Catalysis

Electricity, Air, and Plastic Recycling

Daniel Morton — Tue, 17 Jun 2025 21:15:48 +0000

Electricity, Air, and Plastic Recycling Daniel Morton Tue, 06/17/2025 - 15:15

Daniel Morton

This collaboration between four RASEI Fellows shows how electricity can be used to impart ‘superoxide powers’ to oxygen gas molecules from air, enabling the efficient recycling of PET plastics.

In 2012, 32.5 million tons of plastic waste was produced globally. 4.5 million tons of which was poly(ethylene terephthalate), better known as PET. You likely know this as the plastic that has the number 1 in the middle of the recycling symbol. PET is used extensively in materials such as packaging, textiles, films, and flexible electronics. By far and away its main use is in bottled drinks. PET is considered a standout material, it is strong, chemically resistant, transparent, and impermeable to water. Even better, it is possible to recycle PET – it has its own number, right? Unfortunately, this is not quite the full story. Globally, it is estimated that only about 9% of plastic waste is recycled, and while PET waste is one of the best performers, with a recycling rate approaching between 25-30%, the majority of plastic, even PET, ultimately ends up in landfills, incinerated, or worse, polluting our environment. The magnitude of this problem is only increasing; in 2024 the world generated an estimated 240 million tons of plastic waste, representing more than eight-fold increase in 12 years and highlighting the need for more effective solutions.

This teams bring together four RASEI Fellows, Oana Luca (Chemistry, ɫ��Ƶ��), Seth Marder (Chemistry and Chemical & Biological Engineering, ɫ��Ƶ��), Stephen Barlow (RASEI, ɫ��Ƶ��) and Elisa Miller (Chemistry and Nanoscience, NREL) to address the accelerating issue of plastic waste. While there are many parts to this global challenge, this research focuses on how we recycle plastics, specifically PET. When we think about recycling plastic, most of us just think about throwing a plastic bottle, or piece of packaging, into a recycling bin. We rarely give it much thought after that. This really is just the start of a journey that is more complex than many realize. There are actually several different approaches to giving plastic a second life. The most common, and perhaps the method that most people are familiar with, is mechanical recycling.

Think of mechanical recycling like an industrial washing machine combined with a paper shredder. Plastic items are collected, sorted, cleaned, and then chopped up into small flakes or melted down into pellets that can be molded into new products. This approach is efficient and works great for clean, single-type plastics, but there are some significant limitations with this process. In the same way that a white shirt can’t be perfectly restored after being mixed with brightly colored laundry, plastic quality degrades each time it goes through mechanical recycling. This reduction in quality is stark, most mechanically recycled plastics can only go through the process 2-3 times before they become unusable. This makes it financially unattractive and severely limits the long-term efficacy of recycling. How can this be an enduring solution if we can only recycle something a couple of times?

Chemical recycling takes a very different route, instead of the ‘brute-force’ approach of just melting and reshaping the plastic, it employs a more surgical method, breaking down the plastic polymer chains into their constituent molecular building blocks. These molecular building blocks can then be used, either to make new plastics, or for other applications. Because the new plastics are made with molecular control, there is no degradation in quality, and the materials can be recycled over and over, essentially as many times as you wish. Instead of a washing machine combined with a paper shredder, this is more like a LEGO set, where the model can be taken apart brick by brick and be used to build something entirely new. This research describes a new approach to depolymerization, a class of chemical recycling.

The research described in this RASEI collaboration, just published in ACS Sustainable Chemistry and Engineering, offers a new, more efficient approach. By passing an electric charge through the reaction, electrons can be used to activate molecules that can then go on to react with the polymer. In a recent study, that used additive molecules as electron shuttles, the team observed the addition of electrons to oxygen gas molecules in small amounts present in the reaction, that were originally thought to be innocent bystanders in the mixture. This led the team to hypothesize that oxygen gas molecules, directly from air, could be chemically reduced, (that is that they take on an extra electron), leading to the formation of a relatively stable superoxide radical anion, O₂^·–. This activated superoxide now acts in place of the solvent and reacts directly with the polymer. Since the superoxide has an extra electron gained from the electric current, the negatively charged superoxide molecule reacts with the centers that have a positive charge on the polymer. This results in the breaking down of the polymer in a predictable and selective fashion, and the incorporation of oxygen into the building blocks instead of the solvent molecules, leading to the reliable and reproducible formation of the same molecules that were used to build the polymer in the first place. The LEGO bricks are formed cleanly and are ready to be used again, with no degradation in molecular quality. This work demonstrates this technology on a range of different plastics using air, arguably one of the most abundant and cheap reagents, as the primary oxygen source, and all done at room temperature and pressure, a huge improvement on other chemical recycling approaches. While the results are promising and show good efficiencies, this lab-based proof of principle still has a number of challenges to solve before it can be scaled up to meaningful levels.

