Fig. 4: Removal performance and reusability of the laccase-assembled Cellulose-CD-MMT hydrogels, as well as degradation mechanisms and pathways of PAHs.

a Removal efficiency of Nap, Phe, and Pyr at 10, 80, 120 μg L⁻¹ by the laccase-assembled Cellulose-CD-MMT hydrogels (a sum of sorption and degradation), assembled laccase (net degradation), and free laccase. The net degradation efficiency of PAHs by the assembled laccase was investigated by inactivated assembled laccase as the control. Degradation of the three PAHs by the assembled- and free laccase followed the order Pyr < Phe < Nap, which aligns with the chemical stability increases with increasing benzene ring number, thereby decreasing degradability. b Removal kinetics of PAHs (80 μg L⁻¹) by the laccase-assembled Cellulose-CD-MMT hydrogels (a sum of sorption and degradation), assembled laccase (net degradation), and free laccase. Degradation efficiency of three PAHs by free laccase within 48 h was below 42.4%. This could be attributed to limited diffusion of the substrate PAHs, low substrate concentration near the laccase active site, and limited redox potential and electron transfer rate, resulting in limited reaction between the substrate and enzyme. Conversely, equilibrium for the net degradation of the PAHs by the assembled laccase was reached within 12 h. c Reusability of the laccase-assembled Cellulose-CD-MMT hydrogels for removal of PAHs (80 μg L⁻¹), and the hydrogels were recycled 10 times. d Degradation mechanism of PAHs by the assembled laccase. e Phe molecular structure with labeled atomic positions, the HOMO of Phe, and the distribution of electrophilic (\({f}_{A}^{-}\)) attacking sites based on compressed Fukui function (CFF). f Proposed degradation pathways of Phe by the assembled laccase. Bioconcentration factor (g, BCF, Log₁₀) and acute toxicity (h, Daphnia magna 48 h LC50, -Log₁₀, mol L⁻¹) of Phe and its intermediates via the Toxicity Estimation Software Tool (T.E.S.T. 5.1.2). For (a–c), data are presented as mean ± S.D. from three replicates (n = 3).