Fabrication of monodisperse gold-copper nanocubes and AuCu-cuprous sulfide heterodimers by a step-wise polyol reduction

Abstract

Monodisperse gold-copper nanocubes and AuCu-cuprous sulfide (Cu1.96S) heterodimers were fabricated by a step-wise polyol reduction with the aid of oleylamine and 1-dodecanethiol. The geometric configuration was mediated by simply varying the Cu/Au atomic ratio: Au-Cu cubes with sizes of 6.4 and 4.3 nm were yielded at Cu/Au atomic ratios of 1/3 and 1/1, respectively; while AuCu-Cu1.96S heterodimer, consisting of a AuCu cube of 4.6 nm and a Cu1.96S sphere of 6.3 nm was obtained at Cu/Au atomic ratio of 3/1. Detailed structural analysis on the intermediate products, collected at different intervals during the synthesis, revealed that small-sized Au seeds formed at 423 K, followed by the growth of Cu and Cu1.96S crystals at 473 K. Oleylamine coordinated to Au3+ and Cu2+ and thus mediated the particle size; while 1-dodecanethiol bonded to Au3+ and directed the cubic morphology. Excessive Cu2+, at the Cu/Au atomic ratio of 3/1, interacted with 1-dodecanethiol and formed Cu1.96S spherical particle that epitaxially grew over the AuCu cube, resulting in a heterodimer structure. Due to the enriched surficial Cu atoms and their electronic interactions with Au atoms, Au-Cu nanocubes and AuCu-Cu1.96S heterodimers showed pronounced activities for the catalytic reduction of 4-nitrophenol to 4-aminophenol with NaBH4 at 298 K.