Fabrication of hybrid ultrafiltration membranes with improved water separation properties by incorporating environmentally friendly taurine modified hydroxyapatite nanotubes

In this work, hydroxyapatite nanotubes (HANTs) were explored as a novel environment-friendly additive for the fabrication of ultrafiltration (UF) membranes. Hydrophilic modification was conducted to the prepared HANTs, which includes the polydopamine (PDA) coating and the following grafting of taurine (TA), a kind of amino acid with -SO3H group. Subsequently, the modified HANTs (HANTs-DA-TA) were mixed with polyethersulfone (PES) to fabricate nanocomposite UF membranes. The prepared membranes were fully characterized, including the porosity, hydrophilicity, membrane morphology, and practical UF capability. The fabricated PES/HANTs-DA-TA membranes exhibited remarkably elevated water flux (up to 439 L m−2 h−1), which was ~2.6 times that of PES membrane (169 L m−2 h−1), whereas the rejection of PES/HANTs-DA-TA membranes was still kept at a high state. The improved flux mainly benefited from the more porous membrane structure, declined skin layer thickness, and the enhanced hydrophilicity. Meanwhile, the PES/HANTs-DA-TA membranes exhibited increased antifouling capability and the highest flux recovery ratio (FRR) reached 77.9% due to the improved surface hydrophilicity. Furthermore, the short rod-like nano hydroxyapatite (HA) was prepared and functionalized the same way as the HANTs-DA-TA. It was found that compared to rod-like HA, the tubular nano HA was more efficient in facilitating the membrane permeation due to the superiority of nanotubular structure. This work reveals that as a novel green additive, the HANTs have great application potential in fabricating water treatment membranes and can be employed for further studies.