Photocatalytic degradation of water pollutants with visible light-sensitized TiO2 xerogels

To extend its photocatalytic activity to visible light, TiO2 has been
doped in situ through the cogelation sol-gel proces with two dyes : free metal
tetra(4-carboxyphenyl)porphyrin and nickel tetra(4-carboxyphenyl)porphyrin.
DR and FT-IR spectroscopies have been performed to determine the
interaction between porphyrins and TiO2. Cristallinity and specific surface
area have been measured by XRD and N2 adsorption. The photoactivity of the
doped TiO2 xerogels has been evaluated for p-nitrophenol (a model water
pollutant) degradation under visible light and a kinetic study has been
performed. The samples allow the degradation of 40% of p-nitrophenol in 6 h
which makes them very promising for water decontamination under natural
light. A kinetic study of p-nitrophenol degradation with the Ni-doped catalyst
has shown that the best kinetic model involves one type of active site
corresponding to the hole h+ of electron-hole pairs created at the TiO2 surface
by light. The rate determining step consists of the surface reaction between
adsorbed p-nitrophenol and adsorbed OH• radicals.