Immobilization Of Laccase By Cu²⁺ Chelate Affinity Interaction On Surface Modified Magnetic Silica Particles And Its Use For The Catalytic Degradation Of Chlorophenols Pollutants In Water

Laccase is an oxidoreductase that contains Cu2+ and is capable of catalyzing the degradation of many phenolic and non-phenolic aromatic compounds. Compared with free laccase, immobilized laccase possess many advantages such as reusebility. Magnetic Cu (Ⅱ) chelating silica particles using polyacrylamide as a metal-chelating ligand was developed and used for the immobilization of laccase by coordination. The immobilizing conditions which affect the activity of immobilized laccase were discussed at length. The enzymatic property of immobilized laccase and its catalytic capacity for 2,4-dichlorophnol (DCP) removal and influencial factors were evaluated systemically. Furthermore, the catalytic capacity of immobilized laccase and the combined technology of electrochemistry and immobilized laccase for pentachlorophenol (PCP) degradation were primarily compared. The results showed that:The optimum conditions of laccase immobilization:Concentration of PAM was 2 g/L, concentration of Cu2+ was 0.2 mol/L, immobilization time was 1 h, immobilization temperature was 25℃, pH value of buffer solution is 4 and the laccase dosage was 20 mg/g carrier. Temperature and pH value showed obvious influence on the activity of the immobilized laccase. Higher activity of the immobilized laccase occurred at 40℃and in the pH of 3.0 solution, which displaced towards higher temperature and more acidic values compared to the free laccase. Moreover, the immobilized laccase showed remarkably improved thermal stability. The Km value of immobilized laccase was 85.62μM which was slightly higher than that of free laccase (64.99μM). This result means that the immobilized laccase had lower affinity towards the substrate.The degradation of 2,4-DCP by immobilized laccase showed a good catalytic effect and response stability. The removal efficiency reached 91.47% after 12 h when 8 g/L of immobilization laccase for the degradation of 2,4-DCP (volume:50 ml; the initial concentration:24.25 mg/L) was used. When the pH increased from 3.0 to 6.0, the removal efficiency of 2,4-DCP increased. When the concentration of 2,4-DCP ranged from 14.39 mg/L to 257.6 mg/L, the removal efficiency all exceeded 85% after 12 h. The removal efficiency increased with the increasing amount of immobilized laccase. However, too much immobilized laccase would cause the removal velocity decrease. Sulfate ions in the aqueous solution can promote the removal efficiency significantly, while bicarbonate ions inhibited the reaction. The catalytic degradation efficiency of PCP by the immobilized laccase reached 82.89% after 0.5 h reaction (solution volume:50 mL, the initial concentration:28.56 mg/L), but after that the removal efficiency did not change with the increasing time. The combined process of electrochemical-the immobilized laccase catalytic oxidation showed the same removal efficiency for PCP as the immobilized laccase catalytic oxidation, while higher dichlorination capability and lower activity loss of immobilized laccase was found in the combined process. This demonstrated that the combined process can improve the reusability of immobilized laccase and the capacity for the degradation of toxic pollutants in water.