关键词: 磁性纳米颗粒, 漆酶, 固定化, 催化, 降解, 氯酚, 废水

Abstract:

In recent years, laccase has been reported to be successfully immobilized on many different supports. Among them, potential applications of magnetic silica microspheres have been widely investigated for enzyme immobilization and the enzymatic stabilities can improve obviously. However, to the best of our knowledge, there is no report for the laccase immobilization on silica coated nanoparticles via one-step dopamine (DA) self-polymerization method, and nor any reports concerned with the degradation performance of paraphlorophenol (4-CP) by this immobilized laccase. In this work, the immobilized laccase on silica-coated magnetic nanoparticles were prepared through dopamine (DA) in situ entrapment, and then the immobilized laccase was applied for 4-chlorophenol (4-CP) removal. Briefly, the silica-coated magnetic nanoparticles were prepared through a sol-gel method, then the mixture of Fe₃O₄@SiO₂ nanoparticles and DA was added to PBS (pH 6.0) containing laccase, the reaction was performed for 18 h at 25℃ with vigorous stirring, and was separated by an external magnetic field. After being washed 4 times, the product (Fe₃O₄@SiO₂-PDA-Lac) was obtained. The scanning electron microscope images and size distribution analysis indicated that Fe₃O₄@SiO₂ had a spherical and uniform size distribution with the average diameter of about 134 nm. The high saturation magnetization of Fe₃O₄@SiO₂ made it easily to be separated from the reaction system. The results of X-ray diffraction (XRD) revealed that the prepared samples were Fe₃O₄ nanoparticles and Fe₃O₄@SiO₂ nanoparticles. The preparing conditions of the Fe₃O₄@SiO₂-PDA-Lac were optimized by orthogonal experiment. In the best level, the total activity recovery of the Fe₃O₄@SiO₂-PDA-Lac can reach to 43.28%. In the degradation process, the effects of laccase concentration, solution pH and ABTS mediator on the removal efficiency of 4-CP were investigated. The results showed that when solution pH was 6 and laccase concentration was 1.2 U·ml^-1, 95% percentage of 4-CP was removed within 8 h enzymatic catalysis. When 50 μmol·L^-1 of ABTS was added in the reaction system, the removal efficiency of 4-CP kept about 99% within 10 min enzymatic catalysis, which certified that the ABTS as a mediator could enhance the enzymatic reaction rate of the immobilized laccase. After degraded 10 times by the immobilized laccase, the removal efficiency of 4-CP still remained 67%, which exhibited an excellent reusability and operational stability.

Key words: magnetic nanoparticle, laccase, immobilization, catalysis, degradation, chlorophenol, wastewater