Microspheres of Ferrous Oxalate Dihydrate: Formation, Structure, Physical Properties, and Photocatalytic Activities

In the present work, ferrous oxalate dihydrate (FOD) microspheres were prepared by the one-step hydrothermal method using the interaction between ferric chloride and disodium tartrate dihydrate in the presence of β-cyclodextrin (β-CD). Although reaction temperature and time have important effects on the formation of the FOD microspheres, these effects can only be achieved in the presence of β-CD. In the absence of β-CD, the hydrothermal reaction will only form ferrous tartrate (FeTA) nanorods. The role of β-CD is to dominate and promote the time-dependent structural transformation from one Fe(II) complex FeTA to another Fe(II) complex polymer FOD. This discovery is new and meaningful. It provides a new perspective on the synthesis of inorganic micro- and nanomaterials. UV–vis diffuse-reflectance spectra show that these microsphere structures such as 1 and 2 indicate excellent light absorption capacities, including high absorption intensity in a very wide wavelength range (200–1000 nm). Magnetic studies show that these FOD materials exhibit typical paramagnetic properties near room temperature. The correlation between magnetic properties and structures shows that the magnetic similarity of these FOD materials is mainly reflected by the similarity of the surface structure. On the contrary, the difference of magnetism is more reflected by the difference of the crystal structure. In addition, we also found that these FOD microspheres showed good photocatalytic activity for several different types of organic dyes, including cationic Rhodamine B, Rhodamine 6G, crystal violet, and anionic methyl orange. Based on these meaningful experimental results, we have reason to believe that this work will help stimulate the in-depth study of FOD micro- and nanomaterials in controllable synthesis, physical properties, and photocatalytic applications.