In December 2019, researchers from Nanyang Technological University (NTU) in Singapore discovered a way to use sunlight to turn plastic waste into chemicals, according to a daily scientific report from the US news website.
NTU researchers put non-biodegradable plastic waste into a solvent with a catalyst and exposed it to sunlight. The solvent took only six days to decompose and convert the plastic into formic acid.
Formic acid is a widely used natural chemical that can be used as a food preservative, antibacterial cleaner or hydrogen fuel cell.
Malaysian social news website SAYS reports that the technology is the first in the world to enable plastics to disintegrate in such a short time.
Soo Han Sen, an assistant professor at the NTU School of Physics and Mathematics, is leading the project. He said that this new chemical reaction can completely decompose plastics such as polyethylene.
Most plastics are not biodegradable because they contain extremely inert chemical bonds called carbon-carbon bonds, and these chemical bonds will not easily break down if high temperatures are not applied.
The catalyst used by the NTU research team is vanadium.
Vanadium is a silver-gray metal with a high melting point. It is often used as a catalyst in the chemical industry and is known as the metal “vitamin”. Vanadium metal is mostly used in automotive steel alloys and aircraft aluminum alloys.
Vanadium as a catalyst is usually supported by an organic group, abbreviated as LV (O). It uses light energy to drive chemical reactions, so it is also called a vanadium-based photo catalyst.
Su Hansen said that vanadium-based photo catalysts are specifically used to break those carbon-carbon bonds in plastics.
If the carbon-carbon bond is compared to a zipper, the new vanadium-based photocatalyst is the handle of the zipper. When the sun shines, the vanadium-based photocatalyst unlocks the zipper and breaks the carbon-carbon bond.
The conversion rate of the catalyst for non-polyethylene terephthalate (PET) plastic is 100%.
Su Hansen said his research team is trying to get more research funding to attract talent and expand research. It will take at least five years for the plastic decomposition technology to be commercialized.
The research team’s next focus is to understand how to apply this technology to other different types of plastics and reduce the decomposition time.
Currently, most plastic waste in Singapore is burned, and the burnt ashes are transported to Singapore’s Semakau landfill. The landfill is expected to run out of landfill space by 2035.
NTU tests and develops plastic waste solutions to solve the problem of limited space in the Shima Takashima landfill.
Previously, scientists have also tried other methods to convert waste plastics into useful chemicals, but many ways may involve bad reagents or too many steps to expand the scale of production.
For example, researchers have tried to add catalyst cadmium to the solvent to reflect the production of hydrogen, but cadmium is a toxic heavy metal, and the air polluted by cadmium can cause serious harm to the human body.
Catalysts made from vanadium are different from most common catalysts made in the industry from expensive or toxic metals such as platinum, palladium or ruthenium. The vanadium-based photocatalyst has the advantages of rich reserves, low cost, and environmental friendliness.