Micro-nano structure poly(ether sulfones)/poly(ethyleneimine) nanofibrous affinity membranes for adsorption of anionic dyes and heavy metal ions in aqueous solution

In this study, a novel micro-nano structure poly(ether sulfones)/poly(ethyleneimine) (PES/PEI) nanofibrous membrane was fabricated and utilized as an adsorbent for anionic dyes or heavy metal ions from aqueous solutions. A series of adsorption experiments were carried out to investigate the influence of membrane dosage, initial solution pH value, contact time, initial solution concentration and adsorption temperature on the adsorption performance. The experimental results showed that the removal of the anionic dyes and metal ions on this PES/PEI nanofibrous membrane was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 1 for anionic dyes and 5–7 for metal ions, respectively, and the PES/PEI nanofibrous membranes could be regenerated successfully. The adsorption equilibrium data were all fitted well to the Langmuir isotherm equation, with a maximum adsorption capacity values of 1000.00 mg/g, 344.83 mg/g, 454.44 mg/g, 94.34 mg/g, 161.29 mg/g and 357.14 mg/g for Sunset Yellow FCF, Fast Green FCF, Amaranth, Pb(II), Cu(II) and Cd(II), respectively. The kinetic study indicated that the adsorption of metal ions and anionic dyes could be well fitted by the pseudo-second-order equation, suggesting the intra-particle diffusion process as the rate-limiting step of the adsorption process. Thermodynamic parameters such as free energy, enthalpy and entropy of adsorption of anionic dyes and metal ions were also evaluated and the results showed that the adsorption was a spontaneous physical adsorption process. In addition, two different kinds of adsorption mechanism were proposed to explain the adsorption of anionic and cationic compounds on the PES/PEI nanofibrous membrane.