Endogenous Donor Photocatalysis in Hypersaline Brines: An Evidence Framework for Coupled Pollutant Oxidation and H2O2 Production

Concurrent pollutant decay and hydrogen peroxide formation do not establish that a wastewater pollutant acts as an endogenous donor. In hypersaline brines, these observations may arise from parallel oxidation and oxygen reduction (ORR), with additional interference from chloride chemistry and peroxide loss. We define endogenous donor photocatalysis (EDP) as an operational mechanistic assignment within pollutant-assisted photocatalysis, rather than a new fundamental photocatalytic phenomenon. Five criteria connect endogenous pollutant origin, access to the oxidation-active interface, pathway-specific oxidation accessibility, causal changes in carrier competition, and a donor-dependent increase in source-attributed ORR-derived hydrogen peroxide formation. Direct hole oxidation and interface-local oxidation by hole-derived reactive species may qualify when the complete causal chain is supported. Interfacial enrichment provides strong supporting evidence but is distinguished from interface access. Net peroxide accumulation, preservation, and use are evaluated separately as engineering outcomes. Among the representative studies examined here, we did not identify a real DMP-containing brine study that closes all five criteria with orthogonal evidence. We provide matched-control workflows and conditional predictions that distinguish formation from loss and support mechanistic testing in salt-lake flotation tail liquor and other wastewater matrices.