Influence of Formate Adsorption and Protons on Shallow Trap Infrared Absorption (STIRA) of Anatase TiO<sub>2</sub> During Photocatalysis

Savory, David M.; McQuillan, A. James

doi:10.1021/jp404321f

Cited by 32 publications

(49 citation statements)

References 91 publications

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“…In aqueous solutions, the electron charging of a nc-TiO 2 material associates with proton participations, so observing gap states by optical absorptions is affected by proton intercalation. McQuillan et al found a pH-dependent mid-IR absorption peaked at 880 cm −1 in an aqueous solution under excitation with UV light illumination [312]. This peak does not correspond to the Drude-like free electron absorption and the phonon modes of TiO 2 .…”

Section: Transient Optical Absorptionsmentioning

confidence: 99%

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Liu

Zhao

et al. 2019

Journal of Photochemistry and Photobiology C: Photochemistry Re

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Titanium dioxide (TiO 2) is regarded as an important prototype photocatalytic material for several decades. The charge carrier kinetics determines the photocatalytic properties of TiO 2 materials; this is found to be greatly dependent on electronic structures. It has been revealed that the intrinsic intermediate gap states (intrinsic GSs) play a significant role in charge carrier kinetics that drive the photocatalytic processes of TiO 2 materials, which are not well summarized until now. Motivated by this thought, the purpose of this review focuses on physiochemical science of the intrinsic GSs of TiO 2 materials and their important role in charge carrier kinetics. We first give a summary on the chemical resources of the intrinsic GSs in TiO 2 and their physiochemical nature. Their general energy distribution, charge carrier population, and the associated thermodynamic properties are also elaborated from an overall viewpoint. We further carefully summarize and compare the experimental studies on the energy and the density distribution of the intrinsic GSs and discuss the associated chemical resources and charge carrier localizations. Trapping is the dominant function of intrinsic GSs in the charge carrier kinetics of TiO 2 materials. The significant effect of trapping on the transport, recombination, and interfacial transfer of charge carriers are also comprehensive summarized. Furthermore, the effects of charge carrier kinetics on photocatalytic performances are also discussed to some extents. Because of the importance of intrinsic GSs in modulating charge carrier kinetics, it is expected to increase the photocatalytic activity by engineering the intrinsic GSs, not only for TiO 2 materials, but also for the other semiconductor photocatalysts.

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Section: Transient Optical Absorptionsmentioning

confidence: 99%

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Liu

Zhao

et al. 2019

Journal of Photochemistry and Photobiology C: Photochemistry Re

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“…These peaks could be assigned to the CO stretching mode of HCO 3 À . 33 Since CO 2 in air was dissolved in solution as a form of HCO 3 À , it photoadsorbed on the surface of TiO 2 . The broad signal ranging from 1100 to 900 cm À1 could be attributed to Ti-OO À based on the spectral change with H 2 O 2 in the following experiments and the spectra in D 2 O (Fig.…”

Section: Change Of Tio 2 Surfaces Upon Irradiationmentioning

confidence: 99%

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

Kakuma

Nosaka

2015

Phys. Chem. Chem. Phys.

160

125

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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.

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“…Electron excitation from these states to the conduction band and inter-conduction-band transitions (Drude-type absorption) were proposed to contribute to the broad IR signal. 11 , 12 Interestingly, such IR signals were detected not only under high-vacuum conditions but also upon band gap excitation of TiO 2 in contact with aqueous solutions of hole acceptors 13 , 14 and upon cathodic polarization in acidic aqueous electrolytes. 14 − 17 …”

Section: Introductionmentioning

confidence: 98%

Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO₂ Nanocrystal Aggregates

2021

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Anatase TiO 2 nanoparticle aggregates were used as model systems for studying at different water activities the reactivity of electron centers at semiconductor surfaces. The investigated surface conditions evolve from a solid/vacuum interface to a solid/bulk electrolyte interface. Hydrogen-related electron centers were generated either chemically—upon sample exposure to atomic hydrogen at the semiconductor/gas interface—or electrochemically—upon bias-induced charge accumulation at the semiconductor/electrolyte interface. Based on their corresponding spectroscopic and electrochemical fingerprints, we investigated the reactivity of hydrogen-related electron centers as a function of the interfacial condition and at different levels of complexity, that is, (i) for dehydrated and (partially) dehydroxylated oxide surfaces, (ii) for oxide surfaces covered by a thin film of interfacial water, and (iii) for oxide surfaces in contact with a 0.1 M HClO 4 aqueous solution. Visible (Vis) and infrared (IR) spectroscopy evidence a chemical equilibrium between hydrogen atoms in the gas phase and—following their dissociation—electron/proton centers in the oxide. The excess electrons are either localized forming (Vis-active) Ti 3+ centers or delocalized as (IR-active) free conduction band electrons. The addition of molecular oxygen to chemically reduced anatase TiO 2 nanoparticle aggregates leads to a quantitative quenching of Ti 3+ centers, while a fraction of ∼10% of hydrogen-derived conduction band electrons remains in the oxide pointing to a persistent hydrogen doping of the semiconductor. Neither trapped electrons (i.e., Ti 3+ centers) nor conduction band electrons react with water or its adsorption products at the oxide surface. However, the presence of an interfacial water layer does not impede the electron transfer to molecular oxygen. At the semiconductor/electrolyte interface, inactivity of trapped electrons with regard to water reduction and electron transfer to oxygen were evidenced by cyclic voltammetry.

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Influence of Formate Adsorption and Protons on Shallow Trap Infrared Absorption (STIRA) of Anatase TiO₂ During Photocatalysis

Cited by 32 publications

References 91 publications

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

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

Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO₂ Nanocrystal Aggregates

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Influence of Formate Adsorption and Protons on Shallow Trap Infrared Absorption (STIRA) of Anatase TiO2 During Photocatalysis

Cited by 32 publications

References 91 publications

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

Intrinsic intermediate gap states of TiO2 materials and their roles in charge carrier kinetics

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

Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO2 Nanocrystal Aggregates

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Product

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Influence of Formate Adsorption and Protons on Shallow Trap Infrared Absorption (STIRA) of Anatase TiO₂ During Photocatalysis

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

Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO₂ Nanocrystal Aggregates