Immobilization Of Laccase On Cu-based Metal Organic Frameworks And Its Catalytic Degradation Of Bisphenol A

Bisphenol A（BPA）is widely used in the production of baby bottles,toys,and medical equipment owing to the highly malleable.Due to the unreasonable treatment of these domestic waste,BPA has been detected in various environmental media.The bioenzyme method is widely used to treat BPA because of the green and efficient characteristics.However,practical applications of enzymes are limited because of easy solubility in water and poor stability,and the concept of immobilized enzymes was proposed.In this study,we immobilized laccase using copper-based metal-organic frameworks（Cu-PABA）and synthesized biocomposites（Cu-PABA@Lac）by co-precipitation via a one-pot method under room temperature and water environment,which was greener and faster.Besides,we also explored the application of biocomposites in BPA degradation.The research results are as follows:（1）The changes of structure and properties of the materials before and after loading laccase were investigated by different characterization methods.The results proved that laccase was successfully immobilized on the material;after the immobilization of laccase,the crystal morphology of the material did not change,and the morphology was more ellipsoid,while the specific surface area decreased;the spatial structure of laccase changed;the binding between laccase and Cu-PABA depends on the interaction between carboxyl group,amino group,hydroxyl group and metal site.（2）The optimum conditions for laccase immobilization were obtained by optimizing different parameters of immobilization process.Finally,p H=7（final p H=5.5）,PVP of 2mg·m L^-1 and laccase of 0.5 mg·m L^-1 were selected as the optimal conditions for further study,and the encapsulation efficiency and retention activity of laccase were 64.1%and 41.7%,respectively.After immobilization of laccase,its stabilities（heat,p H,organic reagents,storage）were improved because of the protection of the material shell and the increase in the rigidity and stability of laccase.Owing to the suitable microenvironment provided by Cu-PABA,the reaction affinity increased（K_m decreased）.（3）The results of the catalytic degradation experiments indicated that the ability of Cu-PABA@Lac to remove BPA was significantly higher than that of Cu-PABA.When 2,2′-azino-bis（3-ethylbenzothiazoline-6-sulfonic acid）diammonium salt（ABTS）was added into the system,the degradation rate of BPA was 84.7%after 12 h.After eight times of recycling experiments,Cu-PABA@Lac can still maintain 67.4%of the original ability to the catalytic degradation of BPA,and its structure was not destroyed.The optimization results of response surface model illustrated that temperature had a significant effect on the catalytic degradation process,and the optimal catalytic degradation conditions were as follows:0.29 m M ABTS,2.80U·m L^-1 initial immobilized enzyme dosage,39.86℃,and the degradation rate was 88.84%.（4）The mechanism of the catalytic degradation system was electron transfer.After the introduction of ABTS,the electron transfer rate of the system increased,which was more conducive to the catalytic degradation of BPA.After the immobilization of the laccase,the synergistic effect of copper ions between Cu-PABA and laccase further promoted the electron transfer and catalytic degradation,and the catalytic degradation process of BPA primarily included oxidation,fragmentation,recombination,and ring-opening reactions.