Incorporation of Iron(III) in Silica Aerogels
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- Institutt for kjemi 
Silica aerogels containing both single site Fe3+ as well as small FexOy nanoparticles of oxide/hydroxide species were synthesized from a waterglass precursor using co-precursor and ambient pressure drying techniques. Fe3+ was incorporated by adding ferrous nitrate to the synthesis before the sol-gel step. ICP-MS was used to measure the iron loadings of the gels, XRD was used to determine the existence of crystalline species and nitrogen adsorption was used to determine information of the surface. To determine the exact nature of the iron species the samples were analysed by UV-vis and X-ray absorption spectroscopy. The aerogel consisted of amorphous silica with large populations of micropore and mesopores as well as some macropores and a porosity ranging from 50 to 70% for most successful samples. The iron loading for some samples were as high as 10 wt%, and addition of iron caused the average pore diameter to rise, but lowered the overall porosity. Some aerogel samples contained a crystalline species visible by XRD, and this species grew more prominent in samples with higher iron loadings. The iron species was determined to be a mixture of largely tetrahedral single-site Fe3+ and nanoparticles of a oxide/hydroxide species suspected to be similar to ferrihydrite and/or hematite. Annealing caused the nanoparticles to shrink to a smaller size, hypothesized to be due to interaction with the silica surface. The exact nature of the annealed samples were left inconclusive due to noisy EXAFS data.