Comprehensive in situ and ex situ analysis of the phase evolution during the synthesis of CoO nanostructures in tetra-ethylene glycol

Abstract

The polyol synthesis is a well-established wet chemistry one-pot method employed for the synthesis of CoO nanostructures, yielding aggregates of tens to hundreds of nanometres in diameter, depending on the synthesis parameters. These aggregates are composed of smaller primary particles showing evidence of oriented attachment. Traditionally, the synthesis is carried out in di-ethylene glycol; however, recent investigations have demonstrated the advantages of employing tetra-ethylene glycol as an alternative solvent medium, which substantially raises the temperature at which the synthesis can be performed without significant formation of impurities, and offers notable operating benefits by acting on easily controllable synthesis parameters (e.g., water/cation ratio and temperature). These advantages, coupled with the importance of CoO in materials science research, have prompted a more comprehensive examination of the reaction mechanism. To this end, we have combined in situ and ex situ synchrotron radiation studies to monitor the reaction progression and elucidate the CoO formation processes.

A scheme of the experimental setup. During the reaction, small aliquots are withdrawn, brought to the measurement cell, and then back to the reaction flask. The measurement cell is illuminated with X-ray synchrotron light. 2D-X-ray powder diffraction patterns are measured over time, integrated and collected. The panel with the resulting phase evolution is displayed on the right.