Impact of Fe, Mn co-doping in titanate nanowires photocatalytic performance for emergent organic pollutants removal.

The unexpected incorporation of ionic Mn and Fe in the crystalline structure of titanate nanowires was accomplished when a contaminated a titanium source was used. The presence of Mn (8.1 mg L-1) and Fe (4.3 mg L-1) result in the production of a novel co-doped (Fe,Mn) titanate nanowires (TNW) material with improved optical and photocatalytic properties. After structural characterization, the results indicate that both Mn and Fe were incorporated in the TNW structure by replacement of Na+ in the interlayers, together with Ti4+ substitution in the TiO6 octahedra. The potential of this new material to be used for pollutants photocatalytic degradation was further investigated. The terephthalic acid was used as probe molecule to first evaluate the catalytic ability of the pristine and FeMnTNW modified powders for the photo-assisted hydroxyl radical formation. Afterwards, the degradation process of a model emergent pollutant, caffeine, was studied. The results showed that FeMnTNW was the best photocatalyst, with the complete caffeine removal (20 mg L-1) within 60 min of radiation (13 mg catalyst/L solution). The action of several oxidant species, including h+, OH• and O2•-, during caffeine removal was carefully analyzed using specific radical scavengers. A mechanism for the charge-transfer in irradiated FeMnTNW particles, including the possibility of a photo-Fenton and photodegradation combination process, is proposed and discussed.