Prospects of 2D graphdiynes and their applications in desalination and wastewater remediation

Abstract

Water is an indispensable part of human life that affects health and food intake. Water pollution caused by rapid industrialization, agriculture, and other human activities affects humanity. Therefore, researchers are prudent and cautious regarding the use of novel materials and technologies for wastewater remediation. Graphdiyne (GDY), an emerging 2D nanomaterial, shows promise in this direction. Graphdiyne has a highly symmetrical π-conjugated structure consisting of uniformly distributed pores; hence, it is favorable for applications such as oil-water separation and organic-pollutant removal. The acetylenic linkage in GDY can strongly interact with metal ions, rendering GDY applicable to heavy-metal adsorption. In addition, GDY membranes that exhibit 100% salt rejection at certain pressures are potential candidates for wastewater treatment and water reuse via desalination. This review provides deep insights into the structure, properties, and synthesis methods of GDY, owing to which it is a unique, promising material. In the latter half of the article, various applications of GDY in desalination and wastewater treatment have been detailed. Finally, the prospects of these materials have been discussed succinctly.

Fig. 1. Various carbon allotropes composed of different hybridized carbon atoms. Reproduced with permission from Chen et al. Copyright 2017, Wiley.

Fig. 2. Some possible atomic motifs of GY-like structures, which have been assigned the terminologies GY1′–GY5′ in the text. Reproduced with permission from Ivanovskii, Copyright 2013, Elsevier Science Ltd.

Fig. 3. Representation of the 26 2D structures identified and investigated in this work. The unit cells and plane groups are indicated. α-, β-, γ-, and δ-GDYs are labeled. Reproduced with permission from Sarafini et al. Copyright 2021, ACS Publications.

Fig. 4. Selected structures of synthesized benzannellated dehydroannulene-based molecules (1–3) and perethynylated dehydroannulene-based molecules (4–6) as building blocks for GY- and GDY-sheet synthesis. Reproduced with permission from Diederich and Kivala. Copyright 2010, Wiley.

Fig. 5. Schematic of the simulated nanoribbon structures. Structures (a) and (c) are nanoribbons in the armchair and zigzag directions, respectively. Structures (b) and (d) are constructed based on structures (a) and (c), respectively, by adding side chains onto the edges. Reproduced with permission from Wan et al. Copyright 2019, American Chemical Society.

Fig. 6. (a) α-, (b) β-, and (c) γ-GY structures maintaining the armchair direction along the x-axis and the zigzag direction along the y-axis with sp- and sp²-hybridized carbon atoms depicted in grey and black, respectively. Rhombohedral (red) and rectangular (blue) unit cells are also shown. (A colored version of this figure can be viewed online.) Reproduced with permission from Puigdollers et al. Copyright 2016, Elsevier Science Ltd.

Fig. 7. (a) Geometric structure of optimized GY. The unit cell is represented using green dashed lines. (b) Contour plots of total electron density of GY (left panel) and Gra (right panel) for comparison. Reproduced with permission from Zhou et al. Copyright 2011, American Institute of Physics.

Fig. 8. Four Gra allotropes: (a) C1 (pentaheptite) consisting of pentagons and heptagons, (b) C2 consisting of squares and octagons, (c) C3 consisting of triangles and enneagons, and (d) C4 (GDY) consisting of two acetylenic linkages between hexagons. EOSs for Gra and four allotropes revealing the phase transition from Gra to C4 at F = −7.0 N m⁻¹. Reproduced with permission from Andrew et al. Copyright 2012, APS. (e) EOS for graphene and four allotropes showing a phase transition from graphene to C4 at F = −7.0 N m⁻¹.

