2.2 Synthesis of MOF nanosheets
The MOF nanosheets were solvothermally synthesized under continuous
ultrasonication as reported in literature.[37]Primarily, 0.375 mmol CoCl2·6H2O and
0.375 mmol NiCl2·6H2O were fully
dissolved in 32 mL DMF. Then, ethanol (2 mL), water (2 mL), and TEA (0.8
mL) were added into the solution under constant stirring, followed by
adding 0.375 mmol organic ligands (BDC, NH2-BDC, or
CH3-BDC). The organic ligands were completely dissolved
in solution and it was further stirred for 2 h to obtain a uniform
colloidal suspension. Whereafter, the colloidal suspension was
continuously ultrasonicated for 20 h under airtight condition and the
precipitates were collected via centrifugation. The obtained MOF
nanosheets were then washed with ethanol by 4 times to remove the
residual reactants, and vacuum dried at room temperature. Finally, MOF
nanosheets were dispersed in ethanol for further utilization.
2.3
Preparation of hierarchical MOF lamellar membranes
Hierarchical MOF lamellar membranes were prepared by
double-needled electrostatic
atomization technology as shown in Scheme 1. Primarily, Nylon substrates
were smoothly adhered on the receiver roller. MOF-CH3nanosheet dispersion (0.1 g L-1)
was injected into one syringe (A),
and MOF-CH3, MOF-BDC or MOF-NH2nanosheet dispersion (0.1 g L-1) was injected into
another syringe (B). The two syringes both connected with a high voltage
of 18 kV, and the tip-to-collector distance was 15 cm. Subsequently, 240
mL MOF-CH3 nanosheet dispersion in A syringe was pumped
out at a speed of 0.005 mm s-1 along with scanning
cyclically along roller surface at a speed of 160 rpm to prepare support
layer. After that, 3 mL solution in B syringe was sprayed on the support
layer under the same conditions, to construct ultrathin membrane surface
layer.