Response surface methodology mediated optimization of diclofenac and norfloxacin biodegradation using laccase immobilized on metal–organic frameworks

Abstract

In this work, laccase immobilized on a zeolitic imidazolate framework (Lac-ZIF) is used as a biocatalytic composite to decontaminate pharmaceutically active compounds (PhACs): diclofenac (DFC), and norfloxacin (NOR). A central composite face (CCF) design was used, and operational parameters were optimized using a quadratic response surface methodology (RSM) regression model, resulting in pH 6.4, 10 mg Lac-ZIF dosage, 10.4 mg L−1 initial concentration, and 8 h contact time. The model proved viable and effective for application in this study, giving predictions of 93.9 and 95.1% removal efficiencies of DFC and NOR, which were confirmed by actual experimental results with high accuracy. The Lac-ZIF revealed enhanced thermal stability with subsequently higher deactivation energies (Ed) than the free form of laccase. Additionally, the application of the biocatalyst in the treatment of real water samples, outperformed the free laccase by approximately 1.5 folds. Furthermore, the Lac-ZIF preserved 79 and 83% residual removal efficiencies after 6 cycles of reuse, with enhanced storage stabilities of 87.2 and 91.1% efficacies at 25 days for storage for DFC and NOR elimination, respectively. This study, therefore, demonstrates the potential of laccase immobilized on ZIFs for efficient biodegradation of DFC and NOR, which can be exploited for the remediation of wastewater containing PhACs.