Fractal Charge Carrier Kinetics in TiO<sub>2</sub>

Sieland, Fabian; Schneider, Jenny; Bahnemann, Detlef W.

doi:10.1021/acs.jpcc.7b07087

Cited by 27 publications

(32 citation statements)

References 51 publications

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“…For the analysis of the decay kinetics we employed a second‐order kinetic model as given in Equation (2), where

A

is related to the initial height of the signal,

k

is the decay rate constant,

t

the time, and

B

the baseline

true Δ J ((), t) = \frac{A}{A \cdot k \cdot t + 1} + B

…”

Section: Resultsmentioning

confidence: 99%

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

et al. 2019

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Screen-printing is a commonly used method for the preparation of photoelectrodes. Although previous studies have explored the effect of the number of printed layers on the efficiency of dye-sensitized solar cells, its interplay with the photoelectrocatalytic properties of the electrodes has rarely been examined. This study focuses on this issue by studying the photoelectrocatalytic oxidation of methanol over TiO 2 electrodes. Incident photon-to-current efficiencies reached 87 % at the optimal conditions of monochromatic (338 nm) irradiation of one-layer films at 0.2 V vs NHE. However, the irradiation wavelength and applied bias strongly influenced the relative behavior of the films. For instance, at 0.5 V and 327 nm irradiation, the one-layer electrode was 6 times more efficient than the four-layer one, while at 385 nm the four-layer electrode was 3.5 times more efficient. The results were explained on the basis of differing light absorption properties and charge carrier lifetimes. Modelling and quantification of the electron diffusion length (5.7 μm) helped to explain why the two-layer electrode (4.89 μm thick) showed the most consistent efficiencies across all conditions. Complementarily, transient absorption spectroscopy was used to correlate the thicknesses with charge carrier lifetimes. Electron transfer to FTO was apparent only for the thinner electrode. Our work shows that the optimization of photoelectrocatalytic processes should include the number of layers as a key variable.[a] C.The concentration of the transients follows a linear relation with the change in reflectance as long as the latter is lower than 10 %. [33] The measurements were performed in the wavelength range from 400 to 630 nm in 10 nm steps, 50 shots were averaged, and the data points were reduced to 200. 4 5 6 7 8

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“…For the analysis of the decay kinetics we employed a second‐order kinetic model as given in Equation (2), where

A

is related to the initial height of the signal,

k

is the decay rate constant,

t

the time, and

B

the baseline

true Δ J ((), t) = \frac{A}{A \cdot k \cdot t + 1} + B

…”

Section: Resultsmentioning

confidence: 99%

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

et al. 2019

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“…The details of the fractal dynamics approach and the differences to the second order kinetics with a baseline have been described elsewhere. 15 In short, the difference between the two models is the diffusion of the reactive species. In both models two species of trapped charge carriers (electrons and holes) are the reactive species.…”

Section: Transient Absorption Spectroscopymentioning

confidence: 99%

“…However, the simple second order approach describes the reaction of the species in a free three-dimensional space, while the fractal model assumes that the diffusion of the species is limited to the surface of the TiO 2 particles. 15 The structured two-dimensional surface of the agglomerated particles limits the diffusion and represents a fractal dimension.…”

Section: Transient Absorption Spectroscopymentioning

confidence: 99%

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Photocatalytic activity and charge carrier dynamics of TiO₂ powders with a binary particle size distribution

Sieland

Schneider

Bahnemann

2018

Phys. Chem. Chem. Phys.

