Hydroxyl Spillover in Fe–Se Dual-Site Catalysts for Mixed Plastics Assay

The complex composition of real plastic wastes poses a significant challenge for their large-scale disposal. A responsive on-site compositional analysis of plastics is informative in choosing downstream processing methods. Nanocatalyst-based assay kit is highly qualified for this scene; however, there remain no efficient nanocatalysts for plastics due to their highly inert chemistry. Herein, we first unveiled the hydroxyl spillover effect in an Fe-Se dual-site catalyst (FeSe/NC) and devised a prototype colorimetric assay kit for mixed plastics. Experimental and theoretical results unveiled that Fe sites acted as the main active sites for H₂O₂ activation to produce adsorbed hydroxyl (*OH) intermediates, which subsequently desorb as hydroxyl radicals (^•OH) and transfer to Se sites, supports, and even plastics for further catalysis. Specifically, ^•OH transferred to different plastics shows varying activities, where signal outputs were hereby used as the fingerprint for plastic identification. Moreover, the remaining *OH could respond to redox interferences in the samples for enhanced accuracy. In contrast to traditional techniques involving precise apparatus and complex pretreatments, our approach enables a rapid assay (∼10 min) of raw powdery mixed plastic wastes with an ultralow cost (0.0012 $). This discovery fills a crucial gap in the plastic assay, offering new technical guidance for diverse upcycling and recycling strategies to tackle the global plastic waste crisis.