Síntese rápida por precursores poliméricos e caracterização de ZnO nanocristalino dopado com Co e Cu

Abstract

Zinc oxide (ZnO) is a highly attractive material due to its electronic and photocatalytic properties. It is a versatile semiconductor with a band gap of 3.4 eV, which can be applied in photovoltaic activities, photocatalytic, among others, besides serving as substrate for the growth of other semiconductors. In this way, zinc oxide has many applications such as UV detector, varistor, photocatalysis and gas sensors. When doped with transition metals such as Ni, Mn and Co, this material exhibits ferromagnetic arrangement at room temperature. In the present work, the nanostructured compositions ZnO: Cu and ZnO: Co were synthesized at different doping levels by the modified polymer precursor based method whose polymer is water soluble. This process allows the synthesis of nanoparticles in reduced time of about six hours when compared to methods based on conventional polymeric precursors such as Pechini and sol-gel, besides dispensing with the need of the aging step. The synthesized powders were characterized in terms of chemical composition (X-ray fluorescence (FRX)) and the present phases (X-ray diffraction (XRD)) and morphologically (scanning electron microscopy (SEM) and transmission (TEM)). They presented agglomerated particulate (SEM) common to this method. The diffractograms showed high crystallinity of the powders and, following Rietveld's refinement (by the GSAS II program), the sizes of crystallites inferred by the Scherrer equation were lower than 50 nm. These reduced sizes of primary particulate were proved by MET, with nanoflowers (nanoflowers) morphology. It was found that the dopant concentration as well as the temperature affect the mean crystallite size and unit cell parameters, but not the crystallinity of the material (at high heat treatment temperatures). The electrical behavior of zinc oxides doped with Co and Cu were studied, where they showed high electrical resistivity at 1050 ºC (sintering) at high dopant concentrations, at higher sintering temperatures the conductivity is increased, however the material still has semiconductor behavior, being conductive in high electric field.