Polysaccharide-based superporous hydrogel embedded with copper nanoparticles: a green and versatile catalyst for the synthesis of 1,2,3-triazoles†
In this contribution, we a report a facile synthesis and stabilization of copper nanoparticles (CuNPs) in a superporous hydrogel based on chitosan (Cs) and poly(vinyl alcohol) (PVA). The functional groups of Cs and PVA stabilized the CuNPs and, as a result, several properties (e.g. thermal, morphological and liquid uptake) of the final materials exhibited remarkable improvements in terms of stability and catalytic activity. The metallic nature of CuNPs was confirmed by XRD and XPS analyses. From the XRD data, the Cu nanoparticle size was estimated to range from 3 to 7 nm. Moreover, EDS mapping analysis revealed that the CuNPs are homogeneously distributed throughout the hydrogel surface. The Cs/PVA-CuNP hydrogel was found to be an excellent catalyst for the synthesis of 1,2,3-triazoles using phenyl azide and phenylacetylene as model substrates under mild optimized conditions (>90% yield). Reuse studies revealed that this original CuNP-containing catalyst can be employed in at least 5 consecutive cycloaddition reactions without demonstrating a clear loss of efficiency. Moreover, the copper leaching from the hydrogel matrix was negligible during these consecutive reactions under the investigated conditions. The Cs/PVA-CuNP hydrogel could also efficiently catalyze cycloaddition reactions involving different substituted azide and alkyne precursors.