Polydopamine passivation of amyloid fibril confined nano-hydrated alumina: improving stability in actual harsh wastewater to achieve efficient defluoridation.

Al-based adsorbents are widely used for fluoride removal due to strong Lewis acid-base affinity between Al (aluminium) sites and fluoride ions. However, their application in acidic, ligand-rich wastewater is severely limited by amphoteric instability, causing catastrophic Al leaching, rapid degradation, and secondary contamination. Resolving the trade-off between adsorption reactivity and durability remains critical for sustainable water purification. Here we report a stability-oriented nanohybrid (AFL-Al@PDA), where amyloid fibril-confined (AFL) nano-hydrated alumina is encapsulated within a crosslinked polydopamine (PDA) shell. The cooperative PDA-amyloid network forms a 3D barrier that excludes organics and buffers proton attack; this localized buffering is directly visualized by fluorescence probe, revealing pH differences between the microenvironment and bulk solution. As a result, Al leaching is suppressed to < 0.8% in concentrated organic acids (400 mg/L; citric, oxalic, and tartaric acids) and to ∼3% at pH 3, versus 91% for pristine AFL-Al. Attributable to its strong stability, AFL-Al@PDA achieves an outstanding defluorination capacity of 83.87 mg/g in highly acidic media-over 12 times higher than AFL-Al (6.80 mg/g). Importantly AFL-Al@PDA simultaneously achieves high operational robustness, treating 3263-4350 kg wastewater per kg adsorbent in semiconductor, domestic and photovoltaic effluent, demonstrating a generalizable strategy for stabilizing Al-based adsorbents under chemically challenging conditions.