Dual lewis acid sites generated by co single atoms and sulfur vacancy on defective ZnCdS: Enhanced photocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

The photocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) offers a promising pathway to produce biomass-derived industrial chemicals materials. Lewis acid sites play a key role in facilitating cleavage of O-H and C-H bonds. To increase the Lewis acid sites in catalyst, we introduce a breakthrough strategy by combining cobalt single atoms and sulfur vacancies to create dual Lewis acid sites in ZnCdS, significantly boosting the photooxidation of HMF to DFF. The Co single atoms, coordinated with sulfur atoms, exhibit a positive oxidation state that induces electron deficiency, generating strong acidic sites. Meanwhile, sulfur vacancies, created through chemical etching with H 2 O 2 , expose Cd²⁺ species, which provide medium-strength acidic sites due to their empty 5 s and 5p orbitals. Density functional theory (DFT) calculations and in situ DRIFTS studies reveal that these strong and medium-strength sites efficiently lower the energy barrier for C-H and O-H cleavage respectively. The dual Lewis acid sites work in synergy, accelerating HMF oxidation to DFF, showing 94 % conversion and 97 % selectivity within just 6 h—far surpassing the performance of ZnCdS (30 % conversion, 35 % selectivity). This innovative approach offers a promising pathway for constructing photocatalysts with multiple Lewis acid sites, advancing the field of efficient biomass conversion. In this study, a combined single atom and defect strategy is proposed to generate dual Lewis acidic sites on ZnCdS and thus to convert HMF to DFF efficiently. Sulfur vacancies (S v ) in ZnCdS (ZCS v ) results in the reduction of coordination number of partial Cd with S from 4 to 3, leading to the exposure of Cd site, which provide medium-strength acid sites, lowered the activation energy for O-H bond cleavage. Co single atoms provide strong acid sites, facilitate the activation of alcohol C−H bonds. The synergistic effect between Co single atoms and S v accelerates the kinetics of HMF oxidation, showing 94 % conversion and 97 % selectivity within just 6 h—far surpassing the performance of pristine ZnCdS (30 % conversion, 35 % selectivity). • A combined single-atom and defect strategy is used to create dual Lewis acidic sites on ZnCdS for efficient conversion of HMF to DFF. • The two different Lewis acidic sites promote the cleavage of O-H bonds and C-H bonds respectively, accelerating the conversion of HMF. • Sulfur vacancies and Co single atoms synergize, reaching 94 % con., 97 % sel. after 6 h irradiation.