Nanofiber Production| Quaternary amine-functionalizedelectrospun nanofibers for selective goldcapture: Experimental and DFT calculationstudy

Gold (Au) has irreplaceable application value in electronics, catalysis, and high-end jewelry manufacturing due to its excellent conductivity, stable chemical properties, and unique catalytic characteristics. With increasing resource scarcity, gold recovery from secondary resources has become crucial. Recently, novel adsorbents like MOFs, COFs, and functionalized polymers have shown promise for gold recovery, but face challenges including complex synthesis, high costs, poor acid resistance, and regeneration difficulties. In contrast, electrospun nanofibers attract attention for their simple preparation, cost-effectiveness, and recyclability. More importantly, these materials offer excellent acid-base stability and high surface area, providing ideal substrates for functional modification to ensure efficient exposure and utilization of adsorption sites. Thus, developing novel functional electrospun nanofibers for efficient gold recovery from metallurgical wastewater has strategic significance for sustainable precious metal utilization.

Recently, Associate Professor He Hongxing, Associate Professor Zhang Yi, and Researcher Nie Zhifeng from Yunnan Key Laboratory of Metal-Organic Molecular Materials and Devices, Kunming University, published their latest electrospinning research in Separation and Purification Technology: "Quaternary amine-functionalized electrospun nanofibers for selective gold capture: Experimental and DFT calculation study". The team successfully developed a novel quaternary ammonium-functionalized electrospun nanofiber material (GA-PVA/PEI-Cl) through electrospinning combined with quaternization modification, applying it to efficient gold recovery from metallurgical wastewater. The material achieved adsorption equilibrium within 6 hours, with kinetics and capacity surpassing most reported adsorbents. GA-PVA/PEI-Cl showed high selectivity for Au(III) in simulated wastewater, with a distribution coefficient reaching 49249.6 mL/g, and maintained stable adsorption efficiency after 5 cycles.

Fig. 1: Morphology and structure of GA-PVA/PEI-Cl nanofibers

Fig. 2: FTIR, BET and EDS characterization

GA-PVA/PEI-Cl nanofibers with ionic liquid characteristics were prepared via electrospinning and quaternization. As shown in Figure 1, the pristine PVA/PEI nanofibers exhibited randomly oriented networks with smooth, bead-free surfaces (average diameter: 350±10 nm). After glutaraldehyde (GA) crosslinking, fibers formed interwoven porous structures with increased roughness (diameter: 370±10 nm). Post-quaternization, fibers maintained morphology with increased diameter (425±10 nm), likely due to propyl group incorporation. Successful modification was confirmed by FT-IR, SEM, and TEM. XPS and EDS verified gold adsorption. Studies on pH, temperature, concentration, and time effects revealed spontaneous endothermic adsorption with capacity increasing with temperature. Kinetic and isotherm analyses indicated monolayer chemisorption-dominated adsorption. In simulated industrial wastewater, GA-PVA/PEI-Cl showed remarkable Au(III) selectivity. DFT calculations and XPS analysis revealed synergistic electrostatic, coordination, and redox mechanisms.

Fig. 3: pH and temperature effects

Fig. 4: Adsorption kinetics and isotherms

Fig. 5: Selectivity and recyclability

Fig. 6: XPS spectra and electrochemical characterization

Fig. 7: DFT calculations

Fig. 8: Adsorption mechanism

The study investigated the effects of various conditions (pH, temperature, initial concentration, and time) on the adsorption process. Results demonstrated the entire adsorption process was a spontaneous endothermic reaction, with adsorption capacity increasing with temperature. Kinetic and isotherm analyses revealed the adsorption was primarily monolayer-controlled chemisorption. In simulated industrial wastewater environments, GA-PVA/PEI-Cl exhibited remarkable selectivity and effective adsorption rates for Au(III).Mechanistic analysis through density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) revealed the adsorption process mainly involved synergistic effects of three mechanisms: electrostatic interaction, coordination, and redox reaction.In conclusion, this study not only successfully developed a high-performance nanofiber gold adsorbent, but also provided in-depth mechanistic understanding through the integration of experimental and theoretical calculations. With its simple preparation, high efficiency, excellent selectivity, and recyclability, GA-PVA/PEI-Cl nanofibers offer a promising new technological solution for efficient gold recovery from complex systems such as e-waste leachates and metallurgical wastewater. This advancement holds significant importance for promoting sustainable utilization of precious metal resources.

Article link: https://doi.org/10.1016/j.seppur.2025.133945