Superhydrophilic Quaternized Electrospun Nanofibers for Fast and Efficient Removal of Cr(VI) from Metallurgical Wastewater

Due to the low adsorption capacity, slow adsorption kinetics, and insufficient selectivity of conventional adsorbents in highly acidic environments, therefore, the removal of highly toxic Cr(VI) from industrial metallurgical wastewater remains a great challenge. Herein, a novel superhydrophilic quaternized nanofiber adsorbent was synthesized using electrospinning technology. The superhydrophilic nanofiber adsorbent facilitated water molecule movement during the adsorption process, which increased the system's free energy and thus promoted the efficient and rapid selective removal of Cr(VI). The adsorbent was completely wetted within 0.06 s and reached a maximum adsorption capacity of 450.33 mg/g in a Cr(VI) solution with an initial concentration of 400 mg/L and equilibrated within 20 min. Adsorption experiments showed that the correlation coefficients of the pseudo-secondary kinetics and Langmuir model of the process were as high as R22 = 0.994 and RL2 = 0.971-0.993, respectively, suggesting that the adsorption process is mainly surface adsorption driven by chemisorption. Moreover, the adsorption mechanism by Zeta potential analysis and XPS and DFT simulations revealed that the selective adsorption for Cr(VI) is the synergistic action of ion exchange and coordination by electrostatic attraction. In addition, the dynamic column adsorption test demonstrated that the adsorbent could adsorb 6000 times its own mass of Cr(VI) ions in metallurgical wastewater, the recovery of Cr(VI) by nanofibers could still reach 89.7% after five cycles, and the removal efficiency was as high as 95.64% in real metallurgical wastewater, which highlighted the potential of its practical application.