Synthesis, optical properties, stability, and encapsulation of Cu-nanoparticles

•Hexahedral starch capped Cu-nanoparticles synthesized for the first time.•Brownish-red color copper sols were unstable in absence of starch.•Addition of KI–I2 reagent does not replace the nanoparticles from the inner helix of amylose.•Concentrations of starch has no effect on the nucleation and growth processes.

Starch-capped copper nanoparticles (CuNPs) were prepared by a chemical reduction method using hydrazine, copper sulfate and starch as reducing, oxidizing and stabilizing agents, respectively, for the first time at room temperature. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction patterns (EDX), X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR) spectroscopy, thermo-gravimetric analysis (TGA), and ultraviolet–visible spectroscopy. The effect of [starch], [hydrazine] and [copper sulfate] on the optical properties of CuNPs were studied by UV–visible spectrophotometrically. The hydrazine concentrations have large impact on the surface Plasmon resonance absorbance, nature of the reaction time curves and reaction rates decreases with [hydrazine]. Starch concentrations have no effect on the path of the CuNPs formation. The hexahedral with some irregular shaped CuNPs were formed in presence of starch with diameter 900 nm. Starch acted as a stabilizing, shape-directing and capping agent during the growth processes. The KI–I2 reagent could not replace CuNps from the inner helical structure of starch.

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