| Paper food packaging are wildly used because of its low cost, excellent expansibility, abrasion-resistant, easy to carry and other advantages. But in the paper food packaging production process, large number of heavy metals may be supplied by raw materials, ink and other ways, leading to food safety issues. The intake of heavy metals is harmful to human body and affect people’s health seriously. With the national food safety monitoring increasingly strict, using appropriate methods to remove heavy metals in paper food packaging should also be taken seriously.With the development of molecular imprinting technology,the application in the field of heavy metals adsorptionis more and more widely.The magnetic-molecularly imprinted polymers which are produced by the combination of magnetic nanomaterials and molecular imprinting technique not only have strong adsorption capacity for heavy metals, but also can be recycle uesd. In this paper, at first, the influence of some factors in the production process of Pb(Ⅱ) magnetic-molecularly imprinted polymers were studied.The Pb (Ⅱ) imprinting content, the amount of chitosan, the crosslinking time, the dosage of the cross-linking agent and the consumption of Fe3O4nanoparticles are the main factors which affecting the adsorption performance. The influence of the consumption of Fe3O4nanoparticles, the Pb (Ⅱ) imprinting content, the dosage of the cross-linking agent are particularly significant.According to Box-Behnken design experiments, Ⅰ studied the influence of the consumption of Fe3O4nanoparticles, the Pb (Ⅱ) imprinting content, the dosage of the cross-linking agent to the adsorption capacity. The Pb (Ⅱ) imprinting content and the dosage of the cross-linking agent have particularly significant influence to the adsorption capacity. There are certain interactions between the three factors, including the consumption of Fe3O4nanoparticles&the Pb (Ⅱ) imprinting content and the Pb (Ⅱ) imprinting content&the dosage of the cross-linking agent that have particularly significant influence to the adsorption capacity.The optimal conditions to produce the magnetic-molecularly imprinted polymers are:the consumption of Fe3O4nanoparticles in amount of0.50g, the Pb (Ⅱ) imprinting content in amount of0.41mmol, the dosage of the cross-linking agent in amount of0.55mL, and other conditions of chitosan dosage in amount of0.2g, the cross-linkingreaction were running under the water bath at60"C with stir evenly for4h.I do a series of characterization experiments about the adsorption materials. The TEM images show that magnetic-molecularly imprinted polymers’ average diameter is40nm, which is bigger than the size of Fe3O4nanoparticles, maybe due to the cladding effect of the Fe3O4nanoparticles to the surface of chitosan. The Fe3O4nanoparticles, chitosan and magnetic-molecularly imprinted polymers are analyzed by infrareds pectroscopy.I infer that epoxy chloropropane participated in the crosslinking reaction, and Fe3O4nanoparticles have coated in the polymers. By X-ray scattering techniques I infer that the crystalform are not changed during the production process, which proof that imprinted polymer containing Fe3O4nanoparticles.Then I study the adsorption properties of the Pb(Ⅱ) magnetic-molecularly imprinte dpolymers. Studies show that the Pb(Ⅱ) magnetic-molecularly imprinted polymers have high magnetic adsorption capacity of38.01mg/g. The magnetic-molecularly imprinted polymers adsorb Pb(Ⅱ) quickly, about200mins take to reach equilibrium. With the simulation results of first order kinetics equation and false secondary dynamics equation we know that the equilibrium adsorption capacity q (34.84mg/g) which is fitted by false secondary dynamics equation is closer to the experimental value qm (33.15mg/g), the correlation index R2is0.9988, this shows that false secondary dynamics equation can be used to illustrate the adsorption process and the adsorption process is chemisorption.The results from Langmuir isotherm and Fredunlich model simulation show that the experimental data is more similar to calculated results of the Langmuir model, and the adsorption mechanism is monolayer adsorption. Selective adsorption experiments show that in the mixed solution which include other metal ions, magnetic-molecularly imprinted polymers for Pb (Ⅱ) ion has strong selective adsorption capacity than other ions, the relative selectivity coefficient K’of Pb(Ⅱ)/Cu(Ⅱ) is2.86and Pb(Ⅱ)/Zn(Ⅱ) is3.01, which can be used for selective adsorption separate.The magnetic-molecularly imprinted polymers can be used repeatedly, the adsorption capacity turns to92.43%of the initial level after reused five times. The decline is not significant and the economic value is higher. Through the adsorption separation experiment after the paper food packaging samples pretreatment, the Pb (Ⅱ) ion absorption rate is95.2%、97.6%and99.3% respectively,shows that the magnetic-molecularly imprinted polymers can be used in paper food packaging Pb (Ⅱ) ion adsorption separation of paper food packaging effectively.Finally, I compound Cd (Ⅱ)magnetic-molecularly imprinted polymers. Experments show that pH=7is the favorable condition for adsorption. After80mins, the system reach to equilibrium, and the adsorption capacity is25.33mg/g. Selective adsorption experiments show that in the mixed solution which include other metal ions, magnetic-molecularly imprinted polymers for Cd (Ⅱ) ion has strong selective adsorption capacity than other ions, the relative selectivity coefficient K’ of Cd(Ⅱ)/Cu(Ⅱ) is2.53and Cd(Ⅱ)/Zn(Ⅱ) is2.36. The adsorption capacity turns to90.35%of the initial level after reused five times, the quality still reach87.30%of the original. Through the adsorption separation experiment after the paper food packaging samples pretreatment, the Cd (Ⅱ) ion absorption rate are greater than90%, shows that the magnetic-molecularly imprinted polymers can be used in paper food packaging Cd (Ⅱ) ion adsorption separation of paper food packaging effectively. |
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