Recent advances on graphyne and its family members as membrane materials for water purification and desalination

Graphyne and its family members (GFMs) are allotropes of carbon (a class of 2D materials) having unique properties in form of structures, pores and atom hybridizations. Owing to their unique properties, GFMs have been widely utilized in various practical and theoretical applications. In the past decade, GFMs have received considerable attention in the area of water purification and desalination, especially in theoretical and computational aspects. More recently, GFMs have shown greater prospects in achieving optimal separation performance than the experimentally derived commercial polyamide membranes. In this review, recent theoretical and computational advances made in the GFMs research as it relates to water purification and desalination are summarized. Brief details on the properties of GFMs and the commonly used computational methods were described. More specifically, we systematically reviewed the various computational approaches employed with emphasis on the predicted permeability and selectivity of the GFM membranes. Finally, the current challenges limiting their large-scale practical applications coupled with the possible research directions for overcoming the challenges are proposed.

Mechanistic studies on the anomalous transport behaviors of water molecules in nanochannels of multilayer graphynes

An in-depth understanding of directed transport behaviors of water molecules through nanoporous materials is essential for the design and development of next-generation filtration devices. In this work, we perform molecular dynamics (MD) simulations to explore transport properties of water molecules through nanochannels of multilayer graphyne with different pore sizes. Our simulation results reveal that the orientations of confined water molecules would periodically reverse between two opposite directions as they diffuse along the nanochannels, and such a transport mechanism shows similarities with water transport in aquaporin channels. Further, we observe that, for each orientation reversal, there is an obvious difference in the HB breaking frequency among the three graphyne systems, with an order of graphyne-4 > graphyne-5 > graphyne-3. Besides, the average HB number is found to display a periodic fluctuation with a pulse-like pattern along the diffusion direction, wherein the graphyne-4 system has the maximum fluctuation, while the graphyne-3 system has the minimum one. Such anomalous HB breaking frequency and average HB number fluctuation results finally lead to a nonmonotonic relationship between water diffusion rate and graphyne pore size, and the diffusion order follows graphyne-4 > graphyne-5 > graphyne-3. Herein, we provide a new insight into the transport mechanisms of water molecules through nanoporous materials and our findings open up opportunities for the design and development of high-performance graphyne-based membranes used for water purification and desalination.

Multiscale Design of Graphyne-Based Materials for High-Performance Separation Membranes

By varying the number of acetylenic linkages connecting aromatic rings, a new family of atomically thin graph-n-yne materials can be designed and synthesized. Generating immense scientific interest due to its structural diversity and excellent physical properties, graph-n-yne has opened new avenues toward numerous promising engineering applications, especially for separation membranes with precise pore sizes. Having these tunable pore sizes in combination with their excellent mechanical strength to withstand high pressures, free-standing graph-n-yne is theoretically posited to be an outstanding membrane material for separating or purifying mixtures of either gases or liquids, rivaling or even dramatically exceeding the capabilities of current, state-of-art separation membranes. Computational modeling and simulations play an integral role in the bottom-up design and characterization of these graph-n-yne materials. Thus, here, the state of the art in modeling α-, β-, γ-, δ-, and 6,6,12-graphyne nanosheets for synthesizing graph-2-yne materials and 3D architectures thereof is discussed. Different synthesis methods are described and a broad overview of computational characterizations of graph-n-yne's electrical, chemical, and thermal properties is provided. Furthermore, a series of in-depth computational studies that delve into the specifics of graph-n-yne's mechanical strength and porosity, which confer superior performance for separation and desalination membranes, are reviewed.

Graphynes for Water Desalination and Gas Separation

Selective transport of mass through membranes, so-called separation, is fundamental to many industrial applications, e.g., water desalination and gas separation. Graphynes, graphene analogs yet containing intrinsic uniformly distributed pores, are excellent candidates for highly permeable and selective membranes owing to their extreme thinness and high porosity. Graphynes exhibit computationally determined separation performance far beyond experimentally measured values of commercial state-of-the-art polyamide membranes; they also offer advantages over other atomically thin membranes like porous graphene in terms of controllability in pore geometry. Here, recent progress in proof-of-concept computational research into various graphynes for water desalination and gas separation is discussed, and their theoretically predicted outstanding permeability and selectivity are highlighted. Challenges associated with the future development of graphyne-based membranes are further analyzed, concentrating on controlled synthesis of graphyne, maintenance of high structural stability to withstand loading pressures, as well asthe demand for accurate computational characterization of separation performance. Finally, possible directions are discussed to align future efforts in order to push graphynes and other 2D material membranes toward practical separation applications.