Gold, an unexpected recycling ally

In addition to gold’s usefulness in the financial, ornamental and technological fields, it can also contribute to the sustainability of the planet. Research has found that a nanoparticle catalyst of this precious metal can convert waste materials, such as biomass and polyester, into useful organic silicon compounds. 

Plastic waste is a problem for humanity. That is why many resources are being invested in the search for ways to recycle them and give them a new useful life. Several lines of research aim to convert these waste materials into useful compounds and products in an efficient way.

One of them, involving scientists at Tokyo Metropolitan University, has found that gold nanoparticles supported on a zirconium oxide support can convert waste materials, such as biomass and polyester, into organosilane compounds, which are valuable chemicals with a wide range of applications. The results of their study were recently published in the prestigious Journal of the American Chemical Society.

The new protocol takes advantage of the combination of gold nanoparticles with a zirconium oxide support, whose characteristics allow it to react both as a base and as an acid. This makes it possible to recycle the waste under less demanding conditions and in a more environmentally friendly way than with the systems investigated so far.

New life for plastic waste

The research team has been working for some time on converting plastic and biomass into organosilanes, which are organic molecules with a silicon atom attached to carbon used in high-quality coatings and in the production of pharmaceuticals and agrochemicals. 

The problem until now was that the addition of the silicon atom involved the use of air- and moisture-sensitive reagents that require high temperatures and extremely acidic or basic conditions. As a result, the conversion process was not at all environmentally efficient.

A key step

The big finding is that the new gold nanoparticle catalyst causes ether and ester groups, both of which are abundant in plastics such as polyester and biomass compounds such as cellulose, to react with the disilane to form useful organosilanes. All that is needed is gentle heating in solution. 

The researchers have identified that the key to the effectiveness of this conversion lies in the combination of the gold nanoparticles and the amphoteric nature of the zirconium oxide support, i.e. its ability to act interchangeably as a base and an acid.

Double advantage

Not only does this system allow polyesters to be decomposed under much less demanding conditions than those used so far. More importantly, the reaction products are valuable compounds ready for use. 

The research team hopes that this new way of producing organosilanes will lead to a carbon-neutral future by allowing plastic waste to be recycled efficiently and preventing thousands of tonnes of plastic waste from burning in incineration plants.

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