Oxygen evolution is the process of producing molecular oxygen through a chemical reaction. Mechanisms of oxygen evolution include the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and the evolution of electrocatalytic oxygen from oxides and oxoacides.
Video Oxygen evolution
Evolution of oxygen in nature
The evolution of oxygen photosynthesis is a fundamental process whereby breathable oxygen is produced in the Earth's biosphere. This reaction is part of a light-dependent photosynthetic reaction to cyanobacteria and chloroplasts of green algae and plants. It utilizes light energy to separate water molecules into protons and their electrons for photosynthesis. Free oxygen is produced as a byproduct of this reaction, and released into the atmosphere.
Biochemical reactions
The evolution of photosynthetic oxygen takes place through the oxidation of the light-dependent water to oxygen molecules and can be written as the following simplified chemical reaction:
- 2H 2 O? 4e - 4H O 2
The reaction requires four photons of energy. Electrons from oxidized water molecules replace electrons in the P 680 component of photosystem II which have been transferred into the electron transport chain through light-dependent excitation and transfer of resonance energy to plastoquinone. Therefore, Photosytem II has also been referred to as a water-plastoquinone water-reductase oxidizer. The proton is released into the thylakoid lumen, thus contributing to the formation of proton gradients across the thylakoid membrane. This proton gradient is the driving force for ATP synthesis through photophosphorylation and coupling of light energy absorption and water oxidation for the creation of chemical energy during photosynthesis.
Oxygen-evolved complex
Water oxidation is catalyzed by a manganese cofactor contained in a photosystem II known as an oxygen-evolved complex (OEC) or water separation. Manganese is an important factor, and calcium and chloride are also needed in order for the reaction to occur.
X-ray crystallographic data has been used to propose structure and action mechanisms for oxygen evolving complexes and manganese groups. Based on structural and spectroscopic experiments, the evolution of oxygen involves a three-plus-three nucleus group of three manganese ions and one calcium ion, with one additional manganese, oxidized through an intermediate state called S-states . O-O bonds of molecular oxygen are formed between manganese-lubricated oxygen atoms in the most oxidized state, or S4. The reaction procedure in S-state is almost completely understood by the Dolai S-state diagram. Ref. Dolai, U (2017). "Chemical Scheme of Air-Process Pitting during Photosynthesis by means of Experimental Analysis". 12 (6): 65-67 doi: 10.9790/3008-1206026567. ISSN 2319-7676.
History of discovery
It was not until the end of the 18th century that Joseph Priestley accidentally discovered the plant's ability to "restore" the air "wounded" by the burning of wax. He followed up his experiments by showing that the air "restored" by vegetation was "not at all inconvenient." He was then awarded a medal for his discovery that: "... vegetables grow in vain... but cleanse and purify our atmosphere." The Priestley experiment was followed up by Jan Ingenhousz, a Dutch physician , which shows that the "restoration" of the air only works in the presence of light and green plant parts.
Ingenhousz suggested in 1796 that CO 2 (carbon dioxide) was split during photosynthesis to release oxygen, while carbon was combined with water to form carbohydrates. Although this hypothesis is interesting and plausible and thus widely accepted for a long time, it then proves to be wrong. Graduate student C. Van Niel at Stanford University found that purple sulfur bacteria reduce carbon to carbohydrates, but accumulate sulfur rather than release oxygen. He boldly proposed that, in analogy with the sulfur-forming element sulfur from H 2 S (hydrogen sulfide), the plant would form oxygen from H 2 O (water). In 1937, this hypothesis was corroborated by the discovery that plants were able to produce oxygen in the absence of CO 2 . The invention was made by Robin Hill, and then the release of light-driven oxygen in the absence of CO 2 is referred to as the Hill reaction. Our current knowledge of the mechanism of evolution of oxygen during photosynthesis is further established in experiments that track oxygen isotopes from water to oxygen gas.
Maps Oxygen evolution
Evolution of oxygen technology
The evolution of oxygen occurs as a by-product of hydrogen production through water electrolysis. While oxygen production is not the main focus of industrial applications of water electrolysis, it becomes essential for life support systems in situations requiring oxygen generation for air revitalization. Human exploration in areas that lack breathable oxygen, such as the deep ocean or outer space, requires reliable tools to produce oxygen separate from the Earth's atmosphere. Submarines and spacecraft utilize either electrolytic mechanisms (water or solid oxide electrolysis) or chemical oxygen generators as part of their life support equipment.
See also
- Large Oxygen Show
References
External links
- Online Plant Physiology, 4th edition: Topic 7.7 - Evolution of Oxygen
- Evolution of oxygen - Lecture notes by Antony Crofts, UIUC
- The evolution of the atmosphere - Lecture notes, the University of Michigan Bupati
- How to make oxygen and hydrogen from water using electrolysis
Source of the article : Wikipedia
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