P25 TiO2 Powder Research Articles

Scanning electrochemical microscopy investigation of the photodegradation kinetics of 4-chlorophenol sensitised by TiO2 films

Scanning electrochemical microscopy (SECM) has been used to investigate quantitatively the photodegradation kinetics of 4-chlorophenol (4-CP), in aerated and oxygenated aqueous solutions, at back-illuminated TiO2 films deposited from a suspension of Degussa P25 TiO2 powder at the end of an optical fibre. A potentiometric Ag/AgCl ultramicroelectrode (UME), positioned at a known distance above the TiO2 film, was used to monitor directly the Cl− production from the photodegradation of 4-CP. The effects of both light intensity and 4-CP concentration were investigated and the associated kinetics were determined. Amperometric measurements with a Pt UME demonstrated that O2 was depleted significantly adjacent to the TiO2 surface under these conditions. A theoretical model, which employs a Langmuir–Hinshelwood type kinetic equation, has been developed to interpret the kinetics of the photodegradation process and determine the associated quantum efficiency.

Adsorption and Photoactivity of Tetra(4-carboxyphenyl)porphyrin (TCPP) on Nanoparticulate TiO2

Tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbs strongly onto nanoparticulate TiO2 and serves as an efficient photosensitizer for solar-energy conversion by TCPP-sensitized TiO2 electrodes. Nanoparticulate TiO2 electrodes were prepared from Degussa P25 TiO2 powder in the standard manner for a Gratzel cell. Adsorption studies of TCPP onto these sintered TiO2 electrodes gave a saturation surface coverage of 47 μmol/g. Adsorption studies of TCPP onto colloidal dispersions of Degussa P25 in ethanol gave a saturation surface coverage of 77 μmol/g. The difference between the saturation coverages is attributed to the reduction of the available surface area in the TiO2 films after sintering, from 55 m2/g as a free colloid to about 34 m2/g as a sintered electrode. The nature of the binding of TCPP onto the TiO2 electrodes was investigated using X-ray photoelectron spectroscopy (XPS) and Resonance Raman Spectroscopy (RRS). In the XPS spectra of TiO2 with adsorbed TCPP, the O (1s) and Ti (2p3/2) peaks of TiO2 were sh...

Photoelectrochemistry of oxalate on particulate TiO2 electrodes

Abstract TiO2 electrodes were prepared by the electrophoretic immobilisation of Degussa P25 TiO2 powder on titanium alloy (Ti–6Al–4V). These electrodes were used as photoanodes in a two compartment photoelectrochemical cell to investigate the photocatalytic oxidation of oxalate. The effects of electron acceptors, i.e. oxygen and Fe3+, on the rate of mineralisation of oxalate were determined. Significant increases in the short-circuit photocurrent densities were observed upon the addition of oxalate to the anode compartment when oxygen was present only in the cathode compartment. When oxygen was present in both the anode and cathode compartments, little photocurrent was observed. Oxygen scavenges both conduction band electrons from the TiO2 surface and primary radicals formed in the initial one electron oxidation of oxalate. An increase in the anodic photocurrent and rate of degradation of oxalate was observed when oxygen was replaced with Fe3+ as the electron acceptor in the cathode compartment. The TiO2 coated anodes behaved as microporous nanocrystalline film electrodes where the anodic photocurrent is dependent on the diffusion of majority charge carriers through the film. Oxalate acts as an efficient hole acceptor, inhibiting the photoanodic production of oxygen.