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Identifier

000399749

Title

Φωτοκαταλυτική παραγωγή Η2 με μεταλλοπορφυρίνες

Alternative Title

Photocatalytic H2 evolution with metalloporphyrins

Author

Παναγιωτόπουλος, Αθανάσιος Α.

Thesis advisor

Κουτσολέλος, Αθανάσιος

Reviewer

Αγγαρίδης, Παναγιώτης
Λαζαρίδης, Θεόδωρος

Abstract

Energy is embedded in all types of goods and is needed to produce any kind of service. What makes the life of modern, affluent people so easy, compared to the lives of our ancestors or even to the lives of billions of individuals that still live in poverty, is a steady flux of cheap and plentiful energy in the form of fossil fuels. However, we know that oil, natural gas, and carbon will not last forever, and we have also learnt that their use has caused, and is still causing, severe damage to the Earth‟s atmosphere. Σherefore, there is the need to produce alternative fuels in order to be pollution-free, storable and economical. A promising solution that fulfills these requirements is hydrogen production via photocatalytic water splitting. Photocatalysis is defined as the chemical reaction induced by photoiradiation in the presence of a catalyst (photocatalyst). This procedure is inspired by nature where a well known photocatalyst is chlorophyll in photosynthesis by plants. Therefore, various photocatalytic hydrogen evolution catalysts and different photosensitizers (dyes) have been extensively studied. Among, the catalysts that have been used so far, cobaloximes are particularly attractive due to their high activity and easy preparation. Porphyrins have found prominent use as sensitizers in hydrogen production, since nature use them as energy harvesters and electron transfer agents. In general porphyrin molecules appear as a very promising class of new photosensitizers or catalysts for photocatalytic hydrogen production. In the first part of Master Thesis, photocatalytic systems for H2 production in aqueous pH 7 solutions are reported. They consist of various cobaloxime catalysts [Co(dmgH) ₂ (L)Cl] (L = nitrogen-based axial ligands) and water soluble porphyrin photosensitizers. They were assayed in the presence of triethanolamine as sacrificial electron donor. Optimal turnover numbers are obtained when L is an imidazole ligand (1131 TONs with N-methyl imidazole). Lower stabilities are observed with various pyridine axial ligands (443 TONs for para-methylpyridine), especially for those containing electron-acceptor substituents. Interestingly, when L is the para-carboxylatopyridine the activity of the system is increased from 40 to 223 TONs in the presence of TiO₂ nanoparticles. Herein we report the first systematic study for cobaloxime-based H₂ photoproduction in aqueous medium. In the second part of Master Thesis, present for the first time in history of artificial photosynthesis, a very efficient system for photochemical hydrogen production (12100 ΣΟΝ) containing two different metalloporphyrins absorbed on TiO₂ nanoparticles in the presence of TEOA as an electron donor. Both metalloporhyrin derivatives contain four tetracarboxy groups on their periphery making them water-soluble. The Pt-TCPP porphyrin plays the role of the catalyst and the Pd-TCPP porphyrin acts as photosynthesizer.

Language

Greek

Subject

Artificial photosynthesis

Catalyst

Cobaloximes

Hydrogen Production

Photocatalysis

Photosensitizer

Proton reduction

Solar energy

TiO2