Preparation Of GDY/MOFs(Fe) Composites And Study On Photo-fenton Co-catalytic Degradation Of Pesticide Dinotefuran

Dinotefuran（DTF）is the third-generation nicotinic insecticide,which is widely used for pest control in agricultural sector.It is highly stable and cannot be easily disintegrated in water,resulting in a disturbance of the ecological order.Furthermore,it can be easily absorbed in the living body,causes serious hazardous effects on aquatic life and induces water pollution.It is therefore of great significance to develop a technology that can degrade DTF efficiently and rapidly.As a typical representative of advanced oxidation methods,photo-Fenton oxidation technology is a highly effective method and has marginal impact on the environment and hence has earned a vital position as the main degradation strategy for aquatic organic pollutants remediation.The main challenge in this regard is the designing of novel materials and catalyst with enhanced catalytic performance and practical applications.Metal organic frameworks（MOFs）is a new class of porous coordination polymer with flexible structure formed by self-assembly of organic ligands and inorganic metal ions/clusters,due to its excellent light absorption properties,it has been widely applied in the field of photocatalysis.However,the poor conductivity of MOFs leads to low efficiency of photogenerated electron separation and poor stability due to the free radicals attack,which limits its application in photocatalytic degradation through Photo-Fenton approach.Thus in this work,Graphdiyne（GDY）with high electrochemical activity was introduced into the MOFs via in situ Fe bridging and in-hole polymerization strategies.Novel catalysts with high electron density,remarkable stability and high catalytic activity of Fe-GDY@MIL（Fe）with C=C-Fe|O cluster interface and GDY@MIL（Fe/Cu）with pore-limited growth of GDY were prepared,respectively.The main tasks of current study are as follows:（1）The novel GDY materials with alkenes/acetylene surface functionalities and highly dispersed Fe atomic metal sites were constructed by Fe catalysis（Fe-GDY）.Then the prepared Fe-GDY material was implanted in MIL-100（Fe）to synthesis a highly photoactive Fe-GDY@MIL（Fe）catalyst.Physical characterization and electrochemical measurements results indicated the formation of new interfacial connection between Fe-GDY and MIL-100（Fe）by C=C-Fe|O bridging.The Interface acts as a link between the Fe-GDY and MIL-100（fe）,reducing the band gap of the catalyst and the recombination of photogenerated electron hole pairs,and improving the photo-efficiency,conductivity and photostablity of the catalyst.At the same time,the asymmetric coordination at the interface between the components enhanced the catalytic Lewis acid sites and ligand vacancies.Due to these unique feathers of the Fe-GDY₃@MIL（Fe）,DTF was completely degraded within 60 min,and its degradation rate was 6.4 times higher than that of pure MIL-100（Fe）.In addition,the mineralization rate of DTF reached 97.3%after 5 h degradation.Interestingly,due to the tight interfacial connection within Fe-GDY₃@MIL（Fe）,the Fe-GDY₃@MIL（Fe）catalyst achieved more photostability than the pristine MIL-100（Fe）and the durability of photocatalyst remained intact even after 20cycles of photocatalysis reactions.Besides,it was found that Fe-GDY₃@MIL（Fe）formed Z-type heterojunction.The proposed mechanism for photo-Fenton degradation of DTF illustrated that the photogenerated electrons were rapidly transferred from the MIL-100（Fe）conduction band to the Fe-GDY valence band by electron bridging at the interface.The photoinduced electron/hole reacted with oxygen and atmospheric water vapors and generated abundant·OH and·O₂^-radicals.These photoactive radicals were the main contributors of high photocatalytic activity of the Fe-GDY₃@MIL（Fe）.（2）Based on pore polymerization strategy,Cu was implanted in situ into the MIL-100（Fe）framework and GDY was polymerized at the Cu sites in the pores using the MIL（Fe/Cu）as a substrate for the preparation of a new composite GDY@MIL（Fe/Cu）with high conductivity,high electron density and ultrahigh catalytic activity.Physical characterization and photoelectric properties were investigated.It was found that the GDY was coupled and polymerized at Cu sites within the MIL（Fe/Cu）at（333）crystal plane.The Cu（II）/Fe（III）of the MIL（Fe/Cu）metal cluster was partially reduced to Cu（I）/Fe（II）due to the role of the power supply,which enhanced the Lewis acidic sites of the material.Meanwhile,the growth of GDY within the pore-limited domain was linked to the MIL（Fe/Cu）at multi-points,forming a conductive interface network which greatly improved the conductivity of the catalyst and shortened the electron transportation distance and separation efficiency of photogenerated electrons.As a result,the DTF was completely degraded within 30 min over GDY₂₀@MIL(Fe/Cu₃₀).The degradation rate of which was 15.9 and 10.4 times higher than that of MIL-100（Fe）and MIL（Fe/Cu）respectively.Under the same conditions,the degradation rate of GDY₂₀@MIL(Fe/Cu₃₀)is 4.2 times that of Fe-GDY₃@MIL（Fe）,and the DTF mineralization rate reached 98%after 2 h degradation.For GDY₂₀@MIL(Fe/Cu₃₀),GDY was polymerized and introduced in the pores of MIL（Fe/Cu）through the Cu-O cluster compact connection,its stability was much higher than that of MIL（Fe/Cu）and it remained stable after more than 20 testing cycles.Systematic studies showed that the Z heterojunction between the in-hole GDY and the MIL（Fe/Cu）was constructed to analyze the degradation mechanism of the GDY₂₀@MIL(Fe/Cu₃₀),the photogenerated electrons were rapidly transferred from the MIL（Fe/Cu）conduction band to the GDY valence band in the pore was realized,which promoted the formation of active superoxide radicals and effectively improved the photocatalytic degradation rate of DTF via photo-Fenton approach.