ARTIFICIAL PHOTOSYNTHESIS

 Artificial photosynthesis (AP) harnesses solar energy and converts the captured carbon dioxide to carbon monoxide (CO), which can be used as a fuel for internal combustion engines.

Mechanism

• In artificial photosynthesis (AP), scientists are essentially conducting the same fundamental process in natural photosynthesis but with simpler nanostructures.
• They have designed an integrated catalytic system.
• The system is based on a metal-organic framework (MOF-808) comprising of a photosensitizer that can harness solar power and a catalytic centre that can eventually reduce CO2 to CO.
  • A catalytic converter is a device that accelerates a redox reaction.
  • In AP, we would need the catalyst to reduce CO2 to CO and oxidize water to produce oxygen (O2).

Redox Reactions

• Metal-organic frameworks (MOFs) are organic-inorganic hybrid crystalline porous materials that consist of a regular array of positively charged metal ions surrounded by organic 'linker' molecules. The metal ions form nodes that bind the arms of the linkers together to form a repeating, cage-like structure.
• A photosensitizer is defined as a chemical entity, which absorbs light and transfers the electron from the incident light into another nearby molecule. It then induces a chemical and physical alteration of nearby chemical entity.

• Here, the Photosensitizer, is a chemical called ruthenium bipyridyl complex ([Ru(bpy)2Cl2]).
• The catalytic part is another chemical called rhenium carbonyl complex ([Re(CO)5Cl]), inside the nanospace of metal-organic framework for artificial photosynthesis.
• Both these molecular entities stay in close proximity in the confined nano-space of a porous metal-organic framework system resulting in excellent CO2 uptake capability at room temperature.
• The catalyst exhibits visible-light-driven CO2 reduction to CO with more than 99% selectivity.
• The catalyst also oxidizes water to produce oxygen (O2).
• The integrated catalytic assembly can be reused for several catalytic cycles without losing its activity.

Significance

• Chemical Fuels: Artificial photosynthesis is envisioned as a promising strategy to convert sunlight, a practically unlimited and sustainable source of energy, into chemical fuels.
• Lower CO2 in atmosphere: Through AP we would also be able to lower carbon dioxide concentrations in the atmosphere, while also producing sugar that we could use for food and energy production.
• Energy alternative: Fossil fuels are in short supply and they are contributing to pollution and global warming. AP could offer a new, possibly ideal way out of our energy predicament.
• Storable Fuel: It has benefits over Photovoltaic Cells found in today’s solar panels. The direct conversion of sunlight to electricity in photovoltaic cells makes solar power a weather and time dependent energy, which decreases its utility and increases its price. AP, on the other hand could produce a storable fuel.
• More than one Fuel: Unlike most methods of generating alternative energy, AP has the potential to produce more than one type of fuel.
• Clean Fuel: AP produces a clean fuel without generating any harmful by-products, like greenhouse gasses an makes it an ideal energy source for the environment.
• Powering Vehicles: Producing a new fuel that can power vehicles from naturally occurring input materials, CO2, water and Sunlight.
• Saleable CO2: It makes Carbon storage more economically viable as the CO2 can be used to create a saleable product.
• Reuse of CO2: If we are able to tap into existing big producers of CO2, such as power station exhaust we are able to use the CO2 twice before it enters the atmosphere.

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