Hydrothermal synthesis of iron(III) phosphates in the presence of urea

Iron(III) phosphates have been synthesized directly under mild hydrothermal conditions. The reaction of FeCl3, H3PO4 and (NH2)2CO aqueous solutions at 180 °C leads to the formation of four individual compounds: FePO4·2H2O, Fe(NH4)(HPO4)2, Fe2(NH4)(OH)(PO4)2·2H2O and Fe(NH3)2PO4. The reaction product depends on the Fe∶P∶C molar ratio in the reaction mixture. The effect of urea on the reaction route is discussed.