Iron oxide materials were synthesized by an easy and rapid hydrothermal method using different iron precursors (FeCl3 center dot 6H(2)O, Fe(NO3)(3)center dot 9H(2)O and K4Fe(CN)(6)center dot 3H(2)O), solution pHs (acid and basic) and reaction times (3 h and 6 h). The synthesized materials were thoroughly characterized by transmission electron microscopy and it was found that, depending on the synthesis conditions, iron oxide samples with crystalline or with amorphous structures could be obtained. Except for the materials synthesised from K4Fe(CN)(6)center dot 3H(2)O and FeCl3 center dot 6H(2)O under acidic conditions all the samples show mean particle sizes below 70 nm. The materials were further tested as catalysts for the degradation of 100 mg l(-1) diphenhydramine aqueous solutions by the photo-Fenton process at 25 degrees C, pH = 2.8, 100 mg l(-1) of catalyst and 16 mM of H2O2 concentration. The best results in terms of pollutant removal and mineralization extent were obtained with the catalysts prepared from Fe(NO3)(3)center dot 9H(2)O and K4Fe(CN)(6)center dot 3H(2)O, under basic conditions, after 3 h of synthesis reaction time (complete degradation of diphenhydramine and total organic carbon removal higher than 60% after 60 min of reaction). Leaching of iron species from these catalysts was measured below 1.5 mg l(-1), a value complying with European Union Directives.
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