Preparation of organic fluids with high loading concentration of Ag 2 S nanoparticles using the extractant Cyanex 301

Stable organic fluids containing Ag2S nanoparticles modified by Cyanex 301 (di-(2,4,4-trimethylpentyl) dithiophosphinic acid) have been prepared directly in alkane via a solvent extraction synthesis method. The organic fluids are so stable that the nanoparticles do not precipitate at room temperature even after more than one year even when the content of Ag2S nanoparticles is as high as 42 g L−1. The Ag2S nanoparticles are characterized by XRD, TEM, IR, UV-vis and TG-DSC, showing that the particles are well modified by the extractant Cyanex 301. The obtained nanoparticles can be well dispersed again in organic solvents and the new fluids are also very stable. The loading concentration of Ag2S nanoparticles prepared through the extraction synthesis method is much higher than that prepared via a two-step (preparation and dispersion) synthesis method and found to decrease with an increase of the solvent polarity. The tribological properties of the Ag2S nanoparticles modified by Cyanex 301 in liquid paraffin (LP) for a steel–steel friction pair are evaluated on a four-ball machine, showing that such a fluid, LP + Ag2S, has a low friction coefficient.