Systematic synthesis and analysis of change in morphology, electronic structure and photoluminescence properties of pyrazine intercalated MoO3 hybrid nanostructures

Abstract

High aspect ratio molybdenum trioxide (MoO3) nanorods grown along the [100] direction were successively synthesized by a simple hydrothermal method. We used sodium molybdate and hydrochloric acid as starting materials and from their reaction we obtained MoO3 nanorods of high aspect ratio. The dimensions of the nanorods were found to be uniform in size, with well-defined boundaries. The intercalation of an organic molecule (pyrazine) into these nanorods has resulted in single-crystalline MoO3 microstructures, with a change in their length and breadth of a few orders. Pyrazine has acted as a stitching molecule and has bound the nanorods together along their length to form micron sized single crystalline MoO3. The presence of pyrazine and its intercalation was confirmed by a uniform shift in the XRD [0k0] peak positions. As the size of the pyrazine is similar to the van der Waals gap of the orthorhombic MoO3 crystal, it seemed to fit well within the gap and thereby helped to bind the nanorods along the [0k0] direction. The Raman ring deformation modes, at 714 and 996 cm−1, have also supported the intercalation of the pyrazine in the van der Waals gap. The deintercalation process was done by calcinating the sample at 400 °C and the removal of pyrazine was confirmed by TGA and XRD measurements. The influence of pyrazine in the valence band electronic density of states (DOS) of MoO3 was also analyzed by XPS and XES methods. The replacement of oxygen at the van der Waals gap by nitrogen from the intercalating pyrazine caused a shift in the valence band towards the Fermi level. A photoluminescence study was also conducted, reflecting the intercalation effect on the emission characteristics of the MoO3 nanostructures.