Single-phase Oxygen-mediated Metal Porphyrin Organic Framework Materials For Efficient Removal Of Contaminants And Kinetics

Porous metal-organic frameworks (MOFs) exhibit permanent porosity, high surface area, excellent thermal stability and modifiable pore surface. We are currently developing porous MOFs with photosensitizers in the MOF backbone in an effort to develop sorbents that generate singlet oxygen. Based on this, we firstly employ the zirconium-porphyrin metal-organic framework for efficient synergetic removal of bisphenol A by ultrahigh adsorption and singlet-oxygen mediated degradation under visible light. Then we further investigate the relationship between the particle size of MOFs and kinetics production rate of singlet oxygen. The singlet oxygen degradation mechanism for porphyrin-MOF in the degradation of pollutants under visible light irradiation was further studied. This study is not only significant to the understanding of these reactions but also it will guide the selection of porphyrin-MOF catalyst for the development of singlet-oxygen mediated catalysis. The contents were summarized as follows:1. Ultrahigh adsorption and singlet-oxygen mediated degradation for efficient synergetic removal of bisphenol A by a stable zirconium-porphyrin metal-organic frameworkBisphenol A (BPA), one of 23 most important endocrine disrupting chemicals has posed a big threat to human health, was efficiently removed and sequentially photodegraded by a zirconium-porphyrin metal-organic framework (MOF) catalyst under visible light for water treatment. Well control of photodegradation allows the kinetic separation of adsorption step and photodegradation step. Ultrahigh adsorption uptake of 487.69 ± 8.37 mg g-1 is observed, while efficient photodegradation could be observed within 20 min at rate of 0.004 mg min-1. The synergetic effect boosts the photocatalytic efficiency as well as confirms that the catalysis happens inside the MOF pores other than in the solution phase. Furthermore, the mechanism was elucidated by the control experiments with 1O2 scavenger, darkness and changes of light sensitizing ligand. It confirmed that BPA was oxidized by the 1O2 which was generated by porphyrin ligand in MOFs under visible-light. The excellent reusability and wide range of suitable pH range makes the Zr-porphyrin MOFs practical for the photocatalytic water treatment processes.2. Size-dependent kinetics of singlet oxygen generation based on metalloporphyrin MOFsPorphyrin-MOFs can effectively produce singlet oxygen, due to the excellent photosensitivity of porphyrin. The kinetics of singlet oxygen generation depend on the size of micro and nano particles of MOFs. In this study, we use hydrothermal method to synthesize a series of porphyrin-MOF materials with different sizes and metal ions by changing the reaction solvent, reaction time, temperature and acid modifier. The effect of the pore structure and particle size of porphyrin-MOFs on the production rate of 1O2 was investigated by measuring the UV-Vis absorbance of the singlet oxygen quencher DPBF. In addition, we used SiO2 particles to coat the outer surface of porphyrin-MOF materials to show the active sites for 1O2 production. The results showed that 1O2 is produced from the porphyrin-MOF under visible light. PCN-222 with the size of nanometers has the highest ability to produce 1O2 and the rate constant of 1O2 generation was 0.047 s-1. Furthermore, the particle size and pore structure of porphyrin-MOFs have great effect on the activity of of 1O2 generation.With the large pore size of porphyrin-MOFs and small steric hindrance, the particle size had no significant effect on the productive rate of 1O2. However, when the pore size of porphyrin-MOFs approaches to the size of oxygen molecule, the steric hindrance effect becomes significant.