Controllable synthesis and formation mechanism of pure and Fe-doped h-MoO3 microrods under hydrothermal reaction conditions

Abstract

In the present work, pure and Fe-doped h-MoO₃ microrods were successfully synthesized via the hydrothermal method using (NH₄)₆Mo₇O₂₄·4H₂O and concentrated HNO₃ as the raw materials. Various technologies, such as XRD, FESEM-EDS, TEM, and SAED pattern, were adopted to characterize the resulting products. The result showed that the optimum conditions for the controllable synthesis of pure h-MoO₃ microrods were 150 °C, 16 h, and with a solid–liquid ratio of 1 : 2. Due to the similar ionic radius of Fe³⁺ and Mo⁶⁺, it was discovered that adding a small amount of Fe dopant (1–5 mass%) would not lead to an obvious change in the lattice parameters; however, the particle size of the as-synthesized Fe-doped h-MoO₃ would be increased gradually. Also, the photocatalytic performances of the Fe-doped h-MoO₃ increased first and then decreased with increasing the amount of Fe dopant. NH₄⁺ and OH⁻ existing in the system played crucial roles on the formation of h-MoO₃ microrods, likely by acting as structure-directing and stabilizing agents for h-MoO₃ crystalline. In addition, it was found that the transformation process from h-MoO₃ microrods to α-MoO₃ nanofibers obeyed the dissolution–recrystallization mechanism.