Study On Dispersive Solid Phase Extraction Based On ZIF-8 Composite For The Detection Of Fluoroquinolone Antibiotics

Fluoroquinolone antibiotics are amphoteric compounds with antibacterial properties that are widely used in the medical,animal husbandry,and aquaculture industries.They have been detected in surface water,groundwater,and even drinking water sources as a result of their migration and transformation in the environment,posing a serious threat to human health and the ecological environment.Therefore,it is critical to conduct research and develop sensitive and dependable analytical methods for monitoring FQs concentrations in aquatic environmental samples.Due to the low concentration of FQs and the complex composition in the environmental water sample,a suitable pretreatment process is required to eliminate interference and pre-enrich before analysis.Solid phase extraction is one of the most commonly used methods for pretreatment with the advantages of low solvent consumption,short extraction time and easy operation.Among the common adsorbents,metal-organic framework materials have attracted widespread attention because of their special properties.In this paper,a series of ZIF-8 matrix composites were designed and prepared by using the designability of MOF materials and the structural characteristics of fluoroquinolone antibiotics,and the efficient and rapid detection of fluoroquinolone antibiotics in water was realized by combining high performance liquid chromatography.The specific work content is as follows:（1）According to the structural characteristics of fluoroquinolone antibiotics,ZIF-8/DNA composites were successfully prepared by introducing biomolecular single-stranded DNA into the porous structure of ZIF-8 with ZIF-8 as the mother,and was employed in dispersed solid phase extraction to study its performance in the adsorption and extraction of FQs.The doping of DNA increased the number of active sites,improves pore structure,and changes the charged properties of the material.Further characterization of the materials by SEM,TEM,FTIR and others proved that the DNA had been successfully doped without changing the regular hexahedral structure of ZIF-8.Applying it to the adsorption experiment of the representative antibiotic ofloxacin,ZIF-8and ZIF-8/DNA conformed to the quasi-secondary kinetic model and the Langmuir thermodynamic model,and quickly reached equilibrium within 20 minutes,with maximum adsorption capacities of103.7 and 209.8 mg g^-1,respectively,proving that this process is monolayer chemo adsorption.Then,It was used for the pre-enrichment of four fluoroquinolone antibiotics in water,with a recovery rate of 90.3%～107.9%,and detection limits as low as 0.01μg L^-1 and 0.02μg L^-1.This work not only provided a methodological basis for the efficient and sensitive detection of fluoroquinolone antibiotics in aqueous environment,but also expands the application of biomaterials combined with MOFs in the field of extraction.（2）To improve the stability of ZIF-8/DNA,by introducing dopamine in the precursor solution to form a layer of polydopamine film on the surface of the material,a new functionalized ZIF-8/DNA/DA composite was successfully prepared with ZIF-8/DNA as the mother.It improved the interfacial compatibility of the material and realized structural regulation.ZIF-8 was transformed from a protohexahedral to a more stable diamond-shaped dodecahedral structure.Dopamine is rich in amino and catechol,which provides more active sites for the adsorption of fluoroquinolone antibiotics.The materials were characterized by SEM,TEM EDS mapping,XRD,FTIR,etc.,and the results showed that the successful self-polymerization of dopamine on the surface of the material and the formation of a diamond-shaped dodecahedral structure.According to the results of adsorption experiment,ZIF-8/DNA/DA conformed to the quasi-secondary kinetic model and the Langmuir thermodynamic model,and quickly reached equilibrium within 20 minutes.The maximum adsorption capacity was 272.3 mg g^-1,and the process of ZIF-8/DNA/DA adsorption ofloxacin was monolayer chemo adsorption.It was used for pre-enrichment of four fluoroquinolone antibiotics in actual water samples with recovery limits as low as 0.01μg L^-1 and 0.02μg L^-1.This work provides a basis for adjusting the material structure to improve the water stability of MOF materials,and further expands the application of ZIF-8 in the field of water treatment.（3）To solve the problem of complicated centrifugation of powdered MOF materials and realize practical application,potato starch was used as the substrate,glyoxal（GLY）was used as the crosslinking agent,and the characteristics of starch gelatinization and cooling molding were used to realize self-crosslinking,the ZIF-8@PSC composite foam materials were prepared by freeze-drying design.The prepared materials had loose layered structures and porous structures on the surface,and characterized by SEM,XRD,FTIR and other characterization methods.It is used for the adsorption and extraction of fluoroquinolone antibiotics,it has superior adsorption capacity,and a large number of hydroxyl groups of potato starch provide rich adsorption sites for the adsorption of fluoroquinolone antibiotics.Moreover,the ZIF-8@PSC is biodegradable,in line with the concept of environmental protection,reducing secondary pollution to the environment.The adsorption of ofloxacin by ZIF-8@PSC composite foam was dominated by chemical adsorption,and the more composite Freundlich model was fitted,indicating that it was multilayer adsorption on heterogeneous surfaces.The adsorption reached equilibrium within 2 h,and the adsorption capacity reached 309.6 mg g^-1.More notably,the foam material is easy to handle and can be quickly separated from the aqueous solution,which eliminates the centrifugation step and is more conducive to the reuse of the material.After 5 cycle extraction experiments,the extraction recovery rate of foam material is still above 85%.This research not only provides ideas for the synthesis of starch foam and its combination with MOF materials,but also introduces environmentally friendly bio-based materials into the field of adsorption and extraction of pollutants,which is in line with the concept of green environmental protection.