Formulation of laccase nanobiocatalysts based on ionic and covalent interactions for the enhanced oxidation of phenolic compounds

Abstract

Oxidative biocatalysis by laccase arises as a promising alternative in the development of advanced oxidation processes for the removal of xenobiotics. The aim of this work is to develop various types of nanobiocatalysts based on laccase immobilized on different superparamagnetic and non-magnetic nanoparticles to improve the stability of the biocatalysts. Several techniques of enzyme immobilization were evaluated based on ionic exchange and covalent bonding. The highest yields of laccase immobilization were achieved for the covalent laccase nanoconjugates of silica-coated magnetic nanoparticles (2.66 U mg-1 NPs), formed by the covalent attachment of the enzyme between the aldehyde groups of the glutaraldehyde-functionalized nanoparticle and the amino groups of the enzyme. Moreover, its application in the biotransformation of phenol as a model recalcitrant compound was tested at different pH and successfully achieved at pH 6 for 24 h. A sequential batch operation was carried out, with complete recovery of the nanobiocatalyst and minimal deactivation of the enzyme after four cycles of phenol oxidation. The major drawback associated with the use of the nanoparticles relies on the energy consumption required for their production and the use of chemicals, that account for a major contribution in the normalized index of 5.28 × 10-3. The reduction of cyclohexane (used in the synthesis of silica-coated magnetic nanoparticles) led to a significant lower index (3.62 × 10-3); however, the immobilization was negatively affected, which discouraged this alternative.