Biodegradation of acid orange-7 dye by immobilized laccase on functionalized ZSM-5 zeolites: Investigation of the role of functionalization and SiO2/Al2O3 ratio of zeolite on the catalytic performance

Abstract

It is known that SiO2/Al2O3 ratio and functionalization affect the features of zeolites. Considering these facts, in this study, two ZSM-5 zeolites with different SiO2/Al2O3 ratios of 200 and 80 (Z(80) and Z(200)) were synthesized and successively functionalized with (3-chloropropyl) triethoxysilane, melamine, and glutaraldehyde to furnish F-Z(80) and F-Z(200). The samples were utilized for the immobilization of laccase generating four biocatalysts, Lac@Z(80), Lac@Z(200), Lac@F-Z(80), and Lac@F-Z(200), able to biodegrade acid orange-7 dye. Comparison of the catalytic performance of the catalysts with free laccase indicated the remarkably improved performance of the supported laccase. Furthermore, Lac@F-Z(80) and Lac@F-Z(200) exhibited higher activity, recyclability, and storage stability compared to Lac@Z(80) and Lac@Z(200). Functionalization also enhanced the stability of biocatalysts over the change of pH and temperature. These observations were attributed to the role of the functional group in improvement of anchoring of laccase through covalent interactions. In the cases of Lac@Z(80) and Lac@Z(200), SiO2/Al2O3 ratio did not significantly affect the stability of the catalysts, while Lac@F-Z(80) was less susceptible to temperature and Lac@Z(200) showed higher pH stability. LC-MS analysis was also conducted and showed that the main compounds produced from biodegradation of acid orange-7 dye were 4-aminobenzenesulfonic acid, 2-amino-1-naphthol, and 1-amino-2-naphthol, 1,4-naphthoquinone, and 2-naphthol.