1 Introduction
2 Separation mechanism of 2D membranes
3 Preparation of 2D nanosheets and 2D membranes
4 Different types of 2D membranes
4.1 2D membranes based on porous nanosheets
4.1.1 Zeolite membranes
Fig.2 (a) Illustration of the floating-particle coating method to prepare MFI nanosheet monolayer seed coating; (b) SEM images of MFI nanosheet seed coatings on porous substrate via the LangmuirSchaefer (left) and the floating-particle coating (right). Reprinted with permission from Ref. [20], copyright 2018 Wiley VCH; (c) Microscopic characterizations of the silicalite nanosheets. Reprinted with permission from Ref. [21], copyright 2018 American Association for the Advancement of Science. |
4.1.2 MOF membranes
Fig.3 (a) SEM images of (I) the top view and (II) cross-section view of an ultrathin Zn2(bim)4 nanosheet on a-Al2O3 support. Reprinted with permission from Ref. [4], copyright 2014 American Association for the Advancement of Science; (b) Comparison of the Al-MOF membrane for ion separation with other representative 2D laminar membranes. Reprinted with permission from Ref. [47], copyright 2020 American Association for the Advancement of Science; (c) Illustration of the fabrication of b-oriented ZIF-L film and c-oriented ZIF-L film. Reprinted with permission from Ref. [53], copyright 2015 The Royal Society of Chemistry. |
Fig.4 (a) Illustration of Zn2(bim)4 nanosheet membranes formation via GO guided self-conversion of ZnO nanoparticles. Reprinted with permission from Ref. [55], copyright 2018 The Royal Society of Chemistry. (b) Illustration of Co2(bim)4 nanosheet membranes formation via vapor phase transformation of Co-based gel. Reprinted with permission from Ref. [57], copyright 2018 Elsevier. |
4.1.3 COF membranes
4.1.4 Graphitic carbon nitride membranes
4.1.5 Nanoporous graphene (NPG) membranes
Fig.7 (a) Illustration of the partially decoupled defect nucleation and pore expansion to prepare NPG membranes. Reprinted with permission from Ref. [103], copyright 2019 American Association for the Advancement of Science; (b) Schematic illustration of GNM/SWNT membranes fabrication. Reprinted with permission from Ref. [106], copyright 2019 American Association for the Advancement of Science. |
4.2 2D membranes based on non-porous nanosheets
4.2.1 GO and reduced GO membranes
Fig.9 (a) Synergistic effects of molecular sieving and carrier-facilitated transport by imitating biological protein nanochannels. Reprinted with permission from Ref. [145], copyright 2019 John Wiley and Sons; (b) Schematic of the design of surface-charged GO membranes. Reprinted with permission from Ref. [15], copyright 2019 Nature Publishing Group; (c) Scheme illustration of the preparation of the PHGOM. (d) Scheme of the working mechanism of a PHGOM-based device for water desalination. Reprinted with permission from Ref. [146], copyright 2020 Wiley VCH. |
