Simultaneous High-Efficiency Photocatalytic Production of H2O2 and Synthesis of 3-HBA Using COFs Broadened by π Conjugate Networks and Photogenerated Charges

The coupling of H2O2 photosynthesis with photogenerated electrons and holes, when used separately, not only realizes the production of value-added products but also maximizes energy utilization. However, achieving this remains a challenge. Here, we report three variations of triazine-based covalent organic frameworks (COFs) featuring phenyl π-π-conjugated structures and furthermore introduce the phenoxy COF with a p-π-conjugated structure as a control to effectively produce hydrogen peroxide. It is found that the strong π-π conjugate network triggers a pronounced optical response and provides channels for charge transfer and electron enrichment. The results showed that the H2O2 yield of TTBA-TP-COF (TTBA = 4,4,4-(1,3,5-triazine-2,4,6-triyl) tris (([1,1-biphenyl]-4-amine)), TP = 2,4,6-triformylphloroglucinol) reached an impressive 11,982 μmol/g/h, which was 1.49 times, 8.77 times, and 7.20 times that of TAPT-TP-COF (TAPT = 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline), MA-TP-COF (MA = melamine), and TTTT-TP-COF (TTTT = 4,4',4″-((1,3,5-triazine-2,4,6-triyl)tris(oxy))trianiline), respectively. Considering the atomic economy, we pioneeringly put forward the strategy of using photogenerated electrons and holes separately. Concurrently, with the photocatalytic production of hydrogen peroxide, acetaldehyde produced by hole oxidation, sacrificial ethanol served as primary feedstock, and aldol condensation of acetaldehyde was successfully catalyzed to produce 3-hydroxybutyraldehyde (3-HBA) under alkaline conditions provided by a small amount of triethylamine. The concentration of 3-HBA produced was confirmed to be 23.84 mmol/L by means of mass spectrometry and high-performance liquid chromatography.