Polycyclic aromatic hydrocarbons (PAHs) contained two or more benzene rings are the organic pollutants with strong carcinogenic, mutagenic and teratogenic effects [[1], [2], [3]]. These pollutants enter the environment mainly through human activities such as straw and wood burning, coal burning, power plants, coke ovens, and automobile exhaust [4]. They are ubiquitous throughout the environment, e.g., atmosphere, surface water, soil, sediments, plants, aquatic organisms, and even the human body [[5], [6], [7]]. PAHs show the characteristics such as persistence and long-distance transportation, and have the potential hazards to human health [8]. Long term exposure to PAHs can cause many adverse health effects on humans and organisms (such as, teratogenic, carcinogenic, mutagenic, arteriosclerosis, infertility, etc.), which is a common problem in modern society [9]. The monitoring and determination of PAHs in environmental samples has been a matter of great concern. Therefore, developing feasible, fast and accurate analytical methods is very important.

The migration of PAHs in real samples is characterized by low concentrations accompanied by complex matrix effects. It is difficult to obtain satisfactory results when the actual samples are directly measured by testing instruments. Sample pretreatment technology can selectively enrich trace analytes from complex matrices and eliminate interfering substances, which is crucial for meeting the detection level of analytical equipment to obtain high reliability and accuracy of detection results [[10], [11], [12]]. Compared to traditional extraction methods, solid-phase microextraction (SPME), as a simple sample preparation method, simplifies the procedures by allowing multiple processes such as sampling, extraction and concentration to occur simultaneously [[13], [14], [15]]. Due to the characteristics of simple, fast, solvent-free, high sensitivity and environmental protection, SPME is widely used in environmental [16,17], food [18,19] and biology [20,21] and other fields in a simple and effective way to enrich trace analytes. As one of the methods of SPME, headspace solid-phase microextraction (HS-SPME) is favored for its ability to protect fiber coatings from contamination by matrix substances [[22], [23], [24]].

The choice of coating material for fibers is an important factor influencing the extraction performance for the target analytes. Many commercial coatings have been developed [[25], [26], [27]]. However, the limited extraction capacity, poor thermal stability, low specific surface area and expensive price of commercialized coatings limits their practical applications. Metal-organic frameworks (MOFs), which possess regular crystal structures, tunable pore topologies, large specific surface areas, and easy tailoring, have been widely used in adsorption and separation, catalysis, chemical sensing, and energy storage and conversion [28,29]. Nevertheless, the weak coordination between metal nodes and organic ligands results in poor stability of most MOFs, which greatly hinders their widespread applications. MOF-derived carbon materials fully inherit the characteristics of the parent MOFs and concurrently improve the stability of material, accompanying by high specific surface area, structural diversity, abundant porosity, and other characteristics of porous carbon [[30], [31], [32], [33]]. Ni-MOF is a promising MOF precursor because of the simple preparation process, and low cost. Although Ni-MOF-derived materials have been applied on a large scale in the fields of electrocatalysis [34,35] and supercapacitors [36], there are relatively research on they are used as SPME coatings for enriching trace pollutants in the environment.

Inspired by the above ideas, a one-step solvothermal method was carried out to synthesize Ni-MOF precursor, which was subjected to high-temperature carbonization under N2 atmosphere, and the specific surface area, pore volume and pore size of the materials (Ni@C-acid) were increased by further acid etching. The obtained Ni@C-acid was applied as coatings material in HS-SPME process for separation and enrichment of trace PAHs from complex matrices. The enrichment performance of Ni@C-acid with acid treated and Ni@C without acid treated for PAHs was compared, and the results showed that Ni@C-acid exhibited better adsorption capacity. This might be related to the fact that the Ni@C-acid material with acid treated possessed the higher specific surface area, rougher surface and more exposed action sites. Finally, the established Ni@C-acid-HS-SPME-GC-FID method was successfully applied to detect trace PAHs in tea infusions samples. It was verified that the prepared Ni@C-acid material showed excellent potential as a selective adsorbent for separation and concentration of pollutants in complex matrices.