Molecular insights into porphyrin adsorption on nanostructured metal oxide surfaces and associated ion exchange reactions are key to the development of functional hybrids for energy conversion, sensing, and light emission devices. Here we investigated the adsorption of tetraphenyl-porphyrin (2HTPP) from toluene solution on two types of MgO powder. We compare MgO nanocubes with an average size d < 10 nm and MgO cubes with 10 nm ≤ d ≤ 1000 nm. Using molecular spectroscopy techniques such as UV/vis transmission and diffuse reflectance (DR), photoluminescence (PL), and diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy in combination with structural characterization techniques (powder X-ray diffraction and transmission electron microscopy, TEM), we identified a new room temperature metalation reaction that converts 2HTPP into magnesium tetraphenyl-porphyrin (MgTPP). Mg(2+) uptake from the MgO nanocube surfaces and the concomitant protonation of the oxide surface level off at a concentration that corresponds to roughly one monolayer equivalent adsorbed on the MgO nanocubes. Larger MgO cubes, in contrast, show suppressed exchange, and only traces of MgTPP can be detected by photoluminescence.
Adsorption and reaction of formic acid on stoichiometric CeO 2 (111), partially reduced CeO 2−x , and Pt/ CeO 2 (111) films prepared on Cu(111) were studied by means of synchrotron radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES), infrared reflection absorption spectroscopy (IRAS), and temperatureprogrammed desorption (TPD). On all studied samples, the principal species formed during formic acid adsorption below 160 K were formate and molecular formic acid. In the presence of Pt particles, formate species were predominantly localized on Pt at 100 K, and on ceria at or above 300 K. Below 400 K, molecular formic acid decomposes to formate with partial release of CO 2 , CO, hydrogen, and water. Analysis of the TPD fragmentation suggests additional evolution of methane. Above 400 K, desorption of CO 2 , CO, hydrogen, and water is observed. This process is controlled by the stoichiometry of ceria and the presence of Pt particles. In particular, desorption of CO 2 is suppressed on CeO 2−x but is enhanced on Pt/CeO 2 . RPES suggests that the reaction of formic acid does not alter the oxidation state of cerium cations on CeO 2 (111). By contrast, we observed significant reoxidation on partially reduced CeO 2−x , between 250 and 400 K, followed by reduction between 400 and 500 K.
Sequential butanediol lactonization and transfer hydrogenation/hydrogenolysis of furfural-derivatives offers new opportunities for reductive upgrading of biomass.
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 × 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.