As a non-alcoholic beverage, tea is widely enjoyed for its distinct flavor and multiple health benefits [1,2]. In 2020, despite economic and logistical obstacles worldwide, global tea production still reached an impressive figure of 6.269 million tons. Tea exports similarly remained robust, totaling 1.822 million tons. Tea is abundant with beneficial components such as catechins, tea pigments, and tea polysaccharides, which grant it antioxidant, antitumor, and immune-enhancing attributes [3,4]. Unfortunately, the hot and humid conditions that most tea plants grow in make them vulnerable to various pests and diseases, requiring pesticide application to safeguard both the yield and quality of the tea. Despite the reduction of applied pesticides through self-degradation and the growth dilution effect in tea plants, the manufacturing process, which involves significant moisture loss, could increase residual pesticide concentrations [5,6]. Given the extensive specific surface area of tea leaves, these plants are more prone to accumulating pesticide residues than other crops. Huang et al. determined 102 pesticides in 45 green tea samples, and 11 pesticide residues in 18 samples exceeded the maximum residue limit set by European Community [7]. Research by Wang et al. showed that the transfer potential of pesticides from dry tea to tea infusion was associated with their high water solubility. For neonicotinoids, with a low octanol-water partition coefficient (KOW), the migration rate was as high as 83.3–103.6% [8]. Pesticide residues could potentially threaten human health through acute or chronic dietary exposure [9]. Many countries and regions have established strict limit standards for the residue of pesticides and their metabolite in tea [10]. Rigorous monitoring and analysis of pesticide residues in tea products are crucial to ensure consumer safety and address the 'green trade barriers' associated with tea export. Furthermore, variations in manufacturing procedures can create significant discrepancies in the matrix of different teas [11]. Therefore, the adoption of universal analytical methods could substantially streamline the process of detecting pesticide residues in tea.

Belonging to a unique class of insect growth regulators (IGRs), benzoylureas function as inhibitors of chitin synthesis and accelerators of its degradation, consequently disrupting the target pest's epidermal development [12]. Since the 1970s, the significant insecticidal activity and unique mechanism of action of benzoylurea insecticides have made them a preferred replacement for traditional organophosphorus and organochlorine pesticides in numerous pest control applications [13]. Nevertheless, recent research has exposed potential dangers of benzoylureas and their metabolites, highlighting their environmental persistence and toxicity to non-target biological entities [14], [15], [16]. The European Union has banned individual benzoylurea insecticides inclined to be bio-enriched, like flufenoxuron. The US Environmental Protection Agency (EPA) has classified several benzoylurea insecticides as substances with medium toxicity [17]. Both qualitative and quantitative analyses of benzoylurea insecticides regularly utilize high-performance liquid chromatography (HPLC), complemented with various detectors [18,19]. However, due to the complexity of the matrix and the trace-level presence of pesticide residue, sample pretreatment before instrumental analysis is vital for target concentration [20]. Traditional pretreatment techniques like liquid-liquid extraction (LLE) and solid phase extraction (SPE) typically necessitate significant labor and organic solvent inputs, thereby contradicting the principles of green chemistry [21,22]. Diversified new miniaturized sample pretreatment techniques are flourishing, among which magnetic solid phase extraction (MSPE) based on magnetic composite stands out with its convenient operation and customizability [23]. Unlike SPE, which packs adsorbents into columns, MSPE directly disperses adsorbents within the sample solution, facilitating simple collection using an external magnetic field during both adsorption and desorption phases. This direct engagement ensures optimum contact with the sample solution, resulting in enhanced extraction efficiency [24,25]. Ye et al. skillfully incorporated iron oxide into pre-synthesized octahedral MOF-808 nanoparticles in situ. The resultant magnetic composites demonstrated remarkable MSPE efficiency for the extraction of seven benzoylureas from both tea beverage and juice samples, achieving recovery rates within the range of 84.6–98.3% [26]. Similarly, Duo et al. developed a magnetic iron-based MOF adsorbent (Fe3O4-NH2@MOF-235), which was employed for MSPE of five benzoylureas in honey, juice, and tap water samples. Due to the synergistic effects of π-π stacking and hydrophobic interactions, they achieved satisfactory recovery rates (76.5–90.7%) and detection limits (0.25–0.5 μg L−1) [27].

UiO-66 is a series of metal-organic frameworks (MOFs) characterized by terephthalic acid acting as organic linkers and zirconium functioning as metal nodes. Cavka et al. first reported UiO-66, and its name derives from the University of Oslo's abbreviation [28]. The robust Zr-O bond equips UiO-66 MOFs with exceptional thermal, acid-base stability, and mechanical resilience [29]. Leveraging the inherent advantage of the ultra-high specific surface area in MOFs, UiO-66 offers vast potential in adsorption and extraction applications [30,31]. To boost the adsorption capacity and selectivity of UiO-66, various ligands are often used to functionalize these MOFs. Typically, the functionalization process adheres to two strategies: pre-installation and post-synthetic modification (PSM) [32,33]. Pre-installation employs ligands with integrated functional groups, partially substituting original organic ligands to directly fabricate functionalized MOFs, whereas PSM alters the synthesized MOFs using covalent bonding or coordination [34,35]. PSM offers a more extensive range of modifier options, as it has fewer limitations due to steric hindrance and reaction conditions [36]. Li et al. incorporated non-polar naphthyl groups into UiO-66 MOFs using 1,4-naphthalene dicarboxylic acid and terephthalic acid as mixed ligands. The MOFs created through pre-installation displayed increased hydrophobicity and a 69% higher adsorption capacity for volatile toluene compared to raw UiO-66 [37]. Wang and his team used 5-adenosine for the PSM of UiO-66-NH2, which resulted in a substantial increase in its adsorption capacity for lead and chromium ions post modification [38]. Jia and his colleagues attached poly(sodium 4-styrene sulfonate) brushes to the amino groups of UiO-66-NH2 through a process known as surface-initiated atom transfer radical polymerization (SI-ATRP). The resultant composite materials demonstrated a superior selective affinity for cationic dyes, achieving satisfactory recoveries between 90.3 and 101.3% [39].

This study focuses on synthesizing a magnetic amino-functionalized UiO-66 MOF, purposed for the magnetic solid-phase extraction of five types of benzoylurea insecticides. The porous structure of UiO-66-NH2 aids in augmenting the adsorbent's surface area, thus providing an advantageous platform for future modifications. In a bid to further enhance extraction efficiency, 4-carboxylphenylboronic acid (4-CPBA) was attached to the abundant amino groups of UiO-66 MOF via a one-step condensation reaction. Benzoylureas, being rich in nitrogen atoms and benzene rings, can be adsorbed by the proposed adsorbent via B-N coordination and various secondary interactions.