Bio-assisted synthesized Ag(0) nanoparticles stabilized on hybrid of sepiolite and chitin: efficient catalytic system for xanthene synthesis.

In this work, with the use of two natural compounds, chitin and sepiolite clay, a novel covalent hybrid is fabricated and applied as a support for the stabilization of silver nanoparticles with the aid of Kombucha extract as a natural reducing agent. The resultant catalytic system, Ag@Sep-N-CH, was characterized via XRD, TEM, FTIR, ICP, SEM, TGA, UV-Vis and BET. It was found that fine Ag(0) nanoparticles with mean diameter of 6.1 ± 1.8 nm were formed on the support and the specific surface area of the catalyst was 130 m2 g-1. The study of the catalytic performance of Ag@Sep-N-CH for catalyzing synthesis of xanthenes in aqueous media under mild reaction condition confirmed that Ag@Sep-N-CH exhibited high catalytic activity and could promote the reaction of various substrates to furnish the corresponding products in high yields. Moreover, the contribution of both chitin and sepiolite to the catalysis has been affirmed. It was found that hybridization of these two components led to synergistic effects and consequently improved the observed catalytic activity. Notably, the catalyst was recyclable up to several reaction runs.

Biocompatible starch-halloysite hybrid: An efficient support for immobilizing Pd species and developing a heterogeneous catalyst for ligand and copper free coupling reactions.

Combining the exceptional features of halloysite and starch, a unique hybrid was synthesized based on conjugation of amine-functionalized starch with Cl-halloysite nanoclay followed by coordination of Pd (II) acetate. The resultant hybrid catalyst, Pd@Hal-SA, was used as a heterogeneous catalyst for promoting copper and ligand-free coupling reactions under mild reaction condition. The catalyst exhibited high catalytic activity and recyclability (up to 10 reaction runs) with slight loss of the catalytic activity that stemmed from slight Pd leaching. The comparison of the catalytic activity of Pd-Hal, Pd-SA and Pd@Hal-SA confirmed the superior performance of the latter, indicating the contribution of two components, SA and Hal to the catalysis. Moreover, the catalytic activity of Pd@Hal-SA was higher than that of Pd@Hal + SA, implying that the use of hybrid system was more efficient that use of individual components in a separated form, due to the synergism between SA and Hal.