Magnetically separable carbon capsules loaded with laccase and their application to dye degradation

Abstract

A synthetic method to generate uniform sub-micrometric magnetic mesoporous carbon capsules (diameter ∼440 ± 20 nm) made up of ferrite nanoparticles (size ∼18 nm) inserted inside the mesoporous shell (∼50 nm of thickness) is presented. The fabrication procedure consists of two steps: a) the synthesis of carbon capsules by using the porogen agent employed to create silica microspheres as a carbon source, and b) the incorporation of magnetic iron oxide nanoparticles inside the mesoporous shell. Although a large quantity of iron oxide nanoparticles is incorporated (∼30 wt%), the magnetic nanocomposite still retains a large and accessible porosity made up of mesopores in the 2–8 nm range. This magnetic composite was used to immobilize a valuable bulky industrial enzyme (laccase). The large amount of immobilized biomolecules, (∼1000 mg g⁻¹ of support) suggests that a considerable fraction of this substance is accommodated in the hollow core of the capsules. The catalytic activity of the immobilized laccase was demonstrated by the degradation of two anthraquinone dyes (i.e. Acid Green 25 and Remazol Brilliant Blue R). It was found that the immobilized enzyme retains its activity (>90%) even after multiple cycles and also after long storage times. The incorporation of ferrite nanoparticles greatly facilitates the manipulation of the immobilized biocatalyst, since it can be easily and quickly recovered from liquid media by the simple application of an external magnetic field.