Catalytic Degradation of Microplastics: From Apparent Removal to True Destruction and Carbon Valorization

Microplastic control often removes particles from water without destroying polymer carbon and transfers this carbon to sludge or other residual streams. Catalytic treatment can deconstruct the polymer, yet surface oxidation, particle loss, chain scission, and mineralization are frequently reported as equivalent outcomes. This Review defines an evidence hierarchy that distinguishes interfacial ageing, backbone scission, product-resolved deconstruction, and terminal carbon conversion. Degradation denotes measurable chemical change of the polymer. Destruction denotes irreversible elimination of the polymeric particulate phase. Mineralization denotes conversion to CO2 or inorganic carbon. Valorization denotes formation of chemically defined, recoverable products. Microplastics with carbon-carbon backbones are limited by hydrophobicity and inert C-C bonds, whereas hydrolysable polyesters permit depolymerization and subsequent conversion. Representative studies are evaluated by the analytical evidence supporting each claim. Required measurements include carbon balance closure, identification of dissolved and volatile products, detection of secondary nanofragments, and separate toxicity assessment of residual solids and aqueous products. Selective valorization is environmentally credible mainly for concentrated, polymer-defined streams that permit product recovery. Dilute or mixed environmental microplastics require verified polymer deconstruction, reduced toxicity, and a traceable terminal carbon fate.