Ferrate (K2FeO4) is a powerful oxidant and up to 3 mol of electrons could be captured by 1 mol of ferrate in the theoretical conversion of Fe­(VI)–Fe­(V)–Fe­(IV)–Fe­(III). However, it is reported that the utilization efficiency of the ferrate oxidation capacity is quite low because of the rapid autodecomposition of intermediate iron species, which negatively influences the potential of ferrate on organic pollutants control. We accidentally found that for the ferrate oxidation of carbamazepine (CBZ), bisphenol S (BPS), diclofenac (DCF), and ciprofloxacin (CIP), the determined reaction rate constants were 1.7–2.4 times lower in phosphate buffer than those in borate buffer at pH 8.0. For the reaction of ferrate with 2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonate) (ABTS) at pH 7.0, the determined reaction stoichiometries were 1:1.04 in 100 mM phosphate buffer, 1:1.18 in 10 mM phosphate buffer, and 1:1.93 in 10 mM borate buffer, respectively. The oxidation ability of ferrate seems depressed in phosphate buffer. A kinetic model involving the oxidation of ABTS by Fe­(VI), Fe­(V) and Fe­(IV) species was developed and fitted the ABTS•+ formation kinetics well under different buffer conditions. The results showed that phosphate exhibited little influence on the oxidation ability of Fe­(VI) and Fe­(IV) species, but decreased the specific rate constants of ABTS with Fe­(V) species by 1–2 orders of magnitude, resulting in the outcompeting of Fe­(V) autodecomposition pathway. The complexation between phosphate anions and Fe­(V) species may account for the inhibition effect of phosphate buffer. Considering that many studies regarding ferrate oxidation were carried out in phosphate buffer, the actual oxidation ability of ferrate may be underestimated.

Photocatalytic dissociation of methanol (CH 3 OH) on a TiO 2 (110) surface has been studied by temperature programmed desorption (TPD) at 355 and 266 nm. Primary dissociation products, CH 2 O and H atoms, have been detected. The dependence of the reactant and product TPD signals on irradiation time has been measured, allowing the photocatalytic reaction rate of CH 3 OH at both wavelengths to be directly determined. The initial dissociation rate of CH 3 OH at 266 nm is nearly 2 orders of magnitude faster than that at 355 nm, suggesting that CH 3 OH photocatalysis is strongly dependent on photon energy. This experimental result raises doubt about the widely accepted photocatalysis model on TiO 2 , which assumes that the excess potential energy of charge carriers is lost to the lattice via strong coupling with phonon modes by very fast thermalization and the reaction of the adsorbate is thus only dependent on the number of electron−hole pairs created by photoexcitation. ■ INTRODUCTIONSince the discovery of the photocatalytic splitting of water (H 2 O) on TiO 2 electrodes by Fujishima and Honda in 1972, 1 tremendous research efforts have gone into understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO 2 . 2 These efforts have been driven by the potential benefits to renewable energy, energy storage, and environmental cleanup. 3,4 In particular, TiO 2 has attracted much attention because of its applications in heterogeneous catalysis, photocatalysis, solar energy devices, etc. 5−14In an ideal photocatalyst, all photon energy invested in the generation of charge carriers would be available for redox chemistry. The higher the potential energy of the electron (or hole) the more reductive (or oxidative) capacity there is.15 But charge carrier thermalization is rapid. For example, Gundlach and co-workers used two photon photoemission (2PPE) to track thermalization following electron injection from two dyes adsorbed on rutile TiO 2 (110). 16,17 Fast initial decay of the 2PPE signal resulting from thermalization of the injected electron occurred on the 10 fs time scale. This result suggests that excess potential energy is lost to the lattice via strong coupling with phonon modes, thus reducing the potential advantage gained by the specificity in the absorption event. Additional evidence for the rapid thermalization of electrons comes from photoemission spectra of Ag clusters on rutile TiO 2 (110) 18 as a function of injection electron energy and from photoluminescence spectra of rutile TiO 2 (110) 19,20 with 3.35 eV photon irradiation. In both these studies, a constant energy of the emitted photons was observed (at and below the band gap energy3.05 eV), independent of the energy of the exciting electron or photon. Furthermore, experimental investigations indicate that the photodesorption yield and translational energy of O 2 from an O 2 -adsorbed TiO 2 (110) surface are independent of the excitation photon energy above 3.4 eV, but instead depend on the photon flux. 21...

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