Modification Of Fe₃O₄/SiO₂–laccase By Copper Ions And Decolorization Of Azo Dye

As the largest group of synthetic dyes, azo dyes are widely used in textile dyeing. However, they have the characteristic of stronger resistance to acid and oxidation etc. Therefore, it is difficult to be removed from wastewater by the traditional physical method or chemical method. The development of technology of laccase immobilization presents laccase with unusual performance for dye decolorization and easy separation under an external magnetic ?eld.In addition, some studies shows that different metal ions can affect the activity of laccase. Some metal ions can inhibit the activity of enzyme, while some metal ions can improve the activity of laccase, copper ions belong to the latter. The results reported by Jun Ge demonstrated that free laccase modified by copper ion increased the specific surface of laccase, thus improved the activity and stability of laccase for substrate decocolorization.Rapid decolorization of phenolic-like azo dyes by laccase immobilized on Fe3O4 /SiO2 nanoparticles with particle size below 30 nm were carried out previously in our group, and the color removal of the azophloxine in 20 min was 80 %, which is obviously better than the reports obtained by others immobilized laccase.Therefore, the modification of the immobilized laccase with Fe3O4/SiO2 nanoparticles as support was investigated in present work. The main work is as follows:(1) Investigate the modification of laccase immobilized on Fe3O4/SiO2 nanoparticles with particle size below 30 nm by copper ions, laccase loading on the immobilized laccase has reached saturation;(2) Investigate the modification of free laccase by copper ions(3) Investigate the decolorization of Azophioxine by the modified immobilized laccase and free laccase;(4) Investigate the operational stability of decolorization of Azophioxine by the modified immobilized laccase;The experimental results showed that the relative activity of the immobilized laccase modified by copper ion with different concentrations presents different increase. Compared with the modification under 100 mM and 140 mM of Cu2+, the immobilized laccase with saturated laccase loading modified by 120 mM of Cu2+ has the best relative activity, and this result was supported by the largest specific surface area of the immobilized laccase modified by 120 mM of Cu2+ compared with the other two Cu2+ concentrations; the operational stability of decolorization of Azophioxine by the modified immobilized laccase was better than that performed by unmodified immobilized laccase; the decolorization percentage of Azophioxine after treated by the modified immobilized laccase and the unmodified immobilized laccase, respectively, shows little difference in the first several cycles, but with cycles running, the decolorization of Azophioxine by the modified immobilized laccase was better than that performance on unmodified immobilized laccase; the decolorization of Azophioxine by free laccase modified by copper ions is not good as expectations, on the contrary, the decolorization percentage was lower than that performed by free laccase without modification, therefore, the key role of the Fe3O4/SiO2 support with diameter below 30 nm is more obviously, having the laccase possess unusual ability to decolorize azo dyes, the non-substrate of laccase.