Impurity-driven simultaneous size and crystallinity control of metal nanoparticles.

Both the size and crystallinity should be optimized for practical applications utilizing metallic nanoparticles because they strongly influence the nanoparticles property. Herein a liquid phase chemical reduction method controls the defects (crystallinity) in metallic Cu nanoparticles simply and easily. Although the addition of an impurity substance, which cannot be thermodynamically alloyed with Cu, reduces the crystallinity of synthesized Cu nanoparticles, it also affects the deposition behavior, and consequently, the nanoparticle size changes unexpectedly. Therefore, a precise control of the synthesis condition is required to synthesize the nanoparticles having optimal size and crystallinity. To clarify the nanoparticle formation mechanism in an impurity-containing solution, the catalytic activity of the reductant and the redox potential change due to the metastable product are electrochemically evaluated to reveal the correlation between nanoparticle formation behavior and synthesis condition. Finally, the synthesis of two types of Cu nanoparticles, which have similar sizes but different crystallinities is demonstrated. This simple nanomaterial design approach to control the crystallinity and the interpretation of the deposition process in an impurity-containing condition should be widely applicable to metallic nanoparticle syntheses.