2.3 Pretreatment of the substrate
The purchased microporous stainless steel substrate was polished to
smooth the surface and then ultrasonically cleaned three times with a
commercial cleaning agent, absolute ethanol, and deionized water for 0.5
h, respectively. The impurities on the stainless steel surface were
washed off and the substrate was dried for subsequent use. An
appropriate amount of multi-walled CNTs was weighed and poured into 1 L
deionized water with ultrasonic treatment for 60 min to prepare a
solution of CNTs with uniform density for use. The tubular porous
stainless steel (SS) was then cut with appropriate length and immersed
in the as-prepared CNTs solution, followed by vacuum filtration to
modify the outer wall of the stainless steel to decrease the pore size
with good electrical conductivity for subsequent electrophoretic
deposition. We would wipe the CNTs on the tube surface to better fill
the substrate’s pores and large holes. The surface flatness was further
improved, which is beneficial to reduce membrane defects in the
subsequent nanosheet assembly process.