Utilization of Biological Solar Energy and ...

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Utilization of Biological Solar Energy and Development of Artificial .... visible solar radiation, however, the energy used for splitting water and converting carbon ...
Utilization of Biological Solar Energy and Development of Artificial Photosynthesis in Combating Climate Change for Self-Reliance and Sustainable Development.

1, 2

A.S. SAMBO, I. H. ZARMA2 and D.O. OTOKPA3

1, 2

Energy Commission of Nigeria, opposite central mosque, Abuja, Nigeria

3

Department of Mechanical Engineering, Benue State Polytechnic, Benue State, Nigeria

[email protected], [email protected], [email protected]

Abstract Biological solar energy is the energy of the sun that is utilized by living organisms such as plants and animals through the process of photosynthesis. This process is sub-divided into light and dark reaction which enable the earth to maintain its carbon cycles. This paper discusses solar energy efficiencies and how artificial photosynthesis can support the natural one by creating either artificial sun or artificial plant. Finally, conclusions were made that artificial photosynthesis can be one of the better options in combating climate charge. Keywords: light reaction, dark reaction, decarbonising, nanotechnology and biomass

1. INTRODUCTION Fossil fuel provide us with almost all the energy needed to power our technological devices, heat our homes and produce different chemicals and raw material that support everyday life, obviously the quantities of fossil fuel available to us will dwindle at no distant time, and now we are faced with the challenges of increasing level of carbon dioxide in the atmosphere and the consequences of global warming (Hoffert M.T, 2002). It is worthy of note that fossil fuel reserves are derived from the process of photosynthesis which is the process by which plants, algae and certain types of bacteria capture sunlight efficiently and convert into organic molecule that is the building blocks of all living organisms. Photosynthesis produces more than 100 billion tons of dry biomass annually, which would be equivalent to a hundred times the weight of the total human population on our planet at the present time and equal to about 100 TJ of stored energy (Barber, J. 2003)

1.1. Principles of Photosynthesis The raw materials of photosynthesis which are Sunlight, water and carbon dioxide are available in almost unlimited amounts. At the heart of the reaction is the splitting of water by sunlight into oxygen and Hydrogen. Oxygen which is the by-product of photosynthesis is released into the atmosphere where it is available for us to breathe and to use for burning our fuels. The hydrogen is not release into the atmosphere as H2, it is combined with carbon dioxide to make organic molecules of various types. When we burn fossil fuels we combine the carbon stored hydrogen at these organic molecules with oxygen, releasing water and carbon dioxide and effectively reversing the chemical reactions of photosynthesis (Bolton, 1979). Energy is also released from organic molecules when they are metabolized within our bodies by the process of respiration. It is worthy of note that, all energy derived from the products of photosynthesis originates from solar energy as illustrated below:

1.2. Energy Flow in Nature The light reaction of photosynthesis include light absorption, charge separation, water splitting, and electron/proton transfer and provides the reducing equivalents or hydrogen electrons (e) and protons (Hc) to convert carbon dioxide (CO2) to sugars and other organic molecules that make up living organisms (biomass) including those that lie at the bottom of food chains and provide food. Photosynthesis reactions gave rise to the fossil fuel formed millions of years ago.

The reverse of photosynthesis such as oxidation of organic molecules by respiration (controlled oxidation within our bodies) or burning fossil fuels releases CO2 combining the hydrogen back with oxygen to form

water. The energy release in this process originated from the sunlight. This reaction is subdivided into light and dark reaction, the light reaction occur in the presence of sunlight and water at the heart of the process the of water take place within the red region at the visible spectrum which have the largest wave length, the visible spectrum has a wavelength of 7x10-7m comprises of red, orange, yellow, green, blue, indigo and violet rays and the equation of light reaction is

4H2O Water

4H+ Chloroplast

+ Hydrogen Ion

4(OH) Hydroxyl Ion

Then the hydroxyl (OH) is converted to water 4(OH) Hydroxyl Ion

2H2O

+ O2 Water

Fig. 1 Light Reactions or Photosynthesis Oxygen is obtained as a by-product and a co-enzyme Nicotinamide Ademine Denucleotide(NADP) and Adenosine Triphosphate (ATP) is formed whereas, the dark reaction take place in the absence of light. The energy provided by the ATP with the reduced compound NADP lead to the assimilation of carbon dioxide under a controlled enzyme to form simple sugar and represented in the equation below.

