**6. Algal systems for hydrogen**

Biological hydrogen production is a method of photobiological water splitting which done based on the production of hydrogen by algae. In 1939, it was observed that a green - algae would sometimes switch from the production of oxygen to the production of hydrogen. In the late 1990s, professor Anastasios Melis discovered that if the algae culture medium is deprived of sulfur it will switch from the production of oxygen (normal photosynthesis), to the production of hydrogen. However, under normal conditions where oxygen is a byproduct of photosynthesis, sustained algal hydrogen photoproduction cannot be maintained for more than a few minutes. Many research groups are currently trying to find a way to take the part of the hydrogenase enzyme that creates the hydrogen and introduce it into the photosynthesis process. These include molecular engineering of the hydrogenase to remove the oxygen sensitivity and development of physiological means to separate oxygen and hydrogen production. The result would be a large amount of hydrogen, possibly on par with the amount of oxygen created (Federico Rossi & Mirko Filipponi, 2011).

### **7. Carbon capture and storage**

The concentration of carbon dioxide in the atmosphere has risen from 280 to 370 PPM from 1860 to recent years. Industrial emission of CO2 into the earth's atmosphere presently exceeds 1010 tons per year. Storage of the CO2 either in deep geological formations, in deep ocean masses, or in the form of mineral carbonates is a way to decrease of CO2 in atmosphere. In the case of deep ocean storage, there is a risk of decreasing pH an issue that also stems from the excess of carbon dioxide already in the atmosphere and oceans. In this regard, several concepts have been proposed. Injection CO2 by ship or pipeline into the ocean water column at depths of 1000 – 3000 m, forming an upward-plume, and the CO2 subsequently dissolves in seawater, injecting CO2 directly into the sea at depths greater than 3000 m, where high-pressure liquefies CO2, making it denser than water, and is expected to delay dissolution of CO2 into the ocean and atmosphere, storing CO2 in solid clathrate hydrates already existing on the ocean floor or using a chemical reaction to combine CO2 with a carbonate mineral. Geological formations are currently considered the most promising sequestration sites. Geological storage involves injecting carbon dioxide, generally in supercritical form, directly into underground geological formations. Various physical and geochemical trapping mechanisms would prevent the CO2 from escaping to the atmosphere. Recycling CO2 is likely to offer the most environmentally and financially sustainable response to the global challenge of significantly reducing greenhouse gas emissions. Using artificial photosynthesis, scientists try to find a way to produce useful organic compounds from CO2. For example, CO2 and other captured greenhouse gases could be injected into the membranes containing waste water and select strains of organisms causing an oil rich biomass that doubles in mass every 24 hours or to convert CO2 into hydrocarbons where it can be stored or reused as fuel or to make plastics (Cook, 2005).

#### **8. Ribulose-1,5-bisphosphate carboxylase oxygenase**

Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) is an enzyme involved in the Calvin cycle that catalyzes a process by which CO2 are made available to organisms in the

Biological hydrogen production is a method of photobiological water splitting which done based on the production of hydrogen by algae. In 1939, it was observed that a green - algae would sometimes switch from the production of oxygen to the production of hydrogen. In the late 1990s, professor Anastasios Melis discovered that if the algae culture medium is deprived of sulfur it will switch from the production of oxygen (normal photosynthesis), to the production of hydrogen. However, under normal conditions where oxygen is a byproduct of photosynthesis, sustained algal hydrogen photoproduction cannot be maintained for more than a few minutes. Many research groups are currently trying to find a way to take the part of the hydrogenase enzyme that creates the hydrogen and introduce it into the photosynthesis process. These include molecular engineering of the hydrogenase to remove the oxygen sensitivity and development of physiological means to separate oxygen and hydrogen production. The result would be a large amount of hydrogen, possibly on par

The concentration of carbon dioxide in the atmosphere has risen from 280 to 370 PPM from 1860 to recent years. Industrial emission of CO2 into the earth's atmosphere presently exceeds 1010 tons per year. Storage of the CO2 either in deep geological formations, in deep ocean masses, or in the form of mineral carbonates is a way to decrease of CO2 in atmosphere. In the case of deep ocean storage, there is a risk of decreasing pH an issue that also stems from the excess of carbon dioxide already in the atmosphere and oceans. In this regard, several concepts have been proposed. Injection CO2 by ship or pipeline into the ocean water column at depths of 1000 – 3000 m, forming an upward-plume, and the CO2 subsequently dissolves in seawater, injecting CO2 directly into the sea at depths greater than 3000 m, where high-pressure liquefies CO2, making it denser than water, and is expected to delay dissolution of CO2 into the ocean and atmosphere, storing CO2 in solid clathrate hydrates already existing on the ocean floor or using a chemical reaction to combine CO2 with a carbonate mineral. Geological formations are currently considered the most promising sequestration sites. Geological storage involves injecting carbon dioxide, generally in supercritical form, directly into underground geological formations. Various physical and geochemical trapping mechanisms would prevent the CO2 from escaping to the atmosphere. Recycling CO2 is likely to offer the most environmentally and financially sustainable response to the global challenge of significantly reducing greenhouse gas emissions. Using artificial photosynthesis, scientists try to find a way to produce useful organic compounds from CO2. For example, CO2 and other captured greenhouse gases could be injected into the membranes containing waste water and select strains of organisms causing an oil rich biomass that doubles in mass every 24 hours or to convert CO2 into hydrocarbons where it can be stored or reused as fuel or to make plastics (Cook, 2005).

with the amount of oxygen created (Federico Rossi & Mirko Filipponi, 2011).

