Electrospinning Machine | Efficient Hg(II) removal using recyclable poly(thioctic acid)/SH-UiO-66 functionalized polyacrylonitrile fiber: Multifunctional binding strategy

Heavy metal pollution in water bodies, particularly mercury (Hg) pollution, has become a severe challenge in the field of global environmental governance. Traditional adsorbents such as activated carbon, zeolite, mesoporous silica, and polymer resins commonly face issues like slow adsorption kinetics, insufficient adsorption capacity, poor selectivity, and unsatisfactory reusability, making it difficult to meet the demands for efficient Hg(II) removal. In recent years, nanomaterials such as Metal-Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) have been extensively studied for Hg(II) adsorption due to their high internal surface areas and tunable functional structures. However, to achieve high adsorption capacity and improved selectivity, these materials often require a "bottom-up" design of complex organic linkers or a "post-modification" strategy involving covalent grafting of functional groups onto the porous material surfaces. The cumbersome synthesis processes significantly hinder their practical application. More critically, these materials mostly exist as fine powders, which are prone to agglomeration leading to reduced adsorption efficiency, and are difficult to separate and recover from water bodies afterwards. This not only increases treatment costs but also may cause secondary pollution.

In response to the above challenges, the research group of Associate Researcher Ningge Jian and Professor Li'e Liu from the School of Public Health at Zhengzhou University innovatively proposed a "cascade in-situ growth" strategy and successfully prepared a novel self-supporting nanofiber composite membrane—pTA@SH-UiO-66@COOH-PAN. Using a polyacrylonitrile (PAN) nanofiber membrane as the substrate, they first catalytically hydrolyzed the surface cyano groups (-CN) into carboxyl groups (-COOH). Relying on the coordination between carboxyl groups and Zr⁴⁺, they achieved the fixation of SH-UiO-66 on the fiber surface. Subsequently, utilizing the characteristic of thioctic acid (TA) being prone to ring-opening polymerization under heat initiation, it was introduced into the pores of SH-UiO-66 and polymerized in situ to form a poly(thioctic acid) (pTA) coating, ultimately constructing a composite membrane structure with distinct layers and synergistic functions. The related research was published in the journal Chemical Engineering Journal under the title "Efficient Hg(II) removal using recyclable poly(thioctic acid)/SH-UiO-66 functionalized polyacrylonitrile fiber: Multifunctional binding strategy".

Figure 1 Characterization of nanofiber membranes (a) PAN, (b) COOH-PAN, (c) SH-UiO-66@COOH-PAN, and (d) pTA@SH-UiO-66@COOH-PAN nanofiber membrane SEM images; (e-i) pTA@SH-UiO-66@COOH-PAN nanofiber membrane EDS mapping; (j) FTIR analysis of COOH-PAN, SH-UiO-66@COOH-PAN, and pTA@SH-UiO-66@COOH-PAN nanofiber membranes; (k) Zeta potential of SH-UiO-66@COOH-PAN and pTA@SH-UiO-66@COOH-PAN nanofiber membranes under different pH conditions.

Research shows that the pTA@SH-UiO-66@COOH-PAN composite membrane has excellent Hg (II) adsorption performance, featuring fast adsorption kinetics (k2 ~0.0005 g mg−1 min−1), excellent adsorption capacity (static adsorption ~2543 mg g−1, dynamic adsorption 2125 mg g−1), high selectivity, strong anti-interference ability, and good reusability. It is worth noting that the removal rate of Hg(II) (100 μg mL−1) in natural water and industrial wastewater by pTA@SH-UiO-66@COOH-PAN reached as high as 95%, confirming the material's practicality.

Figure 2 Adsorption performance of pTA@SH-UiO-66@COOH-PAN composite membrane (a) Time-adsorption efficiency curve; (b) Adsorption isotherm; (c) Relationship curve between Hg(II) concentration in dynamic adsorption effluent and sample solution volume; (d) Comparison of Hg(II) adsorption performance of different materials; (e) Removal efficiency of pTA@SH-UiO-66@COOH-PAN composite membrane for different metal ions in single solution and (f) mixed solution; (g) Elution efficiency of different eluents (1) 0.5 mol/L sodium hydroxide / 1 mol/L EDTA, (2) 1 mol/L sodium hydroxide, (3) 1% (w/v) thiourea; (h) Time-desorption efficiency curve; (i) Reusability performance.

Through FTIR, XPS characterization combined with theoretical calculations (as shown in Figure 3), the adsorption mechanism was further revealed: the efficient capture of Hg (II) originates from the synergy between SH-UiO-66 and pTA, while the typical spatial structure of pTA@SH-UiO-66@COOH-PAN is conducive to the rapid diffusion of Hg (II) on the surface and inside the material and increases the accessibility of active sites.

Figure 3 (a) FTIR, (b) XPS characterization; pTA@SH-UiO-66@COOH-PAN-Hg(II) high-resolution XPS spectra: (c) Hg 4f, (d) C 1s, (e) O 1s, (f) S 2p.

Figure 4 Theoretical calculation: (a) Electrostatic potential analysis; (b, c) Optimal configuration and adsorption energy.

The development of the pTA@SH-UiO-66@COOH-PAN composite membrane not only provides an efficient and practical material for the remediation of Hg (II) polluted water bodies but also has significant guiding importance in the field of environmental functional material design. Its "cascade in-situ growth" strategy provides new ideas for solving problems such as complex synthesis, single function, and difficult recovery of traditional adsorbent materials, and can be extended to the treatment of other heavy metal ions (such as Pb (II), Cd (II), etc.) or organic pollutants.