Organic Semiconductor Nanosheets for Sulfite Detecting Based on Activation of Sulfite and a Synergetic Chemiluminescence Resonance Energy Transfer Process in a Mild System of Fe2+-SO32.

Sulfur dioxide (SO2) as one kind of air pollution not only causes extreme environmental pollution but also negatively affects human health. Chemiluminescence (CL) methods applied for sulfite analysis with high selectivity based on activating sulfite with oxidants are always implemented in acid media with a high background rise. In this work, we proposed to develop a mild CL system of Fe2+-SO32- to detect sulfite under neutral conditions and provide in situ CL spectral data for deeply studying the CL mechanism of Fe2+-SO32-. Herein, we first synthesized one type of water-soluble supramolecular nanosheets, APDI NSs, which had a strong oxidation potential (+2.9 V) due to a π-conjugated system for activation of sulfite to enhance the generation of SO3̇- and other active radicals, and strong a CL signal from the APDI NSs-Fe2+-SO32- system was generated. By studying the CL mechanism under acidic and neutral conditions, a new CL reaction pathway (path-1) and a key intermediate, S2O42-, from the reaction of Fe2+ and SO32- were found. The CL signal was emitted by SO2* after oxidation of S2O42- by strong oxidants like SO4•- and further amplified by APDI NSs through the CL resonance energy transfer (CRET) process. Based on the APDI NSs-Fe2+-SO32- system under neutral conditions, a CL method for detecting SO32- was established. The detection limit was 2.7 × 10-8 M (S/N = 3), and the recovery rates in spiked water samples were in the range of 87%-101%. This study strengthens the understanding of the CL reaction process of the Fe2+-SO32- system and provides a mild sulfite sensing platform for environmental samples.