A ‘green’ chitosan–silver nanoparticle composite as a heterogeneous as well as micro-heterogeneous catalyst

Abstract

In this paper, we report on the catalytic activity of a new metal nanoparticle-polymer composite consisting of Ag nanoparticles (NPs) and environmentally friendly ('green') chitosan. The polymer (chitosan) not only acted as the reducing agent for the metal ions, but also stabilized the product NPs by anchoring them. The majority of the particles produced in this way had sizes less than 5 nm. The catalytic activity of the composite was investigated photometrically by monitoring the reduction of 4-nitrophenol (4NP) in the presence of excess NaBH(4) in water, under both heterogeneous and micro-heterogeneous conditions. The reaction was first order with respect to the concentration of 4NP. We also observed that the apparent rate constant, k(app), for the reaction was linearly dependent on the amount of Ag NPs present in the composite. Moreover, the turn-over frequency (TOF) of the catalyst was found to be (1.5 ± 0.3) × 10(-3) s(-1), when the reaction was carried out under heterogeneous conditions. The Ag NPs in the composite retained their catalytic activities even after using them for ten cycles. Our observations also suggest that the catalytic efficiency under micro-heterogeneous conditions is much higher than under heterogeneous conditions. Thus the composite we have represents an ideal case of an environmentally friendly and stable catalyst, which works under heterogeneous as well as micro-heterogeneous conditions with the advantage of nanoscopic particles as the catalyst.

Natural reducing agents for electroless nanoparticle deposition: Mild synthesis of metal/carbon nanostructured microspheres

“…The reduction rate of 4-nitrophenol is negligible in aqueous solutions of NaBH 4 , however, it is catalysed by the presence of noble metal nanoparticles [19,54,55]. Fig.…”

“…In order to achieve this goal, several research groups have focused on developing supported Ag nanoparticles, e.g. Ag/polysaccharide [16,19], Ag/graphene [20] or Ag/polymer [18] nanocarrier composites, improving transport and modulating aggregation of Ag nanoparticle active centres.…”

Silver Nanoparticles – Universal Multifunctional Nanoparticles for Bio Sensing, Imaging for Diagnostics and Targeted Drug Delivery for Therapeutic Applications

“…Various reagents have been reported to serve as stabilizing agent. A number of reports adjusted the shape and size of silver nanoparticles using capping agents such as dendrimer, (Esumi et al, 2004) chitosan, (Murugadoss and Chattopadhyay, 2008) ionic liquid, ) and poly(vinylpyrrolidone) (PVP) (Sun and Xia, 2002), based on controlling the growth of silver nanoparticles through reaction confinement within the matrix or through preferential adsorption on specific crystal facets. Most of these methods are extremely expensive and they also involve the use of toxic, hazardous chemicals which are not environmental friendly.…”

Microwave-assisted synthesis of anisotropic gold nanocrystals in polymer matrix and their catalytic activities

“…On the other hand, Gronnow et al [30] have used an expanded starch-supported Pd catalyst with high activity for Suzuki, Heck and Sonogashira reactions. Among the metal NPs, Ag NPs are known to be efficient catalysts for the reduction of organic dyes [31] and also for the reduction of 4-nitrophenol (4NP) to 4-aminophenol (4AP), [32][33][34][35] etc. Gold nanocrystals with different shapes (triangular, branch-like and rod-shaped) have been used as reusable heterogeneous catalysts to reduce 2,4,6-trinitrophenol (TNP) to 2,4,6-triaminophenol (TAP) by NaBH 4 .…”