Quici Natalia, Litter Marta I
Gerencia Química, Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica (CNEA), Av. Gral. Paz 1499, CP 1650, San Martín, Prov. de Buenos Aires, Argentina.
Photochem Photobiol Sci. 2009 Jul;8(7):975-84. doi: 10.1039/b901904a. Epub 2009 Apr 29.
UV/TiO(2)-heterogeneous photocatalysis was tested as a process to degrade gallic acid (Gal) in oxygenated solutions at pH 3. In the absence of oxidants other than oxygen, decay followed a zero order rate at different concentrations and was slow at concentrations higher than 0.5 mM. Addition of Fe(3+), H(2)O(2) and the combination Fe(3+)/H(2)O(2) improved Gal degradation. In the absence of H(2)O(2), an optimal Fe : Gal molar ratio of 0.33 : 1 was found for the photocatalytic decay, beyond which addition of Fe(3+) was detrimental and even worse in comparison with the system in the absence of Fe(3+). TiO(2) addition was beneficial compared with the same system in the absence of the photocatalyst if Fe(3+) was added at low concentration (0.33 : 1 Fe : Gal molar ratio), while at high concentration (1 : 1 Fe : Gal molar ratio) TiO(2) did not exert any significant effect. H(2)O(2) addition (1 : 0.33 Gal : H(2)O(2) molar ratio, absence of Fe(iii)) also enhanced the heterogeneous photocatalytic reaction. Simultaneous addition of Fe(3+) and H(2)O(2) was more effective than the addition of the separate oxidants. This system was compared with Fenton and photo-Fenton systems. At low H(2)O(2) concentration (0.33 : 1 : 0.2 Fe : Gal : H(2)O(2) molar ratio), the presence of TiO(2) also enhanced the reaction. The influence of the thermal charge transfer reaction between Gal and Fe(iii), which leads to an important Gal depletion in the dark with formation of quinones, was analysed. The mechanisms taking place in these complex systems are proposed, paying particular attention to the important charge transfer reaction of the Fe(iii)-Gal complex operative in dark conditions.
紫外光/二氧化钛多相光催化被作为一种在pH值为3的含氧溶液中降解没食子酸（Gal）的工艺进行了测试。在除氧气外无其他氧化剂的情况下，不同浓度下的降解遵循零级反应速率，且浓度高于0.5 mM时降解缓慢。添加铁离子（Fe(3+)）、过氧化氢（H(2)O(2)）以及铁离子/过氧化氢的组合均能促进没食子酸的降解。在无过氧化氢的情况下，光催化降解的最佳铁与没食子酸摩尔比为0.33 : 1，超过此比例添加铁离子会产生不利影响，甚至比无铁离子体系更差。若以低浓度添加铁离子（铁与没食子酸摩尔比为0.33 : 1），与无光催化剂的相同体系相比，添加二氧化钛（TiO(2)）是有益的，而在高浓度（铁与没食子酸摩尔比为1 : 1）时二氧化钛没有显著作用。添加过氧化氢（没食子酸与过氧化氢摩尔比为1 : 0.33，无铁离子（iii））也能增强多相光催化反应。同时添加铁离子和过氧化氢比单独添加氧化剂更有效。该体系与芬顿和光芬顿体系进行了比较。在低过氧化氢浓度（铁 : 没食子酸 : 过氧化氢摩尔比为0.33 : 1 : 0.2）下，二氧化钛的存在也能增强反应。分析了没食子酸与铁离子（iii）之间的热电荷转移反应的影响，该反应在黑暗中会导致没食子酸大量消耗并形成醌类。提出了这些复杂体系中发生的反应机制，特别关注了在黑暗条件下起作用的铁离子 - 没食子酸络合物的重要电荷转移反应。
