Photocatalytic and photoelectrochemical properties of titania-chloroplatinate(IV)

Rutile (Ald), anatase (TH), and the mixed anatase/rutile powder (P25) were surface modified by chemisorption of H-2[PtCl6] from aqueous solution. The resulting materials photocatalyzed the degradation and mineralization of 4-chlorophenol with visible light. Ald adsorbed only traces and was inactive, P25 adsorbed 1.1 wt.% and exhibited medium activity, whereas TH adsorbed 4.0% and was six times more active than P25. In neutral water 4.0%Pt(IV)/TH is stable towards thermal and photochemical desorption of platinate, even in the presence of strongly adsorbing fluoride ions. Contrary to this, complete photodesorption occurred in 0.1 M hydrogen chloride solution. It is postulated that adsorption affords a surface tetrachloroplatinate(IV) complex covalently linked to the titania surface through a [Ti]O-Pt bond. The flatband potential of 4.0%Pt(IV)/TH at pH 7 is determined as -0.28 +/- 0.02 V (vs. NHE), which is more anodic by 260 mV as compared with unmodified TH. Solar experiments revealed that 4.0%Pt(IV)/TH is a much better photocatalyst than 1.1%Pt(IV)/P25, P25, and TH. It catalyzed the photodegradation also in diffuse indoor daylight, conditions under which all other tested materials were inactive. Upon UV excitation 4.0%Pt(IV)/TH is even more active than P25. (C) 2002 Elsevier Science B.V. All rights reserved.