Stabilization of strong quantum confined colloidal bismuth nanoparticles, one-pot synthesized at room conditions

This report outlines the synthesis of zerovalent bismuth nanoparticle (ZV-Bi NP) colloidal dispersions, in dimethyl sulfoxide. For the general preparation pathway of these colloids, a commercial bismuth(III) salt and also a conventional reducing agent were used. All reactions took place immediately and under mild conditions. Stable, for more than three months, under room conditions, ZV-Bi NP colloids are obtained when using sodium citrate and a deficit of the reducing agent respect to the bismuth salt. This reaction mixture yields small, well-faceted, and also quasi-spherical crystalline particles, with an average size of 3.3 nm, SD of 1.0 nm, determined by HR-TEM. These are the smallest ZV-Bi NPs, synthesized by a fast and straightforward colloidal method, found in the literature. Indirect and direct energy gaps were discovered in the near-infrared spectral range (1400-1600 nm) of the ZV-Bi NPs, indicating the displacement of the conduction and valence bands due to the strong quantum confinement; bulk bismuth itself is a semimetal. This is the first time that energy gaps of quantum confined ZV-Bi NPs are found at room conditions. The dry ZV-Bi NP powders that precipitated from the colloids are totally stable in storage, at room conditions, for more than three years.