Abstract
With over 8 billion tons of plastic produced since 1950, polymers represent one of the most widely used—and most widely discarded—materials. Ambient-temperature photoreforming offers a simple and low-energy means for transforming plastic waste into fuel and bulk chemicals but has previously only been reported using precious-metal- or Cd-based photocatalysts. Here, an inexpensive and nontoxic carbon nitride/nickel phosphide (CNx|Ni2P) photocatalyst is utilized to successfully reform poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA) to clean H2 fuel and a variety of organic chemicals under alkaline aqueous conditions. Ni2P synthesized on cyanamide-functionalized carbon nitride is shown to promote efficient charge separation and catalysis, with a photostability of at least 5 days. The real-world applicability of photoreforming is further verified by generating H2 and organics from a selection of nonrecyclable waste—including microplastics (polyester microfibers) and food-contaminated plastic—and upscaling the system from 2 to 120 mL while maintaining its efficiency for plastic conversion.
Highlights
The majority (86%) of plastic packaging accumulates in landfills or escapes into the environment.[1−4] Plastic pollution represents a global environmental crisis and a loss of valuable resources
Small polymer pieces known as microplastics are problematic for recycling.[5−7] Microplastics are present in a variety of products and are formed when plastic degrades over time.[6]
The system was still active after 8 days, suggesting that higher H2 conversions could be achieved at longer time scales
Summary
The majority (86%) of plastic packaging accumulates in landfills or escapes into the environment.[1−4] Plastic pollution represents a global environmental crisis and a loss of valuable resources. 7% of recycled poly(ethylene terephthalate) (PET) bottles, for example, are recast as bottles.[1] Existing management structures are currently incapable of sustainably and economically processing the vast variety of plastic waste, and new technologies for transforming end-of-use polymers into valuable products are urgently required One such technology is photoreforming (PR), in which sunlight and a photocatalyst generate H2 from an organic substrate and water. We demonstrate that the CNx|Ni2P photocatalyst can be employed under alkaline conditions to produce H2 and organic chemicals from PET and poly(lactic acid) (PLA, a biodegradable but not typically recycled alternative to PET) We further apply this system to real-world, nonrecyclable waste, including polyester microfibers and oil-contaminated PET, and show that it can be upscaled from 2 to 120 mL without efficiency losses. This proof-of-concept demonstration of noble-metal-free, Cd-free, and visible-light-driven plastic PR with CNx|Ni2P offers a sustainable and scalable route toward simultaneous plastic waste elimination and renewable fuel and chemical synthesis
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