# Applications of Nanomaterial Coatings in Solid-Phase Microextraction (SPME)
## 6 SPME Based on Nanoporous Structures  
Porous structures are prevalent in nature, appearing in materials such as wood, cork, trabecular bone, and plant parenchyma. The invention of synthetic porous materials was a great leap in human civilization. Early examples included polymeric porous materials, termed \"polymeric foams\", with pore diameters exceeding 200 \(\upmu\)m [124]. Nanoporous materials allow for selective adsorption depending on molecular configurations since their pores are similar in size to those of tiny molecules. For applications like fixed-bed devices that need good adsorption selectivity and capacity, zeolites--which are mostly made of silicon and oxygen--are perfect since they are plentiful, stable, and reasonably priced. Zeolitic imidazolate frameworks (ZIFs), covalent organic frameworks (COFs), and metal-organic frameworks (MOFs) are new types of nanoporous materials that provide substantial void volumes, great stability, and tunable, uniform cavities. In general, porous materials have interconnected voids that might or might not show three-dimensional translational repetition. As an illustration, consider porous silica frameworks (PSFs), porous organic frameworks (POFs), and layered double hydroxides (LDHs). Applications in adsorption, separation, and catalysis are driven by their wide gas-solid interfaces,as demonstrated by solid foams, a simple porous system [125; 126; 127]. From conventional applications such as desiccants to more sophisticated ones, nanoporous materials have enormous potential in materials science. They function as size- and shape-selective reaction chambers for purification, which includes symmetric or asymmetric synthesis, heterogeneous catalysis, adsorption, and optical resolution of enantiomers. Modern technologies like chemical sensors, electrodes, data storage, imaging materials, and lasers are also using them more and more [128]. Overcoming difficulties in creating distinct phases at the nanoscale is necessary to fabricate nanoporous polymeric materials. Numerous methods have been devised, such as foaming, phase separation, molecular imprinting, microemulsion templating, and selective block removal in nanostructured copolymers. These techniques, which are frequently seen with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), allow polymers to develop nanoscale porous architectures [124; 129]. In general, pores fall into one of three shapes: slit, inkbottle, or cylindrical. They can be arranged to create 2D, 3D, crystalline, semi-crystalline, or amorphous structures. Analytes can be adsorbed by porous frameworks according to host-guest interactions (MOFs, POFs), anion exchange (LDHs), hydrophilicity (aluminosilicates), size (zeolites), or hydrophobicity (pure silica sieves) [125]. By functionalizing hexagonally ordered nanoporous silica (SBA-15) with 3-amino propyl triethoxysilane (APTES), [PERSON] et al. reported creating a highly porous fiber covering a specialized solid-phase microextraction (SPME) apparatus for use in conjunction with gas chromatography-mass spectrometry (GC-MS) for the detection of trace levels of polycyclic aromatic hydrocarbons (PAHs) in water samples. Temperature, duration, ionic strength, and sonication were among the extraction parameters that were optimized, the researchers noted, one factor at a time. According to their findings, detection limits under ideal circumstances varied from 4.2 to 26.1 pg/mL, with relative standard deviations ranging from 3.3% to 7.7%. They also pointed out that the SPME fiber maintained a consistent extraction efficiency throughout 50 extractions, proving its robustness and appropriateness for environmental study [130]. [PERSON] et al. reported the effective synthesis of high-surface-area nanoporous carbon (NPC) using the metal-organic framework ZIF-90 as both a template and precursor, with furfuryl alcohol serving as a secondary carbon source. The resulting ZIF-90-NPC was applied to a stainless steel wire to form an SPME fiber.