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METAL OXIDE HETEROSTRUCTURES FOR EFFICIENT PHOTOCATALYSTS

Uddin, Md. Tamez (2014):
METAL OXIDE HETEROSTRUCTURES FOR EFFICIENT PHOTOCATALYSTS.
Darmstadt, Germany, TU Darmstadt, [Online-Edition: http://tuprints.ulb.tu-darmstadt.de/4199],
[Ph.D. Thesis]

Abstract

Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention as potentially efficient, environmentally friendly and low cost methods for water/air purification as well as for renewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies have been found due to the fast recombination of the charge carriers. Development of heterostucture photocatalysts by depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable band edge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw new prospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor (SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor (NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition, texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, a suitable combination of UV–visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for each system. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2 for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen. Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %) and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen. These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPS measurements along with their good textural and structural properties. This concept of semiconducting heterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future to remove undesirable organics from the environment and to produce renewable hydrogen.

Item Type: Ph.D. Thesis
Erschienen: 2014
Creators: Uddin, Md. Tamez
Title: METAL OXIDE HETEROSTRUCTURES FOR EFFICIENT PHOTOCATALYSTS
Language: English
Abstract:

Photocatalytic processes over semiconducting oxide surfaces have attracted worldwide attention as potentially efficient, environmentally friendly and low cost methods for water/air purification as well as for renewable hydrogen production. However, some limitations to achieve high photocatalytic efficiencies have been found due to the fast recombination of the charge carriers. Development of heterostucture photocatalysts by depositing metals on the surface of semiconductors or by coupling two semiconductors with suitable band edge position can reduce recombination phenomena by vectorial transfer of charge carriers. To draw new prospects in this domain, three different kinds of heterostructures such as n-type/n-type semiconductor (SnO2/ZnO), metal/n-type semiconductor (RuO2/TiO2 and RuO2/ZnO) and p-type/n-type semiconductor (NiO/TiO2) heterojunction nanomaterials were successfully prepared by solution process. Their composition, texture, structure and morphology were thoroughly characterized by FTIR, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and N2 sorption measurements. On the other hand, a suitable combination of UV–visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) data provided the energy band diagram for each system. The as-prepared heterojunction photocatalysts showed higher photocatalytic efficiency than P25 TiO2 for the degradation of organic dyes (i.e. methylene blue and methyl orange) and the production of hydrogen. Particularly, heterostructure RuO2/TiO2 and NiO/TiO2 nanocomposites with optimum loading of RuO2 (5 wt %) and NiO (1 wt %), respectively, yielded the highest photocatalytic activities for the production of hydrogen. These enhanced performances were rationalized in terms of suitable band alignment as evidenced by XPS/UPS measurements along with their good textural and structural properties. This concept of semiconducting heterojunction nanocatalysts with high photocatlytic activity should find industrial application in the future to remove undesirable organics from the environment and to produce renewable hydrogen.

Place of Publication: Darmstadt, Germany
Uncontrolled Keywords: Semiconducting metal oxides, heterojunction nanocatalysts, XPS, UPS, energy band alignment, photocatalytic activity, hydrogen production, organic dye degradation
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
Date Deposited: 26 Oct 2014 20:55
Official URL: http://tuprints.ulb.tu-darmstadt.de/4199
URN: urn:nbn:de:tuda-tuprints-41990
Additional Information:

I am an Erasmus Mundus PhD student. My host university is University of Bordeaux, France and my second partner university is The Technical University of Darmstadt, Germany. My CV is included in the manuscript. Please let me know if everything is fine. I have sent the print version of the thesis.

Referees: LOUIS, Mrs. Catherine and Cassaignon, Mrs. Sophie
Refereed / Verteidigung / mdl. Prüfung: 16 September 2013
Alternative keywords:
Alternative keywordsLanguage
Halbleitende Metalloxide, Heteroübergangs-Nanokatalysatoren, XPS, UPS, Energiebandanordnung, photokatalytische Aktivität, Wasserstoffproduktion, Zersetzung organischer Farbstoffe.German
Alternative Abstract:
Alternative abstract Language
Photokatalytische Prozesse an Halbleiteroxid-Grenzflächen sind von weltweitem Interesse, da sie ein hohes Potential für effiziente, umweltfreundliche und ökonomisch günstige Anwendungen in den Bereichen Wasser- und Luftaufbereitung sowie für die Erzeugung von erneuerbarem Wasserstoff besitzen. Die bisher erreichbaren Wirkungsgrade werden allerdings durch die Rekombination von Ladungsträgern begrenzt. Die Entwicklung von Heterostruktur-Photokatalysatoren durch die Abscheidung von Metallen an der Oberfläche von Halbleitern oder durch Kopplung von zwei Halbleitern mit passender Bandkantenposition kann die Rekombinationsphänomene durch vektorielle Trennung der Ladungsträger reduzieren. Um sich neuen Perspektiven in diesem Arbeitsgebiet anzunähern, wurden drei verschiedene Arten von Heterostrukturen wie n/n-dotierte Halbleiter (SnO2/ZnO), Metall/n-dotierte Halbleiter (RuO2/TiO2 und RuO2/ZnO) und p/n-dotierte Halbleiter (NiO/TiO2) Nano-Heterostrukturen erfolgreich durch Lösungsprozesse präpariert. Ihre Anordnung, Textur, Struktur und Morphologie wurde sorgfältig durch FTIR, X-ray Diffraktion (XRD), Raman Spektroskopie, Transmissionselektronenmikroskopie (TEM) und N2 Sorptionsmessungen charakterisiert. Dem gegenüber lieferte eine passende Kombination von Daten aus UV-VIS diffuser Reflektionsspektroskopie (DRS), X-ray Photoelektronen-Spektroskopie (XPS) und ultravioletter Photoemissions-Spektroskopie (UPS) das Energiebanddiagramm für jedes System. Die so präparierten Heteroübergangs-Katalysatoren zeigten höhere photokatalytische Effizienz als P25 TiO2 für die Zersetzung von organischen Farbstoffen (d. h. Methylenblau und Methylorange) und die Produktion von Wasserstoff. Insbesondere erreichten Heterostruktur-RuO2/TiO2 und NiO/TiO2-Nanoverbundstrukturen mit optimaler Ladung von RuO2 (5 wt %) und NiO (1 wt %) jeweils die höchsten photokatalytischen Aktivitäten für die Produktion von Wasserstoff. Diese verbesserten Leistungen wurden auf die passende Bandanordnung zurückgeführt, wie durch XPS/UPS Messungen bewiesen wurde, sowie auf die guten texturellen und strukturellen Eigenschaften. Dieses Konzept von Halbleiter-Heteroübergangs-Nanokatalysatoren mit hoher photokatalytischer Aktivität sollte in Zukunft industrielle Anwendung finden, um unerwünschte organische Stoffe aus der Umwelt zu entfernen und erneuerbaren Wasserstoff zu produzieren.German
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