical and chemical stability. The excellent mechanical strength of C-MoS₂-0.26 is also evidenced by its high Young's modulus of 0.251 TPa (Supplementary Fig. 14). When synthetic seawater (containing KCl, NaCl, Na₂SO₄, CaCl₂, and MgCl₂; ionic strength: ~1.15 M) was used as the feed, the C-MoS₂-0.26 membrane exhibited >99.9% ion rejection and a water permeance of ~214 mol m⁻² h⁻¹ bar⁻¹ (Supplementary Fig. 15).

Exploration of the separation mechanism

The excellent water/ion separation ability of C-MoS₂ membranes is believed to originate from the unique size-exclusion effect of 8-MR as hydrated ions encounter a considerably higher energy barrier than water molecules when entering the subnanometer-sized pores³⁰^,^31,32. To gain more insight into the separation mechanism, we calculated the Arrhenius activation energy (E_A) for water transport through the C-MoS₂-0.26membrane based on the water fluxes measured at different temperatures. The results showed that E_A is barely affected by the system pH (e.g., E_A = 15.1 and 15.3 kJ mol⁻¹ at pH 3.0 and 7.8, respectively, Fig. 4a); this finding indicates a lack of proton concentration–governed water–pore interactions. Therefore, it is more likely that the energy barrier is associated with the drastic change in the H-bond configuration when water molecules are transported from the bulk solution into the 8-MR pores. Likewise, different anion species did not have considerable impact on the water/Na⁺ separation performance of the C-MoS₂-0.26 membrane (Fig. 4b), confirming the irrelevance of solution chemistry to the separation.

The C-MoS₂-0.26 membrane was also evaluated using a reverse osmosis (RO) configuration. For these tests, membranes were fabricated by supporting monolayer C-MoS₂-0.26 films on highly porous anodized aluminum oxide (AAO) substrates. The use of AAO substrates occasionally resulted in the generation of pinholes in the membrane; these pinholes could be sealed subsequently via an interfacial polymerization strategy^4,12 (see details in the experimental section). At a feed salt concentration of 0.01 M and an operating pressure of 2 bar, the C-MoS₂-0.26 membrane exhibited the following ion diameter–dependent rejection (R) sequence: R (AlCl₃) > R (MgCl₂) > R (Na₂SO₄) > R (NaCl) > R (KCl) (Fig. 4c). The fact that MgCl₂ is rejected to a greater extent than Na₂SO₄ rules out the Donnan exclusion as the main separation mechanism. When tested with NaCl, the membrane exhibited a high water permeance of ~46 L m⁻² h⁻¹ bar⁻¹with an NaCl rejection of ~97%, which is considerably higher than that of the reported 2D material–based membranes (<90%)^2,33-35 (Supplementary Table 2). Its separation performance remained mostly constant with increasing applied pressure up to 13 bar, feed concentration up to 6000 ppm (confirming that the Donnan exclusion effect is negligible), and under continuous long-term operation up to 450 h (Supplementary Fig. 16). In addition to common cations, C-MoS₂ membranes can effectively exclude boron, which exists as B(OH)₃ in neutral solutions with a low molecular weight of 61.8 g mol⁻¹. Compared with the commercial polyamide thin-film composite membrane SW30, the C-MoS₂-0.26 membrane exhibited a higher boron rejection (~90.5% vs. ~70%; at pH = 7) and an approximately 40-fold increase in water permeance (Fig. 4d). Furthermore, unlike SW30 whose boron rejection is pH-sensitive, the high boron rejection of the C-MoS₂-0.26 membrane remained almost constant in the pH range of 6–10. These results collectively indicated that the strong molecular-sieving effect of 8-MR pores, rather than the surface charge, is the primary mechanism responsible for the exceptional water/ion selectivity of C-MoS₂ membranes, regardless of the type of driving force (FO or RO) for the water transport.

