Abstract
Trivalent iron (0.21–1.21 mol% equivalent Fe 2 O 3 ) was introduced into silica gel monoliths prepared via sols obtained from tetraethyl orthosilicate and metal salts at different final sol pH values. The UV-visible spectra indicated a change from an octahedral to tetrahedral Fe 3+ environment as the pH increased. An electron paramagnetic resonance spectral resonance at g = 4.22 appeared, in addition to that at g = 2.0, as the final pH increased. The resonance at g = 4.22 was also observed for some gels upon heat treatment. Colloidal precipitation of Fe 2 O 3 was noted with increase in cation concentration and temperature of heat treatment. The effects of processing on light transmission of gels were measured. The results indicated several processing conditions leading to total cut-off of ultraviolet light through the doped gel monoliths.
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