Today, most plastics are recycled using mechanical recycling, which is like the combination of an industrial washing machine and a paper shredder, producing low-quality products and reducing the possibility of future recycling, leading many to explore chemical recycling as an alternative to gain access to more valuable chemical building blocks. Current mainstream chemical recycling methods are like using a sledgehammer, they typically require high temperatures and lots of energy to break the chemical bonds. The development of electrochemical methods offers a more controlled approach, breaking down plastics at the molecular level and reliably producing build blocks that can be used over and over again. New recycling technologies could transform how we handle plastic waste, opening the door to recycling previously un-recyclable plastics, doing it in a more energy efficient way, producing higher quality recycled plastics, and making recycling economically competitive with virgin plastic production from oil. The development of more effective and general recycling strategies isn’t just an environmental imperative. As plastic waste continues to accumulate, it is rapidly becoming an economic necessity. We already have so much plastic in the world, if we can develop methods to regenerate and reuse the building blocks from plastic waste it will turn landfills into gold mines.

How amazing would it be if instead of society wasting plastics, filling landfills, and polluting our environments, we viewed used plastics as a commodity for future applications?

June 2025

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Understanding light-driven production of hydrogen could unlock future insights for harnessing light for chemistry

Daniel Morton — Mon, 09 Jun 2025 16:27:04 +0000

Understanding light-driven production of hydrogen could unlock future insights for harnessing light for chemistry Daniel Morton Mon, 06/09/2025 - 10:27

Daniel Morton

Light to fuel: clean hydrogen production. Improved understanding of the light-driven production of hydrogen holds the promise not just to make the reaction more efficient in producing a fuel, but also to offer a framework to better understand future light-driven chemistries.

Many chemical reactions require the input of energy to activate the transformation. This can often be in the form of heat, or chemical energy. One of the most efficient ways of introducing energy into a reaction is by using light. If you don’t have to heat up a reaction, or add extra chemicals to it, and instead shine a light on it, you can save significant energy. However, it can be difficult to control and optimize light-driven reactions. This research, just published in Chem, is a collaboration between the Dukovic Group at the ɫ��Ƶ�� (ɫ��Ƶ��) and the King Group at the National Renewable Energy Lab (NREL) and provides a holistic understanding of the light-driven production of hydrogen gas using a nanocrystal-enzyme complex as the catalyst, and a computational framework that can be used more generally to understand other light-driven chemical reactions in the future. The code for this model is being made available in the supplementary documents of this article.

Chemical catalysis is a special type of reaction, one that increases the speed of a transformation and often reduces the amount of waste produced by the process. Think of it like an assembly line. The catalyst is like a station on the line, bringing together two or more components to create a new product that is then passed along. Without the catalyst the components might, by chance, bump together and form the desired product, but it will be much slower, and much less frequent. The catalyst remains unchanged in the process and can repeat the transformation many times.

Enzymes are Nature’s catalysts. On the cellular level, whenever a change needs to happen, an enzyme is usually involved. The speed of an enzyme, and its selectivity, that is its ability to only react with the desired molecules out of the soup of molecules present in a typical cell, is fantastic. Enzymes are often superior to catalysts we can make in a lab, and as such, much research has gone into finding ways to harness such enzymes to do reactions for us in the lab. Unfortunately, it is not as easy as just grabbing some enzyme out of a cell. Enzymes often require specific environments and partners to react with.

Redox enzymes are a special, and particularly attractive, class of enzymes. They are capable of adding, or removing, an electron from a chemical reaction, a key step in the production of hydrogen gas. Redox enzymes rarely exist by themselves. Returning to the assembly line analogy, to get a station that can add the electrons to the protons (H⁺) to make hydrogen gas, many other stations need to be added before in a specific order. In a cell there is a chain of enzymes that pass the electrons along before the reaction can take place.

This is where the artificial component comes in. The nanocrystal, which, when exposed to light, releases an electron, replaces the long chain of enzymes and can directly transfer an electron to the enzyme. So, you reduce your assembly line down from a chain of many stations to just two. “This work was really only possible through collaboration” explains Gordana Dukovic, the lead researcher at ɫ��Ƶ��. “The team at NREL have vast expertise in hydrogenase (the redox enzyme that creates hydrogen gas), and we have the expertise in making and tailoring the nanocrystals and studying what they do after they absorb light”. Getting the enzyme to work with the artificial electron donor took some work.

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This Research

Characterization of Photochemical Processes

Electron Transfer Kinetics

Competition between electron transfer processes

Activation Thermodynamics

Role of Surface-Capping Ligands

Quantum Efficiency of Charge Transfer

2020 Review of this research area