Hydrophilic modification of polylactic acid synergistic MMT@ZIF-8@TA nanocomposite membrane for dye wastewater purification

Combined NVP grafting and MMT@ZIF-8@TA modification raised pure water flux to 836.84 L·m⁻²·h⁻¹, ~6.8× of pristine PLA membrane. • The membrane retained over 95% rejection for four cationic/anionic dyes, realizing charge-selective adsorption (98% MeB removal, 99% AO removal). • PZ4 membrane removed 78.59% methylene blue under UV in 150 min; its rate constant (0.00995 min⁻¹) was ~110 times the blank group. • Superoxide (•O₂⁻) and hydroxyl (•OH) radicals were verified as the main active species during photocatalytic degradation. Rapid industrialization and urbanization have exacerbated water scarcity and pollution. Traditional polymer membranes are non‑renewable and non‑biodegradable. Polylactic acid (PLA) is a biodegradable and renewable alternative, but its hydrophobicity and lack of functional groups restrict its direct application in water purification. To address these limitations, we grafted N‑vinylpyrrolidone (NVP) onto PLA chains via free‑radical polymerization to obtain PLA‑g‑PVP with enhanced hydrophilicity. Zeolitic imidazolate framework‑8 (ZIF‑8) was grown in situ on montmorillonite (MMT) and coated with tannic acid (TA) to obtain MMT@ZIF‑8@TA nanoparticles, which synergistically improve membrane porosity, adsorption capacity, and photocatalytic activity. A series of PLA‑g‑PVP/MMT@ZIF‑8@TA (PZ) membranes were fabricated by non‑solvent induced phase separation. The PZ4 membrane exhibited a pure water flux of 836.84 L·m⁻²·h⁻¹ , approximately 6.8 times that of pristine PLA, and achieved over 95% rejection for four representative dyes, including both cationic (auramine O, methylene blue) and anionic (congo red, methyl blue) dyes. After five cycles, the flux recovery rate remained 81.03% with dye rejection > 90%, showing excellent reusability. The PZ membranes also demonstrated adsorption and photocatalytic activity. The PZ4 membrane degraded 78.59% of methylene blue within 150 min under UV irradiation, attributed to efficient separation of photogenerated electron‑hole pairs and synergistic oxidation by hydroxyl (·OH) and superoxide (·O 2 ⁻) radicals, leading to dye mineralization. This eco‑friendly membrane integrates high separation efficiency, which shows great potential for the purification of dye-containing wastewater, and sheds light on the design of multifunctional composite filtration membranes. Download: Download high-res image (266KB) Download: Download full-size image