Direct seawater splitting and selective proton transport

Water/ion separation membranes enable the combination of the FO process with electrolysis to produce hydrogen directly from seawater, avoiding side reactions on the electrodes and corrosion issues³⁶. An electrolytic cell was assembled for this application, in which the inner electrolyte (7.1 mL of 0.8 M NaH₂PO₄) and the outer solution (0.5 L of 0.6 M NaCl) were separated by the C-MoS₂-0.26membrane (Fig. 5a). The C-MoS₂-0.26 membrane balanced the water influx and outflux at ~32.5 L m⁻² h⁻¹ under a constant current of 76 mA, with ~100% faradaic efficiencies for both hydrogen evolution and oxygen evolution reactions. Owing to its high water flux, the C-MoS₂-0.26membrane achieves a remarkable energy storage efficiency of 43.68 kJ h⁻¹ cm⁻² via H₂ generation, which is nearly 40 times that of commercial cellulose acetate membranes³⁶ (Fig. 5a and Supplementary Note 3). Notably, this performance remained constant over 80 h of continuous operation (Supplementary Fig. 17 and Table 3). Conversely, the electrochemical splitting of seawater without using a membrane yielded poor energy conversion efficiency even in a short operating period (Supplementary Fig. 18).

In addition to their water/ion separation capacity, C-MoS₂ membranes also demonstrate an interesting ability for selective proton transport. The single-file water chains can adopt two configurations that differ in the manner of formation of H-bonds between water molecules (Fig. 5b). When a water molecule forms H-bonds with two adjacent water molecules via one O and one H, it can facilitate proton transport through the Grotthuss mechanism³⁷. According to MD simulations, ~13% of the water molecules in MoS₂ 8-MRs adopt this configuration.

The proton transport properties of the C-MoS₂-0.26 membrane were tested using a simple device fabricated by transferring the C-MoS₂-0.26 film onto a silicon nitride substrate with an aperture of 5 µm diameter (Fig. 5c). Because the MoS₂ grains were substantially smaller than the aperture area, abundant GBs could be used for ion transport. The assembled device exhibited low areal conductance (<100 S m⁻²) for various aqueous solutions, containing 0.1 M of KCl, NaCl, LiCl, CaCl₂, or MgCl₂. In contrast, a high areal conductance (~1.3 × 10⁴ S m⁻²)was observed when 0.1 M HCl solution was used for the measurement, demonstrating the selective proton transport capability of C-MoS₂-0.26 (Fig. 5d). The measured selectivity of H⁺relative to other cations (e.g., H⁺/Li⁺ of ~170, H⁺/Na⁺ of ~160, and H⁺/K⁺ of ~127) is higher than that of various artificial proton channels (Supplementary Table 4).

The ion transport behaviors of the device hardly changed after soaking in 0.1 M HCl solution for 10 h, indicating that the GB structures of C-MoS₂ have good acid resistance (Supplementary Fig. 19). Replacing the C-MoS₂-0.26 film with a single-crystalline defect-free MoS₂ film in the device caused loss of proton transport ability (Supplementary Fig. 20), confirming the critical role played by the defect structure in proton transport.

Proton transport through C-MoS₂-0.26 was further investigated using several HCl concentration pairs, each with a four-fold concentration difference: 0.4 M/ 0.1 M, 0.2 M/ 0.05 M, and 0.1 M/ 0.025 M (Supplementary Fig. 21). For all the tests, the zero-voltage current remained positive, and the zero-current voltage was nearly constant at ~−35 mV, indicating that H⁺ ions were the primary contributors to the net current. The diffusive proton permeability was calculated to be ~1 × 10⁻⁴ cm² s⁻¹, which is comparable to that achieved by single water chains confined in carbon nanotubes^18,38,39 (Supplementary Note 4).

This study demonstrates that “perfect” water/ion separation can be achieved using a monolayer MoS₂ membrane with specially designed structural defects. Precise control of the orientation and size of MoS₂ grains is important for the successful preparation of high-performance separation membranes. When all MoS₂ grains have a fixed-orientation relationship (0° or 60°), the desired 8-MR defects dominate at the GBs, resulting in the formation of membranes with high water/ion selectivity. Meanwhile, the grain size determines the number of GBs and thus the density of the 8-MR pores. The single-file water transport behavior of the MoS₂ 8-MR pores is similar to that in protein aquaporins; nevertheless, inorganic MoS₂ membranes can be fabricated more easily over large areas and can be widely used in various nonbiocompatible environments. Owing to the strong molecular-sieving effect and unique water selectivity, the optimized MoS₂ membranes exhibit outstanding performance in several applications, including FO and RO water/ion separation, hydrogen production by seawater electrolysis, and water-assisted selective proton transfer. The synthesis method reported herein represents a new strategy for the controlled generation of local structures on 2D materials to modulate their properties, with general implications for various research systems.

