One pot synthesis of nano Ag in calcium alginate beads and its catalytic application in p‐Nitrophenol reduction with kinetic parameter estimation and model fitting

Abstract

In this work, one step process of synthesis of silver nanoparticles (Agnp) embedded in insitu formed calcium alginate (CA) beads is stated. CA, formed from the reaction between sodium alginate and calcium hydroxide, acts as reducing and stabilizing agent as well as support for nanoparticles. The reaction mechanism for the formation and stabilization of Agnp is proposed where the vicinal dihydroxy groups of alginate are assumed to act as the reducing agent for Ag + to Ag. Transmission electron microscopy (TEM), x-ray diffraction (XRD), UV-vis spectroscopy, field emission scanning electron microscopy (FESEM), and atomic absorption spectroscopy (AAS) were used to characterize the Agnp. The formation of spherical nanoparticles with average size range of 4-5 nm was confirmed by TEM. Catalytic activity of this nano silver-calcium alginate (Agnp-CA) composite was evaluated in the reduction of pnitrophenol. Concentrations of sodium alginate, calcium hydroxide, and AgNO 3 are found to be the parameters that critically affect the synthesis of Agnp. The efficacy of the catalyst is expressed on the basis of suitable reaction parameters. Both pseudo-homogeneous and heterogeneous kinetic models are proposed for the reaction to find the best model and the Eley-Riedel model is found to fit well with the experimental data. The novelty of this work is that the tandem process of CA bead formation, Agnp formation, and Agnp entrapment in CA have been transformed into a single-step process. Moreover, elaborations of each step of the ionic mechanisms of Agnp formation and p-NP reduction with Agnp and the establishment of a heterogeneous kinetic model for the reaction are reported for the first time here.

Experimental Advances in the Real-Time Recording of Cross-Linking Alginate In Situ Gelation: A Review

“…It critically depends on the physicochemical characteristics of the reactants, such as their concentration, the kind of cations, and the molecular weight, Mw, and M/G of alginate, as shown in Figure 2 [18]. The divalent metals bind mainly with G-and MGsequences of the polymer backbone through physical cross-linking [19][20][21]. The dimerization of alginate chains is induced, and multimer structures are formed following the zipper mechanism [22,23].…”