Tannic acid (TA)-aminopropyltriethoxysilane (APTES) coating has
excellent hydrophilicity, and can be applied to a variety of materials. But it
has poor stability in the air. To improve its stability, we have developed
TA-APTES-Fe(III) coating in our previous work, but there are still some
problems remained such as tedious steps, and undesirable anti-crude
oil-adhesion performance, etc. Besides, both TA-APTES and TA-APTES-Fe(III)
coating cannot realize the hydrophilic modification of the inner surfaces of
porous polypropylene (PP) membrane. To solve the above mentioned problems, we
developed superhydrophilic and stable TA-APTES- tetraethylorthosilicate (TEOS)
coating via one-step process in this study. The new coating can realize the
superhydrophilic modification of the inner surfaces of porous PP membrane, and
endows the PP membrane with good water permeability, which cannot be realized
by our previously reported TA-APTES and TA-APTES-Fe(III) coating. Besides, the
stability of the coating is greatly improved by introducing stable alcoholic
hydroxyl groups derived from TEOS, and the resultant modified membrane can keep
superhydrophilic (CA about 0°) and underwater superhydrophobic (underwater oil
CA above 150°) even after being stored in air for more than 6 months,
ultrasonic treatment for 10 min, or being rinsed by water for 24h (3000r/min),
exhibiting outstanding stability. More importantly, the crude oil adhesion
force of the new coating is as low as 4 μN even under the preload force of
300μN, showing excellent anti-crude oil-adhesion property. The PP membrane
modified by the new coating possesses ultrahigh water flux (10384 L m-2
h-1 bar-1) and can realize highly efficient separation of
oil-in-water emulsion (above 99%). This work is expected to accelerate the
practical application of TA-APTES coating.