Plastic and organic waste photoreforming for green hydrogen evolution and valuable products

Abstract

As the world transitions to a carbon-neutral future, photoreforming offers a promising route to address two challenges simultaneously: waste reduction and renewable energy production. In this process, a photocatalyst harnesses sunlight to drive water reduction to hydrogen and waste oxidation to organic compounds under ambient conditions. This thesis investigates ambient-temperature photoreforming of plastic and biomass waste using platinum-loaded graphitic carbon nitride (Pt/g-C3N4 or Pt/CN) for its visible-light response, chemical stability, and availability. Four nitrogen-rich precursors (dicyandiamide, melamine, thiourea, urea) were studied to assess their effect on g-C3N4 properties and PET photoreforming. Melamine-derived g-C3N4 with 3 wt.% Pt achieved the highest hydrogen evolution rate (7.33 mmol H2 gcat-1 h-1) and stable PET conversion to valuable organics over 8 days, attributed to its higher crystallinity and chemical resistance. To further improve performance, post-thermal and chemical oxidation treatments were applied to melamine-derived g-C₃N₄, producing high-surface-area (>400 m2 g-1), hydrophilic photocatalysts. These enabled efficient photoreforming of biomass-derived 5-(hydroxymethyl)furfural (HMF) in neutral water, achieving hydrogen evolution rates nearly four times higher than untreated CN and maintaining stability over five days. The influence of synthesis temperature on CN properties was also explored for real-world plastic waste. Pt/CN550 showed high activity for PET and other plastics, outperforming P25. Its optimal performance arose from balanced crystallinity, surface reactivity, and co-catalyst formation. Overall, this work demonstrates the potential of g-C₃N₄-based catalysts for integrated hydrogen production and sustainable plastic/biomass waste reforming, providing valuable insights for future recycling strategies.