Tracing SO₂ Heterogeneous Oxidation Dual-Pathway via Hydrogen-Bond-Enriched Interfacial Radical Chemiluminescence

Elucidating the SO₂ heterogeneous oxidation mechanism at the gas-liquid interface is critical for understanding haze formation. However, the dominant pathways and the oxidant's relative contributions remain ambiguous. This study developed a methodology that coupled a radical interfacial enrichment strategy with chemiluminescence (CL) detection, establishing a CL system capable of discriminating between the dissolved oxygen (DO) pathway and the non-DO oxidation pathway. By anchoring sorbic acid (SA)-functionalized Cr³⁺-doped ZnGa₂O₄ nanoparticles (ZGC NPs) at the interface of SO₂ microbubbles, we constructed a highly efficient CL reaction interface with nanoscale characteristics. This design facilitated hydrogen-bond-driven spatial enrichment of SO₂ and its radical intermediates at the gas-liquid interface. The radical-enriched interface induced a highly sensitive CL signal from the ZGC-SA-SO₂ system, which displayed composite characteristics from both pathways. Deciphering the signals revealed that the heterogeneous oxidation mechanism of SO₂ evolved dynamically with concentration. The dependence on the DO pathway decreased as the concentration increased. Additionally, the proposed method has been successfully implemented in the monitoring of automotive exhaust SO₂ and the rapid assessment of food freshness. The generality of this approach was further demonstrated by the observable interfacial CL signals across various ZGC-type NPs-unsaturated fatty acid-SO₂ systems. This work not only deciphers the dynamic, oxidant-dependent mechanism of SO₂ oxidation but also establishes a universal platform for SO₂ gas detection under mild conditions.