Specific Recognition And Targeted Degradation Of Phthalates In Wastewater On Molecularly Imprinted MOFs

Phthalates are widely detected in environmental and industrial wastewater.Advanced oxidation is one of the important methods to treat these refractory organics.However,the traditional advanced oxidation process has some problems,such as free radical non-selective catalysis and low catalytic efficiency for refractory pollutants.For this shortage,this paper carried out the iron base MOFs（metal organic framework）MIL-100 as a basement catalyst and the surface molecular imprinting technique adopted to carry out the research of functional assembly.On this basis,the persulfate oxidation process realized the complicated system of diethyl phthalate（DEP）selective recognition and targeted catalytic degradation process.Concrete research content including molecularly imprinted system dynamics simulation and different imprinting system components research on the effect of prepolymer.Synthesis of iron metal organic framework and surface imprinting materials and its catalytic degradation DEP mechanism.Targeted catalytic materials compound recognition site optimization and regulation of mass transfer system.Targeted catalytic materials catalytic degradation process of research and the multicomponent imprinting system and its application in wastewater.Through the above research contents,the main conclusions of this study are as follows:（1）It is feasible to select functional monomer and solvent in molecularly imprinted components by molecular dynamics simulation.The molecular imprinting system was optimized by comparing the binding energies of 9 functional monomers and template molecules and analyzing the internal weak interaction forces.The results show that acrylamide（AC）and acrylic acid（AA）as functional monomers can form more hydrogen bonds for four kinds of phthalate pollutants.The electrostatic force of DEP prepolymerization optimization system can reach more than 1000 kcal/mol,and the prepolymer structure of DEP-2（AA,AC）can be formed.The intermolecular hydrogen bond length between functional monomer and template in the prepolymer is about 1.7-1.8?.The simulation results show that the influence of solvent on the prepolymer is carbon tetrachloride<trichloromethane<acetone<acetonitrile<ethanol<methanol<H₂O.（2）MIL-100 and MIL-100 CUS substrate containing unsaturated sites were rapidly synthesized by room temperature in water.The results showed that the targeted catalytic ability of DEP was improved after surface imprinting.The pore volume decreased from 0.66 cm³ g^-1 to0.05 cm³ g^-1.The results of response surface model（RSM）showed that the selective catalytic ability of imprinted materials on DEP was mainly influenced by the amount of crosslinking agent,imprinting time and temperature.MIL-100 CUS has slightly higher catalytic activity than MIL-100,but its defective structure makes it easy to cause iron ion dissolution.（3）Although the targeted DEP removal ability of the molecularly imprinted materials on the surface has been improved to a certain extent compared with that of MIL100 substrate,it has not been greatly improved.Therefore,it is necessary to further optimize and regulate the composite identification sites and mass transfer system of materials.In this study,the Scatahard model was used to evaluate the number of identification sites and the selectivity identification characteristics of imprinted materials synthesized with different functional monomers.The results show that AA can form more imprinted holes with compound multi-recognition sites.This can achieve more accurate identification and targeted catalytic ability in the process of multi-component system identification of pollutants.In addition,1.1nm characteristic pore can be formed by optimizing the imprinted material synthesized with divinylbenzene（DVB）as cross-linking agent.This dense structure can ensure the mass transfer of persulfate and sulfate radical while maintaining the structural stability of the material.The results showed that through the synergistic action of adsorption and catalysis,the DEP could be removed to more than 105mg g^-1.Adjusting the mass transfer characteristics of the imprinted layer by controlling the crosslinking agent can maintain the selective recognition ability of the material and at the same time have a good catalytic effect.Catalytic reaction rate constant can be significantly increased by about 8 times.At the same time,the degradation efficiency of DEP per PS dosage is also increased by more than 3 times.（4）Studies on the specific recognition mechanism of surface imprinted materials indicate that the recognition process mainly consists of multi-site hydrogen bond,electrostatic force and the hydrophobic effect ofπ-πstack.Under the precise recognition of multiple sites,imprinted materials show good specific recognition performance and stable targeted catalytic ability in complex water environment.Studies have shown that DEP removal remained stable above 50mg/g under different concentrations of humic acid（FA）and HCO₃^-.The selectivity of DEP under the co-existence of multiple pollutants is also better than that of traditional activated carbon,zero valent iron and other materials.At the same time,due to the cross-linking effect of DVB,the DEP recognition ability of the material is less affected by temperature than that of MIL-100 substrate.When the temperature is 40℃,the non-uniform index m value is always stable in the range of 8.2-8.5.These characteristics make it more advantageous in terminal treatment and targeted catalysis of wastewater.（5）In order to remove the residual organic ligands in MIL-100 and increase the relative Fe content in the material,the high-temperature carbonization method was used to improve the stability of MIL-100.The content of Fe increased to 79%after carbonization.On this basis,through the establishment of multi-component imprinting system,the hole surface of the material covered with about 5nm imprinting layer to get the ability of targeted removal of a variety of phthalates.Compared with carbonized MIL-100 substrate,the imprinted material obtained by this method has a stronger COD removal ability on actual wastewater.The removal capacity of DMP and DBP was increased by 44.5% and 64.6% respectively.In addition,controlling the appropriate ratio of functional monomer can not only ensure the catalytic performance but also improve the overall hydrophilicity of the material.The mechanism of the material’s targeted catalytic degradation of pollutants in water first adsorbs DEP to the surface of the material accurately and rapidly through the compound recognition site of the surface imprinting layer.And then PS generates sulfate radical through the activation of the surface molecular imprinting layer to the base material.As free radicals are transferred to the surface of the material,the catalysis process was started.In this process,the contact probability between the active radical and the target pollutant was significantly increased,which greatly improved the catalytic reaction efficiency.To sum up,this study obtained the influence mechanism of different imprinted system components on prepolymer.And this study obtained targeted catalytic materials with selective recognition of DEP and their catalytic mechanism through composite identification site optimization and mass transfer system regulation.This study provides the basis and ideas for the application of surface molecular imprinting in water treatment and the improvement of advanced oxidation efficiency.