General Synthesis and Phase Control of Metal Molybdate Hydrates MMoO4·nH2O (M = Co, Ni, Mn, n = 0, 3/4, 1) Nano/Microcrystals by a Hydrothermal Approach: Magnetic, Photocatalytic, and Electrochemical Properties

Different phases and morphologies of molybdate hydrates MMoO4·nH2O (M = Co, Ni, Mn, n = 0, 3/4, 1) nano/microcrystals, which include NiMoO4·H2O microflowers, MnMoO4·H2O microparallelogram plates, and CoMoO4·3/4H2O microrods, can be selectively synthesized by a hydrothermal process. The pH and reaction temperature have a crucial influence on the synthesis and shape evolution of the final products. Uniform CoMoO4·3/4H2O and NiMoO4·H2O nanorod bundles can be produced by a hydrothermal process with the assistance of PEG-400. The calcination of CoMoO4·3/4H2O and NiMoO4·H2O at 500 and 550 °C, respectively, allows the formation of monoclinic β-CoMoO4 and α-NiMoO4. The antiferromagnetic property of MnMoO4·H2O, MnMoO4, and CoMoO4·3/4H2O has been studied for the first time. The photocatalytic activity of metal molybdate particles with different morphologies has been tested by degradation of acid fuchsine under visible light. Electrochemical performances of MMoO4 (M = Ni, Co) nanorod bundles and MnMoO4 microrods have been evaluated.