WO3–EDA hybrid nanoplates and nanowires: synthesis, characterization, formation mechanism and thermal decomposition

Abstract

Previously the WO₃–EDA hybrid material was obtained only from solvothermal reactions. In this study this hybrid was prepared by two novel methods: a solid–gas phase heterogeneous reaction, and a wet chemical process. In the case of the solid–gas phase reaction the effects of the composition, crystal structure, and the particle size of the WO₃ powder and the presence of H₂O vapor were studied, while in the case of the wet chemical process the effect of the solvent was investigated. The structure, composition, morphology and thermal decomposition of the as-prepared WO₃–EDA hybrid were investigated by XRD, FTIR, solid-state NMR, elemental analysis, SEM, TEM and TG/DTA-MS measurements. In addition, its catalytic activity was tested in a Knoevenagel condensation model reaction. Based on the results the WO₃–EDA empiric formula was proposed to replace the current WO_x–EDA formula. From the solid–gas phase reaction WO₃–EDA nanoplates were obtained for the first time. Furthermore, a new formation mechanism was proposed for the solid–gas phase formation of this hybrid material. The thermal decomposition of the hybrid resulted m-WO₃ in air, and an amorphous tungsten oxide phase in nitrogen. During annealing, the evolved EDA transformed into a series of heterocyclic aromatic compounds in both atmospheres. The as-prepared hybrids had the same catalytic properties as the hybrids obtained previously from the solvothermal reactions.