In-situ growth of MnO2 on three-dimensional layered Bi2MoO6/kaolinite with enhanced oxygen adsorption sites for efficient photocatalytic oxidation of 5-hydroxymethylfurfural

The existing photocatalytic systems are difficult to achieve high selectivity and conversion for the oxidation of 5-hydroxymethylfurfural (HMF) under mild conditions. MnO2 exhibits notable tunability in valence state, but its photocatalytic oxidation efficiency is limited by the poor absorption in near-infrared region, insufficient oxygen adsorption, and slow charge transfer. To overcome these limitations, an innovative MnO2@Bi2MoO6/kaolinite (MnO2@BMO/KL) composite photocatalyst was synthesized by the hydrothermal and co-precipitation techniques, and the as-prepared photocatalyst was used for selective photocatalytic oxidation of HMF to produce 2,5-diformylfuran (DFF). The combination of MnO2, three-dimensional layered Bi2MoO6 (BMO), and kaolinite enhanced electron transport and oxygen adsorption. The incorporation of kaolinite as a support material led to the structural transformation of BMO, while the in-situ grown amorphous MnO2 trapped and accelerated electron transfer to adsorbed O-2, thus efficiently segregating the photo-generated charges to enhance the utilization rate. MnO2@BMO/KL achieved almost complete conversion of HMF (>99.0 %) and a DFF yield of 83.0 % after 6 h of visible light irradiation. Additionally, MnO2@BMO/KL exhibited excellent structural stability over 6 cycles. The synergistic action of singlet oxygen (O-1(2)) and superoxide (center dot O-2(-)) was crucial in promoting the selective oxidation of HMF, while minimal generation of hydroxyl radical (center dot OH) reduced the risk of overoxidation. This study provides new insights into the development of economical and stable non-precious metal photocatalysts for highly selective conversion of biomass-derived chemicals.