Direct processing of porous nano-structured ZnO-CoOx films

Highly porous nano-structured films and powders of ZnO:Co (0–5 metal% Co) or ZnO:Co and (Zn,Co)3O4 (10–35% Co) particles were obtained by deposition of mixed Zn- and Co-methoxy-ethoxide precursors on spinning or non-spinning substrates, and heating to 600 °C. The Co- and Zn-methoxy-ethoxide solutions were prepared by metathesis of CoCl2 and potassium methoxy-ethoxide, and reaction of diethylzinc and methoxy-ethanol, respectively. Compositions in the range 0–35% Co were investigated by IR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The gels obtained consisted of hydrated amorphous oxo-carbonates and were of good elemental homogeneity in the TEM. Thermogravimetric analysis showed that all residual groups had been removed at 550–600 °C, 5 °C min− 1. The materials heated to 600 °C contained ZnO of the hexagonal modification with cell-edges in close agreement with un-doped ZnO regardless of composition and temperature. TEM-EDS studies showed that the ZnO:Co and (Zn,Co)3O4 spinel particles were well mixed, of similar shape and size, ca 10–25 nm. Heating of the 10% Co sample to 800 °C decomposed the spinel phase and left Co-doped ZnO.