Degradation of Rhodamine B Wastewater Using Laccase-Immobilized Floating CN-Doped Copper Alginate Beads

The environmental challenges posed by printing and dyeing wastewater are becoming increasingly severe. Rhodamine B (RhB), in particular, is a typical refractory pollutant due to its stable chemical structure and significant biotoxicity. To address the common issues in photoenzyme-coupled catalytic systems, such as difficulties in solid–liquid separation, low light utilization efficiency, and poor enzyme stability, this study developed an innovative floating spherical photoenzyme hybrid catalyst (SA-BT/CN-LC). Using copper alginate (SA) microspheres as a carrier, laccase (LC) and graphite-phase carbon nitride (CN) were coimmobilized via an embedding method, enabling efficient synergistic photoenzymatic degradation. Radical trapping experiments demonstrated a pronounced synergistic effect between photocatalysis and enzymatic catalysis within the confined microenvironment of the microspheres. The relative contributions of active species to RhB degradation were identified as h+>·O2−>·OH>e−. After immobilization, the optimal pH for LC activity shifted from 3.0 to 4.0, and the optimal temperature increased from 40°C to 50°C, markedly enhancing its environmental adaptability. Under optimized conditions, i.e., 10 mg/L initial RhB, 50°C, and pH 5.0, a high degradation rate of 93.2% was achieved. The catalyst exhibited excellent reusability and stability, retaining 73.84% degradation efficiency after six consecutive cycles, owing to its unique floating spherical structure, which facilitates recovery and reduces enzyme leakage. This study provides an effective strategy to overcome the limitations of conventional powdered catalysts and enzyme leaching in continuous wastewater treatment applications.