铁氧化物光催化氧化锰的实验研究及其环境意义

Photo-Oxidation of Mn;Catalyzed by Common Fe Oxides Minerals and Its Environmental Significance

天然锰氧化物广泛存在于地表多种生态环境中,了解其形成过程对于厘清地表物质演化与元素循环具有重要意义。本研究首次开展了在常见氧化铁矿物催化作用下Mn^(2+)的直接快速光氧化途径与反应机理实验。实验结果显示,不同水溶液体系中赤铁矿、针铁矿的光催化氧化Mn^(2+)速率可达3.5~12.3μM/h,可形成钡硬锰矿、斜方水锰矿等不同类型的氧化产物。反应过程中铁氧化物矿物价带上的空穴直接氧化Mn^(2+)形成Mn(Ⅲ/Ⅳ),氧气充当导带电子的唯一受体。矿物催化剂种类和溶液化学成分能显著影响光氧化速率与最终产物的晶体结构。本研究揭示的光化学过程与地表暴露环境中广泛存在的铁锰共生现象吻合,可为揭示天然锰氧化物结构的多样性提供新的解释。

Natural Mn(Ⅲ/Ⅳ)oxides spread widely in various terrestrial environments.Understanding their formation process is of fundamental significance for improving knowledge of substance evolution and element cycling on earth surface.In this study,we revealed,for the first time,a new direct photochemical pathway of Mn^(2+)oxidation catalyzed by common Fe oxide minerals.The experiments showed the reaction rate of Mn oxidation reached 3.5-12.3μM/h when catalyzed by hematite and goethite in different aqueous systems,and several kinds of Mn(Ⅲ/Ⅳ)oxides were formed including romanechite and groutite.During the photo-oxidation process,Mn^(2+)was directly oxidized by holes in the valence band and O;was the only acceptor of photo-generated electrons in our experiments.The characteristics of mineral catalyst and solution chemistry exerted great influence on the photo-oxidation rate and crystal structure of final products.The direct photochemical process revealed in this study can be consistent with the widespread Fe-Mn symbiosis phenomenon on earth surface,and can provide a new explanation for revealing the diversity of natural Mn oxide structures.