DFT-guided design of biochar-based composites for photocatalytic degradation of fluoroquinolone antibiotics in soil-water systems: Non-targeted metabolomics and structural equation modeling

Abstract

The accumulation of fluoroquinolone antibiotics (FQs) in soil-plant systems causes ecotoxicity. Traditional photocatalysts have high electron-hole recombination and unknown degradation product toxicity, making multi-media treatment difficult. This study used DFT-guided Ce/MIL-88b-NH₂@BC composites to elucidate FQs’ degradation mechanism of six FQs and assessed the effects of the composite on plant metabolism and system repair. By integrating non-targeted metabolomics and structural equation models, the "material-contaminant-plant" interaction network was analyzed. Ce/MIL-88b-NH₂@BC achieved a 98.9 % FQs degradation rate in 90 min under UV–Vis light, dropping slightly to 82.5 % under sunlight. SO₄·^- and ·OH were the key radicals driving degradation pathways, such as piperazine ring rupture and decarboxylation, converting the parent FQs into low-toxicity substances. The content of FQs in lettuce leaves was less than or equal to 1 ng g⁻¹, well below the planetary boundary (PB) of 153.7 μg kg⁻¹ of antibiotic concentrations in agricultural soils worldwide. Ce/MIL-88b-NH₂@BC reduced plant toxicity by degrading pollutants, inhibiting overactivated stress pathways, restoring normal physiology, and shifting resources to growth-related metabolism. Structural equation models were used to quantify the relationships between key metabolites and plant physiological indices. The whole chain strategy of "computational design-experimental validation-system modeling" is pioneered in this study to provide a predictable intelligent solution for antibiotic pollution control.