Removal of cadmium ions from water using coaxially electrospun PAN/ZnO-encapsulated PVDF nanofiber membranes

Electrospun nanofiber membranes have been widely used as heavy metal ion adsorbents. However, they are usually mechanically weak, which reduces the chances of employing such materials in environments that involve stresses and strains. In this work, core–shell nanofiber membranes were directly produced by coaxial electrospinning of polyvinylidene fluoride (PVDF) nanofibers as core nanofibers to provide mechanical support, and zinc oxide (ZnO) nanoparticles loaded PAN as shell nanofibers to enhance the adsorption of cadmium ions. The effect of pH, time and concentration on the adsorption properties was investigated. The incorporation of ZnO nanoparticles to the membrane matrix led to a significant enhancement of 75% in adsorption capacity compared to the membrane without ZnO nanoparticles (i.e., 350 mg/g for PVDF-PAN/ZnO compared to 200 mg/g for PVDF-PAN). The nonlinear optimization method showed that the experimental results are better fitted with the pseudo-second-order kinetic model and Langmuir isotherm equation. In addition, the tensile breaking strength values for PAN, PVDF, PVDF-PAN and PVDF-PAN/ZnO nanofiber membranes were 1.3 ± 0.3, 8.2 ± 0.3, 8.4 ± 0.1 and 3.1 ± 0.3 MPa, respectively, which suggests the enhancement of mechanical properties with the addition of PVDF as core nanofibers.