Stable and sustained formaldehyde degradation in enclosed environments, combined with precise concentration quantification, remains a pivotal challenge in advancing air purification technologies. Based on photocatalytic semiconductor Ag₃PO₄ and gas-sensing semiconductor In₂O₃,this work innovatively designed and constructed a multidimensional Ag₃PO₄@In₂O₃/MXene S-scheme heterojunction, achieving dual-functional integration of efficient photocatalytic formaldehyde degradation and sensitive gas sensing under visible light illumination. The synthesis details can be described as the following steps. Initially, 0D Ag₃PO₄nanoparticles, 1D In₂O₃ nanorods, and 2D MXene nanosheets were separately synthesized via liquid-phase precipitation, precursor-controlled calcination, and chemical etching. Then, the ternary S-scheme heterojunction was precisely synthesized through electrostatic self-assembly(for In₂O₃/MXene) combined with liquid-phase deposition(for Ag₃PO₄ anchoring), ensuring intimate interfacial contact and structural stability. Subsequently, advanced characterization techniques, including HRTEM and XPS, revealed the formation of well-defined heterojunction interfaces and chemical bonding interactions. The unique S-scheme band structure, confirmed by UV-vis DRS and Mott-Schottky analysis, facilitates the spatial separation of photogenerated electrons and holes while preserving strong redox potentials. Under visible light irradiation, the Ag₃PO₄ component activates formaldehyde degradation through hydroxyl radical-mediated oxidation, while MXene nanosheets serve as electron highways to accelerate reaction kinetics, leading to mineralization of formaldehyde to CO₂. Concurrently, the In₂O₃/MXene interface exhibits modulated surface conductivity upon formaldehyde adsorption, enabling real-time gas sensing through light-enhanced charge transfer dynamics. Operando FTIR further elucidated the synergistic mechanism between photocatalytic degradation and gas sensing. This work not only establishes a novel paradigm for multifunctional heterojunction design but also provides a scalable strategy for developing integrated air purification systems capable of simultaneous pollutant removal and environmental monitoring.

Mengjuan Yang

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