Synthesis of Magnetic Zn–Al LDHs Immobilized Cellulase for Enhanced Enzyme Activity and Congo Red Removal From Wastewater

A reusable magnetic cellulase (CEL) immobilized composite, MF@CS-LDHs@CEL, was developed by integrating α-FeOOH–Fe 3 O 4 magnetic nanoparticles (MF), chitosan (CS), and zinc–aluminum layered double hydroxides (LDHs) with CEL for the removal of Congo red (CR) from aqueous media. The optimal CEL immobilization conditions were an initial enzyme concentration of 3 mg/mL, a glutaraldehyde concentration of 4%, a cross-linking time of 2 h, an immobilization pH of 5.0, and an immobilization temperature of 50°C. Under optimized operational conditions (50 mL of 100 mg/L CR solution, 50°C, pH 5.0, 300 min reaction time, and 30 mg of adsorbent), the experimental maximum adsorption capacity of MF@CS-LDHs@CEL for CR reached 140.64 mg/g. The material maintained an 87.66% CR removal efficiency even after eight consecutive reuse cycles. The adsorption data were best described by the Redlich–Peterson isotherm ( R 2 = 0.99591) and pseudo-second-order kinetic models ( R 2 > 0.999), suggesting heterogeneous adsorption involving strong adsorbate–surface interactions. The removal of CR was primarily associated with hydrogen bonding, electrostatic interactions, and anion-exchange processes acting in combination. In addition, MF@CS-LDHs@CEL exhibited favorable adsorption performance, convenient magnetic separation, and good reusability, demonstrating its potential as an adsorbent for treating dye-containing wastewater. Graphical A recyclable magnetic cellulase composite, MF@CS-LDHs@CEL, is developed for Congo red (CR) removal from wastewater. It reaches an adsorption capacity of 140.64 mg/g and retains 87.66% removal after eight reuse cycles. CR uptake is mainly associated with hydrogen bonding, electrostatic interactions, and anion exchange, while magnetic separation allows straightforward recovery and reuse.