Study On 4-Nitrophenol Molecularly Imprinted Polymer’s Synthetic Methods And Characteristics

In recent years,nitrophenolic contaminants listed in the list of priority pollutants have attracted widespread attention.Among them,4-nitrophenol as a typical nitrophenolic contaminant is difficult to remove,which due to its carcinogenicity,high toxicity,refractory and other problems as well as the low content of natural water source.Therefore,it is particularly important to find an effective method to identify and remove trace amounts of nitrophenolic contaminants in the presence of interfering substances.In this thesis,4-NP was used as the target pollutant,and the surface molecular imprinting technique and the sol-gel technique were combined to prepare the imprinted adsorption material with specific recognition ability for 4-NP.From the results of single factor experiments,it can be found that the molar ratio of template molecule to functional monomer,the molar ratio of template molecule to crosslinker,the type of porogen and the type of extract have different effects on the preparation of molecularly imprinted materials.Based on the single factor experiment,the orthogonal experimental results show that the optimal preparation conditions of the nitrophenol molecularly imprinted material are as follows:the molar ratio of template molecule to functional monomer is 1:8,and the molar ratio of template molecule to crosslinker is 1:10,the porogen is ethanol,and the extract is methanol/acetic acid（7:3,V/V）.At this time,the removal rate of 4-NP by the imprinted material is 77.87%.The range analysis showed that the order of influence of each influencing factor on the removal rate of 4-NP was:porogen type>extract type>molar ratio of template molecule and functional monomer>molar ratio of template molecule and crosslinker.The results of scanning electron microscopy showed that the surface of MIP_4-NP-NP and NIP_4-NP-NP was rough and irregular,and the pores in MIP_4-NP were more than NIP_4-NP.The imprinting process could increase the specific surface area of MIP_4-NP and NIP_4-NP,and the polymer is mainly composed of mesoporous structure;Fourier transform infrared spectroscopy analysis shows that activated silica gel before and after imprinting The functional groups of the MIP_4-NP and NIP_4-NP are basically the same.The thermogravimetric analysis results show that the pyrolysis of activated silica gel,MIP_4-NP and NIP_4-NP are divided into water dispersion and small molecules.The polymer decomposition and organic matter volatilization are completely three stages,in which the thermogravimetric curves of MIP_4-NP and NIP_4-NP are similar;the surface that MIP_4-NP and NIP_4-NP was acidic,and the absolute value of the zeta potential of MIP_4-NP was lower than that of NIP_4-NP.The maximum apparent binding number Q_m of MIP_4-NP was 95.95μmol/g by Scatchard equation.It was found that the size,shape and chemical properties of the MIP_4-NP imprinted space complement the 4-NP molecules and can be combined with the 4-NP molecules through the action of hydrogen bonds and covalent bonds.MIP_4-NP can effectively remove 4-NP from water,and NIP_4-NP has no effect on the removal of 4-NP without MIP_4-NP.Solution pH,initial 4-NP concentration,adsorption time,solution temperature and amount of imprinted material all had different effects on the removal of 4-NP.The results of response surface test showed that the optimal process parameters were:initial 4-NP concentration of 10μmol/L,MIP_4-NP dosage of1.46 g/L,solution temperature of 294.2 K,and solution pH of 5.60.At this condition,the predicted removal rate of MIP_4-NP to 4-NP was 79.63%.The results of the degree of influence analysis indicated that the order of influence of each factor on the removal of4-NP by MIP_4-NP was:pH>solution temperature>initial 4-NP concentration>MIP_4-NP-NP dosage.The Elovich model is a good description of the kinetic response of MIP_4-NP to 4-NP at different initial 4-NP concentrations.For the kinetic reaction of NIP_4-NP to remove4-NP,at the low concentration（10μmol/L）,which can be better described by the Elovich kinetic model;at higher concentrations（50μmol/L and 100μmol/L）,which can be better described by the pseudo second-order dynamics model.Both liquid membrane diffusion and intraparticle diffusion can limit the reaction rate of MIP_4-NP-NP and NIP_4-NP to 4-NP adsorption,but the main factor is liquid membrane diffusion.The calculation results of activation energy indicate that the adsorption process of 4-NP by MIP_4-NP and NIP_4-NP is mainly chemical adsorption.The Freundlich isotherm model can well describe the adsorption equilibrium reaction of MIP_4-NP and NIP_4-NP to 4-NP at different temperatures.The polanyi adsorption potential decreases with the increase of initial 4-NP concentration.The analytical results of nitrophenol surface imprinted materials show that the methanol/acetic acid（7:3,V/V）analytical solution has a good analytical regeneration effect on the adsorbed MIP_4-NP.MIP_4-NP can be reused,but the repeated times were limited.After MIP_4-NP is resolved for 5 times,the removal rate of 4-NP is reduced from67.32%to 52.63%.The results of selective adsorption experiments of nitrophenol surface imprinted materials showed that the removal rate and adsorption capacity of 4-NP for MIP_4-NP-NP were higher than those of the three systems of 4-NP,phenol and bisphenol A（BPA）.The two phenolic compounds are also higher than the removal rate and adsorption capacity of three phenolic compounds by NIP_4-NP.In the two binary systems of 4-NP and phenol,4-NP and BPA,compared with MIP_4-NP and NIP_4-NP,the selective adsorption capacity of 4-NP is strong and the recognition is good.The Freudlich isotherm model is more suitable for describing the adsorption equilibrium process of 4-NP on MIP_4-NP and NIP_4-NP in two binary systems.In the ternary system of 4-NP,phenol and BPA,the competitive adsorption of two phenolic substances with 4-NP in solution is enhanced,but the removal of 4-NP by MIP_4-NP was not obvious.The Freudlich isotherm model is also more suitable for describing the adsorption equilibrium process of 4-NP by MIP_4-NP and NIP_4-NP in the ternary mixed system.The humic acid in the water had a certain degree of inhibition on the adsorption and removal of 4-NP by MIP_4-NP and NIP_4-NP,but it was not obvious.