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