Laccase–mediator co-immobilized doped-HKUST-1 cellulose composite beads and their application for the biodegradation of carbazole

Abstract

The co-immobilization of laccase and a mediator is essential for water treatment due to the fact that the free laccase and mediator cannot be recovered and reused simultaneously. Herein, a spherical solid biocatalyst, Lac@Ce-GMA-Cu-DA@AS, was prepared via the co-immobilization of laccase and acetosyringone mediator in a functionalized cellulose composite doped with HKUST-1. The Lac@Ce-GMA-Cu-DA@AS microbeads exhibited higher catalytic activity, better reusability and superior degradation efficiency for the substrate compared to the undoped HKUST-1. Specifically, 96% degradation efficiency of carbazole solution with a concentration of 20 mg L⁻¹ was achieved after treatment with 1.0 g (wet weight) of Lac@Ce-GMA-Cu-DA@AS beads for 8 h under the conditions of 30 °C, pH 5.0, and 20 mM ionic strength. Based on the analysis and identification of the degradation intermediates of carbazole, the possible pathways for the degradation of carbazole by the Lac@Ce-GMA-Cu-DA@AS microbeads were proposed. It was found that the toxicity of the carbazole solution was lower after treatment than the original. Natural polymeric cellulose composite doped with HKUST-1 displayed an excellent performance for co-immobilizing laccase–mediator and can provide a practical new approach for the degradation of carbazole pollutant in water.