Plastic waste accumulation has become one of the most pressing global environmental challenges, yet direct upcycling of post-consumer plastics remains limited by contamination and compositional heterogeneity. Conventional recycling technologies largely depend on high-purity feedstocks, making substantial quantities of waste plastics unsuitable for value-added applications. To overcome this limitation, this study presents a direct upcycling strategy that repurposes post-consumer polystyrene (PS) as a porous structural scaffold for water treatment without requiring energy-intensive purification or chemical transformation. The proposed strategy is based on the deliberate decoupling of structural and adsorptive functions. Waste PS serves as the porous structural scaffold, while embedded powdered activated carbon (PAC) serves as the active adsorbent for contaminant removal. By separating these functions into distinct components, the adsorption performance becomes independent of the intrinsic adsorption properties and compositional heterogeneity of the waste plastic, enabling heterogeneous post-consumer PS to be directly converted into a functional environmental material. The feasibility of the proposed strategy was demonstrated using sucralose, a persistent and highly water-soluble artificial sweetener, as a representative emerging micropollutant. Rather than treating waste plastics as recyclable feedstocks that require chemical conversion, this strategy directly utilizes their inherent structural properties. This function-decoupled design provides a new pathway for plastic waste upcycling and sustainable water treatment.