A UIO-66/tannic acid/chitosan/polyethersulfone hybrid membrane-like adsorbent for the dynamic removal of dye and Cr (VI) from water

The water-soluble pollutant including dye and heavy metal was a challenge to the water and environment. Adsorption was among one of the most promising technique for the recycle of dye but it usually required a long contact time. A membrane-like adsorbent was fabricated by mixing and depositing tannic acid, chitosan and metal organic framework (MOF, UIO-66) on polyethersulfone (PES) membrane in this study. The material was dense enough to conduct filtration like a membrane to remove both the anionic and cationic dye (acid brilliant scarlet and methylene blue), as well as Cr(VI) from water. When the ratio of MOF/Chitosan was 30% and the pH for mixing was 3.5, the pollutant removal reached 99% in the filtration for 200 min. The adsorbent in the dynamic filtration showed a pollutant loading capacity 3 times of the capacity in the static adsorption, which was caused by the enhanced driving force brought by the concentration polarization in the filtration. The particle size of the TA/CS/MOF mixture were characterized by dynamic light scattering as well as Zeta potential, FTIR, XRD, TEM and XPS. The morphology of membrane was observed by SEM. The result showed that the MOF played as core to disperse the tannic acid-chitosan mixture to improve the pollutant removal. TEM showed the TA/CS mixture formed an uniform coating outside the MOF particle at the pH of 3.5. The pseudo 1st order and pseudo 2nd order model fitted the adsorption kinetics well, while the Elovich model did not fit very well.