Synthesis of shaped Pt nanoparticles using common anions or small molecules as shape-directing agents: observation of a strong halide or pseudo-halide effect

Abstract

Chemical reduction of Pt(II) and Pt(IV) salts by H₂, hydrazine, or borohydride ion, in the presence of common anions or small molecules is surveyed to discover shape-directing agents suitable for selective formation of Pt metal nanocubes or nanotetrahedra. Surfactants tested include a variety of amino acids, HSCH₂CO₂H, Ph₂PCH₂CO₂H, polycarboxylate species, such as glycolate or tartrate ion, and several common anions (including CF₃SO₃⁻, ClO₄⁻, NO₃⁻, CO₃²⁻, PO₄³⁻, SO₄²⁻, Cl⁻, Br⁻, or I⁻). Although carboxylate, chloride, bromide, carbonate, nitrate, perchlorate, phosphate, sulfate, or triflate ions show poor shape-directing influence, the presence of hydroxide and iodide ions gives an unexpected halide (or pseudo-halide) effect. Hydrogen reduction of [Pt(OH)₆]²⁻ ion at basic pH gives high yields of cubic Pt nanoparticles, while hydrogen reduction of [PtI₆]²⁻ ion at basic pH gives high yields of tetrahedral Pt nanoparticles.