Photoinduced Abosorption Spectroscopy Of Photoelectrocatalytic Methylene Blue Oxidation On Titaniaand Hematite:The Thermodynamic And Kinetic Impacts On Reaction Pathways

In this study,the performance of methylene blue（MB）oxidation by titanium dioxide（Ti O₂）and hematite（α-Fe₂O₃）and the appropriate degradation conditions were studied by photoelectrochemical（PEC）method.Metal oxide semiconductors（such as Ti O₂）are the most widely studied class of semiconductor photocatalysts,and their nanostructured form can efficiently produce hydrogen gas from water and degrade organic dyes efficiently under ultraviolet irradiation.However,visible light is a large part of the solar radiation spectrum,and the wide band gap characteristics of most metal oxides prevent visible light from being absorbed,which makes the utilization of light energy not high.Semiconductor nanostructures such as hematite（α-Fe₂O₃）have relatively narrow band gaps,showing great potential as visible light response photocatalysts.When developing novel nanostructured semiconductors for use in photo driven photocatalysis,it is important to select semiconductor materials that have high absorption coefficients over a wide spectral range and can be safely used in real-world environments.In this study,Ti O₂/FTO andα-Fe₂O₃/FTO were successfully prepared on FTO containing fluorine by in-situ metal deposition as representative semiconductor photoanodes for UV and visible light absorption.The optimal conditions of photocatalytic oxidation of methylene blue with two kinds of photocatalysts were investigated by establishing a traditional three-electrode system with electrochemical workstation.Photoinduced absorption spectroscopy（PIAS）was used to study the dynamics of photogenerated holes and carriers in the process of MB oxidation by Ti O₂andα-Fe₂O₃.When Ti O₂is used as a photocatalyst,at room temperature and p H 6,MB can be completely mineralized into CO₂and H₂O,while at p H 14,MB can only be oxidized to fade.This result is related to the preference for water oxidation under alkaline p H conditions.Whenα-Fe₂O₃is used as a photocatalyst,maintaining p H 14 to ensureα-Fe₂O₃stability,MB can only be oxidized to fade without further mineralization.This result is related to the valence band potential to clarify the advantages of using Ti O₂as a more efficient and sustainable industrial method for degradation of organic pollutants and the necessity of regulating the valence band potential of semiconductors such asα-Fe₂O₃to achieve high efficiency clean water resources.