In situ synthesis of well-dispersed silver nanoparticles from silver nanoclusters hydrogel for catalytic reduction of 4-Nitrophenol

Facile, efficient and steady immobilization of metal nanoparticles upon various matrixes is an interesting topic in materials chemistry and heterogeneous catalysis. This study reports a facile in situ method for the synthesis and immobilization of silver nanoparticles (Ag NPs) from silver nanoclusters (Ag NCs) in the hydrogel at room temperature. Ag₉-NCs ((NH₄)₉[Ag₉(mba)₉], H₂mba = 2-mercaptobenzoic acid) acted as both gelator and silver source which combined with Ba(NO₃)₂ to construct hydrogel while sodium borohydride (NaBH₄) was used as a typical reductant during the synthesis process to generate Ag NPs in situ. As a result, Ag NPs with mean diameter of 1.96 nm were conveniently synthesized and firmly immobilized on the nanofibers of Ag₉-NCs/Ba(NO₃)₂ hydrogel without sophisticated manipulation. Accompanied with the reduction process, the coordination interaction combined with the hydrogen bonding, π-π stacking and hydrophobic interactions drove the assembly of Ag NPs/Ag₉-NCs/Ba(NO₃)₂. Moreover, the Ag NPs exhibited good catalytic activity toward the reduction of 4-nitrophenol (4-NP) and could be easily recovered and reused for more than eight cycles owing to the high stability based on hydrogel. This work provides an innovative strategy for metal NCs which could be highlighted as the promising candidates to be used as supramolecular assembly templates and metal sources for in situ preparation of metal nano-catalysts.