Synthesis Of Zr-MOF Composite Adsorbents And Their Application In Removal Of Glyphosate Residues

Due to the widespread application of organophosphorus pesticides?OPPs?in agricultural producion,raw materials of food were contaminated by OPPs.The contaminate foods are ingested and continuously enriched in the human body,which induces various diseases.In order to reduce the OPPs in food sample and assure food safety,this work develops two novel Zr-MOF?UiO-67?based adsorbents and applies them to control and remove glyphosate?one of OPPs?from food systems.The detail work what we have done is listed as follows:?1?Synthesis of Zr-MOF/graphene oxide composite adsorbents?UiO-67/graphene oxide?and its properties of adsorption of Glyphosate.Graphene oxide and UiO-67/graphene oxide adsorbents were prepared and characterized systematically by Scanning electron microscopy,X-ray photoelectron spectroscopy,Fourier infrared transform spectroscopy,and X-ray diffraction.The results demonstrate the successful synthesis of Zr-MOF/graphene oxide adsorbents.The conditions for removal of glyphosate pesticide residues were optimized,and the optimal conditions were:pH 4,adsorbent concentration 20.0 mg/L,adsorption time 180minutes.Under the optimised adsorption conditions,the adsorption performance of glyphosate was evaluated.The results showed that the adsorption capacity of the composite adsorbent was significantly higher than that of graphene oxide.Moreover,it was applied in purification of food samples and the adsorption process is well fitted with the pseudo-second-order kinetic and Langmuir isotherm models,its maximum adsorption q_maxax could reach 482.69 mg/g.Based on the study of the adsorption mechanism,Zr-MOF/graphene oxide composite adsorbent fully utilized the advantages of Zr-MOF and graphene oxide,and achieved the purpose of highly effective adsorption of glyphosate residues.?2?Preparation and application of magnetic Zr-MOF?UiO-67?adsorbents.The Fe₃O₄@SiO₂@UiO-67 named FSU was prepared by the"layer by layer"method,and it was systematically characterized by Scanning electron microscopy,Transmission electron microscopy,Fourier infrared transform spectroscopy and X-ray diffraction pattern.The results demonstrate the successful synthesis of FSU.Due to its magnetic property,FSU adsorbed glyphosate can be separated from the food system by an external magnetic field,which avoid the secondary pollution of the adsorbent to the food sample.The conditions for removal of glyphosate were optimized,and the optimal conditions were:pH 4,adsorbent concentration30.0 mg/L,adsorption time 60 minutes.Under the optimised conditions,the adsorption process of glyphosate was studied.The results showed that the process of glyphosate adsorption on FSU was chemical adsorption and well fitted with the pseudo-second-order kinetic and Langmuir isotherm adsorption model.In addition,the adsorption mechanism was analyzed by XPS and FTIR.The results indicated that the Zr-O groups in the FSU play a vital role in the adsorption of glyphosate,and the quantity of Zr-O groups directly affected the efficiency of glyphosate removal.FSU also exhibited good adsorption removal effect in the removal of glyphosate.?3?The study of detection performance of FSU on glyphosate.The optical properties of the FSU were evaluated using a fluorescence spectrophotometer and an UV spectrophotometer.The results show that the adsorbent has great fluorescence characteristics.The mixing of glyphosate molecules with adsorbent can increase the fluorescence intensity of FSU,and the relationship between glyphosate concentration and the degree of fluorescence enhancement was studied.The results indicated that there was a linear relationship between the concentrations of glyphosate and fluorescence enhancement within a certain range.Moreover,the method for fluorescence detection of glyphosate had a wide detection range?0.01-40.0 mg/L?and a lower detection limit?0.093 mg/L?.In addition,the luminescent group of FSU was found to be the Zr groups by analyzing the fluorescence characteristics of each adsorbent component,and the fluorescence intensity of FSU was significantly enhanced by increasing the concentration of glyphosate pesticide.The detection method has high credibility and the recovery rate is 90-97%.Besides,the selectivity of the detection method was also determined by comparing the intensity of the fluorescence enhancement effect of six different types of organophosphorus pesticides on the adsorbent,and it was found that the glyphosate exhibited higher effect than the other on the fluorescence enhancement of FSU.Zr-MOF?UiO-67?based adsorbents have a good effect on controlling the organic pollutants in food samples and removing glyphosate residues from food systems.These results suggest the novel adsorbents will be a good choice to ensure food quality and safety in the furture.