Construction And Mechanism Investigation Of Highly Efficient MOF-based Heterojunctions

Due to the tunable structure and property as well as high porosity,MOFs-based materials have been regraded as one of the most promised materials for the practical application of photocatalytic technology in the near future.How to enhance its light adsorption and improve the separation of photo-induced electron/hole are currently a very challenging subject in this field in order to promote its photocatalytic efficiency.This paper proposes to study the construction of an efficient MOF-based heterojunction photocatalyst and its photocatalytic mechanism in order to solve these two core problems simultaneously and improve the performance of MOFs based photocatalysts.For the current MOF-based heterojunctions,there are still some problems such as the limited kinds of substrate materials,random distribution,and the ambiguous mechanism.In this paper,we have developed two novel MOF-based heterojunction photocatalysts with novel components and ordered structure,repectively,and investigate their photocatalytic properties and revealed their photocatalytic mechanism,which has important theoretical value and practical significance.In this work,g-C₃N₄ is introduced to the iron-center MOFs for the first time to contruct g-C₃N₄/NH₂-MIL-88B?Fe?Fenton-like heterojunction.The formation and interaction of heterojunction are characterized by powder X-ray diffraction,Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,transmission electron microscopy,UV-Vis diffused reflectance spectroscopy.100%of organic pollutant MB is degraded by the composite within 120 min under visible light,twice and 4 times greater than NH₂-MIL-88B?Fe?and g-C₃N₄,repectively.The synergistic index in the heterojunction and H₂O₂ with visible light reaches as high as 305%.Based on the electron spin resonance and photoluminescence analysis,the excitation of H₂O₂ over composite is attributed to three possible ways,including Fenton-like excitation by NH₂-MIL-88B?Fe?,photo-induced Fenton-like excitation by NH₂-MIL-88B?Fe?and Fenton-like excitation driven by g-C₃N₄,which offers a new revenue to design MOFs-based heterojunction and Fenton-like photocatalysts.In this work,amorphous TiO₂@NH₂-MIL-125?Ti?homologous MOF-encapsulated heterostructures is constructed by a facile reflux strategy.The degradation of tetraciline is achieved at 92%within 30 min,which takes the NH₂-MIL-125?Ti?120 min to reach the same extent.one-pot synthesis.In the photocataytic oxidation of benzyl alcohol,the amorphous TiO₂@NH₂-MIL-125?Ti?shows 2 times higher photocatalyic activity than pristine MOF,and also shows better performance than the Pt/NH₂-MIL-125?Ti?,TiO₂/NH₂-MIL-68?In?and TiO₂/NH₂-MIL-101?Cr?,as well as CdS.At the same time,the selectivity to benzaldehyde over amorphous TiO₂@NH₂-MIL-125?Ti?is as high as 99%,significantly higher than the commercial photocatalyst P-25?8.9%?.The electron spin resonance is conducted to investigate the reactive oxygen species during the photocatalytic reaction,furthermore,this technology is carried out in extremely low temperature and innert atmosphere to indentify the active center and sites.Combining electrochemical experiment,although amorphous TiO₂ itself dispalys negligible photocatalytic activity,its conduction band can act as a platform to transfer the elctrons generated by NH₂-MIL-125?Ti?,which constructs the Ti⁴⁺-Ti³⁺intervalence cycles to efficiently separate the photoinduced electrons,leading to enhanced photocatalytifc performance.