Synthesis And Photocatalytic Property Under Visible Light Of TiO₂ Sensitized By Porphyrinic MOFs

Recently,TiO₂ is a widely studied photocatalyst due to its low cost,nontoxicity,chemical stability,high photocatalytic activity.However,TiO₂ is a wide band gap semiconductor and photogenerated electron–hole pairs are easily recombined,which significantly diminishes the efficiency of the photocatalytic reaction.Porphyrin MOFs have excellent optical,thermal,and chemical stability as well as strong absorption in the visible region.In order to broaden the optical absorption to visible light region and improve the photocatalytic activity of TiO₂ under solar irradiation,the photocatalyst which combined porphyrin MOFs with nano-TiO₂semiconductor are prepared in this paper.Based on 5,10,15,20-meso-tetra?4-carboxyphenyl?porphyrin?HTCPP?,cobalt5,10,15,20-meso-tetra?4-carboxyphenyl?porphyrin?CoTCPP?and zinc 5,10,15,20-meso-tetra?4-carboxyphenyl?porphyrin?ZnTCPP?was prepared by metallation reaction.Two-dimensional porphyrin MOF?PPF-1-Co,PPF-1-Zn?was prepared by hydrothermal synthesis reaction and the loading of two-dimensional porphyrin MOF on TiO₂ was achieved by in-situ synthesis.The structure was characterized by XRD,FT-IR and ¹H-NMR.The results showed that the morphologies of TiO₂ was successfully sensitized by porphyrin,and metalloporphyrin as well as MOF were not changed.The photodegradation performance of the above catalyst was tested,and the results were as follows:PPF-1-Co-TiO₂>PPF-1-Zn-TiO₂>HTCPP-TiO₂>CoTCPP-TiO₂>ZnTCPP-TiO₂>TiO₂.Two kinds of three-dimensional porphyrin MOF sensitized TiO₂:MOF-P5-TiO₂ and MOF-P4-TiO₂ were sythesised by in-situ synthesis.The structures were determined by XRD,FT-IR,SEM,TEM,XPS and other characterization methods.The results show that most of the outer layer of MOF-P5-TiO₂ is covered by TiO₂,which makes it difficult to expose the active sit.Although its chemical stability is very prominent,the photocatalytic activity of the catalyst is inferior to that of HTCPP-TiO₂ and PPF-1-Co-TiO₂.However,for the MOF-P4-TiO₂,TiO₂ is uniformly present on the surface of MOF-P4,and the active site of MOF-P4 is fully exposed.The kinetic analysis of the photodegradation and repetitive degradation experiments confirmed that the MOF-P4-TiO₂ exhibited the highest photocatalytic performance and repeated use performance in all catalysts of this paper:under xenon lamp irradiation,the photodegradation efficiency of MOF-P4-TiO₂ to methylene blue reached 90%in 4 hours.In order to explore the reasons for the broadening of the photoresponse range of TiO₂before and after sensitization,the mechanism were analyzed by XRD,FT-IR,SEM,TEM,XPS and other characterization methods.At the same time,by analyzing the phenomenon of blue shift of the maximum absorption wavelength in the degradation process of methylene blue,the degradation process of the removal of N-methyl derivatives was analyzed.Through the above research,it is expected that organic pollutants can be rapidly degraded under visible light,which can open up new ideas for visible light catalysts and provide theoretical guidance for photocatalytic treatment of wastewater.