Zirconium-based Metal-organic Framework Nanozymes For Monitoring The Catalytic Degradation Of Nerve Agent Simulants

Nerve agents are a class of organophosphate compounds,which have an inhibitory effect on acetylcholine enzyme（ACh E）and then destroy the central nervous system of the human body.Therefore,it is very important to effectively destruct of nerve agents.The nanozymes have been widely studied due to superior performances to biological enzymes and applied to the catalytic degradation of nerve agents and their simulants.Among them,the metal-organic frameworks（MOFs）are a type of nanozymes,which has special activity in degradation of nerve agents and simulants.In this paper,several factors,such as thickness,single atomic doping,and functional groups have been studied for different hydrolysis capabilities of nerve agent simulants with Zr MOFs,and besides,a variety of methods are used to monitor the process of hydrolysis.The specific contents are as follows:（1）Zr-BTB-NH₂,a metal-organic layers（MOLs）of Zr₆ cluster with 2′-amino-5′-（4-carboxyphenyl）-[1,1′:3′,1″-terphenyl]-4,4″-dicarboxylic acid（BTB-NH₂）as ligands and HCOOH as the regulator were synthesized.We tuned the thickness of the Zr-BTB-NH₂ by controlling the amount of water during the synthesis.The addition of water can reduce the stacking of the layers,thereby increasing the exposure of Lewis acidic sites of Zr-BTB-NH₂.Therefore,it was applied to the catalytic hydrolysis of a nerve agent simulant,ethyl paraoxon（POX）,in which the catalytic half-life(t_1/2)of Zr-BTB-NH₂-0.25 with the best catalytic effect was 23.1 min.（2）Cu@UiO-66-NH₂ single-atom catalyst（SACs）was synthesized using a MOF UiO-66-NH₂ as a substrate by doping with Cu element under illumination.It was demonstrated that Cu was immobilized on UiO-66-NH₂ at the atomic level and coordinated to two N atoms with a distance of 1.97?.Subsequently,the catalytic hydrolysis ability of different doping Cu amounts of Cu@UiO-66-NH₂ for POX was investigated.It was found that they all exhibited stronger catalytic effects on POX degradation than pristine UiO-66-NH₂.The 4%doping Cu@UiO-66-NH₂ showed the best catalytic performance with a t_1/2 of only 2.41 min and a good catalytic recyclability.The mechanism studies demonstrated that the Cu single atoms interacted with POX in a single-dentate binding mode during the catalytic degradation process,thus achieving the hydrolysis of the nerve agent simulant and the rapid regeneration of the catalyst.（3）Switchable fluorescence of an aminated UiO-66 derivative（UiO-66-NH₂）derived from linker-cluster charge transfer（LCCT）was achieved through the design of fluorescent ligands,based on which the degradation of nerve agent simulants was visualized and monitored in real time.During the UiO-66-NH₂-catalyzed hydrolysis of the nerve agent simulants,the decomposition products were bound to the Zr-oxo cluster,which in turn perturbed the coordination environment in the framework and subtly inhibited the LCCT process,thereby stimulating the recovery of fluorescence observed with the naked eye.This method proved to be superior to conventional UV-vis and ³¹P NMR spectra monitoring methods due to its low technical requirements,good reusability and applicability to other simulants.Furthermore,by integrating UiO-66-NH₂ into an agarose hydrogel,a versatile“soft”solid-state platform was simply constructed,allowing direct observation of the degradation of gaseous simulants without the addition of bulk water,which would be more suitable for practical applications under realistic conditions than the reported textiles or fibers modified by MOFs.