Microstructure and optical vibration features of complex cobalt molybdates synthesized by the microwave and conventional hydrothermal processes

Abstract

Complex cobalt molybdates were prepared by conventional (CH) and microwave-assisted (MW) hydrothermal methods. Structural, morphological and vibrational properties of the obtained NaCo2(H3O2)(MoO4)2 and Co2(MoO4)(OH)2 materials were investigated. The first compound was obtained as majority phase for all tested MW processing conditions; conversely, for the CH method the second composition (desodiated) was the majority phase. Phase-pure, round-shaped Co2(MoO4)(OH)2 was obtained by CH processing in the temperature range 150−250 °C, for 24 h. On the other hand, the MW process produced micrometer-size rods with high anisotropy. Raman spectroscopic analysis of the monoclinic NaCo2(H3O2)(MoO4)2 materials, using conventional peak fitting procedures to resolve the vibrational modes, showed a good agreement between experimental results and group theory predictions. Raman spectra of the orthorhombic Co2(MoO4)(OH)2 showed similarities with the spectra of other hydroxy molybdates.