Enhancement of wastewater separation and photocatalytic cleaning ability for polyvinylidene fluoride membranes modified by CNT-COOH@ZIF-8@TA particles

Wastewater treatment remains a critical global environmental challenge. In this study, zeolitic imidazolate framework-8 (ZIF-8) was first grown in situ on carboxylated carbon nanotubes (CNT-COOH), followed by coating with tannic acid (TA). The CNT-COOH@ZIF-8@TA composite was successfully synthesized. Subsequently, a series of polyvinylidene fluoride (PVDF)/CNT-COOH@ZIF-8@TA (PZC) separation membranes were fabricated by the non-solvent-induced phase separation (NIPS) method. Separation tests demonstrated the high removal efficiencies (>99%) of PZC membranes for methylene blue (MeB) and auramine O (AO) dyes, along with effective retention of corn oil and pump oil emulsions. Furthermore, the engineered PZC membranes exhibited significant adsorption capacity for aqueous dyes, achieving removal rates exceeding 98% for both MeB and AO. The adsorption characteristics and underlying mechanisms were elucidated through kinetic, isothermal, and intra-particle diffusion modeling. Additionally, the PZC membranes demonstrated catalytic activity towards MeB degradation, and the PZC4 membrane achieved a degradation efficiency of 88.3%. Moreover, to enhance membrane longevity, membrane regeneration was achieved through photocatalytic cleaning under UV irradiation, offering an alternative to conventional cleaning methods. This study systematically analyzed the chemical structure, surface morphology, hydrophilicity, and charge properties of the material through multiple characterization techniques, including Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), contact angle measurement, and Zeta potential analysis. The membrane's wastewater purification capability was comprehensively evaluated by combining filtration performance, adsorption experiments, and photocatalytic testing. The designed separation membranes offer promising solutions for the post-treatment of oil spills and the remediation of dye-contaminated wastewater.