Study On The Mechanism Of Nano-biocatalytic Degradation Of Phenolic Compounds In Environmental Water

Enzyme plays an important role in the field of Biochemistry, and enzyme biocatalysis method is widely used for environment remediation due to its high efficiency and specificity. Some drawbacks of free enzymes including loss of activity, high cost for preparation and poor recovery hampered their further application in industry. The immobilized enzyme came into being in order to solve these problems and improved the activity, stability, and recycling capacity of enzyme. Recently, many scholars at home and abroad have paid more attention to the research on the use of enzyme immobilization technology to removal the phenolic compounds in the environment. Choose a support of immobilized enzyme is a very important problem. Nowadays, there are various of materials as support for enzyme immobilization such as carbon nanotubes, mesoporous material, magnetic particles and polymer. Enzyme composite prepared by these support significantly improved enzyme catalytic activity, stability and efficiency for pollutants removal. In this paper, we chose two special properties of nanoscale materials, graphene oxide and biochar, as the substrate of immobilized tyrosinase. Among them, graphene oxide, a novel carbon material, is already widely used in medical, biological sensors and other aspects of environmental remediation and has attracted much attention of researchers as enzyme immobilization carriers due to its special characteristics of large surface area, good mechanical properties, good conductivity, hydrophilicity and rich functional groups. Biochar is biomass pyrolysis burning to produce a porous material in the absence of oxygen. Biochar of more pores, large surface area, environmentally friendly and rich functional group selected as an enzyme carrier has the potential prospect in terms of cost-effectiveness of resource utilization.We chose graphene oxide and biochar as the substrate of immobilized tyrosinase and proposed construction composites of tyrosinase immobilized magnetic graphene oxide and biochar adsorption tyrosinase, respectively. And then catalytic degradation of phenol with the enzyme composite was performed to study the pollutant degradation mechanism. Effect of various of factors such as substrate concentration, enzyme concentration, pH, temperature on degradation efficiency for phenolic compounds of the immobilized tyrosinase were investigated as well as the stability and reuse.The conclusion was obtained:(1) The magnetically-separable and stabilized composites formed by immobilized tyrosinase enzyme on the surface of graphene oxide can be highly efficient catalytic degradation of phenol and bisphenol A. Graphene oxide can immobilize more enzyme molecules than a common support due to special surface area(two accessible sides). By electron microscopy analysis, multilayer cross-linked composites of immobilized tyrosinase on graphene oxide can load more enzyme molecules and magnetic particles. Multi-layer cross-linked composites are equivalent to about 4.6 layers of Tyr enzymes and MNPs attached on each side of GRO sheet. Multi-layer cross-linked composites show 1.5 fold higher catalytic activities than covalent immobilized enzyme suggesting multi-layer cross-linked composites have higher catalytic capacity.(2) Cross-linked composites of immobilized tyrosinase on graphene oxide can degrade 100% of 0.5 mM of phenol after 1.5 h and up to 74.5% of 100 μM bisphenol A in 2 h reaction, respectively. And the composites can be separated and recovered quickly under the external magnetic field. The process of enzyme immobilization and reusability could be simplified. After 5 times of repeated use, the degradation efficiency of phenol retained 56.8% of initial activity.(3) Cross-linked composites of immobilized tyrosinase on graphene oxide have a broad pH and temperature range. Its storage stability has almost no change in 30 days suggesting that multi-layer cross-linked composites of immobilized tyrosinase on graphene oxide show strong resistance to complex environment and have potential prospect in real water environment remediation.(4) Tyrosinase is immobilized on surface of biochar by physical adsorption method. The optimal adsorption time is 2 h. The composites of immobilized tyrosinase on biochar have the highest enzyme loading and highest enzymatic activity at pH 4.0, and enzyme loading and enzymatic activity were 0.063 mg / mg and 216.1 Unit / mg, respectively.(5) The composites of immobilized tyrosinase on biochar had higher catalytic efficiency for bisphenol A degradation. The composites of immobilized tyrosinase on biochar of 1 mg/mL, 3 mg/mL and 5 mg/m L can degrade bisphenol A up to 54.2%、72.9%�'� 78% in 24 h reaction, respectively.