Key Laboratory of Science and Technology of Eco-Textile, Ministry of Education, College of Chemistry and Chemical Engineering, Donghua University, Shanghai, 201620, China.
Shanghai Jahwa United Co., Ltd., Shanghai, 200082, China.
Adv Sci (Weinh). 2023 Mar;10(9):e2206685. doi: 10.1002/advs.202206685. Epub 2023 Jan 22.
Photoelectrochemical oxidation of methylene blue is investigated, with particular focus on the difference in kinetics and thermodynamics of decoloration and mineralization employing photoinduced absorption spectroscopy. Hematite and titania photoanodes are used for the comparison of both reactions, which is determined to be associated with the depth of the valence band (3.2 vs 2.5 V for titania and hematite, respectively). Methylene blue is mineralized by the titania photoanode, however it is only oxidized to small fragments by hematite. Such difference is related to the valence band potential that provides the thermodynamic driving force for photogenerated holes in both materials. In addition, the kinetic competition of water oxidation is found to occur on titania by controlling the pH of the electrolyte. In the pH 14 electrolyte, mineralization of methylene blue is suppressed due to the faster and dominant kinetics of water oxidation, in contrast to the complete mineralization in the near neutral electrolyte where water oxidation kinetics are modest. These results clearly address the importance considering both thermodynamic and kinetic challenges of methylene blue oxidation, which has been thought to be an easy molecule to oxidize, as the model reaction in the application of photo(electro)catalysis using metal oxides.
研究了亚甲基蓝的光电化学氧化，特别关注了用光诱导吸收光谱法研究褪色和矿化的动力学和热力学差异。使用氧化铁和二氧化钛光阳极来比较这两种反应，结果表明这与价带的深度有关（分别为 3.2 V 和 2.5 V）。亚甲基蓝被二氧化钛光阳极矿化，但只有氧化铁将其氧化成小碎片。这种差异与价带电位有关，价带电位为两种材料中光生空穴提供了热力学驱动力。此外，通过控制电解质的 pH 值，发现水氧化的动力学竞争在二氧化钛上发生。在 pH 值为 14 的电解质中，由于水氧化的动力学更快且占主导地位，亚甲基蓝的矿化受到抑制，而在近中性电解质中，水氧化的动力学适中，亚甲基蓝完全矿化。这些结果清楚地表明，在考虑到亚甲基蓝氧化的热力学和动力学挑战时，需要将其作为使用金属氧化物的光电（电）催化的模型反应，这是一种易于氧化的分子。