Acknowledgments

The financial support for this work was provided by Baseline Funds (BAS/1/1372-01-01) to Y.H. and (BAS/1/1323-01-01) to I.P. from King Abdullah University of Science and Technology (KAUST). This research used resources of the Core Laboratories of KAUST. L.L. thanks the support from the Jockey Club Hong Kong to the JC STEM lab of 3DIC, and the Research Grant of Council of Hong Kong (CRS_PolyU502/22), and the National Key R&D Project of China (2022YFB4044100). G. S. thanks the support from the National Natural Science Foundation of China (U1932123, 12105166). J.-H. Fu and V.T. are indebted to the financial support from the University of Tokyo. V.T is beholden to the support from the KAUST Office of Sponsored Research (OSR) under Award CCF-3079 and Office of Technology Development under RTF grant. We thank P. Guo for the constructive suggestions.

Competing interests

The authors declare no competing interests.

Wang, L. et al. Fundamental transport mechanisms, fabrication and potential applications of nanoporous atomically thin membranes. Nat. Nanotech.12, 509-522, (2017).
Yang, Y. et al. Large-area graphene-nanomesh/carbon-nanotube hybrid membranes for ionic and molecular nanofiltration. Science364, 1057-1062, (2019).
Feng, J. et al. Single-layer MoS₂ nanopores as nanopower generators. Nature536, 197-200, (2016).
Cheng, C., Lyengar, S. A. & Karnik, R. Molecular size-dependent subcontinuum solvent permeation and ultrafast nanofiltration across nanoporous graphene membranes. Nat. Nanotech.16, 989-995, (2021).
Shen, J., Liu, G., Han, Y. & Jin, W. Artificial channels for confined mass transport at the sub-nanometre scale. Nat. Rev. Mater.6, 294-312, (2021).
Jiang, D.-e., Cooper, V. R. & Dai, S. Porous graphene as the ultimate membrane for gas separation. Nano Lett.9, 4019-4024, (2009).
Cohen-Tanugi, D. & Grossman, J. C. Water desalination across nanoporous graphene. Nano Lett.12, 3602-3608, (2012).
Heiranian, M., Farimani, A. B. & Aluru, N. R. Water desalination with a single-layer MoS₂ nanopore. Nat. Commun.6, 8616, (2015).
Celebi, K. et al. Ultimate permeation across atomically thin porous graphene. Science344, 289-292, (2014).
Surwade, S. P. et al. Water desalination using nanoporous single-layer graphene. Nat. Nanotech.10, 459-464, (2015).
Feng, J. et al. Electrochemical reaction in single layer MoS₂: Nanopores opened atom by atom. Nano Lett.15, 3431-3438, (2015).
O’Hern, S. C. et al. Nanofiltration across defect-sealed nanoporous monolayer graphene. Nano Lett.15, 3254-3260, (2015).
Zhao, J. et al. Etching gas-sieving nanopores in single-layer graphene with an angstrom precision for high-performance gas mixture separation. Sci. Adv.5, eaav1851, (2019).
Griffin, E. et al. Proton and Li-ion permeation through graphene with eight-atom-ring defects. ACS Nano14, 7280-7286, (2020).
Aljarb, A. et al. Substrate lattice-guided seed formation controls the orientation of 2D transition-metal dichalcogenides. ACS Nano11, 9215-9222, (2017).
Hu, S. et al. Proton transport through one-atom-thick crystals. Nature516, 227-230, (2014).
Song, W. et al. Artificial water channels enable fast and selective water permeation through water-wire networks. Nat. Nanotech.15, 73-79, (2020).
Tunuguntla, R. H. et al. Enhanced water permeability and tunable ion selectivity in subnanometer carbon nanotube porins. Science357, 792-796, (2017).
