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.

What is photosynthesis?

Photosynthesis is the process by which green plants use sunlight to synthesize foods from carbon dioxide and water. The process combines 6 molecules of carbon dioxide and 6 molecules of water to produce one molecule of glucose and 6 oxygen molecules. The glucose is stored in the plant as starch and cellulose which are simply long chain glucose molecules (known as polysaccharides) as a source of food for the plant to survive and grow. The oxygen that is produced as a byproduct of photosynthesis is what most animals rely on to breath, so the process plants and trees fulfill on our behalf is critical to our survival.

Artificial Photosynthesis

In Artificial Photosynthesis we replicate the photosynthetic process completed by plants

Steps

Light capture and moving the electrons to the reaction centers.
Splitting water into Hydrogen and Oxygen
Reducing Carbon Dioxide

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.