Synthesis of Bi2S3 Nanostructures from Bismuth(III) Thiourea and Thiosemicarbazide Complexes

Rod-shaped nanostructures of Bi2S3 were synthesized by the solution decomposition of the two new bismuth(III) complexes [Bi6(pydc)8(Hpydc)2(tu)8] (1) and {[Bi2(pydc)3(tsc)(H2O)2]·H2O}∞ (2) (H2pydc = 2,6-pyridinedicarboxylic acid also known as dipicolinic acid; tu = thiourea, tsc = thiosemicarbazide). They were obtained by treatment of Bi2O3 with dipicolinic acid in the presence of the sulfur-containing ligands. The complexes were characterized with the aid of elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. The dipicolinate anions behave as tridentate ligands toward Bi(III), but two modes of coordination are found. In both cases the ligand serves as a pincer ligand O,N,O-bonded to one bismuth(III) center, but it can also function as a bridging ligand through one carboxylate group that assembles into hexanuclear molecules (1) or a polymeric chain (2). The air-stable complexes 1 and 2 have been used as starting materials in the preparation of bismuth sulfide nanoparticles (NPs) in the presence of different surfactants. Decomposition of 1 and 2 gave Bi2S3 in all cases, but addition of a small amount of 1-dodecanethiol (DT) or 1-octadecanethiol (OT) at 120 °C resulted in better crystallite growth with the observation of nanorods up to several hundreds of nanometers in length. These were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of various reaction conditions on the shape and size of the nanocrystals is discussed. The high resolution (HR) TEM images reveal a number of linear and planar crystal defects and atomic distortions that account for the splitting of bismuth sulfide nanocrystals as observed previously. The growth mechanism is believed to involve decomposition of the precursors and formation of Bi2S3 seeds, followed by the preferential [001] growth of larger particles. Crystal splitting caused by defects and atomic distortions as well as Ostwald ripening processes play important roles in shaping the morphologies of the final Bi2S3 nanostructures.