**8. Ribulose-1,5-bisphosphate carboxylase oxygenase** 

Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) is an enzyme involved in the Calvin cycle that catalyzes a process by which CO2 are made available to organisms in the

**6. Algal systems for hydrogen** 

**7. Carbon capture and storage** 

form of energy-rich molecules such as glucose. RuBisCO catalyzes either the carboxylation or the oxygenation of ribulose-1,5-bisphosphate.

It is believed that RuBisCO is rate-limiting for photosynthesis in plants and it is proposed that may be possible to improve photosynthetic efficiency by modifying RuBisCO genes in plants to increase its catalytic activity (Spreitzer & Salvucci, 2002). Engineered changes in Rubisco's properties Unpredictable expression of plastid transgenes and assembly requirements of some foreign Rubiscos that are not satisfied in higher-plant plastids provide challenges for future research.

There are the most important titles in artificial photosynthesis but we could increase our list as important titles in artificial photosynthesis and as it is considered by Pace, artificial photosynthesis is an umbrella term. As you see in each title, inspired by natural photosynthesis, in artificial photosynthesis novel approaches used to develop technologies for non-polluting electricity generation, fuel production and carbon sequestration using solar energy. (Pace, 2005). Researchers and scientists are trying to learn a great about the detail of natural photosynthetic systems and have been able to understand at least parts of this process. Therefore, artificial photosynthetic goal and capable of converting sunlight into chemically-bound energy seem to be a realistic scenario in near future.

#### **9. Acknowledgment**

Authors are grateful to Institute for Advanced Studies in Basic Sciences for financial support.

#### **10. References**

Bockris, J.O.M. (1977) Energy-the solar hydrogen alternative, Wiley&Sons, New York.


**Fundamental Aspects** 

Umena, Y.; Kawakami, K.; Shen, J.R. & Kamiya, N. (2011) Crystal structure of oxygenevolving photosystem II at a resolution of 1.9Ǻ. *Nature*, v.473, p.55-60 **Part 2**  evolving photosystem II at a resolution of 1.9Ǻ. *Nature*, v.473, p.55-60 **Part 2** 

**Fundamental Aspects** 

10 Artificial Photosynthesis

Umena, Y.; Kawakami, K.; Shen, J.R. & Kamiya, N. (2011) Crystal structure of oxygen-

**2** 

*Turkey* 

**Artificial Photosynthesis from a** 

Bahar Ipek and Deniz Uner *Middle East Technical University,* 

**Chemical Engineering Perspective** 

Green plants and photosynthetic bacteria are responsible for storing solar energy in chemical bonds via photosynthesis. Photosynthesis is not only the major source of food, fuel and oxygen on earth, but it is also the key player in the global carbon cycle by converting

Conversion of solar energy into chemical energy through utilization of inorganic materials by photocatalytic CO2 reduction; which is also known as *'Artificial Photosynthesis'* is the next challenge for a sustainable development. In the present state-of-the art artificial photosynthesis processes, nature is so far mimicked only to the extent that CO2 is reduced by water to valuable 1- carbon chemicals, not to the multi-carbon equivalents of glucose or cellulose yet. Although mimicking nature is viable by photocatalytic means, enhancing photocatalytic CO2 reduction rates is vital in order to achieve artificial photosynthesis in industrial scales. To illustrate the gap between photosynthetic and photocatalytic rates, we

Water oxidation is the key step both in photocatalysis and photosynthesis for being the carbon free hydrogen source and also for providing oxygen for the oxygen consuming organisms. Completion of an S cycle taking place in a Mn4 cluster which is responsible for water oxidation was reported to last for 1.59 ms in order to produce one molecule of oxygen at that one particular site (Haumann et al., 2005). In other words, molecular oxygen is produced in photosynthesis, with a turn over frequency of 630 molecule/site/s. On the other hand, typical rates of photocatalytic synthesis of hydrocarbons are of the order of 30 µmoles/g cat/h, (Ozcan et al., 2007; Uner et al., 2011) which amounts to 1.11\*10-5 molecule/site/s if the typical surface areas of 45 m2/g cat and typical site densities of 1015/cm2 are used. Of course the remarkable rates of 9 µmoles of O2/cm2/s (Kanan & Nocera, 2008), giving a turn over frequency of 5400 molecule/site/s for an oxygen evolving cobalt- phosphate catalyst operating at neutral water is keenly followed by the academic community. Considering the huge gap between photosynthetic and photocatalytic rates reported above, one can easily claim that there is room for further investigation and

It is also important to see the thermodynamic energy demand of the some of the reactions between CO2 and H2O. For this, a number of products are chosen and the standard Gibbs free energy of formation values are listed in Table 1.1 for comparison. The interesting

will compare the turnover frequencies of water oxidation process below.

development in photocatalytic CO2 reduction systems.

**1. Introduction** 

120 gigatonnes of carbon per year.
