SELECTIVE ADSORPTION OF WATER ON AMORPHOUS FERRIC-OXIDE HYDROXIDE

The amorphous ferric oxide hydroxide particles, prepared by the forced hydrolysis reaction of ferric chloride solution in the presence of citrate ions, adsorbed H2O molecules much more than CH3OH, CCl4, and N2. This selectivity of H2O adsorption was enhanced dramatically with increasing the concentration of residual citrate ions in these particles. The strong adsorption interaction of the polar adsorptives such as H2O and CH3OH was identified by the large hysteresis loops which do not close until low relative pressure. Consequently, the selective adsorption of H2O could be interpreted by penetration of polar H2O molecules into the amorphous particle and coordination to the citrate-Fe complexes. Such selectivity was varied with changing the content of citrate ions in the particles, the outgassing temperature, and the aging period. It was further found that the micropores with narrow size distribution are simply formed in these amorphous particles by raising the outgassing temperature and/or extending the aging period.