Effect of Fe-doping and post annealing temperature on the structural and optical properties of MoO₃ nanosheets

In this article, pure and 5 wt% Fe-doped h-MoO₃ nanosheets have been successfully synthesized using a hydrothermal method and annealed the 5 wt% Fe-doped sample at 200 °C and 300 °C. The influence of Fe-doping and post annealing temperature on the structural, morphological, elemental, functional and optical properties of the developed nanosheets has been investigated by XRD, FESEM, EDS, FTIR and UV–Vis–NIR spectrophotometer, respectively. The XRD results revealed that all samples are polycrystalline in nature with no impurities, although, after Fe incorporation the phase transformation behavior observed from hexagonal to mixed phases (hexagonal and orthorhombic) and after annealing it showed identical diffraction patterns. Scherrer method, Williamson–Hall analysis and Halder–Wagner method were used to investigate the crystallite size, lattice strain and dislocation density of the samples. A deterioration of crystallinity is obtained in crystallite size after Fe doping, which signifies the incorporation of Fe inside the MoO₃ lattice network. The crystallinity improves gradually with increasing annealing temperature. The lattice strain and dislocation density showed reverse trend to crystallite size. All samples consist almost entirely of densely packed and randomly oriented nanosheets with an average width of 100–150 nm and length of 1000–1800 nm, confirmed from FESEM images. The iron incorporation in the h-MoO₃ matrix is confirmed by EDX analysis. The FTIR spectra reveal the information about formation and stability of phase. The optical band gap becomes narrow from 2.83 to 2.70 eV after Fe-doping and then widens from 2.70 to 2.79 eV with increasing annealing temperature up to 300 °C.