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Photochemical and Photoelectric Applications of II-VI Semiconductor Nanomaterials
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In this work we investigated fabrication of semiconductor nanomaterials and evaluated their potential for photo-chemical and photovoltaic applications. We investigated two different II-VI semiconductor nanomaterial systems; (i) ZnO oriented nanowire arrays non-epitaxially grown from a substrate; and (ii) colloidal CdTe nanotetrapods synthesized by solution-based thermal decomposition of organo-metallic precursors. In both the cases our main focus has been optimizing material synthesis for improving potential applications based on photon-electron interactions.

We have studied the synthesis of vertically aligned ZnO nanowire arrays (NWA), by a wet chemical process on various substrates. The synthesis is based on epitaxial growth of ZnO seed-layer on a substrate in a chemical bath consisting of an aqueous solution of zinc nitrate and hexamethylenetetramine (HMT). We have suggested an additional role played by HMT during the synthesis of ZnO nanowire arrays. We have also extended this synthesis method to fabricate hierarchical nanostructures of nanofibers of poly-L-lactide acting as a substrate for the radially oriented growth of ZnO nanowires. The combination of high surface area of the nanofibrous substrate with the flexibility of the PLLA-ZnO hierarchical nanostructure enabled the proof-of-principle demonstration of a ‘continuous-flow’ water treatment system that could effectively decompose single and combination of known organic pollutants in water, as well as render common waterborne bacteria nonviable.

We have studied another chemical synthesis that is commonly used for size controlled synthesis of colloidal quantum dots, which was modified to obtain anisotropic nanocrystals mainly for CdE (E=S, Se, Te) compositions. In this work we demonstrate by use of oleic acid (instead of alkylphosphonic acids) it is possible to synthesize CdTe and CdSe nanotetrapods at much lower temperatures (~180 ºC) than what is commonly reported in the literature, with significantly different  formation mechanism in the low-temperature reaction.

Finally, we have performed preliminary photoconduction measurements with CdTe nanotetrapods using gold ‘nanogap’ electrodes fabricated in-house, and obtain up to 100 times enhancement in current levels in the I–V measurements under illumination with a white light source.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , v, 47 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2010:03
Keyword [en]
ZnO, Nanowire arrays, Photocatalysis, Nanofibers, CdTe, Nanotetrapods, Ostwalds ripening, Photoconduction, Nano-gap electrodes
Identifiers
URN: urn:nbn:se:kth:diva-12808ISBN: 978-91-7415-624-9 (print)OAI: oai:DiVA.org:kth-12808DiVA: diva2:318913
Presentation
2010-05-05, C2, Electrum, Isafjordsgatan 22, Kista, 10:30 (English)
Opponent
Supervisors
Note
QC20100607Available from: 2010-06-07 Created: 2010-05-11 Last updated: 2010-06-07Bibliographically approved
List of papers
1. Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine
Open this publication in new window or tab >>Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine
2006 (English)In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 39, no 1, 49-56 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:kth:diva-13234 (URN)10.1007/s10971-006-6969-y (DOI)000239432100006 ()
Note
QC20100614Available from: 2010-06-07 Created: 2010-06-07 Last updated: 2017-12-12Bibliographically approved
2. Low-temperature synthesis of photoconducting CdTe nanotetrapods
Open this publication in new window or tab >>Low-temperature synthesis of photoconducting CdTe nanotetrapods
Show others...
2010 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 20, no 6, 1208-1214 p.Article in journal (Refereed) Published
Keyword
SHAPE-CONTROLLED SYNTHESIS, CDSE NANOCRYSTALS, SOLAR-CELLS, NANORODS, GROWTH, TETRAPODS, NANOPARTICLES, MONODISPERSE, COMPOSITES, EVOLUTION
National Category
Physical Chemistry Materials Engineering
Identifiers
urn:nbn:se:kth:diva-13235 (URN)10.1039/b916208a (DOI)000273961900028 ()2-s2.0-77949558021 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, UAW2004.0224
Note
QC 20110121Available from: 2010-06-07 Created: 2010-06-07 Last updated: 2017-12-12Bibliographically approved
3. A ‘Continuous flow’ Photochemical Water Treatment System Based on Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide Nanofibers
Open this publication in new window or tab >>A ‘Continuous flow’ Photochemical Water Treatment System Based on Radially Oriented ZnO Nanowires on Flexible Poly-L-Lactide Nanofibers
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Several oxide ceramics, notably ZnO and TiO2 are known to catalyze decomposition of organic molecules in water under ultra-violet irradiation. Here we describe fabrication of highly flexible ZnO-based hierarchical nanostructure obtained by growing radially oriented ZnO nanowires on poly-L-lactide nanofibers. Utilizing the flexibility and high surface area of polymeric nanofibers as novel ‘substrate’ for growth of the photochemically active ZnO nanowires we show a proof-of-principle demonstration of a ‘continuous flow’ water treatment set-up. We have monitored photocatalytic decomposition of known organic pollutants, such as methylene blue, monocrotophos and diphenylamine under illumination with ultraviolet light using this highly flexible hierarchical nanostructure.

Keyword
ZnO nanorods, Electrospinning, PLLA nanofibers, Photocatalysis, Hierarchical nanostructures
Identifiers
urn:nbn:se:kth:diva-12806 (URN)
Note
QC20100614Available from: 2010-06-07 Created: 2010-05-11 Last updated: 2010-06-14Bibliographically approved

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