Promotion of SERS and catalytic activities with bimetallic and ternary concave nanolayers

Abstract

A seed growth process accompanied by a galvanic replacement reaction (etching and alloying) using CTAB/HAuCl₄/AgNO₃/ascorbic acid was developed to fabricate silver nanocubes with concave AuAg nanolayers. The solid nanostructure consisted of a concave face of the inner Ag solid counterpart with a hole surrounded by an AuAg nanowall. We found that the CTA⁺ ions played a vital role in the adsorption of Au(I)/CTA⁺ micelles selectively at the {100} facets to trigger galvanic replacement etching. Meanwhile, the reaction involving AgNO₃ helped to switch the co-reduction of metal atoms from the [110] sites to the [100] vector and favored AuAg co-reduction of atoms along the {100} vector for concave AuAg nanolayer formation. Such AuAg atoms at the concave layer induced strong charge transfer-based surface-enhanced Raman scattering (SERS) when thiol molecules were bound to the active atoms and enabled the detection of the toxin malachite green at the fM level via physisorption. These highly active atoms at the concave facets aided superior electron-transfer catalysis. After etching with H₂O₂ to produce pure-Ag-removed and concave AuAg nanowalls, the efficiencies of the SERS and catalytic performances were degraded due to the decrease in the active atom density. This reaction strategy of simultaneous etching and co-reduction could be further extended to the trimetallic AuAg:Pd concave nanocomposite synthesis to improve the hydrogenation reaction thus obtaining a very high kinetic constant.