Development of new reactors for the photocatalytic treatment of polluted aquifers

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Autorschaft

  • Lena Megatif

Organisationseinheiten

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Details

OriginalspracheEnglisch
QualifikationDoctor rerum naturalium
Gradverleihende Hochschule
Betreut von
  • Detlef Bahnemann, Betreuer*in
Datum der Verleihung des Grades17 Okt. 2019
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 2019

Abstract

Eine Steigerung der Aktivität photokatalytischer Systeme erfordert eine effiziente Reaktorauslegung und eine geeignete Standardmethode, um die Leistung verschiedener Systeme zu vergleichen. Bei allen Methoden wird die Reaktionsgeschwindigkeit durch die optischen Eigenschaften von Photokatalysatoren durch Reflexion und Streuung beeinflusst. Darüber hinaus erfordert die quantitative Beurteilung der Leistung von photokatalytischen Systemen die Messung der Anzahl der im Reaktor absorbierten Photonen. In der vorliegenden Arbeit wird ein Standardverfahren zum Vergleich verschiedener Photokatalysatoren unter Verwendung eines Schwarzkörperreaktors vorgeschlagen. In einem Schwarzkörperreaktor wird fast das gesamte in den Reaktor einfallende Licht von den Photokatalysatorteilchen absorbiert. Daher ist die volumen-gemittelte Reaktionsgeschwindigkeit nahezu unabhängig von den Streuungseigenschaften des Photokatalysators und die photokatalytische Aktivität kann durch Messungen der Reaktionsgeschwindigkeit verglichen werden. Für diese Arbeit wurde Dichloressigsäure (DCA) als Modellschadstoff ausgewählt; Titandioxide und einige andere halbleitende Oxide wurden als Photokatalysatoren eingesetzt. Experimentelle Parameter einschließlich der Anfangskonzentration des Modellschadstoffs (C0), der Beladung mit dem Photokatalysator (γ) und des Reaktionsvolumens (V) wurden variiert, um eine von den genannten Parametern unabhängige Methode für die vergleichende Bewertung von Photokatalysatoren bereitzustellen. Die Abbaurate von DCA, definiert als die umgewandelte Menge an Molekülen pro Zeiteinheit, erwies sich bei allen Reaktionsvolumina als konstant und unabhängig, wenn C0 und γ größer als 5 mM bzw. 1 g L-1 waren. Es wurde festgestellt, dass das vorgestellte Verfahren allgemein für verschiedene Photokatalysatoren auf Titan- und Nicht-Titanbasis anwendbar ist. Darüber hinaus wurde zur Ermittlung der Reaktionsgeschwindigkeit eine kinetische Untersuchung sowohl für den Zerfall der Reaktanten als auch für die Produkterzeugung durchgeführt. Photonenfluss und Photonenflussdichte beeinflussen die Rekombination von Ladungsträgern sehr stark und haben somit auch Einfluss auf die Reaktionsgeschwindigkeit und die Quantenausbeute einer photokatalytischen Reaktion. Der Schwarzkörperreaktor wurde daher auch benutzt, um die Auswirkung der Geometrie des Lichteinlasses auf die Reaktionsgeschwindigkeit und die Quantenausbeute der photokatalytischen DCA-Oxidation zu untersuchen. Mit einem Lichteinlass, der eine gleichmäßige Lichtverteilung und eine niedrige Photonenflussdichte ermöglichte, wurden konstante Quantenausbeuten ermittelt. Bei hoher Photonenflussdichte wurde jedoch eine Quadratwurzelkorrelation zwischen der Quantenausbeute und dem Photonenfluss beobachtet.

Zitieren

Development of new reactors for the photocatalytic treatment of polluted aquifers. / Megatif, Lena.
Hannover, 2019. 161 S.

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Megatif, L 2019, 'Development of new reactors for the photocatalytic treatment of polluted aquifers', Doctor rerum naturalium, Gottfried Wilhelm Leibniz Universität Hannover, Hannover. https://doi.org/10.15488/5585
Megatif, L. (2019). Development of new reactors for the photocatalytic treatment of polluted aquifers. [Dissertation, Gottfried Wilhelm Leibniz Universität Hannover]. https://doi.org/10.15488/5585
Megatif L. Development of new reactors for the photocatalytic treatment of polluted aquifers. Hannover, 2019. 161 S. doi: 10.15488/5585
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title = "Development of new reactors for the photocatalytic treatment of polluted aquifers",
abstract = "An enhancement of the activity of photocatalytic systems requires an efficient reactor design and a suitable standard method to compare the performance of various systems. In almost all recommended measuring methods, the reaction rate is affected by the optical properties of photocatalysts through reflection and scattering. Moreover, the quantitative assessment of the performance of photocatalytic systems requires the determination of the amount of absorbed photons inside the photoreactor. In the present work, a standard method for the comparison of different photocatalysts is proposed employing a black body reactor. In a black body reactor almost the entire incident light will be absorbed by the photocatalyst particles. Therefore, the volume-averaged reaction rate is almost independent from the scattering properties of the photocatalyst and the photocatalytic activity can be compared through reaction rate measurements. In this study, dichloroacetic acid (DCA) was chosen as the probe compound. Titanium dioxide and some other semiconducting oxides were applied as the photocatalysts. Variation of effecting parameters including the initial concentration of the probe molecule (C0), the photocatalyst loading (γ), and the reaction volume (V) were studied in order to provide a comparison method which is independent from the mentioned parameters. The degradation rate of DCA defined as the converted amount of molecules per unit time was found to be constant at all reaction volumes and independent when C0 and γ were larger than 5 mM and 1 g L-1, respectively. The presented method was found to be generally applicable for different titanium and non-titanium based photocatalysts. Moreover, to determine the reaction rate, a kinetic study was performed for both, reactants decay and product generation. Photon flux and photon flux density are known to strongly affect the charge carriers{\textquoteright} recombination and, consequently, the reaction rate and the quantum yield. The black body reactor was employed to investigate the impact of the geometry of the light inlet on the reaction rate and on the quantum yield of a photocatalytic reaction. Accordingly, employing a hollow sphere light inlet providing uniform light distribution and low photon flux density, the quantum yield was constant and independent from the photon flux. However, in systems with high photon flux density, a square root correlation between the quantum yield and the photon flux was observed.",
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