钴镍笼状双金属氢氧化物/多壁碳纳米管复合材料对环境水样中农药的高效富集 Translated title: Efficient enrichment of pesticides from environmental water samples by cobalt-nickel double metal hydroxide nanocage/multiwalled carbon nanotube composites

Abstract

建立高效、灵敏的农药分离、富集和检测方法具有重要意义。该实验采用一步法合成了钴基沸石咪唑骨架/多壁碳纳米管(ZIF-67/MWCNTs)复合物,并以该复合物为模板通过溶剂热法合成了钴镍笼状双金属氢氧化物/多壁碳纳米管(CoNi-LDH/MWCNTs)复合材料,将CoNi-LDH/MWCNTs用作固相微萃取(SPME)的纤维涂层富集环境水样中的6种农药,结合高效液相色谱(HPLC)测定了环境水样中的6种农药。通过扫描电镜、能谱分析、红外光谱、粉末X射线衍射和N ₂吸附/脱附对所制备的各种材料进行了表征。利用正交设计试验优化SPME的萃取条件,包括萃取温度、萃取时间、搅拌速率、解吸时间和盐浓度。在最优化的条件下,该方法具有较宽的线性范围(百菌清为0.015~200 μg/L,戊唑醇为0.140~200 μg/L,毒死蜱为0.250~200 μg/L,仲丁灵为0.077~200 μg/L,溴氰菊酯为1.445~200 μg/L,哒螨灵为0.964~200 μg/L)、较低的检出限(0.004~0.434 μg/L)和良好的重复性。单个纤维和不同批次纤维间的相对标准偏差(RSD)分别为0.5%~5.7%和0.5%~4.8%。在10.0 μg/L和50.0 μg/L 2个水平下的加标回收率为83.9%~108.2%, RSD< 5.3%。此外,与其他涂层纤维相比,CoNi-LDH/MWCNTs涂层对农药具有更高效的富集能力,这归因于它的高比表面积以及CoNi-LDH/MWCNTs涂层与目标分析物之间存在的 π- π堆积作用、疏水作用、阳离子- π相互作用和氢键作用。该方法可以实现环境水样中农药残留的高选择性、高灵敏度及高准确性的分析测定。

Translated abstract

Pesticides are widely used in agriculture to increase grain yields and prevent crop diseases and insect pests. However, pesticides pose a serious threat to ecosystems and human health owing to their high toxicity and persistence. Therefore, it is imperative to establish an efficient and sensitive detection method for pesticides in water samples. Rapid and accurate detection of trace pesticides in environmental water samples has been a challenge because of complex matrix effects and trace concentrations. Appropriate sample pretreatment is a critical step for the effective extraction of analytes and removal of interferences, and the development and design of novel and stable nanomaterial adsorbents is key to continuous innovation in sample pretreatment technology. In recent years, carboxylated multiwalled carbon nanotubes (MWCNTs-COOH) and layered double hydroxide (LDHs) have been widely used as new adsorbent materials for various pretreatment technologies because of their large specific surface area, good stability, and easy functionalization. Based on this background, MWCNTs-COOH and LDHs were combined to obtain a new efficient composite adsorbent, so that the synergistic effect of the individual components could be exploited in entirety. In this study, a zeolitic metal organic framework ZIF-67/multiwalled carbon nanotube (ZIF-67/MWCNTs) composite was prepared by a simple one-step method, and a cobalt-nickel double metal hydroxide/multiwalled carbon nanotube (CoNi-LDH/MWCNTs) hybrid material with a three-dimensional cage-like structure was synthesized by a solvothermal method using ZIF-67/MWCNTs as templates. The cage-like structure of the CoNi-LDH/MWCNTs composite, which is different from the traditional layered bimetallic hydroxide, could accelerate mass transfer. Given the excellent properties of the CoNi-LDH/MWCNTs composite, it was used as a solid-phase microextraction (SPME) coating for the efficient enrichment of six pesticides (chlorothalonil, tebuconazole, chlorpyrifos, butralin, deltamethrin, and pyridaben) and combined with high performance liquid chromatography-ultraviolet (HPLC-UV) detection for the determination of the six pesticides in real water samples. The prepared materials were characterized by scanning electron microscopy, electron dispersion spectroscopy, infrared spectroscopy, X-ray powder diffraction, and N ₂ adsorption/desorption. The results confirmed that the CoNi-LDH/MWCNTs composite was successfully synthesized, and that its surface area and pore volume were 281.4 m ²/g and 0.49 cm ³/g, respectively. An orthogonal array design was used to optimize the extraction conditions of SPME, including the extraction time, extraction temperature, stirring rate, salt effect, and desorption time. The optimal extraction conditions were as follows: extraction temperature, 40 ℃; extraction time, 30 min; stirring rate, 500 r/min; desorption time, 6 min; and salt (NaCl) mass concentration, 150 mg/L.

Under optimal conditions, the method had a wide linear range (chlorothalonil: 0.015-200 μg/L, tebuconazole: 0.140-200 μg/L, chlorpyrifos: 0.250-200 μg/L, butralin: 0.077-200 μg/L, deltamethrin: 1.445-200 μg/L, pyridaben: 0.964-200 μg/L), low detection limit (0.004-0.434 μg/L), and good reproducibility. The relative standard deviations (RSDs) of single fiber and fiber-to-fiber were in the range of 0.5% to 5.7% and 0.5% to 4.8%, respectively. The spiked recoveries at two levels of 10.0 μg/L and 50.0 μg/L were in the range of 83.9%-108.2%, with RSDs less than 5.3%. Compared with other coated fibers (MWCNTs-COOH, ZIF-67, ZIF-67/MWCNTs, and silicone sealant), the CoNi-LDH/MWCNTs-coated fibers showed a better enrichment effect for pesticides, which was attributed to their high specific surface area and π- π interactions, hydrophobic interactions, cation- π interactions, and hydrogen bonding interactions between the CoNi-LDH/MWCNTs coating and the target analytes, which can enhance their ability to extract pesticides. The stability test on the SPME fibers revealed that after 128 cycles, the extraction efficiency of the CoNi-LDH/MWCNTs-coated fibers for the six pesticides decreased only slightly (< 10%), implying that the coated fibers had good stability and reusability. Therefore, this method can be used to detect pesticide residues in environmental water samples with high selectivity, sensitivity, and accuracy.