Synthesis of hureaulite by a reflux process at ambient temperature and pressure

Abstract

Hureaulite was first successfully synthesized by reflux reactions of Mn(H2PO4)2 and MnCl2/H3PO4/NaClO solutions at 40–100°C under atmospheric pressure. Powder X-ray diffraction (XRD), Rietveld structure refinement, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were utilized to characterize the crystal structures and morphologies of the products. Cell parameters of the as-prepared hureaulites were compared with those formed by hydrothermal reaction. Hureaulites obtained from different reaction systems exhibited various morphologies. Rod-like hureaulite was synthesized from a mixture of 30mmol H3PO4 and 100mL of 0.3molL−1 Mn(H2PO4)2 solution with or without NaClO solution to the system at 100°C. However, hureaulite could only be formed from the MnCl2 and H3PO4 solutions by the addition of NaClO solution. The formation mechanism of hureaulite was investigated by refluxing 100mL of 0.3molL−1 Mn(H2PO4)2 solution at 40°C. A mixture of hureaulite and MnHPO4·3H2O was formed, and the former was approximately 59.24% and 86.11% by mass as the reflux reaction lasted for 12 and 24h, respectively. Single-phase hureaulite was formed when the reaction was prolonged up to 48h at 40°C. Results of Rietveld structure refinement showed that the lattice parameters were compressed in the c direction and β decreased, and the crystal density increased as the reflux temperature was increased. The present work facilitates a thorough knowledge of the natural genesis of hureaulite, and the preparation and applications of hureaulite in the field of materials science and chemistry.