Birnessite is regarded as an efficient oxidizing agent that would significantly influence the environmental fate of elements such as arsenic. This study compared the chemical and photocatalytic oxidation of As(III) over birnessite. During the chemical oxidation, As(III) was oxidized to As(V), while Mn(IV) was reduced to Mn(II), subsequently forming MnOOH. The coverage of the reactive sites by MnOOH inhibited the chemical oxidation of residual As(III). At pH 5.0, after 360 min of reaction, 61% of As(III) was oxidized to As(V), and the oxidation of As(III) decreased with an increase in pH. The photocatalytic oxidation of As(III), where almost all As(III) could be oxidized to As(V) over a pH range of 5.0–8.0 and 360 min, was much more efficient compared to chemical oxidation. In contrast to chemical oxidation, the formation of MnOOH slightly affected the photocatalytic performance of birnessite. It was demonstrated that •O₂⁻ radicals and holes (h_vb⁺) played an important role in the photocatalytic oxidation of As(III) over birnessite. Our findings confirmed that light dramatically promoted the oxidation of As(III) by birnessite, broadening the understanding of the environmental behaviors of arsenic.

水钠锰矿被认为是一种有效的氧化剂，可以显着影响砷等元素的环境命运。本研究比较了水钠锰矿上 As(III) 的化学氧化和光催化氧化。在化学氧化过程中，As(III)被氧化为As(V)，而Mn(IV)被还原为Mn(II)，随后形成MnOOH。 MnOOH 对反应位点的覆盖抑制了残留 As(III) 的化学氧化。在pH 5.0下，反应360 min后，61%的As(III)被氧化为As(V)，并且As(III)的氧化随着pH的增加而减少。 As(III) 的光催化氧化在 pH 范围 5.0–8.0 和 360 分钟内几乎所有 As(III) 都可以氧化为 As(V)，与化学氧化相比效率要高得多。与化学氧化相反，MnOOH的形成轻微影响了水钠锰矿的光催化性能。结果表明，•O ₂ ^-自由基和空穴（h _vb ⁺）在水钠锰矿上As(III)的光催化氧化中发挥着重要作用。我们的研究结果证实，光极大地促进了水钠锰矿对 As(III) 的氧化，拓宽了对砷环境行为的理解。