Selective Detection of Pesticide using Monolayered HON-100 and HON-101

Abstract

Pesticide contamination in the environment has major human health and ecological concerns, especially from long-lasting nitroaniline compounds such as 2,6-dichloro-4-nitroaniline (DCN), a high-volume fungicide. Traditional detection techniques such as gas chromatography (GC), high performance liquid chromatography (HPLC), and mass spectroscopy (MS), though accurate, are limited by high costs, time demands, and lack of portability. This study introduces monolayer hydrogen-bonded organic nanosheets (HON-100), exfoliated from pyrene-based hydrogen-bonded organic frameworks (HOF-100) and (HOF-101), as novel, metal-free, fluorescent sensors for selective and sensitive detection of DCN. The nanosheets were synthesized through Suzuki coupling, followed by exfoliation using optimized sonication and solvent-assisted techniques. Structural and morphological characterization via Nuclear Magnetic Resonance (NMR) Spectroscopy, Powder X-ray Diffraction (PXRD), Atomic Force Microscopy (AFM), and Thermogravimetric Analysis (TGA) confirmed the formation of few-layer nanosheets, particularly effective in solvents like toluene. AFM analysis revealed nanosheet thickness as low as ~5 nm and lateral sizes of ~10 µm, ideal for optical sensing applications. TGA data indicated reduced thermal stability in exfoliated forms due to disruption of the hydrogen-bonded framework. Fluorescence spectroscopy revealed strong emission from HONs, with HON-100 displaying significant quenching upon interaction with DCN. Control experiments ruled out solvent and handling effects as major contributors to quenching. The optimal dilution for sensing was 0.12 M, and titration studies with solid DCN further confirmed direct molecular interaction. A linear fluorescence response to increasing DCN concentrations was observed with a poor correlation (R² = 0.585), and the calculated Limit of Detection (LOD) was 354 µM. Overall, this work demonstrates that HON-100 offer promising, metal-free, for real-time DCN detection.