Iron-bearing halloysite for wetland remediation: Curvature-controlled oxidation pathways and ecological implications

The fate of emerging contaminants in natural waters is increasingly influenced by mineral-mediated oxidation processes. Here we report that iron-anchored halloysite-a naturally occurring tubular aluminosilicate mineral-can activate hyperoxide (e.g. peroxymonosulfate, PMS) to generate reactive oxygen species for pollutant degradation, with its inherent curvature playing a decisive role in determining the oxidation pathway. Unlike its planar polymorph kaolinite, halloysite's tubular structure induces electronic reconstruction of Al-O moieties, creating oxygen-coordinated Lewis acid sites that preferentially cleave the O-H bond of PMS to yield SO₅^•- intermediates, which subsequently dimerize into singlet oxygen (¹O₂). This curvature-directed pathway switching from radical-dominated to ¹O₂-mediated oxidation achieves 99% removal of norfloxacin with 81% PMS utilization efficiency and minimal iron leaching when trace iron is naturally present or intentionally introduced (0.75 wt%). Using water and sediment from East Dongting Lake wetland-a Ramsar-protected ecosystem-we demonstrate that this mineral-mediated process operates stably for at least 24 h in a continuous-flow microcosm, achieving complete micropollutant removal while preserving indigenous microbial community diversity (Shannon index variation <0.03). These findings reveal that the geological curvature of natural halloysite can be harnessed for the controlled attenuation of emerging contaminants in wetland water, offering a sustainable approach for ex-situ or end-of-pipe treatment scenarios while aligning with green chemistry and ecosystem protection principles.