Ultrafast and Stable Adsorption–Desorption Performance for Recovery of Valuable Rare-Earth Ions using High-Density Polyacrylic Acid Brush-Grafted Polypropylene Fibers Optimized by RSM Models

Abstract

Polyelectrolytes with abundant ionizable groups always possess excellent adsorption capacity for metal ions. However, these polymer chains are limited for direct application, resulting from lacking a fixed shape. In this paper, polypropylene (PP) fibers decorated with high-density polyacrylic acid (PAA) brushes were prepared using modified ultraviolet-induced graft technology and used as an efficient adsorbent for recovering rare-earth elements from wastewater. The preparation conditions for the degree of grafting were optimized with the response surface methodology mode. After grafting, apparent expansion happened to the fibers, and scanning electron microscopy images indicated that the fiber diameter increased from 48 to 175 μm along with the increase of the degree of grafting. By means of attaching one end of PAA chains onto the PP substrate, the free end would be exposed to the surrounding medium, which leads to a huge number of highly accessible adsorption sites and further guaranteed us with a fast adsorption–desorption rate and larger adsorption capacity. Adsorption could reach above 85% of the maximum adsorption capacity, with a magnitude of 435.19 mg·g–1 within 5 min toward a model rare-earth element Ce3+. Isotherm and kinetic analyses were also undertaken. Moreover, the recycling experiment suggested that the adsorbent taken with almost 100% desorption efficiency could be reproduced robustly for several cycles. In addition, the modified PP fiber can be considered as potential column packing because it exhibits higher adsorption capacity and desorption efficiency than commercial D113 and DL001 resins.