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Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces
Uppsala University, Uppsala, Sweden.
Uppsala University, Uppsala, Sweden.
Mälardalen University, School of Sustainable Development of Society and Technology.
Uppsala University, Uppsala, Sweden.
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2007 (English)In: Applied Surface Science, ISSN 0169-4332, Vol. 253, no 18, p. 7540-7548Article in journal (Refereed) Published
Abstract [en]

The immobilisation of thiol-derivatized cobalt porphyrins on gold surfaces has been studied in detail by means of combined scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). S-thioacetyl has been used as a protective group for the thiol. Different routes for deprotection of the acetyl groups were performed in acidic and in basic conditions. The results show the formation of monolayer films for the different preparation schemes. The immobilisation of the molecules on the gold surface takes place through the thiol-linkers by the formation of multiple thiolate bonds. In the case of layers formed with protected porphyrins approximately 60% of the linkers are bonded to the gold surface whereas for deprotected layers the amount of bonded linkers is increased up to about 80%. STM measurements revealed that the molecules arrange in a disordered overlayer and do not exhibit mobility on the gold surface. Annealing experiments have been performed in order to test the stability of the porphyrin layers. Disordered patterns have been observed in the STM images after annealing at T= 400 degrees C. XPS revealed that the sulphur content disappeared completely after annealing at T= 180 degrees C and that the molecules did undergo significant modifications.

Place, publisher, year, edition, pages
2007. Vol. 253, no 18, p. 7540-7548
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:mdh:diva-4164DOI: 10.1016/j.apsusc.2007.03.066ISI: 000247863800034Scopus ID: 2-s2.0-34249905896OAI: oai:DiVA.org:mdh-4164DiVA, id: diva2:121038
Available from: 2008-02-06 Created: 2008-02-06 Last updated: 2015-07-02Bibliographically approved
In thesis
1. Heterogenization of a Cobalt Porphyrin Catalyst Investigated by Scanning Probe Microscopy and X-Ray Photoelectron Spectroscopy: The Effect on Catalysis of Oxidation Reactions
Open this publication in new window or tab >>Heterogenization of a Cobalt Porphyrin Catalyst Investigated by Scanning Probe Microscopy and X-Ray Photoelectron Spectroscopy: The Effect on Catalysis of Oxidation Reactions
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Construction of advanced materials through self-assembly on the molecular level is an important route to achieve novel functionality. Self-assembly of thiols onto gold has during the last decades shown greate promise in the creation of functional nanomaterials, such as sensors or catalysts, but for many applications silicon should be a better substrate since it offers semiconducting properties and better processing abilities in addition to being cheaper. This work describes an efficient novel method to incorporate reactive disulfide bonds onto a silica surface under mild reaction conditions. The reactive thiol groups introduced onto the silica surface will be oxidized but is then converted into highly reactive thiopyridyl groups, which can easily be utilized for further organic synthesis involving thiol-containing molecules.

Cobalt tetraarylporphyrins with thioacetate-functionalized carbon chains on the aryl groups were synthesized (CoTPP-L) and were used as a model system for investigating catalytic activity in homogeneous and heterogeneous oxidation catalysis. For heterogeneous catalysis CoTPP-L was immobilized onto gold surfaces through thiol-gold self-assembly, and onto silica surfaces by the above mentioned disulfide exchange method.

The properties of the molecular layers were characterized on the molecular level by means of X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). The immobilization on gold surfaces took place through the formation of multiple thiolate bonds and it could be controlled by varying the preparation scheme. More thiolate bonds form if the thioacetyl protective groups of the thiol linkers are cleaved off prior to immobilization. The CoTPP-L molecules were in all cases found to form stable disordered monolayers on gold surfaces. On silica surfaces the CoTPP-L forms patchwise multilayers.

The catalytic performance of the heterogenized systems (CoTPP-L immobilized onto gold or silicon wafers) was evaluated and it was found that the strong inactivation observed for their homogeneous congener was avoided. As a result, the turnover number per molecule in heterogeneous catalysis was at least 100 times higher than that of the corresponding homogeneous catalyst. It is thus demonstrated that the performance of these catalysts can be dramatically improved if the catalyst arrangement can be controlled on the molecular level. Work is ongoing to extend the system to high surface area materials.

Place, publisher, year, edition, pages
Akademin för hållbar samhälls- och teknikutveckling, 2008
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 57
National Category
Other Chemical Engineering
Research subject
Bioteknik/kemiteknik
Identifiers
urn:nbn:se:mdh:diva-492 (URN)978-91-85485-71-0 (ISBN)
Public defence
2008-03-07, Filen, Verktyget, Smedjegatan 37, Eskilstuna, 10:00
Opponent
Supervisors
Available from: 2008-02-06 Created: 2008-02-06

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