Photocatalytic upcycling of PET into methane, hydrogen and high-value liquid products

TL;DR

This paper explores using photocatalysis to convert PET plastic waste into methane, hydrogen, and useful chemicals, offering a sustainable solution to plastic pollution.

Contribution

The study identifies key parameters for efficient PET upcycling and demonstrates methane generation directly from PET under solar light.

Findings

Pt co-catalysts increase hydrogen production by four orders of magnitude with AQY up to 0.45%.

Methane is directly generated from PET without hydrogenation reactions.

High-value liquid products like acetic acid and ethanol are produced with selectivity influenced by catalysts and conditions.

Abstract

The harmful effects of daily plastic use are increasingly evident, with most waste burned or landfilled, leading to the formation of microplastics that pollute the environment and the food chain. While the full impact remains unclear, photoreforming of plastics has emerged as a promising sustainable abatement method. This study demonstrates the commercial potential of P25 TiO2 towards photocatalytic upcycling of polyethylene terephthalate (PET) microplastics by systematic exploration of the effect of co-catalysts, reaction temperature and oxygen presence on the generation of solar fuels and high-value liquid products. We demonstrate that while neat P25 yields minimal H2 evolution, increasing the reaction temperature enhances its production significantly, and the addition of Pt further boosts H2 generation by four orders of magnitude, resulting in 15.35 µmol h−1 of H2 and apparent quantum yield (AQY) values up to 0.45%. On par with H2, we observe the generation of CH4 from the reaction mixture, which we conclude to originate directly from PET rather than hydrogenation reactions. Liquid-phase analysis reveals diverse photoreforming products, including acetic acid, oxalic acid, formic acid and ethanol, with selectivity influenced by catalyst composition and reaction conditions. The feasibility of large-scale application of the process is further validated through prolonged irradiation tests using solar-simulated light and an upscaled setup, which demonstrate remarkable AQYs reaching 0.84%. These findings suggest PET photoreforming as a promising route for producing solar fuels and valuable chemicals, paving the way for sustainable plastic processing and upcycling.

We systematically study the key process parameters of polyethylene terephthalate (PET) microplastic photoreforming. We uncover that not only hydrogen (H2) but also methane (CH4) is generated and provide valuable mechanistic insights into the process.

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