Revealing the structure-activity relationship of Mn3O4/TiO2 via phase engineering for enhanced photocatalytic CO₂ reduction

The structure-activity relationship plays a crucial role for enhanced photocatalytic performance, nevertheless, precisely controlling the phase of transition metal oxides remains a significant challenge. Herein, we developed 2D-layered Mn 3 O 4 decorated with TiO 2 catalyst to investigate the effects of manganese oxide phase on photocatalytic CO 2 reduction activity. We optimized the manganese oxide phase by varying the amount of the TiCl 4 precursor. During the synthesis reaction, TiCl 4 is a key role for determining the oxidation state of manganese oxide. We identified that Mn 3 O 4 is the best phase for photocatalytic CO 2 reduction, and Mn 3 O 4 /TiO 2 exhibits 20.1-, 7.8-fold enhanced photocatalytic CO 2 reduction performance than pristine TiO 2 and Mn 3 O 4 , respectively. The improved photocatalytic activity is relevant to the phase of manganese oxide, the enhanced separation of charge carriers and prolonged lifetimes of charge carriers. In situ X-ray Absorption Near-Edge Structure (XANES) confirms the changes of oxidation state under photocatalytic CO 2 reduction conditions. Furthermore, the photocatalytic mechanism is proposed by in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. This study provides an effective design strategy for modulating oxidation state of transition metal oxide-based photocatalyst for enhanced solar fuels generation. • Structure-activity relationship between manganese oxide phase and photocatalytic activity is comprehensively illustrated. • The TiCl₄ precursor concentration determines the manganese oxidation state for final Mn 3 O 4 /TiO 2 catalyst. • Optimized Mn₃O₄/TiO₂ heterojunction promotes superior charge separation and prolonged carrier lifetimes.