Constructing novel metal-free HCOF-Ph@g-C3N4 heterojunctions through molecular expansion to enhance photogenerated carrier involved molecular oxygen activation and photocatalytic hydrogen evolution

Abstract

Modification of covalent organic frameworks (COFs) have exceptional stability as well as tunable structures is the key to efficient photocatalysts. In this study, hyper-crosslinked COF-Ph was constructed with g-C3N4 to obtain a novel HCOF-Ph@g-C3N4 heterojunction, and the lamellar mesoporous of g-C3N4 was successfully embedded into the pores of 3D HCOF-Ph. The synthetic strategy greatly enhanced the photocatalytic properties and molecular oxygen activation capability of the catalyst. 10 mg of HCOF-Ph@g-C3N4 heterojunction could completely degrade 30 mg/L of tetracycline (TC) within 14 min, and the rate of hydrogen generation reached 9214.69 μmol g−1 h−1. The active species in this process of photocatalysis were verified through tests with free radical trapping and ESR spectra. In addition, the molecular oxygen activation capacity of heterojunction interface and the yield of superoxide radicals were examined by 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation and degradation of nitrotetrazolium nlue chloride (NBT) experiments, respectively. We found that the molecular expansion strategy can change molecule energy band structure to improve absorption of sunlight, and the efficient segregation of the photogenerated charge were ensured by the complementary energy band structure between g-C3N4 and HCOF-Ph. This study created an efficient molecular expansion method for the synthesis of COF-based catalysts with potential uses in the energy and environmental fields.