Stabilizing MXene-based nanofiltration membrane by forming analogous semi-interpenetrating network architecture using flexible poly(acrylic acid) for effective wastewater treatment

Two-dimension MXene (Ti3C2Tx) membrane has attracted widespread interest in water treatment to relieve the problem of clean water shortage. Nevertheless, notorious swelling and subsequent instability problems of the MXene-based membrane when immersing in water hinder its wide application, owing to the weak interaction between the adjacent MXene laminates. Herein, a feasible strategy is proposed to stabilize and tune the nanochannels of MXene-based membranes and achieve superior nanofiltration efficiency. Poly(acrylic acid) (PAA) macromolecules are firstly inserted into the MXene nanosheets and form PAA-modified MXene (PAA-MXene) dispersion. Then, the dispersion is vacuum filtered on the electrospun polyacrylonitrile (PAN) nanofibrous substrate to form an ultra-thin PAA-MXene hydrogel barrier layer, thus assembling into PAA-MXene/PAN composite membrane. The MXene laminates will be intertwined by the long chain of flexible PAA macromolecules and thus form homologous semi-interpenetrating network structure with MXene as physical crosslinker through strong hydrogen-bond interaction, which will restrict the obvious structural change of MXene nanosheets and effectively adjust their d-spacing at ∼14.28 Å with MXene: PAA mass ratio of 1:0.5. The synergic effect of PAA and MXene nanosheets, as well as electrospun PAN nanofibrous substrate, endows the PAA-MXene/PAN membrane with superior nanofiltration performance to various dyes. The optimum PAA-MXene/PAN membrane possesses permeate fluxes of 271.26, 516.34, 300.83 L m−2 h−1 and rejections of 98.92%, 99.52%, 98.12% to DR80, AB8GX and AB90 at 0.1 MPa, respectively, which exhibit distinct advantage than the MXene-based membrane in literature. In addition, the PAA-MXene/PAN membrane has good long-time durability and is more suitable for low pressure nanofiltration. All these make PAA-MXene/PAN membrane a promising nanofiltration membrane for wastewater treatment.