Synthesis of highly-branched Au@AgPd core/shell nanoflowers for in situ SERS monitoring of catalytic reactions

Alloy and small size nanostructure s are favorable to catalytical performance,but not to surface-enhanced Raman spectroscopy(SERS) applications.Integrating SERS and catalytic activity into the nanocrystals with both alloy and small size structures is of great interest in fabrication of SERS platform to in situ monitor catalytical reaction.Herein,we report a facile method to synthesize Au@AgPd trimetallic nanoflowers(Au@AgPd NFs) with both SERS and catalytic activities,through simultaneous selective growth of Ag and Pd on Au core to form highly-branched alloy shell.These nanocrystals have the properties of small sizes,defects abundance,and highly-dispersed alloy shell which offer superior catalytic activity,while the merits of monodisperse,excellent stability,and highly-branched shell and core/alloy-shell structure promise the enhanced SERS activity.We further studied their growth mechanisms,and found that the ratio of Ag to Pd,sizes of Au core,and surfactant cetyltrimethylammonium bromide together determine this special structure.Using this as-synthesized nanocrystals,a monolayer bifunctional platform with both SERS and catalytical activity was fabricated through selfassembly at air/water interface,and applied to in situ SERS monitoring the reaction process of Pdcatalyzed hydrogenation of 4-nitrothiophenol to 4-aminothio p henol.

Existence of a Heterogeneous Pathway in Palladium-Catalyzed Carbon–Carbon Coupling Reaction:Evidence from Ag@Pd_(3)Cu Intermetallic Nanoplates

Palladium(Pd)-catalyzed cross-coupling reaction is a widely studied process with significant economic interest and represents one of the most successful nanocatalytic examples.Owing to the observed leaching of Pd ions from both monometallic and short-range-ordered Pd bimetallic nanocatalysts,there is ambiguity regarding whether the coupling reaction has a heterogeneous component.Herein,facilitated by theoretical calculations,we discovered that the Pd ion leaching-free Pd_(3)Cu intermetallic compound was able to catalyze the cross-coupling reaction heterogeneously with activity comparable with that of Pd ions leached from monometallic Pd.The observation that Pd_(3)Cu acted as a heterogeneous catalyst was further confirmed by the reaction-promoting effect of hot electrons generated by the Ag core in Ag@Pd_(3)Cu nanoplates upon photon adsorption and could only participate in the reaction on the surface of the nanocatalyst.Additionally,it demonstrated experimentally the effectiveness of the heterogeneous route in the coupling reaction.This study shows that the combination of plasmonic catalysis and intermetallic compounds is a promising strategy for designing robust nanocatalysts to synthesize value-added chemicals.