Study on the hydrothermal reaction of FeCl3 solution in the presence of poly(vinyl alcohol)

A 0.5 dm(3) 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=110-200 degreesC). Highly ordered red corpuscle-like hematite particles around 2 mum in diameter were produced after aging the solution at T-h=110 degreesC for 7 days, though large numbers of spherical PVA microgels around 2-4 mum in diameter were produced together with the red corpuscle-like particles at T(h)greater than or equal to120 degreesC. 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 degreesC had high specific surface areas and showed high mesoporosity. The mesoporosity appeared to be more pronounced after evacuating the particles above 300 degreesC. The diameter of the mesopores after evacuation above 300 degreesC ranged from 2 to 20 nm, with a maximum at around 5-6 nm. The H2O and N-2 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 degreesC. Furthermore, the micropores produced after evacuation of the particles at 400 degreesC exhibited a high size restriction effect, i.e., the micropores produced were accessible to H2O (diameter 0.253 nm) and N-2 (diameter 0.318 nm) molecules but not to CCl4 (diameter 0.514 nm).