Abstract: Rational design of composite catalysts with efficient charge separation and transfer is of great significance to achieve efficient degradation of pollutants. Herein, CuInS₂ nanoparticles are skillfully deposited on TiO₂ nanofibers through a hydrothermal method. The formation of S-scheme heterojunction is confirmed through free radical trapping experiments, in‐situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) measurements, density functional theory (DFT) calculations and femtosecond transient absorption spectroscopy (fs-TAS) results. These results reveal that the built-in electric field within the S-scheme heterojunction significantly enhances charge separation and transfer, boosting the catalyst's redox capabilities. The TiO₂/CuInS₂ photocatalyst exhibits superior photocatalytic performance, achieving a degradation rate of 89 % within 21 min of light irradiation, which is almost 2.2 times higher than that of TiO₂. Additionally, the degradation products of TCH are investigated using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and liquid chromatography-mass spectrometry (LC-MS), offering insights into the degradation pathway. This study highlights the potential advantage of ultrafast charge carrier transfer in S-scheme heterojunction, providing a promising strategy for designing high-efficiency photocatalytic systems for environmental remediation. The findings offer new directions for improving the degradation of persistent pollutants like tetracyclines.

Key words: TiO₂ nanofiber, CuInS₂ nanoparticle, S-scheme heterojunction, Tetracycline hydrochloride, Femtosecond transient absorption spectroscopy