Chitosan as an active support for assembly of metal nanoparticles and application of the resultant bioconjugates in catalysis.

Metal nanoparticle-chitosan (NPs-chitosan) bioconjugates were formed by exposure of chitosan to an aqueous solution of metal salts under thermal treatment. The metal nanoparticles that are formed strongly bound to chitosan, which encouraged us to investigate their catalytic performance. It was demonstrated that the metal NPs-chitosan bioconjugates functioned as effective catalysts for the reduction of 4-nitrophenol in the presence of NaBH(4), which was monitored by means of spectrophotometry as a function of reaction time. The silver NPs-chitosan bioconjugates exhibited excellent catalytic activity and were reusable for up to seven cycles. In contrast, the gold NPs-chitosan catalyst displayed poor catalytic activity, even in the second cycle. A highlight of our approach is that chitosan simultaneously acts as an active support for the synthesis and assembly of nanoparticles, and the resultant bioconjugates bear the advantage of easy separation from the reaction medium. Copyright 2009 Elsevier Ltd. All rights reserved.