Preparation Of Zinc And Cadmium Coordination Polymers With Nitrogen-heterocycle Aromatic Ligand For Detecting And Adsorbing Of Pesticides

As one of the hot issues of global concern,pesticides can protect the crops and promote production.However,the increased pesticide use also increased the risk of excessive pesticide residues in food and environment,and posed serious threats to human health and eco-environment.Thus there is an urgent need to develop a safe portable device to detect and remove pesticide residues in the environment.As an advanced multifunctional hybrid material,coordination polymers have wide application prospects in environmental analysis due to the structural diversity,adjustability and porosity,as well as the interaction between framework and guest molecules.Coordination polymers provide more reliable and effective technologies for fluorescence detection and adsorption platforms.The ingenious design and development of modularized coordination polymer composites make up for this practical application to a large extent.This thesis is guided by crystal engineering theory,eight zinc and cadmium coordination polymers were synthesized by flexible imidazole aromatic dicarboxylic acid 5-（（4’-（imidazol-1-yl）benzyl）oxy）isophthalic acid（H₂dbia）,flexible triazole aromatic dicarboxylic acid5-（（4’-（triazol-1-yl）benzyl）oxy）isophthalic acid（H₂tbia）with same numbers of aromatic rings and different nitrogen sites,and rigid nitrogen heterocyclic5-[4-（1H-1,2,4-triazol-1-yl）]phenyl-2H-tetrazole（Htpt）by hydro/solvothermal method.According to the specific requirements of detection and adsorption,functionalized composites were constructed.Through a series of structural characterization and performance tests,the influence of host-guest interaction on fluorescence detection and adsorption performance was clarified.We proposed the design idea of zinc/cadmium coordination polymer composites and their application value in the field of detection and adsorption.Using 5-（（4’-（triazol-1-yl）benzyl）oxy）isophthalic acid as organic ligand,2D coordination polymer{[Cd₃（dbia）₃·3H₂O]·H₂O}_n（Cd1）was constructed.Through regulating the coordination mode of ligand and central metal,another 3D coordination polymer[Zn（dbia）]_n（Zn1）with higher stability was constructed.Inspired by the pitaya core-shell structure,a series of coordination polymer-based gel capsules were designed by ZIF-8/M/SA（M=Cd1,Zn1）.The ZIF-8/Cd1/SA and ZIF-8/Zn1/SA capsules exhibited sensitive detection of alachlor（a representative pre-emergence acetanilide pesticide）,with detection limits of 0.35μM and 0.23μM,respectively.The strategy presented the universality of pitaya-like composites,and they can also be extended to the visual detection platform of various coordination polymers.In addition,the ordered porous structures of ZIF-8/Cd1/SA and ZIF-8/Zn1/SA capsules provided ideal channels and open sites for the removal of pesticides in water,which laid a foundation for the synthesis of multifunctional coordination polymer-based composites in the future.Based on imidazole aromatic dicarboxylic acid,the flexible triazole aromatic dicarboxylic acid ligands with more nitrogen sites were selected.Two cases of cadmium coordination polymers{[Cd₂（tbia）₂·2H₂O]·2H₂O}_n（Cd2）and{[Cd（tbia）·H₂O]·2H₂O}_n（Cd3）with kgd topological network were constructed.We designed a hydrogel bead consisting of biocompatible host material（sodium alginate）and fluorescent center with blue emission（Cd2 and Cd3）,which was further developed for high-efficiency and naked-eye 2,6-dichloro-4-nitroaniline（DCN）monitoring in fruits and vegetables,with the lowest detection limit of 0.09μM.Meanwhile,it had excellent stability and easy recycling.The Cd3-based gel beads also showed excellent adsorption capacity for DCN due to the porous structure,hydrophobic interaction,π-πstacking and hydrogen bonding,and realized the fluorescent detection and removal of DCN from the environment simultaneously.By continuing the selection of triazole aromatic dicarboxylic acid ligands.Two2D zinc coordination polymers{Zn（Htbia）₂·H₂O}_n（Zn2）and{[Zn（tbia）·H₂O]·H₂O}_n（Zn3）were constructed by controlling the coordination mode of carboxyl group.From the structural point of view,the twist of“–CH₂–and–O–”centers endow coordination polymer Zn3 with high stability and abound open sites.The crystal layers with different functions were assembled by“one-to-one”coordination bonds on the surface,and the ZIF-8-on-Zn3/SA composite based on sodium alginate was prepared.Among them,the Zn3 layer as the detection layer,can produce a specific luminescence response to quinclorac（QNC）through electron transfer and competitive absorption excitation light processes,with detection limits as low as 0.08μM.ZIF-8-on-Zn3/SA combined the advantages of abundant metal sites and microporous–macroporous structure,displaying good adsorption capacity for QNC,with the maximum adsorption capacity of 142.1 mg·g^-1.In order to obtain higher-dimensional zinc coordination polymers,the rigid nitrogen heterocyclic ligand 5-[4-（1H-1,2,4-triazol-1-yl）]phenyl-2H-tetrazole（Htpt）with more nitrogen-containing sites and greater degree of conjugation was chosen.A zinc coordination polymer{[Zn（tpt）₂·2H₂O]}_n（Zn4）with a 1D structure was constructed.A 3D zinc coordination polymerization{[Zn₂（tpt）₂（bdc）]}_n（Zn5）was synthesized by introducing auxiliary ligands and adjusting the connecting angle.The exposed nitrogen-rich sites make coordination polymerization Zn5 a self-assembly core to further fabricate a ZIF-8-on-Zn5/SA composite by wrapping ZIF-8 on the outside surface.Inheriting the excellent fluorescent emission of coordination polymerization Zn5,the composite module exhibited highly sensitive and rapid detection of thiophanate-methyl（TM）in real fruits and vegetables with a broad linear range（10～100μM）,and low limit of detection（LOD=0.14μM）.To realize the multi-functional integration of composites in the field of environmental protection,the adsorption capacity of the metabolite（carbendazim）was studied.The 3D network structure promoted the coordination polymer to full contact with pesticides,and the maximum adsorption capacity was 161.8 mg·g^-1.Simultaneously,it exhibited good recycling performance.Under the practical application requirements,the integrated home-made device ZIF-8-on-Zn5/SA was developed into a portable sensing platform and pesticide purifier,especially suitable for regions with serious pesticide environmental pollution.