Dual-Functional Fe-Doped TiO ₂ Photocatalyst for Visible-Light-Driven 2,4-D Remediation in Contaminated Soil and Plant Growth Promotion

While photocatalytic remediation is promising, its ecological compatibility and impact on post-treatment soil productivity remain critically under-explored. This study addresses this gap by developing a dual-functional Fe-doped TiO2 photocatalyst via microwave-assisted synthesis for the remediation of contaminated agricultural soil. The 0.5 wt % Fe-doped TiO2 exhibited enhanced visible-light absorption and suppressed charge recombination, achieving 88% 2,4-dichlorophenoxyacetic acid (2,4-D) degradation and 56% total organic carbon (TOC) removal at pH 4.2 within 90 min. Radical scavenging experiments identified hydroxyl radical (•OH) as the primary reactive species driving the degradation, while hole (h+) and superoxide radical (•O2–) played secondary roles in the reaction mechanism. Crucially, the comprehensive ecological safety assessment using Chinese cabbage (Brassica rapa) revealed a vital safety threshold for practical application. The optimal 0.5 wt % Fe-doped TiO2 not only eliminated herbicide toxicity but also actively enhanced plant growth compared to the control, acting as a beneficial dual-agent. In contrast, toxicity and growth inhibition were observed at higher Fe doping concentrations (>1.0 wt % Fe) due to iron toxicity, highlighting the necessity of precise dopant optimization. By integrating herbicide mineralization with soil vitalization, this work provides a sustainable strategy for restoring herbicide-contaminated lands while ensuring agricultural productivity.