In situ fabrication of nitrogen doped graphitic carbon networks coating for high-performance extraction of pyrethroid pesticides

Highlights

• Graphitic carbon networks coated fiber was fabricated via in-situ method.

• Graphitic structure and abundant nitrogen-doped can improved the adsorption capacity.

• The proposed SPME-GC-MS/MS method exhibited low detection limits and high stability.

Abstract

The tailor-prepare solid phase microextraction (SPME) coatings with stable and excellent properties to effectively extract analytes from sample matrix still remains a challenge. Herein, a nitrogen doped graphitic carbon networks (NG-CNTW) coated fiber was fabricated by direct carbonization of nanosized ZIF-67 crystals (nano-ZIF-67) that grown on stainless steel wire. The NG-CNTW coated fiber coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) was applied for enrichment and determination of pyrethroids. The NG-CNTW coating exhibited high surface area and hierarchical porous structures that facilitate diffusion and accessibility of target molecules. Simultaneously, the nitrogen doped and highly graphitic structures endow the coating with high adsorption affinity for aromatic compounds. Under optimum conditions, the SPME-GC-MS/MS method presented wide range of linearity performance (0.08–200.0 ng g⁻¹), low limits of detection (0.02–0.5 ng g⁻¹) and good repeatability (RSD < 9.6%) for 8 kinds of pyrethroids. Furthermore, the proposed method was successfully applied in the determination of pyrethroids in grape and cauliflower samples, as the results were in the range of 3.16–15.06 ng g⁻¹and 2.08–9.29 ng g⁻¹, respectively. This work not only provides a new method by fabricating carbon nanomaterial coatings in situ derived from MOFs, but also shows great potential of MOFs derivative materials in environmental analysis field.

Introduction

Solid-phase microextraction (SPME) is considered as an easy operation, less solvent consumption, high enrichment factor and environment friendly technique, with rapid and simple extraction of organic semi-volatile and volatile compounds [1]. In virtue of these remarkable features, SPME have attracted particular attention and widely used in food [2,3], biological [4], medicine [5] and environment [6] samples. Apparently, SPME is based on the distribution balance between analytes and fiber coating, an appropriate material as stable and efficient adsorbent is crucial factor to affect the performance and applications of SPME. The current commercial fibers with the low adsorption capacity and easy breakage are restricted to the potential practical applications in some cases [7,8]. To circumvent this, numerous efforts have explored the novel and high-performance coating materials for SPME during the past decade [9,10]. Among these, two-dimensional nanomaterials [11], metal organic fameworks [6], covalent organic frameworks [7], ionic liquid [8] and nanoporous canbon materials [12] and so on, have been used as a coating for SPME due to the high extraction capacity, certain selectivity, good chemical and thermal stability. Nevertheless, very few studies on in situ fabricated carbon-based SPME coatings have been reported. In particular, the preparation of element doped carbon materials with a certain morphology. It is necessary to tailor-prepare SPME coatings that combines multiple advantages and with stable and efficient properties for effective extraction of various analytes from sample matrix.

Porous carbon nanomaterials, such as carbon nanotubes, carbon nanofibers and fullerene, have the advantages of high specific surface area, excellent adsorption performance, easy modification, high chemical stability and thermal stability, and have been successfully used as SPME coating. Generally, porous carbon nanomaterials with high specific surface area are mostly prepared by carbonizing organic matter. However, its porous structure is poorly designed and difficult to control the chemical composition and the complex multi-step preparation process is not conducive to further large-scale application. In recent years, metal–organic frameworks (MOFs) have been proved to be ideal templates and precursors for the synthesis of functional nanomaterials by high-temperature pyrolysis, due to their high porosity, tunable composition, ordered crystalline structure and carbon-rich organic components. Inspired by this promising method, several MOFs, such as ZIF-8 [13], ZIF-67 [14], MOF-5 [15], IRMOFs [16], have been successfully used as templates for the synthesis of MOF-derived carbon based nanomaterials. However, the studies of tailor-prepare carbon-based SPME coatings with multifunctional are very limited in previous literatures. Besides, the direct carbonization of MOFs may cause solid and may lead to monotonously micropore structure, which hinders the fast mass diffusion and high enrichment factors [17]. From this perspective, the excellent adsorption performance could be achieved by rational design of MOF-derived carbon based nanomaterials with specific structure, morphology and functionalization. It is worthy to note that the previous reported examples of exploit the structural characteristics of the nanomaterials to accelerate mass transfer and enhance enrichment performance [17,18]. In addition, the target molecules from the sample solution could be effectively extracted and intercepted through three-dimensional (3D) interconnected CNT networks [19,20]. On the other hand, changing the surface chemical properties and improving organic pollutants adsorption affinity of carbon nanotubes can be achieved by doping heteroatoms, such as N or B. For instance, the doping of pyridine N can not only make the surface of carbon nanomaterials positively charged, but also enhance the interaction with the aromatic rings [[21], [22], [23]]. Encouragingly, the MOF-derived nanoporous carbons are a potential choice for sensitive SPME of aromatic organic pollutants, due to the presence of graphitic carbon surface and sp² carbon [24,25].

Pyrethroid pesticides are commonly used worldwide as the broad spectrum insecticide agriculture [26]. However, the residues of these pesticides pose potentially harmful to human life and health even at trace levels due to their high activity and low toxicity [[27], [28], [29]]. Accordingly, to protect human health and environment, monitoring the concentration of pyrethroids in food and water samples has attracted particular attention. However, it still remains a big challenge to efficient extraction and determination of pyrethroids at trace levels from complex sample matrixes.

Herein, the polyaniline was modified onto a stainless steel wire by electrodeposition to adsorb the nanosized MOF crystallites through the covalent interaction. Subsequently, a nitrogen doped graphitic carbon networks (NG-CNTW) coated fiber was fabricated by carbonizing the nanosized ZIF-67 crystals (nano-ZIF-67) that grown onto stainless steel wire in situ. In the end, the NG-CNTW coated fiber coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) for detecting pyrethroid pesticides from grapes and cauliflower samples. The NG-CNTW-SPME-GC-MS/MS method combined the advantages of the multiple interactions of the NG-CNTW, nitrogen doped, highly graphitic and hierarchical porous structures. Moreover, it is not ignored that the economy and simplicity of SPME.