Photosynthesis, the process plants use to convert sunlight into energy, is one of nature's most efficient, incredible processes. For years, researchers have been seeking ways to harness this power for the good of the planet. If they could find a way to reproduce the effects of photosynthesis--to create a kind of synthetic photosynthesis--then perhaps they could use it to create clean energy fuels, or even clean pollutants from the air. Now, a team of chemists at the Brookhaven National Laboratory and Virginia Tech have come as close as anyone ever has to actually creating synthetic photosynthesis.
To understand scientists' research in the area of synthetic photosynthesis, one must first understand how natural photosynthesis works, and the effect it has on our planet.
Chlorophyll, the pigment which gives many plants their green color, is vital to the process of photosynthesis. Inside a plant's cells, chlorophyll captures light energy from the sun, which then transfers electrons from water (H2O) to carbon dioxide (CO2), which produces carbohydrates. The plant uses these carbohydrates for energy. In this way, plants are able to use sunlight to obtain the same sort of energy that animals obtain by eating food.
Oxygen is a natural byproduct of photosynthesis. In this way, plants "recycle" the CO2 produced by all breathing animals, including humans, by turning it into oxygen. Without plants, the oxygen in our atmosphere would become depleted within several thousand years, and breathing would become impossible.
To recreate the process of photosynthesis in a laboratory environment is tricky. It is something which researchers have been trying to do for years, and have recently begun to have success at.
In 2015, researchers at the Lawrence Berkeley National Laboratory were able to use solar energy to split a water molecule apart into its oxygen and hydrogen components. This in itself was an important first step down the road to true synthetic photosynthesis. The researchers then took things one step further, by feeding the hydrogen to microbes, which turned it into methane. Because methane can be used to produce electricity, researchers were excited at the clean energy possibilities of their findings.
"...we can now expect an electrical-to-chemical efficiency of better than 50 percent and a solar-to-chemical energy conversion efficiency of 10-percent if our system is coupled with state-of-art solar panel and electrolyzer." Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division, said of the research results.
Now, researchers have found a new catalyst for synthetic photosynthesis--in the form of two lab-created supramolecules. Each supramolecule is made up of light-harvesting ruthenium metal ions, attached to a single catalytic center of rhodium metal ions.
"By building supramolecules with multiple light absorbers that may work independently, we are increasing the probability of using each electron productively,” said Gerald Manbeck, lead author of the study published in the Journal of the American Chemical Society.
In other words, these supramolecules were specifically designed to be efficient at what they do--helping to produce photosynthetic reactions in a lab. Supramolecules may not be chlorophyll, and synthetic photosynthesis may not involve plants at all, but scientists hope that the results of their reactions will be the same: CO2 converted into oxygen, and energy produced.
Currently, the earth is nearing the highest levels of atmospheric CO2 in the past 200 million years. This is bad news, since CO2 is known as a "greenhouse gas"--a gas which traps heat and keeps it from escaping the atmosphere, adding to the problem of global climate change.
But being able to recreate the process of photosynthesis on a large scale, thereby turning the excess CO2 in earth's atmosphere into breathable oxygen, could be a game changer. And if clean energy could be produced at the same time, as it was in the 2015 photosynthesis experiments, then the usefulness of synthetic photosynthesis could be twofold.
As researcher Uribe-Romo explained, "The idea would be to set up stations that capture large amounts of CO2, like next to a power plant. The gas would be sucked into the station, go through the process and recycle the greenhouse gases while producing energy that would be put back into the power plant."
In other words, by creating better, more productive catalysts for synthetic photosynthesis, researchers are opening the door for not just a greater reduction in greenhouse gasses, but also for a cleaner energy future. All thanks to the inspiration of a process which is older than mankind itself.
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