4.2.2 LDH membranes
Fig.10 (a) The formation of ZIF-8 membranes on vertically aligned MgAl-CO3 LDH layers. Reprimted with permission from Ref. [152], copyright 2014 The Royal Society of Chemistry; (b) The formation of ZIF-8 membranes on ZnAl-CO3 LDH buffer layers. Reprinted with permission from Ref. [153], copyright 2014 American Chemical Society; (c) The formation of ZIF-8 membranes via partial conversion of a ZnO buffer layer from a ZnAl-NO3 LDH layer. Reprinted with permission from Ref. [154], copyright 2015 Wiley VCH; (d) Illustration of the vertically aligned COF membrane formation. Reprinted with permission from Ref. [155], copyright 2020 American Chemical Society. |
4.2.3 MXene membranes
Fig.11 (a) The preparation of MXene membranes with Fe(OH)3 served as distance holder. Reprimted with permission from Ref. [16], copyright 2017 Wiley VCH. (b) The fabrication of Ti3C2Tx membranes and c-Ti3C2Tx membranes. Reprinted with permission from Ref. [167], copyright 2020 American Chemical Society. |
4.2.4 TMD membranes
Tab.1 Summary of gas separation for 2D-material membranes |
Feed condition | Membrane | Fabrication approach | Permeability/permeance (of faster species) | Selectivity | Ref. |
---|---|---|---|---|---|
p-Xylene/o-xylene | MFI | Secondary growth | 4 × 10–7 mol∙m–2∙s–1∙Pa–1 | 25–45 | [32] |
p-Xylene/o-xylene | Silicalite-1 | Gel-free secondary growth | 1.3 × 10–7 mol∙m–2∙s–1∙Pa–1 | 1050 | [33] |
p-Xylene/o-xylene | MFI | Gel-free secondary growth | 2.4 × 10–7 mol·m–2·s–1·Pa–1 | 500 | [34] |
p-Xylene/o-xylene | MFI | Gel-free secondary growth | 5.6 × 10–7 mol·m–2·s–1·Pa–1 | 2000 | [35] |
p-Xylene/o-xylene | MFI | Gel-free secondary growth | 2.9 × 10–7 mol·m–2·s–1·Pa–1 | >10000 | [20] |
H2/CO2 | AMH-3/PBI | Casting | 1 Barrer | 35 | [39] |
H2/CO2 | Zn2(bim)4 | Hot-drop coating | 2700 GPU | 291 | [4] |
H2/CO2 | Zn2(bim)3 | Hot-drop coating | 8 × 10–7 mol·m–2·s–1·Pa–1 | 166 | [22] |
H2/CO2 | CuBDC-GO | Vacuum filtration | 9.6 × 10–7 mol·m–2·s–1·Pa–1 | 95.1 | [52] |
H2/CO2 | Zn2(bim)4/GO | Direct growth | 1.4 × 10–7 mol·m–2·s–1·Pa–1 | 106 | [55] |
H2/CO2 | MAMS-1 | Hot-drop coating | 553±228 GPU | 235±14 | [23] |
H2/CO2 | [Cu2(ndc)2(dabco)]n/PBI | Casting | 6.13±0.03 Barrer | 26.7 | [49] |
H2/CO2 H2/N2 H2/CH4 | Zn2(bim)4 | Direct growth | 2.04 × 10–7 mol·m–2·s–1·Pa–1 | 53 67 90 | [56] |
H2/CO2 | Co2(bim)4 | Vapor phase transformation | 1.72 × 10–7 mol·m–2·s–1·Pa–1 | 58.7 | [57] |
H2/CO2 | c-Oriented ZIF-L | Secondary growth | 1.95 × 10–7 mol·m–2·s–1·Pa–1 | 24.3 | [53] |
H2/CO2 | MXene | Vacuum filtration | 2226.6 Barrer | 167 | [17] |
H2/CO2 | Polyimide-PGM | Vapor-liquid interfacial polymerization | 6.85 × 10–6 mol·m–2·s–1·Pa–1 | 6.41 | [105] |
