Hydroxyl Spillover\nin Fe–Se Dual-Site Catalysts\nfor Mixed Plastics Assay

The complex composition of real plastic wastes poses\na significant\nchallenge for their large-scale disposal. A responsive on-site compositional\nanalysis of plastics is informative in choosing downstream processing\nmethods. Nanocatalyst-based assay kit is highly qualified for this\nscene; however, there remain no efficient nanocatalysts for plastics\ndue to their highly inert chemistry. Herein, we first unveiled the\nhydroxyl spillover effect in an Fe–Se dual-site catalyst (FeSe/NC)\nand devised a prototype colorimetric assay kit for mixed plastics.\nExperimental and theoretical results unveiled that Fe sites acted\nas the main active sites for H<sub>2</sub>O<sub>2</sub> activation\nto produce adsorbed hydroxyl (*OH) intermediates, which subsequently\ndesorb as hydroxyl radicals (<sup>•</sup>OH) and transfer to\nSe sites, supports, and even plastics for further catalysis. Specifically, <sup>•</sup>OH transferred to different plastics shows varying\nactivities, where signal outputs were hereby used as the fingerprint\nfor plastic identification. Moreover, the remaining *OH could respond\nto redox interferences in the samples for enhanced accuracy. In contrast\nto traditional techniques involving precise apparatus and complex\npretreatments, our approach enables a rapid assay (∼10 min)\nof raw powdery mixed plastic wastes with an ultralow cost (0.0012\n$). This discovery fills a crucial gap in the plastic assay, offering\nnew technical guidance for diverse upcycling and recycling strategies\nto tackle the global plastic waste crisis.