Fig. 9. Optimized atomic structures of the examined Gra allotropes (13′ – see the text). Unit cells are painted. Reproduced with permission from Enyashin et al. Copyright 2010, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fig. 10. Schematic and stress–strain results of uniaxial tension tests, in reclined-chair (x-axis) and zigzag (y-axis) directions. (a) Reclined-chair direction; uniform strain was applied by displacing the graphyne edges in the x-direction at a constant velocity. The virial stress is calculated over a representative volume, Ω, chosen within the interior of the graphyne sheet to avoid boundary effects. For volume calculations we assume a thickness of 3.20 Å, taken from adhesion energy results (Fig. 3 in Buehler). Fitting the resulting stress–strain data, a Young’s modulus of 532.5 GPa is calculated (or 170.4 N m⁻¹ without consideration of the sheet thickness), with an ultimate stress of 48.2 GPa and maximum strain of 0.0819. Failure is found to be localized to a single edge. (b) Zigzag direction; uniform strain is applied by displacing the graphyne edges in the y-direction at a constant velocity. As before, the virial stress is calculated over the same representative volume, Ω, assuming a thickness of 3.20 Å (Fig. 3). Fitting the resulting stress–strain data, an initial stiffness of 700.0 GPa is calculated (or 224.0 N m⁻¹ without consideration for sheet thickness). The strain along the zigzag direction results in a stiffening behavior, with an increase of the tangent modulus to 888.4 GPa (284.3 N m⁻¹), or 27% increase over the small-deformation modulus. The mechanistic reason for this increase is that the acetylenic groups align towards the applied strain, resulting in higher sustained stress and strain. An ultimate stress of 107.5 GPa and strain of 0.1324 is determined at failure, which is characterized by multiple fracture sites.

Fig. 11. Structural representations of some nanoGDYs: dehydrobenzo [18] annulene (A), “bowtie” bis(annulene) (B), “boomerang” [18] DBA (C), “half-wheel” annulene (D), trefoil (E), “diamond” substructure (F), GDY substructure (G), and wheel-shaped nanoGDY. Reproduced with permission from Hu et al. Copyright 2023, ACS Publications.

Fig. 12. (a) Comparison of C K-edge X-ray absorption near edge structure spectra of single-walled nanotubes (SWNTs), Gra oxide, and GDY exposed to air for 1 week (GD-1w) and 3 months (GD-3m) and (b) Illustration of the GDY structure. Reproduced with permission from Zhong et al. Copyright 2013, American Chemical Society.

Fig. 13. The SEM and TEM images of GDNTs after being annealed: (a) top view of a GDNT array, (b) top view of GDNTs under higher magnification, (c) side view image of a large area of a GDNT array, (d) side view image of a GDNT array under higher magnification, (e) low-magnification TEM images of a GDNT bundle, and (f) highmagnification TEM images of GDNTs. The inset is the corresponding SAED patterns. Reproduced with permission from Li et al. Copyright 2011, American Chemical Society.

Fig. 14. Chemical structures of P3HT, PCBM, and GDY and the structure of a GDY-containing photovoltaic device. Reproduced with permission from Du et al. Copyright 2011, Elsevier Science Ltd.

Fig. 15. (a) Schematic of GY and GDY preparation along with their resultant STM micrographs and (b) potential formation pathways of GDY and GY nanowires from BPBE. Reproduced with permission from Wang et al. Copyright 2018, ACS Publications.

Fig. 16. Different lattice planes of Ag substrates trigger the reaction pathways and main products: homocoupling is dominant on Ag (111), whereas Ag (110) triggers the formation of highly oriented 1D silver acetylide organometallic chains. Reproduced with permission from Liu et al. Copyright 2015, American Chemical Society.

Fig. 17. (a) Schematic of the synthesis process of Cu@GDY–HoMS (HoMS: hollow multishelled structure) and GDY–HoMS. Reproduced with permission from Zhan et al. Copyright 2022, Elsevier Science Ltd.

Fig. 18. (a) Synthesis route for nanoGDY. (i) Pd₂(dba)₃·CHCl₃, CuI, N,N-diisopropylethylamine, DMF/toluene, rt; (ii) (a) KOH, toluene, 120 °C; (b) CuCl (60 equiv.), and (c) Cu(OAc)₂·H₂O (60 equiv.), pyridine, 60 °C. Reproduced with permission from Hu et al. Copyright 2023, American Chemical Society.

