Preparation of iron tungstate (FeWO4) nanosheets by hydrothermal method

Abstract This study reports about the influence of sulfate and iron containing additives on the hydrothermal reaction of sodium tungstate (Na2WO4) and hydrochloric acid (HCl) through which we managed to obtain FeWO4 nanosheets for the first time. The synthesis products were screened by XRD and SEM. The used additives (Na2SO4, FeSO4, (NH4)2Fe(SO4)2, NH4Fe(SO4)2 and FeCl3) and reaction temperatures (180 and 200 °C) had significant effect on the composition and morphology of the products. Oxalic acid as additional reagent improved the crystallinity in all cases. We prepared 20–30 nm thick and 0.5–1 μm wide FeWO4 nanosheets using FeSO4 as additive at 200 °C, while 50–300 nm thick and 5–10 μm long h-WO3 nanorods were obtained in the presence of Na2SO4 both at 180 and 200 °C. With the other additives and temperatures heterogenous products formed, which contained e.g. WO3·0.33H2O, Fe2O3, Fe3(SO4)2(OH)5·2H2O, Fe2(WO4)3·10.7H2O, NH4Fe3(SO4)(OH)6. Bare, single crystalline FeWO4 nanosheets and h-WO3 nanorods were further analyzed by EDX, TEM, FTIR, Raman and UV–vis, and their photocatalytic activity was monitored by UV–vis spectroscopy during the photobleaching reaction of methyl orange. The brown FeWO4 nanosheets (Ebg = 1.73 eV) were 2.5 times better photocatalysts compared to light yellow h-WO3 nanorods (Ebg = 3.05 eV).