Incorporation of amine-grafted halloysite nanotube to electrospun nanofibrous membranes of chitosan/poly (vinyl alcohol) for Cd (II) and Pb(II) removal

Abstract

Amino group grafted halloysite nanotubes (Hal-NH2s) were used to enhance adsorption/filtration performance of chitosan (CS)/poly (vinyl alcohol) (PVA) electrospun nanofibers by coating on the polymeric membrane as well as embedding them into the polymer solution. The novel cactus-like nanofibers exerted considerably higher Cd(II) and Pb(II) adsorption capacity than other functionalized materials. The compositional changes of functionalized Hals were verified by Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD). Morphology of Hal-NH2 loaded nanofibers was characterized as well as thermal/mechanical properties. Impacts of potentially affecting parameters including Hal-NH2 loading, pH, temperature, contact time, and initial concentration of heavy metal ions were optimized in the adsorption process. According to the well-fitted Langmuir model, the maximum adsorption capacity of Cd(II) and Pb(II) ions at 120 min were measured to be 454.5 and 476.2 mg/g for the Hal-NH2 entrapped nanofibers, while for the Hal-NH2 coated nanofibers, higher values of 516.3 and 551.6 mg/g were measured, respectively. Kinetics of the adsorption process was also studied, indicating that a pseudo-second-order model was fitted on the experimental data. In contrast to the Hal-NH2 coated nanofibers, the Hal-NH2 entrapped nanofibers were considered stable, and their adsorption capacity remained almost intact after five adsorption/desorption cycles. These affinity membranes revealed promising Cd(II) and Pb(II) ions removal, and uniform permeation flux, indicating their ability to be the next generation of adsorptive filters.