| Antibiotics have been widely used because of their excellent effect in the treatment of bacterial infection.However,due to the extensive use of antibiotics and inadequate treatment,serious pollution and destruction of water environment are caused,and the bacterial resistance caused by antibiotics is also a serious threat to human health.Therefore,the research on efficient detection and effective removal of antibiotics in water has become a hot spot of environmental protection.Metal-organic frameworks(MOFs)have a variety of structural types,adjustable chemical functions,low density skeletons,high specific surface area and porosity,and excellent mechanical and chemical stability,making them obvious advantages as fluorescent sensors for antibiotic detection and adsorbents for antibiotic adsorption and removal.In this paper,eight new coordination polymers were synthesized by hydrothermal and solvothermal methods,using phenyldiacetic acid isomers as main ligands,different nitroimidazoles as auxiliary ligands,and transition metal ion cadmium(II)as metal sources,such as[Cd(opda)(pbiyb)](1),[Cd(mpda)(pbiyb)0.5(H2O)](2),[Cd(opda)(mbib)(H2O)](4),[Cd2(mpda)2(mbib)2]·2H2O(5),[Cd(ppda)(mbib)](6),[Cd(opda)(tib)]·H2O(7),[Cd4(mpda)4(tib)2(dib)2]·7H2O(8),Cd(ppda)(tib)]·4H2O(9).(H2opda=o-phenyldiacetic acid,H2mpda=m-phenyldiacetic acid,H2ppad=p-phenyldiacetic acid,pbiyb=1,4-bis(-imidazol-1-methylene)benzene,mbib=1,3-bis(1-imidazol-1-phenyl)benzene,tib=1,3,5-tri(1-imidazol-1-phenyl)benzene).The structures and properties of the coordination polymers were characterized by X-ray single crystal diffraction,infrared spectroscopy(IR),elemental analysis,thermogravimetric analysis(TGA),powder X-ray diffraction(XRD),fluorescence analysis,UV absorption spectroscopy and other methods.Coordination polymers 1,2,3,4,6 and 9 are two-dimensional layered structures,and the adjacent two-dimensional layers are stacked together by intermolecular hydrogen bonds and?-?interactions to form three-dimensional supramolecular structures.Coordination polymers 5 and 8 are one-dimensional polymer bands.7 is a three-dimensional porous structure with a good specific surface area(18.14m~2g-1).Coordination polymer 1-3,as a sensor with good fluorescence performance,can be used to detect cefime(CEF)in the water system,whose detection limits are0.37??,0.38??,0.13??,respectively.The fluorescence quenching efficiencies were96.81%,90.74%and 89.96%,respectively.Coordination polymer 4-6 is used as a highly selective and sensitive fluorescent probe to detect antibiotic cefixime(CEF)and tetracycline(TEC)in water,and the detection limits are 0.27??,0.29??,0.53??,0.38??,0.32??,0.42??.The fluorescence quenching efficiencies were 97.25%,97.81%,94.73%and 92.00%,97.21%,94.70%,respectively.Coordination polymer 7-9,as a fluorescence sensor,can sensitively identify tetracycline(TEC)in aqueous solution,the detection limit is 0.21??,0.32??,0.56??,and the fluorescence quenching efficiency is 97.45%,94.13%,96.32%,respectively.The coordination polymer 7 has a high quenching rate for tetracycline(TEC)due to its three-dimensional porous structure.The quenching mechanism of fluorescence is the combination of photoinduced electron transfer and internal filtering effect.The pbiyb ligand has two methylene groups less than mbib,so the non-radiative decay(molecular rotation and vibration)of the pbiyb ligand from the excited state to the ground state is higher,resulting in the relatively weak fluorescence properties of the pbiyb ligand;Tib ligands have one more imidazole ring than mbib ligands and have higher conjugation,Three nitrogen-containing heterocyclic ligands with progressive fluorescence properties were selected to synthesize coordination polymers with better fluorescence properties.The conjugation and fluorescence properties of coordination polymers 1-3,4-6 and 7-9 tend to increase successively.Tetracycline also has high conjugation properties.The coordination polymer 7 synthesized by homophenyl triimidazole(tib)is very effective in detecting tetracycline.Coordination polymer 7 has good fluorescence quenching efficiency for tetracycline(TEC)because of its three-dimensional porous structure and large specific surface area.The removal of tetracycline(TEC)from water by coordination polymer 7 as adsorbent was further studied.The results showed that the adsorption capacity was 64.49 mg g-1.The adsorption data can be better fitted to Langmuir model and pseudo-second-order kinetic equation,so the adsorption process can be judged as monolayer chemisorption.The main adsorption force is the?-?interaction between the coordination polymer 7 and the benzene ring of tetracycline.Adsorption thermodynamics shows that the adsorption is a spontaneous process of endothermic entropy increase.The effects of initial pH and coexisting ions on the adsorption properties of coordination polymer 7 were also investigated. |
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