4H+ Hydroxyl Ion

+

CO2

CH2O Sugar

+

H2O Water

The beauty of this reversible reaction is that the dark reaction returns back the water and CH2O is the carbon structure from which simple sugar, proton, fat and oil are form.

1.3. Efficiency of Photosynthesis It is worthy of note that photosynthetic organisms can efficiency trap light energy at all wavelengths of visible solar radiation, however, the energy used for splitting water and converting carbon dioxide to carbohydrate is only equivalent to the red region of the spectrum. Higher energy photons (shorter wavelength light, towards the violet region) are degraded to heat by internal conversion within the light harvest pigment to the energy level of red photons. For each electron/proton contracted from water and used to reduce carbon dioxide (CO2), the energy of two red photons is required which can be accomplished by linking together in series two photo systems namely photo system 1 (PSI) and photo system II (PSH). The Photo system II (PSII) uses light to extract electrons/protons from water while the photo system I (PSI) uses light to give additional conversion process tocarbohydrate

Fig. 2 Energy flow in Nature (PSII) which generates a strong oxidizing species (P6800), that help to drive the water Each electron extracted from water and transferred to carbon dioxide enquires the energy of two photons of light, one is absorbed by photo system II splitting reaction and a reductant, plastoquinol (PQH2). The other generates a strong reducing species that donate hydrogen to carbon dioxide CO2 to produce sugars and other organic

molecules, symbolized as CH2O and a weak Oxidant P7000. Electron and proton flow from PQH2 to P7000 results in the release energy to convert ADP to ATP. The ATP produced is a store of energy needed along with NADPH2 to convert carbon dioxide to carbohydrate. The production of Oxygen O2 involves the splitting of two water molecules; the overall process requires eight photons of light (Bridgewater, 2004). A typical product of carbon Fixation is glucose (C6 H12O6) whose energy content is 2800KJ per mole; this implies that to make a glucose molecule the energy of 48 red photons is required the free energy G stored per Photon as G = ΩT ΩR ΩS ΩL Ω0 Hv0 (Thorndike, 1996) Where ΩT, Correction for saturation effects; ΩR, Entropy Loss; ΩS, Special distribution of light; ΩL, factor accounting for irreversible energy losses in photo- chemical red biochemical pathways; Ω0, thermodynamic efficiency; Hv0, energy of a photon at the optimum frequency for conversion at red photon. The process of oxygenic photosynthesis principally linked to the light driven water splitting reaction that occurs in enzymes found in plants, algae and cynobacterial known as photo system (PSII) where solar energy is absorbed by chlorophyII and other pigment and is transferred efficiently to the PSII reaction centre in the process called charge separation take place. The initial conversion of light into electrical energy occur at maximum thermodynamic efficiency of greater than 700c and generate a radical per state, (P680 pheo) wh+ere p680 is the chlorophyII. A molecule and pheo is a pheophytin , a molecule ( a chlorophyll molecule without mg ion ligated into its tetrapyrole head group. The essential point is that the energy of the photon has been used to remove an electron from one site and place it on another (pheo). The splitting of water into O2 and the equivalent of 2H2 (two NADPH) requires four electrons and PS11 must absorb four photons(4hr) to drive this reaction; 2H2O

O2

+

4H+ and 4e

4hr

1.4. Artificial Photosynthesis Model Artificial photosynthesis model explained that photosynthesis can be successfully mimicked in two different ways, namely Design and production of artificial sun that can function using the basic operation principles of the light driven charge separation that occurs in photosynthesis reaction such prototype sun will have water as it

primary source of power as

4H2O +

4H

+

4(OH)

Chloroplast Light

Then 2H2

Hydroxyl ion

+

O2

4H2O

+

Heat

+

electricity

This device can be effectively deployed to extremely cold part of the globe to support natural plants for photosynthesized man for heat and electricity. The second option is the design and production of massive prototypes artificial plants that can trap light at all wavelength but most importantly at the heart of its reaction be able to split water within the red region of the spectrum.

