Photoreforming of Plastic Waste to Hydrogen Using Single-Atom Anchored Pt Decorated Graphitic Carbon Nitride

Advancements in catalytic technologies—such as electrocatalysis, thermocatalysis, and photocatalysis—offer promising alternatives to traditional waste disposal methods like landfilling, incineration, and mechanical recycling. Among these, photocatalysis stands out for its applications in sustainable waste management and renewable energy generation. A significant breakthrough in this area is photo-reforming, which transforms plastic waste into hydrogen fuel using sunlight. This method is especially appealing as hydrogen, with its high energy density, is a green energy carrier for transport, heating, and chemical synthesis, contributing to net-zero emissions and a more sustainable energy system.<br/>Graphitic carbon nitride (g-C₃N₄) is notable as a semiconductor with a relatively narrow bandgap of 2.7–2.8 eV, aligning the energy levels of its valence and conduction bands to meet the thermodynamic requirements for water splitting and photoreforming reactions. The structure of g-C₃N₄ is based on a conjugated polymeric system composed of tri-s-triazine units, featuring a two-dimensional layout that promotes electron mobility and enhances the separation of charge carriers within composite materials.<br/>In this study, bulk g-C₃N₄ was initially synthesized using a high-temperature thermal polymerization method. Urea was heated to 550 °C for 3 hours at a 2.0°C/min heating rate. After cooling, the product was acid-washed with HCl and then rinsed with deionized (DI) water until neutral. To obtain g-C₃N₄ nanosheets (C₃N₄-NS), exfoliation of bulk g-C₃N₄ was performed using an ultrasonic processor with isopropanol as a solvent. For the decoration of Pt single atoms, the precursor solution was prepared by dissolving PtCl₂ and NaCl in DI water, then dried in a water bath.<br/>Various polymers were tested for photoreforming using the C₃N₄-Pt photocatalyst to establish photocatalytic performance. Photoreforming of PET, PVC, PMMA, PP, and PS was first evaluated in a sealed photocatalysis system equipped with a xenon lamp. Due to these polymers' chemical inertness and insolubility, they were pretreated in a NaOH solution (stirring for 48 hours at 40 °C) before photoreforming, which contributed to the depolymerization of plastics into their corresponding constituent monomers. Subsequently, the supernatant containing water-soluble monomers was collected and used as feedstocks to initiate the photoreforming reaction.<br/>After 12 hours, PET photoreforming showed the highest hydrogen production of 533.18 μmol g^–1h^–1. This high efficiency can be attributed to the fact that the ester bonds in the PET polymer chain are easily broken under alkaline conditions, forming terephthalic acid (TPA) and ethylene glycol (EG). Exploring the photocatalytic performance across a range of polymers, including PET, PVC, PMMA, PP, and PS, for photoreforming using the C₃N₄-Pt photocatalyst highlights the potential of this technology for sustainable plastic waste management.<br/>The significant hydrogen production observed in PET photoreforming underscores the effectiveness of this approach. The application of photocatalysis to plastic waste recycling presents a promising avenue for converting a wide range of polymers into valuable chemicals and fuels. Future advancements in this field will likely focus on optimizing catalyst design, reaction conditions, and pretreatment processes to enhance efficiency, selectivity, and applicability to various types of plastic waste, paving the way for more sustainable and circular approaches to plastic use and disposal.