H2/CO2 | TpEBr@TpPa-SO3Na | Layer-by-layer assembly | 2566 GPU | 22.6 | [25] |
H2/CO2 | COF-LZU1 | In situ growth | 3654.8 GPU | 31.6 | [155] |
H2/CO2 H2/N2 H2/CH4 | COF-LZU1-ACOF-1 | Temperature-swing solvothermal approach | 2.24 × 10–7 mol·m–2·s–1·Pa–1 2.38 × 10–7 mol·m–2·s–1·Pa–1 1.82 × 10–7 mol·m–2·s–1·Pa–1 | 24.2 83.9 100.2 | [65] |
H2/CO2 H2/N2 | GO | Vacuum filtration | 10–7 mol·m–2·s–1·Pa–1 | 3400 900 | [14] |
H2/CO2 H2/C3H8 | EFDA-GO | External force driven assembly | 840–1200 Barrer 3.9 × 10−7 mol·m–2·s–1·Pa–1 | 29–33 260 | [5] |
H2/N2 | MCM-22/Silica | Layer-by-layer deposition | 2.09 × 10–8 mol·m–2·s–1·Pa–1 | 7.5 | [37] |
H2/N2 | MCM-22/Silica | Deposition cycles | 10–8 mol·m–2·s–1·Pa–1 | >100 | [38] |
H2/CH4 | JDF-L1/6FDA-4MPD+ 6FDA-DABA | Casting | 137±14 Barrer | 35.6±1.4 | [41] |
H2/CH4 | JDF-L1/polysulfone | Casting | 12.5 Barrer | 128±13 | [42] |
H2/CH4 | MCM-41+ JDF-L1/ 6FDA-4MPD+ 6FDA-DABA | Casting | 440 Barrer | 32 | [43] |
H2/CH4 | NiAl-CO3 LDH | In situ growth | 4.5 × 10–8 mol·m–2·s–1·Pa–1 | 78 | [150] |
H2/CH4 | ZIF-8@MgAl-CO3 LDH | In situ growth Secondary growth | 1.4 × 10–7 mol·m–2·s–1·Pa–1 | 12.9 | [152] |
H2/CH4 | ZIF-8@ZnAl-CO3 LDH | In situ growth | 1.4 × 10–7 molm–2·s–1·Pa–1 | 12.5 | [153] |
H2/CH4 | ZIF-8@ZnAl-CO3 LDH | In situ growth | 1.9× 10–8 mol·m–2·s–1·Pa–1 | 83.1 | [154] |
H2/CH4 | Porous graphene | LPCVD | 6045 GPU | 15.6 | [103] |
CO2/CH4 | AMH-3/cellulose acetate | Casting | 10.36±0.25 Barrer | 30.03±0.34 | [40] |
CO2/CH4 | CuBDC/PI | Casting | 2.78±0.02 Barrer | 88.2±1.3 | [48] |
CO2/CH4 | CuBDC/PIM-1 | Casting | 407.3 GPU | 15.6 | [50] |
CO2/CH4 | CuBDC/6FDA-DAM | Casting | 430±10 Barrer | 43±3 | [51] |
CO2/CH4 | LDH () | Spin-casting | 150 GPU | 33 | [151] |
CO2/N2 | MgAl-CO3 LDH | Vacuum-suction | 2.07 × 10–7 mol·m–2·s–1·Pa–1 | 35 | [149] |
CO2/N2 | MoS2-Pebax/PDMS/PSf | Drop-coating | 64 Barrer | 93 | [185] |
CO2/N2 CO2/CH4 | MoS2 SILM | Vacuum filtration | 47.88 GPU | 131.42 43.52 | [186] |
CO2/N2 CO2/CH4 | WS2 SILM | Vacuum filtration | 47.3 GPU | 153.21 68.81 | [19] |
C2H4/C2H6 | Ag/IL-GO | Vacuum filtration Spin-coating | 72.5 GPU | 215 | [145] |
n-Butane/i-butane | MFI | Vacuum filtration | 1923 GPU | 58 | [36] |
Tab.2 Summary of nanofiltration for 2D-material membranes |
Feed system | Membrane | Fabrication approach | Water flux | Rejection/% | Ref. |
---|---|---|---|---|---|
Evans blue | g-C3N4 | Vacuum filtration | 29 L·m–2·h–1·bar–1 | 87 | [26] |
Evans blue | g-C3N4-PAA | Vacuum filtration | 117 L·m–2·h–1·bar–1 | 83 | [69] |
Evans blue | MXene | Vacuum filtration | 1084 L·m–2·h–1·bar–1 | 90 | [16] |
Evans blue | MoS2 | Vacuum filtration | 245 L·m–2·h–1·bar–1 | 89 | [177] |
Evans blue | WS2 | Vacuum filtration | 1850 L·m–2·h–1·bar–1 | 82 | [178] |
Evans blue | NSC-GO | Vacuum filtration | 695 L·m–2·h–1·bar–1 | 83.5 | [126] |
