Interactions between MnO₂ and tire wear particles: Mutual impacts on aging and MnO₂ structural transformation

Manganese oxides (MnO₂), as ubiquitous and reactive minerals, play a crucial role in pollutant transformation within aqueous environments. However, the interactions between MnO₂ and tire wear particles (TWPs) remain inadequately understood. Specifically, it is hypothesized that MnO₂ may accelerate TWPs aging, consequently leading to the release of dissolved organic matter from aged TWPs (TWPs-DOM), which in turn could mediate MnO₂ structural transformation. Herein, we present a comprehensive investigation into the interactions between TWPs and MnO₂ of varying phases (α-, γ-, and δ-MnO₂). Our findings reveal a synergistic effect of MnO₂ and photoaging on TWPs aging. For example, the combined effects of α-MnO₂ and photoaging resulted in a 66% increase in the O/C ratio of TWPs, which exceeds the sum of the increases observed for the UV irradiation-only (20%) and α-MnO₂-only (12%) treatments. The observed phase-dependent acceleration of TWPs aging by MnO₂ is governed by the inherent oxidative potential, electron transport capabilities, and surface charge of the respective MnO₂ phases. Concurrently, a 21-day experimental observation demonstrated a hindering effect of TWPs-DOM on MnO₂ structural transformation. Subsequent analysis elucidated that this inhibitory effect was predominantly controlled by the TWPs-DOM with higher aromaticity and higher molecular weight. Collectively, these findings offer a novel perspective on the critical significance of considering the mutual effects between TWPs and MnO₂ when evaluating the transformation and environmental fate of both entities within aquatic systems.