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

Monodisperse gold-copper nanocubes and AuCu-cuprous sulfide (CuS) 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-CuS heterodimer, consisting of a AuCu cube of 4.6 nm and a CuS 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 CuS crystals at 473 K. Oleylamine coordinated to Au and Cu and thus mediated the particle size; while 1-dodecanethiol bonded to Au and directed the cubic morphology. Excessive Cu, at the Cu/Au atomic ratio of 3/1, interacted with 1-dodecanethiol and formed CuS 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-CuS heterodimers showed pronounced activities for the catalytic reduction of 4-nitrophenol to 4-aminophenol with NaBH at 298 K.