Evans blue | NbN/GO | Vacuum filtration | 20 L·m–2·h–1·bar–1 | 98 | [142] |
Rhodamine B | CDs–GO | Vacuum filtration | 439 L·m–2·h–1 | 96.9 | [130] |
Rhodamine B | Fe3O4@rGO | Filtration-disposition | 296 L·m–2·h–1·bar–1 | 98.14 | [128] |
Rhodamine B | rGO-TH | Vacuum filtration | 8526 · 30 L·m–2·h–1·bar–1 | 99±1 | [121] |
Rhodamine B | Tp-AD | Vacuum filtration | 596 L·m–2·h–1·bar–1 | 98 | [61] |
Rhodamine B | SWCNT/GO | Vacuum filtration | 710 ·50 L·m–2·h–1·bar–1 | 97.4±0.3 | [132] |
Rhodamine B | g-C3N4 NT/rGO | Vacuum filtration | 4.87 L·m–2·h–1·bar–1 | 98 | [134] |
Rhodamine B | CA/GO-TiO2 | Vacuum filtration | 33.2 L·m–2·h–1 | 99.4 | [131] |
Rhodamine B | GO/TiO2 | Vacuum filtration | 89.6 L·m–2·h–1·bar–1 | 99.3 | [135] |
Rhodamine B | rGO-TiO2 | Secondary growth | 9.82 L·m–2·h–1·bar–1 | 98.5 | [136] |
Methylene blue | TAMoS2 | Vacuum filtration | 10000 L·m–2·h–1·bar–1 | 98.26 | [182] |
Methylene blue | BPEI/GO | Vacuum filtration | 2.09 L·m–2·h–1·bar–1 | 96.4 | [117] |
Methylene blue | WS2/GO | Vacuum filtration | 159.6 L·m–2·h–1·bar–1 | 96.3 | [139] |
Methylene blue | GO/MXene | Vacuum filtration | 71.9 L·m–2·h–1·bar–1 | 99.5 | [141] |
Methyl blue | rGO | Vacuum filtration | 21.8 L·m–2·h–1·bar–1 | 99.2 | [137] |
Methyl blue | SPPO/g-C3N4 | Vacuum filtration | 8867 L·m–2·h–1·bar–1 | 100 | [27] |
Methyl red | Zn-TCP(Fe)/PEI | Vacuum filtration | 4243 L·m–2·h–1·bar–1 | 98.2 | [54] |
Methyl orange | MgAlLDH | Vacuum filtration | 298 L·m–2·h–1·bar–1 | 99.5 | [161] |
Methyl orange | MWNTs/GO | Vacuum filtration | 8.69 L·m–2·h–1·bar–1 | 96.1 | [133] |
Congo red | GO/NH2-Fe3O4 | Vacuum filtration | 15.6 L·m–2·h–1·bar–1 | 94 | [129] |
Congo red | GO/MoS2 | Pressure-assisted filtration | ~10.2 L·m–2·h–1·bar–1 | 99.6 | [138] |
Eriochrome black T | MgAl-LDH | In situ growth | 566 L·m–2·h–1·MPa–1 | 98.5 | [160] |
Chrome black T | COF-LZU1 | In situ growth | 760 L·m–2·h–1·MPa–1 | 98 | [64] |
Acid yellow 14 | c-Ti3C2Tx | Vacuum filtration | 344 L·m–2·h–1·bar–1 | 76.4 | [167] |
NaCl | PHGOM | Dual-flow filtration | 1529 L·m–2·h–1·bar–1 | 97 | [146] |
NaCl | GNM/SWNT | O2 plasma drilling | 22 L·m–2·h–1·bar–1 | 98.1 | [106] |
NaCl | MXene | Vacuum filtration | 2.8 L·m–2·h–1 | 96.5 | [168] |
NaCl | MoS2 | Chemical vapor deposition | >322 L·m–2·h–1·bar–1 | >99 | [18] |
NaCl | MoS2 | Vacuum filtration | 33.7 L·m–2·h–1·bar–1 | 82 | [181] |
NaCl | GO-PVAm-Silica | Pressure-assisted filtration | 80.2 · 0.8 kg·m–2·h–1 | 99.99 | [123] |
NaCl | g-C3N4-PA | Interfacial polymerization | 45 g·m–2·h–1 | 98 | [76] |
MgCl2 | GO | Pressure-assisted filtration Dip-coating | 51.2 L·m–2·h–1·bar–1 | 93.2 | [15] |
CoCl2 | Al-MOF | Vacuum filtration | 2.22 mol·m–2·h–1·bar–1 | 100 | [47] |
Na2SO4 | COFs@CNFs | Vacuum filtration | 42.8 L·m–2·h–1·bar–1 | 96.8 | [24] |