Aerosol synthesis of pure and Pt-doped ZnO particles using nitrate and pdda-Pt(IV) complex solutions

Abstract

Pure and Pt-doped ZnO nanophase particles were synthesized by ultrasonic spray pyrolysis. The particles were obtained through the decomposition of zinc nitrate and with a newly developed Pt(IV) complex with 1,3 -propylenediamine-NN'-diacetate tetradentate class ligand (pdda). The complex was characterized by elemental analysis, electronic absorption and infrared spectroscopy. The form of the determined complex structure {trans-[Pt(pdda)Br-2]center dot H2O} implies that Pt(IV) ion has a distorted octahedral coordination due to intramolecular N-H center dot center dot center dot Br interaction. The results of structural refinement (cell parameters, bond lengths, and ion occupancy) of ultrasonically derived pure and Pt-doped ZnO particles suggest either the formation of Zn-i interstitials or platinum ion incorporation into the ZnO lattice in octahedral interstitial positions, respectively. A well-crystallized hexagonal wurtzite structure of ZnO was pronounced in all investigated samples [JCPDS card 36-1415, Joint Committee on Powder Diffraction Standards, defined by International Centre for Diffraction Data (www.icdd.com)]. Phase determination also indicated the presence of a nitrate hydroxide hydrate phase (JCPDS card 24-1460), as a result of incomplete precursor decomposition and a spinel Zn2PtO4 phase (below 1.0 wt%) located in the boundary region for a Pt-doped ZnO sample. Based on x-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy analyses, it was shown that the different particle growing morphologies, which were either spheroidally or pyramidally shaped, were influenced by the precursor chemistry, processing parameters and the presence of platinum ions. The composite internal particle structure revealed by transmission electron microscopy and selected area electron diffraction analyses, implied that the secondary particles represent an assembly of primary particles sized under 60 nm aroused during the processes of nucleation, growth and aggregation. Both hexagonal and spheroidal shape of primary particles was evident. The particle morphology, primarily particle size and the mechanism of Pt4+ ion introduction into the ZnO cell was discussed based on the structural refinement and selected area electron diffraction analysis.