Highly Efficient Degradation of Quinclorac in Soil by Peroxymonosulfate Activated with Sucrose-Montmorillonite Hydrochar

Quinclorac (QNC) is a selective herbicide commonly used in paddy fields for Echinochloa spp. weed control. However, it poses ecological risks due to its persistent soil residue phytotoxicity effects on some crops. An innovative approach for managing pesticide residues involves activating peroxymonosulfate with hydrochar. This study investigates the preparation, characterization, and activation efficiency of hydrochar composites (such as sucrose-montmorillonite hydrochar composites) made from sucrose and montmorillonite. The composite SUCH4@MMT, prepared at a sucrose (SUC)-to-montmorillonite (MMT) ratio of 1:2 (weight-to-weight) at 180 °C, exhibited enhanced peroxymonosulfate activation efficiency compared to pure sucrose hydrochar. Using SUCH4@MMT/peroxymonosulfate, the QNC degradation efficiency in soil reached 88.19% within 12 h. Key surface features of SUCH4@MMT, including sp² carbon, carbonyl groups, and carbon defects, contributed to peroxymonosulfate activation, producing reactive species including SO₄^•−, •OH, O₂^•-, and ¹O₂. Ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry analysis identified 11 major degradation products, and quantum chemical calculations facilitated the proposal of three potential degradation pathways. Toxicity evaluations indicated that the degradation intermediates were much less toxic than QNC, with significant reduction in QNC-induced phytotoxicity to tomato plants. These findings offer a novel, effective approach for mitigating adverse QNC soil residue effects.