Efficient starch-montmorillonite hydrochar for quinclorac detoxification in soil: Synthesis, mechanisms and application.

Quinclorac (QNC) is an excellent rice herbicide with a soil half-life up to 540 d, causing persistent soil contamination and phytotoxicity in rotational crops such as tobacco. Although peroxymonosulfate (PMS)-based advanced oxidation processes can degrade QNC, existing non-hydrothermal carbon materials for PMS activation face limitations including high energy costs, metal leaching risks, and poor catalyst stability. Moreover, no previous study has provided a systematic framework, ranging from clay-mineral hydrochar composite design, and mechanistic elucidation to field validation, for the effective detoxification of QNC-contaminated soils. Here, we synthesized a starch-montmorillonite hydrochar composite (CWSH2@MMT), not previously reported for PMS activation, via hydrothermal carbonization. The system achieved 88.36% QNC removal from soil within 12 h. Quenching experiments, ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analysis combined with density functional theory (DFT) calculations revealed two degradation pathways of QNC driven by •OH, SO4•-, and O2•- radicals. Toxicity assessments by T.E.S.T. and ECOSAR program together with pot experiments confirmed that detected intermediates are less toxic than parent QNC. Critically, unlike lab-only studies, we conducted field trials in tobacco. The CWSH2@MMT/PMS system alleviated QNC-induced phytotoxicity, recovering leaf length, leaf width, and plant height by > 80% with improved yield and quality. This offers a green, efficient, and practical detoxification strategy for addressing soil pollution from herbicide residues.