Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups

Schneider J, Kollhoff F, Schindler T, Bichlmaier S, Bernardi J, Unruh T, Libuda J, Berger T, Diwald O (2016)

Publication Status: Published

Publication Type: Journal article, Original article

Publication year: 2016

Journal

Journal of Physical Chemistry C American Chemical Society

Publisher: AMER CHEMICAL SOC

Book Volume: 120

Pages Range: 26879-26888

Journal Issue: 47

DOI: 10.1021/acs.jpcc.6b08956

Abstract

The understanding of porphyrin adsorption on oxide nanoparticles including knowledge about coverages and adsorbate geometries is a prerequisite for the improvement and optimization of hybrid materials. The combination of molecular spectroscopies with small-angle X-ray scattering provides molecular insights into porphyrin adsorption on MgO nanocube dispersions in organic solvents. In particular, we address the influence of terminal carboxyl groups on the adsorption of free base porphyrins, on their chemical binding, on the metalation reaction as well as on the coverage and orientation of adsorbate molecules. We compare the free base form 5,10,15,20-tetraphenyl-21,23H-porphyrin (2HTPP) with the carboxyl-functionalized 5,10,15,20-tetrakis(4-carboxyphenyl)-21,23H-porphyrin (2HTCPP) and show that without carboxylic anchoring groups the free base form metalates on the nanocube surface and adopts a flat-lying adsorbate geometry. The saturation limit for flat-lying adsorption on nanocubes with an average edge length of 6 nm corresponds to 90 14 molecules per particle. This limit is surpassed when 2HTCPP molecules attach via their terminal carboxyl groups to the surface. The resulting upright adsorption geometry suppresses self-metalation, on the one hand, and allows for much higher porphyrin coverages, on the other (at porphyrin concentrations in the stock solution of 2 X 10(-2) mol.L-1). UV-vis diffuse reflectance results are perfectly consistent with conclusions from SAXS data analysis. The experiments reveal concentration dependent 2HTCPP coverages in the range between 0.4 to 1.9 molecules nm(-2) which correspond to the formation of a shell of upright standing porphyrin molecules around the MgO nanocubes. In contrast, after adsorption and metalation of nonfunctionalized 2HTPP the resulting porphyrin shells are in the range of a tenth of a nanometer and thus too thin to be captured by SAXS measurements. Related insights advance our opportunities to prepare well-defined nanohybrids containing highly organized porphyrin films.

Authors with CRIS profile

Fabian Kollhoff Lehrstuhl für Physikalische Chemie II Torben Schindler Lehrstuhl für Kristallographie und Strukturphysik (ICSP) Tobias Unruh Professur für Nanomaterialcharakterisierung (Streumethoden) Jörg Libuda Professur für Physikalische Chemie

Additional Organisation(s)

Graduiertenkolleg 1896/2 In situ Mikroskopie mit Elektronen, Röntgenstrahlen und Rastersonden Exzellenz-Cluster Engineering of Advanced Materials (EAM) Interdisziplinäres Zentrum, Center for Nanoanalysis and Electron Microscopy (CENEM)

Involved external institutions

Universität Salzburg (Paris Lodron Universität Salzburg) AT Austria (AT) Technische Universität Wien / Vienna University of Technology AT Austria (AT)

How to cite

APA:

Schneider, J., Kollhoff, F., Schindler, T., Bichlmaier, S., Bernardi, J., Unruh, T.,... Diwald, O. (2016). Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups. Journal of Physical Chemistry C, 120(47), 26879-26888. https://doi.org/10.1021/acs.jpcc.6b08956

MLA:

Schneider, Johannes, et al. "Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups." Journal of Physical Chemistry C 120.47 (2016): 26879-26888.

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