Mechanism of Water Photooxidation Reaction at Atomically Flat TiO₂ (Rutile) (110) and (100) Surfaces:  Dependence on Solution pH

Abstract

The mechanism of water photooxidation reaction at atomically flat n-TiO(2) (rutile) surfaces was investigated in aqueous solutions of various pH values, using photoluminescence (PL) measurements. The PL bands, which peaked at around 810 and 840 nm for the (110) and (100) surfaces, respectively, were assigned to radiative transitions between conduction-band electrons and surface-trapped holes (STH), [Ti-O=Ti(2)](s)+, formed at triply coordinated (normal) O atoms at the surface lattice. The PL intensity (I(PL)) decreased stepwise with increasing solution pH, namely, it sharply decreased at around pH 4, near the point of zero charge of TiO(2) (about 5), and then rapidly decreased to zero near pH 13. The first sharp decrease around pH 4 is attributed to the increased rate of nucleophilic attack of a water molecule to a hole at a site of surface bridging oxygen (Ti-O-Ti), the density of which increases with increasing pH. The nucleophilic attack is regarded as the main initiating step of the water oxidation reaction in low and intermediate pH. The high PL intensity at low pH is ascribed to slow nucleophilic attack owing to a very low density of Ti-O-Ti by its protonation at the low pH. The second sharp decrease near pH 13 is attributed to formation of surface anionic species like Ti-O- which can be readily oxidized by photogenerated holes. Interrelations between reaction intermediates proposed in this work and those reported by time-resolved laser spectroscopy are discussed.

Bifunctionality from Synergy: CoP Nanoparticles Embedded in Amorphous CoOx Nanoplates with Heterostructures for Highly Efficient Water Electrolysis

“…Third, literature reported that amorphous metal oxide sample has higher amount of randomly oriented bonds and higher structural flexibility relative to its crystalline counterpart, which translates to the formation of higher amount of surface unsaturated sites for facile reactant adsorption 9. In such metal phosphide, the highly electronegative P atoms can draw electron from metal atoms and act as proton carrier, thus contributing towards enhanced electrocatalytic activity 10. More significant is the fact that our XPS results above do indicate strong electronic interaction between the crystalline CoP and amorphous CoOx phases, which led to the favorable modification in the electronic structure and can lower the free energy for adsorption of intermediates, therefore enhancing the catalytic activity.…”

Direct Functionalization of Aromatic Rings on Platinum-loaded Titanium Oxide Photocatalyst

“…31 In this mechanism, the OH cleavage in an H 2 O molecule corresponds to the deprotonation from the protonated hydroxy group ( + OH 2 ) on the TiO 2 surface. Thus, this OH cleavage would not be the rate-determining step.…”

“…Under the basic conditions, it was proposed that a deprotonated terminal TiO ¹ site traps a photoformed hole to become a surface oxygen radical species. 31 In the hydroxylation, this oxygen species reacts with an H 2 O molecule through the O H bond cleavage in the H 2 O molecule and produces a hydroxyl radical (Scheme 8a). This reaction step should proceed with the isotopic effect of D 2 O, consistent with the results in the basic condition (Entries 5 and 6).…”

“…In addition, ESR spectroscopy by using a spin Scheme 8. Reaction between a surface oxygen radical activated by the photoformed hole 31 and an H 2 O molecule (a) or an NH 3 molecule (b) to produce a hydroxyl radical or an amide radical, respectively, on the TiO 2 surface in basic condition.…”

Lattice distortion mechanism study of TiO2 nanoparticles during photocatalysis degradation and reactivation

“…12 Moreover, it has been known that there exists a lot of lattice changes during TiO 2 photocatalysis. [13][14][15] The urgency for the mechanism drives cutting-edge researches to the relationship between the lattice changes and photocatalytic activity of TiO 2 . In our previous work, 16 we studied the photocatalytic process in an atomic scale by using HRTEM.…”