Visible Light Driven Removal Of Pollutants In Water And The Mechanism Under The Photocatalysis Of Zr-MOF Based Composite Materials

Metal-organic frameworks（MOFs）are the kind of materials which have large specific surface area,easily tunable structure and special electronic structure.Since zirconium-based MOFs are relatively more stable and have great application prospects,they have received extensive attention in the field of photocatalysis in recent years.In this study,two Zr-MOF-based photocatalysts—made of Ui O-66 and Ag/Ag Cl supported on cotton fibers（CF）for flexible composites CF/Ui O-66/Ag/Ag Cl（CUAA）and ternary composites NH₂-Ui O-66constructed from NH₂-Ui O-66,Bi OBr and Ag I（NUBA）.The performance and mechanism of the two composite materials for catalyzing visible light degradation of model pollutants tetracycline and Cr（Ⅵ）in water were investigated.The main work includes:（1）Flexible photocatalysts CUAA were prepared by loading Ui O-66 and Ag/Ag Cl onto cotton fabrics successively through hydrothermal method and room temperature deposition-precipitation method.The prepared photocatalysts were characterized by XRD,SEM,XPS,DRS,ESR and other means.The photocatalytic removal performance of CUAA was tested with 10 ppm TC and 5 ppm K₂Cr₂O₇as model pollutants by simulating a visible light source through a xenon lamp.First,a series of studies were carried out on the photocatalytic degradation of TC by CUAA.After 60 min of illumination,the removal rate of TC reached 92%,and the reaction process conformed to the pseudo-first-order kinetic model.When the p H value was in the range of 2.7-10.5,CUAA exhibited a good visible light degradation performance on TC,which can remove 87%-92%of TC.The free radical trapping experiments showed that^·O₂^-and h⁺were the main active species responsible for the degradation of TC under CUAA.The photocatalytic reduction of Cr（Ⅵ）by CUAA showed that 90%of Cr（Ⅵ）could be removed under visible light irradiation for 60 min at p H=2.5.When TC and Cr（Ⅵ）coexisted,CUAA still had good photocatalytic performance,which could remove 87%of TC and 99%of Cr（Ⅵ）simultaneously.Finally,through a series of characterization analysis,the photocatalytic mechanism of CUAA was proposed to be a heterojunction photocatalytic mechanism using Ag nanoparticles as photosensitizers.This work takes full advantage of the surface plasmon resonance（SPR）of Ag to improve the absorption of visible light,and uses Ui O-66 and Ag/Ag Cl to construct a heterojunction,which is loaded on cotton cloth and beneficial to enhance the photocatalytic activity and improve the recycling performance of the photocatalyst.（2）The ternary composite NUBA composed of NH₂-Ui O-66,Bi OBr and Ag I was prepared by hydrothermal method and room temperature deposition-precipitation method,and characterized by FT-IR,XRD,BET,TEM,SEM,XPS.The composition,structure and morphology of NUBA were tested,and its photocatalytic and photoelectrochemical properties were also studied.The selected contaminants were 10 ppm TC and 10 ppm Cr（Ⅵ）.Under simulated visible light irradiation,the degradation rate of TC by NUBA was 97%.The free radical trapping experiments proved that^·O₂^-and h⁺were the main active species for the degradation of TC.NUBA also showed good removal efficiency on other dyes such as Rh B,X-3B,MB,AOII,and the antibiotic ciprofloxacin（CIP）,proving that NUBA had broad application prospects.The visible light catalytic reduction rate of Cr（Ⅵ）by NUBA was 97%under the illumination at p H=2.5 for 30 min.In the mixed solution consisting of TC and Cr（Ⅵ）,NUBA exhibited synergistically enhanced degradation performance for both pollutants.When illuminated for 10 min,Cr（Ⅵ）in the mixed solution was almost completely reduced to Cr（III）,and the degradation efficiency of TC in the mixed solution was similar to that in the single TC solution.Mechanistic studies have shown that by constructing NUBA complexes,the specific surface area of the catalyst is increased,which is conducive for increased contact with the reaction substrates.At the same time,its unique electronic structure is also conducive to the construction of dual Z-scheme heterojunction,which improves the separation and transfer efficiency of photogenerated charges,and enables NUBA to have stronger redox ability,thereby effectively promoting the oxidative degradation of TC and the reduction of Cr（Ⅵ）.