Fabrication of recyclable UiO-66-NH2/PVDF hybrid fibrous membrane for Cr(VI) removal in wastewater

Abstract

Efficient and recyclable water treatment technology plays a vital role in practical application of Cr(Ⅵ) removal. Zr-based metal–organic framework (UiO-66-NH2) is widely used in wastewater treatment due to its water stability. Powdery UiO-66-NH2 has disadvantages of easy aggregation, reclamation difficulty and secondary pollution. In this work, UiO-66-NH2 was successfully loaded on electrospun polyvinylidene fluoride (PVDF) fibers by in-situ growth to achieve efficient adsorption and photoreduction of Cr(Ⅵ). Grooved surface of PVDF fibers and truncated octahedron shape of UiO-66-NH2 ensured the loading uniformity and firmness. The loading rate and size of UiO-66-NH2 crystals increased with the amount of trifluoroacetic acid (TFA) in the preparation process. Meantime, the introduction of TFA in synthesis was conducive to the separation efficiency of photogenerated carries. When the addition amount of TFA was 5 ml, UiO-PVDF-3 with loading rate of 44.8% exhibited best Cr(VI) adsorption and photocatalysis performance. For the pure adsorption process, the adsorption capacity of UiO-PVDF-3 at 90 min was 3.76 mg/cm2, and the corresponding removal rate was 95.8%. When visible light was applied, the Cr(VI) removal rate for UiO-PVDF-3 reached to about 95.0% at 45 min. Furthermore, regeneration experiments showed UiO-PVDF-3 had excellent adsorption and photocatalysis reusability. Based on this method, synthesized UiO-66-NH2/PVDF hybrid membrane as a bifunctional material for adsorption and photocatalysis realizes the reuse of UiO-66-NH2 crystals conveniently and avoids secondary pollution during Cr(VI) wastewater treatment.