The role of lanthanum in the enhancement of photocatalytic properties of TiO2 nanomaterials obtained by calcination of hydrogenotitanate nanotubes
Résumé
The influence of lanthanum on the thermal stability and photocatalytic
activity of calcined hydrogenotitanate nanotubes (HNT) was herein
evaluated. HNT samples were prepared through the hydrothermal treatment
of TiO2 P25 in a concentrated NaOH solution (11.25 M) at 130 degrees C
during 20 h followed by acid washing. La-doped titanates nanotubes
(La-HNT) photocatalysts with optimum 1 wt% of La were then elaborated by
incipient wetness impregnation method using lanthanum nitrate as
precursor. La HNT and HNT samples were then calcined at temperatures
varying between 400 degrees C and 700 degrees C. Samples were
characterized by means of nitrogen adsorption-desorption isotherms at
77K, X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectance
spectroscopy (DRS), photoluminescence spectroscopy (PL), transmission
electron microscopy (TEM), ICP analysis and photocurrent experiments.
The photocatalytic activities of La-HNT and HNT derived nanomaterials
were then evaluated through the photocatalytic degradation of formic
acid (FA).
Main results reveal that lanthanum inhibits TiO2 crystallite growth
and retards anatase transformation into the less active rutile phase.
The addition of La ions to TiO2 results in a charge imbalance creating a
high proportion of oxygen vacancies as evidenced by photocurrent,
photoluminescence and Raman experiments.
The photocatalytic experiments reveal that La-doped TiO2 helps to
maintain a high photocatalytic activity level even after calcination at
high temperatures contrary to La-free photocatalysts. The determination
of kinetic parameters reveals that the maintaining of a high
photocatalytic activity results from the synergetic effect between
restriction of TiO2 crystallite size growth and formation of a high
proportion of oxygen vacancies.