Polyester and Biomass Upcycled With Gold Nanoparticle Catalyst

Researchers from Tokyo Metropolitan University have found that gold nanoparticles supported on a zirconium oxide surface help turn waste materials like biomass and polyester into organosilane compounds, valuable chemicals used in a wide range of applications. The new protocol leverages the cooperation between gold nanoparticles and the amphoteric (both acid and base) nature of the zirconium oxide support. The result is a reaction that requires less demanding conditions, a greener method for upcycling waste.

Recycling is a big part of humanity’s solution to the global issue of plastic waste. Much of it is about turning plastic waste into plastic products. However, scientists have also been exploring alternative approaches to encourage the use of waste materials as a resource. This includes upcycling, the conversion of waste material into entirely new compounds and products which can be more valuable than the materials used to make them.

A team of researchers from Tokyo Metropolitan University led by Associate Professor Hiroki Miura has been working on the conversion of plastic and biomass to organosilanes, organic molecules with a silicon atom attached to form a carbon-silicon bond. Organosilanes are valuable materials in high-performance coatings and intermediates in the production of pharmaceuticals and agrochemicals. However, the addition of the silicon atom often involves reagents which are sensitive to air, moisture and require high temperatures, not to mention harshly acidic or basic conditions. This potentially makes the conversion process itself an environmental burden.

Now, the team has applied a hybrid catalyst material consisting of gold nanoparticles supported on a zirconium oxide support. The catalyst takes ether and ester groups, both abundant in plastics like polyester and biomass compounds like cellulose and helps them react with a silicon containing compound known as a disilane. Under mild heating in solution, they successfully created organosilane groups where the ester or ether group was situated. Through detailed studies of the mechanism, the team found that the cooperation between the gold nanoparticles and the amphoteric (both basic and acidic) nature of the support was responsible for the effective, high-yield conversion of the raw material under mild conditions.

Given that plastic waste disposal often requires combustion or harshly acidic/basic conditions, the process itself already provides an easy route to decompose polyesters under much less demanding conditions. However, the key point here is that the products of the reaction are themselves valuable compounds, ready for new applications. The team hopes that this new route to organosilane production forms part of our pathway to a carbon neutral future, where plastics do not make their way into the environment, but into more useful products in society.

Reference: Miura H, Doi M, Yasui Y, Masaki Y, Nishio H, Shishido T. Diverse Alkyl–Silyl Cross-Coupling via Homolysis of Unactivated C(sp3)–O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides. J Am Chem Soc. 2023;145(8):4613-4625. doi:10.1021/jacs.2c12311

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