Surface modification of titania powder P25 with phosphate and phosphonic acids – Effect on thermal stability and photocatalytic activity

Phosphorus is frequently reported as a doping element for TiO2 as photocatalyst; however, the previously reported methods used to prepare P-doped TiO2 do not allow control over the location of the phosphorus either in the bulk or at the surface or both. In this study, we report on the surface modification of Evonik P25 with phosphonic (H3PO3) and octylphosphonic acid [C8H17–PO(OH)2], done to limit the introduction of phosphorus only to the photocatalyst surface. The effect of this element on the thermal behavior and photocatalytic properties is reported through characterization using elemental analyses, solid state 31P NMR, X-ray powder diffraction, N2 porosimetry, dilatometry, etc. Thus, the objective of the work reported here is to focus on the role(s) that phosphorus plays only at TiO2 crystallite surfaces. For comparison, other samples were treated with phosphoric acid.

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► Phosphonic acids and phosphate are compared as surface modification agent of TiO2.
► Treatment at 750 °C of P-grafted TiO2 leads to enhanced photocatalytic activity.
► The octylphosphonic acid gives the highest efficiency.