Man, P., Srolovitz, D., Zhao, J. & Ly, T. H. Functional grain boundaries in two-dimensional transition-metal dichalcogenides. Acc. Chem. Res.54, 4191-4202, (2021).
Bertoldo, F. et al. Intrinsic defects in MoS₂ grown by pulsed Laser deposition: from monolayers to bilayers. ACS Nano15, 2858-2868, (2021).
Ly, T. H. et al. Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries. Nat. Commun.7, 10426, (2016).
Gao, N., Guo, Y., Zhou, S., Bai, Y. & Zhao, J. Structures and magnetic properties of MoS₂ grain boundaries with antisite defects. J. Phys. Chem. C121, 12261-12269, (2017).
Najmaei, S. et al. Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers. Nat. Mater.12, 754-759, (2013).
Yu, H. et al. Wafer-scale growth and transfer of highly-oriented monolayer MoS₂ continuous films. ACS Nano11, 12001, (2017).
Graf, M. et al. Fabrication and practical applications of molybdenum disulfide nanopores. Nat. Protoc.14, 1130, (2019).
Watson, A. J., Lu, W., Guimarães, M. H. D. & Stöhr, M. Transfer of large-scale two-dimensional semiconductors: challenges and developments. 2D Materials8, 032001, (2021).
Cao, Y. et al. Movable-type transfer and stacking of van der Waals heterostructures for spintronics. IEEE Access8, 70488-70495, (2020).
Ma, D., Peh, S. B., Han, G. & Chen, S. B. Thin-film nanocomposite (TFN) membranes incorporated with super-hydrophilic metal–organic framework (MOF) UiO-66: Toward enhancement of water flux and salt rejection. ACS Appl. Mater. Interfaces9, 7523-7534, (2017).
Ren, J. & McCutcheon, J. R. A new commercial thin film composite membrane for forward osmosis. Desalination343, 187-193, (2014).
Abraham, J. et al. Tunable sieving of ions using graphene oxide membranes. Nat. Nanotech.12, 546-550, (2017).
Ries, L. et al. Enhanced sieving from exfoliated MoS₂ membranes via covalent functionalization. Nat. Mater.18, 1112-1117, (2019).
Chen, W. et al. Two-dimensional quantum-sheet films with sub-1.2 nm channels for ultrahigh-rate electrochemical capacitance. Nat. Nanotech.17, 153–158, (2021).
Sapkota, B. et al. High permeability sub-nanometre sieve composite MoS₂ membranes. Nat. Commun.11, 2747, (2020).
Hu, M. & Mi, B. Enabling graphene oxide nanosheets as water separation membranes. Environ. Sci. Technol.47, 3715-3723, (2013).
Shen, J. et al. Fast water transport and molecular sieving through ultrathin ordered conjugated-polymer-framework membranes. Nat. Mater.21, 1183-1190, (2022).
Veroneau, S. S. & Nocera, D. G. Continuous electrochemical water splitting from natural water sources via forward osmosis. Proc. Natl. Acad. Sci. U.S.A.118, e2024855118, (2021).
Marx, D., Tuckerman, M. E., Hutter, J. & Parrinello, M. The nature of the hydrated excess proton in water. Nature397, 601-604, (1999).
Tunuguntla, R. H., Allen, F. I., Kim, K., Belliveau, A. & Noy, A. Ultrafast proton transport in sub-1-nm diameter carbon nanotube porins. Nat. Nanotech.11, 639-644, (2016).
Gopinadhan, K. et al. Complete steric exclusion of ions and proton transport through confined monolayer water. Science363, 145-148, (2019).

There is NO Competing Interest.

SupplementaryInformation.pdf
Supplementary Information

Download PDF

Version 1

posted

You are reading this latest preprint version

Engineering grain boundaries in monolayer molybdenum disulfide for an efficient water/ion separation

Status:

Version 1

Abstract

Figures

Main text

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1