1.5. Discussion The first model attempt to aid photosynthesis by creating artificial prototype solar system that work with natural plants to achieve and balanced the system using the equation. 2H2

+

O2

2H2O +

Heat

+

electricity

The second model utilizes artificial prototype plant that mimic natural plant that will be able tosplit water at the pick of the reaction, that is light driven reaction, using the equation, 4H+

4H2O Light Emzyme of Catalyst

+

Hydrogen ion

4(OH) Hydroxyl ion

Then the hydroxyl (OH) is further converted to water as 4(OH)

4H2O

Hydrogen ion

Water

+

O2 Oxygen

1.6. Combating Climate Change Emission from fossil fuel burning are virtually certain to drive the upward trend in atmosphere carbon dioxide level as a result of greenhouse gases such as carbon, nitrous oxide, perfluorocarbons and sulphur hexafluoride that have a lasting effect on atmosphere composition, radiation forcing and climate. It is currently difficult to know the correct greenhouse gases in the atmosphere that is safe, developing countries

are experiencing a dilemma when energy consumption, economic growth, standards of living and transition from civilian to civilian and that affect other researches and innovations, while developed countries are beginning to create energy choices that include low carbontechnologies. No single technology or concept will achieve the global goal of tackling climate change as well as no single policy approach will yield success. The options for combating climate change are decarbonizes energy economics from an established fossil fuel base, development of cleaner and low-carbon technologies. Artificial photosynthesis that is light driven can be achieved as a way of decarbonizing the atmosphere.

2. Policies and Implementations Photosynthesis is the most successful solar energy converter on Earth. It provides energy for all life on our planet and is the source of the fossil fuels that pilot our technologies. The solar energy cell can be massively achieved using a good knowledge of molecular processes of photosynthesis and plant molecular biology to attach the challenge of providing non-polluting renewable energy for the benefit of mankind. The following two avenues can be useful if vigorously explore; i. Artificial photosynthesis: The need to establish or venture into the construction of artificial system capable of exploiting solar energy in order to split water with the aim of producing fuels like methane and simple sugar at an efficiency of at least 10% using the available knowledge of photovoltaic’s and nanotechnology. Biomass: Invest massively in the technology of biomass by world government with the intension of reducing CO2 emission that will mimic man-made global climate change.

2.1. Future Energy Option The most sustainable and reliant sources of future energy is the renewable and water, so it is also imperative to consider a quote from Jules Verne : “I believe that water will one day be used as fuel, because the hydrogen and Oxygen which constitute it, used separately or together, will furnish an inexhaustible source of heat and light. I therefore believe that, when coal deposits are oxidized, we will heat ourselves by means of water. Water is the coal of the future”.

3. CONCLUSIONS Having assessed future energy policy options using artificial photosynthesis as tool for decarbonizing the atmosphere, the most sustainable energy source is renewable energy and water.

4. REFFERENCES [1] Barber, J. 2003. Photo System II. “The Engine of Life”. Quart Revs Biopsy’s. 36,71-89. [2] Bolton, J. R 1979. “Solar Energy Conversion in Photosynthesis:” features relevant to artificial systems for the photochemical conversion of solar energy. In the chemical conversion and Storage of solar Energy(eds. King, J.B, Havtala, R.R. and Kutal C.R), Humana Press, Clipton, N.J. [3] Bridgewater, A.V and Maniatis K 2004. “The Production of Biofuels by the thermo chemical processing of Biomass”. In molecular to global Photosynthesis.(ED. Archer, M.D. 2004) PP 521-611. Pub imperial College Press, London. [4] Gust, D, moore, T.A ed moore, A.L 2001. “Mimicking Photosynthetic Solar Energy Transduction”. ACC. Chem. Res. 34, 40-48. [5] Hoffert, M.T etal. 2002. “Advanced Technology paths to Global Climate Stability”: Energy for a greenhouse planet. Science, 298, 981-987. [6] Kato, H Asakura, K and kudo A. 2003. Highly efficientwater splitting into H2 and O2 over Lanthanum - doped NataO3 photocatalysts with high crystallinity and surface nanostructure J. AM. Chem. SOC. 125, 3082-89. [7] Thomdike, E.H 1996. Energy and the environment, Addison - Wesley, Reading, Mass.. [8] US Department of Energy (DOE) 2005. “Basic Research Needs for Solar Energy utilization” Report of the basic energy science Workshop on solar energy utilization. www.sc.doe.gov. [9] World Energy Council 2001. “Survey of energy Resources”. World Energy conceive (www.worldenergy.org).