Iron-doped titania photocatalysts with different iron contents were prepared by using a sol−gel method in
acidic media. The crystalline structures of the various phases calcined at temperatures ranging from 70 to
800 °C were studied by using the Rietveld technique in combination with XRD experiments. The average
crystallite size of the phases, lattice cell parameters, phase concentrations, and titanium cationic defects in
the crystalline structures of different samples were quantitatively determined. Both iron content and calcination
temperature strongly affected phase transformation and solid-state reaction mechanism. Below 400 °C of
calcination, all the samples had some brookite and a majority of anatase phase. Iron ions were uniformly
distributed in the interstices of titania crystals to form a titanium−iron solid solution when the samples were
calcined at 80, 200, and 400 °C. However, when the temperature was 800 °C, Fe2TiO5 was produced in the
sample containing 5 wt % Fe by a reaction between interstitial iron ions and lattice titanium ions, and in the
10 wt % Fe sample through a reaction of hematite with titania phases. The crystalline structures of titania
phases were distorted at higher calcination temperature. For the first time, it is possible to show that titanium
lattice defects related to the hydroxyl ions in the crystalline structures were created in anatase and rutile
phases. The concentration of titanium defects remained almost constant below 400 °C but decreased as the
calcination temperature was higher than 600 °C due to the decrease of the hydroxyls in the crystalline structure.
MgO prepared with the sol−gel technique had
crystalline structure defects, obtained from X-ray powder
diffraction and crystalline structure refinement, that correlated with
its acidic and basic sites. The acidic
sites, measured by adsorbing pyridine and NH3, were found
when brucite and MgO coexisted, which only
occurred after annealing the sample at 673 K. Two different basic
sites, measured by adsorbing CO2, were
present in a total concentration of about 1021 sites per
gram. These sites correlated to the presence of
magnesium
vacancies in MgO crystal. Both basic site and magnesium vacancy
concentrations diminished when the
sample annealing temperature was increased.
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