In situ formation of tannic (TA)-aminopropyltriethoxysilane (APTES) nanospheres on inner and outer surface of polypropylene membrane toward enhanced dye removal capacity

Tannic acid (TA) − 3-aminopropyltriethoxysilane (APTES) coating (TA-APTES coating) composed of abundant nanospheres with secondary reaction sites has many distinct advantages for surface modification. Herein, an in-situ growth method is proposed to generate TA-APTES nanospheres on both the outer and inner surface of polypropylene (PP) membrane. Compared with previous reported TA-APTES nano spheres coating just on the outer surface of the membrane (named PP-Su-NPs), TA-APTES nano spheres on both outer and inner surfaces prepared with this method (named PP-En-NPs) exhibits much better functional performance after secondary reactions. As a proof of concept, the TA-APTES nanospheres is functionalized by tannic acid, polyethyleneimine (PEI) and Fe3+ to carry positive charges for absorbing anionic dyes, and the dye adsorption performance of the PP-En-NPs after the secondary reactions is 7–8 times higher than that of PP-Su-NPs. Interestingly, the functionalized coating can not only absorb anionic dyes, but also cationic dyes, and selective desorption is also realized for this functionalized coating. The possible mechanism is revealed in this study. This study will accelerate the development of the TA-APTES coating, and make it become a powerful tool for membrane modification.