New light-powered catalysts could aid in manufacturing

Light-driven chemical reactions provide a strong tool for scientists who are developing novel methods of producing medicines and other important chemicals. Photoredox catalysts, which absorb light and transmit the energy to a chemical process, are needed to harness this light energy.

MIT researchers have developed a novel photoredox catalyst that may make it simpler to incorporate light-driven reactions into manufacturing processes. The novel family of materials, unlike most known photoredox catalysts, is insoluble, allowing it to be reused. Catalysts of this type might be employed to coat tubing and execute chemical changes on reactants a
s they flow through it.

"Being able to recycle the catalyst is one of the biggest challenges to overcome in terms of being able to use photoredox catalysis in manufacturing. We hope that by being able to do flow chemistry with an immobilized catalyst, we can provide a new way to do photoredox catalysis on larger scales," says Richard Liu, an MIT postdoctoral researcher and co-lead author of the current work.

The new catalysts, which can be tailored to conduct a wide range of reactions, might potentially be put into other materials such as fabrics or particles.

Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT, is the paper's senior author, and it was published today in Nature Communications. The article is also co-authored by Sheng Guo, an MIT research scientist, and Shao-Xiong Lennon Luo, an MIT graduate student.

Hybrid materials

Photoredox catalysts operate by receiving photons and then converting that light energy into chemical energy, similar to how chlorophyll in plant cells receives solar energy and utilizes it to make sugar molecules.

Chemists have produced two types of photoredox catalysts: homogeneous and heterogeneous catalysts. Organic dyes or light-absorbing metal complexes are commonly used in homogenous catalysts. These catalysts are simple to adjust to execute a specific reaction, but they dissolve in the solution where the reaction occurs. This implies that they cannot be simply removed and reused.

Heterogeneous catalysts, on the other hand, are solid minerals or crystalline materials that form sheets or 3D structures. Because these materials do not degrade, they may be utilized several times. However, these catalysts are more difficult to adjust to obtain the required reaction.

To combine the benefits of both types of catalysts, the researchers opted to insert the dyes that make up homogeneous catalysts into a solid polymer. The researchers used a plastic-like polymer with microscopic holes produced earlier for gas separations for this purpose. The researchers proved that they could combine approximately a dozen distinct homogeneous catalysts into their novel hybrid material in this investigation, but they believe it might work with many more.

"These hybrid catalysts have the recyclability and durability of heterogeneous catalysts, but also the precise tunability of homogeneous catalysts," explains Liu. "You can incorporate the dye without losing its chemical activity, so, you can more or less pick from the tens of thousands of photoredox reactions that are already known and get an insoluble equivalent of the catalyst you need." 

The researchers discovered that integrating the catalysts into polymers made them more efficient. One explanation for this is because reactant molecules can be retained in the pores of the polymer, ready to react. Furthermore, light energy may readily move along the polymer to identify the reactants that are waiting.

"The new polymers bind molecules from solution and effectively preconcentrate them for reaction," Swager explains. "Also, the excited states can rapidly migrate throughout the polymer. The combined mobility of the excited state and partitioning of the reactants in the polymer make for faster and more efficient reactions than are possible in pure solution processes." 

Higher efficiency

The researchers also showed that they could alter the physical features of the polymer backbone, such as thickness and porosity, depending on the application.

For example, they demonstrated the ability to create fluorinated polymers that adhere to fluorinated tubing, which is commonly used in continuous flow production. Chemical reactants flow through a series of tubes when additional materials are introduced or other stages like purification or separation are conducted during this sort of production.

It is currently difficult to include photoredox reactions into continuous flow processes because the catalysts degrade fast and must be introduced to the solution on a continual basis. Incorporating the new MIT-designed catalysts into the tubing used in this type of production might allow photoredox reactions to be done while the process is in continuous flow. The tubing is transparent, allowing light from an LED to reach and activate the catalysts.

"The idea is to have the catalyst coating a tube, so you can flow your reaction through the tube while the catalyst stays put. In that way, you never get the catalyst ending up in the product, and you can also get a lot higher efficiency," Liu explains.

The catalysts might also be used to coat magnetic beads, making them simpler to lift out of a solution after the reaction is complete, or to coat reaction vials or fabrics. The researchers are currently focusing on adding a larger range of catalysts into their polymers, as well as designing the polymers to optimize them for various prospective uses.
Previous Post Next Post