Constructing Highly Efficient Oxygen Capture Tentacles Within Covalent Organic Frameworks for Photocatalytic Water...

Insufficient oxygen mass transfer and inadequate charge separation are two critical factors restricting the photocatalytic efficiency of covalent organic frameworks (COFs) for water purification. Here, we develop a facile strategy to simultaneously boost oxygen mass transfer and charge separation in COFs through constructing efficient oxygen capture tentacles via replacing conventional pyridine groups with nicotinic-acid/methyl-nicotinate groups, which have tunable oxygen affinity. Molecular dynamics simulations and in situ characterizations reveal that compared to pyridine groups in COF-EP1 and nicotinic-acid groups in COF-EP2, respectively serving as weak and medium oxygen capture tentacles, methyl-nicotinate groups in COF-EP3 can serve as strong oxygen capture tentacles due to their superb oxygen affinity, which can enhance oxygen interaction energies and thus promote oxygen mass transfer. Owing to the optimal charge polarization, methyl-nicotinate groups in COF-EP3 also strengthen internal electric fields to facilitate charge separation. COF-EP3 thus achieves exceptional photocatalytic degradation performance towards sulfadiazine (99.5% removal in 25 min, k = 0.21 min^-1), which is 16.2 and 2.8 times higher than that of COF-EP1 (k = 0.013 min^-1) and COF-EP2 (k = 0.076 min^-1), respectively. Besides, COF-EP3 exhibits high sulfadiazine degradation performance in complicated water matrices, continuous-flow system, and scaled-up reactor, demonstrating its practical application potential.