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The effects of the particle size distribution on the charge carrier dynamics and the photocatalytic activity of mixed titanium dioxide (TiO) powder samples were investigated in this work. Instead of the synthesis of the small semiconductor particles, the binary particle size distributions of the powders were obtained by mixing commercially available TiO powders with different particle sizes. The pure anatase samples (average diameters: 7, 20, and 125 nm, respectively) were created via ultrasound treatment and discreet drying. The photocatalytic activity of the powder samples was assessed by the degradation of nitric oxide (NO) and acetaldehyde in the gas phase. Furthermore, the charge carrier kinetics was determined using transient absorption spectroscopy following pulsed laser excitation. Importantly, a recently published model based on fractal dimensions was used to fit the transient signals of the photo generated charge carriers in the TiO powder samples. The effects of the particle size on the acetaldehyde degradation could be explained by the formation of agglomerates, which reduce the available surface area of smaller particles. The fast oxidation of acetaldehyde on the surface of TiO by direct hole transfer was further independent of the observed charge carrier lifetimes on the microsecond time scale. The photocatalytic NO degradation, on the other hand, increased for samples containing larger amounts of small particles. The corresponding photonic efficiencies correlated well with the charge carrier lifetimes determined by the time-resolved studies. Hence, it was concluded that a long charge carrier lifetime generally leads to higher fractional conversions of NO. The employed fractal fit function was proved to be beneficial for the kinetic analysis of charge carrier recombination in TiO, in direct comparison with a second order fit function.

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“…A tentative explanation of the power law in transient reflectance kinetics of photocatalytic powders has been recently proposed by Sieland et al., involving random walk of photoinduced charges in fractal structures. However, the physical relevance of this model in connection to the TiO 2 crystalline particle morphology is not clear.…”

Section: Resultsmentioning

confidence: 99%

Photocatalytic Nanoparticulate Zr_xTi_1‐xO₂ Coatings with Controlled Homogeneity of Elemental Composition

et al. 2018

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The mixed oxide ZrxTi1‐xO2 nanoparticulate photocatalysts of different compositions (0≤x≤1) were prepared via sol‐gel method in a rapid micromixing reactor followed by chemical colloid deposition on borosilicate glass beads, drying and heat treatment at temperatures between 400 to 650 °C. The point‐like reaction conditions in the regime of low Damköhler numbers resulted in nucleation of size‐selected reactive zirconium‐titanium oxo‐alkoxy (ZTOA) nanoparticles from zirconium (IV) propoxide and titanium (IV) isopropoxide precursors, which enable strong covalent bonds with hydrophilic supports. The ZTOA nanoparticles with compositions 0≤x≤0.2 convert after a heat treatment to nanoporous monocrystals in distorted anatase phase. The photocatalytic activity of the prepared nanoparticulate coatings on gaseous ethylene decomposition attained maximum at x=0.043 after heat treatment at 500 °C, which was two times higher than that of pure anatase TiO2. A net correlation between the material photocatalytic activity and amplitude of the slow power decay of photoinduced charges was observed. A model is proposed explaining the power law decay by a thermal release of the localised charges from shallow surface Urbach states. The number density of these states is connected to the specific surface area of the photocatalyst.

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Fractal Charge Carrier Kinetics in TiO₂

Cited by 27 publications

References 51 publications

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

Photocatalytic activity and charge carrier dynamics of TiO₂ powders with a binary particle size distribution

Photocatalytic Nanoparticulate Zr_xTi_1‐xO₂ Coatings with Controlled Homogeneity of Elemental Composition

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Fractal Charge Carrier Kinetics in TiO2

Cited by 27 publications

References 51 publications

Tailoring the Photoelectrochemical Activity of TiO2 Electrodes by Multilayer Screen‐Printing

Tailoring the Photoelectrochemical Activity of TiO2 Electrodes by Multilayer Screen‐Printing

Photocatalytic activity and charge carrier dynamics of TiO2 powders with a binary particle size distribution

Photocatalytic Nanoparticulate ZrxTi1‐xO2 Coatings with Controlled Homogeneity of Elemental Composition

Contact Info

Product

Resources

About

Fractal Charge Carrier Kinetics in TiO₂

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

Tailoring the Photoelectrochemical Activity of TiO₂ Electrodes by Multilayer Screen‐Printing

Photocatalytic activity and charge carrier dynamics of TiO₂ powders with a binary particle size distribution

Photocatalytic Nanoparticulate Zr_xTi_1‐xO₂ Coatings with Controlled Homogeneity of Elemental Composition