Quasi-Operando Quantification of Surface Sulfur Vacancy in Metal Sulfides via Luminol-H2O2 Chemiluminescence.

Sulfur vacancy (SV) is known to act as active center in many metal sulfides, and quantification of SV is essential for understanding the quantitative structure-property relationship. Operando methodology for quantifying SV is highly desirable but remains challenging. In this study, we discovered that metal sulfides containing SV can efficiently trigger intense chemiluminescence (CL) of luminol-H2O2 system, and the CL intensity exhibits a strong linear correlation with the SV concentration. Notably, as CL emission occurs simultaneously with the chemical reaction, this method inherently enables quasi-operando assessment of surface Sv under reactive conditions, bridging the gap between static ex situ characterization and demanding operando studies. Mechanistic investigations reveal that SV serves as catalytic site for the activation of H2O2 to generate hydroxyl radicals (•OH), which subsequently oxidize luminol to produce CL emission. Leveraging this mechanism, we developed a rapid and facile CL assay for the quantitative determination of surface SV. Compared to conventional techniques, such as X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), this method offers distinct advantages, including operational simplicity, low cost, and minimal instrumental requirements. Furthermore, unlike conventional techniques methods that measure Sv under static or vacuum conditions, this quasi-operando approach captures defect states under chemically reactive environments, providing more functionally relevant information for understanding the role of Sv in catalytic processes. This work extends the utility of CL technology to the structural evaluation of metal sulfides, providing a novel toolkit for the quantitative analysis of SV and guiding the rational design of defective metal sulfides.