Construction of LaFe0.5Ni0.5O3/g-C3N4 S-scheme heterojunction for dramatically enhanced photocarrier separation toward efficient photocatalytic deodorization of livestock wastewater: Based on in-situ irradiation XPS and fs-TAS analysis techniques

Abstract

Odor emissions from livestock and poultry farms have become an urgent environmental challenge and a scientific concern. Indole is one of the predominant malodorous compounds responsible for this issue. To explore effective deodorization strategies, indole was selected as a model pollutant for investigating the construction of heterojunction photocatalysts and their degradation mechanisms. Herein, this study developed an S‑scheme heterojunction photocatalyst LaFe_0.5Ni_0.5O₃/g-C₃N₄ (LFN/CN). Under visible‑light conditions without oxidants, the optimally proportioned catalyst 15LFN/CN (15% LFN by weight) exhibited a rate constant of 5.99 × 10^− 2 min^− 1. Its degradation rate constant for indole was 78.8 times that of pristine LFN and 5.24 times that of CN, respectively. Moreover, the catalyst achieved efficient degradation in the pH range of 3–11, with removal rates of 97.79%-100% at pH 9–11. It maintained excellent degradation performance in complex aqueous matrices (interfering ions/organics) and under natural light irradiation. Removal rates of 96.28%-100% were achieved for pollutants such as 3‑methylindole, estrogens, and antibiotics. Moreover, over 90% indole removal efficiency was achieved in three real dairy farm wastewater samples. LC‑MS analysis combined with toxicity assessment elucidated the degradation pathway of indole and its environmental safety. Critically, the accurate identification of the charge‑transfer mechanism in the material serves as the theoretical foundation for understanding the excellent activity of this heterojunction, and this identification heavily relies on spatiotemporally resolved characterization techniques. Accordingly, for the 15LFN/CN catalyst, direct and multidimensional experimental evidence for the S‑scheme pathway was provided: In situ irradiated X‑ray photoelectron spectroscopy revealed the electron migration pathway; Kelvin probe force microscopy demonstrated the highest surface potential variation (169.34 mV); and femtosecond transient absorption spectroscopy resolved an interfacial electron‑transfer lifetime of 164.39 ps and an extended charge‑recombination lifetime of 5.59 ns. These findings establish a reliable methodology for validating the S‑scheme mechanism and offer new insights for the efficient removal of typical odorous compounds in actual livestock wastewater.

Graphical abstract