Simultaneous production of hydrogen with the degradation of organic pollutants using TiO2 photocatalyst modified with dual surface components

Abstract

The simultaneous production of hydrogen and degradation of organic pollutants (4-chlorophenol, urea, and urine) was successfully achieved using titania photocatalysts which were modified with both anion adsorbates (fluoride or phosphate) and (noble) metals (Pt, Pd, Au, Ag, Cu, or Ni). The dual-function photocatalysis worked only when both components coexisted on the surface of TiO₂, whereas TiO₂ modified with a single surface component (F–TiO₂, P–TiO₂, or Pt/TiO₂) was inactive under the same experimental condition. Two main surface-modified photocatalysts, F–TiO₂/Pt (surface fluorinated and platinized) and P–TiO₂/Pt (surface phosphated and platinized), were similarly active for dual-function photocatalysis in the anoxic suspension under UV irradiation. With these catalysts employed, the degradation of 4-chlorophenol (or urea) was accompanied by the concurrent production of H₂. The synergistic effect greatly depended on the kind of metal and pH. The activity of F–TiO₂/Pt gradually decreased with increasing pH, which makes the application of F–TiO₂/Pt limited to the acidic pH region. On the other hand, P–TiO₂/Pt exhibited a consistent activity over a wide range of pH, which makes P–TiO₂/Pt a more practical dual-function photocatalyst. The synergistic effect of anions and metal deposits on the surface of TiO₂ enhanced the interfacial electron transfer and reduced the charge recombination which resulted in a maximum of 20-fold increase of H₂ production compared to metal deposited TiO₂ in the presence of 4-chlorophenol.