Hollow fiber with hierarchical loose cellular pores for treating textile wastewater

Abstract

Hollow fiber membrane (HFM) has been widely used to purify waste dye water. The nanoporous skin of HFM usually provided high rejection to dye molecules, however, it suffered from the problem of conflict between high flux and rejection. In this study, a foaming layer was constructed in hollow spongy fiber (HPF) via coupling the non-solvent induced phase separation (NIPS) with polymer foaming. The boundary condition of cavity appearance was closely related with generated CO₂ diffusion. Based on theoretical analysis of phase-diagrams, the increased gas diffusion promoted instantaneous demixing. The enhanced thermodynamic instability would benefit CO₂ nucleation and growth, resulting in hierarchical cellular structure. CO₂ bubble diffusion broke the free barrier of gel rich-phase, achieving interconnected nanopores on each cell wall. This spongy nanopores located on foaming layers provided absorption sites for dye molecules, generating a layer by layer absorption and interception effect to dye. The as-prepared HPF membranes exhibited a high dye rejection (<98.2 %) and a high flux (24.4 L m⁻²h⁻¹) to Rhodamine B. This proposed coupling principles of bubble nucleation and phase-separation would help to design high-performance HFM with pores optimization.