Effects of shape-controlling cationic and anionic surfactants on the morphology and surface resonance plasmon intensity of silver@copper bimetallic nanoparticles

Abstract

Cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as a soft template to determine the morphology of silver@copper bimetallic nanoparticles. The subsequent addition of ascorbic acid to the Ag+, Cu2+ and surfactants solutions, leads to the formation of prefect transparent pale yellow color with in 5 min at ca. 409 nm. The visual observations and UV–visible spectra reveal that the color (pale yellow, dark brown, and wine red), surface resonance plasmon (SRP) intensity and shape of the spectra depends on the Ag+/Cu2+ molar ratio, [CTAB], and reaction time. Sub-, post- and dilution micellar effects are accountable to the fast and slow nucleation and growth processes. The morphology, SRP and rate constants for the formation of silver@copper decrease with increasing [CTAB]. The typical optical properties were dominated by the silver metal. The absence of SRP peaks at ca. 425 nm, 590 nm and 800 nm ruled out the possibility to the formation of AgNPs, CuNPs and CuO, respectively. Transmission electron microscopy (TEM) also confirms the formation of silver@copper nanoparticles. The pseudo-first order rate constants, activation energy, enthalpy of activation and entropy of activation were calculated and discussed for the degradation of methyl orange. The mole fraction of XAg = 0.50 and XCu = 0.499 were calculated in silver@copper.