The influence of metal organic frameworks(MOFs) after tannic acid etching on the performance and structure of loose nanofiltration membranes for enhanced dyes/salts selective separation

Abstract

This study selects ZIF-L(Co) as the representative of MOFs with etching effect and MIL-53 (Fe) as the representative of MOFs without etching effect, explores the effects of these two representative MOFs on membrane structure and properties before and after tannic acid (TA) etching. Experiments have shown that tannic acid has both chelating and etching effects on ZIF-L(Co), and only chelating effects on MIL-53 (Fe). The effect of tannic acid-modified MOFs on the formation and performance of loose nanofiltration membranes are investigated, and the application of membranes in high salinity textile wastewater is further explored. The results showed that the etched TAZIF-L(Co) improved membrane permeability, dye/salt selectivity, and stability compared with before etching. Through the value of diffusion coefficient D in mean square displacement (MSD), it can be seen that PIP / TAZIF-L (Co)(1.28*10⁻⁹m²s⁻¹) is smaller than PIP / ZIF-L (Co) (1.68*10⁻⁹m²s⁻¹), which proved that the MOFs etched by tannic acid have a greater influence on the diffusion rate of aqueous phase. It is known by density functional theory (DFT) theoretical calculation, the blinding energy of TAZIF-L(Co) (−2.381 eV) and TAMIL-53(Fe) (−2.532 eV) are larger than the corresponding blinding energy before tannic acid etching (−1.282 eV, −1.591 eV). It proved the stability of MOFs in the aqueous phase. Therefore, this study provides experimental and theoretical references for the study of tannic acid-modified MOFs in loose nanofiltration membranes.