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.