Polystyrene Upcycling via Photocatalytic and Non-Photocatalytic Degradation.

The rapid increase in polystyrene (PS) production has led to substantial growth in plastic waste, posing serious environmental and waste management challenges. Current disposal techniques are unsustainable, relying heavily on harsh conditions, high energy input, and generating environmentally harmful byproducts. This review critically discusses alternative green approaches for PS treatment through photocatalytic and non-photocatalytic upcycling methods. Photocatalytic methods utilize light energy (UV, visible, or broad-spectrum irradiation) to initiate radical reactions that cleave the inert carbon backbone of PS. In contrast, non-photocatalytic strategies achieve backbone degradation without direct light activation, often employing catalysts and thermal energy. Both approaches effectively transform PS waste into higher-value compounds, such as benzoic acid and acetophenone, though yields remain moderate for most reported methods. Current limitations, including catalyst performance, low yields, and impurities in real-world PS waste, are highlighted. Future directions toward enhancing the efficiency, selectivity, and scalability of PS upcycling processes are proposed to address the growing plastic waste crisis sustainably.