Circulating microdroplet-driven self-Fenton for micropollutant elimination: The overlook of ligand-to-metal charge transfer and chloride radical

A circulating microdroplet-driven self-Fenton system (MDSFS) was developed for efficient wastewater treatment utilizing the synergism of microdroplet chemistry and metal-to-ligand charge transfer (LMCT) without requiring external light, catalysts, or sacrificial agents. This innovative system was pioneered by nebulizing a ferric chloride–sulfamethoxazole complex solution into microdroplets via ultrasonic technology. The MDSFS achieved a superior performance with a H₂O₂ yield of 258.5 μM, achieving an 11-fold faster iron cycling rate and a 5-fold higher reaction rate constant (0.139 min⁻¹ vs. 0.029 min⁻¹) for sulfamethoxazole removal compared to traditional bulk Fenton system. The microdroplets acted as an active medium, facilitating electron generation, •OH radical formation, H₂O₂ production, and enhancing ligand-to-metal charge transfer via the air-water interfacial electric field. This enables a dual redox cycle of Fe(III)/Fe(II) and Cl⁻/•Cl, generating abundant •OH and •Cl for efficient SMX removal. The study proposes a sustainable, self-driven redox strategy for environmental remediation and health.