Study on the hydrothermal reaction of FeCl 3 solution in the presence of poly(vinyl alcohol)

A 0.5 dm3 aqueous solution of 0.1 M FeCl3 dissolving 1 wt% poly(vinyl alcohol) (PVA) was treated hydrothermally in a stainless steel autoclave at various temperatures (T h=110–A200 °C) Highly ordered red corpusclelike hematite particles around 2 m in diameter were Aproduced after aging the solution at T h=110 °C for 7 days, though large numbers of spherical PVA microgels around 2–4 m in diameter were produced together with the red corpuscle-like particles at T h120 °C. The number of red corpuscle-like hematite particles decreased but that of spherical PVA microgels increased with increasing T h, leading to the proposal that the method carried out in the present study will become a new synthetic method of polymer microgels. The ferric ions acted as a cross-linking agent to make PVA insoluble in water. The red corpuscle-like hematite particles produced at T h=110 °C had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 °C. The diameter of the mesopores after evacuation above 300 °C ranged from 2 to 20 nm, with a maximum at around 5–6 nm. The H2O and N2 adsorption experiments revealed that there are no ultramicropores in the particles. The H2O and CCl4 adsorption experiments further disclosed that the surface hydrophobicity of the particles is low even though PVA molecules remain after evacuation of the particles at 100–400 °C. Furthermore, the micropores produced after evacuation of the particles at 400 °C exhibited a high size restriction effect, i.e., the micropores produced were accessible to H2O (diameter 0.253 nm) and N2 (diameter 0.318 nm) molecules but not to CCl4 (diameter 0.514 nm).