Di-n-hexadecyldithiophosphate (DDP) capped Cu nanoparticles were chemically synthesized in a two-phase system including tetrahydrofuran and saturated NaCl solution by using two-phase method. Various factors, which affected preparation of Cu nanoparticles were discussed systematically, and transmission electron microscopy (TEM) was used to analyze the effects of the amount of reducing agent, concentration of Cu^2＋, molar ratio of ammonium di-n-hexadecyldithiophosphate (ADDP) to Cu^2＋ on the size and distribution of the as-prepared Cu nanoparticles. The structure of Cu nanoparticles obtained under the optimal prepariation conditions was investigated by infrared spectroscopy (IR), X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The results showed that when pH value of solution was about 12, reaction temperature was above 30 ℃, molar ratio of NaBH₄/Cu^2＋ was between 8∶1 to 12∶1, concentration of Cu^2＋ was below 0.05 mol•L^－1, and molar ratio of ADDP/Cu^2＋ was 2∶1 and 2.5∶1, mono-dispersed and superfine DDP capped Cu nanoparticles were obtained. The prepared Cu nanoparticles consist of an amorphous nano-Cu core and a layer of DDP chemically absorbed on its surface, and the structure of modifier DDP was not changed after reaction.

Key words: ammonium di-n-hexadecyldithiophosphate (ADDP), two-phase method, TEM, Cu nanoparticle