Light-induced dissolution of hematite in the presence of oxalate. A case study
Light-induced dissolution of hematite in the presence of oxalate. A case study
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DOI：
10.1021/la00056a014
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发表时间：
1991-08
期刊：
影响因子：
3.9
通讯作者：
C. Siffert;B. Sulzberger
中科院分区：
文献类型：
--
作者：
C. Siffert;B. Sulzberger
赤铁矿在草酸存在下的光诱导溶解发生(a)通过赤铁矿的光化学还原溶解，形成溶解的铁（II）和氧化的草酸；(b)通过铁（II）催化赤铁矿热溶解，形成溶解的铁（III）。这两种溶解途径通过溶解铁（III）的光化学还原耦合，即铁（III）草酸配合物的光解，导致赤铁矿的自催化溶解。赤铁矿的光化学还原溶解速率具有很强的波长依赖性，该反应仅发生在近紫外波段（X< 400 nm）。根据波长依赖性，我们得出结论，在这种非均相光氧化还原反应中，电子激发态是一种配体到金属的电荷转移态，要么是铁（III）草酸表面配合物，要么是块赤铁矿（或两者兼有）。在光的作用下，氧对赤铁矿的还原性溶解有强烈的抑制作用。这种现象可以解释为氧对还原表面铁的再氧化和表面铁（II）向溶液中的相转移之间的竞争。这些观察结果表明，在该体系中，表面Fe （II）脱离晶格是整个溶解过程的速率决定步骤，而不是电子转移。在有氧存在的情况下，赤铁矿作为草酸盐被氧氧化的光催化剂。这种光催化草酸氧化的速率表现出与赤铁矿的光化学还原溶解相似的波长依赖性。
The light-induced dissolution of hematite in the presence of oxalate occurs (a) through the photochemical reductive dissolution of hematite resulting in formation of dissolved Fe (II) and oxidized oxalate and (b) through the Fe (II)-catalyzed thermal dissolution of hematite, resulting in formation of dissolved Fe (III). These two dissolution pathways are coupled via the photochemical reduction of dissolved iron (III), ie photolysis of iron (III) oxalato complexes, leading to an autocatalytic dissolution of hematite. The rate of the photochemical reductive dissolution of hematite is strongly wavelength-dependent, and the reaction occurs only in the near-UV (X< 400 nm). From this wavelength-dependence we conclude that the electronically excited state involved in this heterogeneous photoredox reaction is a ligand-to-metal charge-transfer state, either of the iron (III) oxalato surface complex or of the bulk hematite (or both). Oxygen strongly inhibits the reductive dissolution of hematite under the influence of light. This phenomenon is interpreted in terms of competition between reoxidation of reduced surface iron by oxygen and phase transfer of surface Fe (II) into solution. These observations indicate that in this system detachment of surface Fe (II) from the crystal lattice is the rate-determining step of the overalldissolution process rather than electron transfer. In the presence of oxygen hematite acts as a photocatalyst for the oxidation of oxalate by oxygen. The rate of this photocatalytic oxalate oxidation exhibits a similar wavelength-dependence as does the photochemical reductive dissolution of hematite.