Efficient photocatalytic degradation of water contaminants via Ag decorated porphyrin-based organic framework materials

With high specific surface area, strong photoabsorption efficiency and outstanding semiconducting properties, porphyrin-based organic frameworks (MOFs) have become the focus of research on efficient photocatalysts. However, the rapid compounding of electrons and holes results in low efficiency of photogenerated electrons, hindering the photocatalytic performance of this type of catalyst. In this work, MOF-525 composite catalysts modified with Ag (Ag@MOF-525) were prepared by photoreduction method and applied to the visible photocatalytic degradation of pollutants in water. Owing to the formation of a Schottky barrier on the surface of porphyrin-based MOFs with Ag nanoparticles (AgNPs), the unique surface plasmon resonance (SPR) effect is generated, which promoted the absorption of visible light by MOF-525; meanwhile, Ag acts as an electron trap, resulting in an effective suppression of electron-hole complexation, boosting the electron transfer between them and the semiconductor MOFs and improving the efficiency of the photogenerated carriers, thus promoting the improvement of photocatalytic activity. Taking rhodamine B (RhB) and tetracycline (TC) as the target degradants, Ag@MOF-525 showed higher photocatalytic activity compared with the MOF structural unit (TCPP) and MOF-525. The degradation rate of RhB was achieved at 91% in 60 min; and the degradation rate of TC, which is very difficult to mineralize, was also achieved at 81% in 200 min. Through a series of detailed analyses including XRD, HRTEM and DRS on the structure, composition and light response range of the samples, it is demonstrated that the successful loading of singlet Ag could effectively extend the light response range of MOF-525 and promote the separation of electrons and holes. In addition, the radical trapping experiments indicated that h+ and •O2− are the main active species and possible degradation mechanisms are discussed.