Laccase-Carbon nanotube nanocomposites for enhancing dyes removal

Adsorption can effectively remove recalcitrant micro-pollutants in wastewater. However, its industrial application is constrained by the adsorption saturation. This work introduces a novel technique to directly immobilize the laccases onto the CNTs (Laccase-Carbon nanotubes) to improve its adsorption performance. Comprehensive investigations were carried out to compare and understand the adsorption performance at various operational conditions for Carbon nanotube and Laccase-Carbon nanotubes. By calculating the adsorption thermodynamics, adsorption kinetics and particle diffusion kinetics, the removal improvement mechanisms were revealed. The results showed that Laccase-Carbon nanotubes performed much better regarding the dye removal rate (96% within 3 h) and better stability than Carbon nanotubes (84% within 3 h), under various operating conditions (carbon nanotube concentration (0.02–0.08 g/L), laccase ratio (0.25–1.25), dye concentration (10–60 mg/L), temperature (15–35 °C), and rotating speed (0–250 rpm)). Besides, the isothermal adsorption model and adsorption kinetic indicated that Laccase-carbon nanotubes possessed greater adsorption capacity than carbon nanotubes, which may maybe due to the fact that adsorbed dyes onto carbon nanotubes were timely eliminated by laccases, achieving regeneration of adsorption capacity. Moreover, based on the particle diffusion kinetic, the diffusion rate of dyes onto the surface or into the internal of Laccase-Carbon nanotubes was clearly higher than that of carbon nanotubes. Additionally, Scanning Electron Microscope, BET-specific surface area and Fourier Transform Infrared Spectroscopy were utilized to observe the microstructure of enzyme immobilization. This biomimetic nanocomposite sheds light upon conventional wastewater treatment processes for recalcitrant micro-pollutants.