Facet-Dependent Photocatalytic CO₂ Reduction on TiO₂ Crystals in the Presence of SO₂: Role of Surface Hydroxyl

Photocatalytic CO₂ reduction to solar energy makes great sense to mitigate the greenhouse effect caused by CO₂, and great efforts have been made to promote CO₂ conversion efficiency. However, the effect of impurities in the photoreduction of CO₂ has received relatively little attention. Here, the different CO₂ photoreduction behaviors of TiO₂ exposed (101) facet (TiO₂-101) and (001) facet (TiO₂-001) with an SO₂ impurity were investigated. On TiO₂-101, SO₂ accelerates the deactivation of the catalyst for CO₂ photoreduction activity, since SO₂ mainly binds to the OH_b site of TiO₂-101. This site is highly susceptible to the transfer of photogenerated holes, resulting in the rapid generation of SO₄^2-, which occupies the active site and poisons the catalyst. For TiO₂-001, SO₂ has relatively little negative effect on stability, as SO₂ mainly binds to the weak binding site (OH_t) of TiO₂-001, preventing it from being oxidized to SO₄^2-, which alleviates catalyst deactivation and ensures the continuity of CO₂ reduction. This paper provides further insights into the role of SO₂ in CO₂ photoreduction over distinct TiO₂ facets and reveals the importance of facet engineering in the photocatalytic reduction of CO₂ from industrial flue gas.