Difference in TiO₂ photocatalytic mechanism between rutile and anatase studied by the detection of active oxygen and surface species in water

Abstract

Various kinds of TiO2 photocatalysts have been practically applied in various fields. Knowing the exact surface properties is a prerequisite to develop further and efficient applications. However, the cause of the essential difference in the activities of the two polymorphs of TiO2, rutile and anatase, has not been clearly elucidated yet. We tried to clarify the cause in terms of active oxygen species (˙OH, ˙O2(-), and H2O2) photogenerated on the surfaces, which are considered practically involved in the photocatalytic reactions. It was revealed that for anatase the rate of ˙OH generation was high, but it decreased in the presence of H2O2. On the other hand, for rutile, ˙OH generation was very low but it increased in the presence of H2O2. The formation rate of ˙O2(-) for rutile was higher than that for anatase, suggesting that the photoinduced reduction process should not be accountable for the higher photocatalytic activity of anatase. Since the Ti-Ti distance on a rutile surface is smaller than that for anatase, rutile is capable of forming a surface structure such as Ti-OO-Ti, leading to readily form O2. The mechanism of fast coupling of two photoinduced conduction band holes to form Ti-OO-Ti was proposed, which is accountable for the lower reactivity of rutile. This mechanism was verified by the analysis of surface species with ATR-IR spectroscopy.

Mechanistic studies on versatile metal-assisted hydrogen peroxide activation processes for biomedical and environmental incentives

“…Since the potentials of band gap edges of TiO2 also follow a similar dependence, pH does not seem to be the main factor governing reactions 33 and 34 at the surface of titanium dioxide. Domination of the reduction or oxidation process is mainly related to the crystal structure of titanium dioxide [278,292,293]. As reported by Nosaka, rutile-TiO2 is known to reduce H2O2 efficiently (Eq.…”

“…They can be divided into those involving fluoride [304] and fluoride-free methods [305]. Experimental and theoretical studies [293,306] point at differences in H2O2 adsorption at various anatase and rutile facets, and different reaction paths involving adsorbed hydrogen peroxide molecules. Since the literature on the differences of fate of hydrogen peroxide on specific facets of rutile-and anatase-TiO2 is still very scarce, more detailed studies in this field are expected [307].…”

“…Recently much attention has been drawn to H2O2 activation at the surface of irradiated TiO2 based materials [278,291,292,293]. The reactivity of hydrogen peroxide in the presence of photoactive systems opens new possibilities to use H2O2 as a useful oxidant in several advanced oxidation processes (AOPs).…”

Site-selective deposition of binary Pt–Pb alloy nanoparticles on TiO2 nanorod for acetic acid oxidative decomposition

“…In addition to promoting effect for reduction process in AcOH decomposition by Pt-Pb loading, the oxidation process would be affected by the difference in deposition method of Pt-Pb NPs. For oxidation reaction process, holes directly attack AcOH as first step in radical chain reaction process [29] and also produce OH radical by reacting with water, which radical has been often regarded to play an important role in the oxidation mechanism [36]. Since Pt-Pb NPs catalyze oxygen reduction reaction efficiently, it is probably that Pt-Pb NPs work as electron accepter even though deposited on oxidation site.…”

Preparation of Cu(ii) porphyrin–TiO2 composite in one-pot method and research on photocatalytic property

“…[4][5][6][7] In addition, it has shown a great potential as an inexpensive, environmentally friendly and sustainable treatment technology to remove pollutants from sewage to overcome the shortcomings of the conventional technologies. 8,9 However, the utilization for solar energy is limited by the narrow band gap of light absorption region in TiO 2 , 10,11 which impedes its commercialization.…”