Transforming type-II Fe₂O₃@polypyrrole to Z-scheme Fe₂O₃@polypyrrole/Prussian blue via Prussian blue as bridge: Enhanced activity in photo-Fenton reaction and mechanism insight

Photo-Fenton reaction is a more effective technique for pollutant disposal than photocatalytic reaction. Herein, Fe₂O₃@polypyrrole/Prussian blue (Fe₂O₃@PPy/PB) with a hierarchical porous structure was prepared by a reactive-template method. After transforming typical type-II Fe₂O₃@PPy to Z-scheme Fe₂O₃@PPy/PB via PB as a bridge, the degradation rate was increased by 1.4 times in photocatalytic reaction and 4.0 times in photo-Fenton reaction due to higher visible-light harvest, enhanced separation efficiency of photoinduced charges, lower interface resistance, and especially well-preserved redox potentials of holes and electrons. Mechanism studies revealed that holes were quenched by H₂O₂, and this led to ^•O₂⁻ generation and efficient separation of electrons. Meanwhile, O₂ was reduced by separated electrons, and this further increased ^•O₂⁻ yield. Therefore, the main radicals changed from hole in photocatalytic reaction to ^•O₂⁻ in the photo-Fenton reaction, leading to an increase as high as 12.1-fold enhancement in the degradation rate. Conversely, only H₂O₂ participated into photocatalytic reaction using Fe₂O₃@PPy while O₂ was absent, resulting in merely 4.2-fold improvement. This manuscript gives a comprehensive understanding on mechanisms of type-II and Z-scheme heterojunctions in both photocatalytic and photo-Fenton reactions. Obviously, the outcomes are beneficial for designing catalysts with high photo-Fenton activity.