Fractal Charge Carrier Recombination Kinetics in Photocatalytic Systems

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Autoren

  • Fabian Sieland

Organisationseinheiten

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Details

OriginalspracheEnglisch
QualifikationDoctor rerum naturalium
Gradverleihende Hochschule
Betreut von
  • Detlef Bahnemann, Betreuer*in
Datum der Verleihung des Grades23 Apr. 2018
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 2018

Abstract

Die Photokatalyse ermöglicht die Zersetzung von zahlreichen ungewünschten Verbindungen aus Luft und Abwasser. Jedoch sind die grundlegenden Elementarreaktionen der Photokatalyse in den vergangenen Jahrzehnten größtenteils unerforscht geblieben, obwohl das genaue Verständnis der geschwindigkeitsbestimmenden Reaktion die Entwicklung aktiverer Photokatalysatoren ermöglichen sollte. Der Photokatalysator Titandioxid (TiO2) ist bisher am intensivsten erforscht worden, trotzdem gibt es noch viele ungeklärte Fragestellungen, im Besonderen im Bereich der kinetischen Analyse der Ladungsträgerrekombination. Weiterhin ist noch immer strittig, welchen Einfluss die Änderung der Partikelgrößenverteilung oder einfach Zusätze wie Karbonate auf den photokatalytischen Prozess besitzen. Im Rahmen dieser Arbeit wurde die Rekombination der lichtinduzierten Ladungsträger in TiO2 Pulvern mit Hilfe der Laserblitzphotolyse Spektroskopie untersucht. Dafür wurden die transienten Reflektionssignale der getrappten Ladungsträger in TiO2-Pulvermischungen mit binärer Partikelgrößenverteilung und TiO2-Pulvermischungen mit baustoffähnlichen Zusatzstoffen detektiert und analysiert. Auf der Basis der fraktalen Dimensionen der Pulveroberflächen wurde schließlich ein Modell für die mathematische Analyse der Rekombinationskinetik hergeleitet. Dieses Modell zeigt im Vergleich zu anderen Fit Funktionen eine höhere Verlässlichkeit in der Anwendung und ermöglicht den schnellen Vergleich der Ladungsträgerkinetik von Pulverproben. Darüber hinaus korrelieren die Messungen des photokatalytischen NO Abbaus der Proben sehr gut mit den Ergebnissen aus der Laserblitzphotolyse. Proben mit hoher photokatalytischer Aktivität zeigen gleichzeitig entweder besonders langlebige oder besonders hohe Ladungsträger-Signale. Das fraktale Modell ermöglicht hierbei die einfache Identifikation des Wirkmechanismus der zu TiO2 zugegebenen Additive. Der Zusatz von Natrium-Ionen führt beispielsweise zu einer schnelleren Ladungsträgerrekombination in TiO2, welche die photokatalytische Aktivität der entsprechenden Proben verringert.

Zitieren

Fractal Charge Carrier Recombination Kinetics in Photocatalytic Systems. / Sieland, Fabian.
Hannover, 2018. 146 S.

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Sieland, F 2018, 'Fractal Charge Carrier Recombination Kinetics in Photocatalytic Systems', Doctor rerum naturalium, Gottfried Wilhelm Leibniz Universität Hannover, Hannover. https://doi.org/10.15488/3300
Sieland, F. (2018). Fractal Charge Carrier Recombination Kinetics in Photocatalytic Systems. [Dissertation, Gottfried Wilhelm Leibniz Universität Hannover]. https://doi.org/10.15488/3300
Sieland F. Fractal Charge Carrier Recombination Kinetics in Photocatalytic Systems. Hannover, 2018. 146 S. doi: 10.15488/3300
Download
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abstract = "Photocatalysis can be utilized to decompose several undesired organic and inorganic compounds present in air and water. However, the underlying basic reactions of the photocatalytic process have remained largely unexplored during the past few decades, even though detailed knowledge about the rate limiting step makes it possible to facilitate the development of photocatalysts with higher photocatalytic activity. The most studied photocatalyst is TiO2; nevertheless, there are still many unsolved questions, in particular in the area of the kinetic analysis of charge carrier recombination. Moreover, the effects of the particle size distribution of TiO2 and the addition of carbonates on the photocatalytic process are still discussed controversially. In this study, the recombination of photo-generated charge carriers in TiO2 was investigated employing laser flash photolysis spectroscopy. The transient reflectance signals of trapped charge carriers in TiO2 powder samples were detected. TiO2 mixtures with binary particle size distribution and TiO2 mixtures with additives related to construction materials were analyzed, respectively. Subsequently, a model for the mathematical analysis of charge carrier recombination was derived from the fractal geometry of the powder samples. In comparison to other fit functions, the fractal model shows a higher reliability and facilitates the fast comparison of the charge carrier recombination kinetics of powder samples. Furthermore, the detected photocatalytic NO degradations of the samples correlate well with the results obtained by laser flash photolysis spectroscopy. Samples with higher photocatalytic activity display relatively high or long-lived charge carrier signals. In this context, the fractal model enables the identification of the effects observed upon mixing with different additives. The addition of sodium ions, for instance, causes a faster charge carrier recombination in TiO2, which explains the smaller photocatalytic activities detected for the respective samples.",
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