Single-atom catalysis steers polymerization pathways in water treatment: from atomic-level mechanisms to low-carbon engineering

Unlike mineralization, polymerization pathways can convert wastewater pollutants into recoverable solid polymers, cutting oxidant use and carbon emissions while recovering carbon. Single-atom catalysts (SACs), featuring atomically dispersed metal centers, tunable coordination environments, and maximal atomic utilization, are ideal for steering polymerization pathways. Although research on SACs in polymerization pathways continues to advance, a multi scale framework that systematically integrates their electronic structure design with engineering applications is still lacking. To fill this gap, this review presents such a framework across microscopic, mesoscopic, and macroscopic scales. At the microscopic level, d-band center, spin-state, and coordination microenvironment are regulated to confine reactive species within the polymerization-favorable thermodynamic window. From a mesoscopic perspective, nanoconfinement, forced convection, and multi active site synergy overcome mass transfer and radical-collision bottlenecks. As for a macroscopic level, reactor scale up, polymer product separation/recovery, resource utilization, and economic assessment are discussed. This review provides theoretical guidance and design principles for advancing SACs driven polymerization pathways from fundamental research toward low-carbon water treatment technologies.