Preparation and characterization of epoxy-functionalized magnetic chitosan beads: laccase immobilized for degradation of reactive dyes

Abstract

Cross-linked magnetic chitosan beads were prepared by phase-inversion technique in the presence of epichlorohydrin under alkaline condition, and used for covalent immobilization of laccase. The activity of the immobilized laccase on the magnetic chitosan was about 260 U (g/dry beads) with an enzyme loading of about 16.33 +/- 0.39 mg [(g/dry beads) mg/g]. Kinetic parameters, V (max) and K (m) values were determined as 21.7 U/mg protein and 9.4 microM for free enzyme, and 15.6 U/mg protein and 19.7 microM for the immobilized laccase, respectively. The operational and thermal stabilities of the immobilized laccase were improved compared to free counterpart. The immobilized laccase was operated in a batch reactor for the decolorization of reactive dyes from aqueous solution. The laccase immobilized on magnetic chitosan beads was very effective for removal of textile dyes from aqueous solution which creates an important environmental problem in the discharged textile dying solutions.

Immobilization of Laccase on Magnetic Carriers and Its Use in Decolorization of Dyes

“…In contrast to our results, immobilization mostly causes pH optimum to move about pH 0.5 higher 11,15,27,28 . Decrease in activity from pH optimum to pH 2.5 and 6.2 is similar as in articles 10,11 . An enzyme may slightly change conformation after immobilization, and this could be the reason the pH optimum changes.…”

“…Immobilized enzyme on magnetic microparticles retained 47 % of initial activity after nine repetitions and error bars ranged between values of 4 % and 6 %. In other articles, laccase immobilized on magnetic nanoparticles had higher activity after nine repetitions (about 85 %) 10,15,23 . Immobilization depends on many things (carrier, carrier surface, immobilization method or structure of enzyme).…”

“…This phenomenon could have been caused by accumulation of the product of the decolorizing reaction, which inhibited the laccase reaction. It could have been also caused by loss of concentration gradient of dye, therefore more difficult movement of dye to laccase 10 . Chitosan composites also adsorb metal ions 41 .…”

“…Low stability of laccase, when used in wastewater treatment, as well as the enzyme's price, discourage its use. Using relatively pure enzyme with good specific activity may lower the cost 10,11 . These problems can be resolved by immobilization of enzyme on a suitable carrier.…”

Chitosan: The Most Valuable Derivative of Chitin

“…Grafting chitosan is a common way to improve chitosan properties such as formation of inclusion complexes [99], bacteriostatic effect [100], or to enhance adsorption properties [101,102]. Although the grafting of chitosan modifies its properties, it is possible to retain some interesting characteristics such as mucoadhesivity [103], biocompatibility [104,105] and biodegradability [106]. Many routes for chitosan grafting have been investigated, such as ring opening polymerization of lactides.…”