Light-Matter Interaction Converts Plastic Waste to Functional Materials

To assist in the reduction of plastic waste, an international research team led by the University of Texas at Austin (UTA) developed a method that uses a low-power laser to initiate carbon-hydrogen (C-H) activation in plastics and other materials.

The UTA-led team included researchers from the University of California Berkeley, Tohoku University, Lawrence Berkeley National Laboratory, Baylor University, and The Pennsylvania State University.

During C-H activation, the carbon-hydrogen bonds in organic molecules are selectively broken and transformed into new chemical bonds. The molecules are broken down to their smallest parts for possible reuse.

The researchers used C-H activation to break the chemical bonding of plastic molecules and create new chemical bonds that could be synthesized into luminescent carbon dots.

To mediate C-H activation in long-chain molecules, the team used 2D transition metal dichalcogenides (TMDCs). The molecules were placed on top of the TMDC materials and irradiated with a laser. The 2D TMDCs catalyzed C-H activation, enabling optical synthesis and the patterning of luminescent carbon dots on solid substrates.

Siyuan Huang, a graduate student in Yuebing Zheng’s lab, demonstrates the technology that uses plastics and other materials with a laser to break them down into their smallest parts for future reuse. Courtesy of the University of Texas at Austin.

The luminescent carbon dots could be used as memory storage devices in next-generation computer devices. “It’s exciting to potentially take plastic that on its own may never break down and turn it into something useful for many different industries,” said researcher Jingang Li.

Although C-H activation in long-chain organic molecules is rarely reported, the derivation of C-H bonds in these complex molecules holds significant potential for synthesizing functional organic complexes and transforming environmental pollutants into more valuable chemicals. The light-driven C-H activation process demonstrated by the research team could be applied to many long-chain organic compounds, including polyethylene and surfactants commonly used in nanomaterial systems. The demand for carbon-based nanomaterials is high, because of their multifunctionality.

In a demonstration of the new approach, the researchers achieved the light-driven transformation of a long-chain quaternary ammonium surfactant — cetyltrimethylammonium chloride — into luminescent carbon dots on TMDC monolayers. By combining experimental characterizations with theoretical calculations, the researchers uncovered the role of defects and oxidized states on TMDCs in the promotion of hydrogen adsorption and C-H activation reactions. They also showed that 2D TMDCs can facilitate carbon-carbon coupling with a lowered energy barrier to catalyze C-H activation in complex organic molecules.

Plastic pollution has become a global environmental crisis, with millions of tons of plastic waste accumulating in landfills and oceans each year. Conventional methods of plastic degradation are energy-intensive, environmentally harmful, and ineffective.

Although further research is needed to optimize the light-driven C-H activation process and scale it up for industrial applications, the study is a big step forward in the quest for sustainable solutions to plastic waste management. The team believes that its ecofriendly approach to disassembling plastic waste and reassembling it into useful materials by using lasers and TMDCs will lead to the development of efficient plastic recycling technologies.

“By harnessing these unique reactions, we can explore new pathways for transforming environmental pollutants into valuable, reusable chemicals, contributing to the development of a more sustainable and circular economy,” said professor Yuebing Zheng. “This discovery has significant implications for addressing environmental challenges and advancing the field of green chemistry.”

The 2D TMDC-mediated, light-driven C-H activation process in complex organic molecules could have applications in chemical synthesis and photonic materials, in addition to plastic recycling. Potential applications for the light-driven synthesis of luminescent carbon dots include data encryption, information technology, and solid-state LED technology.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-024-49783-z).