Loading...

Model Systems for Oxygen – Evolving Complex in Photosystem II: Manganese Oxides and Manganese Complexes with O and N Donor Ligands

Najafpour, Mohammad Mahdi | 2009

738 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39946 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Mohammadi Boghaei, Davar
  7. Abstract:
  8. The aim of this study is to mimic water oxidizing complex to find new materials and also to understand their rules in this matter. To achieve this, manganese complexes containing 2,4,6-tris (2-pyridyl)-1,3,5-Triazine, 1,10-phenanthroline, 1,10-bipyridine, Schiff base, amino acids, 2,6-pyridinedicarboxylic acid, 2-pyridinecarboxylic acid have been synthesized and characterized by elemental analysis, IR, EPR, ESI-MS, electronic absorption spectroscopy, electrochemistry, X-ray diffraction and oxygen evolution in presence of oxone and Ce(IV). It is shown that the reaction between Mn(II) complexes containing 2,4,6-tris¬(2-pyridyl)-1,3,5-Triazine, 1,10-phenanthroline, 1,10-bipyridine, 2,6-pyridinedicarboxylic acid, 2-pyridinecarboxylic acid and potassium peroxomonosulfate (oxone) produces oxygen with a turnover number of 0.1 – 5.0 (mol of O2 / mol of the complex). A dinuclear manganese complex (III, IV) is detected as a intermediate in all reactions produce oxygen with these complexes. Complexes containing one 2,6-pyridinedicarboxylate per manganese is the best complex for oxygen evolution among these complexes in presence of oxone with a turnover number of 5.0 (mol of O2 / mol of the complex). Oxygen evolution was also observed upon mixing solid manganese(III) tetradenta and bidentate Schiff base complexes with aqueous solutions of cerium(IV) ammonium nitrate. The Effect of solvent, oxygen, ethanol, electron-donating and electron-withdrawing substituents on ligand have been considered on oxygen evolution reaction. In order to find out roles of calcium and manganese in inorganic core of water oxidizing complex, Mn2O3, CaMn2O4.nH2O (n= 0,1 and 3) have been synthesized using hydrothermal technique and characterized by atomic absorbtion, IR, Raman, EDX, XRD, SEM, TG and DTG electrochemistry, X-ray diffraction under supervision of Dr. Philipp Kurz in University of Kiel at Germany. The rate and amount of oxygen evolution in presence of oxone, H2O2, Ce(IV) and [Co(NH3)5Cl]2+/Ru(bpy)32+/light are studied. Oxide materials of this study can be easily synthesised from cheap and abundant starting materials. Results of oxygen evolution experiments shows calcium-manganese oxides are promising candidates to act as water-oxidation catalysts for artificial photosynthesis. The role of calcium in natural water oxidation catalysis can be reproduced by the rather simple model of a mixed calcium manganese oxide. Calcium has been suggested as binding and activation site for H2O in the OEC – both roles of calcium can be envisioned for the reactions of CaMn2O4.nH2O (n= 0,1 and 3) presented here as well. These results could also help scientists for architecturing of advanced material in order to understand of mechanism of water oxidation in natural photosynthesis and also as a road map for new research in this subject
  9. Keywords:
  10. Manganese Complex ; Chemical Synthesis ; Oxygen ; Water Oxidation Complex ; Manganese Oxide ; Nitrogen and Oxygen Ligands

 Digital Object List

  • محتواي پايان نامه
  •   view

 Bookmark

No TOC