Electrospinning Machine | Reusable aminated electrospun nanofiber mat for enhanced phosphorus removal: Fabrication and performance evaluation

With the increasing intensity of human activities, excessive phosphorus discharge has evolved into a global environmental issue that urgently needs resolution. The abnormal rise in phosphorus concentration in water bodies significantly accelerates the explosive proliferation of algae and other plankton, directly triggering eutrophication. This process severely disrupts the structural balance and functional stability of aquatic ecosystems, ultimately leading to significant water quality deterioration and massive death of aquatic organisms. Given that phosphorus mainly exists in the form of phosphate in natural water bodies, efficiently removing such phosphorus pollutants becomes a core step in inhibiting harmful algal blooms and maintaining aquatic ecological health. Therefore, developing phosphorus adsorption materials with long-term stability and high adsorption performance has become an urgent need in environmental governance. However, the practical application of current adsorption materials still faces multiple challenges: how to design adsorption materials that simultaneously achieve high adsorption efficiency (rapid and massive capture of phosphate), easy separation characteristics (material reuse while avoiding residual secondary pollution), and sustainable recyclability (reducing usage costs and solid waste generation) remains a core technical bottleneck awaiting breakthrough.

Recently, the research team led by Zheng Yuming at the Institute of Urban Environment, Chinese Academy of Sciences, published their latest research findings titled "Reusable aminated electrospun nanofiber mat for enhanced phosphorus removal: Fabrication and performance evaluation" in the journal Separation and Purification Technology. The research team successfully developed a ZIF-8-embedded polyacrylonitrile (PAN)/polyethyleneimine (PEI) nanofiber membrane (APPZ-5), offering a potential solution for efficient and sustainable phosphorus removal from wastewater.

Figure 1 SEM images of ZIF-8, PAN nanofiber membrane, and PPZ nanofiber membrane.

SEM images show the successful preparation of ZIF-8 nanocrystals with hexagonal and quasi-cubic morphologies (Figure 1a). Pure PAN nanofibers exhibit a smooth surface and uniform morphology, with an average fiber diameter of 157.6 nm (Figure 1b). After the introduction of PEI into the system, the average fiber diameter significantly increased to 732.3 nm due to the notable rise in the viscosity of the spinning solution (Figure 1c). The incorporation of ZIF-8 not only markedly reduced the fiber diameter but also resulted in a rougher surface and a more uniformly distributed structural morphology. This morphological change can significantly enhance the interaction between the material and PO₄³⁻ (Figures 1d and e). It is noteworthy that when the ZIF-8 loading was increased to 10%, significant nanoparticle aggregates were observed on the fiber surface, accompanied by the formation of distinct bead-like structures (Figure 1f).

Figure 2 Adsorption isotherm and kinetic fitting of APPZ-5 for phosphorus.

Compared to the aminated PAN/PEI nanofiber membrane without ZIF-8, the APPZ-5 nanofiber membrane's phosphorus adsorption capacity increased nearly threefold, reaching 139.07 mg-P g⁻¹. Adsorption isotherm model fitting analysis results showed that the Redlich-Peterson model had the highest fit (R² = 0.9974), indicating that the adsorption process follows a multilayer adsorption mechanism. This mechanism originates from the heterogeneity of the material surface and the interactions between PO₄³⁻ ions. Specifically, the embedding of ZIF-8, on one hand, expands the contact area between the material and phosphorus by reducing fiber diameter and increasing surface roughness; on the other hand, by introducing more active adsorption sites, it forms a heterogeneous structure with multi-level affinity on the fiber membrane surface, providing favorable conditions for multilayer adsorption of PO₄³⁻, ultimately facilitating the realization of an efficient multilayer adsorption mechanism. Moreover, the APPZ-5 nanofiber membrane also exhibits excellent adsorption kinetics performance, requiring only 90 minutes to reach adsorption equilibrium. Kinetic studies further showed that at two initial concentrations of 55 mg-P·L⁻¹ and 100 mg-P·L⁻¹, the pseudo-second-order kinetic model highly matched the experimental data, with correlation coefficients (R²) reaching 0.9998 and 0.9997, respectively, strongly proving that chemical adsorption is the dominant mechanism for phosphorus adsorption by the APPZ-5 nanofiber membrane.

Figure 3 Study on the influence of coexisting ions and desorption cycling performance during phosphorus adsorption by APPZ-5.

Coexisting ion interference experiments showed that NO₃⁻ and Cl⁻ had minimal impact on the adsorption effectiveness, while SO₄²⁻ and F⁻ ions exhibited moderate competitive interference. Regeneration performance test results indicated that the APPZ-5 nanofiber membrane, after adsorption saturation and regeneration, still maintained efficient phosphorus adsorption performance with no significant decay in adsorption capacity, highlighting excellent long-term cycling stability. This provides an important reference for reducing practical application costs and achieving sustainable phosphorus removal. Furthermore, the ZIF-8-embedded nanofiber membrane demonstrated good structural integrity. Inductively coupled plasma analysis detected no zinc ion leaching, confirming the strong binding between ZIF-8 and the fiber matrix. This effectively avoids secondary pollution risks and ensures the material's environmental safety and application reliability.

Figure 4 Adsorption column experiment of APPZ-5 for phosphorus.

To further validate the feasibility of APPZ-5 nanofiber membrane in practical application scenarios, the research team conducted adsorption column experiments using actual wastewater. The results confirmed the application potential of APPZ-5 nanofiber membrane under continuous flow conditions. Dynamic adsorption simulation analysis showed that the Clark model achieved the highest consistency with experimental data (R² = 0.989). The fitting results indicated that the adsorption column process of APPZ-5 is not regulated by a single factor, but is simultaneously influenced by both reaction kinetics rate and material surface heterogeneity. This dynamic adsorption characteristic shows high consistency with the Redlich-Peterson model adsorption behavior observed in the adsorption isotherm study, further demonstrating the uniformity of the APPZ-5 adsorption mechanism. This provides theoretical and data support for its transition from laboratory research to potential practical engineering applications.

Paper link: www.sciencedirect.com/science/article/abs/pii/S1383586625033969