Photosynthesis of hydrogen

The appearance on the surface of any acceptor particles resulting in the negative charging of the surface and hence in the lowering of the Fermi level at the surface (in an increase of es- at v = const) must lead, according to (95) or (98), to the weakening of the photocatalytic effect. This is what actually occurs in the photosynthesis of hydrogen peroxide [jsee references (65-67, 71-73, 77)]. 

The fact that the photosynthesis of hydrogen peroxide on irradiated titanium dioxide suspensions is manifestly ineffective is easily understood when one examines together the cathodic and the photoanodic behaviour of H2O2 at a Ti02 electrode . Thus, the reduction of the HOJ ions... 

G. (1996) Die Photochemischen Bildung des Chlorwasserstoffs. Dynamics of Cl + H2 HCl + H on a New Potential Energy Surface The Photosynthesis of Hydrogen Chloride Revisited lOOYears after Max Bodenstein in J Wolfram, H-R Volpp, R Rannacher and J Wamatz (eds), Gas-Phase Reaction Systems Experiments and Models 100 Years after Max Bodenstein, Springer, Heidelberg, pp. 111-24 Manolopoulos, D. E. (1997) The dynamics of the F+H2 reaction, J. Chem. Soc. Faraday Trans. 93, 673-83 Casavecchia, P. (2000) Chemical reaction dynamics with molecular beams. Rep. Prog. Phys. 63, 355-414. 

For obvious reasons, this reaction led to an enormous amount of research into the use of solar radiation in the photosynthesis of hydrogen. However, the process suffers from a number of drawbacks that limit its usefulness, as discussed below. 

Die photochemische Bildung des Chlorwasserstqffs Dynamics of Cl + H2 HCl + H on a New Potential Energy Surface The Photosynthesis of Hydrogen Chloride Revisited 100 Years after Max Bodenstein... 

The Cl + H2 HCl + H reaction has a particularly long and interesting history, including thermal and photochemical studies of the H2-CI2 system, molecular beam experiments, measurements of perhaps the largest number of kinetic isotope effects known for any system, and a host of theoretical treatments. We will mention only a few particularly relevant studies. Early experimental studies of this reaction were often initiated by photodissociation of CI2, and some of the papers are entitled Photosynthesis of Hydrogen Chloride (a translation of die Photochemische... 

Norrish RGW (1926) The role of water in the photosynthesis of hydrogen chloride. Trans... 

The mechanism given below for the photosynthesis of hydrogen bromide has been proposed by various authors [400]. It involves the following elementary steps ... 

Kinetic isotope effects are an important factor in the biology of deuterium. Isotopic fractionation of hydrogen and deuterium in plants occurs in photosynthesis. The lighter isotope is preferentially incorporated from water into carbohydrates and tipids formed by photosynthesis. Hydrogen isotopic fractionation has thus become a valuable tool in the elucidation of plant biosynthetic pathways (42,43). 

A method of detecting herbicides is proposed the photosynthetic herbicides act by binding to Photosystem II (PS II), a multiunit chlorophyll-protein complex which plays a vital role in photosynthesis. The inhibition of PS II causes a reduced photoinduced production of hydrogen peroxide, which can be measured by a chemiluminescence reaction with luminol and the enzyme horseradish peroxidase (HRP). The sensing device proposed combines the production and detection of hydrogen peroxide in a single flow assay by combining all the individual steps in a compact, portable device that utilises micro-fluidic components. 

Colorless, reactive gas. Oxygen was not present in the initial atmosphere of the Earth, although at 50 % it is the most common element in the crust of the Earth (oxides, silicates, carbonates, etc.). The compound with hydrogen is remarkable. The hydrides of all other elements are unpleasant compounds, but H20 is the molecule of life. The 02 found in the air today, of which it makes up 20 %, was formed in the process of evolution by photosynthesis of algae, which then also allowed life on solid land. Oxidation with oxygen became and is still the dominant pathway of life forms for obtaining energy (respiration). Used in medicine in critical situations. Oxidations play a key role in chemistry (sulfuric acid, nitric acid, acetic acid, ethylene oxide, etc.). The ozone layer in space protects the Earth from cosmic UV radiation. Ozone (03) is used in the... 

In conclusion, the rates and efficiencies of hydrogen production by systems directly using photosynthesis fall short of even plausible economic feasibility. Since organic substrates are the ultimate source of hydrogen in photofermentations or indirect biophotolysis processes, it can be argued that it should be simpler and more efficient to extract the hydrogen from substrates using a dark fermentation process, an approach which is discussed next. 

A third area of hydrogen from biomass is metabolic processing to split water via photosynthesis or to perform the shift reaction by photo biological organisms. This is an area of long-term research. 

Although carhon dioxide is released in most of the biomass-to-hydrogen conversion processes, the net CO 2 emission is zero due to the photosynthesis of green plants. 

Greenbaum E (1980) Simultaneous photoproduction of hydrogen and oxygen by photosynthesis. Biotechnol Bioeng Symp 10 1-13... 

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