Fig. 19. X-ray crystallographic structures of 4a (a) and 1c (b and c) at 170 K, (b) side view and (c) top view of 1c, with ortho-substituted 4-(tert-butyl)phenyl groups vertical to the nanoGDY core plane with an included angle of 62.3°; the H⋯Cl hydrogen bonds formed between H atoms of tert-butylphenyl groups in 1c and the Cl atom in the solvent CHCl₃ are shown. Top view (d) and side view (e) of dimer 1c with close contacts (purple dashed lines with labeled distance); the carbon atoms in different layers with close contacts are highlighted in red and blue colors. (f) Enlarged view in red trapezoid to show the CH⋯π interactions. Reproduced with permission from Guilin et al. Copyright 2023, American Chemical Society.

Fig. 20. (a) Schematic of growth of a GDY film, combining a reduction with a self-catalyzed and saturated VLS model. (b) Schematic of growth of a GDY film, combining a reduction with a self-catalyzed and saturated VLS model on the top surface of a single ZnO nanorod (NR). (c) SEM images corresponding to the schematic in (b) of (i) ZnO NRs with smooth top surfaces and thin GDY films; (ii) rough surface and kink sites (marked with arrows) produced by ZnO reduced atop the ZnO NRs; (iii) ZnO nanoparticles, which originated from reoxidized Zn droplets, scattered in the GDY thin films; (iv) a typical droplet-like transparent GDY thin film; (v) many small GDY thin films, produced by a few Zn droplets, connected by two, three, or more fragments of a smaller GDY film; the morphologies of the small GDY films are similar to those of the droplets; (vi) continuous large-area GDY thin films. Reproduced with permission from Qian et al. Copyright 2015, Springer Nature.

Fig. 21. (a) Schematic of the experimental setup. (b) Cross-sectional view of the SEM image of GDY nanowalls on the Cu substrate. (c) AFM image of the exfoliated sample on the Si/SiO₂ substrate. The height profile is taken along the white line, representing a 15.5 nm thick film. Reproduced with permission from Zhou et al. Copyright 2015, American Chemical Society.

Fig. 22. (a) Typical plots of electron-emission current density (J) as a function of applied electric field (E). (b) Corresponding F–N plots and linear fitting. Reproduced with permission from Zhou et al. Copyright 2015, American Chemical Society.

Fig. 23. (a) Process and proposed mechanism to synthesize GDNT arrays. (b and c) SEM images of GDNTs after annealing. Reproduced with permission from Li et al. Copyright 2011, American Chemical Society.

Fig. 24. Seawater desalination properties of GDY. Ion rejection efficiencies of GDY with respect to applied external pressure in the range 10–25 MPa. Cumulative volume of water passed at different hydrostatic pressures. Reproduced with permission from Xu et al. Copyright 2023, Elsevier Science Ltd.

Fig. 25. Performance of GDYMS as an oil accumulation material. (a) Photographs of GDYMS-15 recovering an organic solvent from an oil–water mixture. (b) Adsorption capacities of GDYMS-15 toward various organic solvents and oils. (c) Adsorption recyclability of GDYMS-15 toward petroleum ether and CHCl₃. Reproduced with permission from Li et al. Copyright 2019, American Chemical Society.

Fig. 26. Schematic of the C18 ring of GDY and the highly efficient solar vapor generation process using GDY–HoMS. The HoMS exhibits enhanced light adsorption, water transport properties, and ability to reduce the vaporization enthalpy toward achieving highly efficient photovapor generation. Moreover, the strong interaction between the metal ions and GDY contributes to the ultrahigh ion removal efficiency of the GDY–HoMS. Reproduced with permission from Zhan et al. Copyright 2022, Elsevier Science Ltd.

Fig. 27. (a) Water density maps inside the pores of GDY during the separation process. (b) System-wide water density map at 400 MPa. Reproduced with permission from Majidi et al., Copyright 2023, Elsevier Science Ltd.

Fig. 28. Performance comparison between α-GY, β-GY, GY-3, and conventional RO desalination membranes. The three GY monolayers can desalt water at 100% ion rejection with a throughput significantly faster than commercial RO membranes such as polymeric seawater RO (SWRO), brackish water RO (BWRO), high-flux RO (HFRO), and NF. Reproduced with permission from Xue et al. Copyright 2013, IOP Science.

Adrija Ghosh

Jonathan Tersur Orasugh

Suprakas Sinha Ray

Dipankar Chattopadhyay