Three-Dimensional Graphene-Based Stainless-Steel Mesh as Solid-Phase Extraction Material for Determination of Organophosphorus Pesticides

Graphene oxide and Au nanoparticles were assembled on the surface of stainless-steel mesh via the chemical modification, and then freeze-dried to obtain an Au modified graphene oxide aerogel grafted stainless-steel mesh (Au/GOA-SSM) used as the sorbent for the enrichment and detection of organophosphorus pesticides. Firstly, graphene oxide was chemically bonded to the surface of the pretreated SSM to obtain the graphene oxide aerogel via the freeze-drying, and then Au nanoparticles were deposited on the aerogel via an in-situ chemical reduction. The prepared material combined the excellent extraction performance of graphene oxide aerogel and the three-dimensional geometric structure of SSM to improve the extraction efficiency, and to realize the selective extraction of organophosphorus pesticides through the coordination action of Au-S. The surface morphology and properties of the prepared material were characterized using the scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The skeleton structure of SSM emerged in the SEM images, and Au/GOA was coated on the surface of SSM, which had the lamellar and wrinkle structure. The appearance of Au element in the XPS characterization verified the successful synthesis of Au/GOA-SSM. The effect of extraction and elution conditions on recovery of four organophosphorus pesticides was investigated through a series of single factor experiments. The obtained optimum conditions were as follows: sample volume (15 mL), sample rate (1 mL/min), eluent (1 mL of acetonitrile). Compared with the commercial extraction materials (SAX, C18, -NH₂, Carb, Florisil), the Au/GOA-SSM exhibited higher extraction recoveries for organophosphorus pesticides. Through the comparison of different factors including the oil-water partition coefficient, theoretical adsorption energy and extraction recoveries of different organophosphorus pesticides, it can be seen that the oil-water partition coefficient, that is, the hydrophilicity and hydrophobicity of organophosphorus pesticides, has a great effect on the extraction recovery. Under optimized conditions, the linear ranges of this method for the detection of organophosphorus pesticides were relatively wide (phoxim and fenitrothion: 1~200 μg/L, temephos and fenthion: 0.5~200 μg/L), and all the fitting linearities were good (r≥0.990 6), and the limits of detection were in the range of 0.1~0.2 μg/L. The accuracy and precision of the method (Au/GOA-SSM-based solid-phase extraction coupled high-performance liquid chromatography) were evaluated through the investigation of the repeatability and reproducibility of extraction column. An extraction column was continuously used to extract organophosphorus pesticides for five times, and relative standard deviations of extraction recoveries were less than 5.6%. Then, under the same conditions, five extraction columns were used to extract organophosphorus pesticides and relative standard deviations of extraction recoveries were less than 9.8%. The Au/GOA-SSM packed extraction column exhibited a good repeatability and a good reproducibility. Besides, it exhibited the advantages of simple preparation, low cost, and good sensitivity. It was applied to detect the organophosphorus pesticide in coriander, and no organophosphorus pesticide was detected. Extraction recoveries of samples spiked with standard solutions were in the range of 70.4%~97.7%, and the relative standard deviations were in the range of 3.9%~10.3%.