Modified chitosan as an economic support for hematin: Application in the decolorization of anthraquinone and azo dyes

Abstract

Azo and anthraquinone dyes have been successfully decolorizedusing enzymatic and biomimetic homogeneoussystems.1,2 Hematin, a horseradish peroxidase (HRP) biomimetic, immobilized on chitosan via glutaraldehyde couplingwas ableto decolorize Alizarin Red S and Orange II solutions. A Doehlert experimental design and response surface analysis was appliedto determine conditions for optimalmass of catalyst and catalytic efficiency of the immobilization procedure.RESULTS: The catalysts with supported hematin showed 33% activity (relative to homogeneous hematin as 100%) in decolorizationreactions. After six reuses the catalytic activity was maintained at 60% of the initial one. Hematin anchoring to chitosanwithout alteration of the iron-porphyrin ring was confirmed by ICP, FTIR and UV/visible spectrophotometric methods. Inaddition, the effect on hematin activity in the decolorization of aminopropyltriethoxysilane (APTS) as a ?spacer arm? betweenhematin?glutaraldehyde and chitosan was studied.CONCLUSIONS: An economical heterogeneous catalyst alternative to HRP has been obtained. The spacer arm improves thecatalyst ́s performance with activities as high as 57% relative to homogeneous hematin. These results support the notion thatthe activity loss of supported hematin is caused by the restricted access to Fe of the bulky phenolic dyes.